&EPA
United States
Environmental Protection
Agency
Policy, Planning,
And Evaluation
(PM-221)
EPA-230-05-89-050
December 1989
The Potential Effects
Of Global Climate Change
On The United States
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THE POTENTIAL EFFECTS OF
GLOBAL CLIMATE CHANGE
ON THE UNITED STATES
REPORT TO CONGRESS
Editors: Joel B. Smith and Dennis Tirpak
United States Environmental Protection Agency
Office of Policy, Planning and Evaluation
Office of Research and Development
December 1989
Printed on Recycled Paper
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This document has been reviewed in accordance with the U.S.
Environmental Protection Agency's and the Office of Management
and Budget's peer and administrative review policies and approved
for publication. Mention of trade names or commercial products
does not constitute endorsement or recommendation for use.
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TABLE OF CONTENTS
Foreword ™
Acknowledgments XX111
EXECUTIVE SUMMARY xxv
CHAPTER 1: INTRODUCTION • 1
CONGRESSIONAL REQUEST FOR REPORTS 1
GOALS OF THIS REPORT 2
Sensitivities 2
Direction and Magnitude 2
Linkages 2
National Impacts 2
Regional Impacts • 3
Uncertainties 3
Policy Implications 3
Research Needs 3
STRUCTURE OF THE ANALYSIS 3
Important Systems 3
Regional Case Studies 3
National Studies 4
ANALYTIC APPROACHES 4
PROCESS FOR CONDUCTING THIS REPORT 4
Step 1: Initial Scoping of the Report 4
Step 2: Preparatory Workshops 5
Step 3: Identification of Potential Projects 5
Step 4: Reviews of Proposals 5
Step 5: Planning and Integration 5
Step 6: Analysis 5
Step 7: Preliminary Project Review 5
Step 8: Project and Report Peer Review 5
STRUCTURE OF THIS REPORT 6
RELATIONSHIP TO CURRENT NATIONAL AND INTERNATIONAL ACTIVITIES 6
National Research and Policy Activities 6
International Activities 6
REFERENCES . , 7
CHAPTER 2: GLOBAL CLIMATE CHANGE . 9
THE CLIMATE SYSTEM 10
CLIMATE FORCINGS 12
Greenhouse Gases • 12
Carbon Dioxide (CO2) 12
Methane (CH4) 13
Chlorofluorocarbons (CFCs) 13
Nitrous Oxide (N2O) 15
Ozone (O3) 15
Solar Variations 15
Volcanoes 15
Tropospheric Aerosols 16
Surface Properties • 16
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Internal Variations 16
CLIMATE FEEDBACKS 16
Water Vapor - Greenhouse Effect 16
Snow and Ice 17
Clouds 17
Biogeochemical Feedbacks 18
Oceans , 18
Observational Evidence of Climate Change 19
CLIMATE MODELS 21
Model Projections of a Doubled-CO,, World 24
REFERENCES 25
CHAPTER 3: CLIMATE VARIABILITY 29
FINDINGS 29
NATURE OF CLIMATE VARIABILITY 29
NATURE AND IMPORTANCE OF CLIMATE EXTREMES 31
Temperature ..-.. 32
Maximum Temperatures 32
Minimum Temperatures 33
Precipitation . . . 34
Droughts . . 34
Floods 35
Severe Storms - Hurricanes 35
STUDIES OF CHANGING CLIMATE VARIABILITY 36
Empirical Studies 36
Modeling Studies 37
STUDIES FOR THIS REPORT 38
The GISS Study 38
Interannual Variability 39
Daily Variability 40
Variability of the Diurnal Cycle 40
The NCAR Study 40
Methods 40
Comparison of Observed Versus Chervin Control Runs 43
Variability Comparisons of Three CCM Versions and Observed Data 45
Intercomparisons of the Three CCM Versions and Observed Data 45
Control Versus CO2-Perturbed Runs 45
COMPARISON OF GISS AND NCAR RESULTS 46
Interannual Variability 47
Daily Variability 47
Comparison of Climate Change 49
Limitations of the Two Studies 49
IMPLICATIONS FOR STUDIES OF CLIMATE CHANGE IMPACTS 50
RESEARCH NEEDS 51
Further Investigation of Variability GCMs . . ..-...• 51
Improvements in GCMs 52
Sensitivity Analyses of Reports 52
REFERENCES 52
CHAPTER 4: METHODOLOGY 57
NEED FOR CLIMATE CHANGE SCENARIOS 57
SCENARIO COMPONENTS 57
TYPES OF SCENARIOS 58
Arbitrary Changes 58
VI
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58
Analog Warming • • <-q
General Circulation Models (GCMs) ^
CHOICE OF DOUBLED CO2 SCENARIO JJ
GCMs Used £J
Limitations *£.
OPTIONS FOR CREATING TRANSIENT SCENARIOS 64
Arbitrary Changes ,
Analog Warming • ,.
GCM Transient Runs ™
CHOICE OF TRANSIENT SCENARIO g
Limitations ,,
OTHER SCENARIOS • ~
Sea Level Rise Scenarios °°
EFFECTS ANALYSES ™
RESEARCH NEEDS °-
GCMs *'
Scenarios • • ,-„
REFERENCES •
CHAPTER 5: FORESTS 1}
FINDINGS 71
' Range Shifts , ' j"
Productivity Changes • 71
Combined Impacts With Other Stresses . . if
, Policy Implications „
EXTENT AND VALUE OF U.S. FORESTS IL
Distribution and Ownership 'J1
Value of U.S. Forests L\
RELATIONSHIP BETWEEN FORESTS AND CLIMATE I*
Magnitude 7(-
Rates • yg
Mechanisms _,.
Temperature „
Precipitation • _„
CO2 Concentration ''
Ligfit "
Nutrient Status ''
Atmospheric Chemistry "
Disturbances ''
Landscape Processes ^
Multiple Stresses • • • • • •• • • /s
PREVIOUS STUDIES ON THE NATIONAL EFFECTS OF CLIMATE CHANGE ON
FORESTS ^
STUDIES IN THIS REPORT i?
RESULTS OF FOREST STUDIES • '°
Design of the Studies ,1°
Limitations • S1
Results "{
Magnitude °^
Rates of Decline and Migration £j
Mechanisms of Migration • • • <£
ECOLOGICAL AND SOCIOECONOMIC IMPLICATIONS • • • • • g
Ecological Implications
Tree Distribution and Biomass Productivity o^
Socioeconomic Implications
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Quality of the Human Environment 87
Recreation 37
Wood Products 37
FOREST POLICY AND CLIMATE CHANGE . . ......... 88
How Much Land Should Be Forested? I'.'.'.'.'.'.'.'. 88
How Much Should Be Withdrawn From Timber Production? :.'.'.'. 88
How Should We Manage Federal Forests? 89
How Can We Ensure National Goals? 89
Reforestation 89
Who Should Pay? 90
RESEARCH NEEDS '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 90
Effects of Climate Change 90
Methods 90
Forest Management 9j
Timing of Research 91
REFERENCES '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 91
CHAPTER 6: AGRICULTURE 93
FINDINGS '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 93
Crop Yields 93
Economic Impacts 93
Irrigation Demand I'.'.'.'.'.';'.'.'.'.'.'.'.'.'. 94
Agricultural Pests I'.'.'.'.'.'.'. 94
Farm-Level Adjustments '.'.'.'.'.'.'.'.'.'.' 94
Livestock Effects '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 94
Policy Implications 94
SENSITIVITY OF AGRICULTURE TO CHANGES IN CLIMATE 94
PREVIOUS STUDIES OF CLIMATE CHANGE AND AGRICULTURE ... "96
CLIMATE CHANGE STUDIES IN THIS REPORT ',','.', 97
Structure of and Rationale for the Studies 97
Variability •...'.'. 99
Timing of Effects 99
RESULTS OF AGRICULTURAL STUDIES '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.' 100
Regional Crop Modeling Studies [\\ 100
Design of the Studies 100
Limitations ' IQQ
Results 100
Implications 102
Regional and National Economics Study 102
Study Design '.'.'.'.'. 103
Limitations 103
Results 104
Implications '.'.'.'.'. 106
Demand for Water for Irrigation 107
Irrigation Requirements in the Great Plains 107
Water Resources for Agriculture in California . 108
Implications for Demand for Irrigation Water 109
Direct Effects of CO, on Crops '.'.'.'.'. 109
Climate Impacts on Pest-Plant Interactions '...'.'.'.'.'.'.'.'.'. 110
Study Design and Results HO
Limitations HI
Implications '' m
Effects of Climate Change on Water Quality '..'.-'.'.'.'.'.'.'.'.'.'. Ill
Study Design HI
Limitations
vui
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Results .~
Implications ....»
Climate Variability -.,,
Farm-Level Management Adjustments to Climate Change ^
Study Design -^
Results ^~
Implications ....
Livestock ^4
Design of Studies j-rj
Limitations • ^.
Results . 115
ECONOMIC ANDPECOLOGicAL' iMPLICATIONS OF AGRICULTURAL STUDIES ... 116
Costs and Timing of Adjustment ||
Effects of CO? ^6
Environmental Quality . . .
Global Agriculture • 117
POLICY IMPLICATIONS ^
Commodity Policies ^-,
Land-Use Programs 118
Water-Resource Management Programs f^°
Water Quality Policy tL
Risk Management and Drought Policy
International Trade Agreements
Agricultural Contributions to the Greenhouse Effect j-J°
Agricultural Research • 1 ig
RESEARCH NEEDS |~0
REFERENCES
123
CHAPTER 7: SEA LEVEL RISE ^
FINDINGS 123
Policy Implications 104
CAUSES, EFFECTS, AND RESPONSES - - - gj
Causes ^25
Effects 17r
Destruction of Coastal Wetlands < ^
Inundation and Erosion of Beaches and Barrier Islands u&
Flooding 127
Saltwater Intrusion • „
Responses 10Q
HOLDING BACK THE SEA: A NATIONAL ASSESSMENT *•*
STRUCTURE OF STUDIES FOR THIS REPORT ^
SCENARIOS OF SEA LEVEL RISE ^
RESULTS OF SEA LEVEL STUDIES IN THIS REPORT "j
Loss of Coastal Wetlands and Dryland ^ j-
Study Design
Lunitations • • • • ^2
Results 1 ,,,
Costs of Defending Sheltered Shorelines • f;"
Study Design J34
Limitations • ~~.
Results ..-,,-
Case Study of the Value of Threatened Coastal Property . . f^o
Study Design ^
Limitations
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Results 137
Nationwide Cost of Pumping Sand Onto Recreational Beaches 137
Study Design 137
Limitations 137
Results 137
Synthesis of the Three National Studies 138
Study Design '. . . 138
Limitations 139
Results 140
POLICY IMPLICATIONS . 141
Wetland Protection .... 141
Options for State and Local Governments 141
The Federal Role ' 142
Coastal Protection 142
State and Local Efforts 142
Federal Efforts 143
Sewers and Drains 144
RESEARCH NEEDS 145
REFERENCES 145
CHAPTER 8: BIOLOGICAL DIVERSITY 149
FINDINGS 149
Species Diversity 149
Marine Ecosystems 149
Freshwater Ecosystems 149
Migratory Birds 149
Policy Implications 149
VALUE OF BIOLOGICAL DIVERSITY . . 150
The National Resource 150
GENERAL COMPONENTS OF BIOLOGICAL DIVERSITY 150
Species' Diversity 151
Stressed Biological Diversity 152
Genetic Diversity 152
Community and Ecosystemic Diversity 152
FACTORS AFFECTING THE RESPONSES OF BIOLOGICAL DIVERSITY TO CLIMATE
CHANGE 152
Rate of Climate Change 153
Effect on Genetic Diversity 154
Barriers to Response 154
Reserve and Island Species 154
Mountain Species 155
CLIMATE EFFECTS RESEARCH 155
Forest Ecosystems 155
Tropical Forest Ecosystems 156
Freshwater Ecosystems 156
Saltwater Ecosystems 156
Coral Reef Ecosystems 157
Arctic Ecosystems 157
Migratory Birds 157
Endangered Species 158
Other Direct and Indirect Stresses 158
NATIONAL POLICY IMPLICATIONS 158
Management Options to Maintain Biological Diversity 158
Maintenance of Native Habitats 158
Maintenance of Species in Artificial Conditions . 159
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159
Restoration of Habitat 16Q
Planning Options - 160
RESEARCH NEEDS 160
Identification of Biological Diversity
Species Interactions and Biological Diversity ^
REFERENCES
CHAPTER 9: WATER RESOURCES ^
FINDINGS • 165
Impacts on Water Uses 165
CHANGE ON TOE WATER RESOURCES IN THE UNITED*
STATES ' 166
Current Status of Water Resources
Climate Change, Hydrologic Conditions, and Water Resources |_»
Impacts of Climate Change on Water Uses J^j-
Irrigation ' -. 72
Thermal Power Generation • •
Industrial Uses
Domestic Water Uses • •
Navigation ' ' •
Hydropower ^2
Recreation • YJT.
Climate Change and Water Quality „.
Climate Change and Flood Hazards .
Climate Change and Conflicts Among Water Uses |'*
REGIONAL IMPACTS OF CLIMATE CHANGE ^
The West 176
Pacific Northwest • • • • ' 176
California •••••••
Colorado, Rio Grande, and Great Basins 177
Great Plains -^77
Great Lakes '
Mississippi River • '
Northeast •
Southeast ' 170
POLICY IMPLICATIONS 178
Supply and Structural Policy Approaches
Design for Uncertainty . . . ._„
Surface Water Development • _
Optimization of Water Resource Systems • • • *'*
Demand Management and Nonstructural Policy Approaches |o"
Water Pricing, Water Markets, and Water Conservation . . f»u
Drought Management Policies • •
Water Quality ^
Policies for Floodplains • • ^
RESEARCH NEEDS ' ' 184
REFERENCES '
187
CHAPTER 10: ELECTRICITY DEMAND • • 187
FINDINGS ' " ' 187
Policy Implications 1Ro
CLIMATE CHANGE AND ELECTRICITY DEMAND }j»
PREVIOUS CLIMATE CHANGE STUDIES
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CLIMATE CHANGE STUDY IN THIS REPORT 189
Study Design 189
Limitations 190
Results 191
SOCIOECONOMIC AND ENVIRONMENTAL IMPLICATIONS 194
POLICY IMPLICATIONS 196
RESEARCH NEEDS 196
REFERENCES '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 197
CHAPTER 11: AIR QUALITY ... 199
FINDINGS '.'.'.'.'.'.'.'. 199
RELATIONSHIP BETWEEN CLIMATE AND AIR QUALITY ...... .. ...... '. '. '. '. '. '. '. 200
Ventilation 200
Circulation . !!!!!! 200
Precipitation 200
PATTERNS AND TRENDS IN AIR QUALITY . '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 201
Total Suspended Particulates . . . ; . . . . '.'.'. 201
Sulfur Dioxide 201
Ozone 202
Acid Deposition 202
STUDIES OF CLIMATE CHANGE AND AIR QUALITY '.'.'.'.'.'.'.'.'.'.'.'.'.'. 202
Climate Change and Its Interactions with Air Chemistry .. .. 205
Effect of Climate Change on Ozone Formation 205
MODELING STUDY OF CLIMATE AND AIR QUALITY 210
Study Design ] 210
Limitations 210
Results 211
Central California Study 211
Midwest and Southeast Study 211
Population Exposure 213
ECONOMIC, ENVIRONMENTAL, AND ECOLOGICAL IMPLICATIONS ............ 213
Ozone . 213
Acid Rain 215
POLICY IMPLICATIONS !!.'.' '" 216
RESEARCH NEEDS 216
REFERENCES '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 217
CHAPTER 12: HUMAN HEALTH 219
FINDINGS . . . . 219
CLIMATE-SENSITIVE ASPECTS OF HUMAN HEALTH . . . '. '. .. ...... .... ........ 219
General Mortality and Illness ' . ' 220
Cardiovascular, Cerebrovascular, and Respiratory Diseases 221
Vector-Borne Diseases 222
Human Reproduction 222
POTENTIAL HUMAN HEALTH EFFECTS OF CLIMATE CHANGE' ...'.'.'.'.'.'.'.'.'.'.'.'. 222
General Mortality .. 223
Cardiovascular, Cerebrovascular, and Respiratory Diseases 225
Vector-Borne Diseases , ....... 226
Tick-Borne Diseases 227
Mosquito-Borne Diseases 227
Other Diseases 231
SOCIAL AND ECONOMIC IMPLICATIONS ... . . 232
POLICY IMPLICATIONS . 233
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233
RESEARCH NEEDS • • • 235
REFERENCES
237
CHAPTER 13: URBAN INFRASTRUCTURE ^
FINDINGS 237
Northern and Southern Cities 237
Coastal Cities 237
Water Supply and Demand 237
' ' ' ' ' ' ' '
CLIMATE CHANGE STUDIES ON URBAN INFRASTRUCTURE
URBAN INFRASTRUCTURE STUDY IN THIS REPORT
RESULTS OF THE INFRASTRUCTURE STUDY
Impacts on Miami, Cleveland, and New York City
Study Design ' 240
Limitations 24Q
Results and Implications •• • . ,.
Implications Arising From Other EPA Studies in This Report **>
RESULTS OF RELATED STUDIES 245
Metropolitan Water Supply 245
Washington, DC 246
New Orleans • 246
New York City • 246
Tucson • • • •
IMPLICATIONS FOR URBAN INFRASTRUCTURE • • •
Water • 246
Drainage and Wastewater Systems 247
Coastal Defenses ] 247
Roads • •: 247
Bridges 247
Mass Transit 247
Electricity and Air-Conditioning • • • „,-
POLICY IMPLICATIONS 247
Investment Analysis Methods 248
Water Supply 248
Infrastructure Standards 24g
RESEARCH NEEDS 248
REFERENCES '
251
CHAPTER 14: CALIFORNIA • 2^
FINDINGS ••••- ' 251
Water Resources • ' 251
Wetlands and Fisheries .. • ^52
Agriculture • • • 252
Natural Vegetation ' 252
Air Quality • • ' ' 252
Electricity Demand . . 252
Policy Implications 7r^
CLIMATE-SENSITIVE RESOURCES OR CALIFORNIA g^
Current Climate • 253
Water Resources 253
Water Distribution
Flood Control and Hydroelectric Power •
Sacramento-San Joaquin River Delta ...
Commerce
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Agriculture
Forestry '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 256
Natural Vegetation £7
Wetlands ' f'
Wildlife and Fisheries '.'.'.'.'.'.'.'.'. '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 257
Recreation and Nature Preservation 9<7
PREVIOUS CLIMATE CHANGE STUDIES ' 957
Forests 257
Water Resources 7ro
CALIFORNIA STUDIES IN THIS REPORT '.'.'.'.' '.'.'.'.'.'.'.'. '. '. '. '. '..'.".' " ' .' ' 258
Analyses Performed for This Study ' 258
CALIFORNIA REGIONAL CLIMATE CHANGE SCENARIOS 9fin
RESULTS OF THE CALIFORNIA STUDIES .'.'.'.'.'."""" 262
Hydrology of Catchments in the Central Valley Basin " ' 262
Study Design 262
Limitations .[........ 262
Results !!!!!.'!.'.'!! 262
Implications 263
Water Resources in the Central Valley Basin 264
Study Design . 264
Limitations • • • • ^
Results ...................'.'.'.'.'.'.'.'.'. 264
Implications _ ' ' ' ' 255
Salinity in San Francisco Bay 266
Study Design 266
Limitations !.!!!!....!. 266
Results
_ ,. . • • 26/
Implications 267
Wetlands in the San Francisco Bay Estuary . . . 268
Study Design 268
Limitations 2fi«
Results ' 0--o
T ,. .. • 2oo
Implications 269
California Agriculture '.'.'.'.'.'.'. 269
Study Design '•'-'•'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'."' 270
Limitations ' 270
Results ................. 270
Implications ' ' 271
Regional Implications of National Agriculture Changes . . ...... . . 273
Results 273
Water Quality of Subalpine Lakes 273
Study Design 273
Limitations > 273
Results
Implications ; 273
Summary of Effects on Water Resources ••••••••..,.......
Vegetation of the Sierra Nevada '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'"•"" 275
Study Design 275
Limitations ] • 275
Results ] 276
Implications j7f-
Electricity Demand 277
Results . 277
Implications . 27o
Air Pollution '.'.'.'.'.'.'.'.'.'.'.'.'.'.'. '.'. '.'.'.'.'.'. 278
Results ......'! 278
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T ,. t. 278
Impucations 27»
POLICY IMPLICATIONS • • • • • ,78
Water Supply and Flood Control •
Approaches for Modifying the Water Resource System
Options for Allocating Water Shortages
Sacramento-San Joaquin River Delta •
Delta Island Land Use
Water Quality of the San Francisco Bay Estuary
Water Quality of Freshwater Systems
Terrestrial Vegetation and Wildlife ... •
Agriculture •283
Wetland Vegetation and Fisheries
Shoreline Impacts of Sea Level Rise ^
Energy Demand 283
Air Quality 284
REFERENCES
287
CHAPTER 15: GREAT LAKES • • • • 287
FINDINGS • '...... 287
Lakes • : • ' 287
Water Quality and Fisheries • 288
Forests 288
Agriculture • 288
Electricity Demand 288
RKOURCEs'lN 'THE GREAT'LAKES REGION' '. '. '. '. 289
Current Climate •••'•; '' 290
The Lakes • • 290
Lake Regulation
Climate-Sensitive Uses of the Lakes
Climate and Water Quality
Fluctuating Lake Levels •
Land Around the Lakes • •290
Land Uses • ; •
PREVIOUS CLIMATE CHANGE STUDIES •
GREAT LAKES STUDIES IN THIS REPORT
Direct Effects on Lakes
Impacts of Lake Changes on Infrastructure
Water Quality • 294
Forests • 295
Agriculture . . 295
Energy " ' 295
Policy • •
GREAT LAKES REGIONAL CLIMATE CHANGE SCENARIOS
RESULTS OF THE GREAT LAKES STUDIES
Lakes , • • • • • *296
Lake Levels
Effects of Lower Lake Levels
Ice Cover 302
Shipping 3Q4
Water Quality . ; ' ' ' '
Thermal Structure of Southern Lake Michigan
Eutrophication of the Lake Erie Central Basin
Fisheries
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Forests t 309
Potential Range Shifts 309
Transitional Effects . ; 399
Forest Migration 311
Implications of Forest Studies 311
Agriculture [[[ 312
Crop Yields 313
Regional Shifts ,, ... 314
Adjustments by Illinois Corn Producers 315
Electricity Demand -....., . . . 316
Study Design 316
Results '..'..'.'.'.'.'.'. 316
Implications 316
POLICY IMPLICATIONS '.'.'.'.'.'.','.'.'.'.'.'.'.'.'.'.'.'. 316
Water Supply Issues 317
Lake Regulation r 317
Withdrawals . 317
Shipping 317
Pollution Control 317
Fisheries 317
Land Use 318
Shorelines , 318
Forestry . 318
Agriculture '.....-• 318
Demographic Shifts 318
REFERENCES '.'.'.'.'.'.'.-'.'.'.'.I'.'.'.'.'.'.'.'.'.'. 319
CHAPTER 16: SOUTHEAST 323
FINDINGS .' '.'.'.'.'.'.'.'.'.'.'.'.['.'. 323
Agriculture t [ '.'.'.'.'.'.'.'.'. 323
Forests 323
Water Supplies 323
Sea Level Rise ' . . ] '.','.'.'.'.'.'.'.'.'.'.'.'. 324
Marine Fisheries 324
Electricity Demand ', '. 324
Policy Implications 324
CLIMATE AND THE SOUTHEAST '.'.'.'.'.'.' 325
CLIMATE-SENSITIVE RESOURCES OF THE SOUTHEAST ..... ^ ................. 325
Water Resources 325
Estuaries ; 326
Beach Erosion and Coastal Flooding ' ' 327
Agriculture 327
Forests 327
Indoor and Outdoor Comfort 328
PREVIOUS STUDIES OF THE IMPACTS OF CLIMATE CHANGE ON THE
SOUTHEAST . 328
Flooding 32g
Wetlands 329
Infrastructure 329
CLIMATE CHANGE STUDIES IN THIS REPORT . . . 329
SOUTHEAST REGIONAL CLIMATE CHANGE SCENARIOS 331
RESULTS OF SOUTHEASTERN STUDIES '.'.'.'.'.'.'.'. 333
Coastal Impacts t _ 333
Coastal Wetlands ..'.....':'...'.'.'.'.'.'.'.'.'.'.'.'. 333
Total Coastal Land Loss 334
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Cost of Protecting Recreational Beaches 334
Cost of Protecting Calm-Water Shorelines
Tennessee Valley Authority Studies
TVA Modeling Study
Limitations
Results .
Tennessee Valley Policy Study
Studies of the Impacts on Lake Lanier and Apalachicola Bay
Lake Lanier •
Apalachicola Bay •
Agriculture
' Crop Modeling Study
Shifts in Production
Agricultural Pests
Implications of Agriculture Studies
ForeStS
Potential Range Shifts •
Transitional Effects
Electric Utilities
COASTAL LOUISIANA
POLICY IMPLICATIONS •
Agriculture and Forests
Water Resources
Impacts of Wetter Climate
Impacts of Drier Climate •
Is Current Legislation Adequate?
Estuaries
Beach Erosion • • •
REFERENCES
CHAPTER 17: GREAT PLAINS
FINDINGS • • •359
Agriculture 359
Ogallala Aquifer •
Water Quality
Electricity Demand
Policy Implications
CLIMATE-SENSITIVE RESOURCES IN THE GREAT PLAINS 360
Dryland Agriculture
Irrigated Agriculture
Water Quality ., -
Electricity Demand, .
PREVIOUS CLIMATE IMPACT STUDIES
GREAT PLAINS STUDIES IN THIS REPORT
GREAT PLAINS REGIONAL CLIMATE CHANGE SCENARIOS . . : 364
RESULTS OF THE GREAT PLAINS STUDIES 366
Crop Production ^,,
Study Design *™
Limitations • • • _,
Results • • ' '
Implications ........... • • •
Agricultural Economics
Results
• Implications
xvu
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Irrigation 370
Study Design 370
Limitations 370
Results 370
Implications 371
Water Quality 371
Study Design 372
Results 372
Implications 372
Livestock 373
Electricity Demand 373
Results 373
Implications 374
CLIMATE CHANGE AND THE OGALLAIA AQUIFER 374
POLICY IMPLICATIONS 374
Land-Use Management 375
Water Resource Management 375
Risk Management 375
REFERENCES 376
CHAPTER 18: RESEARCH NEEDS 379
RELATIONSHIP BETWEEN POLICY AND SCIENCE 379
RESEARCH AND ASSESSMENT NEEDS IN THE SOCIAL SCIENCES 381
Institutional Response to Climate Variability and Climate Change 381
RESEARCH AND ASSESSMENT NEEDS IN THE NATURAL SCIENCES 382
Climate System 383
Research Scales 383
Socioeconomic Impacts 383
Data 383
Objectives of Federal Global Change Program 383
Three Major Scientific Objectives 385
THE ROLE OF EPA IN POLICY AND SCIENTIFIC RESEARCH 385
IMPACT ASSESSMENT METHODOLOGY 386
REFERENCES 388
CHAPTER 19: PREPARING FOR CLIMATE CHANGE 389
WHEN IS A RESPONSE WARRANTED? 389
Strategic Assessments 389
Decision-Oriented Assessments 390
Program-Oriented Assessments 390
Problem-Oriented Assessments 390
Criteria for Choosing a Strategy 390
EXAMPLE RESPONSES FOR ADAPTING TO GLOBAL WARMING 393
No Immediate Action 394
Reservoir Operating Rules 394
Choice of Crops 394
Anticipatory Action 394
Modifying Ongoing Projects to Consider Climate Change 394
Undertaking New Projects Primarily Because of Future Climate Change 395
Planning: Changing the Rules of the Game 396
Land Use 395
Water Allocation 398
XVlll
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Research and Education: Increasing Our Understanding
Research and Development . .
Education •
AUTHORS
CONTRIBUTING INVESTIGATORS AND PROJECTS
CONGRESSIONAL REQUEST FOR REPORT
APPENDICES
A: WATER RESOURCES
B: SEA LEVEL RISE
C: AGRICULTURE
D: FORESTS
E: AQUATIC RESOURCES
F: AIR QUALITY
G: HEALTH
H: INFRASTRUCTURE
I: VARIABILITY
J: POLICY
398
398
398
401
403
411
xix
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FOREWORD
I am pleased to transmit the attached Report to Congress: The Potential Effects of Global Climate
Change on the United States. This report, written in response to a congressional request in the Fiscal Year 1987
Continuing Resolution Authority to prepare two reports on climate change, focuses on the health and
environmental effects of climate change. A second draft report, Policy Options for Stabilizing Global Climate,
is being revised in preparation for delivery to Congress.
This report is one of the most comprehensive published studies of the potential impacts of the
greenhouse effect. It examines national effects and, more specifically, impacts on four regions of the United
Statees: California, the Great Lakes, the Southeast, and the Great Plains. Fifty studies conducted by
government, academic, and consulting scientists to examine impacts are included. EPA provided common
scenarios of climate change to the scientists for use in their analyses. This report is an overview of the results
of those studies.
I invite you to carefully read the Executive Summary and the chapters that follow. Although it is difficult
to summarize such a large and comprehensive project in a few words, it is fair to say that climate change could
lead to significant changes in many ecological and socioeconomic systems. The environmental impacts of a
relatively rapid climate change may be particularly acute. Sea level rise could lead to the loss of many coastal
wetlands, while a rapid wanning could reduce the populations of many plants and animals and, in some cases,
lead to extinction of species.
The socioeconomic effects, especially on a regional scale, also may be quite important. Significant
expenditures may be needed for such measures as protecting areas from sea level rise, building dams and
reservoirs for flood and drought protection, modifying infrastructure, and adding electricity capacity.
I urge caution in interpreting the results of these studies. Since we cannot predict regional climate
change or extreme events such as hurricanes or droughts, we cannot predict impacts. The work done for this
study was based on scenarios of climate change and is indicative of what could occur in the future. So, too, this
work does not identify all of the impacts of climate change, the interactions, or the economic damages that could
result.
In examining a study such as this, there is often a temptation to identify "winners" and "losers." One
must be careful in drawing such conclusions. The scenarios are based on a certain point in time (when carbon
dioxide levels have doubled); and they assume that climate stops changing. If emissions are not stabilized,
climate change will not stop at this carbon dioxide doubling, but will continue to warm. With continued wanning,
what was a positive effect could become negative. Responding to climate change would be a matter of keeping
up with increasing rates of change.
I feel this report is a significant contribution to our understanding of climate change impacts. More
work needs to be done on understanding impacts on other systems and regions. Yet, this information will be
helpful as we address the difficult problems associated with climate change.
Terry Davies
Assistant Administrator
Office of Policy, Planning and Evaluation
xxi
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ACKNOWLEDGMENTS
This report was made possible because of the hundreds of people who participated in workshops, conducted
research projects, reviewed draft manuscripts, and contributed ideas that shaped the final product. They shared
a common belief that an objective analysis of global climate change could be undertaken despite the uncertainties
in scientific information. We are grateful for their support and encouragement. It was the difference that
sustained us through this effort. In particular, we wish to acknowledge the authors who organized and integrated
the following chapters.
The following people contributed to this report:
Chapter 1: Introduction
Chapter 2: Global Climate Change
Chapter 3: Climate Variability
Chapter 4: Methodology
Chapter 5: Forests
Chapter 6: Agriculture
Chapter 7: Sea Level Rise
Chapter 8: Biological Diversity
Chapter 9: Water Resources
Chapter 10: Electricity Demand
Chapter 11: Air Quality
Chapter 12: Human Health
Chapter 13: Urban Infrastructure
Chapter 14: California
Chapter 15: Great Lakes
Chapter 16: Southeast
Joel B. Smith
Alan Robock
Linda O. Mearns
Joel B. Smith
Jack K. Winjum
Ronald P. Neilson
Cynthia Rosenzweig
Margaret M. Daniel
James G. Titus
Lauretta M. Burke
Ross A. Kiester
Mark W. Mugler
Michael C. Rubino
Kenneth P. Linder
Joseph J. Bufalini
Peter L. Finkelstein
Eugene C. Durman
Janice A. Longstreth
Ted R. Miller
George A. King
Robert L. DeVelice
Ronald P. Neilson
Robert C. Worrest
Joel B. Smith
James G. Titus
xxiu
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Chapter 17: Great Plains
Chapter 18: Research Needs
Chapter 19: Preparing for Climate Change
Cynthia Rosenzweig
William E. Riebsame
Anthony Janetos
James G. Titus
Special thanks are extended to Roy Jenne of the National Center for Atmospheric Research. Mr. Jenne
and Dennis Joseph of his staff collected data from the GCMs and assembled them in a way that could be easily
used by the effects researchers. In addition, he collected historic weather data for 1951-80 and distributed them
to the researchers as needed.
We wish to thank James Hansen, Syukuro Manabe, Richard Wetherald, and Michael Schlesinger for providing
us with the results from their GCM runs. Special thanks are also necessary to Joan O'Callaghan and Karen
Swetlow for editing; Roberta Wedge for assistance on production of the report; and Margaret Daniel, Michael
Greene, and Chris Parker for research and administrative assistance.
This work was conducted within EPA's Office of Policy Analysis, directed by Richard Morgenstern, within
the Office of Policy, Planning and Evaluation, administered by Linda Fisher, and most recently by Terry Davies.
Support was provided by EPA's Office of Environmental Processes and Effects Research, directed by Courtney
Riordan, within the Office of Research and Development, administered by Eric Bretthauer.
xxiv
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EXECUTIVE SUMMARY
Scientific theory suggests that the addition of
greenhouse gases to the atmosphere will alter global
climate, increasing temperatures and changing
rainfall and other weather patterns. In 1979, the
National Academy of Sciences estimated the most
probable global warming from a doubling of carbon
dioxide concentrations over preindustrial levels to be
between 1.5 and 4.5°C. In 1985, the World
Meteorological Organization (WMO), the United
Nations Environment Programme (UNEP), and the
International Council of Scientific Unions (ICSU)
reaffirmed these estimates. Such a climate change
could have significant implications for mankind and
the environment: it could raise sea level, alter
patterns of water availability, and affect agriculture
and global ecosystems.
Although there is consensus that increased
greenhouse gas concentrations will change global
climate, the rate and magnitude of change are not
certain (see box entitled "Climate Change").
Uncertainties about climate feedbacks from clouds,
vegetation, and other factors make it difficult to
predict the exact amount of warming that a given
level of greenhouse gases, such as doubled carbon
dioxide (CO2) concentrations, would cause. How
quickly climate may change also is not known,
because scientists are uncertain both about how
rapidly heat will be taken up by the oceans and
about some climate feedback processes. Generally,
scientists assume that current trends in emissions
will continue and that climate will change gradually
over the next century, although at a much faster
pace than historically. At this rate, the full effect of
the equivalent doubling of CO, concentrations
probably would not be experienced until after 2050.
It is possible, however, that sudden changes in
ocean circulation could cause abrupt changes in
global climate. Indeed, if climate changed more
rapidly than estimated, adapting to the effects would
be more difficult and more costly. Furthermore,
continued emissions of greenhouse gases could raise
atmospheric concentrations beyond doubled CO2
causing greater and more rapid climate changes,
and larger effects.
To explore the implications of climate change
and ways to control it, Congress asked the U.S.
Environmental Protection Agency (EPA) to
undertake two studies on the greenhouse effect: the
first study was to address "The potential health and
environmental effects of climate change including,
but not be limited to, the potential impacts on
agriculture, forests, wetlands, human health, rivers,
lakes, estuaries as well as societal impacts;" and the
second study was to examine "policy options that if
implemented would stabilize current levels of
greenhouse gas concentrations." The second study,
"Policy Options for Stabilizing Global Climate," is a
companion report to this document.
EPA responded to this request by first holding
workshops with atmospheric scientists to discuss the
use of global climate change models for impact
analyses and then meeting with ecologists,
hydrologists, geographers, and forestry and
agricultural specialists to identify topics for this
study. A major purpose was to bridge the gap in
our ability to relate a rise in average annual surface
temperatures to regional climate changes. Based on
these and other discussions, EPA decided to use
common scenarios of climate change to analyze the
sensitivities of coastal resources, water resources,
agriculture, forests, biodiversity, health, air pollution,
and electricity demand to climate change on
regional and national scales (see Figure 1). These
systems were chosen for analysis because they are
sensitive to climate and significantly affect our
quality of life. EPA decided to conduct regional
analyses for the Southeast, the Great Plains,
California, and the Great Lakes, because of their
climatological, ecological, hydrological, and
economic diversity. Leading academic and
government scientists in the relevant fields used
published models to estimate the impacts on both
the regional and national scales. As a common base
for conducting these analyses, they used the
scenarios specified by EPA.
After consulting with scientific experts, EPA
developed scenarios for use in effects analysis.
Regional data from atmospheric models known as
General Circulation Models (GCMs) were used as
a basis for climate change scenarios (see box on
"Scenarios and Methodology"). The GCMs are
large models of the ocean-atmosphere system that
simulate the fundamental physical relationships in
the system. GCMs provide the best scientific
xxv
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Executive Summary
CLIMATE CHANGE
A panel of experts convened by the National Academy of Sciences (National Research Council,
1987) recently gave the following estimates of scientific confidence in predictions Of the climate response
to increased greenhouse gas concentrations. This table summarizes only their conclusions concerning "the
possible climate responses to increased greenhouse gases," The full report should be consulted for the
details.
Large Stratospheric Cooling (virtually certain). The combination of increased cooling by
additional CO2 and other trace gases, and reduced heating by reduced ozone, "will lead to a
major lowering of temperatures fa the upper stratosphere,"
Global-Mean Surface Warming (very probable). For an equivalent doubling of CO^, "the
long-term global-mean surface warming is expected to be in the range 1,5 to 45°C."
Global-Mean Precipitation Increase (very probable)* ^Increased heating of the (Earth's] surface
will lead to increased evaporation and, therefore, to greater global mean precipitation. Despite
this increase in global average precipitation, some individual regions might welt experience
decreases in rainfall,"
Reduction of Sea Ice (very probable). This will be due to melting as the climate warms,
Polar Winter Surface Warming (very probable). Due to the sea ice reduction, polar surface
air may warm by as much as 3 times the global average.
Summer Continental Drvness/Warming (likely in the long term). Found in several^ but not all,
studies, it is mainly caused by earlier termination of winter storms. "Of course, these
simulations of long-term equilibrium conditions may not offer a reliable guide to trends over
the next few decades of changing atmospheric composition and changing climate.*
Rise in Global Mean Sea Level (probable). This will be due to thermal expansion of seawater
and melting or calving of land ice.
Climate
Scenarios
Core
Analytic
Areas
Forests
Agriculture
Sea Level Rise
Biodiversity
Water Resources
Electricity Demand
Air Quality
Human Health
Urban Infrastructure
— *•
Regional
Case
Studies
California
Great Lakes
Southeast
Great Plains
National
Studies
Forests
Sea Level Rise
Electricity Demand
Health
>•
Outputs
Research
Plan
Models/
Data Bases
Figure 1. Elements of the effects report.
xxvi
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Effects of Climate Change
SCENARIOS AND METHODOLOGY
A number of scenarios were specified by EPA to help identify the sensitivities of natural and
manmade systems to climate change. Scenarios were used as inputs with models of natural resources,
Most researchers used GCM*based scenarios* Some used analog scenarios or expert judgment*
- Regional outputs from three General Circulation Models: {GCMs) were used: the Goddard Institute
for Space Studies (GISS); the Geophysical Fluid Dynamics Laboratory (GFPI/); and Oregon State
University (OSU). All of these models estimate climate change caused by a doubling of CCL
concentrations in the atmosphere. The regional estimates of doubled CO~changes were combined with
1951*80 climate observations to create doubled CO, scenarios* This GISS model has been used to
estimate how climate may change between BOW anrithe middle of the next century. This is called a
transient run* the outputs of which were used to create a transient scenario.
Other approaches were used to supplementthe GCMs* Weather observations from the 1930s were
-used as an analog for global warming, although greenhouse warming may raise temperatures much, higher
than they were in that decade* In some cases, pateoclimatic warmings were studied to provide evidence
of how species respond to climate change. In addition, the use of scenarios was supplemented by expert
judgment (gathered thoughJiterature reviews and workshops with scientific experts) to provide the best
opinions on.potential effects, ,_ —
' - -'.
Since we cannot predict the exact nature of climate change, we cannot predict its impacts. All these
analytic approaches help us-determine the potential sensitivities and vulnerabilities of systems to climate
change, , ~ ' " , - ,
estimates of the impacts of increased greenhouse
gas concentrations on climate. Yet, they use
relatively simple models of oceans and clouds, both
of which will be very critical in influencing climate
change. The GCMs generally agree concerning
global and latitudinal increases in temperature, but
they disagree and are less reliable concerning other
areas, such as regional changes in rainfall and soil
moisture. The GCM data were compared with
historic meteorologic data. In addition, the decade
of the 1930s was used as an analog for global
warming.......
In Figure 2, the temperature changes from the
three GCMs used to create;scenarios are shown for
both the United States and four regions of the
United States for a doubling of carbon dioxide
levels. The GCMs agree on the direction of
temperature changes, but differ hi the magnitude.
Estimates of precipitation changes are shown in
Figure 3. The GCMs agree that annual rainfall
would increase across the country, but disagree
about the direction of regional and seasonal
changes. All models show increased evaporation.
The GCM results should not be considered as
predictions, but as plausible scenarios of future
climate change. Ideally, one would like to use many
regional climate change scenarios to reflect the
potential range of climate change. Resource
constraints allowed us to use only a limited number
of regional climate scenarios. It would also be
useful to estimate the probabilities of occurrence for
each scenario. Given the state of knowledge, it is
difficult to assign probabilities to regional climate
change. Because the regional estimates of climate
change by GCMs vary considerably, the scenarios
provide a range of possible changes in climate for
use in identifying the relative sensitivities of systems
to higher temperatures and sea level rise. Hence,
the results of the studies should not be considered
as predictions, but as indications of the impacts that
could occur as a result of global warming.
There are two other major limitations in the
GCM scenarios. First, the scenarios assume that
climate variability does not change from recent
decades. Second, the scenarios did not change the
frequency of events, such as heat waves, storms,
hurricanes, and droughts in various regions, which
xxvu
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Executive Summary
2xCO2 less 1xCO2
SoutlMt! GraHPttis Gallon* UntedSMes-
WINTER
* Lower 48 States
Great Lakes Southeast Great Plains California United Stales*
Goddard Institute for Space Studies
jg$jfl%;g] Geophysical Fluid Dynamics Laboratory
I | Oregon State University
Southeast Great Plains California United Stales'
Figure 2. Temperature scenarios.
2xCO2 less 1xCO2
ANNUAL
GiMILlliM Southwl CntlPWns California l>i»dSaas'
WINTER
•Lower 49 States
Great Lakes Southeast Great Plains California United Slates'
Goddard Institute for Space Studies
[%$jjjjjjjjj| Geophysical Fluid Dynamics Laboratory
Oregon State University
Great Lakes Southeast Great Plains California United Stales*
NC = No Change
Figure 3. Precipitation scenarios.
xxvui
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Effects of Climate Change
LIMITATIONS
Climate Scenarios
** Differences Between Scenarios. The <3CM and other scenarios do not provide consistent
estimates of climate change,
- Variability, The scenarios assume ao change in variability,
~ Ma|or Climate Events, Tjbe scenarios assume no changes It* hurricanes, droughts, etc,
Societal Changes. Most studies did not consider changes in population technology, and other
areas. There was only limited consideration of responses and adaptation measures, which could
mitigate some of the results presented here,
Linkages, Many indirect effects (e.g., effect of increased irrigation demand on water resources)
were not quantitatively analyzed*
Limited Effects Analyses. Many effects and regions in the United States were not analyzed.
In addition, this report did not analyze the impacts of climate change on other countries,
Compared to the United States, it may be much more difficult for poorer and Jess mobile
societies to respond to climate change. It is not unreasonable to assume that climate change
could have important: geopolitical consequences,, which could have subsequent impacts on the
United States.
Effects Models. These models were calibrated for historic climate conditions and may not
accurately estimate future response to climate change.
would have affected the results presented in this
report (see "Limitations" box). Changes hi
variability as estimated by GCMs were examined for
this report. We found that no firm conclusions can
be drawn about how global warming could affect
variability.
The methods used to estimate impacts (for
example, how forests might change) also have
limitations because our scientific understanding of
physiological processes is limited and subject to
uncertainties. We have no experience with the rapid
wanning of 1.5 to 4.5°C projected to occur during
the next century. Many of the effects are estimated
based on knowledge of the response of systems to
known climate conditions. We cannot be certain
that a forest would be able to migrate, how higher
atmospheric concentrations of CO2 would affect
vegetation, whether fish would fina new habitats,
how agricultural pests would proliferate, or how
impacts would combine to create or reduce stress.
With some exceptions, we did not generally
examine human responses and adaptations to effects
of climate change. The report was intended to
examine sensitivities and potential vulnerabilities of
current systems to climate change. Many other
changes will also take place in the world at the
same time that global climate is changing. We
cannot anticipate how changing technology, scientific
advances, urban growth, and changing demographics
will affect the world of the next century. These
changes and many others may singularly, or hi
combination, exacerbate or ameliorate the impacts
of global climate change on society.
The results are also inherently limited by our
imaginations. Until a severe event occurs, such as
the drought of 1988, we fail to recognize the close
links between our society, the environment, and
climate. For example, in this report we did not
analyze the reductions in barge shipments on the
Mississippi River due to lower river levels, the
xxix
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Executive Summary
increases in forest fires due to dry conditions, or the
impacts of disappearing prairie potholes on ducks;
all these impacts were made vivid during 1988. The
drought reminded us of our vulnerability as a
nation, but it cannot be viewed as a prediction of
things to come.
MAJOR FINDINGS
The findings collectively suggest a world
different from the world that exists today, although
there are many uncertainties about specific effects.
Global climate change could have significant
implications for natural ecosystems; for where and
how we farm; for the availability of water to irrigate
crops, produce power, and support shipping; for
how we live in our cities; for the wetlands that
spawn our fish; for the beaches we use for
recreation; and for all levels of government and
industry.
The rate of global warming may be the most
important factor affecting both natural and managed
systems. The faster the warming, the harder it will
be to adapt. The ability of natural ecosystems
(forests, wetlands, barrier islands, national parks) to
adapt to a rapidly warming climate is limited. Rates
of natural migration and adaptation could be much
slower than the rate of climate change. Populations
of many species and inhabited ranges could
decrease, and many may face extinction. The
ultimate effects could last for centuries and would
be virtually irreversible. Whether human
intervention could mitigate these effects was not
studied.
Managed systems may show more resilience.
For example, although sea level rise may put
additional stresses on coastal cities and although
changes in temperature and rainfall patterns may
require new strategies for managing water resources
and agriculture, we could adapt to changing climate
relatively quickly, if we have enough financial
resources. We would expect that basic
requirements for food and water could be met in
the United States (as crops are shifted and water
management systems are modified), and that
developed areas with high economic value could be
protected against sea level rise (as bulkheads and
levees are built). The total cost of adapting to
global climate change is beyond the scope of this
report. It appears it could be expensive, but
affordable, fora highly industrialized country like
the United States to adapt managed systems in
response to gradual global warming. If change
comes more quickly, adaptation by managed systems
will be more difficult and expensive. If it comes
more slowly, the cost and difficulty of adaptation
will be less.
In many cases, the results of our analysis
appear to be consistent across scenarios, because
either increasing temperatures or higher sea levels
dominate the systems that were studied. For
example, higher temperatures would cause earlier
snowmelt, a northward migration of forests, and a
northward shift in crops, and higher sea levels could
inundate wetlands and low-lying areas. In other
cases, however, only a range of values can be
presented because uncertainties in an important
variable, such as precipitation, make the direction of
change highly uncertain.
The main findings and policy implications of
this report are presented in national and regional
chapters. They are summarized in the following
pages, but the reader is urged to explore the full
report to understand the complete context of these
results.
NATIONAL FINDINGS
Natural Systems
The location and composition of various plants
and animals in the natural environment depend, to
a great extent, on climate. Trees grow in certain
areas and fish exist in streams and lakes because the
local climate and other conditions are conducive to
reproduction and growth. A major focus of this
report was to identify what may happen to plants
and animals, as a result of climate change —
whether they would survive in their current locations
or be able to migrate to new habitats, and how soon
these ecosystems could be affected. The following
descriptions of impacts on natural systems are
subject to uncertainties about climate change and
the responses of natural systems to such change.
Natural Systems May Be Unable to Adapt Quickly
to a Rapid Warming
If current trends continue, climate may change
too quickly for many natural systems to adapt. In
the past, plants and animals adapted to historic
XXX
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Effects of Climate Change
climate changes over many centuries. For example,
since the last ice age 18,000 years ago, oak trees
migrated northward from the southeastern United
States as the ice sheet receded. Temperatures
warmed about 5°C (9°F) over thousands of years,
but they rose slowly enough for forests to migrate at
the same rate as climate change. In the future, the
greenhouse effect may lead to similar changes in the
magnitude of warming, but the changes may take
place within a century. Climate zones may shift
hundreds of miles northward, and animals and
especially plants may have difficulty migrating
northward that quickly.
Forests
Forests occupy one-third of the land area of
the United States. Temperature and precipitation
ranges are among the determinants of forest
distributions. Forests are also sensitive to soils, light
intensity, air pollution, pests and pathogens,
disturbances such as fires and wind, and
management practices.
Several approaches were used to examine
geographic shifts in forests. Potential ranges of
forests were estimated for eastern North America
using temperature and precipitation correlations
from pollen data. Changes in composition and
abundance of particular forests were estimated for
particular sites in the Great Lakes and Southeast
using site-specific models. These regions were
chosen to represent a diversity of forest types and
uses. Finally, the ability of trees to migrate to new
habitats was analyzed using shifts in climate zones
from GCMs and historic rates of tree migration.
This study focused on several species that are widely
dispersed across the northeastern United States.
The direct effects of CO2, which could change
water-use efficiency, pest interactions, and the
competitive balance among plants, were not
modeled, nor were reforestation or the suitability of
soils and sunlight considered. It is not clear how
these results would have been affected if such
factors had been included.
The Range of Trees May Be Reduced
Figure 4 shows the potential shifts in forest
ranges in response to climate change. The scenarios
assume that climate change could move the
southern boundary northward by 600-700 km
Hemlock
Potential Range
Inhabited Range
Present Range
Sugar Maple
Range After 2050: GISS
Range After 2050: GFDL
Present Range
Range After 2050: GISS Range After 2050: GFDL
Scale 0 400Km
Figure 4. Shifts in range of hemlock and sugar maple under alternative climate scenarios.
xxxi
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Executive Summary
(approximately 400 miles), while the northern
boundary would move only as fast as the rate
ofmigration of forests. Assuming a migration rate
of 100 km (60 miles) per century, or double the
known historic rate, the inhabited ranges of forests
could be significantly reduced because the southern
boundary may advance more quickly than the
northern boundary. Even if climate stabilizes, it
could take centuries for migration to reverse this
effect. If climate continues to warm, migration
would continue to lag behind shifts in climate zones.
If elevated CO2 concentrations increase the water-
use efficiency of tree species and pest infestations
do not worsen, the declines of the southern ranges
could be partly alleviated. Reforestation could help
speed the migration of forests into new areas.
Changes in Forest Composition Are Likely
Climate change may significantly alter forest
composition and reduce the land area of healthy
forests. Higher temperatures may lead to drier soils
in many parts of the country. Trees that need
wetter soils may die, and their seedlings could have
difficulty surviving these conditions. A study of
forests in northern Mississippi and northern Georgia
indicated that seedlings currently in such areas
would not grow because of high temperatures and
dry soil conditions. In central Michigan, forests now
dominated by sugar maple and oak may be replaced
by grasslands, with some sparse oak trees surviving.
These analyses did not consider the introduction of
species from areas south of these regions. In
northern Minnesota, the mixed boreal and northern
hardwood forests could become entirely northern
hardwoods. Some areas might experience a decline
in productivity, while others (currently saturated
soils) might have an increase. The process of
changes in species composition would most likely
continue for centuries. Other studies of the
potential effects of climate change in forests imply
northward shifts in ranges and significant changes in
composition, although specific results vary
depending on sites and scenarios used.
Changes May Begin in 30 to 80 Years
Forest change may be visible in a few decades
from now. This would involve a faster rate of
mortality among mature trees and a decline in
seedlings and growth of new species. The studies of
forests in the Southeast and Great Lakes indicate
that these forests could begin to die back in 30 to 80
years. Figure, 5 displays possible reductions in
balsam fir trees in northern Minnesota and forests
in Mississippi in response to two different scenarios
180
160
f 140
t
w 120
i 10°
S 80
a
8 80
40
20
0
MISSISSIPPI FORESTS MINNESOTA BALSAM FIR
— — — GtSSA
"•
_____
— "- '"s. — "1^.
X
^s
v
\
\
\
\
\
\
i I I I I \ !-*•
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s
s
-~
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a_ 4000
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tr
_i
5 2000
n
GISSA*
GISSB**
_^ — i.^
""" *^^^***^^
VN^====^- — "
x "x.
1 > " -..o^-t. 1
1980 2000 2020 2040 2060 1980 2000 2020 2040 2060 2080
YEAR YEAR
* Assumes constant exponential
growth in emissions
" Assumes constant arithmetic
growth In emissions
Figure 5. Forest declines due to temperature increases.
xxxii
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Effects of Climate Change
of wanning. At the same time in Minnesota, for
example, sugar maple could become more abundant.
These forests appear to be very sensitive to small
changes in climate, because dieback starts to
become noticeable after an approximate 1 to 1.5°C
warming. Once this process starts, major dieback
may occur rapidly. The timing of a decline is
sensitive to the rate of climate change; a warming
slower than that assumed in the scenarios would
delay the dieback.
Other Factors Will Influence Forest Health
The health of forests will not be determined by
climate change alone. The drier soils expected to
accompany climate change could lead to more
frequent fires, warmer climates may cause changes
hi forest pests and pathogens, and changes in air
pollution levels could reduce the resilience of
forests. Continued depletion of stratospheric ozone
would also further stress forests. None of these
outcomes was considered by the forest studies in
this report, although they could speed forest
declines.
Biodiversity
Biological diversity can be defined as the
variety of species in ecosystems, and the genetic
variability within each species and the variety of
ecosystems around the world. Over 400 species of
mammals, 460 species of reptiles, 660 species of
freshwater fishes, and tens of thousands of
invertebrate species can be found hi this country, in
addition to some 22,000 plant species. About 650
species of birds reside in or pass through the United
States annually. Biological diversity is needed to
provide food, medicine, shelter, and other important
products.
This report examined the impacts of climate
change on specific plants and animals by using
climate change scenarios and models of particular
species or systems within a region. Analyses have
been performed for impacts on finfish and shellfish
in the Apalachicola Bay in the Florida Panhandle,
fish hi the Great Lakes, and marine species in San
Francisco Bay. Additional information on potential
impacts on biodiversity was gathered from the
published literature.
Extinction of Species Could Increase
Historic climate changes, such as the ice ages,
have led to extinction of many species. More
recently, human activities, such as deforestation,
have greatly accelerated the rate of species
extinction. The faster rate of climate warming due
to the greenhouse effect, absent an active program
to preserve species, would most likely lead to an
even greater loss of species. The uncertainties
surrounding the rate of warming, the response of
individual species, and interspecies dynamics make
it difficult to assess the probable impacts, although
natural ecosystems are likely to be destabilized in
unpredictable ways.
As with trees, other plants and animals may
have difficulty migrating at the same rate as a
rapidly changing climate, and many species may
become extinct or their populations maybe reduced.
The presence of urban areas, agricultural lands, and
roads would restrict habitats and block many
migratory pathways. These obstacles may make it
harder for plants and wildlife to survive future
climate changes. On the other hand, some species
may benefit from climate change as a result of
increases in habitat size or reduction hi population
of competitors. The extent to which society can
mitigate negative impacts through such efforts as
habitat restoration is not clear.
Impacts on Fisheries Would Vary
Freshwater fish populations may grow in some
areas and decline in others. Fish hi such large
water bodies as the Great Lakes may grow faster
and may be able to migrate to new habitats.
Increased amounts of plankton could provide more
forage for fish. However, higher temperatures may
lead to more aquatic growth, such as algal blooms,
and decreased mixing of lakes Gonger stratification),
which would deplete oxygen levels hi shallow areas
of the Great Lakes, for example Lake Erie, and
make them less habitable for fish. Fish hi small
lakes and streams may be unable to escape
temperatures beyond their tolerances, or then-
habitats may simply disappear.
Warmer temperatures could also exceed the
thermal tolerance of many marine finfish and
shellfish hi some southern locations, although some
marine species could benefit. The full impacts on
marine species are not known at this tune. The loss
of coastal wetlands could further reduce fish
populations, especially shellfish. And while
increased salinity hi estuaries could reduce the
abundance of freshwater species, it could increase
the presence of marine species. Whether finfish and
xxxui
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Executive Summary
shellfish could migrate to new areas and the
effectiveness of restocking were not studied.
Effects on Migratory Birds Would Depend on
Impacts on Habitats
Migratory birds are likely to experience mixed
effects from climate change, with some arctic-
nesting herbivores benefiting, and continental
nesters and shorebirds suffering. Some winter
habitats could experience increased productivity.
On the other hand, the loss of wintering grounds,
which may result from sea level rise and changing
climate, could harm many species, as would the loss
of inland prairie potholes resulting from potentially
increased midcontinental dryness.
Sea Level Rise
A rise in sea level is one of the more probable
impacts of climate change. Higher global
temperatures will expand ocean water and melt
some mountain glaciers, and may eventually cause
polar ice sheets to discharge ice. Over the last
century, global sea level has risen 10 to 15 cm (4 to
6 inches), and along the U.S. coastline, relative sea
level rise (which includes land subsidence) has
averaged about 30 cm (1 foot). Published estimates
of sea level rise due to global warming generally
range from 0.5 to 2.0 meters (1.5 to 7 feet) by 2100.
Sea level rise could be greater than or less than this
range because uncertainties exist regarding the rate
of atmospheric wanning, glacial processes, oceanic
uptake of heat, precipitation in polar areas, and
other variables.
The studies estimate the potential nationwide
loss of wetlands, and the cost of defending currently
developed areas from a rising sea, for three
scenarios (50, 100, and 200 cm) of sea level rise by
the year 2100. The scenarios are based on
quantitative estimates of sea level rise, but no
probabilities have been attributed to them. Wetland
loss estimates were based on remote-sensing data
and topographic maps for a sample of sites along
the U.S. coast. The cost of holding back the sea
was based on (1) the quantity of sand necessary to
elevate beaches and coastal barrier islands as sea
level rises; (2) rebuilding roads and elevating
structures; and (3) constructing levees and
bulkheads to protect developed lowlands along
sheltered waters.
Protectins Developed Areas May Be Expensive
Given the high property values of developed
coastlines in the United States, it is likely that
measures would be taken to hold back the sea along
most developed shores. Preliminary estimates
suggest that the cumulative capital cost (including
response to current sea level rise) of protecting
currently developed areas would be $73 to $111
billion (in 1988 dollars) through 2100 for a 1-meter
global rise (compared with $4 to $6 billion to
protect developed areas from current trends in sea
level rise). A 1-meter sea level rise would lead to
a cumulative inundation of 7,000 square miles of
dryland — an area the size of Massachusetts (see
Table 1). If the oceans continue to rise at current
rates, approximately 3,000 square miles of dryland
would be lost.
Most Coastal Wetlands Would Be Lost
Historically, wetlands have kept pace with a
slow rate of sea level rise. However, in the future,
sea level will probably rise too fast for some
marshes and swamps to keep pace. Although some
wetlands can survive by migrating inland, a study on
coastal wetlands estimated that for a 1-meter rise,
26 to 66% of wetlands would be lost, even if
wetland migration were not blocked. A majority of
these losses would be in the South (see Table 2).
Efforts to protect coastal development would
increase wetland losses, because bulkheads and
levees would prevent new wetlands from forming
inland. If all shorelines are protected, 50 to 82% of
wetlands would be lost. The different amounts of
dryland lost for different regions and scenarios are
shown in Figure 6.
The loss of wetland area would have adverse
ecological impacts, with the ability of ecosystems to
survive a rising sea level depending greatly on how
shorelines are managed. For many fish and shellfish
species, the fraction of shorelines along which
wetlands can be found is more important than the
total area of wetlands. This fraction could remain
at approximately present levels if people do not
erect additional bulkheads and levees. In Louisiana,
with 40% of U.S. coastal wetlands, large areas of
wetlands are already being converted to open water
as a result of natural subsidence and the effects of
human activities, and most could be lost by 2030 if
current trends continue.
xxxiv
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Effects of Climate Change
Table 1. Nationwide Impacts of Sea Level Rise
Alternative
Sea Level Rise by 2100
Baseline*
50cm
100cm
200cm
If Densely Developed Areas
Are Protected
Shore protection costs
(billions of 1986 dollars)
Dryland lost (mi2)
Wetlands lost (%)
If No Shores Are Protected
Dryland lost (mi2)
Wetlands lost (%)
If All Shores Are Protected
Wetlands lost (%)
4-6
1,500-4,700
9-25
N.C.
32-43
2,200-6,100
20-45
73-111
4,100-9,200
29-69
169-309
6,400-13,500
33-80
N.C. 3,300-7,300 5,100-10,300 8,200-15,400
N.C. 17-43 26-66 29-76
38-61
50-82
66-90
N.C. = Not calculated.
*Baseline assumes current global sea level rise trend of 12 cm per century. Given coastal subsidence trends, this
implies about a 1-foot rise in relative sea level along most of the U.S. coast.
Source: Assembled by Titus and Greene.
Table 2. Loss of Coastal Wetlands from a One-Meter Rise in Sea Level
Region
Northeast
Mid-Atlantic
South Atlantic
South and West
Florida
Louisiana3
Other Gulf
West
United States
Current
wetlands
area (mi2)
600
746
3,813
1,869
4,835
1,218
64
13,145
All
dryland
protected
(% loss)
16
70
64
44
77
85
56
50-82
Current
development
protected
(% loss)
10
46
44
8
77
76b
gain0
29-69
No
protection
(% loss)
2
38
39
7
77 :
75 :
• b
gain"
26-66
aLouisiana projections do not consider potential benefits of restoring flow of sediment and freshwater.
bPotential gain in wetland acreage not shown because principal author suggested that no confidence could be
attributed to those estimates. West Coast sites constituted less than 0.5% of wetlands in study sample.
Source: Adapted from Park et al.
xxxv
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Executive Summary
A. DRYLAND LOSS BY 2100 WITHOUT SHORE PROTECTION
ss
Northeast
SEA LEVEL RISE
SCENARIO:
Mld-
Atlantlc
South
Atlantic
South
&West
Florida
Louisiana other Gull
B. DRYLAND LOSS BY 2100 WITH PROTECTION OF DEVELOPED AREAS
2.6
26
2,4
22
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
02
0.0
Mid-
Atlantic
South
Atlantic
South
&West
Florida
Figure 6. Dryland loss by 2100.
Estuaries May Enlarge and Become More Saline
Although future riverflows into estuaries are
uncertain, a rise in sea level would increase the size
and salinity of estuaries and would increase the
salinity of coastal aquifers. For example, sea level
rise may result in a more saline and enlarged
Sacramento-San Joaquin Delta, and Miami, New
York, and other coastal communities would have to
step up current efforts to combat salinity increases
in surface water and groundwater supplies.
Agriculture
The temperate climate and rich soils in the
United States, especially in the Midwest, have
helped make this country the world's leading
agricultural producer. Agriculture, a critical
component of the U.S. economy, contributed 17.5%
of the gross national product in 1985, with farm
assets totaling $771 billion. Crop production is
sensitive to climate, soils, management methods,
and many other factors. During the Dust Bowl
years of the 1930s, wheat and corn yields dropped
by up to 50%, and during the drought of 1988, corn
yields declined about 40%.
The agricultural analyses in this report
examined potential impacts on crop yields and
productivity from changes hi climate and direct
effects of CO2. (Higher CO2 concentrations may
increase plant growth and water-use efficiency.)
The studies used high estimates of the beneficial
effects of CO2 on crops. Changes in dryland and
irrigated corn, wheat, and soybean yields and hi
irrigation demand were estimated for the Southeast,
Great Plains, and Great Lakes regions using widely
validated crop growth models. Crop yield changes
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Effects of Climate Change
were estimated for California using a simple
agroclimatic index. The studies did not examine
effects on yields of introduction of crops, such as
citrus, into new areas; changes in weed
growthcaused by higher CO, concentrations; or new
technologies, such as biotechnology. Some of these
changes could enhance the ability of agriculture to
adapt to global warming.
The estimated yield changes from the four
regional crop modeling studies and runoff changes
from the GCMs were used in a nationwide
agricultural economic model to estimate regional
and national changes in crop production, land use,
and demand for irrigation. The economic model
did not consider the introduction of new crops,
changes in government policies on agriculture,
change in demand for water for nonagricultural
uses, and global agricultural changes. Both a
modeling study and a literature review were used to
estimate changes in plant-pest interactions. An
agricultural runoff and leaching model was used to
estimate potential changes in water quality in the
Great Plains. Some farm-level adjustments,
including the effects of changed planting dates and
use of different varieties, were investigated in
various studies, and the potential national
implications on livestock were analyzed using
modeling studies and a literature review.
Yields Could Be Reduced. Although the Combined
Effects of Climate and CO2 Would Depend on the
Severity of Climate Change
In most regions of the country, climate change
alone could reduce dryland yields of corn, wheat,
and soybeans, with site-to-site losses ranging from
negligible amounts to 80%. These decreases would
be primarily the result of higher temperatures,
which would shorten a crop's life cycle. In very
northern areas, such as Minnesota, dryland yields of
corn and soybeans could increase as warmer
temperatures extend the frost-free growing season.
The combined effects of climate change and
increased CO2 may result in net increases in yields
in some cases, especially in northern areas or in
areas where rainfall is abundant. In southern areas,
however, where heat stress is already a problem,
and in areas where rainfall is reduced, crop yields
could decline.
Productivity Mav Shift Northward
Under all of the scenarios (with and without
the direct effects of increased CO2), the relative
productivity of northern areas for the crops studied
was estimated to rise in comparison with that of
southern areas. In response to the shift in relative
yields, grain crop acreage in Appalachia, the
Southeast, and the southern Great Plains could
decrease, and acreage in the northern Great Lakes
States, the northern Great Plains, and the Pacific
Northwest could increase (see Figure 7). A change
in agriculture would affect not only the livelihood of
farmers but also agricultural infrastructure and
other support services. The sustainability of crop
production in northern areas was not studied.
Changes in foreign demand for U.S. crops, which
would likely be altered as a result of global warming
and could significantly alter the magnitude of the
results, were not considered in this analysis.
The National Supply of Agricultural Commodities
Mav Be Sufficient to Meet Domestic Needs. But
Exports Mav Be Reduced
Even under the more extreme climate change
scenarios, the production capacity of U.S.
agriculture was estimated to be adequate to meet
domestic needs. Only small to moderate economic
losses were estimated when climate change
scenarios were modeled without the beneficial
effects of CO2 on crop yields. When the combined
effects of climate and CO2 were considered, results
were positive with a relatively wetter climate change
scenario and negative with the hotter, drier climate
change scenario. Thus, the severity of the economic
consequences could depend on the type of climate
change that occurs and the ability of the direct
effects of CO2 to enhance yields. A decline in crop
production would reduce exports, which could have
serious implications for food-importing nations. If
climate change is severe, continued and substantial
improvements in crop yields would be needed to
fully offset the negative effects. Technological
improvements, such as improved crop varieties from
bioengineering, could be helpful in keeping up with
climate change. These results could be affected by
global changes in agriculture, which were not
considered in the analysis.
Farmers Would Likely Change Many of Their
Practices
Farm practices would likely change in response
to different climate conditions. Most significantly,
in many regions, the demand for irrigation is likely
to increase as a result of higher temperatures. If
national productivity declines, crop prices may rise,
making irrigation more economical and increasing
xxxvu
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Executive Summary
r i GISS
II GFDL
GISS +Dlrect Effects of CO2
GFDL+Dlrect Effects of CO2
Figure 7. Percent change in regional agricultural acreage.
I I GISS
II GFDL
GISS +Dlrect Effects of COg
GFDL+Dlrect Effects of CO2
Southern Plains
Figure 8. Change in regional irrigation acreage (100,000 of acres).
xxxvm
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Effects of Climate Change
the use of it (see Figure 8). Irrigation equipment
may be installed in many areas that are currently
dryland farms, and farmers already irrigating may
extract more water from surface and groundwater
sources. Changes in competing demands for water
by municipal and industrial users, which could raise
the cost of irrigation, were not considered. Farmers
may also switch to more heat- and drought-resistant
crop varieties, plant two crops during a growing
season, and plant and harvest earlier. Whether
these adjustments would compensate for climate
change depends on a number of factors, including
the severity of the climate change. Under extreme
climate change conditions, some farms could be
abandoned.
Ranees of Agricultural Pests May Extend
Northward
Warmer temperatures may result in the
northward extension of the range of diseases and
pests that now afflict livestock in the South, and
could make conditions more favorable for the
introduction of new livestock diseases into the
southern United States. This extension could
reduce crop yields and affect livestock.
Shifts in Agriculture Mav Harm the Environment in
Some Areas
Expansion of irrigation and shifts in regional
production patterns imply more competition for
water resources, greater potential for surface water
and groundwater pollution, loss of some wildlife
habitats, and increased soil erosion. A northward
migration of agriculture would increase the use of
irrigation and fertilizers on sandy soils, thus
endangering the quality of underlying groundwater.
Chemical pesticide usage may change to control
different crop and livestock pests. Thus, climate
change could exacerbate environmental pollution
and increase resource use from agriculture in some
areas.
Water Resources
The United States is endowed with a bountiful
supply of water, but the water is not always in the
right place at the right time or of the right quality.
In some regions, such as the Great Basin and the
Colorado River Basin, the gap between demand and
supply of water is narrow. In these basins, such
offstream uses as irrigation and domestic
consumption often conflict with each other and with
other needs, such as maintaining flow to preserve
environmental quality.
Although global precipitation is likely to
increase, it is not known how regional rainfall
patterns will be affected. Some regions may have
more rainfall, while others may have less.
Furthermore, higher temperatures would most likely
increase evaporation. These changes would likely
create new stresses for many water management
systems.
To discuss the potential impacts of climate
change on water resources, this report studied water
resources in California, the Great Lakes, and the
Southeast, estimated the demand for irrigation in
the Great Plains, and drew on information from the
literature. These studies focused on changes in
runoff and, for California and the Southeast,
considered management responses. The studies
examined the water management systems as they
are currently configured and did not examine new
construction. Among other factors not considered
were changes in demand for water resources (which
would most likely lead to greater changes in water
management systems) and changes in vegetation due
to climate change and increased CO^, which could
affect runoff. The studies did not estimate impacts
on groundwater.
The Direction of Change in Some Water Bodies
Can Be Estimated, but Total Impacts in the United
States Cannot Be Determined
Results of hydrology studies indicate that it is
possible in some regions to identify the direction of
change in water supplies and quaiity due to global
wanning. For example, in California, higher
temperatures would reduce the snowpack and cause
earlier melting. Earlier runoff from mountains
could increase winter flooding and reduce deliveries
to users. In the Great Lakes, reduced snowpack
combined with potentially higher evaporation could
lower lake levels (although certain combinations of
conditions could lead to higher levels). In other
areas, such as the South, little snowcover currently
exists, so riverflow and lake levels depend more on
rainfall patterns. Without better rainfall estimates,
we cannot determine whether riverflow and lake
levels in the South would rise or fall.
Water Quality in Many Basins Could Change
Changes in water supply could significantly
affect water quality. Where riverflow and lake
xxxix
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Executive Summary
levels decline, such as in the Great Lakes, there
would be less water to dilute pollutants. On the
other hand, where there is more water, water
quality may improve. Higher temperatures may
enhance thermal stratification in some lakes and
increase algal production, degrading water quality.
Changes in runoff and leaching from farms and
potential increases in the use of irrigation for
agriculture could affect surface and groundwater
quality in many areas.
Water Use Conflicts May Increase
In some regions, decreased water availability
and increased demand for water, such as for
irrigation and powerplant cooling, may intensify
conflicts among offstream uses. Conflicts between
these offstream uses and instream uses such as
flood control and wildlife habitat also may be
intensified.
Electricity Demand
The demand for electricity is influenced by
economic growth, by changes in industrial and
residential/commercial technologies, and by climate.
The principal climate-sensitive electricity end uses
are space heating and cooling and, to a lesser
degree, water heating and refrigeration. These uses
of electricity may account for up to a third of total
sales for some utilities and may contribute an even
larger portion of seasonal and daily peak demands.
This report analyzed potential changes hi the
national demand for electricity in 2010 and 2055,
using the relationship between demand and climate
for several major utility systems. The study
estimated changes in demand due to nonclimate
factors, such as increases in population and GNP.
The impacts of climate change are expressed as an
increase over non-climate growth, and results are
given on nationwide and regional bases. The study
did not consider changes in technology and
improvements in energy efficiency; the impacts of
higher temperatures on the demand for natural gas
and oil for home heating, which will most likely
decrease; changes in electricity supplies, such as
hydropower; or changes in demand for electricity
for such uses as irrigation.
National Electricity Demand Would Rise
Global warming would increase annual demand
for electricity and total generating capacity
requirements in the United States. The demand for
electricity for summer cooling would increase, and
the demand for electricity for winter heating would
decrease. Annual electricity generation in 2055 was
estimated under the transient scenarios to be 4 to
6% greater than without climate change. The
annual costs of meeting the increase due to global
warming, assuming no change in technology or
efficiency, was estimated to be $33-$73 billion (in
1986 dollars). These results differ on a regional
basis and are shown in Figure 9. States along the
northern tier of the United States could have net
reductions in annual demand of up to 5%, because
decreased heating demand would exceed increased
demand for air-conditioning. In the South, where
heating needs are already low, net demand was
estimated to rise by 7 to 11% by 2055.
Generating capacity requirements are
determined largely by peak demand, which occurs
in the summer in all but the far northern areas of
the country. By 2010, generating requirements to
meet increased demand could rise by 25 to 55
gigawatts (GW), or by 9 to 19% above new capacity
requirements, assuming no climate change. By
2055, generating requirements could be up by 200 to
400 GW, or 14 to 23% above non-climate-related
growth. The cumulative cost of such an increase in
capacity, assuming no change in technology or
improvements hi energy efficiency, was estimated to
be between $175 and $325 billion (hi 1988 dollars).
The South would have a greater need than the
North for additional capacity, as shown hi Figure 10.
Increases in capacity requirements could range from
0 to 10% in the North, to 20 to 30% in the South
and Southwest. U.S. emissions of such greenhouse
gases as CO2 could increase substantially if
additional powerplants are built to meet these
capacity requirements, especially if they burn coal.
Improvement in the efficiency of energy production
and use would reduce these emissions.
Air Quality
Air pollution caused by emissions from
industrial and transportation sources is a subject of
concern hi the United States. Over the last two
decades, considerable progress has been made hi
improving air quality by reducing emissions. Yet
high temperatures hi the summer of 1988 helped
raise tropospheric ozone levels to all-tune highs hi
many U.S. cities. But air quality is also directly
affected by other weather variables, such as
xl
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Effects of Climate Change
Figure 9. Changes in electricity generation by state, induced by climate change scenarios in 2055.
Figure 10. Changes in electricity capacity additions by state, induced by climate change scenarios in 2055.
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Executive Summary
windspeed and direction, precipitation patterns,
cloud cover, atmospheric water vapor, and global
circulation patterns.
A literature review of the relationship between
climate and air pollution was conducted for this
report. In addition, air quality models were used
for a preliminary analysis of the changes in ozone
levels in several regions. The latter analysis did not
consider reduction in emissions of air pollutants due
to enforcement of the Clean Air Act.
Climate Changes Could Increase Air Pollution.
Especially Smog
A rise in global temperatures would increase
manmade and natural emissions of hydrocarbons
and manmade emissions of sulfur and nitrogen
oxides over what they would be without climate
change. Natural emissions of sulfur would also
change, but the direction is uncertain. Although the
potential magnitude of the impacts of the increased
emissions on air quality is uncertain, higher
temperatures would speed the reaction rates among
chemicals in the atmosphere, causing higher ozone
pollution in many urban areas than would occur
otherwise. They would also increase the length of
the summer season, usually a time of high air
pollution levels. As shown in Figure 11, preliminary
analyses of a 4°C temperature increase in the San
Francisco Bay area (with no changes in other
meteorologic variables, such as mixing heights),
assuming no change in emissions from current
levels, suggest that maximum ozone concentrations
would increase by 20%, and that the area exceeding
the National Ambient Air Quality Standards would
almost double. Studies of the Southeast also show
expansion of the areas violating the standards, but
they show smaller changes in levels. Although the
impacts of higher temperatures on acid rain were
not analyzed, it is likely that sulfur and nitrogen
would oxidize more rapidly under higher
temperatures. The ultimate effect on acid
deposition is difficult to assess because changes in
clouds, winds, and precipitation patterns are
uncertain.
Exceeds Standard
<6 >6 >8
Base Case
August 6, 1981
Climate Sensitivity Scenario No. 1
4°C Temperature Increase
Figure 11. Changes in maximum daily ozone concentrations.
xlii
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Effects of Climate Change
Health Effects
Human illness and mortality are linked in
many ways to weather patterns. Weather affects
contagious diseases such as influenza and
pneumonia, and allergic diseases such as asthma.
Mortality rates, particularly for the elderly and the
very ill, are influenced by the frequency and severity
of extreme temperatures. The life cycles of disease-
carrying insects, such as mosquitoes and ticks, are
affected by changes in temperature and rainfall, as
well as by habitat, which is itself sensitive to climate.
Finally, increased air pollution, which is related to
weather patterns, can heighten the incidence and
severity of such respiratory diseases as emphysema
and asthma.
Both expert judgment and modeling were used
to study the potential impacts of climate change on
human health. A literature review and workshop
were conducted to identify potential changes in
vector-borne diseases caused by ticks, fleas, and
mosquitoes (such as dengue and malaria). Models
were used to estimate potential geographic shifts in
the prevalence of Rocky Mountain spotted fever and
malaria. Potential changes in mortality from heat
and cold stress were quantitatively estimated,
although such estimates did not consider changes in
air pollution levels. The total impacts of climate
change on human health are difficult to assess; these
analyses looked at a limited number of potential
effects and are only indicative of possible changes in
mortality and morbidity.
Summer Mortality Could Increase. While Winter
Mortality Could Decrease
Global warming may lead to changes in
morbidity and increases in mortality, particularly for
the elderly during the summer. Morbidity and
mortality may decrease because of milder winters,
although net mortality may increase. If the
frequency or intensity of climate extremes increases,
mortality is likely to rise. If people acclimatize by
using air-conditioning, changing their workplace
habits, and altering the construction of their homes
and cities, the impact on summer mortality rates
may be substantially reduced.
Regional Morbidity Patterns Could Change
Changes in climate as well as in habitat may
alter the regional prevalence of vector-borne
diseases. For example, some forests may become
grasslands, thereby modifying the incidence of
vector-borne diseases. Changes in summer rainfall
could alter the amount of ragweed growing on
cultivated land, and changes in humidity may affect
the incidence and severity of skin infections and
infestations such as ringworm, candidiasis, and
scabies. Increases in the persistence and level of air
pollution episodes associated with climate change
would have other harmful health effects.
Urban Infrastructure
The value of municipal infrastructure in the
United States, excluding buildings and electric
power production, probably approaches one trillion
dollars. The majority of the nation's investments
are in water supply, wastewater transport and
treatment facilities, drainage, roadways, airports,
and mass transit facilities. Like the regions studied
for this report, urban areas would feel a variety of
impacts from climate change. This report examined
the potential impacts of climate change on
Cleveland, New York City, and Miami. These areas
encompass a diversity of climates and uses of
natural resources.
Much of the current inventory in urban
infrastructure will most likely turn over in the next
35 to 50 years. A warmer global climate would
require changes in the capital investment patterns of
cities for water supplies, peak electric generating
capacity, and storm sewer capacity. Urbanized
coastal areas might have to invest additional billions
of dollars into coastal protection to defend
developed areas from a rising sea. In Miami, for
example, this could imply an increase of 1 to 2% in
the city's capital spending over the next 100 years.
Generally, northern cities such as Cleveland may
fare better, since reductions in the operating and
maintenance costs associated with heating public
buildings, snow removal, and road maintenance
should offset increasing costs for air-conditioning
and port dredging (see Table 3).
REGIONAL IMPACTS
Studying the national impacts of climate change
may disguise important differences in regional
effects across the country. Shifting demands for
economic and natural resources may cause stresses
that cannot be seen at a national level.
Furthermore, changes in one system, such as water
supply, may affect other systems such as irrigation
xliii
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Executive Summary
Table 3. Estimated Impacts of Doubled CO2 Scenarios on Cleveland's Annual Infrastructure Costs (millions of
1987 dollars)
Cost category
Annual
operating costs
Heating
Air-conditioning
Snow and ice control
Frost damage to roads
Road maintenance
Road reconstruction
Mass transit
River dredging
Water supply
Stormwater system
Total
-2.3
+6.6-9.3
-4.5
-0.7
-0.5
-0.2
summer increase offsets
winter savings
less than $0.5
negligible
negligible
-1.6 to +1.1
Source: Walker et al.
for agriculture. These combined effects may be
most evident on a regional scale. The designs of
the regional studies on agriculture, forests, and
electricity were described above.
The studies discussed below considered only
some of the potential regional impacts. Many
potential impacts were not analyzed — for example,
demographic shifts into or out of the Southeast,
recreational impacts in the Great Lakes, direct
effects on such aquifers as the Ogallala in the Great
Plains, and impacts on many specialty crops in
California In addition, current GCMs often
disagree significantly about simulated regional
changes, particularly about such key variables as
precipitation. Their spatial resolution is roughly of
the same size as the regions of concern; for
example, there are two simulation points in
California. The discussion that follows should not
be viewed as comprehensive, but rather as providing
examples of important issues for each region.
California
California contains a highly managed water
resource system and one of the most productive
agricultural regions in the world. The state
produces 14% of the nation's cash receipts for
agriculture. California's water resources are poorly
distributed in relation to its needs. Precipitation is
abundant in the north, with the highest levels in the
winter, while water is needed in the south for
agriculture and domestic consumption. The Central
Valley Project (CVP) and State Water Project
(SWP) were built basically to capture runoff from
the north and deliver it to uses in the south. These
xliv
-------
Effects of Climate Change
projects also provide flood protection, hydroelectric
power, and freshwater flows to repel salinity (known
as carriage water) in the Sacramento-San Joaquin
River Delta. Islands in the delta are highly
productive farmlands and are protected by levees.
The California case study focused on the
Central Valley. First, changes in runoff in the valley
were estimated. These results were then used to
estimate changes in deliveries from the CVP and
SWP and in agricultural water use. These results
were combined with sea level rise estimates and
were used to model how the salinity and shape of
the San Francisco Bay estuary may change and how
the demand for carriage water may be affected.
The estimated changes in salinity and sea level rise
were used to examine impacts on the ecology of the
bay. Yield changes for a number of crops grown in
the state were estimated, as were changes in ozone
levels in central California and changes in electricity
demand (see Figure 12).
California's Water Management System Would
Have to Be Modified
Warmer temperatures would change the
seasonalhy of runoff from the mountains
surrounding the Central Valley. Runoff would be
TEMPERATURE SCENARIOS
2X00316331X00,,
GFOL
OSli
WINTER SPRING SUMMER FALL
PRECIPITATION SCENARIOS
2xCO, lesslxCO,
Water Resources
Regional warming could cause:
• higher winter, lower summer runoff
• decreased deliveries from Central
Valley Project and State Water Project
• decreased water quality in subalpine
lakes
Wetlands and Fisheries
Sea level rise could cause:
• gradual inundation of wetlands
• increased salinity in and size of
San Francisco Bay
• shift from brackish and freshwater
species to marine species.
Agriculture
Increases in temperature and CO2
concentrations could cause:
• variable crop responses
• a northward shift in agricultural
production
• increased irrigation demand
resulting in groundwater extraction
and decreased water quality
Air Quality
Higher temperatures would increase
ambient ozone levels in central California
Electricity
Higher temperatures could increase
electricity demand
WINTER SPRING SUMMER FALL
Figure 12. California.
xlv
-------
Executive Summary
higher in the winter months as a result of less
snowpack and more precipitation in the form of
rain. Consequently, runoff would be lower in the
late spring and summer. Under these conditions,
the current reservoir system in the Central Valley
would not have the capacity to provide adequate
flood protection in the winter and store enough
water to meet deliveries in the summer. Thus,
much of the earlier winter runoff would have to be
released. This would leave less water in the system
for late spring and summer deliveries, when runoff
would be lower. Under the three GCM scenarios,
annual water deliveries from the SWP were
estimated to decrease by 200,000 to 400,000 acre-
feet (7 to 16% of supply). In contrast, the increase
in statewide demand for water from the SWP due to
non-climate factors, such as population growth, may
total 1.4 million acre-feet by 2010. Reduced
snowpack and earlier runoff could occur throughout
the West, exacerbating water management problems
in a region that is currently short of water.
Climate Change Is Likely to Increase Water
Demand
On the whole, California's water demand could
increase with a warmer climate. Twice as much
carriage water may be needed to repel higher
salinity levels resulting from a 1-meter sea level rise.
In addition, consumptive uses may also increase.
Irrigation, which may come from groundwater, may
increase in some parts of the state. If new
powerplants are built, they will need water for
cooling, which could come from surface water
supplies, depending on the location. Although it
was not studied, municipal demand for water may
also rise.
Sea Level Rise Would Affect the Size and
Environment of San Francisco Bay
A sea level rise would increase the salt
concentrations of San Francisco Bay. It is estimated
that a 1-meter rise could cause the salt front in the
Sacramento-San Joaquin River Delta to migrate
upstream 4 to 10 km (2.5 to 6 miles). Sea level rise
would also increase the difficulty of maintaining the
Sacramento-San Joaquin Delta islands. If the levees
around the delta islands were strengthened and
raised, a 1-meter rise could increase the volume of
the San Francisco Bay estuary by 15% and the area
by 30%. If the levees were not maintained and the
islands were flooded, there would be a doubling and
tripling, respectively, of the volume and area of the
bay. As a result of these changes, some wetlands
would be lost, marine aquatic species would become
relatively more abundant, and freshwater species
would decline.
Climate Change Could Degrade Air Quality in
California
Air quality is currently a major concern in
California. The area of central California in
violation of ozone quality standards could increase
as a result of higher temperatures. Under one
climate scenario, with a 4°C rise and current
emission levels, the maximum size of the area with
ozone levels in excess of the EPA standard of 0.12
ppm could double. This scenario assumed that such
climate variables as windspeed and mixing height
(the volume of air in which pollutants are diluted)
would not change.
Great Lakes
The Great Lakes contain 18% of the world's
supply and 95% of the U.S. supply of surface
freshwater, and they are an important source of
commerce and recreation for the region. In recent
years, reductions in pollutant loadings have
significantly unproved the quality of such water
bodies as Lake Erie. The Great Lakes States
produce 59% of the country's corn and 40% of its
soybeans, and their forests have important
commercial, recreational, and conservation uses.
Models were used to estimate the potential
impacts of climate change on lake levels and ice
cover. Results from these studies were used to
analyze impacts on navigation and shorelines.
Changes in the thermal structure of the Central
Basin of Lake Erie and southern Lake Michigan
were estimated. Output from these studies was
used along with scenario temperatures to analyze
potential impacts on fishes in the lakes. Changes in
crop yields were estimated for corn and soybean,
and changes hi forest composition were analyzed for
Michigan and Minnesota (see Figure 13).
Lake Levels Could Drop and Ice Cover Duration
Could Decrease
Higher temperatures would likely reduce
snowpack and could increase evaporation, which
would lower lake levels. The level of Lake Superior
was estimated to be reduced under the climate
scenarios by 0.4 to 0.5 meters (1.2 to 1.5 feet), and
xlvi
-------
Effects of Climate Change
TEMPERATURE SCENARIOS
2xCO. lesslxCO,
G1SS
GFDt
OSU
WINTER SPRING SUMMER FALL
PRECIPITATION SCENARIOS
2xCO2Iess1xCO2
WINTER SPRING SUMMER FALL
Lakes
Climate change could:
. cause average lake levels to fall by
0.5 to 2.5 meters
. reduce ice cover duration by 1-3 months
Adjustments may be required, including:
. increased dredging of harbors and
channels, or
• lower cargo capacities on ships
Water Quality
Changes in temperature and precipitation
could cause:
• greater stratification in lakes and
increased growth of algae, which in turn
could cause lower dissolved oxygen
levels in shallow areas
• an increase in pollutants resulting from
more dredging
Wetlands and Fisheries
Higher temperatures could cause:
• an increase in fish habitats in fall, winter,
and spring, and a decrease in summer
• accelerated growth for some fish species
• potential invasion by new species
Forests
Higher temperatures could result in:
• loss of mixed northern hardwood and
oak in southern areas
• shifts of mixed northern hardwood and
boreal forests in northern areas to all
northern hardwood
• forest declines evident in 30 to 60 years
Agriculture
Higher temperatures could cause:
• corn and soybean yields to increase in
North, decline in Cornbelt; mixed results
under climate change and COg
• acreage could expand in the North,
leading to increased erosion and runoff
Figure 13. Great Lakes.
that of Lake Michigan by 0.9 to 2.5 meters (3 to 8
feet). Diversions out of the lakes for irrigation or
to supply other basins would further lower lake
levels, although these impacts were not analyzed.
These results are very sensitive to assumptions
made about evaporation and under some
circumstances, lake levels could rise.
Higher temperatures would also reduce ice
cover on the lakes. Specifically, they could cut ice
duration by 1 to 3 months on Lake Superior and by
2 to 3 months on Lake Erie, although ice still would
form on both lakes. Changes in windspeed would
affect the reduction in duration of ice cover. In
response to lower lake levels, either ships would
have to sail with reduced cargoes or ports and
channels would have to be dredged. On the other
hand, a shorter ice season would allow a longer
shipping season.
xlvii
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Executive Summary
Water Quality May Be Degraded in Some Areas
Higher temperatures could lengthen
stratification of the lakes (where summer
temperatures warm the upper part of lakes and
isolate the cooler lower layers of lakes). Analysis of
the Central Basin of Lake Erie showed that longer
stratification, combined with increased algal
productivity, would most likely reduce dissolved
oxygen levels in the lower layers of the lake (see
Figure 14). Reducing pollutant loadings in the lake
would likely result in less severe impacts. One study
raised the possibility that the annual mixing of a
lake such as Lake Michigan may be disrupted. If
winds and storms increased, such outcomes would
be less likely. Disposal of contaminated dredge
soils could increase water pollution.
Fish Productivity in Open Areas Mav Increase
The average annual thermal habitat would
increase with a warmer climate (see Figure 15). If
sufficient oxygen is present, growth rates and
productivity for such fish as bass and lake trout in
open areas of large lakes may increase, provided
that the forage base also increases. However,
reduced ice cover and decreased water quality could
harm some species in shallow basins of the Great
Lakes. The effects of increased species interaction,
changes in spawning areas, and possible invasion of
exotic species were not analyzed.
Northern Agriculture Mav Benefit
As a result of the relative increase in northern
agricultural productivity, agriculture could be
enhanced in Minnesota, Wisconsin, and northern
Michigan with additional opportunities for the
agriculture support sector. The presence of
relatively poor soils, however, could limit
agricultural expansion. Increased cultivation in
northern areas could increase erosion and runoff,
with negative impacts on surface and groundwater
quality.
AUGUST 1970*
BASE CASE
40.6%
80.5%
94.4%
100%
AUGUST 1975*
0.0%
0.0%
5.9%
28.8%
* Base Case Years \///X Area That Is Anoxic (Has No Oxygen)
Figure 14. Area of central basin of Lake Erie that becomes anoxic under doubled CO2 scenarios.
xlviii
-------
Effects of Climate Change
± 2°C OF OPTIMUM TEMPERATURE
± 5°G OF OPTIMUM TEMPERATURE
100
JAN
DEC
Figure 15.
scenarios.
Increases in thermal habitat for lake trout in southern Lake Michigan under alternative climate
Abundance and Composition of Forests Could
ge
Northern hardwood forests in dry sites in
Michigan may die back and could become oak
savannas or grasslands. In northern Minnesota,
mixed boreal and northern hardwood forests may
become completely northern hardwoods.
Productivity in some wet sites in Michigan could
improve. Commercially important softwood species
could be replaced by hardwoods used for different
purposes. Changes in forests could be evident in 30
to 60 years. Whether reforestation with southern
species not currently in the region and CO2
fertilization would mitigate these impacts was not
studied.
Southeast
The Southeast is distinguished from the other
regions in this study by its warm temperatures,
abundant rainfall, large coastal plain, and productive
marine fisheries. The region supplies about half of
the nation's softwood and hardwood timber, and
tobacco, corn, and soybeans are among its major
crops. Over 85% of the nation's coastal wetlands
are in the Southeast, and over 43% of the finfish
and 70% of the shellfish harvested in the United
States are caught hi the region.
This report focused on two regions within the
Southeast: the Tennessee Valley and the
Chattahoochee and Apalachicola Rivers. The
Tennessee Valley Authority examined the potential
vulnerability of its water management system to
high and low riverflow scenarios (based on runoff
estimates from GCMs). Flow in the Chattahoochee
River Basin was estimated using hydrologic analysis
to study impacts on the management of Lake
Larder, which supplies water to Atlanta. The
estimates of outflow from the lake, along with
estimates of the flow in the Apalachicola River,
were combined with potential wetland losses
attributable to sea level rise to identify impacts on
finfish and shellfish in Apalachicola Bay. Sea level
rise impacts for the entire Southeast were derived
xlix
-------
CHAPTER 1
INTRODUCTION
Since the beginning of the Industrial Revolution,
human activities have led to increased
concentrations of greenhouse gases in the
atmosphere. Fossil fuel burning, which releases
CO2> CO, N2O, and other pollutants, has expanded
many times over. Changes in agriculture have led
to increased emissions of CH4 and
N2O.
Population growth has contributed to deforestation
in many areas of the globe, which in turn has
affected the global carbon cycle. Atmospheric
concentrations of tropospheric ozone and
chlorofluorocarbons have also increased, primarily
because of industrial activity.
Scientists have concluded that the increase in
greenhouse gas concentrations will eventually
change global climate. In 1979, the National
Academy of Sciences stated that a doubling of
carbon dioxide levels would lead to an increase of
1.5 to 4.5°C (2 to 8°F) in global air temperatures.
Since then, other researchers have examined the
increase in all greenhouse gases and have concluded
that a greenhouse gas increase equivalent to CO2
doubling could occur as early as the 2030s, with a
hypothesized commensurate global warming lagging
by several decades.
The Earth's atmosphere has undergone many
cycles of warming and cooling in the past.
Paleoclimatologists have estimated that at the glacial
maximum of the last ice age, which was about
18,000 years ago, the Earth was approximately 5°C
(9°F) cooler than at present. This is generally
attributed to changes in orbital characteristics
combined with lower trace gas concentrations and
different climate feedbacks.
Two aspects may make the current greenhouse
warming different from past climate changes. First,
it will raise temperatures higher than the planet has
experienced in the last 125,000 years. (During the
Pliocene Epoch (2 to 5 million years ago), global
temperatures were several degrees higher than they
are now.) Second, past climate changes of
comparable magnitude have generally occurred over
tens of thousands of years. Estimates are that the
greenhouse effect may raise atmospheric
temperatures several degrees in less than a century.
CONGRESSIONAL REQUEST
FOR REPORTS
The significant implications of the greenhouse
effect have been the subject of discussion within the
scientific community for the past three decades. In
recent years, Members of Congress have held
hearings and have begun to explain the implications
for public policy. This interest was accentuated
during a series of hearings held hi June 1986 by the
Senate Subcommittee on Pollution of the
Environment and Public Works Committee.
Following the hearings, members of the Senate
Environment and Public Works Committee sent a
formal request to the EPA Administrator, which
asked the Agency to undertake two studies on
climate change due to the greenhouse effect. (The
letter is reprinted in Appendix C of this report.)
One of the studies we are requesting should
examine the potential health and
environmental effects of climate change.
This study should include, but not be limited
to, the potential impacts on agriculture,
forests, wetlands, human health, rivers, lakes,
and estuaries, as well as other ecosystems
and societal impacts. This study should be
designed to include original analyses, to
identify and fill in where important research
gaps exist, and to solicit the opinions of
knowledgeable people throughout the
country through a process of public hearings
and meetings.
Congress also requested that EPA prepare a
study on policy options to stabilize current levels of
atmospheric greenhouse gas concentrations. That
study analyzes policy options for limiting gas
concentrations including energy efficiency,
alternative technologies, reforestation options,
chlorofluorocarbon (CFC) reductions, and other
options for limiting CH4 and N2O. It is entitled
-------
Effects of Climate Change
These changes could be evident in 30 to 80 years.
The forest studies did not consider whether more
southern species could be transplanted and survive
in the region, nor did they account for higher CO2
concentrations, which could mitigate some losses.
The combined effects of reduced agriculture and
forestry could lead to significant economic losses in
the Southeast.
Some Coastal Fish Species Would Be Harmed
Sea level rise could inundate most of the
coastal wetlands and raise salinity levels, which
could reduce the populations of gulf coast fisheries.
In addition, higher temperatures may exceed the
thermal tolerances of many species of shellfish in
gulf coast estuaries, further reducing fish
populations. Whether these species would be able
to migrate to cooler water was not considered.
Some species, however, could increase in
abundance, while others may migrate into the
region.
The Studies Were Unable to Determine Regionwide
Impacts on Water Resources
The Southeast currently has little winter
snowcover. Therefore, seasonal runoff depends
much more on changes in rainfall than on changes
in temperature that affect the size of snowpack.
Analysis of the rivers managed by the Tennessee
Valley Authority showed that increased runoff could
lead to higher riverflow and higher flood
probabilities, while less runoff could reduce flood
probabilities, but could lead to lower riverflow and
problems maintaining adequate supplies for
industrial use, powerplants, and dilution of effluent.
Use of climate change scenarios produced
inconclusive results concerning the potential change
in flow in the Chattahoochee River. A study of the
management of Lake Lanier concluded that changes
in operating rules would be sufficient to handle
higher or lower flows estimated in the scenarios,
although some uses would be restricted.
The Great Plains
Agriculture is one of the main sources of
income in the Great Plains. The States of Kansas,
Nebraska, Oklahoma, and Texas produced 80% of
the nation's sorghum and 30% of the wheat crop in
1982. In recent years, increased use of water from
the Ogallala Aquifer has reduced groundwater levels
in the region, with potential long-term consequences
for agriculture and the economy.
The studies in this report focused on Nebraska,
Kansas, Oklahoma, and Texas, and concentrated
mainly on agriculture-related impacts. They
estimated changes in corn, wheat, and soybean
yields and in the demand for irrigation. Changes in
runoff and leaching of chemicals from farms were
also examined (see Figure 17).
Crop Acreage Could Decline
The crop yield and economic adjustment
studies indicate that grain crop acreage could
diminish in the region. The direction of changes in
wheat and corn yields depends on the direct effects
of CO2 on crop growth and the severity of climate
change. If climate becomes hotter and relatively
drier, yields could decrease. Whatever the climate
change, relative productivity may decline compared
with northern areas. As a result, crop acreage was
estimated to drop by 4 to 22%. Such a reduction in
agriculture could adversely affect the economy of
the region. These studies did not consider use of
new technologies or introduction of new crops.
Demand for Irrigated Acreage Would Increase
The demand for irrigation on the farms that
continue to grow grain crops could increase.
Irrigated acreage, which currently makes up about
10% of the total acreage and is growing, could
increase by 5 to 30%. This report did not examine
how this demand would be satisfied, although the
Ogallala Aquifer could be a candidate. Other
impacts of global warming could change ground and
surface water supplies and, possibly, surface water
quality. Changes in precipitation could affect the
leaching of pesticides into groundwater and runoff
to surface waters in some cases, although the
direction of change cannot be determined because
runoff and leaching of pesticides and soils are very
sensitive to rainfall variability.
FINAL THOUGHTS AND POLICY
IMPLICATIONS
Because this is the most comprehensive study
to address the issue of the environmental effects of
climate change in the United States, we expect that
a sizable debate will follow its publication.
-------
Executive Summary
TEMPERATURE SCENARIOS
ZxCO, less 1xCO.
tin
WINTER SPKHQ SUMMER FALL
PRECIPITATION SCENARIOS
2xCO,less1xCO,
Agriculture
Higher temperatures could:
• reduce corn and wheat yields, and
could have mixed effects on yields
when considering both climate change
and increased CO2
• reduce crop acreage
Irrigation Demand
Changes in agriculture are likely to
result in increased irrigation demand
and acreage
Water Quality
Changes in rainfall, runoff, pesticide
loadings, erosion, and irrigation
could affect water quality
Electricity
Higher temperatures could increase
electricity demand
WINTER SPttHO SUMMER FALL
Figure 17. The Great Plains.
Considerable additional research and analyses are
likely to amplify, improve, and challenge these
findings. We expect further research to develop
new insights into the role of climate, but precise
forecasts must await more advanced climate models,
which may require many years to develop. For
some time to come, our ability to provide national
and local officials with guidance may be limited to
effects driven primarily by temperature and sea level
changes.
Apart from strategies to limit emissions of
greenhouse gases (discussed in the companion
report), policymakers should consider policy options
for adapting to global warming. Consideration of
these options is complicated by the uncertainties
identified in this report by delays in the onset of
climate change, and by the pressure to solve today's
problems. Many adaptations would undoubtedly
occur as climate changes, but some decisions being
made today have a long enough lifetime and
sufficient risk to support consideration of the
potential range of impacts of the greenhouse effect.
These decisions should be made if they make
economic and environmental sense for today's
conditions and are sufficiently flexible to handle
changing climate. Given the uncertainty about the
timing, magnitude, and regional scope of climate
change, we cannot plan for specific climate
conditions in the future, but we can strive to be
ready to respond to significantly changed climate
conditions in the future.
lii
-------
Effects of Climate Change
Conversely, natural resource management
should not assume that climate will not change. All
managers of natural resources that are sensitive to
climate should consider the vulnerabilities of their
systems to climate change and whether anticipatory
steps are prudent. In some cases, no anticipatory
action would be needed — the systems can be
adjusted and adapted as climate changes. In other
areas, where long-term decisions on sensitive
systems may result in irreversible impacts,
anticipatory actions to mitigate these potential
effects may be required. It may make sense in
some instances to change the rules under which
long-term planning is done, such as zoning laws, to
allow for consideration of climate change in private-
sector decisions. Finally, research and education
are needed in many areas to improve our ability to
respond to these changes. In any case, managers
should reexamine their systems to consider ways to
improve the flexibility and resiliency of the systems
to handle these and other changes. The criteria to
guide decisions should include consideration of the
following factors:
• the uncertainties in the magnitude and
timing of effects;
• whether the lifetime of the plan, project,
or policy is long enough to be affected by
climate change;
• whether effects of climate change are
irreversible;
• whether the policy or project will increase
flexibility and resilience or restrict future
options;
• whether a policy or action makes
economic or environmental sense, even
without climate change;
• the uniqueness of the ecosystems or
manmade structures that may need
protection; and
• whether the impacts would be greater if
no anticipatory action were taken.
The U.S. government is strongly supporting the
Intergovernmental Panel on Climate Change
(IPCC) under the auspices of the United Nations
Environment Programme and the World
Meteorological Organization. The IPCC has
established a process for governments to follow
when reviewing scientific information and policy
options. The federal government is conducting
other activities on global climate change. The
Global Climate Protection Act of 1987 calls for a
scientific assessment of climate change, which is to
be completed by 1989. This work will be sponsored
by EPA and other federal agencies such as the
National Aeronautics and Space Administration, the
National Oceanic and Atmospheric Administration,
and the National Science Foundation, and
coordinated through the IPCC. Also, the
Department of Energy and EPA have been asked to
report to Congress on policy options for reducing
CO, emissions in the United States. In addition,
various federal agencies conduct significant research
programs on climate. These research efforts on
climate change are coordinated by the National
Climate Program Office and the Committee on
Earth Sciences. The latter has produced a plan
called Our Changing Planet: A United States
Strategy for Global Change Research, which
outlines federal research activities.
The federal government can also take the lead
in pursuing prudent policies in anticipation of
climate change, and many agencies can play a role
in preparing the country for the impacts. These
include the Departments of the Interior, Energy,
Health and Human Services, and Agriculture; the
U.S. Environmental Protection Agency; and the
U.S. Army Corps of Engineers (see box on "Federal
Activities"). However, adaptation should not occur
just at the federal level, for there will likely be a
need to involve other nations, state and local
governments, industry, and even individuals. The
regional studies in this report demonstrate that
climate change cuts across manmade and natural
systems, geographic boundaries, and government
agencies. Research, technical guidance, planning,
and creative approaches to resource management
will be needed in the future to prepare for the
impacts of climate change on the United States.
liii
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Executive Summary
FEDERAL ACTIVITIES THAT SHOULD CONSIDER CLIMATE CHANGE
Sample questions relating to climate change impacts that federal agencies should consider;
XJ.S. Environmental
Protection Agency
. department of
the Interior
U.S. Department of
Agriculture
tf-S. Army Cdrps
of Engineers
Federal Emergency
Management Agency
U.S. Department of
Health and Human
Services
Policy Question
How should current wetlands protection programs be modified to
accommodate future sea level rise and precipitation, changes?
Should regulatory approaches to air pollution 1>e supplemented with incentive
systems, new chemicals, or relocation policies?
Should national parks and wildlife refuges purchase land to accommodate the
migration necessitated by climate change? Should additional parks and refuges
be created?
Are current activities increasing the vulnerability of species that might be
threatened by climate change?
Should the U.S. Geological Survey produce coastal area maps with finer
contour intervals? How will climate change alter projected groundwater levels?
Will current water policies in the West prove to have been ill-advised if the
" climate changes?
Do price support programs help or hinder the adjustments that climate change
may necessitate? % ,
To what extent could irrigation be increased on a sustainable basis if climate
became drier?
What actions would be necessary to maintain national forests as the climate
changes? ' '"
How does a consideration of future climate change alter the relative merits
of alternative approaches to coastal protection, flood control, and navigation?
Will climate change affect the success: of wetlands protection efforts in
Louisiana as administered under Section 404 of the Clean Water Act?
Will current rate caps on premiums enable the National Flood Insurance
Program to remain solvent if climate changes?
Are current programs adequate to address potential changes in. mortality and
shifts in diseases resulting from climate change?
liv
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Executive Summary
from the national studies. Crop yields were
estimated for corn and soybeans, and changes in
forest composition were analyzed at several sites
across the region (see Figure 16).
Adverse Impacts on Agriculture and Forests Could
Hurt the Region
Decreases in the relative productivity of
southeastern agriculture were estimated under the
scenarios to lead to the abandonment of 10 to 50%
of the agricultural acreage in the region. The
studies did not consider introduction of new crops,
such as citrus, or the use of new technologies, such
as biotechnology.
Most forests in the Southeast were estimated
to have difficulty surviving the assumed climate
change. Dieback of existing forests in such areas as
Georgia and Mississippi could be particularly large.
TEMPERATURE SCENARIOS
2xCO Jess 1xCO,
WINTER SPRING SUMMER FALL
PRECIPITATION SCENARIOS
2xCOJess1xCO.
WINTER SPRING SUMMER FALL
Agriculture
Climate change could:
• decrease corn and soybean yields in
hotter areas and could have mixed
results elsewhere
• decrease cultivated acreage
• increase need for irrigation
• increase pest infestations
Forests
Higher temperatures could result in:
• significant dieback of southern forests
with declines evident in 30 to 80 years
• regeneratbn of species becoming
difficult
Water Resources
Increased temperature and changes
in precipitation could:
• produce uncertain effects for water
resource availability
• affect water quality and flood risks
• lower levels in some recreational lakes
Sea Level Rise
Rising sea level could:
• inundate a significant proportion of the
region's coastal wetlands
• flood some dry land areas
• create significant costs for protecting
coastal resources
Fisheries
Higher water temperatures and rising
sea level could reduce fish and
shellfish populations
Electricity
Higher temperatures could increase
electricity demand
Figure 16. The Southeast.
1
-------
Chapter 1
Policy Options for Stabilizing Global Climate and is
a companion to this report. Congress requested the
studies in the Fiscal Year 1987 Continuing
Resolution.
GOALS OF THIS REPORT
This report builds on the past contributions of
many scientists throughout the world, most notably
the reports by the National Academy of Sciences
(1979, 1983, 1987), the World Meteorological
Organization and the International Council of
Scientific Unions (1986), the United Nations
Environment Programme (1986), Scope 29 (1986),
and the U.S. Department of Energy (1985a,b). It is
an attempt to identify some of the sensitivities,
direction and magnitude, linkages, regional
differences, national impacts, policy implications,
and uncertainties associated with the effects of
global climate warming.
We hope it will provide useful information to
climate modelers and effects researchers. We also
hope that officials, at all levels of government, will
be encouraged to examine the implications of
climate change for long-term policies. Since this is
the first study of this type, we expect that a great
deal more research, analysis, and planning will be
needed in the future. We do not pretend to have all
the answers.
This report has been designed to identify the
following:
Sensitivities
Since the rate and extent of climate change on
a regional level are uncertaia we cannot predict
effects. However, we can identify the sensitivities of
systems to climate change. Our goal was to use a
variety of scenarios to determine what climate
variables are important in causing impacts and the
degree to which systems are sensitive to changes in
these variables. Specifically, we were interested in
identifying the sensitivity of systems to higher
temperatures and sea level, which are among the
changes most likely to occur following increased
greenhouse gas concentrations. (For further
discussion, see Chapter 2: Climate Change.)
Direction and Magnitude
Since the scenarios do not encompass all
possible combinations of climate change due to
increased greenhouse gases, the results do not
represent the entire range of possible effects. For
example, there could be more or less rainfall, or
higher or lower temperatures than estimated by
climate models. Yet, the results from various
scenarios help define the direction and magnitude of
effects. First, we examined them to see if a
direction of change (e.g., more water, lower crop
yields) is evident. Second, we attempted to
determine if the magnitude of change is significant.
Third, we asked whether the results are consistent
with scientific theory. Outcomes outside the bounds
of our results cannot be ruled out at this time.
Linkages
Individual environmental systems will not be
affected by climate change in isolation. Water
resources, for example, maybe affected not only by
changes in water supply but also by changes in
demand for water for such purposes as irrigation.
Wildlife may be directly affected by changes in
climate and indirectly affected by changes in habitat
due to climate change. This report attempts to
identify linkages among effects, quantitatively where
possible and qualitatively elsewhere. Linkages are
identified mainly in regions. Quantitative analysis
of all linkages would change the numerical results of
this report, in many cases exacerbating impacts.
National Impacts
Impacts were analyzed on a national scale to see
how the country as a whole may be affected by
climate change and to see if latitudinal patterns
(such as northward shifts in species) are detectable.
Some analyses, such as coastal wetland impacts and
changes in electricity demand, were conducted on a
national basis. Other national analyses, such as
forests, were based on results from regional studies.
In some cases, national analyses estimated total
costs over the next century. No attempt was made
to assess the total national impact from climate
change, and conclusions about the total costs and
benefits of climate change should not be made.
-------
Introduction
Regional Impacts
Effects were examined in several regions of the
United States for a number of reasons. As pointed
out above, linkages exist among many of the effects,
and these are likely to be seen on a regional scale.
For example, the supply of water in a river basin
may change as a result of climate change. The
water resource in that basin may also be affected by
changes in the demand for water for irrigation,
powerplant cooling, and other uses. Analysis of
similar systems in different regions allows for
comparison of impacts among regions. This report,
however, does not attempt to identify "winners and
losers."
Uncertainties
Many uncertainties are related to our knowledge
about the rate and magnitude of warming and
changes in regional weather patterns. As discussed
in Chapter 2: Climate Change, we do not know how
much and how quickly climate may change and how
regional climates may change. Uncertainties also
exist about how ecological and other systems will be
affected by climate change. We do not have
empirical evidence on how these systems will
respond to higher temperatures and CO2 levels, as
well as to different rainfall amounts. These
uncertainties are reflected in the models used to
estimate climate change and impacts. This report
attempts to clearly state these limitations.
Policy Implications
The management of most natural resources has
generally been undertaken assuming that climates
will not change. A change in climate could affect
many of these resources and raise implications for
resource management. This report discusses some
policy implications of climate change, but it does not
lay out a prescriptive policy agenda.
Research Needs
The analysis in this report should provide climate
modelers with information concerning how general
circulation models could be improved. It should
also help define research needs for future analysis
of the potential impacts of climate change.
Fundamentally, these goals center on the
identification of important issues and state-of-the-
science investigations in each environmental system.
Because each component of science and policy
development is at an early stage, the goals of the
report are to develop insights and estimates of the
ranges of possible future effects and to use that
information for identifying where the policies and
research programs of EPA and other agencies
should be reexamined.
STRUCTURE OF THE ANALYSIS
Important Systems
This report focuses on the following systems,
which are important, are sensitive to climate, and
may be particularly affected by climate change:
Forests
Agriculture
Sea Level Rise
Biodiversity
Water Resources
Electricity Demand
Air Quality
Human Health
Urban Infrastructure
Regional Case Studies
Four regional case studies were selected: the
Southeast, the Great Lakes, California, and the
southern Great Plains. These regions were picked
because each is important for economic, social, and
environmental reasons, and each offers some unique
current characteristics that make it an interesting
example of the range of possible environmental
issues that may need to be considered. The
Southeast depends heavily on forestry and
agriculture, and has extensive and fragile wetlands
and coastal ecosystems. The Great Lakes are the
dominant natural resource in their region, supplying
freshwater, fishery resources, and a pathway for
shipping and transportation, and providing a natural
laboratory for environmental issues that affect both
the United States and Canada. California already
must carefully manage its water supplies, and its
agricultural industry provides many crops for the
United States and a large share of the international
-------
Chapter 1
market; it is among the most productive agricultural
regions in the world. The Great Plains is one of the
largest producers of grain crops in the world.
Although these regions are diverse, they do not
encompass the entire range of regional differences
in the United States. The analysis of effects in
these regions does not cover all potential impacts hi
the United States.
National Studies
The effects on a number of systems were
quantitatively analyzed on a national scale. National
agricultural markets were analyzed with respect to
their sensitivities to changes in yield derived from
our agricultural models. Options for adapting to a
sea level rise were examined on a national scale, as
were possible health impacts. Forestry, water
management, air quality, and biodiversity issues
were explored by analyzing the results of several of
the regional case studies with a broader perspective.
In each case, the national-level analyses provide an
additional level of qualitative integration that a
purely regional analysis could not. The structure of
the regional and national studies is displayed hi
Figure 1-1.
climate scenarios we used were based on outputs
from general circulation models (GCMs) (see
Chapter 4: Methodology). Where possible, we tried
to obtain quantitative estimates of effects.
However, the development of quantitative estimates
was constrained by the availability of well-
documented models that included some interaction
of the particular effect hi question and climatic
variability. We obtained additional information on
sensitivities by reviewing the literature and by
gathering expert judgment. The approach of using
existing models, all of which were originally
constructed for other purposes, makes the
interpretation of results instructive but somewhat
limited with respect to the full range of climatically
relevant questions that could be asked.
PROCESS FOR CONDUCTING
THIS REPORT
We used an eight-stage process to define the
scope of this report, select the projects, write the
chapters, and review the results.
Step 1: Initial Scoping of the Report
ANALYTIC APPROACHES
Since we do not know how climate will change,
this report used scenarios of possible climate change
to identify sensitivities of systems to climate. The
This stage immediately followed the request
from the Senate Environment and Public Works
Committee. We agreed on using the regional case
study approach, on the four regions to be
investigated, and on using climatic scenarios. We
Climate
Change
Scenarios
Core
Analytic
Areas
Forests
Agriculture
Sea Level Rise
Biodiversity
Water Resources
Electricity Demand
Air Quality
Human Health
Urban Infrastructure
Policy
Case
Studies
California
Great Lakes
Southeast
Great Plains
National
Studies
Forests
Agriculture
Sea Level Rise
Electricity Demand
Health
Outputs
Report
to Congress
Research
Ran
Models/
Data Bases
Figure 1-1. Elements of the effects report.
-------
Introduction
also decided not to attempt to analyze
environmental effects outside the United States in
this report. Our rationale; for this decision was
based on available time and funds, and on the lack
of suitable models that would be immediately
accessible to us.
Step 2: Preparatory Workshops
We held two workshops in February-and April
1987 in Boulder, Colorado, to prepare the report.
In the February workshop, sponsored and organized
by the National Center for Atmospheric Research,
general circulation modelers convened to discuss
some of the problems inherent in attempting to
understand the regional results from global models.
Several major topics were discussed from the
standpoint of how the results from GCMs should be
used in impact studies. A list of. variables that
would be available for use by effects researchers
was produced at the end of the workshop. In
addition, several potential studies on aspects of the
frequency of extreme weather events were
identified.
The April workshop was organized with the
assistance of the University of Colorado.
Approximately 100 scientists explored the major
climate change-related issues in agriculture, forest
effects, water resources, and sea level rise. Working
groups in each discipline discussed the potential
impacts that climate change might have and the
most important uncertainties to explore to arrive at
better predictions. The working groups were then
rearranged into regionally oriented groups. They
identified a series of studies that would address the
major scientific issues in each region.
Step 3: Identification of Potential Projects
From the lists identified in the two Boulder
workshops, and from additional studies on urban
and regional air quality subsequently identified
internally by EPA, we arrived at list of investigators
from whom we would solicit. proposals. The
decision to solicit proposals was based primarily on
the potential coverage of environmental issues in
each region.
Step 4: Reviews of Proposals
At least one intramural and two extramural
reviewers examined each proposal. We responded
to all comments and modified proposals as
appropriate. EPA used a combination of
cooperative agreements, existing contracts, and
interagency agreements to fund projects for this
report.
Step 5: Planning and Integration
All the researchers met with EPA staff in
October 1987 to discuss scenarios, goals, and
approaches for the studies. Researchers discussed
integration of projects within regions as well as the
commonality of approaches within disciplines.
Step 6: Analysis
The National Center for Atmospheric Research
assembled the scenarios and distributed them to
researchers in the fall of 1987. Researchers
conducted their analysis over the winter and
prepared draft reports in March and April 1988.
Step 7: Preliminary Project Review
In April 1988, EPA assembled panels of
scientists to provide a preliminary review of most of
the agriculture, forestry, and hydrology projects.
The principal investigators of the appropriate
projects were asked to present their work orally and
in written drafts. EPA project managers used the
-comments from the review panels to make
corrections in the conduct of a few projects, and as
a guide to interpreting the results of individual
projects and to writing this report.
Step 8: Project and Report Peer Review
At least two to three peer reviewers examined
the final reports from all principal investigators
before the EPA project managers accepted them.
During this time, EPA staff on the report project
team wrote the overviews that are reflected in this
final report. In November 1988, a special
subcommittee of EPA's Science Advisory Board
(SAB) was convened and asked to review the entire
report. Following the SAB's written review, the
EPA project team responded to comments and
produced the final version of the Effects Report.
The draft of the report was sent to other federal
agencies and the Office of Management and Budget
for review and comment, and these comments were
also taken into account in the final version.
-------
Chapter 1
STRUCTURE OF THIS REPORT
This report is divided into several sections.
Section I consists of Chapter 2 on trends in
emissions of greenhouse gases and potential impacts
on climate; Chapter 3 on changes in variability; and
Chapter 4 on the choice of scenarios and effects
modeling. In Section II, the results of national
analyses are presented. Each chapter covers a
different system. The chapters include an overview
of relevant regional studies, and they present results
from national analyses. Each chapter discusses the
current state of resource, reviews previous literature
on climate change and the resource, discusses
studies used for this report, presents national results
from regional and national studies, and discusses
broader socioeconomic and policy implications. The
design and limitations for each study are presented
only once — in a regional chapter if it is a regional
study or in a national chapter if it is a national
study. Section m contains results from the regional
case studies, with each chapter devoted to different
regions. Each regional chapter describes the
climate-sensitive systems in the region; reviews
previous studies on impacts of climate change on
the region; describes the structure of regional
studies for the report; discusses regional climate
change scenarios; reviews the design, results, and
limitations of the studies; and discusses the broader
socioeconomic and policy implications of climate
change for the region. The regional chapters
include relevant regional results from national
studies. Not all regionally relevant results are
presented in the appropriate regional chapters.
Results for health are presented only in the health
chapter in Section n. Section IV includes
conclusion chapters. Chapter 18 discusses directions
for future research on climate change effects, and
Chapter 19 discusses policy implications and
recommendations.
This report is designed to be an overview of the
individual studies. Those studies are printed in
appendix volumes. In this report, the studies are
referenced by the author's name or names in
parentheses and volume letter. Previously published
work is referenced by the author's name and the
year of publication.
RELATIONSHIP TO CURRENT
NATIONAL AND
INTERNATIONAL ACTTVITIES
National Research and Policy Activities
The Global Climate Protection Act of 1987
requested EPA to develop a national policy on
global climate change and to prepare an assessment
of scientific information. The very scope of this
issue suggests that this request can be fulfilled only
in cooperation with other federal agencies; hence,
EPA is working with these agencies to formulate a
process to achieve this goal. The scientific
assessment will be conducted in coordination with
the National Aeronautics and Space Administration,
the National Oceanic and Atmospheric
Administration, the National Science Foundation,
and other agencies. To the extent possible, this
scientific assessment will also be developed on an
international basis and should be available in 1990.
The development of a national policy will be
coordinated with the Department of Energy and
other natural resource departments. The goal will
be to build on this report and others under
development by federal agencies to identify the
adoptive policies and other measures that may be
appropriate to deal with this issue. The nature of
this issue suggests that a continuous review of
domestic policy will be required for many years.
International Activities
In 1987, the United Nations Environment
Programme (UNEP) and the World Meteorological
Organization (WMO) were asked by member
governments to establish an Intergovernmental
Panel on Climate Change (IPCC) for the specific
purpose of reviewing the scientific information and
potential response strategies. The WMO has
primary responsibility for the World Climate
Research Programme, and UNEP has responsibility
for the World Climate Impacts Programme. The
UNEP was the primary international agency
responsible for negotiations leading to the Montreal
-------
Introduction
Protocol To Protect the Ozone Layer. The first
meeting was held in November 1988, and
subsequent meetings have been held in 1989 to
organize activities. It is expected that the IPCC will
be the primary forum for multilateral discussions
between governments on this issue.
Other governments and international agencies
are also examining this issue. Italy, Japan, and the
Netherlands held conferences in 1989. The United
States has bilateral activities with the Soviet Union
and China The Organization for Economic
Cooperation and Development and the International
Energy Agency are examining their potential
contributions.
REFERENCES
National Academy of Sciences. 1979. Carbon
Dioxide and Climate: A Scientific Assessment.
Washington, DC: National Academy Press.
National Academy of Sciences. 1983. Changing
Climate. Washington, DC: National Academy
Press.
National Academy of Sciences. 1987. Current
Issues in Atmospheric Change. Washington, DC:
National Academy Press.
Scope 29. 1986. The Greenhouse Effect, Climatic
Change, and Ecosystems (SCOPE 29). Bolin, B., B.
Doos, J. Hager, and R. Warrick (eds). Chichester,
England: John Wiley and Sons.
United Nations Environment Programme. 1986.
Effects of Changes in Stratospheric Ozone and
Global Climate. Titus, J.G. (ed). Washington, DC:
U.S. EPA and United Nations Environment
Programme.
U.S. Department of Energy. 1985a. Atmospheric
Carbon Dioxide and the Global Carbon Cycle.
Trabalka, J.R. (ed). Washington, DC: Government
Printing Office (DOE/ER-0239).
U.S. Department of Energy. 1985b. Projecting the
Climatic Effects of Increasing Carbon Dioxide.
MacCracken, M.C., and F.M. Luther (eds).
Washington, DC: Government Printing Office
(DOE/ER-0237).
World Meteorological Organization. 1986. Report
of the International Conference on the Assessment
of the Role of Carbon Dioxide and of Other
Greenhouse Gases in Climate Variations and
Associated Impacts, Villach, Austria, 9-15 October
1985. World Climate Programme Report No. 661.
Geneve, Switzerland: World Meteorological
Organization, The International Council of Scientific
Unions, and the United Nations Environment
Programme.
-------
-------
CHAPTER 2
GLOBAL CLIMATE CHANGE
The Earth's climate has changed continuously
over the entire lifetime of our planet as a result of
various natural causes. Recently, we have come to
the realize that human activities may, in the near
future, produce effects powerful enough to
overwhelm these natural mechanisms and dominate
the changes of climate. By early in the next century,
the planet's temperature may rise to a range never
before experienced by our species, at a rate faster
and to temperatures warmer than the Earth has
experienced in the past million years. This
anticipated temperature increase would be caused
by an enhancement of the greenhouse effect.
Although the overall effect of increased
greenhouse gases is understood, many details are
less clear, including both the timing of the predicted
warming and its spatial distribution. This is because
the response of the climate system to the additional
greenhouse gases, including all the feedbacks and
interactions that would take place, is very
complicated and not completely understood. In
addition, while the human-induced component of
the greenhouse effect increases in magnitude, other
causes of climate change remain important, such as
changes in the amount of energy emitted by the sun,
changes in the atmospheric composition due to
volcanic eruptions and human input of aerosols,
internal redistributions of energy by El Ninos, and
random, unpredictable variations. Thus, the task of
predicting the future evolution of climate involves
not only understanding the response of the climate
system to increased concentrations of greenhouse
gases but also predicting the concentrations of these
gases and the effects of other causes of climate
change.
Several detailed assessments of the current state
of our knowledge of these projected climate changes
have been conducted recently. These include
studies by the National Research Council (NRC,
1979, 1983, 1987), the World Meteorological
Organization (1986a,b), and the "state-of-the-art"
reports of the Department of Energy (MacCracken
and Luther, 1985a,b; NRC, 1985; Trabalka, 1985;
Strain and Cure, 1985; White, 1985). Excellent
shorter summaries include Ramanathan (1988) and
Chapters 2 and 3 ofLashof andTirpak (1989).
These studies should be consulted for more detailed
information.
This chapter describes the climate system, the
important causes of climate change for the next
century, and the so-called climate forcings, and it
summarizes the various trace gases that human
The Greenhouse Effect
Gases in the atmosphere are virtually
transparent to sunlight {shortwave
radiation), allowing it to pass through the
air and to heat the Earth's surface, The
surface absorbs the sunlight and emits
thermal radiation (longwave radiation)
back to the atmosphere. Because several
gases in the atmosphere, particularly
water vapor (ELO) and carbon dioxide
(CO2), are not transparent to the
outgoing thermal radiation, they absorb
some of it and heat the atmosphere, The
atmosphere emits thermal radiation, both
upward to outer space and downward to
the surface, further warming the surface.
This phenomenon is called the
greenhouse effect because in some
respects it describes how an actual
greenhouse works. Even without any
human impacts, this natural greenhouse
makes the Earth's surface about 33°C
(596F) warmer than it would be without
the atmosphere. Gases that are
transparent to sunlight, but not to thermal
radiation, are called greenhouse gases.
If either the concentration Of existing
greenhouse gases increases or greenhouse
gases that were not there before are
added to the atmosphere, more thermal
radiation will be absorbed and re-emitted
downward, making the surface warmer
than before.
-------
Chapter 2
activities put into the atmosphere. It then describes
important feedbacks in the climate system that act
to amplify or dampen the climate change induced by
the forcings. Uncertainties in our understanding of
these feedbacks are an important component of our
current uncertainty of the timing and amount of
future climate change. Next, it discusses the recent
history of climate change, compares these
observations with theory, and presents theoretical
models of the climate and their projections of future
climate change. Finally, the concluding section
summarizes the extent of our knowledge about the
future climate and discusses future research needs.
THE CLIMATE SYSTEM
The climate system includes all the interactive
components of our planet that determine the
climate. This includes the atmosphere, oceans, land
surface, sea ice, snow, glaciers, and biosphere.
Climate change can be measured hi terms of any
part of the system, but it is most convenient to use
surface air temperature as a measure of climate,
since it is the parameter for which we have the best
record, and it is measured where the most
important component of the biosphere — humans —
lives. Other components of the climate system, such
as precipitation, cloudiness, evaporation, windspeed
and direction, and sea level, also have important
impacts on human activities.
Figure 2-1 shows a schematic representation of
the climate system. Changes in the amount of
energy emitted by the sun, changes hi the
atmospheric composition (such as from volcanic
eruptions and human input of aerosols and
greenhouse gases), and changes in the Earth's
surface (such as deforestation) can affect the
Earth's energy balance. Atmospheric and oceanic
circulation can redistribute the energy.
The radiative balance of the planet, as shown in
Figure 2-2, determines the global average vertical
distribution of temperature. If the concentration of
certain trace gases (carbon dioxide (CCO, water
vapor (H2O), methane (CH4), nitrous oxide (NjO),
tropospheric ozone (O3), and chlorofluorocarbons
(CFCs)) increases, the atmosphere's absorption of
longwave radiation (thermal radiation from the
Earth's surface) will increase. Some of this energy
will be radiated downward, heating the surface and
increasing the surface temperature. Because the
concentrations of all these gases are projected to
increase in the future, this effect and its timing must
be compared to the other projected causes of
climate change (forcings), and the response of the
climate system, to project the future climate.
Uncertainties are associated with all these factors.
Changes
Solar Radia
SPACE ft |
Terrestrial
Radiation
3f
ion
ATMOSPHERE
('Clouds Kj
H20, N2, 02, C02, 03, etc. Air-Biomass
Aerosols Precipitation, -Land
Air-Ice Coupling Evaporation Coupling
4 ft Heat Exchange ft Wind Stress BIOMASS
T/^-JL™ ft L j :_ ****
jy 7 mKv^utft
'
Changes of \ Coupling ft Atmosphere-Ocean Coupling / LAND
Atmospheric Composition \ OCEAN ^ __/
Changes of Land Features,
Orography, Vegetation,
Albedo, etc.
1
Changes of Ocean Basin,
Shape, Salinity, etc.
Figure 2-1. The climate system. The principal interactions among components of the atmosphere, ocean, ice,
and land surface, and some examples of external forcings are indicated (Gates, 1979).
10
-------
Global Climate Change
aerbsols
albiedo
balance
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11
-------
Chapter 2
SPACE "^SOLAR0 OUTGOING RADIATION
RADIATION Shortwave Longwave
100 8 17 6 9 40
t f t \
ATMOSPHERE
Absorbed by ^/
Water Vapor. 19 -*^
Dust, O3
J
X^5^—. ,/
( 4 ^~)
Absorbed by
Clouds
Absc
^v / / /
\V\ Backscattered / /
\\\bV/Air / /
\\ //
\ Reflected /
\ by Clouds /
\ ^^^\ /
\(£* \/
V I
\ Reflected
\ by Surface
>rbed \ / LONGWAVE
\ V
t
20
' t
1
Net Emission _r* ^TN
by
f^ '"5
Water Vapor. Emission
CO2,O3 bY Clouds
Absorption
by Clouds 1
Water Vapor, |
infiCO,,O
RADIATION
* t Latent
Sensible
Heat Flux
46 115 100 7 24
OCEAN, LAND
•
Figure 2-2. The Earth's energy balance. If the average amount of solar radiation received by the Earth (342
watts per meter2) is represented as 100 units, then the amplitudes of the various components of the energy flux
are shown proportionately (MacCracken, 1985).
CLIMATE FORCINGS
Both the past and future courses of climate
change are determined by a combination of external
forcings, unforced internal fluctuations, and the
response of the climate system. This section briefly
discusses the forcings that will be important in the
next century.
Greenhouse Gases
If the Earth had no atmosphere, its average
surface temperature, determined by the balance
between incoming solar radiation and emitted
longwave radiation at the surface, would be about
0°F (-18°C), the same as the current temperature of
the moon. The average temperature is actually a
hospitable 59°F (15° C) because of the natural
greenhouse effect of H2O, CO2, and O3. Because
a large amount of the radiation in the wavelength
band 7 to 13 micrometers is not absorbed by these
gases, it is referred to as the "atmospheric window,"
and is a region where longwave radiation can escape
relatively unimpeded to space.
The concentration of a number of trace gases in
the atmosphere is increasing as a result of human
activities. Because the trace gases are very effective
absorbers of longwave radiation in the atmospheric
window region, small (trace) amounts can have
large effects on the radiation balance, in effect
"dirtying" the atmospheric window. Trends and
concentrations of some of these gases are shown in
Table 2-1 and Figure 2-3. The projected relative
effects of these gases are shown in Figure 2-4. Each
of the gases is discussed in more detail below.
Carbon Dioxide (CO2)
Combustion of fossil fuels and deforestation are
increasing the concentration of CO2- Since Keeling
began detailed measurements during the
International Geophysical Year in 1958 at Mauna
Loa, Hawaii, the atmospheric concentration of CO2
has risen from 315 ppmv (0.0315%) to a
12
-------
Table 2-1. Trace Gas Concentrations and Trends
Global Climate Change
Gas
Concentrations
Pre-1850
1987
Current annual Mid-21st
observed trends (%) century
CO2
CHJ
N?O
CFC-11
CFC-12
CH,CC1,
«£
275.00 ppmv3 348.00 ppmv
0.70 ppmv 1.70 ppmv
0.34 ppmv
0.22 ppbv6
0.39 ppbv6
0.13 ppbv6
0.29 ppmv
0
0
0
0
0.08-0.10 ppbv6
10.00-100.00 ppbv^
0.3
0.8-1.0
0.2
4.0
4.0
7.0
400.00-550.00 ppmv
1.80-3.20 ppmv
0.35-0.40 ppmv
0.20-0.60 ppbv
0.50-1.10 ppbv
aUnits of ppmv are parts per million by volume; 1 ppmv = 0.0001% of the atmosphere. Units of ppbv are
parts per billion by volume; 1 ppbv = 0.001 ppmv.
bValue given is for 1986.
°Tropospheric ozone only (below 12 kilometers). Values (below 9 km) for before 1850 are 0 to 25% less than
present-day; values (12 kilometers) for mid-21st century are 15 to 50% higher.
Value given is for 1985.
Source: Ramanathan (1988), Lashof and Tirpak (draft 1989).
current level of 350 ppmv. About half of the CO2
put into the atmosphere each year remains in the
atmosphere, with the rest absorbed in the ocean.
Because society's basic energy sources (combustion
of coal, oil, and natural gas) produce CO2, unless
strong energy conservation measures and shifts to
other energy sources take place, it is projected that
the atmospheric concentration of COj will continue
to increase. As climate changes, the effectiveness of
the oceanic sink for CO2 may also change,
increasing or decreasing the fraction of CO2 that
remains in the atmosphere. CO2 contributes about
half of the total anthropogenic greenhouse forcing.
Methane (CH4)
Although the methane concentration is now
increasing at a rate of about 1% per year and was
much lower during the ice ages, the basic cycle is
not completely understood. Sources include rice
paddies, cows, termites, natural gas leakage,
biomass burning, landfills, and wetlands. Although
methane has a much lower atmospheric
concentration than CO2 (currently 1.7 ppmv), it is
more effective at dirtying the atmospheric window
and accounts for about 18% of current
anthropogenic greenhouse forcing.
Chlorofluorocarbons (CFCs)
These completely anthropogenic gases, the most
important of which are known by the trade name
Freon, have been implicated not only in greenhouse
warming but also in chemical destruction of
stratospheric ozone (O3). Because of this, nations
agreed to limit production of these gases in an
international agreement signed in Montreal in 1987.
The most important of these gases are CFC-11
(CFC13) and CFC-12 (CF^L). CFCs are used in
refrigerants, aerosol propeEants, foam-blowing
agents, and solvents. Substitutes for CFCs are being
developed that are not as stable chemically and,
therefore, would not accumulate as fast in the
atmosphere. The resulting lower concentration
would produce a smaller greenhouse effect and
would be less effective at destroying O3. The
current fractional greenhouse contribution of
CFC-11 and CFC-12 of 14% would probably
decrease in the future, but the total CFC
greenhouse effect would most likely increase for
some time because of the long lifetime of these
gases.
13
-------
Chapter 2
CONCENTRATIONS OF TRACE GASES FROM ICE CORE
AND ATMOSPHERIC SOURCES
ICE CORE DATA
ATMOSPHERIC DATA
1.8
1.4
I 1.2-
g 1.0-
0.8-
CH4
t
1750 1850
Source: Stauffer el al., 1985
1.5
1978 1983
Source: Blake & Rowland, 1988
Mauna Loa and Ice Core Data
350
— 330-
czr
x Mauna Loa
v Ice Core
355
350
z | 340
O —
CO2
Monthly Concentrations of Carbon Dioxide
at Mauna Loa, Hawaii
1 290-
3
i
8 270-
250 •
17
^^-f
CD*25
DCD CD
40 1860 1980
Source: Neftel et al., 1985; Keeling et al., 1982
I 350
I
1
-
8 S 325
°| 320
315
310
19
rt A/l/li
- AA/iM/l/F
i i I* i r
>5 1970 1985
Source: Keeling. 1984; Keeling, unpublished, 1988
310
1. 308
CO
. § 306
c
N2O ^
«!•
^""Xji.^l-"1''
250
t '
N2O
1600
Source: Poarman et al..
1800
2000
304
302
300
>/-'
.•j-
1979
Source: Khahll, 1987
1983
Figure 2-3. Greenhouse gas trends in ice cores and atmospheric instrument data.
14
-------
Global Climate Change
1880-1980
1980s
Figure 2-4. Greenhouse gas contributions to global
warming; estimated values based on concentration
changes (1880-1980: Ramanathan et al., 1985; 1985,
1980s: Hansen et al., 1988).
Nitrous Oxide (N2O)
This gas, with both natural and anthropogenic
sources, contributes about 6% to the enhanced
greenhouse effect, although its concentration is only
'about 0.31 ppmv. Its concentration is increasing at
a rate of about 1 ppbv per year, and sources include
oceans, fossil fuel and biomass combustion,
agricultural fertilizers, and land disturbances.
Ozone (CO
In addition to its role in the stratosphere as an
absorber of ultraviolet shortwave radiation, O, has
an important impact on climate. This role is
complicated by its dependence on the altitude where
O3 occurs. Both ozone increases in the troposphere
and lower stratosphere and ozone decreases in the
upper stratosphere would tend to warm the surface.
Although the ozone concentration is believed to be
increasing in the troposphere, it is active chemically
and has highly variable concentrations in time and
space. Responding to local air pollutants, such as
nitrogen oxides (NO ) and hydrocarbons, ozone
provides a complex link between local air pollution
and global climate change. Other gases, such as
carbon monoxide (CO) and volatile organic
compounds, also play important roles in
atmospheric chemistry and hence affect the
greenhouse problem.
Solar Variations
The sun provides the energy source for all
weather on the Earth, and the balance between
incoming sunlight and outgoing longwave radiation
determines the climate. Small variations in solar
radiation have the potential for causing climate
changes as large as those caused by projected
increases of greenhouse gases. Precise observations
of the sun have been taken only for the past decade
(Willson and Hudson, 1988). They show, however,
that solar variations during this period have been so
small that they would not be important compared
with the other forcings discussed in this section.
Since these high-quality observations have been
taken only for a short period, they do not rule out
past or future variations of the sun that would be
larger. But on the time scale of centuries, solar
variations do not now seem to be an important
factor.
Volcanoes
Large volcanoes can significantly increase the
concentration of stratospheric aerosols, decreasing
the amount of sunlight reaching the surface and
reducing surface temperatures by several tenths of
degrees for several years (Hansen et al., 1978,1988;
Robock, 1978, 1979, 1981, 1984). Because of the
thermal inertia of the climate system (discussed
below), volcanoes can even be responsible for
climate changes over decades. It has been
suggested that a significant part of the observed
global climate change of the past 100 years can be
attributed to the effects of volcanic eruptions
(Robock, 1979). Since large eruptions occur fairly
frequently, this component of climate change will
have to be considered when searching past climate
for a greenhouse signal and when projecting future
climate change.
15
-------
Chapter 2
Tropospheric Aerosols
Natural sources, such as forest fires and sea
spray, and human activities generate atmospheric
aerosols in the troposphere. The concentrations
vary greatly in space and time, and local sources are
important. Furthermore, these aerosols can
produce either warming or cooling, depending on
their concentration, color, size, and vertical
distribution. It is not now possible to definitively
determine their role in global climate.
Surface Properties
The Earth's radiative balance can also be
changed by variations of surface properties. While
interactions with the oceans which cover 70% of the
Earth's surface, are considered internal to the
climate system, land surfaces can exert a strong
influence on the climate. Human activities, such as
deforestation, not only provide a source of CO2 and
CH4 to the atmosphere but also change the surface
albedo and rate of evaporation of moisture into the
atmosphere. Detailed land surface models,
incorporating the effects of plants, are now being
developed and incorporated into climate model
studies (Dickinson, 1984; Sellers et al., 1986).
Internal Variations
Even with no changes in the external forcings
discussed above, climate exhibits variations due to
internal rearrangements of energy both within the
atmosphere and between the atmosphere and the
ocean. The total amplitude and tune scales of these
variations are not well understood; this contributes
to the difficulty of interpreting the past record and
projecting the level of future climate change.
Some studies suggest that these random
variations can have amplitudes and time scales
comparable to climate changes expected to be
caused by greenhouse warming in the coming
decades (Lorenz, 1968; Hasselmann, 1976; Robock,
1978; Hansen et al., 1988). A large El Nino, such as
that observed in 1982-83, can take large amounts of
energy out of the oceans and warm the surface
climate for a few years; this warming is then
superimposed on any warming due to the
greenhouse effect. Our understanding of these El
Nino/Southern Oscillation variations is improving,
allowing us to account for this factor in interpreting
past global climate change (Angell, 1988).
CLIMATE FEEDBACKS
Any imposed imbalance in the Earth's radiative
balance, such as discussed above, will be translated
into a changed climate through feedback
mechanisms that can amplify or decrease the initial
imposed forcing. A feedback in which the final
temperature is higher than what it would have been
without the feedback is termed a "positive
feedback." If the effect of the initially imposed
forcing is reduced, it is termed a "negative
feedback." This section describes several of these
mechanisms that are internal to the physical climate
system and that involve the planet's biology and
chemistry.
Although important climate feedback
mechanisms have been identified, we may not
understand or even know about all the mechanisms
involved in climate feedbacks. Figure 2-5 shows
that even with the known physical climate feedbacks
involved in changing surface temperature, the
potential interactions are complex. Current
state-of-the-art climate models attempt to
incorporate most of the physical feedbacks that have
been identified but are forced, for example, to
provide a very crude treatment for one of the most
important ~ ocean circulation — because of large
computer demands and inadequate ocean climate
models. Another important and inadequately
understood feedback — clouds — has been the
subject of recent climate calculations but, as
described below, is also treated crudely owing to
inadequate understanding of cloud physics and the
small spatial scale on which clouds form as
compared with the resolution of the climate models.
Water Vapor -- Greenhouse Effect
When the climate warms, more water (H2O)
evaporates into the atmosphere from the warmed
surface. This enhances the warming because it
increases the greenhouse effect of the water vapor,
producing still more evaporation. This positive
feedback acts to approximately double imposed
forcings. Thus, an important greenhouse gas, H2O
vapor, is controlled by the climate system itself.
Transformations of HLO between vapor and other
phases, liquid and soUd, provide other important
climate feedbacks discussed below.
16
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Global Climate Change
I
NET ENERGY BALANCE
SENSIBLE HEAT AND
POTENTIAL ENERGY FLUX
Planetary albedo
f
Surface
mospheric moisture
capacity t
V-*g=^// \
\^m/./ \
Atmospheric moistur
content
Figure 2-5. Physical climate feedback relationships. External forcings are indicated in underlined italics (Robock,
1985).
Snow and Ice
When climate warms, snow and ice cover are
reduced, exposing land or ocean with a lower albedo
than the snow or ice. In addition, the albedo of the
remaining snow and ice is reduced owing to
meltwater puddles and debris on the surface. This
acts to absorb more energy at the surface, further
enhancing the warming. This albedo feedback was
originally thought to be the dominant positive
feedback effect of snow and ice, but we now
understand that the thermal inertia feedback of sea
ice plays a much more important role (Manabe and
Stouffer, 1980; Robock, 1983).
The thermal inertia feedback acts to increase
the thermal inertia of the oceans when climate
warms by melting sea ice and exposing ocean waters
to the atmosphere. Since imposed climate change
must then affect the ocean and atmosphere together
rather than the atmosphere alone, this acts to
reduce the seasonal cycle of surface temperature
and is the prime reason for the enhancement of
imposed climate change in the polar regions in the
winter (Robock, 1983).
Clouds
Clouds respond directly and immediately to
changes in climate and may represent the most
important uncertainty in determining the sensitivity
of the climate system to the buildup of greenhouse
gases. Fractional cover, altitude, and optical depth
of clouds can change when climate changes
(Schlesinger, 1985). At the present time, clouds
have a large greenhouse effect, but this is offset
(averaged over the globe) by their even stronger
cooling effect, because clouds reflect sunlight back
to space (Ramanathan et al., 1989). Since the
current greenhouse effect of clouds is larger than
the effect of an increase of CO2 by a factor of 100,
small changes in clouds as climate changes can be
very important in affecting the overall climate
response to increases in trace gases.
If climate becomes warmer, more water will
evaporate into the atmosphere. Coupled with
warmer surface temperatures, this may produce
more upward motion of air, which would produce
more clouds. One way clouds could increase is to
17
-------
Chapter 2
increase in area. This would raise the albedo of the
planet (except over polar snow and ice fields, which
have an albedo larger than clouds), reflecting more
sunlight back to space and having a cooling effect.
Thus, the initially imposed warming is reduced,
producing a negative feedback. Clouds already
increase the planetary albedo from about 17% (if
there were no clouds) to 30% (Ramanathan et al.,
1989). An increase of planetary albedo of only 0.5%
would cut in half the warming imposed by doubled
CO2 (Ramanathan, 1988).
Other studies suggest that, especially in the
tropical regions, convection could increase,
producing taller but narrower clouds. This would
produce additional warming in two ways: (1) by
reducing the cloud area, thus decreasing the
planetary albedo; and (2) by decreasing the cloud
top temperature and reducing longwave radiation to
space. This mechanism would be a positive
feedback. In addition, convective clouds in the
tropical regions (thunderstorms) tend to produce
large shields of high cirrus clouds, which have a
large greenhouse effect further enhancing the
warming. Cirrus clouds allow much sunlight to
penetrate because they are so thin, but the cloud
particles absorb the outgoing longwave radiation
from the surface, efficiently trapping much of it
(Ramanathan, 1988).
In the latest climate model simulations, it was
found that clouds have a net positive feedback on
global climate (Schlesinger, 1988), but the final
answer will be known only after more research. It
is not possible to be certain of the net effect of
cloud feedbacks because of the complexity of clouds
and their response to climate change. The
complexity is because all the above properties of
clouds can change simultaneously, because clouds
affect both longwave and shortwave radiation,
because clouds affect precipitation (which affects
land temperatures), and because the net effect
depends on the location of the cloud, surface
albedo, tune of day, and time of year.
Biogeochemical Feedbacks,
In addition to the physical climate feedbacks
discussed above, a number of positive
biogeochemical feedbacks may be important
(Lashof, 1989). These feedbacks can influence
future concentrations of greenhouse gases, especially
CO2 and CH4, through changes in sources and sinks
of these gases induced by climate change, and they
can influence the climate change itself through
changes in vegetation, and hence the surface heat
and moisture balance. Such processes include
changes in releases of methane hydrates from ocean
sediments, changes of land albedo due to shifting
ecosystems, and changes in the ability of the oceans
to absorb CO2 (this process is discussed in the next
section).
Methane hydrates are combinations of a
methane molecule trapped in a lattice of water
molecules. They are found in ocean sediments and
are stable under current pressure and temperature
conditions in many ocean shelf regions. As the
climate warms, these conditions may change,
releasing more methane into the atmosphere and
enhancing the greenhouse effect.
As the climate warms, forests may shift closer
to the pole, producing a region with a lower albedo.
The surface will thus absorb a larger fraction of
sunlight, warming the Earth and producing a
positive feedback, further enhancing the warming.
Oceans
Oceans play an important role in the climatic
response to changed forcings because they absorb
and emit both heat and CO2, and because changing
ocean circulation can change the redistribution of
energy internal to the climate system, as discussed
above. When any of the above climate forcings are
applied to the climate system, the climate will start
to change. Since both the climate forcings and the
climatic response are time-dependent, and since the
climate system has a certain amount of inertia built
in owing to the response times of the ocean, the
exact relationship between the timing of the forcings
and the timing of the response is complex. Much of
the lag between the imposed forcing and the
climatic response depends on the oceans. The
upper 50 to 100 meters (164 to 328 feet) of the
ocean, called the mixed layer, responds relatively
rapidly to imposed forcings. The deep ocean is also
important because its interactions could impose lags
of as much as 100 years.
The relative depth and role of the mixed layer,
as well as the circulation of the ocean, will change
in a complex way in response to changed climate.
Broecker (1987) has suggested that a rapid shift in
ocean currents, such as the Gulf Stream, may occur
18
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Global Climate Change
as the climate warms, producing large regional and
relatively rapid global climate changes. In
preliminary tests with the Geophysical Fluid
Dynamics Laboratory models, when CO2 is doubled,
the oceanic circulation around Antarctica changes so
as to increase the upwelling of cold bottom water.
As a result, cooling occurs in the Southern
Hemisphere high latitudes for a period of several
decades as the rest of the globe warms! These two
examples suggest that unforeseen climate events
may be possible in the future and that until the
ocean response is well understood, the timing and
amplitude of the climatic response to increased
greenhouse gases and the other forcings will need to
remain the subject of additional research.
Oceans are also the dominant sink of
atmospheric CO2, absorbing about half of all CO2
that is put into the atmosphere each year by the
combustion of fossil fuels and deforestation. The
amount of absorption is a strong function of oceanic
temperature, and shifts in oceanic circulation and
temperature may shift the fraction of CO2 absorbed
in the future and, hence, change the rate of CO2
accumulation in the atmosphere. As the oceans
warm, they may absorb a smaller fraction of the
excess CO2 in the atmosphere, thereby enhancing
the warming (Lashof, 1989). In addition, oceanic
chemical reactions change as climate changes.
Oceanic production of dimethyl sulfide particles
could also change as climate changes (Charlson et
al., 1987). These particles serve as cloud
condensation nuclei and may change the reflectivity
of marine clouds by changing the number of
droplets in the clouds.
Observational Evidence of Climate
Change
Thermometers have been used to actually
measure global climate change for more than 100
years in enough locations to provide an estimate of
how the planet's climate has changed during this
period. The most complete and up-to-date global
surface air temperature record available is shown in
Figure 2-6 (Wigley et al., 1989). Other analyses,
including Hansen and Lebedeff (1988) and Vinnikov
et al. (1987), give similar results. Problems
common to all these data sets include possible
contamination from urban heat islands, inadequate
spatial coverage of the Earth, and corrections
necessary to counteract the effects of changing the
methods used to take observations from ships.
While the gradual warming seen in Figure 2-6
during the past century is consistent with the
increasing greenhouse gases during this period, most
scientists suggest that a clear link has not yet been
established between observed temperatures and the
greenhouse effect. The large interannual variations
and the relatively flat curve from 1940 to 1975 show
that there are also other important causes of climate
change. For example, large volcanic eruptions, such
as Hekla in 1947 and Agung in 1963, and El Ninos
certainly have produced some of the variations
shown in this record. Because of the projected
future emissions of greenhouse gases, global
warming is likely to dominate these factors during
the next century.
The global temperature record shown hi Figure
2-6 can also be compared with the record for the
United States for the same period shown in Figure
2-7 (Hanson et al., 1989). While the globe as a
whole has been generally warming, the lower 48
states of the United States have actually been
cooling for the past 40 to 50 years, although the
high temperatures in the 1980s are among the
warmest on record. Since the lower 48 states of the
United States cover only 1.5% of the planet, this
indicates that regional climatic variations, which may
be caused by changes in sea surface temperature
and wind circulation patterns, can be an important
factor in the climate of small regions of the Earth.
These factors will continue to be important as
global climate warms. For example, such regional
events as the midwestern drought of 1988 may be
related to changes hi ocean temperature (Trenberth
et al., 1988) and can be greater than the effect of
greenhouse gases on a national or larger scale.
On a longer time scale, proxy climate variables
can indicate how climate has changed. An
intriguing record comes from a core drilled in the
antarctic icecap at Vostok and is shown in Figure
2-8 (Barnola et al., 1987). The temperature record
is deduced from the deuterium isotope ratio. The
past CO2 concentration is actually measured from
bubbles of ancient air trapped in the ice. The warm
period of the past 10,000 years is called the
Interglacial and represents an anomalously warm
period compared with the climate of the past
100,000 years. It is projected that because of the
greenhouse effect, our climate will warm to a level
much above even the level of the Interglacial,
warmer in fact than the Earth has experienced for
the past million years. The rate of warming will
19
-------
Chapter 2
o
—0.5
1860
1880
1900
1920 1940
Year
1960
1980
2000
Figure 2-6. Hemispheric and global surface air temperatures, 1861-1988. The 1988 value is preliminary and
includes data only through November. This record incorporates measurements made both over land and from
ships. The smooth curve shows 10-year Gaussian filtered values. The gradual warming during this period is not
inconsistent with the increasing greenhouse gases during this period, but the large interannual variations and the
relatively flat curve from 1940 to 1975 show that there are also other important causes of climate change (Wieley
etaL, 1989).
13-
f 12-
3
a
S. 11-
I •
10-
18
n nL
h A /\A A m / !/ W VW\A / W\ A n J\ n 1
i V
J .»
T • 1 * '•
1 | * /V J J ^ f * i
95 1905 1915 1925 1935 1945 1955 1965 1975 1985
-
-
-850
-800 3
0
-750|
-700 i
-650 §
-600
Year
Figure 2-7. Annual average surface air temperature (solid) and precipitation for the contiguous United States,
1895-1987. Note that the United States has been cooling for the past 50 years (Hansen et al., 1988).
20
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Global Climate Change
also be unprecedented. From Figure 2-8, it appears
that the warming from the chill of the ice age 18,000
years ago to the Interglacial was very rapid, but in
fact a warming of even 2°C in one century would
be much faster than this warming.
(Thousands of years before present)
Figure 2-8. Temperatures and carbon dioxide
concentrations for the past 160,000 years at Vostok,
Antarctica. Since these observations were taken
near the South Pole, they show larger temperature
variations (by a factor of 2 or 3) than took place
averaged over the whole globe (Barnola et al.,
1987).
Figure 2-8 shows that during the entire
160,000-year period, the atmospheric CO2
concentration varied along with the temperature.
When it was warmer, the CO2 concentration was
higher, although it never approached the current
level of 350 ppmv. It is not known whether the
climate change preceded the increase in CO2,
whether the increase in CO2 preceded the warming,
or whether they both happened simultaneously. It
is well accepted that the changing orbit of the Earth
produced the ice ages (the Milankovitch
Hypothesis), and this recently discovered variation
of CO2 certainly worked to enhance the climate
changes caused by the changing orbit. These
natural processes are now being overwhelmed by
the human impact of fossil fuel burning and
deforestation.
Two recent studies of CH4 concentration in
ancient air found in Greenland and Antarctic ice
cores also have shown that CH4 concentration
varied with climate in prehistoric times (Stauffer et
al., 1988; Raynaud et al., 1988). Although the CH4
concentrations were not large enough to have an
appreciable impact on the greenhouse effect, the
CH4 did vary in the same sense as CO^ and climate
(see Figure 2-8). The CH, variations indicate that
sources of CH4 increased in a warmer climate,
which suggests that natural sources of CH4 may also
increase in the future as global climate warms,
further amplifying the greenhouse effect.
CLIMATE MODELS
In many sciences, such as biology, chemistry, or
physics, it is possible to investigate new phenomena
by doing research in a laboratory. In the field of
climate, this is not possible. One cannot bring the
Earth's climate system into a room and perform
experiments on it, changing the trace gas
concentration or increasing the amount of sea ice.
It is not possible to have two identical systems, one
a control and one that is changed to compare the
outcomes. There is only one climate system, and
humans are now performing an uncontrolled
experiment on it by polluting it with CO2, CH4,
CFCs, and other trace gases.
To try to understand how the global climate
will change in response to human activities,
researchers have applied various approaches. The
climates of other planets, particularly Venus and
Mars which are the most Earth-like, can give us
some ideas about climate under very different
conditions. However, their atmospheres are not
similar enough to Earth's to give us definitive
answers about the next 100 years here. The history
of the Earth's climate is another area we could
study, but since many different forcings of similar
strengths have been acting, and since the data
coverage is imperfect, it has not been possible to
definitively isolate the roles of the different forcings.
Attempts have been made to use rotating tanks of
water or other fluids (called dishpan experiments)
as models for the atmosphere, but these are
imperfect as they cannot simulate realistic heating
profiles or the detail of the real climate system.
21
-------
Chapter 2
The most useful tool to investigate future
climate is the computer model of the climate
system. In a climate model, the various physical
laws that determine the climate, such as
conservation of energy, conservation of mass, and
the gas law, are expressed as mathematical
equations that specify the relationship between
different variables, such as temperature, pressure,
wind, and precipitation. By specifying the various
climate forcings, it is possible to calculate the
climate. An experiment can be performed by
doubling CO2, for instance, and comparing the
resulting climate to the current CO, concentration.
Many theoretical calculations can be made to test
the importance of various assumptions and various
proposed feedback mechanisms.
The simplest climate model is the
zero-dimensional global average model, which can
be used to give a global-average measure of climate
but cannot consider many important processes and
cannot give regional distribution of climate changes.
Models that are one-dimensional in the vertical,
called radiative-convective models, or in the
horizontal, called energy-balance models, are very
useful for quickly and inexpensively testing various
components of the climate system. However, to
calculate the location of future climate change, and
to incorporate all the important physical
interactions, especially with atmospheric circulation,
fully three-dimensional general circulation models
(GCMs) are necessary. These sophisticated models
solve simultaneous equations for all the important
climate variables in three dimensions. The world is
broken up into a discrete grid of boxes placed side
by side and stacked to cover the globe. The biggest
and fastest supercomputers available are used, but
computer speed and size constraints limit the size of
these grid boxes to 250 to 1,000 kilometers (150 to
600 miles) on a side and to a height of 1 to 5
kilometers (0.6 to 3 miles). Thus, in one of these
grid boxes, all the complexity of weather and
horizontal variation is reduced to one number for
temperature, one for cloudiness, and so forth. The
equations used to represent the physical and
chemical processes involved are also simplifications
of real-world processes.
Different climate modelers represent physical
processes hi different ways. In all the models, the
radiation schemes attempt to account for the
radiatively significant gases, aerosols, and clouds.
They generally use different schemes for computing
cloud height, cloud cover, and optical properties.
The models also differ in their treatment of ground
hydrology, sea ice, surface albedo, and diurnal and
seasonal cycles (Schlesinger and Mitchell, 1985).
Perhaps the most important differences lie in the
treatment of oceans, ranging from prescribed sea
surface temperatures to "swamp" oceans with mixed-
layer thermal capacity but no heat transport, to
mixed layers with specified heat transport, to full
oceanic GCMs. Models are constantly becoming
more complex and sophisticated as new
understanding of the physics evolves and faster
computers become available.
One of the first experiments used to test any
climate model is its ability to simulate the current
climate. In these tests, the various state-of-the-art
climate models have differences. Crotch (1988) has
recently compared the simulations of surface air
temperature and precipitation of four recent GCM
simulations and found that although they do a
reasonable job of simulating global values, the
simulations at the regional scale are poor. He
compared model simulations and observations on
gridpoints, where each gridpoint "represents a
region of about 400 kilometers (250 miles) by 400
kilometers or larger, or roughly the size of
Colorado, even though regions of this size may have
very diverse local climates" (Crotch, 1988). He
found differences between models and observations
(see Table 2-2), and between models, particularly
for smaller regions. Crotch concluded that GCMs
cannot currently project regional changes of
precipitation or temperature.
Given the current state of the art, how can
these models be used? As discussed in Chapter 4,
model simulations can be of use even in their crude
state. In the first place, even if the models do not
exactly reproduce the current climate, perhaps the
differences between their simulations of current and
future climates provide an estimate of potential
future changes. In addition, the models produce a
data set of all the variables needed for impact
assessment that are physically consistent within the
physics of the model. Thus, although the actual
model projections can not be taken as predictions of
the future, they are useful in providing scenarios for
impact assessment. As model projections become
more accurate in the future, the scenarios they
generate will become more accurate.
22
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Global Climate Change
Table 2-2. Differences Between Winter and Summer Temperature Estimates for Four GCMs and Observed
Temperatures
Variable and model
Global
Domain of comparison
North America
Contiguous U.S.
Midwestern U.S.
Observed median
temperature (°C)
8.5
Difference in median
temperatures
-------
Chapter 2
Model Projections of a Doubled-CCX, World
Several climate modeling groups have
conducted GCM experiments to calculate the
equilibrium climate response to doubled CO2.
These include researchers at the National Center
for Atmospheric Research (NCAR), Oregon State
University (OSU), NOAA's Geophysical Fluid
Dynamics Laboratory (GFDL), NASA's Goddard
Institute for Space Studies (GISS), and the United
Kingdom Meteorological Office (UKMO). The
results from the different experiments depend on
the assumptions made, especially on the treatment
of clouds and of oceans. The models predicted
global temperature increases of 2.8 to 5.2°C and
global precipitation increases of 7 to 16% (see
Table 2-3).
Attempts have also been made to determine
climate sensitivity from past data. If we could
accurately determine the strength and timing of all
the climate forcings that have competed with the
greenhouse effect in the past, we could account for
them, and the residual warming would be a measure
of the greenhouse effect to date. Unfortunately, our
knowledge of both past climate change and the
responsible forcings is too poor to reliably
determine the sensitivity of climate to greenhouse
warming. Wigley and Raper (1987) estimate that if
all of the warming of the past 100 years were due to
greenhouse gases, a doubling of CO2 would warm
climate by about 2°C. If, however, we allow for
other possible forcings (including natural
variability), for uncertainties in ocean heat uptake
and the timing of the climate response, and for
uncertainties in preindustrial greenhouse gas
concentrations (Hansen et al., 1985; Wigley and
Schlesinger, 1985; Wigley et al., 1986), then from
past data we can only say that a CO2 doubling
might produce a global climate change anywhere in
the range of 0 to 6°C (Wigley, personal
communication). Wigley et al. (1989) point out that
while the global warming of the past 137 years is
highly significant statistically, it is not possible to
definitively attribute this warming to a specific
cause.
The actual path that the climate system would
take to approach the equilibrium climate would be
determined by the tune scales of the forcings and
the various elements of the climate system and is
referred to as the transient response. Because the
climate system response lags behind the forcing, a
built-in unrealized warming will always occur in the
future, even if no more greenhouse gases are added.
Thus, some future climate response to the
greenhouse gases that were put into the atmosphere
in the past will certainly occur, even if emissions
were stopped today.
Table 2-3. General Circulation Model Predictions of Globally Averaged Climate Change Due to Doubled CO2
Model
Surface air
temperature
increase (°C)
Precipitation
increase (%)
GFDL
GISS
NCAR
OSU
UKMO
4.0
4.2
3.5
2.8
5.2
8.7
11.0
7.1
7.8
15.8
Source: Karl et al. (1989).
24
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Global Climate Change
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CHAPTER 3
VARIABILITY
FINDINGS
A changecT-climate variability (defined in the
following section of this chapter) associated with
climate change could significantly affect natural
resources. However, lack of information on
potential changes in climate variability has limited
the completeness of climate change impact studies
presented in this report. It is not possible to
definitively state how climate variability will change
with a changed climate because model results are
mixed. At this time, there is not a strong case for
altering the assumption of no change in variability
used in the scenarios for this report.
Analyses of changes in climate variability for a
CO2 doubling estimated by two general circulation
models (GCMs) — Goddard Institute for Space
Studies (GISS) and National Center for
Atmospheric Research (NCAR) — are not
conclusive. Some overall trends, but also some
inconsistencies, are obtained when comparing the
changes in climate variability associated with a
changing climate calculated by the two GCMs for
four U.S. regions.
• The model results suggest that daily and year-
to-year temperature variability could decrease
and precipitation variability could increase.
However, the results for temperature are not
statistically significant. Furthermore, the two
models produce some inconsistent results.
• Results indicate that, the diurnal (day and
night) cycle may be reduced in the summer,
although results for the other seasons are
inconclusive.
To determine the validity of the variability
statistics of greenhouse gas-perturbed experiments,
investigators examined how well the GCMs
reproduce present-day climate variability. A
comparison of observed and model results for the
current climate for the two GCMs for selected U.S.
regions reveals interesting contrasts and similarities
regarding the reproduction of climate variability.
Simulation of variability is reasonably good in
several cases.
• Although some discrepancies exist between
actual and estimated temperature and
precipitation values, the models simulate the
seasonal cycles of temperature and precipitation
reasonably well in the four regions investigated.
• The models make errors (generally
overpredictions) in predicting daily and year-to-
year temperature and precipitation variability.
Explanations for some discrepancies, such as
why the daily temperature variances are too high,
relate to how the surface hydrology is modeled in
both GCMs (NCAR and GISS). More
investigations of model results are necessary to
improve understanding of future climate variability
changes.
NATURE OF CLIMATE
VARIABILITY
Global warming can change the variability of
climate. Although less is known about variability
than about most other aspects of climate change, it
may have greater impacts on some systems than
changes in average climate conditions.
Variability is an inherent characteristic of
climate (Gibbs et al., 1975) and is closely related to
the concept of climate change. However, no clear
universally accepted distinction is made between the
terms "climate variability1 and "climate change."
Both terms refer to fluctuations in climate from
some expected or previously defined mean climate
state. Berger (1980) makes the distinction that
climate change refers to a secular trend that
29
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Chapter 3
produces a change in the average, whereas
variability refers to the oscillations about that mean.
Distinctions can only be made relative to the time
scales of concern. The climate change discussed in
this report refers to a change from the mean global
climate conditions we have experienced in roughly
the past few centuries. On a longer time scale (i.e.,
thousands of years), however, this climate "change"
would be viewed as an instance of climate variability
(i.e., as one of many fluctuations around mean
conditions prevailing over several thousand years).
For the purpose of this report, climate
variability is defined as the pattern of fluctuations
about some specified mean value (i.e., a time
average) of a climate element. Hence, in regard to
the climate change considered here, climate
variability refers to fluctuations of climate around
the new mean condition that constitutes the climate
change, and is expressed on time scales shorter than
the time scale of the climate change. For example,
if it is assumed that the average annual global
surface temperature will be 3°C warmer than it is
currently, then the climate variability on a year-to-
pattern of departures from this mean increase.
One of the main concerns regarding climate
change is whether and how climate variability will
change (i.e., will the pattern of fluctuations around
the new mean at any given location be the same as
that around the "old mean"). This concept of
changing climate variabilities is illustrated in Figure
3-1, which displays three simulated time series of
daily maximum July temperature for Des Moines,
Iowa. In all three cases, the mean maximum
monthly temperature is the same (i.e., 86.2°F), but
the patterns of daily fluctuations about this mean
differ significantly. Changes in climate variability
refer to the differences in these patterns.
The causes of climate variability depend largely
on time scales and may be divided into two major
categories: (1) those arising from internal dynamics
that produce stochastic (random) fluctuations (and
possibly chaotic behavior) within the climate system,
and (2) those arising through external forcing of the
system. Table 3-1 summarizes different causes of
climate variability on different time scales. On very
long time scales (e.g., 100,000 years), astronomical
factors account for much variability (orbital
parameters in Table 3-1).
95
90
85
80
75
70
100
95
90
85
80
75
70
95
90
85
80
75
I |
1 5 9 13 17 21 25 29 33
DAY
Figure 3-1. Simulated July daily maximum
temperature time series at Des Moines, Iowa. All
assume the same average temperature but use
different statistical estimates (first-order
autocorrelation coefficient ) of variability (Mearns
et al., 1984).
Variations of climate on a year-to-year basis
(interannual variability) can arise from external
forcings, such as volcanic eruptions, or from slowly
varying internal processes including, as part of the
internal system, interactions between the
atmosphere and oceans, soils, and sea ice fields.
These interactions can result in shifts in locations of
major circulation features or changes in their
intensity (Pittock, 1980). The largest effect,
presumably, is due to variations in sea surface
temperatures, such as those occurring in El Nino
Southern Oscillation (ENSO) events.
30
-------
Climate Variability
Table 3-1. Major Processes Involved in Climate Fluctuations for Different Time Scales
TIME SCALES related to Earth's history
Years 1010 109 108 1
NATURAL POTENTIAL CAUSAL MECHANISMS
EXTERNAL
INTERNAL (related to)
ci g.o galactic dust
'£ jo -g +j Sun's evolution
«^|^ solar variability
'S S .5 £ orbital parameters
*
•H
--.
Source: Berger (1980).
Daily variability of a nonperiodic nature largely
results from variations in synoptic scale weather
processes, such as high- and low-pressure cells and
upper-atmosphere wind streams, which direct the
movement of such features (atmosphere
autovariation in Table 3-1) (Mitchell, 1976). These
features interact with local topography to provide
location-specific variability. (Variations caused by
these weather processes are largely stochastic and
internal to the climate system.)
This report mainly discusses variations on time
scales of several years or less ~ that is, from
interannual to daily variability. Climate variability
does not have a specific operational statistical
definition, but can be described by a constellation of
statistical properties other than the mean. The most
commonly used measure is the variance (which is
the mean of the sum of squared deviations from the
mean of a time series) or its positive square root,
the standard deviation.
NATURE AND IMPORTANCE OF
CLIMATE EXTREMES
Climate variability is experienced on an impact
level mainly through the occurrence of extreme
climate events. The impact of extreme variability
may be the first indication of climate change. It is
important to note, however, that change in the
frequencies of extreme events (e.g., heat waves,
drought) is not synonymous with change in climate
variability.
To illustrate this point, an example is presented
of a change in the frequency of heat waves in Des
Moines hi July, defined as 5 consecutive days in the
month with maximum temperatures exceeding 95°F.
Just changing the monthly mean of the series by
3°F, without changing variability (as measured by
the standard deviation and/or autocorrelation),
increases the probability of experiencing a heat wave
31
-------
Chapter 3
in July from the current level of 6% to 21%.
However, the increase can be even more dramatic
if the variability is altered as well as the mean. By
increasing the persistence in the time series (i.e., the
day to day dependence of the daily temperatures) as
well as the mean, the probability of a heat wave
increases from 6% to 37% (see Mearns et al., 1984,
for further details). Hence, changes in the
frequencies of extreme events will occur with
changes in the mean climate conditions, but this
change can be reduced or rendered more extreme
by changes in variability.*
The impacts of climate change on society
accrue not necessarily from the relatively slow
trends in the mean of a climate variable, but rather
from the attending shifts in the frequency of
extreme events. This issue has already received
some attention in the literature where the nonlinear
relationship between changes in the mean and
extreme events has been examined (e.g., Schwarz,
1977; Parry, 1978; Mearns et al., 1984). However,
less is known about this factor than about most
other aspects of climate change.
For the purposes of climate impact analysis,
extreme climate events may be considered
perturbations of climate that result in conditions
outside normal ranges that exceed some critical
threshold. What constitutes "normal" (i.e., the
averaging period) is, of course, a central issue in
defining extremes.
Extreme events relevant to climate impacts
function on different time scales, depending upon
the climate variable involved and the impact area of
interest. Thus, events can range from the length of
time (in minutes and hours) that minimum
temperatures in Florida remain below a critical
value, resulting in damage to citrus crops, to the
length of time (in months and years) that
precipitation is particularly low in California,
resulting in serious water shortages for industry and
agriculture. The probability of extreme events can
also vary considerably -- for example, from that of
extreme snowfall in the Buffalo, New York area
such as that of the 1976-77 winter (P = 0.0002)
* Although the scenarios created for this study assume no
change in variability (see Chapter 4: Methodology) they do
assume, for example, increases in heat waves and decreases in
cold waves that result from changes in mean climate conditions.
(Policansky, 1977), to that of heat waves
(temperatures above 100°F for 5 consecutive days)
in Dallas, Texas (P = 0.38).
What defines an event as extreme is not only
a certain statistical property (for example, likelihood
of occurring less than 5% of the time), but also how
prepared a particular system is to cope with an
event of such magnitude. Hence, very few extreme
events have a fixed absolute value independent of
particular response systems at a particular location.
This implies that what constitutes an extreme event
can also change over time because of changes in the
relevant response system (Heathcote, 1985).
It is thus very difficult to comprehensively
review all climate extremes of importance to society,
and what is presented here is far from an exhaustive
catalog. Because one of the purposes of this review
is to highlight the extreme events of importance that
can serve as guides for choosing what extreme
events should be quantitatively analyzed in GCM
experiments, priority is given to events related to
variables that can be relatively easily analyzed.
This review considers the two most important
climate variables — temperature and precipitation -
- and their extremes (maxima and minima), and one
type of major meteorological disturbance — severe
storm effects. Extremes in these variables affect the
areas of energy use and production, human
mortality and morbidity, agriculture, water
resources, and unmanaged ecosystems (although not
all areas are discussed under each climate extreme).
Temperature
Given the scientific consensus that higher
atmospheric concentration of greenhouse gases will
raise average global temperatures, extreme
temperature effects are given priority in this
analysis.
Maximum Temperatures
Extreme temperature effects on human
mortality and morbidity have received the most
attention in the scientific literature (e.g., Kalkstein,
Volume G; Becker and Wood, 1986; Jones et al.,
1982; Bridger et al., 1976; Ellis, 1972). This is partly
because the relevant climate factors (i.e., maximum
32
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Climate Variability
daily temperatures and relative humidity) are readily
available for analysis.
A heat wave is defined as a series of days with
abnormally high temperatures (i.e., temperatures
exceeding some critical threshold). Examples
include the 1980 heat wave in the United States
when Kansas City had 17 consecutive days above
39°C (102°F) (Jones et al., 1982), and Dallas had
42 consecutive days with temperatures above 38° C
(100°F) (Becker and Wood, 1986). The death toll
that year was several times above normal (1,265
lives).
Studies have specifically tried to pinpoint the
most significant meteorological factors associated
with heat-related death and illness. Jones et al.
(1982) determined that high maximum
temperatures, the number of days that the
temperature is elevated, high humidity, and low
wind velocity contributed to excess mortality in
Kansas City and St. Louis in the 1980 heat wave.
Kalkstein et al. (1987) established that runs of days
with high minimum temperatures, low relative
humidities, and maximum temperatures above 33° C
(92°F) contributed to heat-related deaths in New
York City.
Increases in heat waves are virtually certain,
assuming global warming. But how they increase
(longer or greater departure from the mean) very
much depends on changes in variability that would
affect the persistence of high temperatures.
Such crops as corn, soybeans, wheat, and
sorghum are sensitive to high temperatures during
their bloom phases. For example, Shaw (1983)
reported that severe temperature stress during a
10-day period around silking (a critical period
during which the number of kernels on the ear is
determined) will result in crop failure. McQuigg
(1981) reported that the corn crop was severely
damaged in July 1980 as a result of temperatures
exceeding 38°C (100°F). The destructive effects of
runs of hot days on corn yields were particularly
apparent during 1983 in the U.S. Corn Belt.
Although the damage from high temperatures is
best documented for corn, it has also been noted in
wheat and soybean yields (e.g., Neild, 1982;
Mederski, 1983).
Although not as much research has been
performed on the effects of temperature extremes
on natural ecosystems, some research has been
done on forest responses to temperature extremes.
Solomon and West (1985) indicate in their summary
of climate effects on forests that the frequency,
intensity, and lengths of heat waves under climate
change conditions are important factors influencing
seedling survival and can contribute to the loss of a
species from an ecosystem. A run of warm years
can affect the location of tree lines. Shugart et al.
(1986) established that a period of warm summers
at high altitudes during the 1930s, when the mean
annual temperature was no more than 1°C higher
than average, resulted in a burst of regeneration in
boreal forest trees near polar and altitudinal limits
in North America.
High temperatures have their most immediate
impact on energy by causing increased electricity
demand for air-conditioning. Using climate
scenarios similar to those in this report (see
Chapter 4: Methodology), Linder et al. (1987) found
that energy demand in New York would significantly
increase in summer (on the order of 3% for an
average August day in 2015 for the downstate area).
Minimum Temperatures
Extreme minimum temperatures will not
necessarily be less of a problem with CO2-induced
climate warming. For example, changes will most
likely occur in the growing areas of certain crops,
where risks of frost damage may not be clearly
known.
The best example of frost damage to crops is
the effect of low minimum temperatures on citrus
trees. This problem has been studied in depth for
the citrus crop in Florida. (See Glantz, Volume J,
for a discussion of the Florida citrus industry's
responses to freezes in the early 1980s.) The most
striking aspect of these freezes is the very short
freezing time necessary for damage to occur. New
citrus growth (i.e., bloom buds) can be completely
killed during a 30-minute exposure to -3.3°C (26°F)
or a 3-hour exposure to -2.2°C (28°F). The effect
of freezes is exacerbated if the crops have not
hardened with the cold. Thus, if a freeze follows a
warm period (i.e., indicating high daily temperature
variability) when dormancy has been broken, more
damage will occur at less extreme temperatures.
For example, the December 24-26, 1983, freeze
caused the Florida citrus yield to be 30% lower than
it had been the previous year (Mogil et al., 1984).
33
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Chapter 3
Extreme lows on a seasonal basis tend to most
directly affect winter energy use for heating. In the
United States, the difference in heating fuel use
for a warm as compared with a cold winter can vary
by as much as 400 million gallons of oil. During the
extremely cold winter of 1976-77, heating degree
days (calculated on a base of 18°C (65°F)) were
10% greater than normal for the nation as a whole
(Dare, 1981).
Precipitation
Anticipated changes in precipitation resulting
from climate change are not well known at this
point. However, geographic shifts in rainfall
patterns will likely occur. Changes in the
frequencies of extremes of both droughts and floods
must be considered.
Drought is of particular interest at the time of
this writing because of the 1988 drought in the
United States and the energetic speculations being
made concerning its possible connection with
CO2-induced climate change (Wilford, 1988). It
cannot be said that the summer 1988 drought was
caused by CO2-induced climate warming, but rather
that such droughts would be possible and perhaps
more frequent with such, a warming. (In fact, most
recent evidence presented by Trenberth et al. (1988)
indicates that the cause of the drought was primarily
temperature anomalies in the Pacific (i.e., cool
temperatures along the Equator and warmer
temperatures to the North), which led eventually to
the anomalous displacement of the jet stream
northward. These causes are considered to be
natural variations in the coupled atmosphere-ocean
system.)
Droughts
The most basic, general definition of drought
may be lack of sufficient water to meet essential
needs (Gibbs, 1984). From a more strictly
climatological point of view, it may be considered a
condition determined relative to some long-term
average condition of balance between rainfall and
evapotranspiration in a particular region (Wilhite
and Glantz, 1987). Different types of drought are
recognized, such as meteorological drought (a
departure of precipitation from normal), agricultural
drought (insufficient soil moisture based on crop
growth needs), or hydrological drought (based on
departures from normal or relevant hydrologic
parameters, such as streamfiow). These "types" of
drought are not completely independent, but can
show up at different time lags one from the other.
Drought of any kind is anomalous as an
extreme climatological event in that it is a "creeping"
phenomenon; neither its onset nor its end is clearly
punctuated in time. It is difficult to measure
drought severity, since drought is a combination of
factors: duration, intensity, and areal extent.
Drought also can be one of the longer-lived extreme
events in that it can be measured in terms of
seasons or, more frequently, years.
In the United States, major droughts have
usually been defined in terms of several years, and
the rate of occurrence is most strongly influenced by
interannual variability of precipitation.
The effect of drought on crop production is
perhaps the impact of drought that has received the
most research attention. The occurrence of
droughts has been a major cause for yearly
variability in crop production in the United States
(Newman, 1978). During the 1930s, drought yields
of wheat and corn in the Great Plains dropped to as
much as 50% below normal, whereas the drought in
the 1950s brought less dramatic declines in yields
(Warrick et al., 1975). In 1988, national corn yields
were 40% below normal (see Chapter 6:
Agriculture).
Soil moisture deficits affect natural vegetation
as well as crops. Much of the research in natural
ecosystems has been on forests. Soloman and West
(1985) identify drought as the cause for death of
seedlings and for slowed or stopped growth of
mature trees.
Aside from the direct effects of insufficient
moisture on unmanaged ecosystems, indirect effects
also result from increased incidence of fires.
During the drought of 1988, forest fires broke out
across the country; the most notable was the
devastating August fire in Yellowstone National
Park, which blackened 60% of its land area.
The effects of drought on U.S. energy
resources are most apparent with regard to
hydroelectric power generation. Linder et al. (1987)
discussed the effect of decreased streamflow due to
drought on the production of hydroelectric power in
New York (see Chapter 10: Electricity Demand).
34
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Climate Variability
The possibility of combined effects of higher
maximum temperatures and drought on electricity
demand and supply should be noted. Increased
demand (due primarily to increased temperature)
would very likely occur when drought would limit
generating capacity in regions such as New York
and the Pacific Northwest.
Floods
On average, 200 people die each year from
flooding; flash floods account for most of these
deaths (AMS, 1985). Floods also destroy property,
crops, and natural vegetation, and disrupt organized
social systems.
Floods result from a combination of
meteorological extremes (heavy precipitation from
severe storms, such as hurricanes and
thunderstorms), the physical characteristics of
particular drainage basins, and modifications in
drainage basin characteristics made by urban
development. Loss of life and property is increasing
as use of vulnerable floodplains increases.
Major recent floods include the following:
Rapid City, South Dakota (June 1972),
231 deaths and more than $100 million
in property damage;
1.
2. Northeastern UnitedStates (June 1972),
120 deaths and about $4 billion in
property damage — inundation from
Hurricane Agnes;
3. Big Thompson Canyon, Colorado (July
1976), 139 deaths .and $50' million in
property damage — a result of a stalled
thunderstorm system that delivered 12
inches (305 millimeters) of rain in less
than 6 hours (Henz and Sheetz, 1976);
and
4. Johnstown, Pennsylvania (July 1977), 76
deaths and $200 million in property
damage -- a result of slowly moving
thunderstorms that deposited 11 inches
(279 millimeters) of rain in 9 hours.
The recurrence interval of flooding is most
important in applying effective control and
protection mechanisms. These include building
dams, reservoirs, and levees, and improving
channels and floodways (White et al., 1975). For
example, flood control reservoirs are designed to
operate at a certain level of reliability, and the
reliability is determined by a certain flood
magnitude that the reservoir can handle, such as a
100-year flood. The statistics of flooding are vital
for designing for protection and are based on a
certain climate variability determined from the
historical record. As that variability changes, the
reliability of the protection system will change.
Floods in the 1980s have been less serious in
terms of loss of life, but changing frequencies of
severe storms, such as thunderstorms and
hurricanes, as well as general shifting of
precipitation patterns could result in unprecedented
losses from floods in a climate-changed world.
Severe Storms - Hurricanes
Three important kinds of weather extremes
are present in hurricanes: strong winds, intense and
high precipitation amounts, and extreme storm
surges. A hurricane is an extreme form of a
tropical cyclone, characterized by torrential rains,
typically as much as 127 to 254 millimeters (5 to 10
inches) in one storm; high windspeeds, which can
exceed 160 kilometers per hour (100 miles per
hour); very steep pressure gradients, with pressure
at the center as low as 915 millibars (27 inches);and
diameters of 160 to 640 kilometers (100 to 400
miles).
Hurricanes are classified according to their
severity on the Saffir/Simpson Scale (categories 1
through 5), taking into account the central pressure,
windspeed, and surge. Major hurricanes are
considered to be all those of categories 3 through 5
wherein central pressure is less than 945 millibars
(27.9 inches), windspeeds exceed 176 kilometers per
hour (110 miles per hour), and the surge is greater
than 2.4 meters (8 feet) (Herbert and Taylor, 1979).
From 1900 through 1978, 53 major hurricanes
(averaging two major hurricanes every 3 years)
directly hit the United States. Overall, 129
hurricanes of any strength hit the United States
(averaging approximately two each year). In recent
35
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Chapter 3
decades, the number of major hurricanes has
declined. From 1970 to 1978, only three hurricanes
occurred, compared with six or more in earlier
decades. The last hurricane of category 4 or 5 to
strike the United States was Hurricane Camille in
1969. In 1980, Hurricane Allen, which at one time
reached force 5, weakened before it struck a
relatively unpopulated segment of the Texas coast
(Oliver, 1981). Since then, the population of the
south coastal regions of the United States has grown
tremendously, and most inhabitants have never
experienced a major-force hurricane. Building in
coastal areas has also increased with population,
which raises the potential for high property damage.
Thus, the population may be more vulnerable and
less prepared to handle this particularly devastating
extreme event (Sanders, 1982).
Any increase in the frequency and/or intensity
of these storms, which could result from climate
change, would be of great concern to southern
coastal regions of the United States. Hurricane
Gilbert, which occurred in September 1988,
reinforced this concern, even though it did not cause
major damage to the coastal United States.
Hurricane Gilbert may well prove to be the most
powerful hurricane of the 20th century; its lowest
central pressure (883 millibars or 26.13 inches) was
the lowest ever measured in the Atlantic Gulf and
Caribbean regions of tropical storm activity.
Serious damage did occur primarily in Jamaica, the
Cayman Islands, and the northern tip of the
Yucatan Peninsula (Ludlum, 1988).
Coleman (1988) has found in the historical
record some limited evidence for increased
frequency for the number of storms formed in the
North Atlantic during years of warmer-than-average
sea surface temperatures. Emmanuel (1987) has
found through a hurricane modeling experiment that
the intensity of hurricanes increases under warmer
conditions. The extreme intensity of Hurricane
Gilbert in September 1988 is consistent with the
findings. Emmanuel (1988) also asserts the
importance of establishing a general theory of
hurricane development independent of current
atmospheric conditions, so that scientists can predict
changes in frequency and intensity of storms with
climate change.
STUDIES OF CHANGING
CLIMATE VARIABILITY
Empirical Studies
One of the methods available for gaining some
insight into how climate variability may change in a
generally warmer climate is to investigate the
climate record for past relationships between mean
climate change and changes in variability. However,
past research efforts to determine changes in
climate variability and relationships with changes in
mean climate conditions have not resulted in a clear
consensus.
Van Loon and Williams (1978) found
significant differences in interannual temperature
variability in North America during two different 51-
year periods. However, they found no single
connection between trend hi temperature and trend
in its interannual variability. Specifically, they assert
that their results do not support the postulated
association between cold periods and high variability
of temperature. Diaz and Quayle (1980), in a
thorough analysis of the U.S. climate (temperature
and precipitation), found no systematic relationship
between changes in mean temperature and
precipitation and their corresponding variances.
Brinkmann (1983) analyzed the relationship
between mean temperature and variability in
Wisconsin using climate data for three stations. She
found no relationship between mean temperature
and interannual variability, but did find a negative
correlation between winter mean temperatures and
the day-to-day variability, and a corresponding
positive relationship for summer conditions. What
this means is that cold winters are more variable
than warm winters, but that cool summers are less
variable than warm ones. Brinkmann explains these
relationships on the basis of Wisconsin's location
with respect to general circulation patterns.
Lough et al. (1983) analyzed the association
between mean temperature and precipitation and
variability in Europe by using the analog approach
to create climate change scenarios (the analog
36
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approach is further discussed in Chapter 4:
Methodology). They selected two periods when
arctic temperatures were particularly warm and cold
(1934-53 and 1901-20). Results indicate that the
regions of lower winter temperatures roughly
coincide with the region of increased variability, but
the coincidence is far from perfect.
These studies indicate that significant changes
have occurred in both interannual and day-to-day
climate variability in historical times, but that simple
or distinct relationships between changes in mean
climate conditions and changes in variability have
not been established. Moreover, the value of
seeking such relationships in the past as a key to the
future is potentially limited, since the causes of very
short-term warming or cooling in the past are not
known, but in any event, are not caused by increases
in greenhouse gases.
The failure of the analog approach to provide
an empirically consistent and causally coherent
scenario of possible changes in climate variability
contributes to the necessity of examining climate
variability in climate modeling experiments. As
discussed in Chapters 2 and 4, GCMs have
limitations, but they have one clear strength over
empirical attempts to analyze future climate change:
the modeling experiments are constructed such that
the response of the climate system to the true cause
of the change (increased greenhouse gases in the
atmosphere) is simulated.
Modeling Studies
Studies comparing variability statistics of
observed time series with variability statistics of
GCM-generated time series of climate variables
relevant to climate impacts are not numerous in the
atmospheric sciences literature, although studies
first appeared in the early 1980s (e.g., Manabe and
Hahn, 1981; Chervin, 1981). Such studies are
critical if climate change research is to determine
whether the variability statistics of doubled CO2
experiments with GCMs are valid. To accomplish
this, the ability of GCMs to reproduce present-day
climate variability statistics must be examined, and
a thorough understanding of discrepancies must be
attained.
Chervin (1986) used the National Center for
Atmospheric Research Community Climate Model
(NCAR CCM) to investigate interannual climate
Climate Variability
variability and climate prediction. He focused on
the additional variability attributed to external
boundary conditions (i.e., in this modeling context,
external boundary conditions refer to important
conditions outside the atmosphere that cause
changes to the atmosphere but are not in turn
affected by it, such as sea surface temperatures).
He eliminated sources of external variability in the
model, such that discrepancies between modeled
and observed variability would reflect this external
component. The variability of mean sea level
pressure and 700-millibar geopotential height (which
roughly corresponds to the height above the surface
where the atmospheric pressure equals 700
millibars, and is related to large-scale wind patterns)
were analyzed for the Northern Hemisphere, with
particular focus on the United States. Results,
however, indicated no significant differences
between modeled and observed variabilities of mean
sea level pressure over the United States and only
limited areas of differences in the variability of
700-millibar geopotential height.
Bates and Meehl (1986) also used the CCM to
investigate changes in the frequency of blocking
events (stationary pressure systems that block the
flow of upper air currents hi the atmosphere) on a
global scale under doubled CO, conditions.
Blocking events are strongly relatecf to persistent
surface temperature anomalies, such as heat waves
in the summer. They found that the model
generally produces too few extreme blocking events.
Under doubled CO2 conditions, standard deviations
of blocking activity were found to mainly decrease
in all seasons (i.e., the variability of blocking events
decreased).
Two studies were recently conducted on local or
regional scales using the U.K. Meteorological Office
five-layer GCM. Reed (1986) analyzed observed
versus model control run results for one gridpoint in
eastern England. Compared with observations, the
model tended to produce temperatures that were
too cool and variability that was too high as
measured by the standard deviation. For
precipitation, the model produced too many rain
days but did not successfully simulate extreme rain
events of greater than 20 millimeters per day.
More recently, Wilson and Mitchell (1987)
examined the modeled distribution of extreme daily
climate events over Western Europe, using the same
model. Again, the model produced temperatures
37
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Chapter 3
that were too cold, and hence, extreme minimum
temperatures were overestimated. This problem
was most pronounced in grid boxes away from the
coasts. The model also produced too much
precipitation in general, did not successfully
reproduce observed highest daily totals, and
overestimated the number of rain days. Wilson and
Mitchell examined changes under quadrupled CO2
conditions and found that variability of temperature
generally decreased.
Hansen et al. (1988) used the Goddard Institute
for Space Studies (GISS) general circulation model
to simulate the global climate effects of
time-dependent variations of atmospheric trace
gases and aerosols. It was determined that the
model only slightly underestimates the observed
interannual variability across the globe. However,
the model's variability tends to be larger than that
observed over land (i.e., only considering land areas,
not ocean areas).
Among the calculations made with output from
the transient run were changes in the frequencies of
extreme temperature events. This was accomplished
by adding the model-induced temperature change
with climate warming to observed local daily
temperatures, assuming no change in variability.
Results indicate that predicted changes in the
frequency of extremes beyond the 1900s at locations
such as New York, Washington, and Memphis
become quite large and would have serious impacts.
The studies reviewed above indicate some
important shortcomings of GCMs with regard to
their ability to faithfully reproduce observed
variability statistics. More research is clearly
needed to further determine the sensitivity of the
models to changes in physics, resolution, and so
forth, with regard to the determination of variability.
Moreover, only one of these studies explicitly
concerns variables of importance to climate impact
analysis. Studying the higher moments (e.g.,
variance) of climate variable statistics, and carefully
verifying the models' ability to reproduce observed
variability on regional scales, are the necessary
prerequisites to rigorously analyzing possible
changes in these statistics under doubled CO2
conditions.
STUDIES FOR THIS REPORT
Two research efforts were undertaken for this
report to attempt to increase knowledge concerning
how climate variability may change. The climate
change scenarios used in the climate change impact
studies reviewed in this report excluded
consideration of changes in variability (see Chapter
4: Methodology). The following two studies on
GCM estimates of current and future variability
were performed for this report:
• Variability and the GISS Model - Rind,
Goldberg, and Ruedy, Goddard Institute for
Space Studies (Volume I); and
• Variability and the NCAR Model - Mearns,
Schneider, Thompson, and McDaniel, National
Center for Atmospheric Research (Volume I).
It should be recalled that scenarios of climate
change generated by the GISS GCM are used in
most of the impact studies summarized in this
report. The results of these two studies are directly
compared in a later section.
The GISS Study
Rind et al. (1989) examined how well the GISS
GCM simulates the observed variability of climate
by comparing the model and the observed
interannual and daily variations of temperature and
precipitation. They described the model assessment
of changes in variability for these two major climate
variables, under climate change using the GISS
doubled CO2 run (8° x 10° resolution) and the
transient climate change experiment in which trace
gases were increased gradually. The analysis was
conducted for the Great Plains, the Southeast, the
Great Lakes region, and California (see Figure 3-
2). Observed data consist of the average of
observations at nine different stations per grid box.
First, mean conditions were compared for actual
weather observations with the GCM control run (or
single CO2), the doubled CO2 run, and the transient
run. The model values for mean temperatures for
four months in the four regions are generally cooler
than observations (particularly in summer and fall),
38
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Climate Variability
47.0
39.1
31.3
23.5
-135
-125
-115
-105
-65
Figure 3-2. The locations of the four GISS model grids.
but only by a few degrees Celsius. Model
precipitation values are fairly close to observed
values in the Great Lakes and Southeast grid boxes,
but model values are higher than observed for the
other two regions (e.g., January in the southern
Great Plains: model = 2.1 millimeters per day,
observed = 0.46 millimeters per day). Under the
doubled CO2 scenarios, temperatures increase over
the control run by 4 to 6°C (7 to 11°F) in the winter
and 3 to 4°C (5 to 7°F) in the summer. Warming
in the transient scenarios is progressive, but
temperature changes more gradually than with
simply doubling the CO, amount. Winter warms
more than summer, and so the annual seasonal
cycle is reduced under climate change. Precipitation
changes are not statistically significant at individual
grids, but there is an overall tendency for increased
precipitation.
Interannual Variability
Standard deviations of temperature and
precipitation of observed and modeled data were
compared for all months. In most months, the
model year-to-year temperature variability is similar
to the observed variability in the four regions, but in
summer the variability was overestimated by 0.3 to
0.6°C (0.5 to 1.1°F). Precipitation variability is
overestimated in half the cases where precipitation
amount is also overestimated. The relative annual
variability of precipitation (that is, the standard
deviation relative to the mean) of the model is
generally in agreement with observations.
Under conditions of climate change (doubled
CO2), comparing control versus climate change,
there is generally reduced variability of temperature
from January through April. Results for other
seasons of the year are more ambiguous. For
precipitation, the doubled CO2 climate resulted in
increased variability hi most months at the four
grids (hi 31 of 48 cases), but was particularly
striking at the Southeast grid. These changes,
however, were often of the same order as the
model's natural variability (from examination of the
100-year control run). The sign of the change in
39
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Chapter 3
mean value and the sign of change in interannual
variability are highly correlated.
Daily Variability
Daily variability of temperature was analyzed by
taking the daily departures from monthly means and
comparing the resulting model distribution with the
distribution formed in the same manner from the
observational data
Ten years of control run for the transient
experiment for four months (January, April, July,
and October) were compared with 30 years of
observations. Distributions of observed versus
modeled daily temperature data were, in general,
not significantly different. Comparisons were also
made by calculating the standard deviations of the
departures from the mean for the four months
(Table 3-2). These results indicate that the model's
values are significantly greater than the observed
values, which demonstrates that the model is
producing too many extremes.
Results in Table 3-2, comparing standard
deviations, indicate that although changes with time
are not strictly progressive, most cases by the end of
the climate change experiment show reductions in
the standard deviation although these reductions are
not statistically significant. (Note in Table 3-2 that
standard deviations for the future decades are
changes in standard deviation (SD): model current
SD minus future decade SD) Since the results are
not statistically significant, a decrease of daily
temperature variability is not demonstrated.
For precipitation, comparisons are more
complex. For example, the number of observation
stations used to represent a grid box does affect the
results. Model rainfall distributions differ
significantly from observed distributions in half the
cases (in three seasons for California and the
southern Great Flams). The model also produces
fewer days of light rain in general and more
extreme values hi the winter in all four regions
(Table 3-3).
In the transient experiment, the precipitation
distributions differ from the control climate about
one-fourth of the tune with no general progression
over the decades. Figure 3-3 presents a sample set
of distributions for precipitation during several
decades of warming for the West Coast in April. In
comparing standard deviations (Table 3-3), the
warmest tune period exhibits increases in standard
deviations in half of the cases. These results are
again consistent with those for interannual
variability.
Variability of the Diurnal Cycle
It would be expected that the diurnal cycle
would decrease under changed climate as the
additional greenhouse gases could limit nighttime
cooling. Comparisons of control model results with
observations are reasonable hi the four regions.
Under doubled CO2 conditions, it was found that
the amplitude of the diurnal cycle very definitely
decreases in summer but changes inconsistently in
the other seasons. The reason for this is the
dominance of radiative heating in the summer and
of other forms of heating and cloud cover change
in other seasons.
The NCAR Study
In this study, Mearns et al. (1989) analyzed
mean and variance of climate variable time series
from selected empirical stations and those produced
by general circulation model control and doubled
COp runs. They attempted first to determine how
faithfully the GCMs reproduce these measures of
the present variability and then to examine how the
variability is estimated to change in CO2-perturbed
cases. By comparing the relative performance (i.e.,
model versus observations) of various versions of
the NCAR CCM (i.e., versions with different
physical parameterizations or formulations), Mearns
et al. helped to determine what formulations maybe
needed for forecasting certain measures of
variability and how much credibility to assign to
those forecasts.
Methods .
This study used the output from control runs of
three different versions of the NCAR Community
Climate .Model (CCM). These versions use
different parameterizations of important physical
processes in the model, such as surface hydrology.
The Chervin version (Chervin, 1986) is the primary
one used for comparison of observed and model
control output (i.e., model runs to simulate the
actual present-day climate), since it has the longest
tune integration (20 years).
The CCM is a spectral general circulation
model originally developed by Bourke and
40
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Climate Variability
Table 3-2. Daily Temperature Standard Deviations (SD) (°C)
Month
January
April
July
October
Observed
location SD
Southern
Great Plains
Southeast
West Coast
Great Lakes
Southern
Great Plains
Southeast
West Coast
Great Lakes
Southern
Great Plains
Southeast
West Coast
Great Lakes
Southern
Great Plains
Southeast
West Coast
Great Lakes
4.81
4.53
3.63
4.97
3.72
3.71
2.59
4.65
1.74
1.50
2.40
2.38
3.79
3.59
3.15
4.09
Model
Current
SD
8.15
6.90
5.86
5.79
5.77
5.50
4.29
6.15
2.56
2.34
3.56
3.02
5.16
5.21
6.51
5.46
2010s
*±SD
0.61
-0.14
-0.61
0.44
-0.57
-0.65
0.77
-0.51
0.54
0.14
0.03
-0.48
1.16
-0.54
-0.55
-0.37
2030s
ASD
-1.19
-1.14
0.05
-0.33
-0.27
-1.61
0.60
-0.26
-0.19
-0.22
0.54
-0.84
0.97
-0.25
-0.30
0.91
-2060
ASD
-0.83
-0.23
-0.16
-0.44
-0.80
-1.24
0.33
-1.39
0.18
-0.24
0.28
-0.14
1.35
-0.73
-0.80
-0.06
* ASD = Change in standard deviation (model current - future decade).
Source: Rind et al. (Volume I).
collaborators (Bourke, 1974; Bourke et al., 1977),
which has been modified by the incorporation of
radiation and cloud parameterization schemes. The
model has a resolution for physical processes (i.e.,
grid box size) of approximately 4.5 degrees in
latitude and 7.5 degrees in longitude, and has nine
levels in the vertical.
The other two versions of the CCM used are
the Washington version (Washington and Meehl,
41
-------
Chapter 3
Table 3-3. Daily Precipitation Standard Deviations (SD) (mm/day)
Month
January
April
July
October
Observed
Location SD
Southern
Great Plains
Southeast
West Coast
Great Lakes
Southern
Great Plains
Southeast
West Coast
Great Lakes
Southern
Great Plains
Southeast
West Coast
Great Lakes
Southern
Great Plains
Southeast
West Coast
Great Lakes
1.08
4.35
3.23
2.23
2.51
4.35
1.41
3.85
2.79
4.13
0.57
3.68
2.75
3.77
1.86
3.58
Model
Current
SD
2.80
4.62
4.55
4.06
3.26
3.85
2.76
3.29
3.08
3.31
1.53
2.48
1.79
3.88
2.69
2.26
2010s
*ASD
0.05
-1.20
-0.18
-1.07
0.94
0.95
0.07
-0.43
-0.10
0.28
0.44
-0.06
0.52
0.72
1.20
0.52
2030s
±SD
0.05
-1.35
0.34
-0.94
1.99
-0.15
1.02
-0.31
-0.09
0.29
0.24
0.72
0.34
-0.15
-0.63
0.76
-2060
±SD
1.68
-0.85
0.13
-0.50
1.17
0.81
-0.12
0.44
0.36
0.11
0.71
0.35
0.00
-0.28
1.34
0.95
*ASD = Change in standard deviation (model current - future decade).
Source: Rind et al. (Volume I).
1984), which includes an interactive thennodynamic
ocean and surface hydrology; and the Dickinson
version (Dickinson et al., 1986), a version of the
more sophisticated CCM1 containing a diurnal cycle
and a very sophisticated land surface package, the
Biosphere-Atmosphere Transfer Scheme (BATS).
This model calculates the transfer of momentum,
heat, and moisture between the Earth's surface and
atmospheric layers, and includes a very detailed
surface hydrology scheme that accounts for
vegetation type and amount, and water use by the
vegetation.
42
-------
Climate Variability
CONTROL
T~h
,6.0 9.0 12.0 15.0
PRECIPITATION (mm/Day)
6.0 9.0 12.0 15.0
PRECIPITATION (mm/Day)
18.0 21.0
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8.0 12.0 16.0 20.0 24.0 28.0
PRECIPITATION (mm/Day)
6.0 9.0 12.0 15.0
PRECIPITATION (mm/Day)
18.0
Figure 3-3. Sample set of precipitation distributions for the West Coast in April for specified years of the
transient run (Rind et al., Volume I).
The four regions of the United States chosen
for investigation were roughly the same as those
chosen for the GISS study: the Great Plains
(GP; represented by three grid boxes), the
Southeast (SE), the Great Lakes (GL), and the
West Coast (WC). The locations of the grid boxes
and observation stations are indicated on Figure 3-4.
Comparison of Observed versus Chervin Control
Run
Four variables deemed particularly relevant to
climate impact analysis were chosen for this
analysis: daily mean temperature, daily total
precipitation, mean daily relative humidity, and
mean daily absorbed solar radiation.
Temperature
Figure 3-5 displays the time series of daily
average temperature for modeled and observed data
for the four regions investigated. The model
successfully simulates the annual cycle for the four
regions, which represents the seasonal variability.
Solar Radiation and Relative Humidity
Simulation of solar radiation ranges from very
good (the Great Plains region) to only fair at the
Southeast, where the model consistently
overestimated absorbed solar radiation during all
months. The Chervin CCM is poor at simulating
the annual cycle of relative humidity at all four
locations.
43
-------
Chapter 3
• Temperature and
Precipitation Stations
o Relative Humidity and
Radiation Stations
Figure 3-4. NCAR mbdel grid cells and station locations.
35
30
25
20
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1"
3 5
1 «
-10
—15
-20
35
30
25
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GREAT PLAINS I, II, III
OBSERVED DATA
MODEL
120 180 240 300
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SOUTHEAST
OBSERVED DATA
MODEL
60 120 180 240 300
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30
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MODEL
60 120
180 240
DAYS
WEST COAST
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OBSERVED DATA
MODEL
60 120
180
DAYS
300 360
1 I 1 11
240 300 360
rigure 3-5. Average temperature for a 20-year average year (NCAR model and observations) (Mearns et al.,
Volume I).
44
-------
Climate Variability
Precipitation
The Chervin CCM consistently overestimates
precipitation, although the seasonal cycle is well
simulated in the Great Plains region and the West
Coast grid. The authors do not know why the
model overestimates precipitation, but speculate
that it may partly be a result of a precipitation
parameterization criterion of 80% relative humidity^
Variability Comparisons of the Chervin CCM
Interannual variability of temperature is
generally underestimated by the Chervin CCM in
all four regions. Interannual variability of
precipitation (i.e., relative variability, the standard
deviation relative to the mean) is generally in
reasonable agreement with observed data, although
it is occasionally overestimated. This is a
particularly encouraging result for the credibility of
predicting climate changes, given how inaccurate the
control precipitation results are in terms of absolute
values.
In terms of daily variance, the model's relative
humidity tends to be much less variable than
observed values at all locations and in most months.
Results for temperature for January and July
indicate that the Chervin model generally
overestimates daily temperature variance.
Intercomparisons of Three CCM Versions and
Observed Data
Comparing different model versions' simulations
of present-day climate facilitates understanding of
the possible ranges of errors and the effect of a
model's structural differences. The present-day
climate runs of models incorporating physics
different from those of the CCM version of Chervin
(1986) are compared. Both the Washington and
Dickinson runs consist of 3-year integrations.
There is considerable variability in how well the
models reproduce mean total precipitation for the
four grids, ranging from the relatively good results
of Dickinson's model, to the fair results of
Washington's model, to the overestimation of
Chervin's model. On the basis of mean annual and
seasonal comparisons, no one model is clearly
superior to the other two in accurately
reproducing mean climate (temperature and
precipitation) at the four locations.
The Dickinson model most accurately
reproduces daily variability of temperature, while
the other two models overestimate it. This result is
graphically illustrated in the temperature histograms
(three models and observed) for two key months for
the Southeast grid (Figure 3-6).
The reasons for these discrepancies have yet to
be explored in depth, but are likely related to
different land surface packages in the models. A
possible explanation for the lowered daily
temperature variability of the Dickinson model
concerns the more sophisticated surface energy
balance used, which includes consideration of soil
heat capacity.
Control Versus CO2-Perturbed Runs
The authors included a preliminary analysis of
changes in precipitation and temperature, under a
scenario of doubled CO2, using the output from
Washington's control and doubled CO2 runs for the
four regions. Interannual variability could not be
analyzed because the time series are too short.
However, they examined the daily variability of
temperature and precipitation.
An annual temperature increase of about 2 or
3°C (4 to 5°F) occurs at all locations. Annual
total precipitation increases between 22 and 26%
at three locations but decreases slightly (2%) in the
Southeast. There are also potentially important
changes in the seasonal distribution of precipitation.
For example, at the Southeast grid a smaller.
percentage of the annual total occurs during the
summer in the CO2-perturbed case (from 13 to/
6%). : ;
Statistics comparing the daily temperature
variance of the control and perturbed runs for
January, April, July, and October indicate that the
temperature variance in general does not
significantly change (at the 0.05 level of significance)
at these four grids. Without consideration of
statistical significance levels, results are mixed with
both increases and decreases.
The percentage of rain days decreases in the
summer under climate change in three of the four
45
-------
Chapter 3
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Figure 3-6. Histograms of daily temperature, observations and three model versions, for two key months of the
Southeast grid (Mearns et al., Volume I).
grids. Overall, there is a tendency for increased
daily precipitation variability at the four locations,
based on analysis of precipitation distribution
characteristics.
COMPARISON OF GISS AND
NCAR RESULTS
It is difficult to compare the two studies. The
modeling experiments were conducted partly with
different purposes in mind using two different
models (which differ not only in how physical
processes are modeled but also in their spatial
resolutions). They also use different qualitative and
statistical methods for making comparisons. The
GISS experiment was aimed primarily at examining
the changes in variability with climate change,
whereas the immediate purpose of the NCAR
experiment was primarily to examine and
explain discrepancies in variability between model
control runs and observations. Since the spatial
resolutions of the models differ, the grid boxes of
the models do not coincide, and so the regions
analyzed differ. These are only some of the
problems that would affect these comparisons.
Nevertheless, an attempt is made here to compare
some of the results that roughly coincide. Some
regions, such as the Great Lakes grids, coincide
fairly well (see Figures 3-2 and 3-4), and some
similar analyses were conducted.
A brief comparison is made of how the models
reproduce the observed mean climate. In general,
the GISS model is too cool and the NCAR model(s)
too warm. The GISS model overestimates
precipitation at two grids, and the Chervin version
of the NCAR model overestimates precipitation at
all grid boxes (although this is not true of two other
versions of the NCAR CCM).
46
-------
Climate Variability
The following sections compare the observed,
control, and perturbed runs of interannual and daily
variability of temperature and precipitation. Table
3-4 summarizes the comparisons between the
modeled control runs and observations for
variability.
Interannual Variability
Rind et al. used a 100-year control run for
interannual variability calculations. Their
observational data set consists of 30 years (1951-80).
The NCAR study uses a 20-year control run of
Chervin (1986) and a 20-year observational data set
(1949-68). The differences in sample size should be
noted.
Table 3-5 presents the relevant results, winter
and summer standard deviations for temperature,
and annual coefficients of variation (i.e., a measure
of relative variability) for precipitation for the four
regions for both studies. Relative variability values
(standard deviation relative to the mean) for the
GISS study were provided by its authors (Rind,
personal communication). Both models
overestimate the temperature variability of the
Great Plains region in winter. (However, the
difference in the NCAR study was deemed to be
statistically insignificant.) Both models
underestimate the temperature variability (but the
NCAR model much more so than the GISS) for the
West Coast winter. In summer, the GISS model
overestimates, and the NCAR model underestimates
temperature variability at all locations.
Regarding the relative variability of precipitation
(measured by the coefficient of variation), the
results for the two models are rather similar. The
differences between observed and model values are
very close (from 1 to 6 percentage points) in each
study. The NCAR model slightly underestimates
the variability at each location, whereas the slight
errors in the GISS results are mixed.
The reasons for the lack of agreement in the
two studies are far from obvious, and speculation
can only be rough. Certainly the difference in how
the atmosphere-ocean interaction is modeled may
play a role (i.e., the NCAR model uses fixed sea
surface temperatures, whereas the GISS model
computes sea surface temperatures from a simple
ocean mixed-layer model).
Daily Variability
Daily variability of temperature can be
compared for two season months (January and July)
at the four locations using the standard deviations
(Table 3-6). Because of certain problems
concerning necessary statistical assumptions for
quantitative testing, these comparisons must be
Table 3-4. Variability Results for Control Runs vs. Observations3
Interannual
Daily
Model
Temperature Precipitation Temperature Precipitation
(Relative/Absolute)13 (Relative/Absolute)
GISS
High
Good/High
High
Good/High
NCARC
Low
Good/High
High"
Good/High
aValues in chart refer to how the model estimates compare to the observations.
bRelative/absolute refers to comparison of coefficients of variation (relative) and standard deviation (absolute).
°Chervin version of the NCAR model.
dValues are good or slightly low for the Dickinson version of the NCAR model.
47
-------
Chapter 3
Table 3-5. Interannual Standard Deviations, Temperature and Coefficient of Variation, Precipitation, GISS,
and NCAR Control Runs
Model and region
Temperature (°C)
standard deviation
Dec.-Feb.
June-Aug.
Precipitation
coefficient of
variation (%)
(standard deviation/
mean)
GISS fn = 1001
SGP
SE
we
GL
NCAR rn -
GPHI
SE
GL
we
Model
Obs.
Model
Obs.
Model
Obs.
Model
Obs.
20)
Model
Obs.
Model
Obs.
Model
Obs.
Model
Obs.
1.65
1.20
1.65
1.65
1.35
1.45
1.35
1.50
1.3
1.1
1.0
1.8
2.2
1.6
0.8
1.6
1.05
0.75
1.05
0.70
1.35
0.75
1.25
0.70
0.62
1.20
0.38
0.74
0.71
0.88
0.76
0.81
15
21
22
18
18
23
18
18
17
22
10
12
10
11
17
17
SGP = Southern Great Plains; SE = Southeast; WC = West Coast; GL = Great Lakes; GP = Great Plains.
Source: Rind, personal communication; Mearns et al. (Volume I).
viewed strictly qualitatively. In seven of the eight
cases, the studies agree that the models
overestimate daily temperature variability.
In _ both studies, explanations for the
overestimations are related to the modeling of
surface hydrology (i.e., both models fail to
completely account for important
surface-atmosphere interactions that would tend to
reduce daily temperature variability). (The relative
success of the Dickinson version of the CCM in
reproducing daily temperature variability partially
supports such an explanation, since it has a more
sophisticated surface hydrology scheme compared
with the Chervin version.)
The models produce, in the majority of cases,
too few light rain days. The GISS model produces
48
-------
Climate Variability
Table 3-6. Daily Temperature Standard Deviations (°C)
Month
GISS
NCAR
Obs. Model
Obs. Model
Great Plains
Southeast
Great Lakes
West Coast
4.81
4.53
4.97
3.63
8.15
6.90
5.79
5.86
6.18
5.41
5.50
4.10
8.84
5.92
11.20
5.00
July
Great Plains
Southeast
Great Lakes
West Coast
1.74
1.50
2.38
2.40
2.56
2.34
3.02
3.56
2.90
1.55
2.67
2.18
2.79
1.70
2.82
3.52
Source: Rind et al. (Volume I); Mearns et al. (Volume I).
too many extreme rain events in winter at all
locations. The NCAR model tends to produce too
many high extremes in all four seasons. Neither
study accounts for these discrepancies.
Comparison of Climate Change
Comparison of climate change results of the
two models is restricted to changes in daily
temperature variability and daily precipitation
variability for four months for the four locations,
since the NCAR study includes a quantitative
analysis of only daily variability change.
The two studies do not agree on the direction
of change of daily temperature variability. The
NCAR results are mixed, showing both increases
and decreases, although most of these changes are
statistically insignificant. Rind et al. conclude that
in general, there is a decrease in daily temperature
variability on the basis of changes in standard
deviations (but the changes are not statistically
significant). On the basis of the two research
reports, no clear statement may be made about
changes in daily temperature variability under CO2
warming conditions.
A slightly clearer picture is gained from
comparison of results for daily precipitation. The
results of both models point to increased daily
precipitation (although not from analysis of the
same statistic). This is not true for all locations
during all seasons, however.
Table 3-7 summarizes the very tentative
conclusions that can be drawn given all climate
change results regarding changes in climate
variability from the GISS and NCAR studies. The
degree of uncertainty in these conclusions should be
noted, as should the observation that many of the
results are from only one model (GISS).
Limitations of the Two Studies
Both studies underline the importance of
viewing the climate change results of the models in
the context of how well they reproduce the present
climate. Model deficiencies can be expected to limit
the reliability of climate change results, and faith in
quantitative results is probably misplaced.
A major model deficiency is inability to resolve
subgrid-scale atmospheric phenomena that
49
-------
Chapter 3
Table 3-7. Summary of GISS and NCAR Model "Scenarios" for Direction of Variability
Changes from Present Climate to Doubled CO2 Climate for Four U.S. Regions3
Variability Results
CO2-Perturbed Runs
Variable
Temperature
Precipitation
Interannual
V
t?
Daily
111
f??
Question marks indicate degree of uncertainty:
? - results of only one model;
?? = results of two models, but some conflicting results.
contribute to climate variability, such as fronts and
intense cyclones (hurricanes), and important
variations in atmosphere-ocean coupling, such as El
Nino Southern Oscillation (ENSO) events.
(However, it appears that more sophisticated GCMs
incorporating complete ocean models do produce
ENSO-type events (Meehl, 1989).) However, model
results do give crude estimates as to the importance
of some physical processes responsible for variability
and what must be done to improve them. Further
testing is needed to determine how the models'
deficiencies in reproducing present-day climate
affects "predictions" for a CO2-warmed future
climate.
IMPLICATIONS FOR STUDIES
OF CLIMATE CHANGE IMPACTS
As indicated in the second section of this
chapter, virtually all systems affected by climate are
affected by climate variability, although some are
more affected than others. The relative importance
of climate variability and changes in variability, as a
result of climate change, to particular impact areas
is reflected in the results and limitations of some of
the studies summarized in this report.
Of greatest concern is the lack of information
regarding changes in the variability of temperature
and precipitation that would attend climate change.
The lack of this information resulted in the
formation of climate scenarios wherein the temporal
variability of both precipitation and temperature
were not changed (see Chapter 4: Methodology).
This was considered a limitation or concern in many
studies, some of which are discussed in this section.
In the Johnson et al. study on agricultural runoff
and leaching (reviewed hi Chapter 6: Agriculture),
the results were considered to be limited by the
failure to consider changes in storm frequency and
duration that would result from climate change.
The results of this study could be vastly different
from those presented, depending upon assumptions
concerning precipitation duration, frequency, and
intensity, all of which would change if a changed
daily variability were assumed.
Several studies on hydrology summarized in this
report also are highly dependent upon assumptions
about precipitation variability. These include the
Lettenmaier et al. study on the hydrology of
catchments hi the Central Valley and the Sheer and
Randall study on the impact of climate scenarios on
water deliveries, both reviewed in Chapter 14:
California. The scenarios assumed that the number
of days of rainfall remains the same under the
climate change. Model results in terms of
predicting runoff amounts would be quite different
if more rainfall events of lower intensity were
50
-------
Climate Variability
assumed compared with the same number of rainfall
events of (generally) higher intensity.
The studies for the Southeast (Chapter 16) did
not consider changes in the frequency of droughts
or severe storms such as hurricanes, which could
certainly affect the likelihood of flooding for some
coastal communities. However, these concerns are
considered to be secondary to changes in sea level
that would dominate in terms of changing the
likelihood of floods.
Crop yields are very dependent on daily
variability. For example, heat waves occurring
during the grain filling process lower wheat yields.
Whether a drought occurs early or late in the
growing season has differential effects on yields.
Changes in variability were not considered in the
Rosenzweig, Peart et al., Ritchie, and Dudek studies
(see Chapter 6: Agriculture).
Changes in the frequencies of extreme events
are considered to be of great importance to
potential forest disturbance, as discussed in Chapter
5: Forests. The possibility of increases in the
frequencies of events such as droughts, flooding,
wind, ice, or snowstorms may be of greater
significance to forest survival than the gradual mean
change in climate that has been studied so far.
The Kalkstein study, which is reviewed in
Chapter 12: Human Health, is strongly dependent
upon the determination of certain maximum
temperature threshold values beyond which human
mortality increases. In applying the death/weather
effects statistical models to scenarios of climate
change, Kalkstein held temperature variability
constant, so that temperatures that exceed the
threshold values are determined unrealistically.
Changes in the variability of temperature both
seasonally and daily are important to studies
concerned with the effect of temperature change on
electricity demand (discussed in Chapter 10).
Although new generating capacity requirements for
the nation for 2010 and beyond are calculated
assuming climate change, the numbers generated
could be considerably different for any particular
year, depending mainly on air-conditioning needs,
which would be the major use increase for
electricity. Such needs are sensitive to extremes in
daily maximum temperatures and the persistence of
such temperatures (i.e., heat waves).
It would be impossible to quantitatively or even
qualitatively estimate how different the results of
these studies would be if changes in climate
variability had formed part of the climate scenarios
made available as input for the various climate
impact models used. Primarily, it is impossible
because the variability changes are not known;
second, it is impossible because most of the studies
are so complex that the effect of a change in one
variable (a complex change at that) is not intuitively
obvious in most cases. Analyses of the sensitivity of
the impact models involved to changes in variability
would be required to provide specific answers.
What can be said at this point is that the lack of
information on climate variability has limited a
number of studies in this report and has limited the
completeness of the answers they could provide.
RESEARCH NEEDS
The research reported above clearly indicates
that research of changes in climate variability
associated with climate change is truly hi its infancy.
Much needs to be done. Future research needs
may be broken into three categories: further
analysis of GCMs; improvements hi GCMs; and
sensitivity analysis of impacts.
Further Investigation of Variability in
GCMs
Results summarized here represent only an
initial effort at looking at variability in GCMs. We
need to examine in more models and at many more
grid boxes the daily and interannual variability of
many climate variables (such as relative humidity,
solar radiation, and storm frequency) in addition to
temperature and precipitation. Other time scales
of variability also should be examined, such as 7- to
10-day scales, which correspond to the lifetime of
many frontal storms. Moreover, the most
sophisticated statistical techniques must be used or,
where needed, developed, such that uniform
quantitative indicators are available to evaluate both
how well the current models reproduce present
variability and how they forecast the change
51
-------
Chapter 3
in variability under climate change conditions. The
causes for discrepancies in present-day climate
variability and control run variability must be better
understood to attain a clearer understanding of
future climate changes.
Improvements in GCMs
The results of Rind et al. and Mearns et al. give
some indications that oversimplifications in the land
surface packages of GCMs contribute to
overpredictions of daily temperature variability.
This possibility is further underlined by the better
results obtained with Dickinson's model, which
includes a more sophisticated land surface package.
More detailed analyses of current GCMs are
necessary to confirm this speculation, as well as to
determine the causes of other errors in variability,
such as for precipitation. Other known causes of
error, such as the models' relative inability to
simulate subgrid-scale phenomena, must be
investigated further. The next step involves altering
the GCMs so that variability is properly simulated.
Only then can much faith be put in GCM forecasts
of variability changes with a perturbed climate.
Sensitivity Analyses of Impacts
It also must be determined how important
changes in variability will be to different areas of
impact. Since the variability of climate variables
produced from GCMs cannot be "trusted" or even
easily analyzed at this point, these sensitivity
analyses of impact models should be performed with
statistically simulated time series of climate
variables, as has been performed by Schwarz (1976)
and Mearns et al. (1984). By simulating time series,
different levels of autocorrelation and variance in
the time series may be controlled for and
systematically varied. By this means, important
thresholds of variability change for different
variables as they affect the output of impact models
can be determined. Moreover, ranges of possible
impacts of variability change can be determined and
can serve as guides until better information is
available on how variability will change in a
COg-warmed world.
REFERENCES
American Meteorological Society. 1985. Flash
floods: A statement of concern by the AMS.
Bulletin of the American Meteorological Society
66(7):858-859.
Barbecel, O., and M. Eftimescu. 1973. Effects of
Agrometeorological Conditions on Maize Growth
and Development. Bucharest, Romania: Institute
of Meteorology and Hydrology, pp. 10-31.
Bates, G.T., and GA. Meehl. 1986. The Effect of
CO2 concentration on the frequency of blocking in
a general circulation model coupled to a simple
mixed layer ocean model. Monthly Weather Review
114:687-701.
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CHAPTER 4
METHODOLOGY
NEED FOR CLIMATE CHANGE
SCENARIOS
As discussed in Chapter 2: Climate Change,
there is a scientific consensus that increased
atmospheric concentrations of greenhouse gases will
likely increase global temperatures, and that such a
global temperature increase will likely increase
global precipitation and sea levels. There is no
consensus on how regional climates may change.
We do not know whether temperatures will rise in
all regions; we do not know whether precipitation in
any particular region will rise or fall or whether we
will have seasonal changes, and we are uncertain
about the rate and magnitude of change. As
discussed in Chapter 3: Climate Variability,
scientists do not know how variability — that is, the
frequency of droughts, storms, heat waves, and
similar phenomena — may change. Without
knowing how regional climate may change, we
cannot predict impacts.
Despite these uncertainties, we can get a sense
of what the future may look like through the use of
scenarios. Scenarios are plausible combinations of
conditions that may be used to illustrate future
events. They may be used to identify possible
effects of climate change and to evaluate responses
to those effects. To incorporate uncertainties
surrounding regional climate change, regional
scenarios should include a variety of potential
climate changes consistent with the state of
knowledge regarding global warming. By analyzing
many scenarios, we may be able to identify the
direction and relative magnitude of impacts. Yet,
unless scenarios have probabilities assigned to them,
predictions of future impacts cannot be made. In
this report, probabilities are not assigned and results
do not represent predictions. Only the direction of
change and relative magnitude are identified. The
scenarios used in this report do not represent the
entire range of possible climate change. Thus, the
range of effects identified does not represent the
entire range of potential effects.
SCENARIO COMPONENTS
To assess the potential effects of global climate
change, regional scenarios of such change should
have the following characteristics:
1. The scenarios should be internally
consistent with global warming caused by
increases in greenhouse gas emissions. A
doubling of the CO2 concentration in the
atmosphere is thought to increase global
temperatures by approximately 1.5 to 4.5° C
(3 to 8°F). The regional temperature
changes and seasonal distributions may be
higher or lower, as long as they are
internally consistent with the global range.
2. The scenarios must include a sufficient
number of meteorological variables to meet
the requirements for using effects models.
These effect models include models of crop
growth, forest succession, runoff, and other
systems. Some models of the relationship
between climate and a system use only
temperature and precipitation as climate
variables, while others also need solar
radiation, humidity, winds, and other
variables.
3. The meteorological variables should be
internally consistent. While a scenario is
not a prediction, it should at least be
plausible. The laws of physics limit how
meteorological variables may change in
relationship to each other. For example, if
global temperatures increase, global
precipitation must also rise. Regional
changes should be internally consistent with
these large-scale changes.
4. The scenarios should provide
meteorological variables on a daily basis.
Many of the effects models used in this
study, such as crop yield and hydrology
models, need daily meteorological inputs.
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Chapter 4
5. Finally, the scenarios should illustrate what
climate would look like on a spatial scale
fine enough for effects analysis. Many
effects models consider changes in
individual stands of trees or farm fields. To
run them, scenarios must illustrate how
climate may change locally.
TYPES OF SCENARIOS
Two questions should be answered in analyzing
the potential impacts of the greenhouse effect:
What would be the effects of a large climate change
in the future? How quickly will the effects become
apparent over time? The first question asks what
the world will be like in the future; the second is
about the speed of change and the sensitivity of the
system.
One way of examining the first question is to
use scenarios of an equilibrium future climate.
Climate equilibrium is defined as climate in which
average conditions are not changing (although year-
to-year variations could still occur).
A drawback of an equilibrium scenario is that
it occurs at an arbitrary point in the future and
assumes that the climate has reached a stable level
corresponding with the higher concentrations of
greenhouse gases. It does not indicate how climate
may change between now and the equilibrium
condition or how soon effects may be seen.
Furthermore, a "stable" climate has never happened,
nor is it likely to occur.
To help identify sensitivities and give a sense
of when effects may occur, this study uses transient
scenarios of climate change. A transient scenario is
a scenario of how climate may change over time.
The options for creating regional scenarios of
global warming include the following:
1. arbitrary changes in climate;
2. analog warming; and
3. use of general circulation models.
Arbitrary Changes
A simple way of constructing a scenario is to
assume that climate variables change by some
arbitrary amount. For example, one could assume
that temperatures increase by 2 or 4°C, or that
rainfall rises or falls by 10% and all other variables
are held constant. Such scenarios are relatively easy
to use and can help to identify the sensitivities of
systems to changes in different variables. To
determine how sensitive a system is to temperature
alone, one could hold other variables at current
climate levels and change temperature by arbitrary
amounts.
A major drawback to using scenarios with
arbitrary changes is that they may not be realistic,
since evaporation, precipitation, wind, and other
variables will most likely change if global
temperatures change. A combination of unrealistic
meteorological changes may yield an unrealistic
effect. We are not sure how other meteorological
variables would change on a regional scale if
temperature rose a certain amount. Thus, scenarios
with arbitrary changes may be useful for
determining sensitivities to particular variables but
not for determining the possible magnitudes of
effects.
Analog Warming
Many climatologists have advocated the use of
historic warming periods as an analog of how a
future warming may affect regional climates
(Vinnikov and Lemeshko, 1987). The instrumental
weather record can be used by comparing a cool
decade on record, such as the 1880s, with a warm
decade, such as the 1930s (Wigley, 1987), or by
comparing a decade such as the 1930s with the
present.
Paleoclimatic data may also be incorporated
into an analog warming scenario. For example,
6,000 years ago the temperatures were about 1°C
warmer. Paleoclimatologists have determined how
rainfall and temperature patterns on a broad
regional scale differed in the past. The changes
associated with past climates that were warmer than
now may be used as an analog warming scenario.
The advantage of using an analog is that it
gives a realistic sense of how regional and local
weather patterns change as global climate warms.
For example, climate data from 1880 to 1930 show
how daily and local weather changed during a
warming period.
58
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Methodology
However, analogs have several drawbacks.
First, they are not consistent with the range of
global warming now thought likely under the
greenhouse effect: 1.5 to 4.5° C. The warmest
period of the last 125,000 years was 1°C warmer
than the present temperature. (Although the
Pliocene Epoch (2 to 5 million years ago) had
global temperatures several degrees higher than
now, there is virtually no information on the
regional distribution of temperature and rainfall
during that period.) In addition, the past warmings
were not necessarily caused by changes in the
concentration of greenhouse gases, but may have
been due to such factors as shifts in the inclination
of the Earth's axis. These factors caused different
regional climate changes than would be associated
with increases in radiative forcing. Second,
paleoclimatic and historic records dp not provide
enough detail to conduct comprehensive analysis of
the 1°C warming. Paleoclimatic records only
indicate broad regional patterns of change for a few
variables, such as temperature, rainfall, and solar
radiation. We cannot discern local, daily, or
interannual climate from these records. Even using
the 1930s data presents some problems. Daily
records are available only for temperature and
rainfall. Some effects models need more variables,
such as wind or radiation. Furthermore, the
number of weather stations with 1930s data is
limited, which could present problems for creating
comprehensive regional scenarios.
General Circulation Models (GCMs)
GCMs are dynamic models that simulate the
physical process of the atmosphere and oceans to
estimate global climate. These models have been
developed over two decades and require extensive
computations to run. They can be run to estimate
current climates and the sensitivity of climate to
different conditions such as different compositions
of greenhouse gases. The GCMs are often used to
simulate climate caused by a doubling of carbon
dioxide levels, also referred to as doubled CO-.
Estimates of climate change caused by this effective
doubling of CO21 are referred to as "doubled CO2
scenarios." Output is given in regional grid boxes.
The "effective doubling of CO2" means that the total radiative
forcing of all greenhouse gases (CO2, CH4, N2O, CFCs, etc.) is
the same as the radiative forcing caused by doubling carbon
dioxide concentrations, over midcentury levels, alone. In other
words, the combination of all greenhouse gases has the same
radiative forcing as simply doubling CO2.
GCMs have several advantages over the other
approaches for creating scenarios. First, the models
are used to estimate how global climate may change
in response to increased concentrations of
greenhouse gases. Thus, regional outputs are
internally consistent with a global warming
associated with doubled COu. Second, the estimates
of climate variables (for example, rainfall,
temperature, and humidity levels) are physically
consistent within the bounds of the model physics.
Third, GCMs estimate outputs for many
meteorological variables (including wind, radiation,
cloud cover, and soil moisture) providing enough
input for effects models. Fourth, GCMs simulate
climate variability on at least a daily basis.
Among the most important limitations are the
GCMs' simulations of the oceans. The oceans play
a critical role in determining the rate of climate
change, regional climate differences, and climate
variability. The GCMs, however, are coupled to
relatively simple models of ocean circulation, which
either treat the oceans as a "swamp" or. only model
the upper layers of oceans. The models'
assumptions oversimplify the transfer of heat to and
from the oceans. In addition, the GCMs simplify
other important factors that affect climate, including
cloud cover and convection, sea ice, surface albedo
(the amount of light reflected, rather than absorbed,
from the surface) and land surface hydrology (i.e.,
soil moisture), which may also contribute to
uncertainty about the estimates of climate change
(Dickinson, 1986; Schlesinger and Mitchell, 1985;
Gates, 1985). For example, some of the GCMs
model soil moisture storage in a simple manner,
assuming the soils act like a "bucket.'1 (There have
been recent improvements on this method.) This
method of modeling raises uncertainties concerning
estimates of runoff from the models. The -way
GCMs simulate such important climate factors as
oceans, clouds, and other features casts some doubt
on the validity of the magnitude of global warming
estimated by the models. (For a further discussion
of the role of oceans in climate change, see Chapter
2: Climate Change. For a discussion of the GCMs'
ability to estimate climate variability, see Chapter 3:
Climate Variability.)
One of the major disadvantages of using
GCMs for effects analysis is their low spatial
resolution. GCMs give outputs in grid boxes that
vary in size from 4 by 5 degrees latitude to as much
as 8 by 10 degrees longitude. Figure 4-1 shows the
grid boxes from the Goddard Institute for Space
59
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Chapter 4
47.0
39.1
31.3
23.5
-135
-125
-115
-105
-85
-75
Figure 4-1. GISS model of the United States.
Studies (GISS) model overlaid on a map of the
United States. Each grid box is 8 by 10 degrees and
is an area larger than France (Mitchell, 1988).
Within each grid box, the actual climate may be
quite variable. For example, although both are in
the same grid box, the weather in southern
Washington State may be quite different from the
weather in northern California The models,
however, do not account for variations within each
grid box. For any simulated time, they provide a
single value for temperature, for rainfall, and for
other variables for the entire area of the box.
A second disadvantage for effects analysis,
which may be more critical than the first, is that
GCMs generally do not accurately simulate current
regional climate conditions. In general, the
accuracy of GCM climate estimates decreases with
increasing resolution. The GCMs do a reasonable
job of estimating observed global and zonal
climates, but the estimates of regional climate are,
in many cases, far from observed conditions. This
is shown in Table 2-2 (see Chapter 2: Climate
Change), adapted from Grotch (1988), which
displays GCM temperature estimates and actual
observations on different scales. GCM estimates of
rainfall are less reliable on a regional scale. As
Grotch points out, the disparities between GCM
estimates of current regional climate and actual
conditions calls into question the ability of GCMs to
predict climate change on a regional scale.
The disparities among GCM estimates on a
regional scale are due to a number of factors. One
of the most important is the simplified assumptions
concerning the oceans. The assumptions on other
factors such as cloud cover, albedo, and land surface
hydrology also affect regional estimates. The GCMs
also simplify topographic features within grid boxes,
such as the distribution of mountains or lakes. The
large size of the grid boxes means that these
features are oversimplified on a geographic scale.
This contributes to uncertainty regarding estimates
of regional climate change. In sum, as Grotch
concluded, GCM estimates of regional climate
change should not be taken as predictions of
regional climate change. They should be
interpreted as no more than illustrations of possible
future regional climate conditions.
60
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Methodology
CHOICE OF DOUBLED CO2
SCENARIO
GCM outputs were employed as a basis for
constructing the scenarios to be used in our report
because they produce the best estimate of climate
change due to increased greenhouse gas
concentrations and they produce regional climate
estimates internally consistent with doubled CO2
concentrations. Yet, GCMs are relatively new tools
that need a great degree of refinement. Their
results must be applied with caution. The regional
GCM estimates of climate change are considered
to be scenarios, not predictions. Given the
uncertainties about GCM estimates of daily and
interannual variability (see Chapter 3: Variability),
a conservative approach involves using average
monthly changes for each grid box.
The scenarios described in this chapter are a
hybrid between GCM outputs and historic weather
data. The estimates of average monthly change in
temperature, precipitation, and other weather
variables are used from GCM grid boxes. Model
simulations of monthly doubled CO2 conditions are
divided by model simulations of average monthly
current conditions in each grid. The ratios of
(2xCC>2):(lxCC)2) are multiplied by historic weather
conditions at weather stations in the respective grid
boxes. Parry et al. (1987) used this approach in an
analysis of impacts of climate change on agriculture.
Thus, if a grid box is estimated to be 2°C warmer
under the GCM doubled CO2 run, all stations in
that grid are assumed to be 2°C warmer in the
doubled CO2 scenario. The effect of this is to
keep geographic variation from station to station
within a grid the same as in the historic base period.
Furthermore, interannual (year to year) and daily
variability remain the same. If rainfall occurs 10
days in a month, hi the scenario it also occurs 10
days in the month, and the amount of rainfall is
adjusted by the GCM output. Since these scenarios
are hybrids between GCM average monthly
estimates and daily historic weather records, these
scenarios are not strictly GCM scenarios. Each
scenario is referred to by the GCM, whose monthly
output serves as its base (e.g., the "GISS scenario").
The years 1951-80 were chosen as the base
period to which average doubled CO2 changes were
applied. Several decades of data give a wide range
of warm, cold, wet, and dry years. Since the data
are from the most recent decades, they are the most
complete historic data available. A complete daily
record for a number of weather variables only
began in 1948.
GCMs Used
To obtain a range of scenarios, output from
three GCMs was used:
• Goddard Institute for Space Studies (GISS)
(Hansen et al., 1988);
• Geophysical Fluid Dynamics Laboratory
(GFDL) (Manabe and Wetherald, 1987);
and
• Oregon State University (OSU)
(Schlesinger and Zhao, 1988).
The average seasonal temperature and
precipitation for the U.S. gridpoints for each model
are displayed in Figure 4-2. All three models
estimate that average temperatures over the United
States would rise, but they disagree on the
magnitude. OSU gives 3°C, GISS 4.3°C, and GFDL
5.1°C. The seasonal patterns are different, with
GISS having a larger warming in winter and fall,
GFDL having the highest temperature change in the
spring, and OSU having little seasonal variability.
All three models estimate that annual precipitation
over the United States would increase. GISS and
OSU estimate that annual precipitation would rise,
respectively, by 73 millimeters (2.92 inches) and 62
millimeters (2.48 inches), while GFDL estimates a
rainfall increase of only 33 millimeters (1.31 inches).
The first two models have precipitation increases in
all four seasons, while GFDL has a decline in
summer rainfall. As can be seen in the regional
chapters, the models show greater disagreement on
the direction and pattern of regional rainfall
changes than on regional temperature. Overall,
OSU appears to be the "mildest" scenario, with the
lowest temperature rise and largest increase in
precipitation. GFDL appears to be the most
"extreme," with the highest temperature rise, the
smallest increase hi precipitation, and a decrease in
summer rainfall. Some of the important parameters
in the three GCMs are displayed in Table 4-1.
61
Chapter 4
Temperature
0
Precipitation
Wtntor Spring
Spring Summer
Figure 4-2. Average changes in temperature (°C) and precipitation (mm/day) over the grid boxes of the lower
48 states (2xCO2 less lxCO2).
The "extreme" values in the GFDL doubled
CO, scenario are due, in part, to assumptions made
in the model run used in this report. That run did
not constrain sea surface temperature and sea ice,
which yielded seasonal extremes in the northern
hemisphere. A later run, produced too late for use
in this study, constrained sea surface temperature
and sea ice to observed values. Both runs yield the
same average global warming of 4.0°C, while the
later run has greater seasonal extremes in the
southern hemisphere. Both runs show a large
decrease in summer soil moisture (Wetherald,
personal communication, 1988).
Limitations
A major limitation of the doubled CO2
scenarios used for this study is the lack of temporal
and spatial variability. By applying average monthly
changes to the historic data set, it is assumed that
the daily and interannual patterns of climate remain
the same. This assumption is probably unrealistic,
since a change in average conditions will probably
lead to a change in variability. Furthermore,
holding variability constant can have an impact on
effects analysis.
Most climate-sensitive systems are sensitive to
climate variability. For example, riverflow is very
sensitive to the amount and intensity of rainstorms.
Certain crops are sensitive to consecutive days with
temperatures above a certain level. The studies do
not identify how these and other systems could be
affected by changes in temporal climate variability.
Holding spatial variability within a grid box constant
also affects the results of the analyses performed for
this report. Climate change may also lead to
changes in wind patterns, which could change storm
patterns, cloud distribution, deposition of air
pollutants, and other systems. In addition, the years
1951 to 1980 were a period of relatively low weather
variability in the United States. Only adjusting
average conditions from the base period in the
scenarios may underestimate potential increases
invariability. (For further discussion, see Chapter
3: Variability.)
The choice of the three doubled CO2 scenarios
does not necessarily bracket the range of possible
climate change in the latter half of the next century.
Due to the uncertainties about the rate and
magnitude of global warming, it is possible that
average global temperatures could be lower or
higher than indicated by the models. Other climate
variables could be different too. Thus, these
scenarios should be interpreted as illustrations of
possible future conditions, not as predictions.
Furthermore, we did not assign probability to these
scenarios. Currently, there is not enough
information or a methodology for making such a
determination.
62
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Methodology
Table 4-1. Major Features for the Three GCMsa
GCM
When
calculated
Model
resolution
(lat. x long.)
Model
levels'3
Diurnal
cycle
Base
lxCO2
(ppm)
Temp for Increase
doubled
CO2
(°CJ
in global
precipitation
(%)
GISSC
GFDLd
1982
1984-85
7.83 x 10°
4.44 x 7.5d
9
9
yes
no
315
300
4.2
4.0
11
8.7
osu
GISS Transient
1984-85
1984-85
4.00 x 5.0d
7.83 x 10d
2
9
no
yes
326
315
(in 1958)
2.8
7.8
a All models are global in extent and have an annual cycle. All models have a smoothed topography that varies
between models. The later GFDL run has been added for information. All models (except the transient) give
data for the present climate (lxCO2) and double CO2 climate (IxCOJ.
bAU models make calculations for surface conditions as well as for the fisted upper-air levels.
°A gridpoint model with stated resolution.
dThis is a spectral model that has 15 waves.
Note: Oceans in Models:
GISS: This model has a slab ocean not over 65 meters deep; it has some variation of mixed depth over the
seasonal cycle (for example, the depth is shallower in summer than winter in mid-latitudes). It has a
specified pseudo ocean heat transport designed to reproduce the present day sea surface temperature
(SST) in the simulation of the present climate. Ice thickness is predicted. For the GISS transient runs,
the ocean depth was not limited in this way. In it, the average annual maximum mixed-layer depth
was 127 inches.
GFDL: The slab ocean is 68 meters deep. There is no horizontal heat transport that would make the present
day SST come out exactly right. Ice thickness is predicted.
OSU: This model has a slab ocean that is 60 meters deep (only 5 meters deep during spin-up period). It does
not have heat transport that would force the model to reproduce the present day SST (this is being
added in 1989).
If current emission trends continue, the
effective doubling of CCu concentrations will occur
around the year 2030. However, that estimate does
not account for some recent developments that may
slow the increase in greenhouse gas concentrations.
If implemented, the Montreal Protocol would cut
emissions of chlorofluorocarbons (CFCs) by 50%.
If an international agreement is reached on
reduction of nitrogen oxides (NOX), the
concentration of nitrogen dioxide (N2O) may be
slightly reduced. Pollution control measures in
countries such as the United States may also reduce
concentrations of low-level ozone, another
greenhouse gas. Thus, the effective doubling of
CO2 may happen after 2030.
As discussed in Chapter 2: Climate Change,
the change in climate potentially caused by CO2
doubling would not occur at the same time as the
increase hi greenhouse gas concentrations. The
oceans absorb greenhouse gases and heat from the
atmosphere and serve to delay the warming. The
full extent of climate change associated with CO2
doubling could take several decades or more and
may not occur until the latter half of the next
century.
In this report, results from doubled CO.
scenarios are generally not associated with a
particular year. When analysis is necessary, we have
generally assumed that the CO2 warming will occur
in 2060. In some cases, researchers assumed a
different time period for CO2 warming, and those
exceptions are noted as appropriate in the text.
63
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Chapter 4
The doubled CO2 scenarios are often
interpreted as estimates of future static
(equilibrium) conditions. The assumption that the
concentration of greenhouse gases becomes constant
at doubled CO2 levels is an arbitrary one. In fact,
if emissions are not limited, concentrations could
become greater and the global climate would
continue to change. In many places in this report,
responses are presented as if the climate stabilizes
at doubled CO2 conditions. Natural systems and
society, however, may be responding and adapting
to continuing and perhaps, accelerating changes in
climate.
OPTIONS FOR CREATING
TRANSIENT SCENARIOS
The options for developing transient scenarios
are similar to the options for the doubled CO2
scenarios:
1. arbitrary changes;
2. analog warming; and
3. GCM transient runs.
Arbitrary Changes
One could examine the manner in which a
system responds to an arbitrary 1 or 2°C
temperature warming and to small arbitrary changes
in other variables. The problems of physically
inconsistent assumptions about changes among
variables and regions pertain here also. In addition,
the arbitrary warming scenario gives no indication
of when the warming may occur.
Analog Warming
Wigley (1987) has suggested using analogs as
scenarios for climates that may occur within the
next several decades. He noted that the warming
from the late 19th century to 1940 was about 0.4°C,
which may approximate the transient warming over
the next two decades. The problem is that climate
may change faster in the future than in the early
20th century. (The average decadal warming may
be as much as 0.5°C, rather than the 0.1°C
identified for earlier years.) Furthermore, the
analog takes one only as far as a 0.5° C warming or,
in the case of paleoclimatic records, a 1°C
warmkig.lt does not indicate what happens in the
decades after the 0.5 to 1.0° C level is reached. In
addition, the analog may not represent the regional
distribution of climate associated with greenhouse
forcing.
GCM Transient Runs
The Goddard Institute for Space Studies has
modeled how global climate may change as
concentrations of greenhouse gases gradually rise
over the next century. This is called the transient
run. GISS has modeled climate change under
several assumptions of trace gas growth. The
transient runs start in 1958 with the atmospheric
concentrations of greenhouse gases that existed
then. The concentrations of the gases and
equivalent radiative forcing were estimated to
increase from 1958 until an arbitrary point in the
future according to several different assumptions
regarding trace gas growth. The GISS transient run
yields daily climate estimates from 1958 until that
arbitrary point.
For example, one of the transient scenarios,
which is known as GISS A, assumes that trace gas
concentrations continue to increase at historic rates
and net greenhouse forcing increases exponentially.
The scenario is run from 1958 to 2062. The end of
the transient corresponds with a global warming
equivalent to that of the equilibrium climate from
the doubled CO2 run. This scenario does not
account for the potential reduction in CFC
emissions due to the Montreal Protocol or for other
activities that may reduce the growth in emissions.
GISS B assumes a decreasing trace gas
concentration growth rate such that climate forcing
increases linearly (Hansen et al., 1988). It stops in
2029. GISS B includes volcanoes, while GISS A
does not.
Since the GCMs are used to produce this
transient run, the advantages and disadvantages of
using this approach are the same as those described
in the discussion of doubled CO2 scenarios. In
addition, the timing of the changes estimated by the
GCMs is complicated by the uncertainties regarding
the growth of greenhouse gas emissions and the
roles of the oceans and clouds in delaying climate
changes (Dickinson, 1986).
64
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CHOICE OF TRANSIENT
SCENARIO
This study used transient scenarios based on
the GISS transient run because, of all the different
approaches, only this one provides internally
consistent estimates of climate change and allows
examination of the entire range of climate change
between current conditions and doubled CO2
climate.
In creating the transient scenario, an approach
similar to that used for the doubled CO, scenario
was employed. Since relatively little confidence
exists in the GCM's estimates of changes in
interannual and daily variability, the monthly means
were calculated for each decade of the transient.
This process gives average decadal temperature,
precipitation, and other changes. The average
decadal temperature changes in GISS A and B for
the United States are shown hi Figure 4-3.
As in the doubled CO2 scenario, the average
meteorological changes from the transient are
combined with a historic time series. What is
different from the doubled CO2 scenario is that a
gradual change in temperature and other variables
is mixed with a historic time series with its own
variability. This can produce a regular oscillation.
Methodology
In this study, the historic time series 1951-80 is
used, and the transient monthly statistics are applied
'to the time series. The procedure for creating the
transient scenario was to first linearly interpolate
between decadal means. This smoothes out the
sharp decadal changes from the actual transient
GISS results and is shown in Figure 4-4(a). The
baseline 1951-80 weather data were repeated for 80
years, with the last 20 years consisting of a
repetition of the 1951-70 data. Figure 4-4(b) shows
the average U.S. temperatures for 1951-80 repeated
for 80 years. The data transformations displayed in
Figures 4-4(a) and (b) were done for data for each
month for each grid box, site, and climate variable.
The smoothed month-by-month transient data were
added to the repeated 1951-80 data for each site
and variable. Figure 4-4(c) displays the addition of
the smoothed average U.S. transient temperatures
with actual U.S. 1951-80 temperatures, repeated.
Although there is a cooling from the 1950s to the
1960s, followed by a warming in the 1970s, the
underlying warming of the transient, which is 3.7° C
by the middle of the 2050s hi GISS A, is much
greater than the variability in the base period.
Limitations
Since the transient scenarios were also derived
from GCMs, the same limitations concerning
4
3.5
3
2.5
Z
1.5
1
0.5
0
3.72
2.99
1.72
0.70
1980s 1990s 2000s 2010s 2020s 2030s 2040s 2050s
TRANSIENT SCENARIO A
4
3.5
3
1.5
a
•- 1
0.5
0
0.59
0.35
1990s 2000s 2010s
TRANSIENT SCENARIO B
2020s
Figure 4-3. GISS transients "A" and "B" average decadal temperature change for lower 48 states gridpoints.
65
-------
Chapter 4
A. SMOOTHED QISS "A" ANNUAL AVERAGE U.S. TEMPERATURE
1990 2000 2010 2020 2030 2040 2050 2060
B. OBSERVED 1951-1980 ANNUAL U.S. TEMPERATURE REPEATED
2.0
0. TRANSIENT SCENARIO: SMOOTHED GISS "A" COMBINED WITH
1951 AND 1980 REPEATED
Figure 4-4.
change).
Transient scenarios (temperature
temporal and spatial variability pertain as in the
doubled CO2 scenario. An additional limitation in
the transient scenario is the rate of change. The
GISS transient runs assume a gradual rate of
change in temperature. The simplistic treatment of
ocean circulation in the GCM affects the rate of
warming estimated by the model. Broecker (1987)
has shown that past climate changes may have been
abrupt. Broecker, however, analyzed a global
cooling, and the changes occurred over a much
longer period than greenhouse warming. A sudden
warming could mean that significant effects happen
sooner and more suddenly than the results of the
transient analysis used in this study indicate. The
inclusion of the 1951-80 base period in the scenario
yields short-term oscillations.
OTHER SCENARIOS
In a few cases, researchers used meteorologic
data from the 1930s as an analog scenario. This
scenario was used to provide additional information
on the sensitivity of systems to climate change. In
a few other cases, researchers only examined
paleoclimatic records. In these cases, the goal was
to determine how a system responded to past
climate change.
EPA specified that researchers were to use
three doubled CO2 scenarios, two transient
scenarios, and an analog scenario in this study.
Many researchers, however, did not have sufficient
tune or resources to allow for the use of all
scenarios. EPA asked the researchers to run the
scenarios in the following order, going as far
through the list as time and resources allowed:
1. GISS doubled CO2;
2. GFDL doubled CO2;
3. GISS transient A;
4. OSU doubled CO2;
5. Analog (1930 to 1939); and
6. GISS transient B;
Most researchers were able to use at least the GISS
and GFDL doubled CO2 scenarios. Comparison of
results across studies may be limited because of
inconsistent use of scenarios.
Sea Level Rise Scenarios
Unlike the climate scenarios, the alternative
sea level rise scenarios were not based solely on the
differences between various general circulation
models. Instead, they were based on the range of
estimates that previous studies have projected for
the year 2100 (Hoffman et al., 1983,1986; Meier et
al., 1985; ReveUe, 1983; Thomas, 1986), which have
generally considered alternative rates of greenhouse
gas emissions, climate sensitivity ranging from 1.5 to
4.5°C for a CO2 doubling, and uncertainties
regarding ocean expansion and glacial melting.
Estimates for the year 2100 generally range from 50
to 200 centimeters.
66
-------
Methodology
This report uses three scenarios for the year
2100 - 50, 100, and 200 centimeters -- and
compares them to the current trend of 12
centimeters per century. Because most studies have
not reported estimates for the intermediate years,
we followed the convention of a 1987 National
Research Council report (Dean et al., 1987) and
interpolated sea level rise using a parabola. The
rates of sea level rise assumed in this report are
displayed in Figure 7-8 in Chapter 7: Sea Level
Rise. Because various coastal areas are also sinking
(and in a few cases rising), relative sea level rise at
specific locations was estimated by adding current
local subsidence trends. Note that sea level rise
scenarios are presented for the year 2100, while
doubled CO, scenarios are presented for the latter
half of the 21st century.
EFFECTS ANALYSES
In this study, the preferred approach for
analyzing potential impacts of climate change was to
develop quantitative estimates. Most researchers
estimated impacts by running models that simulate
the relationship between weather and the relevant
system. The climate scenarios were used as inputs
into the models. Since the researchers had only
several months to do the analysis, they used either
"off-the-shelf" models or analytic techniques. In
many cases, existing models were calibrated to new
sites. This lack of time also limited the gathering of
new data to a few studies.
A drawback of using empirical models of
systems to estimate sensitivities is that the models
are applied to climates for which they were not
developed. The models estimate relationships with
observed climate. This relationship is then
extrapolated to an unprecedented climate. It is
possible that in the new climate situation, the
statistical relationship maybe different owing to the
crossing of a threshold or for some other reason.
With the drawbacks of empirical models, the
current statistical relationships are the best basis for
quantitatively estimating sensitivities.
For the most part, researchers analyzed the
potential effects of climate change on systems as
they currently exist. Although these changes may be
quite substantial, potential changes in populations,
the economy, technology, and other factors were not
considered. In some cases, researchers ran
additional scenarios with assumptions about
technological and other changes. In addition,
potential responses to climate change were
considered in some, but not all, cases. For these
and many other reasons, the results should be
interpreted only as an indication of the sensitivity of
current systems to global warming, not as a
prediction of what the effects will be.
In some situations, quantitative models of the
relationship between climate and a particular system
did not exist. In those cases, other approaches were
used to try to identify sensitivities. Some
researchers examined how systems responded to
analog warmings. In other cases, expert judgment
was used. This consisted of literature reviews to
assemble information on sensitivities as they appear
in the literature, and workshops and interviews to
poll experts on how they thought systems would
respond to global warming.
RESEARCH NEEDS
The scenarios used in this report help identify
the sensitivities of systems to climate change.
Because of the lack of confidence concerning
regional estimates of climate change from GCMs,
we cannot predict impacts. In order to predict the
effects of climate change, major improvements need
to be made in GCMs. These could take many
years. In the meantime, we will continue to use
scenarios to identify sensitivities. As with GCMs,
scenarios can also be improved.
GCMs
To produce better estimates of regional
climate change, both the resolution of GCMs and
the modeling of physical processes need to be
improved. The GCMs used for this report had
large grid boxes, in which major geographic
features, such as the Great Lakes or the Sierra
Nevada Mountains, which have large impacts on
local .climate, were not well represented. Ideally,
the higher the resolution, the better the
representation of geographic features. But each
increase in resolution means a large increase in
computations and computing power needed to run
the model. Furthermore, at high resolutions, the
GCMs may require new parameterizations. The
67
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Chapter 4
resolution should be increased at least to the point
at which major geographic features are well
represented hi the models.
It is also important that the estimates of
physical processes in the models be improved to
increase the confidence about estimates of >the
magnitude and timing of changes. Three areas need
the most attention: oceans, clouds, and hydrology.
The oceans play an important role in delaying
climate change and have a large influence on
regional climates. However, the ocean models
currently used in GCMs are relatively simple.
Ocean models that better simulate the absorption
and transport of heat and gases would give
improved estimates of transient and regional climate
change. Clouds are a major feedback to global
warming and influence regional climate. More
realistic modeling of clouds by GCMs would
improve the estimates of the magnitude of global
warming and regional change. Finally, more
sophisticated hydrology in GCMs will yield better
estimates of soil moisture and runoff, which will also
improve estimates of regional climate changes.
Scenarios
The scenarios hi this report were based on
changes hi average conditions, either at equilibrium
(doubled CO2) or due to a gradual change hi
average underlying conditions (transient). As
pointed out hi Chapter 3: Variability, many systems
are quite sensitive to changes in the frequency and
intensity of extreme events. In the future, scenarios
should incorporate change hi variability to help
identify sensitivities to variability. Transient
scenarios can also be improved. Such scenarios
should be useful for testing sensitivities to changes
in long-term climate trends as well as year-to-year
variations. At the same time, it is important to
keep scenarios simple. More detailed scenarios,
involving a lot of data (such as daily data from
GCMs) may be difficult to use. The more detailed
the scenario, the more likely it will be applied
incorrectly, which limits the ability to compare
results by different researchers. In addition,
scenarios should be simple, so the assumptions used
in creating them can be easily understood.
Designers of scenarios will have to wrestle with the
competing desires of being more detailed and
maintaining simplicity.
REFERENCES
Broecker, W.S. 1987. Unpleasant surprises in the
greenhouse? Nature 328:123-126.
Dean, R.G., RA. Darylrumple, R.W. Fairbridge,
S.P. Leatherman, D. Nummendal, M.P. O'Brien,
O.H. Pilkey, W. Sturges, R.L. Wiegel. 1987.
Responding to Changes hi Sea Level: Engineering
Implications. National Research Council.
Washington, DC: National Academy Press.
Dickinson, R.E. 1986. How will climate change:
The climate system and modelling of future climate.
In: Bolin, B., B.R. Doos, J. Jager, and RA.
Warrick, eds. Scope 29: The Greenhouse Effect,
Climatic Change and Ecosystems. New York: John
Wiley and Sons. pp. 221-231.
Gates, W.L. 1985. Modeling as a means of studying
the climate system. In: MacCracken, M.C., and
F.M. Luther, eds. Projecting the Climatic Effects of
Increasing Carbon Dioxide. Washington, DC: U.S.
Department of Energy. DOE/ER-0237.
Grotch, S.L. 1988. Regional Intercomparisons of
General Circulation Model Predictions and
Historical Climate Data. Prepared for U.S.
Department of Energy. TR041.
Hansen, J., I. Fung, A. Lacis, D. Rind, G. Russell,
S. Lebedeff, R. Ruedy, and P. Stone. 1988. Global
climate changes as forecast by the GISS 3-D model.
Journal of Geophysical Research 93:9341-9364.
Hansen, J., G. Russell, D. Rind, P. Stone, A. Lacis,
S. Lebedeff, R. Ruedy, and L. Travis. 1983.
Efficient three-dimensional global models for
climate studies: Models I and II. Monthly Weather
Review 3(4):609-622.
Hoffman, J.S., D. Keyes, and J.G. Titus. 1983.
Projecting future sea level rise. Washington, DC:
U.S. Government Printing Office.
Hoffman, J.S., J. Wells, and J.G. Titus. 1986.
Future global warming and sea level rise. In:
Sigbjarnarson G., ed. Iceland Coastal and River
Symposium. Reykjavik, Iceland: National Energy
Authority.
68
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Methodology
Manabe, S., and R.T. Wetherald. 1987. Large scale
changes in soil wetness induced by an increase in
carbon dioxide. Journal of Atmospheric Sciences
44:1211-1235.
Meier, M.F. et al. 1985. Glaciers, ice sheets, and
sea level. Washington, DC: National Academy
Press.
Mitchell, J.F.B. 1988. Local effects of greenhouse
gases. Nature 332:399-400.
Parry, M., T. Carter, N. Konijin, and J. Lockwood.
1987. The Impact of Climatic Variations on
Agriculture: Introduction to the IIASA/UNEP Case
Studies in Semi-Arid Regions. Laxenburg, Austria:
International Institute for Applied Systems Analysis.
Revelle, R. 1983. Probable future changes in sea
level resulting from increased atmospheric carbon
dioxide. In: Changing Climate. Washington, DC:
National Academy Press.
Schlesinger, M.E., and J.F.B. Mitchell. 1985.
Model projections of the equilibrium climatic
response to increased carbon dioxide. In:
MacCracken, M.D., and P.M. Luther, eds.
Projecting the Climatic Effects of Increasing Carbon
Dioxide. Washington, DC: U.S. Department of
Energy. DOE/ER-0237.
Schlesinger, M., and Z. Zhao. 1988. Seasonal
Climate Changes Induced by Doubled CO^ or
Simulated by the OSU Atmospheric GCM/Mrxed-
Layer Ocean Model. Corvallis, OR: Oregon State
University, Climate Research Institute.
Thomas, R.H. 1986. In: Titus, J.G., ed. Effects of
Changes hi Stratospheric Ozone and Global
Climate. Washington, DC: U.S. Environmental
Protection Agency and UNEP.
Vinnikov, K.Y., and NA. Lemeshko. 1987. Soil
moisture content and runoff hi the USSR territory
with global warming. Journal of Meteorology and
Hydrology No. 12.
Wigley, T.M.L. 1987. Climate Scenarios. Prepared
for the European Workshop in Interrelated
Bioclimate and Land-Use Changes. Boulder, CO:
National Center for Atmospheric Research. NCAR
3142-86/3.
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CHAPTER 5
FORESTS
FINDINGS
Global warming could significantly affect the forests
of the United States. Changes could be apparent in
30 to 80 years, depending upon the region, the
quality of a site, and the rate of climate change.
There may be northward shifts in species ranges,
dieback along the southern reaches of species
ranges, and changes in forest productivity. Other
stresses hi combination with climate change may
exacerbate these impacts. Different migration rates
and climate sensitivities may result in changes in
forest composition. Without large-scale
reforestation, large reductions in the land area of
healthy forests are possible during this century of
adjustment to climate changes. Although climate
fluctuations, timber harvests, disease outbreaks,
wildfires, and other factors have affected forests
during the last century, the magnitude of these
changes is substantially less than those projected in
response to climate changes considered in this
report.
Range Shifts
• The southern ranges of many forest species in
the eastern United States could die back as a
result of higher temperatures and drier soils.
The southern boundary could move several
hundred to 1,000 kilometers (up to 600 miles)
in a generally northward direction for the
scenarios studied.
The potential northern range of forest species
hi the eastern United States could shift
northward as much as 600 to 700 kilometers
(370 to 430 miles) over the next century.
Actual northward migration could be limited to
as little as 100 kilometers (60 miles) owing to
the slow rates of migration of forest species.
Without reforestation, full migration of eastern
forests to potential northern distributions could
take centuries. If climate change occurs too
rapidly, some tree species may not be able to
form healthy seeds, thus halting migration.
Reforestation along northern portions of
potential forest ranges could mitigate some of
these impacts.
• If elevated CO2 concentrations substantially
increase the water-use efficiency of tree species,
the southern declines could be alleviated.
* If climate stabilizes, forests might eventually
regain a generally healthy status (over a period
of several centuries). In the meantime,
declining forests could be subject to increased
fires, pest attacks, and replacement with low-
value trees, grasslands, and shrubs. A
continually changing climate could result in
even greater dislocations among forests.
Productivity Changes
• Dieback along the southern limits of
distribution of many species could result in
productivity declines of 40 to 100%, depending
on how dry soils become.
• Productivity could increase along the northern
limits of some eastern tree species, particularly
as slow-growing conifers are replaced by more
rapidly growing hardwoods.
Combined Impacts With Other Stresses
• Large regions of severely stressed forests,
combined with possible increases in fires, pests,
disease outbreaks, wind damage, and air
pollution, could produce major regional
disturbances. These factors were not
considered for this report.
« Additional impacts of changes in forests could
include reductions in biotic diversity, increased
soil runoff and soil erosion, reduced aquifer
recharge, changes in recreation, and changes in
wildlife habitat.
71
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Chapter 5
Policy Implications
• Institutions such as the U.S. Forest Service,
state forest agencies, and private companies
should begin to consider how to factor climate
change in their long-term planning. Global
climate change may need to be a factor in the
Forest Service's 50-year planning horizon.
• Where TLS. forests are clearly reduced by
climate change, forest agencies will have to
consider intensive strategies to maintain
productivity. For example, they could
undertake reforestation on a more massive scale
than now practiced and possibly introduce
subtropical species into the Southeast.
• A coordinated public and private reforestation
effort, together with development of new and
adapted silvicultural practices, would also be
required. Forests are major carbon sinks, so a
large reforestation program would also reduce
atmospheric CO2 concentrations, slowing the
rate of global warming. This study did not evaluate
the effectiveness of reforestation efforts.
EXTENT AND VALUE OF U.S.
FORESTS
Forests occupy 33% of the U.S. land area and
exist on some lands in all 50 states. In total, they
occupy 298 million hectares (738 million acres) and
are rich in such resources as water and wildlife.
Many biotic and abiotic factors influence the
condition of forests, but climate is the dominant
factor (Spurr and Barnes, 1980). This chapter
summarizes the current knowledge and predictions
concerning the effects of rapid climate change on
U.S. forests.
Distribution and Ownership
Eight major forest regions of the conterminous
48 states contain 84% of the forested ecosystems of
the United States (Figure 5-1). The forested areas
STUDY PLOT SITES
• Botkin et ol.
» 0. Dovis
A Urban and Shugart
ALASKA
gggSpruce/hardwood
HI Spruce/hemlock
WESTERN REGIONS
Pacific Northwest
|\^\| Douglas fir/hemlock/fir
California
[%%jPine/fir/red»ooj
Northern Rockies
HH Pine/fir/birch
Southern Rockies
Pinyon/juniper/pine
EASTERN REGIONS
Northeast
jffiQI Spruce/fir
Mople/beech/birch
Central
Mople/beech/birch
gg] Oak/hickory
Southeast
Southern pine
Lake States
K3 Spruce/fir
^•Mople/beech/birch
Figure 5-1. Major forest regions of the United States and their primary tree groups.
72
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Forests
Table 5-1. Area of U.S. Forest Lands in 1977 by Federal, State, Private, and Other Ownerships (millions
of hectares)3
Commercial Forests
Private
Non-
Region/States
Primary Tree Species Federal State Industry Indus Other0 Total Total
EAST
WEST
SEPARATE
STATES
Northeast -
CT, HA, ME, NH, RI, VT
Lake States -
HI, HN, HI, ND, SDCE)
Central -
DE, IA, IL, IN, KA, KY, HD,
HO, NB, NJ, OH, PA, TN, UV
Southeast -
AL, AR, FL, GA, LA, HS, NC,
OK, SC, TN, TX, VA
Northern Rockies -
ID, HT, SD(W), HY
Southern Rockies -
AZ, CO, NH, NV, UT
Pacific Northwest -
OR, WA
California - CA
Alaska - AK
Hawaii - HI
spruce-fir
maple-beech-birch
spruce-fir
maple-beech-birch
maple-beech-bi rch
oak-hickory
loblolly, shortleaf
slash pine
pine-fir-birch
pinyon- juniper-pine
D. fir-hemlock-fir
pi ne- f i r- redwood
spruce-hemlock-hardwood
ohia
0.3
2.3
1.8
5.8
9.1
6.4
7.8
3.4
3.3
.01
0.4 '
2.8
2.0
1.0
0.6
0.3
1.2
.03
1.0
0.2
3.9
1.7
8.6
14.7
0.8
0.0
4.0
1.1
0.0
0.0
7.8
9.9
22.9
54.3
2.7
2.4
3.2
2.0
0.1
0.2
0.7
4.2
2.6
8.0
9.3
24.1
5.3
9.8
43.9
0.4
13.1
20.9
37.9
83.8
22.5
33.2
21.5
16.3
48.3
0.8
4.4 I
7.0
12.7
28.1
7.6
11.1
7.2
5.4
i
16.2
0.3
TOTAL 40.2 9.5 34.8 105.5 108.3 298.3 100
% TOTAL, 13.5 3.1 11.7 35.4 36.3 100
a Hectare x 2.47 = acres.
b Commercial forests are those capable of growing at least 1.4 cubic meters per hectare per year (20 cubic teet
per acre per year) of industrial wood materials.
c Other forests include county and municipal forests and those federal lands withdrawn from industrial and wood
production for use as parks, preserves, and wilderness.
Source: USDA (1982).
of Alaska and Hawaii represent the remaining 16%
(Table 5-1). Each forest region includes one or
more forest types distinguished by the major tree
species present. As a general rule, some types in
each region have predominantly coniferous tree
species (i.e., evergreen, needle-leaved, and
softwoods); other forest types are composed mostly
of deciduous trees (i.e., tree species that are broad-
leaved, have no winter fpliage, and are hardwoods).
Forest types with a mix of coniferous and deciduous
trees, however, are not uncommon.
Superimposed over the natural distribution of
trees, forests, and ecosystems in the United States
is the human infrastructure. Ownerships include
federal, state, and private lands (Table 5-1). Within
the forests classified as "commercial" (64% of 298
million hectares), the federal government ownership
of 40 million hectares (99 million acres) is primarily
in the national forest system managed by the U.S.
Department of Agriculture's Forest Service (36
million hectares or 91 million acres); most of the
remainder is managed by the Department of
73
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Chapter 5
Interior's Park Service, Fish and Wildlife Service,
or Bureaus of Land Management and 'Indian
Affairs. State ownerships total 9 million hectares
(23 million acres). Private lands are divided
between those of industrial forest companies (35
million hectares or 86 million acres) and those of
small, private landowners, who collectively have 106
million hectares (262 million acres) (USDA, 1982).
Another significant segment of American forests
consists of those maintained within urban and
suburban areas. Examples are community parks,
greenbelts, roadside forests, and wooded residential
and industrial zones (USDA, 1981). These forest
areas are important sources of outdoor recreation,
wildlife habitat, and real estate values. In total, the
urban/suburban forests of the United States occupy
approximately 28 million hectares (69 million acres)
(Grey and Deneke, 1978).
To the degree that all forest lands are owned by
some individual or organization, all forest lands are
under some form of management. A continuum of
management policies exists, ranging from lands
intended to have minimal human intervention except
for protection from catastrophic wildfire (e.g., some
parks and most wilderness areas) to lands where
silvicultural practices are intensively applied (e.g.,
the most productive federal, state, and industrial
forest lands dedicated to growing tree crops);
(Table 5-2). These forests under government and
industrial management constitute roughly one-fourth
of the total and might be the easiest to manage
under climatic impacts simply because they are
larger blocks of lands already under strong
management commitments.
Value of U.S. Forests
Most populated regions in the United States are
located close to or within a forested region. For
instance, the Boston-Washington corridor is within
the eastern hardwoods. The populations of Atlanta
and the Southeast are interspersed among the
southern pine forests. Chicago and nearby Great
Lakes communities are surrounded by the mixed
conifer-hardwood forests of that region, and the Los
Angeles to San Francisco populations parallel the
Sierra Nevadas to the east. In addition,
urban/suburban forests exist in or near most of the
nation's cities. Forests, therefore, are part of the
environmental fabric and general habitability for the
majority of U.S. citizens.
All forests shed water to some degree, and two-
thirds of the water runoff in the contiguous 48 states
comes from forested ecosystems. Precipitation
passes through forested ecosystems as canopy
throughfall or flows along tree stems, and then flows
along the ground surface or into the soil; eventually,
some of the water flows into streams. Water yields
from U.S. forests provide about 750 billion liters
(200 billion gallons) of water each day for major
uses such as irrigation, electricity production,
manufacturing, and domestic consumption. These
levels of demand are projected to continue to the
year 2030 (USDA, 1981).
A favorite use of forests is outdoor recreation.
Activities include hiking, camping, hunting,
sightseeing, boating, swimming, fishing, skiing,
sledding, and snowmobiling. A 1977 survey of U.S.
Table 5-2. Percentage of Forest Lands by Level of Management within Four U.S. Regions (estimates for 1977)
Forest Other Reserved/
U.S. regions plantations3 commercial deferred0
East
North
South
West
Rocky Mountains
Pacific Coast
9
21
2
16
80
69
38
44
11
10
60
40
I* Intensively managed plantations.
Moderately managed forests.
c Recreational and protected forests.
Source: USDA (1982).
74
-------
Forests
households indicated that a majority of people
participated in outdoor recreation four or more
times each year (USDA, 1981).
About 190 million hectares (470 million acres),
or 64% of the total U.S. forested ecosystems, are
highly productive commercial forest lands. These
lands represent about 10% of the world's forest
area, but they supplied nearly a quarter of the
world's industrial forest products in the late 1970s
(USDA, 1982). In 1980, 1.7 million people were
employed in timber-based occupations across the
United States. Such employment is basic to the
economic well-being of many small towns and
communities (Schallau, 1988). The total value of
timber products harvested in 1972 was about $6.4
billion, and the total value after such processes as
manufacturing, marketing, transport, and
construction amounted to $48 billion, or 4% of the
nation's gross national product. In 1979, timber
product exports and imports were valued at $7
billion and $9 billion, respectively. Looking ahead,
the consumption of wood products in the United
States is projected to increase between current
levels and the year 2030 (USDA, 1982).
RELATIONSHIP BETWEEN
FORESTS AND CLIMATE
Scientific understanding of forest ecosystems
has greatly advanced with each decade of this
century. Yet the literature contains little
information concerning the direct or indirect effects
of climate change on the complex biological and
physical processes in forest ecosystems. Some
insights are gained from paleobotanical studies of
past rates and magnitudes of ecological change
during glacial-interglacial cycles, as well as changes
in the species composition of forested ecosystems.
Similarly, observations of forest responses to
unusual drought or other weather extremes provide
some knowledge. Estimates of rate, magnitude, and
quality of change have also been derived using
computer models developed by plant ecologists or
forest management scientists for other objectives.
Their validation for understanding how a forest can
adapt to climate change is only in the initial stages.
Climate is a primary determinant of existing
forests. The ranges of annual average temperature
and rainfall variation determine global forest
distributions relative to different biotic regions
(Figure 5-2). Substantial increases in temperature
100 ' 200 300
MEAN ANNUAL PRECIPITATION (cm)
400
Figure 5-2. Approximate distributions of the major groups of world biomass based upon mean annual
temperatures and precipitation (Hammond, 1972).
75
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Chapter 5
or decreases in rainfall could, for example, produce
a shift from a forest to a grassland type. Thus,
accelerated climate change resulting from human
activities and related effects on U.S. forestsds of
high concern to citizens and policymakers alike.
Magnitude
Vegetation has been in an almost constant state
of distributional change and adjustment due to an
almost constantly changing climate over the past
10,000 years and even over the past several hundred
years (Spurr and Barnes, 1980). Lines of evidence
come from studies of fossils, tree rings, carbon-14
dating, plus peat and pollen analyses (Webb, 1987).
Historical climate changes appear to have been
associated with such phenomena as fluctuations in
solar radiation, earth orbit variations, and volcanic
activity. Evidence of repeated continental glacial
advances and contractions in the Northern
Hemisphere dramatically illustrates the large-scale
effects of global climate change.
In response to the glaciation, species shifted
south. Evidence from fossil pollen, for example,
indicates a southward shift of spruce into Georgia
and east Texas during the last glacial advance and
treeless tundra in the Great Lakes region (Spurr
and Barnes, 1980). During the maximum
interglacial warmth of 6,000 to 9,000 years ago,
which was 1.5°C (2.7°F) warmer than the present
temperature level, plant zones were one to several
hundred kilometers (60 to 250 miles) north of
present distributions.
Rates
All forested ecosystems experience change on
both spatial and temporal scales; each biological and
physical forest component may respond to climatic
variation on different spatial and temporal scales.
For example, microorganisms, insects, and birds
come and go with relatively short-term climatic
variation; shrub species' abundances vary within the
timespan of decades; trees, once established, could
persist for centuries. This understanding is
important from the perspective of climate change,
since it implies that forested ecosystems do not
respond as a unit, but in terms of parts. Different
parts respond differently; consequently, future
forested ecosystems under a rapidly changing
climate could be quite different from those existing
today.
At the expected rapid rate of climate change,
the potential rates of forest migration would
become a major concern. Migration rates vary by
species. Paleorecords of the Holocene (10,000 years
ago to present) show that extension of ranges for
tree species of eastern North American (in response
to glacial retreat) varied from 10 to 20 kilometers (6
to 12 miles) per century for chestnut, beech, maple,
and balsam fir (Zabinski and Davis, Volume D).
Other species within the oak and pine groups
extended at faster rates, i.e., 30 to 40 kilometers (19
to 25 miles) per century. It should be noted that
there is some uncertainty as to whether these
migration rates were in response to glacial retreat
plus climate warming or primarily warming alone.
Mechanisms
Knowledge of causal links between weather
patterns and forest response is fundamental to
projecting growth and composition effects resulting
from climate change. Another requirement is to
understand the climatic influences on processes
influencing populations of forest plants and animals.
These include such phenomena as fires, windstorms,
landslides, pest outbreaks, and other disturbances
that affect survival and subsequent colonization by
different species. Furthermore, the processes that
control the dispersal of seeds through a mosaic of
different ecosystem types (such as forest patches
interspersed with agricultural lands, wetlands,
grasslands, and other land-use groups) must be
clearly defined.
Among the important factors now known to
influence the growth and distribution of forests are
the following.
Temperature
The optimum temperature for growth depends
upon the tree species and other conditions.
Warmer temperatures usually increase the growth of
plants. However, high temperatures can decrease
the growth of plants or cause mortality where
temperatures greatly exceed optimum ranges for
growth. Cold temperatures can limit plant
distributions by simply limiting growth at critical
stages or by dkectly killing plants.
Precipitation
Too much or too little precipitation can limit
forest production and survival. Too much rainfall in
76
-------
Forests
some areas can cause flooding or raise the water
table, thus drowning roots by reducing soil air that
contains oxygen required for respiration or by
promoting fungal attack. Too little rainfall can
reduce growth, cause susceptibility to fire or
pestilence, and possibly kill plants. The seasonal
timing of rainfall is more important than total
annual rainfall, although forests also require some
minimum total annual rainfall (see Figure 5-2).
CCX. Concentration
High CO, concentrations could increase tree
growth through increases in photosynthesis rates
and water-use efficiency (primarily hardwood
species) when water and other nutrients are not
limited (Strain and Cure, 1985). Plant responses to
CO2 have been investigated largely in growth
chambers and are difficult to extrapolate to the real
world. Responses are varied and do indicate some
measure of adaptive capability most likely imparted
from ancestral exposure to much higher and lower
levels in the geologic past. However, in natural
situations, water nutrients or temperature usually
are limiting factors in forest growth, thus making
the impacts of CO2 enrichment uncertain. If water-
use efficiency increases, then tolerance to drought
might increase, ameliorating declines in southern
parts of ranges. Unfortunately, the current state of
knowledge does not allow generalizations on this
subject.
Another important relationship between forests
and CO2 is the role forests play as carbon sinks.
Globally, forest vegetation and supporting soil
contain about 60% of the organic carbon stored on
world land surfaces. This organic carbon is largely
cycled between forest ecosystems and the
atmosphere by photosynthesis (uptake of CO2) and
respiration (COu release) in the plants (Waring and
Schlesinger, 1985). Anthropogenically caused
reductions of forests either directly (e.g.,
urbanization, mismanagement) or indirectly (as a
response to CO2-induced global warming) would
tend to increase the "greenhouse effect."
Light
The amount of sunlight bathing an ecosystem
sets the upper limit on net primary productivity.
Thus, the tropics exhibit higher productivity than do
the boreal regions. This potential productivity
would, of course, be limited by other climatic effects
such as drought, cold, heat, and natural
disturbances, and by the time required for forests to
shift into new ranges. The length of day exerts
considerable control on physiological processes such
as release from and onset of dormancy. Significant
northward shifts of forests would alter their day-
length regime, producing uncertain results.
Nutrient Status
In addition to climate, most forest growth is
strongly influenced by availability of soil nutrients.
Disturbances over vast regions, such as drought
followed by fire, can release large quantities of
essential nutrients into the atmosphere or into
surface waters. This leaves soils nutrient deficient.
Lengthy periods of soil development are usually
required to replenish the soil nutrients before a
large, mature forest stand can be supported. In
turn, soils reflect properties of the forests that they
support. This results from decades of nutrient
uptake, litterfall, decomposition, and other
processes.
Atmospheric Chemistry
Much of the nutrient budget of forests involves
deposition of chemicals from the atmosphere as
gases, aerosols, or particles, or in solution with
water as precipitation. Although most of these act
as nutrients, some produce acid deposition that can
leach important soil nutrients (e.g., SO4=), produce
a fertilizing effect (e.g., NO3"), or damage leaf tissue
(e.g., O3). Climate change will alter transport paths
of air pollutants, and increased temperature could
increase the rates at which gases convert to
deleterious forms.
Disturbances
Almost continually, forests experience natural
disturbances or stresses from biotic or abiotic agents
alone or in combination. Examples are insect and
disease outbreaks, plant competition, wildfire,
drought, cold extremes, and windstorms.
These disturbances, which are among the
primary factors controlling the successional
processes in forests (Pickett and White, 1985), may
range from an opening of small gaps in the canopy
as the result of single tree death or of windthrow
occurring when trees are blown down by heavy
winds (predominant successional mechanisms in
eastern hardwoods) to large clearings from fire,
-------
Chapter 5
windthrow, or pestilence (predominant successional
mechanisms in western forests).
Landscape Processes
The horizontal movements of materials such as
soil and biological organisms, together with human
disturbances across the landscape, are critical to
processes controlling tree migration, species
diversity in forests, and the spread of fire,
windthrow, and pestilence effects. These processes
are very poorly understood; quantification in the
emerging field of landscape ecology is just
beginning.
Multiple Stresses
In general, trees or forests stressed by one
factor, e.g., accelerated climate change, are more
susceptible to natural stresses (secondary
disturbances) such as insects, disease, or invading
weed species. The concept of multiple stresses
leading to forest declines is becoming more widely
recognized (Manion, 1981). Regional climate
changes, even if temporary, frequently predispose
forests to damage by other natural or anthropogenic
stresses.
PREVIOUS STUDIES ON THE
NATIONAL EFFECTS OF
CLIMATE CHANGE ON FORESTS
Concern regarding effects of climate change on
U.S. forests has prompted several excellent reviews.
One of the most comprehensive (Shands and
Hoffman, 1987) was the result of a conference
sponsored by EPA, the National Forest Products
Association, and the Society of American Foresters.
While pointing out the high uncertainty associated
with current predictions of climate change, several
authors suggested that if predictions are true,
distributions of key forest species in the United
States will change significantly.
Other recently produced compilations broadly
consider forest effects along with other impacts
(e.g., those on agriculture, prairie land, and the
Great Lakes) (White, 1985; Titus, 1986; Meo, 1987;
Tirpak, 1987). These reviews are largely pioneering
efforts and some overlap occurs, but each presents
some key points.
The methods used in the previous studies are
quite similar to those used in this report. They
include computer modeling of forest processes,
literature surveys, studies of fossil evidence, and
empirical relationships constructed by experts. The
estimates of future change produced from these
studies are generally based on the output of one or
more of the general circulation models (GCMs)
used for this report. Thus, the results of the
previous studies are consistent with those reported
here.
STUDIES IN THIS REPORT
Six studies on forest effects contributed to the
regional case studies reported in this volume. The
purpose was to use existing data bases analyzed in
new ways to estimate effects on U.S. forests from
climate change scenarios. The selection of the six
studies was based upon three criteria: use of
established statistical methods; hypotheses testing
concerning causal mechanisms; and selection of a
mix of studies that complemented each other, such
that the strengths in one approach might overcome
the weaknesses of another.
This report focuses primarily on forests within
the contiguous 48 states. It is worth noting,
however, that the largest magnitude of warming is
expected in the northern latitudes encompassing the
boreal forest and other forest types in Alaska and
Canada. Thus, these large forests could also be
under significant risk from climate warming.
RESULTS OF FOREST STUDIES
Design of the Studies
Characteristics of the six studies are briefly
listed in Table 5-3. With the exceptions of the
Overpeck and Bartlein study and the Woodman
study, the methods are discussed in the regional
case study chapters and will be mentioned only
briefly here. All of the forest studies are in Volume
D.
Two studies used correlations between tree
distributions and climate (Overpeck and Bartlein;
Zabinski and Davis). Overpeck and Bartlein's
approach consisted of correlating the modern pollen
distributions of important tree species with January
and July mean temperature and annual rainfall.
78
-------
Forests
Table 5-3. Principal Investigators, Regional Focus, and Method of Approach for the Regional Forested
Ecosystem Studies
Principal investigator
Region
Method
Overpeck and Bartlein
Urban and Shugart
Botkin et al.
Zabinski and M. Davis
O.Davis
Woodman et al.
Eastern North America
Southeast Uplands
Great Lakes
Great Lakes
California
Southeast, California,
and National
Correlation and fossil studies
Forest dynamics model
Forest dynamics model
Correlation
Fossil studies
Literature review
The correlation was then tested by reconstructing
past pollen distributions from general circulation
model simulations of past climates (during the most
recent glacial-interglacial cycle) for each species and
comparing them to observed pollen distributions
from those periods. Future pollen distributions
were then constructed from the expected doubled
CO2 climate projected from the different model
climate scenarios. The correlations were
constructed on modern pollen distributions, rather
than tree distributions, to allow the direct
comparison to fossil pollen data. Modern pollen
distributions are similar to, but not exactly the same
as, modern tree distributions. The verification
studies indicated that the approach works
reasonably well at a coarse spatial resolution. That
is, northern trees are in the north and southern
trees are in the south, with the regional patterns
being reasonably well represented.
The approach of Zabinski and Davis was
essentially the same as that of Overpeck and
Bartlein, except that the correlations were
constructed from the actual modern tree
distributions rather than from the modern pollen
distributions (see Chapter 15: Great Lakes).
Two of the studies used computer models of
forest dynamics (Botkin et al.; Urban and Shugart).
Growth characteristics of each tree species
occurring in the study region are used by the models
to determine the growth and development
ofindividual trees on a site. These growth
characteristics include sUch attributes as maximum
age, maximum height, maximum diameter, and
ranges in tolerance to stresses of temperature,
moisture, and shade. Both studies explored forest
response starting with bare ground on a range of
soil types from well drained to poorly drained.
Forest growth simulations from bare ground
represent conditions after a fire, logging, or similar
disturbance. Mature stand simulations are useful
for investigating the potential response of present
forests to gradual climate change in the immediate
future.
For the California case study, Davis
reconstructed vegetation patterns in the Sierra
Nevadas from fossil pollen studies for the
interglacial warm periods that occurred between
about 6,000 and 9,000 years ago. These
reconstructions represent possible analogs of a
future warm period at the lower magnitude of the
predicted future warming.
Woodman conducted a literature review for the
Southeast and California forested regions and
peripherally for the entire nation. The purpose was
to ascertain the attributes of the forest resource in
terms of extent, ownership, economic and
recreational value, and policy considerations.
Limitations
Although predicted effects vary, these six
analytical studies have results that are collectively
consistent enough to advance our knowledge and
justify concern regarding the future of U.S. forests
under rapid climate change. The range of
79
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Chapter 5
predicted effects is large; however, uncertainties
exist regarding (1) the climate scenarios; (2) the
kind and rates of responses of individual tree
species; and (3) changes in forested ecosystems as
a whole resulting from environmental change. All
of these factors significantly influence the precision
and accuracy of the results.
A major uncertainty in the simulation model
approach involves the rates of species dispersal into
a region. The current generation of models has no
dispersal mechanisms. A species is simply present
or it is not present. For example, Botkin et al.
excluded most southern tree species so that their
dispersal was unrealistically nonexistent, and these
southern species could never enter the Great Lakes
region. But if they had been included in the
simulations, these species would have entered the
northern forests at the same rate as the climate
change. This would have assumed dispersal rates
far in excess of reality. This limitation can, in part,
be overcome by studies, such as those of Zabinski
and Davis, that provide some insight into actual
dispersal rates and species migration. The
simulations did not consider the impact of
transplanting southern species in these areas.
The timing of forest declines as estimated by
the models should be interpreted with caution.
Declines are triggered by periods of high
environmental stress. Forest models are usually not
operated far beyond current conditions, such as for
extremely dry soils. Therefore, the extreme climate
simulated by these models may not estimate the
timing and behavior of forest declines as accurately
as desired. It should also be remembered that there
is much uncertainty concerning the rate and timing
of the climate change itself.
A further cautionary point is that although the
models considered temperature limitations, nutrient
deficiencies, and soil moisture stress, other
important factors might affect the timing and
magnitude of tree responses. Examples of factors
in need of consideration include disturbance effects
(e.g., impacts from wildfires, pests, and pathogens),
age-dependent differences in tree sensitivities to
stress (e.g., older trees are often more susceptible),
and potential CO2-induced increases in water-use
efficiency.
The models also carry assumptions about the
environmental controls of species limits. In most
cases these assumptions are reasonable, given that
indices of environmental stress, such as July
temperature or annual rainfall, are usually related to
factors that more directly affect plant growth, such
as accumulated warmth or summer drought.
However, large uncertainties exist in some instances.
This is particularly true with regard to the climatic
controls of the southern limits of southeastern
forests, simply because of their association with the
continental margin. Does the climate at that
latitude represent the actual climatic limitation to
the distributions, or are the species simply stopped
by a geographic barrier? No one really knows.
These uncertainties were partially addressed by
Overpeck and Bartlein, who compared their fossil
pollen approach to the modeling approach. The
two approaches use similar relations to climate, and
both can be used reasonably well to simulate forest
distributions in the geologic past.
Several uncertainties with the pollen-climate
correlation approach limit its precision and
accuracy. First, many of the plant taxa used in the
study are plant genera (e.g., pine, oak) rather than
species, and thus the simulated results are not
taxonomically precise. Second, the results are
applicable only on a regional scale; local scale
predictions are not made. Third, and very
significant, the simulated results assume that all the
plants are in equilibrium with the new climate.
Rates of dispersal vary between species, and several
hundred years may pass before plant communities
are again hi equilibrium with climate. How this lag
would affect plant community dynamics is not
addressed hi this study and is an important research
question.
The paleoecological analysis of the past
vegetation hi the Sierra Nevadas (O. Davis) presents
several uncertainties. First, differences with respect
to weather variations (i.e., season to season and year
to year) could produce strikingly different types of
vegetation. Also, there is much uncertainty about
what the most appropriate analog period might be
— or if one even exists. Furthermore, the rate of
climate change in the future is predicted to be much
faster than the rate of climate change during the
past 20,000 years. Lags in the response of species
to the future climate could strongly affect the type
of forest at any one location, whereas in the past,
with a more slowly varying climate, lags in species
response were not as important hi determining
forest composition.
All of the studies are deficient in some very
important processes controlling forest responses to
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Forests
climate, particularly disturbance regimes such as
fires, windstorms, hurricanes, landslides, and pest
outbreaks. Over some forest areas, periods of cloud
cover could change. This is an important
uncertainty, for if the annual total is significantly
increased, reductions in solar radiation could mean
reduced photosynthesis and thus less forest growth.
In addition, the responses of mature trees to
elevated CO2 under conditions of moisture,
temperature, or other nutrient limitations remain
largely unexplored. Most research on elevated CO2
on trees has been performed in controlled chambers
using seedlings, and results show an increase in
photosynthesis and improved water-use efficiency in
some cases (Strain and Cure, 1985). However, the
seedlings were not previously grown in or
acclimatized to high CO2 environments. Evidence
has shown that plants grown under high CO2 will
respond differently to changes in temperature, light,
and moisture conditions (Strain and Cure, 1985).
Another shortcoming is that methods to
extrapolate CO, fertilization results from laboratory
experiments to the natural world are limited, and an
understanding of regional changes in water-use
efficiency is even more limited. Furthermore,
complex interactions between fertilization effects
and changes in water-use efficiency can produce
unexpected problems such as increased heat loads
due to effects on evaporation cooling. These
interactions are not well understood but could
produce major regional changes in forest responses.
Therefore, it is not yet possible to quantitatively
incorporate the direct effects of CO2 on forests into
studies such as these. Further, if water or nutrients
are limiting to forest growth, they would likely
exceed the fertilization effects of elevated CO2.
Also, forest canopies at optimum development have
multilayered leaf areas so that light limitations exist
for the lower portion of the foliage in addition to
frequent water and nutrient limitations. This adds
further weight to the belief that CO2 enrichment
may not significantly affect forest productivity.
Results
The six studies conducted for EPA consistently
indicate that climate changes would significantly
affect the natural forests of the United States. The
distribution of healthy forests in the eastern United
States appears to become greatly reduced from their
present areas during the next century (Figures 5-3
and 5-4). This results from a very slow northward
migration coupled with a fairly rapid decline in the
southern and western parts of species ranges. Drier
forest conditions in the United States, induced as
much by increased temperature as by changes in
rainfall, would mean less tree growth and therefore
reduced forest productivity in general.
The forest simulation models provide an
indication of the importance of uncertainties
imparted by the climate scenarios. The climate
scenarios differ primarily in their representation of
regional rainfall patterns. The model results
indicate that temperature has a large effect on
forest health, either directly through cold and heat
stress or indirectly through exaggeratedg drought
effects. Thus, the overall characteristics of forest
responses are remarkably similar among the three
climate scenarios. However, this generalization is
uncertain because models usually do not incorporate
all possible mechanisms of impact.
Magnitude
Eastern Forests - Northern Limits
All of the study results suggest a northward
expansion of most eastern tree species (Figure 5-3
displays results from Overpeck and Bartlein). That
is, spruce, northern pine, and northern hardwood
species would move north by about 600-700
kilometers (375-440 miles) into the Hudson Bay
region of the Canadian boreal forest (Overpeck and
Bartlein; Zabinski and Davis). New England
coniferous forests would be replaced by more
hardwood forests and especially by the oak species
from the eastern mid-United States (Botkin et al.;
Overpeck and Bartlein; Zabinski and Davis). As
the northern mixed forests shift from spruce-fir to
sugar maple, some sites could actually triple their
present productivity (Botkin et al.).
Additionally, southern pine species could shift
about 500 kilometers (310 miles) into the present
hardwood forest lands of eastern Pennsylvania and
New Jersey (Overpeck and Bartlein; Urban and
Shugart; Solomon and West, 1986; Miller et al.,
1987). Depending upon the severity of climate
change, Urban and Shugart estimated that near the
northern limits of slash pine in East Tennessee,
aboveground woody biomass in 100 years could
range from little change to an extremely low
biomass with almost no trees (i.e., a grassland,
savanna, or scrub). However, even with little
decrease in productivity, species shifts would alter
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Chapter 5
B
Current Climate
Spruce Birch
N. Pines Oak
S. Pines Prairie Forbs
GISS Model Output
Spruce Birch
N. Pines
Oak
S. Pines Prairie Forbs
Figure 5-3. Maps of eastern North America depicting present distributions of major forest genera and herbacious
vegetation compared with potential future distributions after reaching equilibrium with the climate predicted for
doubled CO^. The comparison is based upon (A) simulations using modern pollen data and simulated future
pollen abundances for each of the three doubled CO2 scenarios: (B) GISS; (C) GFDL; and (D) OSU. The
three levels of shading in each scenario map indicate estimated future pollen abundances ranging from 20%
(darkest or strongest chance of future distributions) to 5% and 1% (lightest or least chance of future
distributions) (Overpeck and Bartlein, Volume D).
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Forests
Sugar Maple
Present Range
JH] Potential Range
• Inhabited Range
Range After 2050: GISS
Range After 2050: GFDL
Scale 0 400Km
Figure 5-4. Present and future geographical range for sugar maple (Zabinski and Davis, Volume D).
the forest composition from shortleaf to loblolly
pine, a more commercially valuable tree species.
Eastern Forests - Southern Limits
Ultimately, forest decline and mortality could
truncate southern distributions of tree species by as
much as 1,000 kilometers (625 miles) in many
northern hardwood species (Zabinski and Davis;
Overpeck and Bartlein) or by as little as a few
hundred kilometers (about 120 miles) in southern
pines and hardwoods (Urban and Shugart; Solomon
and West, 1986). Under the driest scenario
(GFDL), Zabinski and Davis estimate local
extinction in the Great Lakes region of many
eastern tree species such as eastern hemlock and
sugar maple (Figures 5-3 and 5-4). These estimates
bear considerable uncertainty for all species.
These uncertainties are particularly true for the
southern limits of southeastern species that border
the continental margin. The actual southern
climatic limitations of these species are not well
known (Urban and Shugart). Nevertheless, under
the most severe climate scenario in the Southeast
with increased temperatures and decreased growing-
season precipitation, Urban and Shugart's results
suggest that the 18 tree species they considered
would no longer grow in the southern half of the
region. Present forest lands in the region would be
replaced by scrub, savanna, or sparse forest
conditions. This estimation results from scenario
conditions of heat that would exceed the tolerance
limits for most tree species. Under the mildest
scenario (OSU), even forest areas in South Carolina
and southward would be marginal, supporting about
half their current biomass.
Biomass accumulations in 100 years for mature
natural forests in productive sites in the Great
Lakes region could be reduced to 23-54% of their
present values (Botkin et al.; Solomon and West,
1986). On poor sites, forests could be converted to
grassland or savanna with very low productivity,
ranging from 0.4 to 28% of their present values.
Western Forests
Similar projections were made for six western
coniferous species: ponderosa and lodgepole pine,
Douglas-fir, western hemlock, western larch, and
Englemann spruce (Leverenz and Lev, 1987).
Estimations are mixed for the West. Because of
the mountainous conditions in the West, upslope
shifts are possible for Douglas-fir, ponderosa pine,
and western hemlock in the northern Rocky
Mountains. In the coastal mountains of California
and Oregon, Douglas-fir could shrink in the
lowlands and be replaced by western pine species
(O. Davis; Leverenz and Lev, 1987). Overall, the
western forest lands are estimated to favor more
drought-tolerant tree species, such as the hard pine
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Chapter 5
A. MISSISSIPPI FORESTS
B. SOUTH CAROLINA FORESTS
£ 140
180
160
140
120
100
80
60
40
20
—— No Climate Change
GISS A
1980
2000
2020
YEAR
2040
2060
Figure 5-5. Estimated changes in biomass of mature forests in Mississippi (A) and South Carolina (B) under
the GISS transient climate change scenario (Urban and Shugart, Volume B).
group, at the expense of fir, hemlock, larch, and
spruce species.
If regional drought persisted, the frequency of
fires could increase, significantly reducing total
forested area. Also, with massive upslope
movement, some species could be pushed off the
tops of mountains into local extinction.
No quantitative estimates have been derived for
productivity for the western forests under potential
warming conditions. However, using the analog
approach of Davis, under the most severe conditions
projected for California, the species composition of
the west-side Sierra Nevada forests would become
more similar to that of the east-side forests. This
could reduce the standing biomass to about 60% of
current levels.
Rates of Decline and Migration
In the Great Lakes region, significant forest
decline and forest compositional change could
become evident within 30 to 60 years (Figure 5-5A;
Botkin et al.). In the Southeast region, forest
declines could become most evident in 60 to 80
years with declines in the drier western portions
occurring even earlier, perhaps in about 30 years
(Figure 5-5B and C); Urban and Shugart). As
previously discussed in this chapter (see Limitations)
there is considerable uncertainty about these
numbers.
. These rapid declines, coupled with the expected
magnitude of climate change, raise the question of
how fast forests can migrate. Based upon fossil
records, Zabinski and Davis have estimated that the
maximum dispersal rate of several tree species in
response to the last glacial retreat was roughly 50
kilometers (30 miles) per century. Under the
expected rapid warming, they estimated that a
dispersal rate of about 1,000 kilometers (600 miles)
per century would be required to maintain species
distributions near their current extent. Such
migration rates are doubtful, suggesting greater
reductions in species ranges under rapid climate
change, with declines in the drier western portions.
Mechanisms of Migration
Distribution changes (i.e., migrations) suggested
by these studies must 'be considered carefully.
Reproductive processes are essential for the
migration of tree species across the landscape. For
many tree species, climate change could reduce
natural regeneration in an existing location and
introduce the species at different latitudes or
altitudes. Reproductive processes in trees, such as
flowering, pollination, seed set, seed germination,
and seedling competitive success, are particularly
sensitive to climate.
Specific regional climate scenarios vary as a
function of the GCM. All scenarios estimate
increases in temperature; however, some include
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Forests
increases in rainfall, and others have decreases. The
northward shifts of species appear to result from a
release from cold temperature stress, which
normally freezes flowers, seedlings, and even adult
trees. However, the western and southern limits of
eastern tree species appear to result from
insufficient moisture and excessive heat stress, which
primarily affect sensitive life history stages but can
also affect mortality rates of adult trees. Though
difficult to detect in the early phases of rapid
climate change, tree mortality is sensitive to chronic
moisture stress and mortality rates would likely
increase among the major forest regions of the
United States.
Two points are important about regional
uncertainties of future rainfall distribution. First,
changes in the seasonal distribution of rainfall are as
or more important than relatively small changes in
the annual total. If summer rainfall decreases while
winter rainfall increases, the trees may still
experience summer drought stress. Second,
evapotranspiration is a log function of temperature.
Therefore, as temperature goes up, water loss from
trees and soils can increase tremendously. If minor
increases in rainfall are not sufficient to override the
evapotranspirational losses of water, drought
impacts will pervade. Both of these mechanisms
appear to dominate the forest impacts in this study.
All of the study approaches used under all of
the climatic scenarios estimate major forest declines
in the southern parts of species ranges and
expansions to the north. These declines, resulting
primarily from drought stress, would occur despite
the differing rainfall predictions among the climate
scenarios used in this study. Global precipitation is
generally projected to increase slightly with global
warming (see Chapter 4: Methodology), but it is not
known whether this increase would be sufficient to
compensate for potential increases in plant moisture
stress caused by higher temperatures. Precipitation
in some regions may decline. Droughts would
become more common. The western limits of
eastern forests could similarly retract as the climate
warms.
Existing forests probably would not shift intact,
but would change in composition. Variations in
migration rates and sensitivities to weather variables
produce individual responses to climate change.
These changes are consistent with the well-known
dynamic nature of ecosystems and were projected
for the forests of all regions. In the Great Lakes
region, for example, beech could decrease in
abundance (Zabinski and Davis), and birch and
maple could increase (Botkin et al.). On some
lands, forest productivity could remain about the
same as today, but changes to less economically
important species could be significant.
Not considered quantitatively in any of the
studies are changes in forest disturbance regimes.
These changes should not be considered lightly.
Extreme and more frequent climatic variations (see
Chapter 3: Variability) could cause much higher
mortality in U.S. forests than the current
experience. Although little is known as yet, some
locations may experience an increase in the
frequency of extreme weather events, for example,
wind, ice, or snow storms, droughts, and flooding.
Besides the direct damage these events can cause,
they can predispose forests to damage from
secondary stresses such as insects, disease, and
wildfires.
ECOLOGICAL AND SOCIO-
ECONOMIC IMPLICATIONS
The effects of doubled CO2 climate changes
may be considered from two perspectives:
ecological and socioeconomic. Evidence for
significant national implications is strong from both
viewpoints.
Ecological Implications
Ecological implications for forests commonly
start with tree response. But strong implications
also exist for other ecosystem components, e.g.,
animals, soils, water, secondary impacts, and as
noted, the atmosphere through which climate
change is mediated. Forest effects are described in
terms of tree distribution changes and biomass
production changes, but many other processes
interact among the other major components. Thus,
significant changes in tree response would be
accompanied by ecological reverberations
throughout all the forested areas of major U.S.
regions.
Tree Distributions and Biomass Productivity
As discussed, migrations of forest tree species
to the North in response to rapid warming in North
America during the next century will be likely.
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Chapter 5
However, significant lag is possible. Even under the
maximum rates of species dispersal estimated by
Zabinski and Davis, healthy forest areas may not
redevelop for several centuries. Furthermore, if
climate continues to change beyond the next
century, then healthy forests may never redevelop.
Meanwhile, distribution ranges may not be under
such constraints, so the extent of healthy forested
regions in the United States probably would be
greatly reduced. Though some locations may have
increased productive potential from a biomass per
hectare standpoint, the large reductions in areas
with healthy forests would likely create a net
reduction in forest productivity for the United States
for several centuries or longer.
Even if a massive reforestation effort were
undertaken, the new forests resulting from species
shifts might or might not be as productive as
existing forests. More northern latitudes or higher
elevations raise other considerations. Farther north,
days are longer in the summer and shorter in the
winter. At higher elevations, damaging ultraviolet
light intensity is greater. All of these conditions
could lower forest productivity below present levels.
Furthermore, it is not clear that reforestation would
be successful. A major intent of reforestation would
be to artificially speed up northward migration of
tree species. However, seedlings that would appear
to be favored on some northern sites several
decades in the future may not survive there now
because of constraints imposed by temperature, day
length, or soil conditions. Similarly, seedlings that
could not survive on those sites now might not be
the best adapted species for those same sites several
decades in the future.
Animals
A change in the size and relative homogeneity
of forests could influence whether some animals can
continue to live in their present locations. Often,
animals are finely adapted to habitats specific to a
certain location. For some animals, migration can
be hindered by boundaries between forests and
other land types or facilitated as animals move
along edges. Furthermore, some animals (e.g.,
many game species) prefer young forests, and others
(e.g., many rare and endangered species) prefer old
forests. In turn, animals can exert a profound
influence on forest structure and composition
through selective browsing of seedlings, insect attack
of different tree species, seed dispersal, and other
effects. All of these factors illustrate that climate
change could influence the regional patterns of
biotic diversity in both plants and animals (see
Chapter 8: Biodiversity).
Soils
Soils under warmer climates also would change,
although at a much slower rate than shifts in species
distribution. Increased soil temperatures, however,
would affect the entire range of physical, chemical,
and biological soil processes and interactions. For
example, populations of bacteria, fungi, and animals
could increase in a way that would accelerate
decomposition of litter and thereby reduce the
availability of nutrients essential for forest growth
(Spurr and Barnes, 1980).
Considerable time may be required to develop
optimum soil conditions for high forest productivity
supporting species at more northern latitudes or
higher elevations. Furthermore, it is not at all clear
how well some northern soils could support more
southern species. The soils of the boreal forest
differ from those under the deciduous forests to the
south.
Water
Where forests give way to drier conditions (e.g.,
in the Great Lakes region and California), many
lands now serving as watersheds might be used for
different purposes. Furthermore, regional-scale
disturbances (such as fire) and applications of
chemicals (such as fertilizers and pesticides) could
degrade regional water quality and increase airborne
toxic chemicals (see Chapter 9: Water Resources).
Sea level rise may impact some coastal forests.
Many forest lands of high value for timber
production (e.g., in the Southeast) or recreation (in
the Northeast, Northwest, and California) are close
to ocean coasts. Inundations, decreases in depth to
the water tables, and saltwater intrusions could
trigger rapid forest declines near these areas.
Secondary Impacts
As the southern bounds of forests tend to shift
north, forest decline (sick and dying trees) could
become extreme over large areas that would
become highly susceptible to weed competition, pest
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Forests
outbreaks, or wildfire. As forests decline, species of
lower economic value, as well as weedy shrubs and
herbs, could invade via wind dispersion. Under
stressful environments, such species are severe
competitors with most commercial tree species.
Trees experiencing less favorable growth
conditions are more stressed and will be vulnerable
to insect and disease attack. These secondary pest
impacts could last "until the most vulnerable forest
stands or tree species are eliminated" (Hedden,
1987). In addition, it is estimated that the incidence
of catastrophic wildfires will increase in U.S. forests
with higher temperatures. Simand and Main (1987)
estimated that fire occurrence and fire-suppression
costs would increase 8 and 20%, respectively.
Socioeconomic Implications
The United States enjoys substantial economic
and cultural benefits from its forests. Until recently,
the nation's forest managers assumed that these
benefits could be sustained by maintaining forests in
a healthy condition (Fosberg, 1988). This was
achieved, for example, by preventing fires or pest
invasions, avoiding careless use, and enhancing
productivity through good silviculture.
Beginning with the possibility of regional air
pollution damage to forests, suspected in the 1980s,
alterations of the environment external to forests
presented a new concern. Research and policy
discussions to deal with this issue are ongoing.
If climate changes as rapidly as predicted, this
additional external influence with its more global
dimensions looms as a possible hazard to forests
and their use. As can be imagined, a list of
potential socioeconomic concerns would be large.
To provide a brief perspective, three issues are
considered.
Quality of the Human Environment
The forest amenities enjoyed by most U.S.
citizens will be affected according to different forest
responses. In the Boston-Washington corridor, a
composition change from predominantly hardwood
to predominantly pine forests, though ecologically
significant, may not be noticed by most people if it
occurs gradually. However, a delay of years or
decades between the decline of existing forests and
replacement by migrating tree species would likely
elicit a strong concern. In the Atlanta-Southeast
region, the southern pine forests, while undergoing
a gradual expansion of their northern boundaries,
would have less vigor in the remaining stands. This
could raise their vulnerability to damage from
insects and disease, reducing esthetic values —
atleast an intermediate impact for most of the local
citizens. In contrast, within some portions of the
Southeast, the Great Lake region, and California,
drier climates may cause the loss of some forest
lands to prairie or desert conditions — a severe
change for the people there, not only in their living
environment but also in the whole spectrum of
forest land use.
Recreation
Forests must be in a relatively healthy condition
to support quality recreational use (Clawson, 1975).
Forests undergoing gradual composition changes
might remain healthy, but rapid changes would most
likely cause stressed or declining forests. Such
forest conditions would have less recreational appeal
because of such factors as less pleasing appearance,
greater threat of wildfire, and reduced hunting
quality when game populations change or are
diminished. Furthermore, drier conditions in U.S.
forests would harm recreational opportunities that
depend on abundant water or snow.
Wood Products
Altered U.S. forest productivity resulting from
climate change would have obvious major economic
impacts. Significant yield reductions could lead to
unemployment, community instability, industrial
dislocation, and increased net imports of wood
products.
Reforestation projects could make up for some
losses in forest productivity and artificially advance
migrations forced by climate change. Reforestation
technology has greatly improved in recent decades
so that success rates also have increased greatly.
Examples are high-vigor seedlings developed
through improved nursery practices, genetic
selection, and vegetative propagation.
Improvements in the field include machine planting,
fertilization, and weed control on selected sites.
Results are evident from the large acreages of
plantations established in the United States in
recent decades, particularly with loblolly pine in the
Southeast and Douglas-fir in the Pacific Northwest
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Chapter 5
(Table 5-2). Large-scale reforestation in the United
States and elsewhere could significantly add to the
total carbon sink provided by world forests, thereby
offsetting some of the buildup of atmospheric CO2-
Although this was not studied, attempts to reforest
some very dry sites may be unsuccessful.
Innovative manufacturing trends should prove to
be timely during times of rapid forest change.
High-strength and durable products from
reconstituted wood (e.g., new particle board
concepts, warp-proof hardwood lumber, paper
products of fiber from multispecies) are now in use
or well along in development. These new methods
will lessen the present overdependency on a few
commercial conifer species from stands above
minimum size and quantity (Ince, 1987). The result
will be an ability to use the timber resources of the
future, however they change in composition.
FOREST POLICY AND CLIMATE
CHANGE
Historically, U.S. forest policies have undergone
continued development to meet national change
(Young, 1982). The earliest policies were adapted
by the New England colonies in the 1600s to
regulate overcutting near settlements. Wood was
needed for fuel and buildings, but existing methods
were not capable of long distance log transportation.
Development of U.S. forest policies has continued
and has been particularly intense this century, as the
national forests, national parks, and wilderness areas
have been established.
At present, forest managers are dealing with
many additional policy issues. Five of these
(Clawson, 1975) are important to climate
change/forest response:
• How much U.S. land should be devoted to
forests?
• How much forest land should be withdrawn
from timber production and harvest?
• How should the federal forest lands be
managed? (That is, the lands under the
USDA Forest Service, USDI Park Service,
Bureaus of Land Management and Indian
Affairs, and other federal agencies that
manage forest lands.)
• What constraints (e.g., mandatory forest
practices) should be placed on forest
managers to ensure national environmental
goals?
• Who should pay the additional costs
incurred in implementing new policies?
The large array of forest ownerships in the
United States, public and private, makes
development and implementation of forest policy
more complicated than in most countries. Around
the world, about 77% of all forests are in some
form of public ownership (Hummel, 1984). The
diversity of owners and managers results in widely
divergent goals and objectives.
How Much Land Should Be Forested?
Changes in forest composition or regional
boundaries induced by rapid climate change would
magnify the complexity of national forest policy even
further. Lands in forests now would require review
relative to such competing needs as agriculture and
residential use, which would also be adjusting to
climate change.
How Much Should Be Withdrawn From
Timber Production?
Where the productivity of wood is significantly
reduced, increased, or shifted, a policy question that
would surely arise concerns whether forest lands
should be reallocated to maintain timber
production. If so, how should competing forest
uses, such as watersheds, parks, and wilderness, be
treated? How much of each can the United States
afford under changed climatic conditions? Should
the federal government purchase more forest lands
to support all public needs?
In the short term, forest managers could
compensate for some loss of productivity by
improved technology, although at increased costs.
An example would be establishment of more
drought-tolerant plantations through genetic
selections, improved nursery stock, and more
intensive silvicultural practices (e.g., weed control
and thinning). Introducing new species adapted to
warmer climates might be possible in some
locations, but this would call for development of
new silvicultural regimes and utilization methods —
possible, but time consuming and costly. In the long
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Forests
term, if growing conditions become extremely
difficult on some U.S. forest lands because of
climate changes, establishing trees for wood
production on such sites may not be economically
justified.
How Should We Manage Federal Forests?
The national forests under the USDA Forest
Service are managed according to a series of
complex legal directives and administrative
procedures, beginning with the Organic Act of 1897
(Woodman and Furiness, Volume D). Ultimately,
the objective became to manage the national forests
for multiple uses, with timber and other forest
resources on a sustained-yield basis and certain
lands set aside as wilderness areas. The National
Forest Management Act of the mid-1970s requires
management plans for each national forest subject
to public review. The plans look ahead 50 years
and are to be updated every 10 years.
Lands managed by the Department of Interior
are under similar mandates. For example, a
congressional act passed in 1976 charged the Bureau
of Land Management to manage its 2.3 million
hectares (5.1 million acres) of forest and range land
according to multiple-use and sustained-yield
principles. Similarly, the National Park Service is
mandated to manage national parks, monuments,
historic sites, and so forth, for the recreational
enjoyment of people. Such activities as .timber
harvesting, hunting, mining, and grazing are not
permitted. In addition to the federal government,
most states, many counties, and some municipalities
own forest lands. ,
The Forest and Rangeland Renewable
Resources Planning Act ,of 1974 requires the
Secretary of Agriculture to make periodic reviews of
the nation's forest and rangeland resources. In the
future, these assessments and planning efforts
should include consideration of the possible effects
of predicted climate changes.
A key issue is the level of priority given to
maintaining forest health under changed climate
conditions. For instance, under more adverse
environments, should national forests be left to
decline as a natural process, thereby losing esthetic
values in parks, water yields from watersheds, and
highly productive timber crops? Or should
silvicultural forest techniques such as thinning, weed
control, fertilization, and reforestation be employed
in an attempt to preserve them? This question and
others will challenge the fundamental concepts of
the benefits of multiple use and sustained yield of
U.S. forests.
How Can We Ensure National Goals?
At the minimum, federal agencies must plan
and act in concert with the state and private forest
organizations. In the first half of this century, the
federal government attempted to regulate forest
harvests on all federal, state, and private lands.
Development of this policy did not survive strong
public concern and intense political debate against
such policy (Worrell, 1970); the same sentiment
would likely exist today. However, under the
influence of climate change, the nation may once
again have to face the touchy issue of what
restraints or forest practices must be regulated for
all public and private lands.
Solomon and West (1985) point out that while
climate change might disrupt forest ecosystems in
the, future, it is uncertain whether forest managers
could or would be able to apply silvicultural
practices on a scale large enough to maintain the
net productivity of commercial forest lands in the
United States. Some states (e.g., Washington,
Oregon, and California) have laws specifying fire
protection requirements, control burn practices, and
reforestation minimums following timber harvests.
Zoning, permits, licenses, and various taxation
measures also have been attempted with mixed
results. It is much easier to prevent owners from
destroying forests than to compel them to
implement silvicultural practices.
Reforestation
To keep pace with the global climate changes
estimated, the U.S. reforestation effort conceivably
would need to be doubled or tripled in size. In
recent years, about 800,000 hectares (2 million
acres) per year (approximately 700+ million
seedlings) have been reforested in the United States
(USDA, 1982). Costs range from $200 to $700 per
hectare ($80 to $280 per acre) depending upon
species, site preparation, plantation density, and
planting method. Using $500 per hectare ($200 per
acre) as a mode, the total annual expenditure is
near $400 million. About 0.4% of the commercial
land base is reforested annually. At this rate, it
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Chapter 5
would take 100 years to reforest 40% of the U.S.
forest lands, assuming no repeat hectares to cover
failures or harvests of the first plantations.
An expansion on the scale suggested above
would require large investments in seed
procurement, tissue culture capability, nursery
capacity, and research to improve knowledge about
the establishment and silviculture of drought-
resistant plantations. Even if the dollar
commitments were made, reforestation at this scale
might be possible only if all forest lands were
managed by one organization. The complex forest
ownership pattern in the United States, therefore,
would be an issue to overcome in a national
reforestation program.
Who Should Pay?
Adjusting forest policies to address the issues
arising from climate change will most likely raise
the costs of using the nation's forests — whether for
water, recreation, esthetics, or timber. Additional
research to answer many new questions will also
require more funds. A major question will be who
should pay for these costs. Land owners? Forest
users? Consumers? All taxpayers? The answers
will come when better information is available on
resulting forest effects, followed by public debate
establishing new priorities for forest use in a
changed climate.
RESEARCH NEEDS
The forest effects resulting from rapid climate
change are at present hypothetical. The change has
not yet occurred, and many uncertainties are
associated with the predictions. Effective policies to
deal with new forest effects will require more
information and fewer uncertainties that must come
through forest ecosystem research. Four broad
questions concerning U.S. forests frame the
research needs for the 1990s: What will the effects
be? How can they be measured reliably? How
should they be managed? How can we ensure that
research will be conducted in a timely fashion?
Effects of Climate Change
What will be the effect on the nation's forest
ecosystems if climate changes occur as predicted by
the middle of the 21st century? While subsets of
this question must include extent, magnitude, and
risk considerations, additional knowledge is needed
concerning the following:
1. Forest migration processes and rates,
including the landscape processes that
control the horizontal movements of forests,
animals, and disturbances;
2. Interactions among the different landscape
components and land-use practices that
affect biodiversity, and water quantity and
quality;
3. The impact of climate change alone and in
combination with other natural or
anthropogenic influences, such as insects,
pathogens, COj enhancement, air
pollutants, UV-B radiation, and acid
deposition on U.S. forests; and
4. The processes and mechanisms that play
key roles in forest ecosystem effects — both
biologically as in photosynthesis and
respiration, and physically as in flows of
energy, carbon, water, and nutrients
through ecosystems.
Methods
How can forest ecosystems be measured to
reliably detect the effects of rapid climate change?
Today, the response of ecosystems to environmental
change is largely based upon extrapolating from
field observations, from knowledge about seedlings
or individual trees of a small number of
commercially valuable species, and from computer
models. The following must be accomplished:
1. A determination of the most useful
integrating variables for forest ecosystems
that indicate the effects of climate change
— particularly variables that are early-
warning indicators of ecosystem response;
2. Effective sampling designs developed for
experiments and long-term monitoring at
the forest ecosystem scale; and
3. Improved models capable of projecting
regional effects on forests across multiple
spatial and temporal scales.
90
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Forests
Forest Management
What options are available to the public and
private forest managers and owners in the United
States to address the changes in the nation's forests
that might occur in the next century? Research is
needed to accomplish the following:
1. Understand the socioeconomic impacts of
all forest ecosystem effects to clarify
economic risks and alternatives; and
2. Develop technology to mitigate the adverse
effects or to exploit the benefits of forest
change, such as breeding, bioengineering,
transplanting, fertilization, irrigation, and
other management approaches.
Timing of Research
The timing of the research is critical. The
effects of climate change may be some decades
away, but this should not lessen the urgency to
begin research toward better information and
methods. The complexities of the science are very
large. Developing a base of knowledge to identify
potential forest changes before they are upon the
nation will require significant time and resources.
REFERENCES
Harbour, M.G., J.H. Burk, and W.D. Pitts. 1987.
Terrestrial Plant Ecology, 2nd Ed. Menlo Park,
CA: Benjamin/Cummings Publishers.
Botkin,D.B. 1979. A grandfather clock down the
staircase: stability and disturbance in natural
ecosystems. In: Waring, R.H., ed. Proceedings of
the 40th Annual Biological Colloquium. Forests:
Fresh Perspectives From Ecosystem Analysis.
Corvallis, OR: Oregon State University Press, pp. 1-
10.
Clawson, M. 1975. Forests for Whom and for
What? Resources for the Future. Baltimore, MD:
Johns Hopkins University Press.
Cubbage, F.W., D.G. Hodges, and J.L. Regens.
1987. Economic implications of climate change
impacts on forestry in the South. In: Meo, M., ed.
Proceedings of the Symposium on Climate Change
in the Southern U.S.: Future Impacts and Present
Policy Issues. New Orleans,
Environmental Protection Agency.
LA: U.S.
Davis, M.D., and D.B. Botkin. 1985. Sensitivity of
the cool-temperate forests and their pollen to rapid
climatic change. Quaternary Research 23:327-340.
Fosberg, MA. 1988. Forest productivity and health
in a changing atmospheric environment. In:
Berger, A., et al., eds. Climate and Geosciences: A
Challenge for Science and Society in the 21st
Century. NATO ASI Series. Series C;
Mathematical and Physical Sciences, Vol. 285.
Dordrecht, The Netherlands: Kluwer Academic
Publishers, pp. 681-688.
Grey, G.W., and FJ. Deneke. 1978. Urban
Forestry. New York: John Wiley and Sons.
Hammond, A.L. 1972. Ecosystem analysis: biome
approach to environmental science. Science 175:46-
48.
Hedden, R. 1987. Impact of climate change on
forest insect pests in the southern U.S. In: Meo,
M., ed. Proceedings of the Symposium on Climate
Change in the Southern U.S.: Future Impacts and
Present Policy Issues. New Orleans, LA: U.S.
Environmental Protection Agency.
Hummel, F.C., ed. 1984. Forest Policy, a
Contribution to Resource Development. The
Hague: Martinus Nijhoff/Dr. W. Junk, Publishers.
Ince, P J. 1987. Technology, timber demand and
timberland investment. In: A Clear Look at
Timberland Investment, Milwaukee, WI; April 27-
29. Conference proceedings. Forest Products
Research Society.
Lavdas, L.G. 1987. The impact of climate change
on forest productivity. In: Meo, M., ed.
Proceedings of the Symposium on Climate Change
in the Southern U.S.: Future Impacts and Present
Policy Issues. New Orleans, LA: U.S.
Environmental Protection Agency.
Leverenz, J.W., and DJ. Lev. 1987. Effects of
carbon dioxide-induced climate changes on the
natural ranges of six major commercial tree species
in the western United States. In: Shands, W.E., and
J.S. Hoffman, eds. The Greenhouse Effect, Climate
Change, and U.S. Forests. Washington, DC:
Conservation Foundation, pp. 123-156.
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Chapter 5
Manion, P.D. 1981. Tree Disease Concepts. New
Jersey: Prentice Hall.
Meo, M., ed. 1987. Proceedings of the Symposium
on Climate Change in the Southern United States:
Future Impacts and Present Policy Issues; May 28-
29. New Orleans, LA: University of Oklahoma and
U.S. Environmental Protection Agency.
Miller, F.W., P.M. Dougherty, and G.L. Switzer.
1987. Effect of rising carbon dioxide and potential
climate change on loblolly pine distribution, growth,
survival and productivity. In: Shands, W.E., and
J.S. Hoffman, eds. The Greenhouse Effect, Climate
Change, and U.S. Forests. Washington, DC:
Conservation Foundation, pp. 157-188.
Pickett, S.TA., and P.S. White. 1985. The Ecology
of Natural Disturbance and Patch Dynamics.
Academic Press, Inc. Harcourt Brace Jovanovich.
Schallau, C.H. 1988. The forest products industry
and community stability: the evolution of the issue.
Montana Business Quarterly Summer: 1-8.
Shands, W.E., and J.S. Hoffman, eds. 1987. The
Greenhouse Effect, Climate Change, and U.S.
Forests. Washington DC: Conservation
Foundation.
Simand.AJ. and WA. Main. 1987. Global climate
change: the potential for changes in wildland fire
activity hi the Southeast. In: Meo, M., ed.
Proceedings of the Symposium on Climate Change
in the Southern U.S.: Future Impacts and Present
Policy Issues. New Orleans, LA: U.S.
Environmental Protection Agency.
Solomon, A.M., and D.C. West. 1985. Potential
responses of forests to CO2 induced climate change.
In: White, M.R., ed. Characterization of
Information Requirements for Studies of CO2
Effects: Water Resources, Agriculture, Fisheries,
Forests and Human Health. Washington, DC: U.S.
Department of Energy. DOE/ER-0236. pp. 145-
1709.
Solomon, A.M., and D.C. West. 1986. Atmospheric
carbon dioxide change: agent of future forest
growth or decline? In: Titus J.G., ed. Effects of
Changes in Stratospheric Ozone and Global
Climate. Vol. 3: Climate Change. Washington, DC:
U.S. Environmental Protection Agency.
Spurr, S.H., and B.V. Barnes. 1980. Forest
Ecology, 3rd Ed. New York: John Wiley and Sons.
Strain, B.R., and J.D. Cure, eds. 1985. Direct
Effect of Increasing Carbon Dioxide on Vegetation.
Washington, DC: U.S. Department of Energy.
DOE/ER-0238.
Tirpak, D.A., ed. 1987. Potential Effects of Future
Climate Changes on Forest and Vegetation,
Agriculture, Water Resources and Human Health,
Vol. V. Assessing the Risks of Trace Gases That
Can Modify the Stratosphere. Washington, DC:
U.S. Environmental Protection Agency. EPA 400/1
- 87/001E.
Titus, J.G., ed. 1986. Climate Change, Vol. 3.
Effects of Changes in Stratospheric Ozone and
Global Climate. Washington, DC: U.N.
Environmental Program and U.S. Environmental
Protection Agency.
USDA. 1981. U.S. Department of Agriculture,
Forest Service. An Assessment of the Forest and
Range Land Situation in the U.S. Forest Resource
Report No. 22.
USDA. 1982. U.S. Department of Agriculture,
Forest Service. An Analysis of the Timber Situation
in the U.S. 1952-2030. Forest Resource Report No.
23.
Waring, R.H., and W.H. Schlesinger. 1985. Forest
Ecosystems, Concepts and Management. Orlando,
FL: Academic Press, Inc.
Webb, T. 1987. The appearance and disappearance
of major vegetational assemblages: long-term
vegetational dynamics in eastern North America.
Vegetation 69:177-187.
White, M.R., ed. 1985. Characterization of
Information Requirements for Studies of CO2
Effects: Water Resources, Agriculture, Fisheries,
Forests and Human Health. Washington, DC: U.S.
Department of Energy. DOE/ER-0236.
Worrell, A.C. 1970. Principles of Forest Policy.
New York: McGraw-Hill.
Young, RA., ed. 1982. Introduction to Forest
Science. New York: John Wiley and Sons.
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CHAPTER 6
AGRICULTURE
FINDINGS
Climate change would affect crop yields and result
in northward shifts in cultivated land, causing
significant regional dislocations in agriculture with
associated impacts on regional economies. It would
expand crop irrigation requirements, stress livestock
production, and increase infestations of agricultural
pests and diseases. Preliminary results suggest that
although U.S. crop production could decline,
supplies would be adequate to meet domestic needs.
The potential for reduction of the national
agricultural capacity and the many uncertainties
surrounding the interactive effects on the
agricultural system create the necessity to respond
to the climate change issue.
Crop Yields
• The effects of climate change alone may
reduce average yields of corn, soybeans, and
wheat, both rainfed and irrigated, except in the
northernmost latitudes where warmer
conditions provide a longer frost-free growing
season. Decreases in modeled yields result
primarily from higher temperatures, which
shorten a crop's life cycle.
• When the direct effects of CO2 on crop
photosynthesis and transpiration are
approximated along with the effects of climate
change, average rainfed and irrigated corn,
soybean, and wheat yields could overcome the
negative effects of climate change in some
locations. If climate changes are severe, yields
could still decline. The extent to which the
beneficial direct effects of CO2 will be seen
under field conditions with changed climate is
uncertain.
• Even if the patterns of climate variability are
unchanged, yield stability may decrease,
particularly under rainfed conditions. This
may occur because there would be more days
above temperature thresholds for particular crops in
some locations. The exact magnitude of change will
be sensitive to changes in climatic variability,
particularly the frequency of droughts.
Economic Impacts
• Under three out of four scenarios, a small to
moderate aggregate reduction in the nation's
agricultural output was estimated. The
estimated production levels appeared to be
adequate to meet domestic consumption
needs. If droughts occur more frequently
under changing climate, effects on agriculture
may be more severe.
• Assuming no change in export demand,
reduced outputs would decrease exports, which
could negatively affect global food supplies and
the U.S. trade balance. This report did not
analyze global changes in agriculture, which
could have a major effect on demand for U.S.
products.
• Under the most severe climate change
scenarios, continued technological
improvements, similar to those in recent years,
would have to be sustained to offset losses.
Increasing food demand from higher U.S. and
world population would aggravate the
economic losses due to climate change.
• The economic response of agriculture to
changes in regional productivity may be to
shift crop production and associated
infrastructure in a northward direction. This
is because yields in northern areas generally
increase relative to yields in southern areas.
Although availability of agricultural soils was
included in the economic analysis, neither the
sustainability of crop production hi northern
areas nor the introduction of new crops into
southern areas was studied.
93
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Chapter 6
Irrigation Demand
• The demand for irrigated acreage is likely to
increase in all regions. This is due to the
reliability of irrigated yields relative to dryland
yields and to higher commodity prices that
make expansion of irrigated production more
economically feasible. Actual increases in
irrigated acreage would depend on the
adequacy of water supply and on whether the
cost of water to farmers increases.
• Demand for more irrigation would increase
stress on and competition for regional water
supplies. If irrigation does increase, it could
increase surface and groundwater pollution
and other forms of environmental degradation.
Agricultural Pests
• Climate warming could change the ranges and
populations of agricultural pests. Temperature
increases may enhance the survival of insect
pests in the winter, extend their northward
ranges, increase pest species with more than
one generation per year, and allow pest
establishment earlier in the growing season.
These effects could result in a substantial rise
hi pesticide use, with accompanying
environmental hazards. Changes in pests will
also depend on regional shifts in crop
production.
Farm-Level Adjustments
• Farmers may adjust to climate change by using
full-season and heat-resistant crop species or
varieties, by altering planting dates, by planting
two crops during one growing season, by
increasing or altering their scheduling of
irrigation, by using more pesticides, and by
harvesting earlier. If climate change is not
severe, these adjustments may mitigate losses
in crop yields; more severe climate change is
likely to make major adaptation necessary.
Livestock Effects
• Higher temperatures may increase disease and
heat stress on livestock in some regions.
Existing livestock diseases may shift north,
while tropical diseases may extend their ranges
into southern regions of the United States. Cold
stress conditions may be reduced in the winter, but
heat stress is likely to increase in the summer.
Reproductive capabilities may also decrease.
Policy Implications
• Global climate change has important
implications for all parts of the agricultural
system. The agricultural research structure,
which is dedicated to maintaining U.S. farm
productivity, should expand climate change
research in activities ranging from the field
level to the national policy level.
• Current U.S. Department of Agriculture
(USDA) research on heat- and drought-
tolerant crops and practices and maintenance
of crop germ plasm should be sustained and
enhanced to limit, vulnerability to future
climate change.
• The USDA should evaluate current legislation
in regard to its ability to allow adaptation to
global warming. Flexibility in shifting crop
types and farm practices will speed adjustment.
Such adaptation strategies should consider the
impacts on soil erosion and water quality.
• The USDA, the Department of Commerce,
the U.S. Trade Representative, and the State
Department should consider the implications
of potential long-term changes in the level of
U.S. crop exports for the U.S. balance of trade
and strategic interests.
• A national drought policy is strongly needed to
coordinate federal response to the possibility
of increased droughts due to climate change.
Even without climate change, such a policy is
necessary not only for the agricultural sector
but also for other sectors.
SENSITIVITY OF AGRICULTURE
TO CHANGES IN CLIMATE
Agriculture is a critical American industry,
providing food for the nation's population and as
much as $42.6 billion in exports for the nation's
trade balance (Figure 6-1). Agriculture employs 21
million people ~ more than any other industry,
94
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Agriculture
Others
' ' Fruits, nuts, and vegetables
ESJ Cotton
Livestock and by-products
Oilseeds and by-products
Grains and preparations
72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
Figure 6-1. Value of U.S. agricultural exports by commodity, 1972-86 (not adjusted for inflation). Livestock
excludes poultry and dairy products (The World Food Institute, 1987; U.S. Department of Agriculture, Economic
Research Service, Foreign Agricultural Trade of the United States, Washington, DC, January-February 1987,
and various other issues).
when taking into account workers on farms and in
meat, poultry, dairy, baking, and food-processing
activities (Council for Agricultural Science and
Technology, 1988). The U.S. agricultural
production system includes farm equipment
manufacture, fertilizer and seed supplies, rural
banking, and shipping. Total farm assets were $771
billion in 1985; food and fiber were 17.5% of the
total gross national product in the same year.
Wheat, corn, soybeans, cotton, fruits and vegetables,
and livestock are among the most important U.S.
agricultural commodities.
Worldwide, agricultural products must provide
sustenance for the world's growing population, now
estimated at about 5 billion and projected to rise to
8.2 billion by 2025 (Zachariah and Vu, 1988).
Global production and consumption of grain have
grown steadily since 1960, although regional food
shortages continue to occur owing to climate
variability and socioeconomic factors. Technological
advances, such as improved hybrids and irrigation
systems, have reduced the dependence of crop yields
on local environmental conditions, but weather is
still an important factor in agricultural productivity.
For example, failure of the monsoon season
caused shortfalls in crop production in India,
Bangladesh, and Pakistan in 1987. The 1980s have
also seen the continued deterioration of food
production in Africa, despite adequate world food
supplied elsewhere, because of persistent drought,
internal wars, poor distribution, weak infrastructure,
and a deteriorating environment. Climate extremes
have had large effects on U.S. agriculture. During
the Dust Bowl years of the 1930s, U.S. wheat and
corn yields dropped by up to 50%. Midsummer
1983 saw an unpredicted drought in the U.S. Corn
Belt and in the southeastern United States, causing
U.S. corn yields to fall by about a third, from over
7,000 kilograms per hectare to about 5,000
kilograms per hectare (from about 110 to 80 bushels
per acre).
The 1988 drought recently demonstrated the
impact that climate variability can have on
agricultural productivity. This drought decreased
U.S. corn yields by almost 40%, and the cost of the
1988 Drought Relief Bill is estimated to be $3.9
billion (Schneider, 1988). The 1988 drought
emphasizes anew the close link between agriculture
and climate.
95
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Chapter 6
Light from the sun, frost-free growing seasons,
and the hydrologic cycle largely govern the
suitability of geographic areas for crop production
and affect crop productivity. Livestock production
is responsive to climate through differing levels of
heat and cold stress and altered ranges of disease-
carrying vectors such as mosquitoes and ticks.
Higher levels of COp in the air would also
affect crops. Increased CO2 has enhanced crop
photosynthesis and has improved crops' use of water
in experimental settings. Because experimental
research has rarely simultaneously investigated both
the climatic and the direct effects of CO2 on plants,
it is difficult to assess the relative contributions of
CO2 and increased temperature to plant responses.
This remains one of the most crucial questions in
the analysis of impacts of climate change and
increased CO2 on agriculture.
The presence and abundance of pests affecting
both crops and livestock are highly dependent on
climate. The severity of the winter season, wind
patterns, and moisture conditions determine in large
part where pests will be prevalent. The
geographical distribution of pests also depends on
locations of crop types.
Much of U.S. agricultural production takes
place under technologically advanced cropping
systems that are primarily monocultural. Likewise,
livestock production is highly specialized, both
technically and geographically, and a high degree of
integration exists between grain and livestock
production. Any significant level of economic
robustness associated with general, multiple-
enterprise farms has long since passed from the
scene. The ability of our agricultural system to
adapt to climate change may be more limited now
in some ways than it was in the past.
Agriculture strongly affects the natural
environment. It often increases soil erosion,
intensifies demand for water, degrades water
quality, reduces forested land, and destroys wildlife
habitats. Many agricultural practices contribute to
soil degradation, groundwater overdraft, loss of
plant and aquatic communities, and generally
reduced resilience in environmental and genetic
resources. Therefore, climate-driven shifts in
agricultural regions have implications for
environmental quality.
Thus, climate plays a major role in
determining crop and livestock productivity.
Agricultural productivity determines profitability and
decisionmaking at the farm level, which in turn
define farming systems at the regional level and
import-export supply and demand at the national
and international levels. These complex
interrelationships necessitate a broad consideration
of the impacts of potential climate change on U.S.
agriculture.
PREVIOUS STUDIES OF
CLIMATE CHANGE AND
AGRICULTURE
Relationships between climate and agriculture
have been studied intensively for many years.
However, relatively few studies have specifically
addressed both the climatic and the direct effects
that the growth in trace gases will have on
agriculture. Even fewer studies have addressed
these potential effects in an integrated approach
that links both biophysical and economic spheres of
analysis.
Most research attention in the United States,
supported primarily by the U.S. Department of
Energy, has focused on the direct effects of CO2 on
crops. These studies are reviewed by Acock and
Allen (1985) and Cure (1985), who found an
average increase in yields of about 30% .and
increases in water-use efficiency for crops growing
in air with doubled CO2 (660 ppm) and favorable,
current climate conditions. Kimball (1985) and
Decker et al. (1985) suggested that the potential
effects of CO2 and/or climate change on
agricultural production systems may include shifts in
production areas and changes in levels of livestock
stresses, water availability, and pest control
management.
Integrated approaches to the impacts of
climate change on agriculture involving both
biophysical and economic processes have been
considered in studies by Callaway et al. (1982), the
Carbon Dioxide Assessment Committee (1983),
Warrick et al. (1986), and the Land Evaluation
Group (1987). A benchmark international study on
both the agronomic and economic effects of climate
change on agriculture was conducted by the
International Institute for Applied Systems Analysis
(Parry et al., 1988). No study has as yet
96
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Agriculture
comprehensively examined the combined effects of
climate change and the direct effects of CO2 on
U.S. agriculture.
CLIMATE CHANGE STUDIES IN
THIS REPORT
Structure of and Rationale for the Studies
The regions studied for this report are
important agricultural production areas (see Table
6-1). The Great Lakes and Southeastern States are
major corn and soybean producers, and the Great
Plains States grow mainly wheat and corn.
California annually produces about 10% of U.S.
cash farm receipts from cotton, grapes, tomatoes,
lettuce, and many other crops.
The agricultural studies involve the following
research topics (see Table 6-2): (1) crop growth and
yield, (2) regional and national agricultural
economics, (3) demand for water for irrigation, (4)
water quality, (5) pest-plant interactions, (6) direct
effects of CO2 on crop growth and yield, (7)
impacts of extreme events, (8) potential farm-level
adjustments, (9) livestock diseases, and (10)
agricultural policy.
Production of corn, wheat, and soybeans is
critical to the economic well-being of the nation's
farmers and the national trade balance. These
crops make up about two-thirds of the total U.S.
agricultural acreage, and their economic value is
equal to that of all other crops combined. These
three crops were selected for the modeling studies
on the effects of climate change on yields.
The results from the regional studies of crop
production (not including California), hydrological
predictions from the climate models, and an
agricultural economics model were linked in an
integrated approach to enable investigators to
translate the estimated yield changes from the crop
modeling studies and predicted changes in water
availability into economic consequences (see Figure
6-2). Such a coordinated analytical framework is
necessary to account for the effects of market forces
on the total agricultural sector, including livestock,
and to evaluate the adequacy of the nation's
resource base for agricultural production under
climate change. Economic forces may lead farmers
to grow more crops in areas with relatively high
productivity and fewer crops in areas with relatively
low productivity.
The studies of demand for irrigation water,
water quality, and farm-level adjustment were also
linked with the integrated modeling studies by
common assumptions, sites, or outputs. Because
California grows a large and diverse number of crop
commodities, a simple approach was used to
estimate crop yield changes for the California case
study based on heat, sunlight, and photosynthetic
response to CO2. These yield changes were then
used in a model of agricultural land and water use
in California. Adjustment experiments were
included in several studies to test possible
adaptation mechanisms, such as changes in planting
dates and crop varieties.
Table 6-1. Crop Production by Region
EPA study areas
Corn
Wheat
(thousands of bushels)
Soybeans
Harvested
acres
(thousands)
Southeast
Great Lakes
Great Plains
California
Total (48 states)
311
4,644
921
38
8,209
272
297
755
63
2,507
306
822
136
1,990
29
92
71
6
337
Source: U.S. Department of Commerce (1983).
97
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Chapter 6
Table 6-2. Agriculture Projects for EPA Report to Congress on the Effects of Climate Change
Regional Studies
• Effects of Projected CO2-Induced Climate Changes on Irrigation Water Requirements in the Great Plains
States - Allen and Gichuki, Utah State University (Volume C)
• Climate Change Impacts upon Agriculture and Resources: A Case Study of California - Dudek,
Environmental Defense Fund (Volume C)
• Farm-Level Adjustments by Illinois Corn Producers to Climate Change - Easterling, Illinois State Water
Survey (Volume C)
• Impacts of Climate Change on the Fate of Agricultural Chemicals Across the USA Great Plains and Central
Prairie - Johnson, Cooter, and Sladewski, Oklahoma Climatological Survey (Volume C)
• Impact of Climate Change on Crop Yield in the Southeastern U.S A.: A Simulation Study - Peart, Jones,
Curry, Boote, and Allen, University of Florida (Volume C)
• Effects of Global Climate Change on Agriculture: Great Lakes Region - Ritchie, Baer, and Chou, Michigan
State University (Volume C)
• Potential Effects of Climate Change on Agricultural Production in the Great Plains: A Simulation Study -
Rosenzweig, Columbia University/NASA Goddard Institute for Space Studies (Volume C)
National Studies
• The Economic Effects of Climate Change on U.S. Agriculture: A Preliminary Assessment - Adams, Glyer,
and McCarl, Oregon State University and Texas A&M University (Volume C)
• Analysis of Climate Variability in General Circulation Models - Mearns, Schneider, Thompson, and
McDaniel, National Center for Atmospheric Research (Volume I)
• Direct Effects of Increasing CO,-, on Plants and Their Interactions with Indirect (Climatic) Effects - Rose,
Consultant (Volume C)
• Potential Effects of Climatic Change on Plant-Pest Interactions - Stinner, Rodenhouse, Taylor, Hammond,
Purrington, McCartney, and Barrett, Ohio Agricultural Research and Development Center and Miami
University (Volume C)
• Agricultural Policies for Climate Changes Induced by Greenhouse Gases - Schuh, University of Minnesota
(Volume C)
• Changing Animal Disease Patterns Induced by the Greenhouse Effect - Stem, Mertz, Stryker, and Huppi,
Tufts University (Volume C)
• Effect of Climatic Warming on Populations of the Horn Fly - Schmidtmann and Miller, USDA, Agricultural
Research Service (Volume C)
98
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Agriculture
f Economic Consequences
Land Use and Irrigated
Acreage Changes /
Figure 6-2. Flow chart of model interactions in
EPA studies of the effects of global climate change
on U.S. agriculture (Dudek, 1987).
The agricultural studies performed for this
EPA report explore the sensitivities of the different
parts of the agricultural system (shown in Table 6-
2) to climate change scenarios. They are not meant
to be predictions of what will happen; rather, they
aim to define ranges and magnitudes of the
potential responses as the system is currently
understood. Regional results were extrapolated to
other areas to give estimates of changes in national
production.
Variability
All of the modeling studies used the doubled
CO2 climate change scenarios developed for the
report (see Chapter 4: Methodology). These
scenarios were developed from estimated changes in
monthly mean climate variables from general
circulation models (GCMs), without alterations in
climate variability. For example, the number of
days of precipitation remains the same in the
baseline and climate change scenarios, and the
amount of precipitation on each of those days is
adjusted by the GCM ratio for climate change.
Extreme events, such as maximum temperature,
vary in the climate change scenarios according to
the ratios, but the daily and interannual patterns of
warm episodes are determined by the observed
baseline climate.
The lack of changes in the daily and
interannual patterns of extreme events may result in
underestimation of impacts of climate change. This
is because runs of extreme climate variables (for
example, prolonged heat spells during grain filling
and drought) can decrease crop productivity. For
rainfed crops, yields may change considerably,
depending on whether a change in precipitation is
caused by more or fewer events or by higher or
lower precipitation per event. The frequency,
intensity, and/or duration of extreme climatic events
can be much more consequential to crop yields than
are simple changes in means.
Timing of Effects
The timing of climate change is uncertain —
rates of future emissions of trace gases, as well as
when the full magnitude of their effects will be
realized, are unknown. CO2 concentrations are
estimated to be about 450 ppm in 2030 and 555
ppm in 2060 if current emission trends continue
(Hansen et al., 1988). Other greenhouse gases
besides CO2 (e.g., methane (CH4), nitrous oxide
(N2O), and chlorofluorocarbons (CFCs)) are also
increasing. The effective doubling of CO2 means
that the combined radiative forcing of all
greenhouse gases has the same radiative forcing as
doubled CO2 (usually defined as 600 ppm). The
effective doubling of CO, concentrations will occur
around the year 2030, u current emission trends
continue. The climate change caused by an effective
doubling of CO2 may be delayed by 30 to 40 years
or longer.
99
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Chapter 6
RESULTS OF AGRICULTURAL
STUDIES
Regional Crop Modeling Studies
Design of the Studies
Widely validated crop growth models -
CERES-Wheat and CERES-Maize (Ritchie and
Otter, 1985; Jones and Kiniry, 1986) and SOYGRO
(Jones et al., 1988) - were used to simulate wheat,
corn, and soybean yields at selected geographically
distributed locations within the Great Lakes, the
Southeast, and the Great Plains. Representative
agricultural soils were modeled at each site.
California crop yield changes were predicted
separately by using an agroclimatic index. (See the
regional chapters, Chapters 14 through 17 of this
report, for descriptions of individual studies.)
Changes in temperature, precipitation, and solar
radiation were included in the crop modeling
studies. The crop models simulated both rainfed
and irrigated production systems. The crop
modeling approach allowed for analysis of
latitudinal gradients in changes in crop yields and
provided compatible results for each climate change
scenario to be used as Inputs hi the agricultural
economics study. (See Ritchie et al., Peart et al.,
and Rosenzweig, Volume C.)
The direct effects of CO2 — i.e., increased
photosynthesis and improved water-use efficiency
-- were also included with the climate change
scenarios in some model runs to evaluate the
combined effects. The direct effects were
approximated by computing ratios of elevated CO2
(660 ppm) to ambient CO2 (330 ppm) values for
daily photosynthesis (Table 6-3) and
evapotranspiration rates (see Peart et al., Volume
C, for detailed description of method).
Limitations
Uncertainties in the crop modeling studies
reside in climate model predictions, locations of the
climate stations (not always in production centers),
crop growth models, and estimates of the direct
effects of CO,. In particular, the climate change
scenarios did*^ not include changes in climate
variability, even though changes in the frequencies
of extreme events may considerably affect crop
Table 6-3. Increase in Daily Canopy Photosynthesis
Rates Used hi Crop Modeling Studies
Soybean Wheat Corn
Increase in
photosynthesis 35
25
10
Source: Peart et al. (Volume C); Ritchie et al.
(Volume C); Rosenzweig (Volume C).
yields. Technology and cultivars were assumed not
to change from present conditions.
The CERES and SOYGRO models describe
relationships between plant processes and current
climate. These relationships may or may not hold
under differing climatic conditions, particularly the
high temperatures estimated for the greenhouse
warming. Lack of analysis of the nature and extent
of agricultural soils at each modeling site adds
uncertainty to the results.
The direct effects of CO2 in the crop modeling
results maybe overestimated for two reasons. First,
experimental results from controlled environments
may show more positive effects of CO2 than would
actually occur in variable, windy, and pest-infested
(weeds, insects, and diseases) field conditions.
Second, since the study assumed higher CO2 levels
(660 ppm) in 2060 than will occur if current
emission trends continue (555 ppm), the simulated
beneficial effects of CO2 may be greater than what
will actually occur.
Under climate change scenarios alone, without
the direct effects of CO2, yields of corn, soybeans,
and wheat were generally estimated to decrease in
the Great Lakes, Southeast, arid Great Plains
regions, except in the northernmost latitudes, where
warmer conditions provided a longer frost-free
growing season. Figures 6-3 and 6-4 show change
in modeled rainfed corn and soybean yields for the
GISS and GFDL scenarios. The northern locations
where yields increased included sites in Minnesota.
100
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Agriculture
GISS +Direct Effects of COa
GFDL + Direct Effects of CO2
Figure 6-3. Percent change in rainfed corn yields simulated by the CERES-Maize model for baseline (1951-
80) and GISS and GFDL climate change scenarios with and without the direct effects of CO2 for selected
locations (Peart et al., Volume C; Ritchie et al., Volume C; Rosenzweig, Volume C).
Decreases in modeled yields resulted primarily from
higher temperatures, which would shorten the crop
life cycle thus curtailing the production of usable
biomass. In the Southeast, rainfall reductions were
a major factor in the GFDL results. Modeled
rainfed yields were estimated to decrease more than
irrigated yields.
When increased photosynthesis and improved
water-use efficiency were included in the crop
models along with the climate change scenarios,
yields increased over the baseline in some locations
but not in others (see Figures 6-3 and 6-4).
Particularly when combined with the hotter and
drier GFDL climate change scenario in the
Southeast, the direct effects of CO2 would not fully
compensate for changes in climate variables — net
yields were estimated to decrease significantly from
the base case. Elsewhere, yields were generally
estimated to increase, with relatively greater
increases at the northern locations.
The crop models were also used to test several
possible adaptations by farmers to the predicted
climate changes. For example, a corn variety that is
better adapted to longer growing seasons was tested
in Indiana. Use of this later maturing variety would
not compensate entirely for the yield decreases
caused by the warmer climate change scenarios.
101
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Chapter 6
| | GISS
GFDL
GISS +Direct Effects of CC>2
GFDL + Direct Effects of CO2
Figure 6-4. Percent change in rainfed soybean yields simulated by the SOYGRO model for baseline (1951-80)
and GISS and GFDL climate change scenarios with and without the direct effects of CO2 for selected.locations
(Peart et al., Volume C; Ritchie et al., Volume C).
Implications
The potential for climate change-induced
decreases in crop yields exists in many agricultural
regions of the United States. In some northern
areas, crop yields may increase. Farmers would
need varieties of corn, soybeans, and wheat that are
better acclimated to hotter and possibly drier
conditions to substitute for present varieties.
If the major agricultural areas are to continue
to provide a stable supply of food under the
predicted changes in climate, supplemental
irrigation may be required for many soils. Pressure
for increased irrigation may grow in these regions.
This could further tighten water supply problems in
some areas and increase pollution from nonpoint
sources (i.e., pollution that is not traceable to any
one distinct source, such as agricultural chemicals
from farmers' fields). Considerable uncertainty
exists regarding the future availability of surface
water and groundwater supplies with climate
change, and concerning the competing demands for
and costs of using or extracting the water (see
Chapter 9: Water Resources).
Regional and National Economics Study
The estimated yield changes from the crop
modeling studies (not including California) and
102
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Agriculture
projected changes in irrigation water demand and
availability were introduced into an agricultural
economic model to translate the physical effects of
climate change into economic consequences.
Adams et al. (see Volume C) estimated the regional
and national economic implications of changes in
yields of wheat, corn, soybeans, and other crops and
in the demand for and availability of water
associated with alternative global climate change
scenarios.
Study Design
A spatial equilibrium agricultural model
developed by Adams et al. (1984) was used to
represent production and consumption of numerous
agricultural commodities for the U.S. farm
production regions as designated by the USDA
(Figure 6-5). The model has been used to estimate
agricultural losses due to increased ultraviolet-B
(UV-B) radiation caused by stratospheric ozone
depletion (Adams et al., 1984). It consists of farm-
level models for production regions, integrated with
a national-level model of the agricultural sector.
Acreage available for production is based on current
definition of agricultural land classes. Both irrigated
and nonirrigated crop production and water supply
relationships are included for most regions. The
model simulates a long-run, perfectly competitive
equilibrium and was developed using 1980-83
economic and environmental parameters.
A set of model runs was conducted, using the
GISS and GFDL climate change scenarios, with and
without the direct effects on crop yields. Potential
changes in technology and in future U.S. and world
food demand due to population growth were also
introduced into the climate change analysis.
Limitations
The economic approach used in this study has
several limitations. The economic model is static in
the sense that it simulates an equilibrium response
to climate change, rather than a path of future
changes. Substitution of crop varieties, new crops,
and adjustments hi farm management techniques
were not included; thus, the negative effects of
Figure 6-5. Farm production regions in the United States (USDA, 1976).
103
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Chapter 6
climate change were possibly overestimated. Since
CO2 levels were assumed to be high in the crop
modeling study, estimates of the beneficial direct
effects of CO2 on crop yields may have biased the
economic results in the positive direction in some
scenarios.
Furthermore, changes in yields used as inputs
to the economic model were modeled for only
wheat, corn, and soybeans for a limited number of
sites and regions. The regional crop yield analyses
cover 72% of current U.S. corn production, 33% of
wheat production, and 57% of the soybean output.
National estimates were extrapolated from these for
all other crop commodities in the model. Changes
in risk, where risk is defined as increases in variance
of crop yields, were not explicitly included in the
economic analysis. The accuracy of the estimates of
changes in water supply and crop water
requirements derived from the GCMs cannot be
ascertained. Potential increases in the demand for
water by nonagricultural users, which would reduce
water available for irrigation, were not included. All
of these assumptions introduce uncertainties into
the results.
Potential changes in international agricultural
supply, demand, and prices due to climate change
are not explicitly included hi the model. Such
changes could have major impacts on U.S.
agriculture. For example, warming may enhance
the agricultural capabilities of high-latitude countries
such as Canada and the U.S.S.R. While the net
effect of climate change on the rest of the world is
uncertain, global changes could overwhelm U.S.
national impacts. A net negative effect on
agriculture abroad would improve the position of
U.S. agricultural producers through enhanced
exports, but could increase the negative impacts on
U.S. consumers through increases in global
commodity prices.
Results
It is important to note that the results of the
economic study are not predictions. Rather, they
are initial estimates of how the current agricultural
system would respond to the projected climate
change scenarios.
The economic model showed a small to
moderate aggregate loss in economic welfare
associated with the estimated crop yield and
hydrologic changes derived from the climate change
scenarios (see Table 6-4). For the moderate GISS
climate change scenario, net losses were small; for
Table 6-4. Aggregate Economic Effects of GISS and GFDL Doubled CO2 Climate Change on U.S.
Agriculture with and without the Direct Effects of CO2 on Crop Yields
Economic effects
(billions of 1982 dollars')
Run
GISS Analysis 4a:
without CO2
GISS Analysis 4:
with CO2
GFDL Analysis 4:
without CO2
GFDL Analysis 4:
withCO2
Consumer
-7.3
9.4
-37.5
-10.3
Producer
1.5
1.3
3.9
0.6
Total
-5.9
10.6
-33.6
-9.7
Analysis 4 includes the crop yield and irrigation water supply and demand consequences of climate change
throughout the United States.
Source: Adams et al. (Volume C).
104
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Agriculture
the more extreme GFDL scenario, they were
greater. The magnitudes of these changes, which
are annual, may be compared with the estimated
$2.5 billion (in 1982 dollars) in agricultural losses
due to increased UV-B radiation caused by
stratospheric ozone depletion of 15% (Adams et al.,
1984). In general, consumers lose and producers
gain because of the increased prices of agricultural
commodities and inelastic demand (i.e., insensitivity
to price changes) for agricultural crops.
Higher CO2 levels could reduce negative
economic impacts (Table 6-4). Under the less
severe GISS climate scenario, the CO2 direct effects
were estimated to sufficiently counter the climatic
effects in most regions, so that both producers and
consumers gain. With the more severe GFDL
climate change scenario combined with the direct
effects of CO2, lower yields led to higher prices, but
not by as much as occurred with the climate change
scenarios alone. However, significant changes in
regional agricultural land use occurred even when
the beneficial direct effects of CO2 were taken into
account.
Production of most crops was reduced because
of yield declines and limited availability of land and
resources. With climate change alone, corn
production decreased 12 and 47% in the GISS and
GFDL scenarios, respectively, while soybean
production was estimated to be reduced by 12 and
53% for the same scenarios. In all scenarios, land
under production in Appalachia, the Southeast, the
Mississippi Delta, and the Southern Plains could
decrease on average by 11 to 37%, while in the
Lake States, the Northern Plains, and the Pacific it
could increase by small amounts (see Figure 6-6).
While availability of agricultural soils was included
in the economic analysis, the sustainability of crop
production in northern areas was not studied.
Irrigated acreage was estimated to increase in
all areas, primarily because irrigation becomes
economically feasible as agricultural prices rise (see
Figure 6-7). These changes reflect both increased
demand by farmers for irrigation water and changes
in water availability as estimated by the GCM
scenarios, but do not take into account changes in
competition with industrial or municipal users.
I | GISS
JIM GFDL
GISS +Direct Effects of OO2
GFDL + Direct Effects of CO2
Figure 6-6. Percent change in regional agricultural acreage simulated by an economic model of the U.S.
agricultural sector for the GISS and GFDL climate change scenarios with and without the direct effects of CO2
on crop yields (Adams et al., Volume C).
105
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Chapter 6
P.cilto I I GISS
GFDL
[552 Glss +Dlrect Effects of COz
HI GFDL+Direct Effects of C02
Southern Plains
Figure 6-7. Change (100,000s of acres) in regional irrigation acreage simulated by an economic model of the
U.S. agricultural sector for the GISS and GFDL climate change scenarios with and without the direct effects of
CO2 on crop yields. Changes are not shown in the Great Lakes, Corn Belt, Appalachia, and Northeast because
currently irrigated acreage is small (2% of total U.S. irrigated acreage) in these regions (Adams et al.,
Volume C).
Technological changes, such as higher yielding
crop varieties, chemicals, fertilizers, and mechanical
power, have historically enabled agriculture to
increase production with the same amount of, or
less, land, labor, and other resources. When the
effect of future technological change (based on yield
increases from 1955 to 1987) was modeled along
with the less severe GISS climate change (without
the direct effects of CO2), most of the adverse
climate effects were estimated to be offset. Under
the severe GFDL climate change scenario,
continued and substantial improvements in yields
would be required to overcome the climate change
effects. Stated another way, the adverse effects of
climate change could negate most of the higher
output attributable to improved technology over the
next 50 years. It is important to note, however, that
the rate of future technological advances is very
difficult to predict. Increasing food demand from
higher TLS. and world population aggravated the
estimated economic losses from the climate change
scenarios.
Implications
Food Supply and Exports
The economic analysis implies that although
climate change could reduce the productive capacity
of U.S. agriculture, major disruption in the supply of
basic commodities for American consumers would
not occur. Domestic consumers would face slightly
to moderately higher prices under some analyses,
but supplies could be adequate to meet current and
projected domestic demand. However, if droughts
occur more frequently under changed climate,
effects on agriculture may be more severe.
Exported commodities in some scenarios
decline by up to 70%, assuming the demand for
exports remains constant. Thus, climate change
could affect the United States in its role as a
reliable supplier of agricultural export commodities.
It is likely that supply of and demand for
106
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Agriculture
agricultural commodities could shift among
international regions, and responses of U.S.
agriculture will take place in this global context.
There is a great need to determine the nature of
these changes in global agriculture by analyzing the
potential impacts of climate change on both major
world agricultural production regions and potentially
vulnerable food deficit regions.
Regional Economics and Land Use
Regional shifts in U.S. agricultural production
patterns (not only grain crops but also vegetables
and fruits) are highly likely, as all climate change
scenarios tested show that the southern areas of the
United States become less productive relative to the
northern areas. This is primarily because the high
temperatures estimated for climate change would
stress crop production more in southern areas than
in northern areas where crops are currently limited
by lower temperatures and shorter growing seasons.
However, increased agricultural production may be
difficult to sustain in the North, because some soils
may be less fertile and may have lower water-
holding capacity. Crops grown in soils with lower
water-holding capacity require more evenly
distributed rainfall to produce comparable yields.
Regional changes in agriculture would have
important implications for rural communities. As
production areas shift, climate change effects would
reverberate through these communities and are
likely to result in structural changes in local
economies, such as relocation of markets and
transportation networks. At its most extreme,
climate change could cause dislocation of rural
communities through farm abandonment.
Environmental Concerns
Regional agricultural adjustments could place
environmental resources at risk. Where agricultural
acreage would increase, demands for natural
resources, such as soil and water, might intensify
current pressures on environmental elements, such
as rivers, lakes, aquifers, wetlands, and wildlife
habitats. Northern States, such as Minnesota and
North Dakota, could become more productive for
annual crops like corn and soybeans because of
warmer temperatures and a longer frost-free
growing season. Given the presence of forests and
wetlands in these regions, increased agricultural
production in the area might threaten natural
ecosystems, including wildlife habitats such as
prairie potholes for ducks and flyways for bird
migrations.
In addition, many of the glacial till soils in the
northern latitudes are not as productive as Corn
Belt soils. Thus, large increases in production of
crops would most likely require greater applications
of chemical fertilizers. The use of these fertilizers
in humid regions on glacial till and sandy soils is
now creating an environmental hazard to the
underlying groundwater, receiving waters, and
aquatic habitats in many areas. With climate
change, water and fertilizer use would have to be
carefully managed to minimize still more leaching of
water-soluble nutrients such as nitrogen and potash.
Demand for Water for Irrigation
Water is the single most critical factor in
determining the development, survival, and
productivity of crops. The amount of water that
crops use and thus the demand for irritation water
are governed largely by the evaporation process.
Higher air temperatures due to increasing trace
gases hi the atmosphere could heighten evaporative
demands. Increased irrigation to satisfy these
higher demands could accelerate depletion of
groundwater and surface water resources. Also, the
rate of evaporation might outstrip precipitation, thus
decreasing crop yields.
Studies reported in the California and the
Great Plains case studies (see Chapters 14 and 15)
explicitly examined the potential changes in demand
for water for irrigation. The studies did not
consider changes hi competing demands for water
such as industrial and residential use, which also
may change in a warmer climate. The California
study, however, considered changes hi supply due to
earlier snowmelt and sea level rise. In these
regions, water is a critical resource for agriculture;
California and the parts of the Great Plains fed by
the Ogallala Aquifer, in particular, depend very
heavily on irrigation for crop production.
Irrigation Requirements in the Great Plains
Allen and Gichuki (see Volume C) computed
irrigation water requirements for sites in the Great
Plains for the baseline climate and the GISS and
GFDL climate change scenarios. The direct effect
of CO2 on water use was also included. (For study
design and limitations, see Chapter 17: Great
Plains.) Major changes in irrigation water
107
-------
Chapter 6
requirements were estimated for all locations in the
Great Plains and for all crops (see Figure 6-8). The
most significant would be the persistent increases in
seasonal net irrigation water requirements for
alfalfa, which would be driven by the climate
changes in temperature, wind, humidity, and solar
radiation, and by the lengthening of the growing
season. Decreases in irrigation requirements were
estimated for winter wheat in most regions. These
decreases would be the result of earlier planting
dates and shorter crop life cycle due to high
temperatures. When crop varieties appropriate to
the longer growing season were modeled, irrigation
water requirements for winter wheat were estimated
to increase. Simulated irrigation water
requirements during peak periods increased in
almost all areas (see Figure 6-9).
ALFALFA
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i 20
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-
-
-
-
~ ^
wi/.
P"
^
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K^
1>>V
—
^
6
n
-
.
-
-
_
Nebraska Kansas Oklahoma Texas
CORN
I 20
I"
* n
1
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-
-I
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i — |
P5?
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-
Nebraska Kansas Oklahoma Texas
WHEAT
i o
i "*
i:
f '"
° .18
I'"
a .«
P7TH
1
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y
1 1
1
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-
0 GISS
I | GFDU
Nooraska Kansas Oklahoma Texas
Figure 6-8. Percent change in net seasonal
irrigation requirements for GISS and GFDL climate
change scenarios with direct effect of CO, on crop
water use included (Allen and Gichuki, Volume C).
Figure 6-9. Percent change in peak irrigation
requirements of corn for GISS and GFDL climate
change scenarios with direct effect of CO, on crop
water use included (Allen and Gichuki, Volume C).
While farmers in the Great Plains would
probably shift to longer season crops, climate
change conditions (warmer temperatures and drying
in some areas) during the later summer months
could increase irrigation requirements and elevate
leaf temperatures to a point that exceeds optimum
temperatures required for high productivity. This
might make it uneconomical to take full advantage
of the longer growing season, especially if the higher
CO2 levels increase photosynthesis and offset the
effects of a shorter season to some degree.
Water Resources for Agriculture in California
In the California regional case study, Dudek
(see Volume C) characterized the potential shifts in
demand for water for agricultural production that
would accompany shifts in cropping patterns driven
by changing climate. Changes in competing
demands for water from industrial or municipal
users were not considered. (For description of
study design and limitations, see Chapter 14:
California.) When climate change was considered
alone, groundwater extraction and surface water use
were estimated to decline in California as a result of
changes in both supply of (derived from GCM
climate change scenarios) and agricultural demand
for water. When the direct effects of CO2 on crop
yields were included, groundwater extraction would
increase because of improved yields of all crops
108
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Agriculture
except corn and because of enhanced economic
welfare. Institutional responses to changes in
surface and groundwater use could include water
transfers, which could improve irrigation efficiency.
When water markets were included in the
simulations, economic welfare was improved by 6 to
15% over the base, while crop acreage increased
and groundwater extraction decreased.
Implications for Demand for Irrigation Water
Expanded use of irrigation is implied from the
regional crop modeling studies for the Great Lakes,
the Southeast, and the Great Plains (see Chapters
15, 16, and 17, respectively). Increases in irrigated
acreage are also estimated for most regions when
the economics of crop production are factored in
(see Adams et al., Volume C). When these results
are considered along with the irrigation studies, it
appears that climate change is likely to increase the
demand for water from the agricultural sector in
many regions.
In the Great Plains, heightened evaporative
demand and variability of rainfall may increase the
need for irrigation in dryland farming regions. The
simulated changes in irrigation water requirements
are varied, and specific crops and locations probably
would be affected differently. Higher peak
irrigation water requirements for some crops may
require larger capacity irrigation systems and may
enlarge energy demands.
Intensified extraction of water poses serious
environmental and economic problems, especially in
areas where groundwater is being overdrawn.
Streamflows also may slacken if more surface water
is used for irrigation, thereby aggravating water
quality problems. This in turn would harm fish,
wildlife, and recreational activities.
Regional changes in cropping locations and
patterns of water use also could exacerbate
agricultural, nonpoint source pollution, and could
further deplete groundwater resources, institutional
responses, such as markets for water transfers,
could help improve irrigation water management
and alleviate some of these negative effects.
The economic and social costs of shifting the
location of irrigated agriculture could be
considerable. The construction of irrigation systems
consisting of reservoirs, wells, ditches, pipes, pumps,
and sprinklers currently requires about $1,500 to
$5,000 per hectare in capital investment (Postel,
1986).
Direct Effects of CO2 on Crops
Global increases in CO, are likely to influence
crop metabolism, growth, aria development directly
through physiological processes and indirectly
through climate. Rose (see Volume C) reviewed
recent experimental work performed on the direct
effects of CO2 on crops, with emphasis on wheat,
corn, soybeans, and cotton.
Elevated concentrations of CO2 directly affect
plant processes such as photosynthesis and
transpiration. Higher CO2 concentrations are also
expected to influence these processes indirectly
through predicted increases in temperature and
other changes in climate variables such as
precipitation. Because experimental research has
rarely simultaneously studied both the direct and
indirect effects of plant responses, it is difficult to
assess the relative contributions of elevated CO2
and climate changes to predictions of crop
responses.
Research on the physiological effects has
focused primarily on responses of rates of
photosynthesis and transpiration to increasing
concentrations of atmospheric CO2. Photosynthesis
rates have increased in these crops in relatively ideal
experimental environments. At moderate
temperatures, most crops will probably show
increases in size and possibly yield as CO2
concentrations rise. However, plants also have
internal regulation mechanisms that may lessen
these effects under field conditions.
Transpiration rates per unit leaf area decrease,
while total transpiration from the entire plant
sometimes increases because of greater leaf area.
Drought-stressed plants exposed to high partial
pressures of CC^ should be better able to cope with
water deficits. Leaf temperatures in all species are
expected to rise even more than air temperatures;
this may inhibit plant processes that are sensitive to
high temperature.
Few studies have examined the interactive
effects of CO2, water, nutrients, light, temperature,
pollutants, and sensitivity to daylength on
photosynthesis and transpiration. Even fewer
109
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Chapter 6
studies have examined the effects of these
interactions on the growth and development of the
whole plant. Therefore, considerable uncertainty
exists concerning the extent to which the beneficial
effects of increasing CO2 will be seen in crops
growing in the field under normal farming
conditions with climate change.
Climate Impacts on Pest-Plant
Interactions
Compared with the existing information on the
potential effects of climate change on crop
production, relatively little effort has been directed
toward assessing the influence of climate change on
plant-pest interactions. Atmospheric increases in
temperature and CO,, and changes in moisture
regimes, all can directly or indirectly affect
interactions between pests and crops. Changes in
pests will also depend on regional shifts in crop
production. Although crop pests may be defined as
weeds, insects, or disease pathogens, the EPA work
on this subject focused on insects.
Study Design and Results
Stinner et al. (see Volume C) conducted a
literature survey and modeling experiments on the
major mechanisms through which climate change
may affect pest-plant interactions. This study
emphasized the major insect pest and pathogen
species of corn and soybeans. The survey indicates
that temperature and precipitation patterns are the
key variables that affect crop-pest interactions. The
temperature increases associated with the climate
change scenarios would bring about the following
trends: (1) increased survival for migratory and
nonmigratory insect pest species in the whiter; (2)
northern range extensions of current pests hi the
higher latitudes and migration of southern species
into the northern Grain Belt regions; (3) an increase
in pest species with more than one generation per
year in the northern Grain Belt; (4) earlier
establishment of pest populations in the growing
season; and (5) increased abundance of pests during
more susceptible crop growth stages.
The potential changes in the overwintering
ranges of four major pests were mapped for the
GISS and GFDL climate change scenarios and were
compared to present ranges. The overwintering
capability of the four major pests may extend
northward with both climate change scenarios.
For example, the potato leafhopper, a serious pest
on soybeans and other crops, at present overwinters
only hi a narrow band along the coast of the Gulf of
Mexico (Figure 6-10). Warmer winter temperatures
in the GFDL and GISS scenarios could cause a
doubling or tripling of the overwintering range hi
the United States, respectively. This would increase
the invasion populations hi the northern states by
similar factors. The invasions also would be earlier
hi the growing season, assuming planting dates do
not change. Both features are likely to lead to
greater insect density and damage. This pattern is
repeated with the other three pests studied and
indicates that these pests, and possibly others, may
move northward and invade cropping systems earlier
in the growing season under climate change
conditions.
Potato leafhopper
GISS
GFDL
Present
Figure 6-10. Present and potential (GISS and
GFDL climate change scenarios) overwintering
range of the potato leafhopper, Empoasca fabae. a
major pest of soybeans (Stinner et al., Volume C).
The Soybean Integrated Crop Management
(SICM) model (Jones et al., 1986) was run with the
GISS and GFDL climate change scenarios to
estimate changes hi damages caused by corn
earworm. Modeling results show that earworm
damage to soybeans would increase hi severity in
the Grain Belt under a warmer climate. Such
damage could cause grain farmers hi the Midwest to
suffer significant economic losses. These results
were particularly marked with the warmer and drier
GFDL scenario.
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Agriculture
Limitations
Lack of knowledge about the physiological
effects of CO, on crop plants and lack of
experimental evidence of direct CO2 effects on
insect-plant interactions make the study of pest-
plant interactions particularly difficult. Only one
cultivar was used in the modeling study under both
the baseline and the climate change scenarios, and
planting dates remained the same. In reality,
farmers would probably switch to a more
climatically adapted cultivar as climate changed, and
they would advance planting dates in response to
longer growing seasons.
Implications
Increased pest-related crop damage could
intensify pesticide use. The economic and
environmental ramifications of such an increase
could be substantial, not only in current farming
regions but also in new areas if agriculture shifts to
the more northern regions such as the northern
Plains, the Great Lakes States, and the Pacific
Northwest (see Figure 6-6).
Increased use of pesticides would create
additional threats to the integrity of ecosystems
through soil and water contamination and could
increase risks to public health. If agricultural
production is not to rely increasingly on chemicals
that are potentially harmful to the environment, an
increased need will exist for alternative pest
management strategies such as biological control,
genetic resistance, and innovative cropping systems.
Effects of Climate Change on Water
Quality
Agricultural pesticides are ranked as a high-
priority pollution problem in many rural regions.
Potentially toxic agricultural chemicals can be
transported away from fields via runoff of surface
soils and via downward leaching and percolation
through the soil. An understanding of these
processes is needed to evaluate potential threats to
drinking water quality caused by climate change.
Study Design
Johnson et al. (see Volume C) modeled the
partitioning of agricultural pesticides among uptake,
degradation, surface runoff, and soil leaching for
wheat, corn, and cotton production regions in the
Great Plains and the Corn Belt. (For details of the
study, see Chapter 17: Great Plains.) They used
the Pesticide Root Zone Model (PRZM) (Carsel et
al., 1984), which simulates the vertical movement of
pesticides in the soil. The model consists of
hydrological and chemical transport components
that simulate runoff, erosion, plant uptake, leaching,
decay, foliar washoff, and volatilization of a
pesticide. The interactions among soil, tillage,
management systems, pesticide transport, and
climate change were studied.
Limitations
The frequency and duration of precipitation
remain the same in the climate change scenarios,
even though these storm characteristics are critical
factors in determining the transport of agricultural
chemicals and may change. The scenarios assume
that the number of days with rainfall does not
change, but the intensity of rainfall increases or
decreases. Runoff and leaching estimates would
most likely be different if the number of days of
rainfall changed and daily rainfall amounts were
held constant.
The PRZM is a one-dimensional, point model
that does not simulate the transport of water below
the root zone. Thus, results on a regional basis
must be extrapolated with care. The direct effects
of CO2 on crop growth, which may increase the size
of the plants and the extent to which crops cover
the soil, are not included.
Results
Regional changes in chemical loadings of
water and sediment are likely due to climate change
but probably will not be uniform. There appears to
be some consensus between the GCM scenarios
concerning the estimated regional changes (Table
6-5). Modeled pesticides in runoff increase in the
cotton production area, and pesticides carried by
sediments decrease in the spring wheat and corn
regions. Leaching of pesticides tends to be less
everywhere owing to changes in seasonal
precipitation and increased evaporation.
Implications
When the changes in water quality from the
predicted climate change scenarios are considered
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Chapter 6
Table 6-5. Summary of GISS and GFDL GCM Model Consensus of PRZM Pesticide Transport by Cropping
Region and Pesticide3
Crop and
pesticide type
Surface
pesticide
runoff losses
Surface
pesticide
erosion losses
Pesticide
leaching
Spring wheat
Highly soluble/short-livedb
Highly soluble/long-lived
Slightly soluble/long-lived
Winter wheat
Highly soluble/short-lived
Highly soluble/long-lived
Slightly soluble/long-lived
Cotton
Highly soluble/short-lived
Highly soluble/long-lived
Slightly soluble/long-lived
Corn
Highly soluble/short-lived
Highly soluble/long-lived
Slightly soluble/long-lived
+ indicates that median values increase under climate change; - indicates that median values decrease under
climate change; blank indicates no consensus among median values.
Example: median value of all tillage, soil, weather site scenarios for highly soluble/short-lived pesticides in the
spring wheat crop area.
Source: Johnson et al. (Volume C).
in conjunction with the estimated increases in pests
and implied higher applications of pesticides
described in the study on pest-plant interactions, the
potential for changes in the nation's water quality
becomes apparent. Any deterioration in water
quality could adversely affect public drinking water
supplies and human health.
Climate Variability
The impacts of climate change result not only
from a slow change in the mean of a climate
variable but often from shifts in the frequency of
extreme events. Droughts, freezes, and prolonged
periods of hot weather have strong effects on
agricultural production. Although the agricultural
modeling studies did not include the effects of
potential changes in climate variability, a review of
literature on agriculture and extreme events that
focuses on the nature and magnitudes of significant
impacts is included in Chapter 3: Climate
Variability.
Corn, soybeans, wheat, and sorghum are
sensitive to high maximum temperatures during
blooming. Lower yields of corn, wheat, and
soybeans have been correlated with high
temperatures. The damaging effect of runs of hot
days on corn yields was particularly evident in the
U.S. Corn Belt in 1983.
Although the problems associated with low
temperatures may diminish with climate change,
risks of frost damage to crops may change in the
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Agriculture
growing areas of certain crops. Citrus trees are very
vulnerable to low minimum temperatures. Winter
wheat is often damaged by low temperatures known
as winter kill, especially in the absence of snow.
Even with warmer winters and fewer frosts, more
damage may occur at less extreme temperatures.
For example, the effect of freezing temperatures is
exacerbated if crops have not yet been hardened by
cold temperatures or if the crops are no longer
dormant and a cold snap occurs.
Drought is a major cause of year-to-year
variability in crop production. In the Dust Bowl
years of the 1930s, yields of wheat and corn in the
Great Plains dropped to as much as 50% below
normal. In 1988, agricultural disaster in areas of the
northern Great Plains demonstrated a high
vulnerability to drought, and nationwide corn yields
decreased by nearly 40%. Reduction in vegetative
cover associated with drought also brings about
severe wind erosion of soils, which will affect future
crop productivity. Low yields of forage crops during
droughts result in food shortages for livestock and
premature selling of livestock. If frequency of
drought increases with climate change, impacts on
agriculture can be severe.
Farm-Level Management and Adjustments
to Climate Change
Adjustments to existing production practices
would be the first course of action in the face of
climate change. The net effect of climate change
with adjustment by farmers may be significantly
different from the estimated effects of climate
change alone.
Study Design
Several studies addressed possible adjustments
that could modify the effects of climate change.
These adjustments include changes in planting and
harvesting dates, tillage practices, crop varieties,
application of agricultural chemicals, irrigation
technology, and institutional responses for water
resource management.
Results
Ritchie et al. demonstrated that the yield
reduction in corn in the Great Lakes could be partly
overcome with selection of new varieties that have
a longer growing season (see Chapter 15: Great
Lakes). Rosenzweig (see Chapter 17: Great Plains)
showed that adjusting the planting date of winter
wheat to later in the fall would not ameliorate the
effects of climate change, but that changing to
varieties more suited to the predicted climate could
overcome yield decreases at some locations.
Dudek's California study found that flexible
institutional responses to climate change would help
to compensate partly for negative climate change
effects (see Chapter 14: California). By allowing
movement of water around the state by transferral
of water rights, California's water resource
managers could alleviate some groundwater
extraction and compensate, for surface water
reductions.
Easterling (see Chapter 15: Great Lakes)
found that potential farmer adjustments to climate
change include changes in tillage practices,
increased application of fertilizers, selection of more
full-season and heat-resistant varieties, changes in
planting densities, higher use of pesticides, earlier
harvest, and reduced artificial drying. Different
adjustments could occur at different times in the
cropping season. With the hotter and drier GFDL
scenario, farmers may have to adopt production
practices different from those in use today. Climate
changes that leave soils drier during summer than
they are at present will most likely lead to an
increased use of irrigation in the Corn Belt. This
increased irrigation is also supported by the
projected price increases for all crops grown in
Illinois.
Implications
Although detrimental climate change effects on
agriculture may be partly offset naturally by
Increased photosynthesis and water-use efficiency
caused by higher levels of atmospheric carbon
dioxide, farmers themselves would use a variety of
adjustments to adapt to climate change. Market
forces also would aid adaptation to climate change
because they help to allocate resources efficiently.
Each crop and region would respond differently to
climate change, and adjustment strategies would
need to be tailored to each situation.
Costs of adjustments are likely to vary
considerably from region to region. Costs would be
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Chapter 6
relatively small in regions where fanners can switch
from one variety to another or from one grain crop
to another, thus enabling continued use of existing
farm machinery and marketing outlets. However, at
locations near the present limit of major agricultural
regions (e.g., the boundary between wheat farming
and ranching), relatively small changes in climate
may require a substantial switch in type of farming.
This may require substantial costs in new equipment
and other changes in agricultural infrastructure.
Severe climate change may necessitate farm
abandonment in some regions.
Improvements in agricultural technology also
may be expected to ease adjustment through
development of appropriate farming practices, crop
varieties, and livestock species. Adjustment and
adaptation to climate change should be included in
agricultural research programs to enable this
process to occur.
Livestock
Animal products are a critical source of
protein, energy, vitamins, and minerals. U.S.
livestock production, mainly from cattle, swine,
sheep, and poultry, was estimated to be worth over
$31 billion in 1986 (USDA, 1987).
Climate is known to significantly affect many
aspects of animal health and production. The direct
effects of climate warming on animal health include
differences in incidence of heat and cold stress,
changes in weight gain, and decline in reproductive
capabilities. Indirect effects may involve trends in
the availability and prices of animal feeds and the
expanded geographic distribution and activity of
disease-carrying vectors.
Higher winter temperatures may lower the
incidence of respiratory diseases in livestock
(Webster, 1981). Conversely, warmer summers may
necessitate more hours of indoor cooling during
which pathogens are confined to housing structures.
Climate warming may significantly increase the costs
of air-conditioning in poultry housing. Changes in
reproductive capabilities such as decreased ovulation
rates, shortened intensity and duration of estrus,
decreased fertility of males, and increased
embryonic mortality also have been shown to occur
with high temperatures (Ames, 1981).
Climate change may also affect the
survivability, activity, and geographic distribution of
vectors responsible for the transmission of infectious
diseases in livestock. The activity and reproduction
of disease-carrying vectors infecting livestock,
humans, and crops are driven primarily by
temperature, humidity, and precipitation. These
impacts are likely to be similar to those on mortality
and morbidity of disease in humans (see Chapter
12: Human Health), and they also are similar to
changes predicted for crop pests.
Design of Studies
Stem et al. (see Volume C) studied the
available literature on four livestock diseases to
evaluate the range of potential changes in disease
distribution and occurrence under climate change
conditions. Schmidtmann and Miller (see Volume
C) used a population dynamics simulation model to
estimate the effects of the GFDL climate change
scenario on the life cycle of the horn fly, a
ubiquitous pest of pastured cattle throughout the
United States.
Limitations
The horn fly model is based on population
counts taken at various times under different
weather and management conditions. However, the
prediction of current horn fly populations appears to
be well correlated with observations. The model is
not validated for the high temperatures predicted
for the climate change. Schmidtmann and Miller
used only the hottest cliniate change scenario,
GFDL; the other scenarios may have resulted in a
smaller geographic shift in the range of the horn fly.
It should also be noted that the horn fly analysis is
based on current livestock management, breeds, and
distribution. Possible changes in these factors are
beyond the scope of this study. For example,
changes in location and extent of grassland regions
and forage production caused by climate warming
would affect livestock production and horn fly
distributions.
Stem et al. found that under warmer
conditions, livestock diseases currently causing
serious economic losses in tropical countries could
spread into the United States. Rift Valley fever is
transmitted principally by mosquitoes, and the
disease may spread as rising winter temperatures
become able to support an increase in the mosquito
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Agriculture
population (see Figure 6-11). African swine fever
also may become a greater threat.
The ranges and activities of disease-carrying
agents of blue tongue and anaplasmosis, diseases
currently causing severe losses in cattle and sheep
production in the United States, may expand. If
disease-carrying insects increase their winter survival
and reproduce year-round in more states, the
geographical distribution of blue tongue, which is
caused by a virus, may expand northward and
eastward. Anaplasmosis, a rickettsial infection of
ruminants, is the second most important disease of
cattle in the United States. Distribution of the
insect carrier's habitat could expand to northern
states with climate change, and the insects' day-to-
day activity may increase; this process may also
cause an increase in disease transmission.
The horn fly causes annual losses of $730.3
million in the beef and dairy cattle industries
(Drummond, 1987). Schmidtmann and Miller found
that with the very warm GFDL climate change
scenario, the horn fly season throughout most of the
United States could be extended by 8 to 10 weeks.
The increase in horn fly populations could
substantially reduce the average daily gain of
growing beef cattle. Also under the GFDL
simulation, increased pest activity was estimated in
dairy cattle in the North and Northwest -- a result
that could significantly decrease milk production.
Conversely, under the same scenario, the
summertime activity of the horn fly could decrease
in the South because the warmer climate would
exceed the horn fly's tolerance to high temperatures.
Implications
With climate change, patterns of livestock
diseases and pests may also change. Tropical
livestock diseases may become an increased threat,
because more geographical areas are potential
ranges for the insect carriers of the diseases.
Temperature conditions may improve in the winter
but may be exacerbated in the summer.
Reproductive capabilities may be lower. Livestock
production would also be affected if rangeland areas
shift and forage production levels change.
| CURRENT & DOUBLED CO2
! DOUBLED CO2
Figure 6-11. States where significant Culex spp. activity permits establishment of Rift Valley fever for current
and doubled CO2 levels (Stem et al., Volume C).
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Chapter 6
ECONOMIC AND ECOLOGICAL
IMPLICATIONS OF
AGRICULTURAL STUDIES
The U.S. agricultural system has historically
been able to adopt new technologies rapidly and
may be less vulnerable to climate change than
natural ecosystems. In fact, global warming may
cause a number of benefits. Potential benefits of
CO2-induced climate change include increases in
length of growing season and hi air temperatures,
which would benefit regions where crop growth is
constrained by short summers and low
temperatures. Longer growing seasons would likely
lead to increased yields of hay and other perennial
crops. Energy costs for grain drying may be
reduced, since annual crops would reach maturity
earlier and would have more opportunity to dry in
the fields. Furthermore, in places where
precipitation increases during the growing season,
irrigation requirements could be reduced. If
irrigation requirements are lessened, demand on
regional water resources and associated costs to
farmers may fall.
However, many reasons to avoid complacency
about the predicted climate change remain.
Concern for our major resources (especially land
and water), rural communities, and the environment
is justified. While many critical uncertainties exist
regarding the magnitude and timing of impacts, it
appears that climate change is likely to affect U.S.
agriculture significantly in the coming century.
Costs and Timing of Adjustment
Since our agricultural production system
primarily consists of specialized farms producing
commodities in geographically specialized
production patterns, the costs of adjusting to
changed comparative advantage among agricultural
regions, with ensuing changed resource use and
changed agricultural infrastructure, may be quite
high in some regions. These shifts would also entail
involvement of and costs to the federal government.
If warming occurs rapidly, U.S. agriculture will
have less tune to adjust and costs may be greater.
As climate continues to warm, costs may rise at an
increasing rate. Finally, unless CO2 and other trace
gas emissions are limited, we may be facing a
continual and possibly accelerating rate of
atmospheric accumulations and climate change. As
the agricultural system strives to adapt to a changing
climate, there may be no chance of optimizing for
static conditions. Rather, the system maybe caught
in forever playing catch-up.
Effects of CO2
It is also important to note that the crop
modeling studies showed that the direct CCueffects
on crop photosynthesis and water-use efficiency
ameliorate the negative effects of climate change in
some locations under certain climate conditions;
however, such, effects do not occur uniformly, and
they do not occur everywhere. Regional changes in
U.S. agriculture occurred with the GISS and GFDL
climate change scenarios both with and without the
direct effects of CO2- While much work must be
done to improve both climate and crop models,
policy analysis should consider that the beneficial
direct effects of CO2 may not offset the negative
effects of climate change.
Environmental Quality
Changes in the agricultural production system
are likely to have significant impacts on resource
use and the environment. Many of the agricultural
studies suggest that climate warming could result in
accelerated rates of demand for water for irrigation
(see Chapter 9: Water Resources), increases in
pesticide usage to control changes in pest vectors,
and changes in water quality from agricultural
chemicals. Decreases in biological diversity may
limit the adaptive capacity of agriculture, which
requires a broad base of germ plasm for modifying
current crops and developing new ones (see Chapter
8: Biodiversity).
A northward migration of agriculture would
increase the use of irrigation and fertilizers on sandy
soils, thus endangering underlying groundwater
quality. From South Dakota to southern Canada,
critical prairie wetlands may be lost to drainage and
conversion to cropland. Many of these areas are
important wildlife habitats. Shifts in agricultural
activities may increase the susceptibility of soils to
wind and water erosion. Climate change could thus
exacerbate many of the current trends in
environmental pollution and resource use associated
with agriculture as well as initiate new ones.
Sea level rise; an associated impact of climate
change, will threaten low-lying coastal agricultural
regions with seasonal -- and in some instances
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Agriculture
permanent ~ flooding, saltwater intrusion of
freshwater aquifers and rivers, and salt
contamination of soils. Agricultural lands in coastal
regions may be lost. (See Chapter 9: Water
Resources, and Chapter 7: Sea Level Rise, for
linkages with agriculture.)
Furthermore, climate change will act on
agriculture simultaneously with other environmental
stresses. Levels of UV-B radiation caused by
depletion of stratospheric ozone are likely to
increase in the future, as are levels of tropospheric
ozone and acid precipitation. The interactions
among these multiple stresses and climate change
need to be studied in agricultural settings.
Global Agriculture
Finally, U.S. agriculture is an integral part of
the global, international agricultural system.
Consequently, the adjustment of U.S. agriculture to
climate change cannot be considered in isolation
from the rest of the world. The optimal
configuration of U.S. adjustments will depend very
much on how simultaneous changes in regional
climates affect global agriculture and how other
countries, in turn, respond to those changes.
POLICY IMPLICATIONS
Since climate change appears likely to
reconfigure the agricultural activities and
demographics of rural America, policies should be
examined in light of these potential effects.
Agricultural policies should be designed to ease
adjustments to climate change and to ensure the
sustainability of our natural and human resources
(see Schuh, Volume C, and Dudek, Volume C).
Following are specific policy areas that policymakers
could investigate to respond appropriately to the
projected climate change.
Commodity Policies
Agricultural pricing and production policies
should promote efficient adjustment to the changing
conditions of global supply and demand induced by
the greenhouse effect, which may include shifts in
comparative advantage among regions and increased
likelihood of droughts in some regions. Although
these shifts may be slow, the cumulative effects may
be large and they deserve close monitoring. Market
forces as well as government programs would play
a crucial role in creating the flexibility to respond to
climate changes by sending signals on the efficient
use of resources, and in mitigating their ultimate
impact as they have done in the past. Agricultural
policies should be evaluated to ensure that they are
appropriate to both current and possible future
conditions hi regard to their ability to facilitate
adaptation to climate change. For example,
flexibility hi shifting crop types and farm practices
will speed adjustments.
Land-Use Programs
Federal legislation aimed at reducing the use
of newly plowed grasslands, e.g., the "Sod-Buster
Bill," and the related "Swamp-Buster Bill," which
restricts agricultural encroachment into wetlands
subject to flooding and water-logging, are examples
of new policies meant to protect marginal lands.
The basic goals of these new laws, which are part of
the 1985 Farm Bill, are to protect the most erodible
farmland by removing it from crop production and
to use conservation as a tool for reducing
overproduction. Nearly 80 million acres of U.S.
cropland were retired under these and other farm
programs in 1988. Policy research should address
how these programs may fare under changing
climate conditions.
Another program established in the 1985 Farm
Bill that may help alleviate the negative effects of
climate change is the Conservation Reserve
Program. This program is aimed at removing from
crop production the cropland classified as "highly
erodible" by the Soil Conservation Service. The bill
created a new form of long-term contract of up to
10 years and provides payments to farmers who
apply conservation practices, such as maintaining a
grass cover, on those acres. If successful, the
Conservation Reserve Program may reduce the
impact of climate fluctuations on total grain
production by taking the most sensitive lands out of
use.
The 1988 drought, however, demonstrated that
the Conservation Reserve Program may be difficult
to maintain in the face of climate stress. As the
drought worsened during the summer, use of the
set-aside lands was requested so that badly hit
farmers could salvage some economic benefits from
these acres. Such conflicts may be more common
hi the future, and land retirement strategies must be
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Chapter 6
weighed against possible needed increases in
production.
Awareness of potential changes in agricultural
land use due to regional climate change should be
built into land-use planning programs, especially in
regions where agricultural activities may expand into
natural, unmanaged ecosystems. Large-scale
drainage and water projects would need
environmental impact studies to carefully assess this
potential expansion of agricultural land (see
Baldwin, Volume J).
Water-Resource Management Programs
Current water supply policies do not generally
encourage optimum water-use efficiency. A greater
degree of water efficiency should promote flexibility
in light of the potential for increased irrigation
demands with climate change. Policies such as
water transfers and markets should be considered
for irrigated areas.
Water Quality Policy
The increased use of agricultural chemicals,
along with changes in the hydrological cycle,
potentially threaten both soil and water supplies,
and eventually, public health. Negative
consequences could be avoided or lessened by
including potential climate change effects in water
quality planning and by supporting alternative pest
management strategies that use such techniques as
biological control, genetic resistance, and innovative
cropping systems.
Risk Management and Drought Policy
Changes in the frequency, intensity, and
location of extreme events are important for
agriculture and the regional income that it produces.
The adequacy of the private crop insurance and
federal disaster payment programs should be
assessed in the face of climatic uncertainty. For
example, only about 20 to 25% of potentially
insurable acreage is currently covered by crop
insurance. Farmers tend to rely on federal disaster
relief programs to bail them out of such disasters as
droughts, floods, hail, and windstorms. Financial
risk is also part of the credit structure that covers
land, equipment, and production in modern farming.
The frequency and magnitude of climate
extremes may be altered with climate change.
Responding to the changes may be costly for the
government if crops fail frequently. The Drought
Relief Bill for the drought of 1988 is scheduled to
cost $3.9 billion to cover just 1 year of a climatic
extreme. On the other hand, some areas that
currently suffer from climate extremes may benefit
from climate change. Risk policy mechanisms for
relief, recovery, and mitigation of climate change
should be examined so that they will be ready to
help farmers adjust.
A national drought policy is strongly needed to
coordinate federal response to the possibility of
increased frequency and duration of future droughts
due to climate change. Even without climate
change, such a policy is needed not only for the
agricultural sector but also for other sectors.
International Trade Agreements
Policies designed to ease the adjustment to
greenhouse effects must be global in scope because
the effects, although varied, are global in nature.
Comparative advantage will likely shift significantly
both within the United States and in other
countries. Population and economic activities also
would change geographically with climate change,
thus affecting the location of demand for
agricultural products. It is already a goal of U.S.
agricultural policy to incorporate global conditions
of supply and demand into the agricultural sector.
The potential seriousness of the impacts on the
agricultural production system of the greenhouse
effect may provide added incentive to establish such
policies both nationally and internationally. The
vulnerability of current and potential food-deficit
regions to climate change should also be considered.
Agricultural Contributions to the
Greenhouse Effect
Agriculture itself is an active contributor to the
greenhouse effect. Clearing of forested land for
agriculture often involves burning of trees and
shrubs that release CO2. The biomass that is not
burned tends to decay gradually, also emitting CO2.
Agricultural activities release other radiatively active
trace gases. Flooded rice fields emit methane
(CH4) as a product of the anaerobic decomposition
of organic matter. Ruminants also release methane
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Agriculture
as a consequence of their digestive processes. In
addition, soils may volatilize some of the
nitrogenous fertilizer applied to them in the form of
nitrous oxide (N2O). Finding effective ways to
reduce these emissions presents a major challenge
to the agricultural research community. In this
regard, the Conservation Reserve Program and
forestation efforts could provide a partial solution,
since vegetation fixes CO2 from the air. (See
Lashof and Tirpak, 1989, for further discussion of
agriculture's contribution to the greenhouse effect.)
Agricultural Research
The agricultural research community should
enhance climate change research from the field level
to the national policy level. It should continue to
breed heat- and drought-resistant crop varieties and
new crop species in preparation for global warming.
Research in biotechnology may also be directed
toward alleviating the negative effects of climate
change. Improved water-use and irrigation
efficiency also take on renewed importance in the
light of potential climate change. Energy
requirements of the agricultural system under
climate change should be defined, given the
potential for increases in energy-intensive activities
such as irrigation and application of agricultural
chemicals. Research attention also should be
directed toward reducing agricultural emissions of
trace gases.
RESEARCH NEEDS
1. International agriculture — Study the
potential shifts in international comparative
advantage and the vulnerability of food-
deficit regions, and evaluate the
implications of such shifts for the United
States.
One of the most crucial areas for further
research is the projection of potential
climate change effects at the international
level. Potential changes in agricultural
yields and production of major crops, and
impacts on regions that are food-deficient
now or that may become food-deficient in
the future, all need to be studied.
Economics and policy research should
consider the implications of shifts in global
agriculture for the levels of U.S. crop
exports and the role of the United States as
a reliable supplier of agricultural export
commodities.
2. Crop and livestock productivity — Study the
interactive effects of climate variability and
change, CO2, tropospheric ozone, UV-B
from stratospheric ozone depletion, and
other environmental and societal variables
on agricultural productivity. Determine
how changed climatic variability may
amplify or lessen the preliminary EPA
results.
Because of the significant production
changes indicated by these studies, the need
for better simulation of the direct effects of
CO2 in the crop models, and the limited
adjustment studies performed, further crop
research should be conducted on a longer
term basis. Necessary work includes
resolving the differences in forecasts of the
GCMs, and designing more appropriate
scenarios including transient climate change
and changes in climatic variability.
Physiologicallybasedsubmodels are needed
for the effects of increased CO2 on various
crops. The effects on other major crops
such as cotton also should be studied. Crop
models should be improved in their
simulation of the effects of increasing
temperatures.
Research on the direct CO2 effects on
crops to this point has provided windows of
knowledge concerning certain crops at
specific stages of their life cycles. Both the
direct and the climate change effects of
high CO2 are probably quite different at
different stages of development. Research
should evaluate the interactive effects of
CO, and temperature over the whole life
cycte of the plant, with varying conditions of
water and nutrition, rather than with plants
under optimal conditions. Then crop
response to the combined climatic and
physiological effects of CO, may be
predicted more realistically. Much more
research on climate change and livestock
production is needed. Important research
areas include crop-livestock interactions,
reproduction, and diseases.
119
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Chapter 6
3. Adaptation strategies — Study the dynamic
nature of climate change: What is the rate
of adaptation of regional agricultural
systems compared with the rate of climate
change? Evaluate the thresholds of
sensitivity of U.S. agriculture. Studies
should analyze the ability of various aspects
of the agricultural production systems to
adapt to various rates and degrees of
climate change to determine these
thresholds of sensitivity. It would also be
useful to identify the costs of different types
of adjustments and the regions most likely
to experience greater costs.
4. Agricultural economics — Expand the
national analysis to include crops and
regions not now included (for example,
cotton and grasslands, and the western
regions of the United States). Conduct
further analyses of regional shifts in
agriculture. Studies that link water
resource and agriculture models are needed
to estimate changes in water demand
among agriculture and competing users.
Thus, estimates of actual changes in
irrigated acreage could be made.
5. Environmental impacts - Elucidate the
impacts of climate change on water
quantity, water quality, and other
components of the environment caused by
shifts in crop and livestock production and
related industries.
6. Agricultural emissions of trace gases —
Discover effective ways to reduce emissions
of methane from livestock, nitrous oxide
from fertilizer application, and other
agricultural sources of trace gases.
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responses to elevated carbon dioxide concentrations.
In: Strain, B.R., and J.D. Cure, eds. Direct Effects
of Increasing Carbon Dioxide on Vegetation.
Washington, DC: U.S. Department of Energy.
DOE/ER-0238. pp. 33-97.
Adams, R.M., SA. Hamilton, and BA. McCarl.
1984. The Economic Effects of Ozone on
Agriculture. Corvallis, OR: U.S. Environmental
Protection Agency. EPA-600/3-84-090.
Ames, David R. 1981. Effect of climate on
livestock production data. In: Knapp, F.W., ed.
Systems Approach to Animal Health and
Production. Lexington, KY: University of
Kentucky, pp. 148-148.
Callaway, J.M., FJ. Cronin, J.W. Currie, and J.
Tawil. 1982. An analysis of methods and models
for assessing the direct and indirect impacts of CO2-
induced environmental changes in the agricultural
sector of the U.S. economy. Richland, WA: Pacific
Northwest Laboratory, Battelle Memorial Institute.
PNL-4384.
Carbon Dioxide Assessment Committee. 1983.
Changing Climate. Washington, DC: National
Academy of Sciences.
Carsel, R.F., C.N. Smith, LA. Mulkey, J.D. Dean,
and P. Jowise. 1984. Users Manual for the
Pesticide Root Zone Model (PRZM). Athens, GA:
U.S. Environmental Protection Agency. EPA-
600/3-84-109.
Council for Agricultural Science and Technology.
1988. Long-Term Viability of U.S. Agriculture.
Ames, IA: Council for Agricultural Science and
Technology. Report No. 114.
Cure, J.D. 1985. Carbon dioxide doubling
responses: A crop survey. In: Strain, B.R., and J.D.
Cure, eds. Direct Effects of Increasing Carbon
Dioxide on Vegetation. Washington, DC: U.S.
Department of Energy. DOE/ER-0238. pp. 99-
Decker, W.L., V. Jones, and R. Achutuni. 1985.
The impact of COg-induced climate change on U.S.
agriculture. In: White, M.R., ed. Characterization of
Information Requirements for Studies of CO2
Effects: Water Resources, Agriculture, Fisheries,
Forests and Human Health. Washington, DC: U.S.
Department of Energy. DOE/ER-0236. pp. 69-93.
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Dudek, D.J. 1987. Economic implications of
climate change impacts on southern agriculture. In:
Meo, M., ed. Proceedings of the Symposium on
Climate Change in the Southern United States:
Future Impacts and Present Policy Issues. Norman,
OK: University of Oklahoma, Science and Public
Policy Program, pp. 44-72.
Drummond, R.O. 1987. Economic aspects of
ectoparasites of cattle in North America. In:
Leaning, W.H.D., and J. Guerrero, eds. Proceedings
of the MSB AGVET Symposium, The Economic
Impact of Parasitism in Cattle. XXIII. World
Veterinary Congress. Montreal, Quebec, pp. 9-24.
Hansen, J., I. Fung, A. Lacis, D. Rind, G. Russell,
S. Lebedeff, R. Ruedy, and P. Stone. 1988. Global
climate changes as forecast by the GISS 3-D model.
Journal of Geophysical Research 93(D8):9341-9364.
Jones, CA., and J.R. Kiniry, eds. 1986. CERES-
Maize: A Simulation Model of Maize Growth and
Development. College Station, TX: Texas A&M
University Press.
Jones, J.W., K.J. Boote, S.S. Jagtap, G.
Hoogenboom, and G.G. Wilkerson. 1988.
SOYGRO V5.41: Soybean Crop Growth Simulation
Model. User's Guide. Florida Agr. Exp. Sta.
Journal No. 8304, IFAS. Gainesville, FL: University
of Florida.
Jones, J.W., J.W. Mishoe, G. Wilkerson, J.L. Stimac,
and W.G. Boggess. 1986. Integration of soybean
crop and pest models. In: Frisbie, P.E., and P.
Adisson, eds. Integrated Pest Management on
Major Agriculture Systems. Texas Agriculture
Experiment Station. Publication No. MP-1616.
College Station, TX: Texas A&M University.
Kimball, B A. 1985. Adaptation of vegetation and
management practices to a higher carbon dioxide
world. In: Strain, B.R., and J.D. Cure, eds. Direct
Effects of Increasing Carbon Dioxide on Vegetation.
Washington, DC: U.S. Department of Energy.
DOE/ER-0238. pp. 185-204.
Land Evaluation Group. 1987. Implications of
climatic warming for Canada's comparative position
in agricultural production and trade. Guelph,
Ontario: University of Guelph, University School of
Rural Planning and Development.
Agriculture
Lashof, D., and D. Tirpak, eds. 1989. Policy
Options for Stabilizing Global Climate. Draft
report. Washington, DC: U.S. Environmental
Protection Agency.
Parry, M.L., T.R. Carter, N.T. Konijn, eds. 1988.
The Impact of Climatic Variations on Agriculture.
Vol. 1. Assessments in Cool Temperate and Cold
Regions. Dordrecht: Kluwer.
Postel, S. 1986. Altering the Earth's Chemistry.
Assessing the Risks. WorldWatch Paper 71.
Washington, DC: Worldwatch Institute.
Ritchie, J.T., and S. Otter. 1985. Description and
performance of CERES-Wheat: A user-oriented
wheat yield model. In: Willis, W.O., ed. ARS
Wheat Yield Project. Washington, DC: U.S.
Department of Agriculture, Agricultural Research
Service. ARS-38. pp. 159-175.
Schneider, K. 1988. Drought cutting U.S. grain
crop 31% this year. The New York Times August
12A1.
USDA. 1976. U.S. Department of Agriculture.
Handbook of Agricultural Charts. Agricultural
Handbook 504. Washington, DC: U.S. Government
Printing Office.
USDA. 1987. U.S. Department of Agriculture.
Agricultural Statistics. Washington, DC: U.S.
Government Printing Office.
U.S. Department of Commerce. 1983. U.S.
Department of Commerce, Bureau of the Census.
1982 Census of Agriculture, Vol. 1. Geographical
Area Series", Part 51, United States Summary and
State Data. Washington, DC: U.S. Government
Printing Office. s
Warrick, R.A., R.M. Gifford, M.L. Parry. 1986.
CO2, climatic change and agriculture. Assessing the
response of food crops to the direct effects of
increased CO2 and climatic change. In: Bolin, B.,
B.R. Doos, J. Jager, and RA. Warrick, eds. The
Greenhouse Effect, Climatic Change and
Ecosystems. A Synthesis of the Present Knowledge,
SCOPE 29. New York: John Wiley and Sons. pp.
393-473.
Webster, A.J.F. 1981. Weather and infectious
disease in cattle. The Veterinary Record 108:183-
187.
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Chapter 6
World Food Institute. 1987. World Food Trade
and UJS. Agriculture, 1960-1986. Ames, IA: Iowa
State University.
Zachariah, K.C., and Vu, M.T. World Bank. 1988.
World Population Projections. 1987-1988 Ed. Short-
and Long-Term Estimates. Baltimore, MD: Johns
Hopkins University Press.
122
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CHAPTER 7
SEA LEVEL RISE
FINDINGS
Global warming could cause sea level to rise 0.5 to
2 meters by 2100. Such a rise would inundate
wetlands and lowlands, erode beaches, exacerbate
coastal flooding, and increase the salinity of
estuaries and aquifers.
• A 1-meter rise could drown approximately 25 to
80% of the U.S. coastal wetlands; ability to
survive would depend largely on whether they
could migrate inland or whether levees and
bulkheads blocked their migration. Even
current sea level trends threaten the wetlands of
Louisiana.
• A 1-meter rise could inundate 5,000 to 10,000
square miles of dryland if shores were not
protected and 4,000 to 9,000 square miles of
dryland if only developed areas were protected.
* Most coastal barrier island communities would
probably respond to sea level rise by raising
land with sand pumped from offshore. Wide
and heavily urbanized islands may use levees,
while communities on lightly developed islands
may adjust to a gradual landward migration of
the islands.
• Protecting developed areas against such
inundation and erosion by building bulkheads
and levees, pumping sand, and raising barrier
islands could cost $73 to $111 billion
(cumulative capital costs in 1985 dollars) for a
1-meter rise by the year 2100 (compared with
$6 to $11 billion under current sea level trends).
Of this total, $50 to $75 billion would be spent
(cumulative capital costs in 1985 dollars) to
elevate beaches, houses, land, and roadways by
the year 2100 to protect barrier islands
(compared with $4 billion under current trends).
Developed barrier islands would likely be
protected from sea level rise because of their
high property values.
• The Southeast would bear approximately 90% of
the land loss and 66% of the shore protection
costs.
Policy Implications
• Many of the necessary responses to sea level
rise, such as rebuilding ports, constructing
levees, and pumping sand onto beaches, need
not be implemented until the rise is imminent.
On the other hand, the cost of incorporating sea
level rise into a wide variety of engineering and
land use decisions would be negligible compared
with the costs of not responding until sea level
rises.
• Many wetland ecosystems are likely to survive
sea level rise only if appropriate measures are
implemented in the near future. At the state
and local levels, these measures include land use
planning, regulation, and redefinitions of
property rights. The State of Maine has already
issued regulations to enable wetlands to migrate
landward by requiring that structures be
removed as sea level rises.
• The coastal wetlands protected under Section
404 of the Clean Water Act will gradually be
inundated. The act does not authorize measures
to ensure survival of wetland ecosystems as sea
level rises.
• The National Flood Insurance Program may
wish to consider the implications of sea level
rise on its future liabilities. A recent HUD
authorization act requires this program to
purchase property threatened with erosion. The
act may imply a commitment by the federal
government to compensate property owners for
losses due to sea level rise.
• The need to take action is particularly urgent hi
coastal Louisiana, which is already losing 100
square kilometers per year.
123
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Chapter 7
CAUSES, EFFECTS, AND
RESPONSES
Global warming from the greenhouse effect
could raise sea level approximately 1 meter by
expanding ocean water, melting mountain glaciers,
and causing ice sheets hi Greenland to melt or slide
into the oceans. Such a rise would inundate coastal
wetlands and lowlands, erode beaches, increase the
risk of flooding, and increase the salinity of
estuaries, aquifers, and wetlands.
In the last 5 years, many coastal communities
throughout the world have started to prepare for the
possibility of such a rise. In the United States,
Maine has enacted a policy declaring that shorefront
buildings will have to be moved to enable beaches
and wetlands to migrate inland to higher ground.
Maryland has shifted its shore-protection strategy
from a technology that can not accommodate sea
level rise to one that can. Seven coastal states have
held large public meetings on how to prepare for a
rising sea. Australia, the Netherlands, and the
Republic of Maldives are beginning to undergo a
similar process.
Causes
Ocean levels have always fluctuated with
changes in global temperatures. During the ice ages
when the earth was 5°C (9°F) colder than today,
much of the ocean's water was frozen in glaciers
and sea level often was more than 100 meters (300
feet) below the present level (Dorm et al., 1962;
Kennett, 1982; Oldale, 1985). Conversely, during
the last interglacial period (100,000 years ago) when
the average temperature was about 1°C (2°F)
warmer than today, sea level was approximately 20
feet higher than the current sea level (Mercer,
1968).
When considering shorter periods of time,
worldwide sea level rise must be distinguished from
relative sea level rise. Although climate change
alters worldwide sea level, the rate of sea level rise
relative to a particular coast has greater practical
importance and is all that monitoring stations can
measure. Because most coasts are sinking (and a
few are rising), the range of relative sea level rise
varies from more than 3 feet per century in
Louisiana and parts of California and Texas to 1
foot per century along most of the Atlantic and
gulf coasts, to a slight drop in much of the Pacific
Northwest (Figure 7-1). Areas such as Louisiana
provide natural laboratories for assessing the
possible effects of future sea level rise (Lyle et al.,
1987).
TIME, YEARS
1850 1865
1880 1895 1910 1925 1940 1955 1970 1985
SITKA, AK
CHARLESTON, SC
MIAMI BEACH, FL
GALVESTON, TX
Figure 7-1. Tune series graph of sea level trends
for New York, Charleston, Miami, Galveston, and
Sitka (Lyle et al., 1987).
Global sea level trends have generally been
estimated by combining the trends at tidal stations
around the world. Studies combining these
measurements suggest that during the last century,
worldwide sea level has risen 10 to 15 centimeters
(4 to 6 inches) (Barnett, 1984; Fairbridge and
Krebs, 1962). Much of this rise has been attributed
to the global warming that has occurred during the
last century (Meier, 1984; Gornitz et al., 1982).
Hughes (1983) and Bentley (1983) estimated that a
complete disintegration of West Antarctica hi
response to global warming would require a 200- to
500-year period, and that such a disintegration
would raise sea level 20 feet. Most recent
assessments, however, have focused on the likely
rise by the year 2100. Figure 7-2 illustrates recent
estimates of sea level rise, which generally fall into
the range of 50 to 200 centimeters.
124
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Sea Level Rise
4.0
f 3.0
I
to
CO
EA LEVEL RISE RELATIVE TO 1
r* ro
= b
0.0
r-
• Hoffman (1983) High
_
* Olacler Volume Estimate of Polar • Hoffman (1983) Mid-High
_ Board Augmented With Thermal
Expansion Estimates by NRC • Meier (198Sb) High
(1983)
• WMO(1986) High
> Hoffman (1983) Mid-Lorn
111/
/ / • Reve!le(1983)
/ / •!• • Hoffman (1983) Low
^ Past Century ( //^S^'' Meler " 9B5b) Low"
Estimated I ^x^^iwiMO (1986) Lov«
0.12m Rise \^P^*^ | |
~^~ 2000 2050 2100
YEAR
Figure 7-2. Estimates of future sea level rise
(derived from Hoffman, 1983, 1986; Meier, 1985:
Revelle, 1983).
Although most studies have focused on the
impact of global warming on global sea level, the
greenhouse effect would not necessarily raise sea
level by the same amount everywhere. Removal of
water from the world's ice sheets would move the
earth's center of gravity away from Greenland and
Antarctica and would thus redistribute the oceans'
water toward the new center of gravity. Along the
U.S. coast, this effect would generally increase sea
level rise by less than 10%. Sea level could actually
drop, however, at Cape Horn and along the coast of
Iceland. Climate change could also affect local sea
level by changing ocean currents, winds, and
atmospheric pressure; no one has estimated these
impacts.
Effects
In this section and in the following sections, the
effects of and responses to sea level rise are
presented separately. However, the distinction is
largely academic and is solely for presentation
purposes. In many cases, the responses to sea level
rise are sufficiently well established and the
probability of no response is sufficiently low that it
would be misleading to discuss the potential effects
without also discussing responses. For example,
much of Manhattan Island is less than 2 meters
above high tide; the effect of sea level rise would
almost certainly be the increased use of coastal
engineering structures and not the inundation of
downtown New York.
A rise in sea level would inundate wetlands and
lowlands, accelerate coastal erosion, exacerbate
coastal flooding, threaten coastal structures, raise
water tables, and increase the salinity of rivers,
bays, and aquifers (Earth and Titus, 1984). Most of
the wetlands and lowlands are found along the gulf
coast and along the Atlantic coast south of central
New Jersey, although a large area also exists around
San Francisco Bay. Similarly, the areas vulnerable
to erosion and flooding are also predominately in
the Southeast; potential salinity problems are spread
more evenly along the U.S. Atlantic coast. We now
discuss some of the impacts that would result if no
responses were initiated to address sea level rise.
Destruction of Coastal Wetlands
Coastal wetlands are generally found between
the highest tide of the year and mean sea level.
Wetlands have kept pace with the past rate of sea
level rise because they collect sediment and produce
peat upon which they can build; meanwhile, they
expanded inland as lowlands were inundated (Figure
7-3). Wetlands accrete vertically and expand inland.
Thus, as Figure 7-3 illustrates, the present area of
wetlands is generally far greater than the area that
would be available for new wetlands as sea level
rises (Titus et al., 1984b; Titus, 1986). The
potential loss would be the greatest in Louisiana
(see Chapter 16: Southeast).
In many areas, people have built bulkheads just
above the marsh. If sea level rises, the wetlands will
be squeezed between the sea and the bulkheads (see
Figure 7-3). Previous studies have estimated that if
the development in coastal areas were removed to
allow new wetlands to form inland, a 1.5- to 2-meter
rise would destroy 30 to 70% of the U.S. coastal
wetlands. If levees and bulkheads were erected to
protect today's dryland, the loss could be 50 to 80%
(Titus, 1988; Armentano et al., 1988).
125
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Chapter 7
5000 YEARS AGO
TODAY
SEDIMENTATION AND
PEAT FORMATION
FUTURE
SUBSTANTIAL WETLAND LOSS WHERE THERE IS VACANT UPLAND
FUTURE
3— SEA LEVEL
COMPLETE WETLAND LOSS WHERE HOUSE IS PROTECTED
IN RESPONSE TO RISE IN SEA LEVEL .
FUTURE
. SEA LEVEL
- CURRENT
SEA LEVEL
D
PEAT ACCUMULATION
Figure 7-3. Evolution of marsh as sea rises. Coastal marshes have kept pace with the slow rate of sea level rise
that has characterized the last several thousand years. Thus, the area of marsh has expanded over time as new
lands have been inundated. If in the future, sea level rises faster than the ability of the marsh to keep pace, the
marsh area will contract. Construction of bulkheads to protect economic development may prevent new marsh
from forming and result in a total loss of marsh in some areas.
Such a loss would reduce the available habitat for
birds and juvenile fish and would reduce the
production of organic materials on which estuarine
fish rely.
The dryland within 2 meters of high tide
includes forests, farms, low parts of some port cities,
cities that sank after they were built and are now
protected with levees, and the bay sides of barrier
islands. The low forests and farms are generally in
the mid-Atlantic and Southeast regions; these would
provide potential areas for new wetland formation.
Major port cities with low areas include Boston,
New York, Charleston, and Miami. New Orleans is
generally 8 feet below sea level, and parts of
Galveston, Texas City, and areas around the San
Francisco Bay are also well below sea level.
Because they are already protected by levees, these
cities are more concerned with flooding than with
inundation.
Inundation and Erosion of Beaches and Barrier
Islands
Some of the most important vulnerable areas
are the recreational barrier islands and spits
(peninsulas) of the Atlantic and gulf coasts. Coastal
barriers are generally long narrow islands and spits
with the ocean on one side and a bay on the other.
Typically, the oceanfront block of an island ranges
from 5 to 10 feet above high tide, and the bay side
is 2 to 3 feet above high water. Thus, even a 1-
meter sea level rise would threaten much of this
valuable land with inundation.
Erosion threatens the high part of these islands
and is generally viewed as a more immediate
problem than the inundation of the bay sides. As
Figure 7-4 shows, a rise in sea level can cause an
ocean beach to retreat considerably more than it
would from the effects of inundation alone. The
visible part of the beach is much steeper than the
underwater portion, which comprises most of the
active "surf zone." While inundation alone is
determined by the slope of the land just above the
water, Bruun (1962) and others have shown that the
total shoreline retreat from a sea level rise depends
on the average slope of the entire beach profile.
Previous studies suggest that a 1-foot rise in sea
level would generally cause beaches to erode 50 to
100 feet from the Northeast to Maryland (e.g.,
Kyper and Sorensen, 1985; Everts, 1985); 200 feet
along the Carolinas (Kana et al., 1984); 100 to 1,000
126
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Sea Level Rise
Figure 7-4. The Bruun Rule: (A) initial condition;
(B) immediate inundation when sea level rises; (C)
subsequent erosion due to sea level rise. A rise in
sea level immediately results in shoreline retreat
due to inundation, shown in the first two examples.
However, a 1-meter rise in sea level implies that
the offshore bottom must also rise 1 meter. The
sand required to raise the bottom (X1) can be
supplied by beach nourishment. Otherwise, waves
will erode the necessary sand (X) from upper part
of the beach as shown in (C).
feet along the Florida coast (Bruun, 1962); 200 to
400 feet along the California coast (Wilcoxen, 1986);
and perhaps several miles in Louisiana. Because
most U.S. recreational beaches are less than 100
feet wide at high tide, even a 1-foot rise in sea level
would require a response. In many areas,
undeveloped barrier islands could keep up with
rising sea level by "overwashing" landward. In
Louisiana, however, barrier islands are breaking up
and exposing the wetlands behind them to gulf
waves; consequently, the Louisiana barrier islands
have rapidly eroded.
Flooding
If sea level rises, flooding would increase along
the coast for four reasons: (1) A higher sea level
provides a higher base for storm surges to build
upon. A 1-meter sea level rise would enable a
15-year storm to flood many areas that today are
flooded only by a 100-year storm (e.g., Kana et al.,
1984; Leatherman, 1984). (2) Beach erosion also
would leave oceanfront properties more vulnerable
to storm waves. (3) Higher water levels would
reduce coastal drainage and thus would increase
flooding attributable to rainstorms. In artificially
drained areas such as New Orleans, the increased
need for pumping could exceed current capacities.
(4) Finally, a rise in sea level would raise water
tables and would flood basements, and in cases
where the groundwater is just below the surface,
perhaps raise it above the surface.
Saltwater Intrusion
A rise in sea level would enable saltwater to
penetrate farther inland and upstream into rivers,
bays, wetlands, and aquifers. Salinity increases
would be harmful to some aquatic plants and
animals, and would threaten human uses of water.
For example, increased salinity already has been
cited as a factor contributing to reduced oyster
harvests in the Delaware and Chesapeake Bays, and
to conversion of cypress swamps to open lakes in
Louisiana. Moreover, New York, Philadelphia, and
much of California's Central Valley obtain their
water from areas located just upstream from areas
where the water is salty during droughts. Farmers
in central New Jersey and the city of Camden rely
on the Potomac-Raritan-Magothy Aquifer, which
could become salty if sea level rises (Hull and Titus,
1986). The South Florida Water Management
District already spends millions of dollars every year
to prevent Miami's Biscayne Aquifer from becoming
contaminated with seawater.
Responses
The possible responses to inundation, erosion,
and flooding fall broadly into three categories:
erecting walls to hold back the sea, allowing the sea
to advance and adapting to the advance, and raising
the land. Both the slow rise in sea level over the
last thousand years and the areas where land has
been sinking more rapidly offer numerous historical
examples of all three responses.
For over five centuries, the Dutch and others
have used dikes and windmills to prevent inundation
from the North Sea. By contrast, many cities have
been rebuilt landward as structures have eroded; the
127
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Chapter 7
town of Dunwich, England, has rebuilt its church
seven times in the last seven centuries. More
recently, rapidly subsiding communities (e.g.,
Galveston, Texas) have used fill to raise land
elevations; the U.S. Army Corps of Engineers and
coastal states regularly pump sand from offshore
locations to counteract beach erosion. Venice, a
hybrid of all three responses, has allowed the sea to
advance into the canals, has raised some lowlands,
and has erected storm protection barriers.
Most assessments in the United States have
concluded that low-lying coastal cities would be
protected with bulkheads, levees, and pumping
systems, and that sparsely developed areas would
adapt to a naturally retreating shoreline (e.g., Dean
et al., 1987; Gibbs, 1984; Schelling, 1983). This
conclusion has generally been based on estimates
that the cost of structural protection would be far
less than the value of the urban areas being
protected but would be greater than the value of
undeveloped land.
Studies on the possible responses of barrier
islands and moderately developed mainland
communities show less agreement but generally
suggest that environmental factors would be as
important as economics. Some have suggested that
barrier islands should use seawalls and other "hard"
engineering approaches (e.g., Kyper and Sorensen,
1985; Sorensen et al., 1984). Others have pointed to
the esthetic problems associated with losing beaches
and have advocated a gradual retreat from the shore
(Howard et al., 1985). Noting that new houses on
barrier islands are generally elevated on pilings,
Titus (1986) suggested that communities could hold
back the sea but keep a natural beach by extending
the current practice of pumping sand onto beaches
to raising entire islands in place.
Responses to erosion are more likely to have
adverse environmental impacts along sheltered
water than on the open coast (Titus, 1986).
Because the beach generally is a barrier island's
most important asset, economics would tend to
encourage these communities to preserve their
natural shorelines; actions that would prevent the
island from breaking up also would protect the
adjacent wetlands. However, along most mainland
shorelines, economic self-interest would encourage
property owners to erect bulkheads; these would
prevent new wetland formation from offsetting the
loss of wetlands that were inundated.
Most of the measures for counteracting
saltwater intrusion attributable to sea level rise have
also been employed to address current problems.
For example, the Delaware River Basin Commission
protects Philadelphia's freshwater intake on the
river and New Jersey aquifers recharged by the river
by storing water in reservoirs during the wet season
and releasing it during droughts, thereby forcing the
saltwater back toward the sea. Other communities
have protected coastal aquifers by erecting
underground barriers and by maintaining freshwater
pressure through the use of impoundments and
injection wells.
HOLDING BACK THE SEA: A
NATIONAL ASSESSMENT
The studies referenced in the previous section
have illustrated a wide variety of possible effects
from and responses to a rise in sea level from the
greenhouse effect. Although they have identified
the implications of the risk of sea level rise for
specific locations and decisions, these studies have
not estimated the nationwide magnitude of the
impacts. This report seeks to fill that void.
It was not possible to estimate the nationwide
value of every impact of sea level rise. The studies
thus far conducted suggest that the majority of the
environmental and economic costs would be
associated with shoreline retreat and measures to
hold back the sea, which can be more easily
assessed on a nationwide basis. Because the
eventual impact will depend on what people actually
do, a number of important questions can be
addressed within this context:
• Would a gradual abandonment of
moderately developed mainland areas
significantly increase the amount of
wetlands that survived a rise in sea level?
• Would the concave profiles of coastal areas
ensure that more wetlands would be lost
than gained, regardless of land-use
decisions?
• Should barrier islands be raised in place by
pumping sand and elevating structures and
utilities?
128
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Sea Level Rise
Decision to Use
Island Raising
Scenario
CASE STUDY
NATIONAL ANALYSIS
Figure 7-5. Overview of sea level rise studies and authors.
Would a landward migration of developed
barrier islands or encircling them with dikes
and levees be feasible alternatives?
How much property would be lost if barrier
islands were abandoned?
STRUCTURE OF STUDIES FOR
THIS REPORT
A central theme underlying these questions is
that the implications of sea level rise for a
community depend greatly on whether people
adjust to the natural impact of shoreline retreat or
129
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Chapter 7
undertake efforts to hold back the sea. Because no
one knows the extent to which each of these
approaches would be applied, this study was
designed to estimate the impacts of sea level rise for
(1) holding back the sea, and (2) natural shoreline
retreat.
The tasks were split into five discrete projects:
1. Park et al. estimated the loss of coastal
wetlands and dryland.
2. Leatherman estimated the cost of pumping
sand onto open coastal beaches and barrier
islands.
3. Weggel et al. estimated the cost of
protecting sheltered shores with levees and
bulkheads.
4. Yohe began a national economic
assessment by estimating the value of
threatened property.
5. Titus and Greene synthesized the results of
other studies to estimate ranges of the
nationwide impacts.
Figure 7-5 illustrates the relationships between
the various reports. (All of the sea level rise studies
are in Volume B of the Appendices to this report.)
As the top portion shows, the assessment began
with a case study of Long Beach Island, New Jersey,
which was necessary for evaluating methods and
providing data for purposes of extrapolation. The
Park and Leatherman studies performed the same
calculations for the case study site that they would
subsequently perform for the other sites in the
nationwide analysis. However, Weggel and Yohe
conducted more detailed assessments of the case
study whose results were used in the Leatherman
and Titus studies.
Because it would not be feasible for
Leatherman to examine more than one option for
the cost of protecting the open coast, Weggel
estimated the cost of protecting Long Beach Island
by three approaches: (1) raising the island in place;
(2) gradually rebuilding the island landward; and (3)
encircling the island with dikes and levees. Yohe
estimated the value of threatened structures. Titus
analyzed Weggel's and Yohe's results and concluded
that raising barrier islands would be the most
reasonable option for the Leatherman study and
noted that the cost of this option would be
considerably less than the resources that would be
lost if the islands were not protected as shown in
Figure 7-6.
Once the case study was complete, Park,
Leatherman, and Weggel proceeded independently
with their studies (although Park provided
Weggel with elevation data). When those studies
were complete, Titus synthesized their results,
developing a nationwide estimate of the cost of
holding back the sea and interpolating Weggel's
200-centimeter results for the 50- and 100-
centimeter scenarios.
In presenting results from the Park and Weggel
studies, the sites were grouped into seven coastal
regions, four of which are in the Southeast: New
England, mid-Atlantic, south Atlantic, south
Florida/gulf coast peninsula, Louisiana, other gulf
(Texas, Mississippi, Alabama, Florida Panhandle),
and the Pacific coast. Figure 7-7 illustrates these
regions.
™ Lost Rent
- From Not
_ Raising the Island
Costs of Raising
Island^,
2000 8020 2040
Year
Figure 7-6. Annual cost of raising island versus
annual costs (lost rent) from not protecting the
island (in 1986 dollars) (Titus and Greene, Volume
B).
SCENARIOS OF SEA LEVEL RISE
Although the researchers considered a variety of
scenarios of future sea level rise, this report focuses
130
-------
Sea Level Rise
WEST COAST
NORTHEAST
,' SOUTHERN
WEST FLORIDA
Figure 7-7. Coastal regions used in this study.
on the impacts of three scenarios: rises of 50, 100,
and 200 centimeters by the year 2100. All three of
these scenarios are based on quantitative estimates
of sea level rise. No probabilities were associated
with these scenarios. Following the convention of a
recent National Research Council report (Dean et
al., 1987), the rise was interpolated throughout the
21st century using a quadratic (parabola). For each
site, local subsidence was added to determine
relative sea level rise. Figure 7-8 shows the
scenarios for the coast of Florida where relative sea
level rise will be typical of most of the U.S. coast.
Sea level would rise 1 foot by 2025, 2040, and 2060
for the three scenarios and 2 feet by 2045, 2065, and
2100.
RESULTS OF SEA LEVEL
STUDIES IN THIS REPORT
Loss of Coastal Wetlands and Dryland
Park (Volume B) sought to test a number of
hypotheses presented in previous publications:
• A rise in sea level greater than the rate of
vertical wetland accretion would result in
a net loss of coastal wetlands.
• The loss of wetlands would be greatest if all
developed areas were protected, less if
shorelines retreated naturally, and least if
barrier islands were protected while
mainland shores retreated naturally.
• The loss of coastal wetlands would be
greatest in the Southeast, particularly
Louisiana.
Study Design
Park's study was based on a sample of 46
coastal sites that were selected at regular intervals.
This guaranteed that particular regions would be
represented in proportion to their total area in the
coastal zone. The sites chosen accounted for 10%
of the U.S. coastal zone excluding Alaska and
Hawaii. To estimate the potential loss of wet and
dry land, Park first had to characterize their
elevations. For wetlands, he used satellite imagery
to determine plant species for 60- by 80-meter
parcels. Using estimates from the literature on the
131
-------
Chapter 7
19M 2000
Figure 7-8. Sea level scenarios (Miami Beach).
frequency of flooding that can be tolerated by
various wetland plants, Park determined the
percentage of time that particular parcels are
currently under water. From this, Park inferred
wetland elevation based on the known tidal range.
For dryland, he used spot elevation measurements
to interpolate between contours on U.S. Geological
Survey topographic maps.
Park estimated the net loss of wetlands and
dryland for no protection, protection of developed
areas, and protection of all shores. For the
no-protection scenario, estimating the loss of
dryland is straightforward. However, for calculating
net wetland loss, Park had to estimate the loss of
existing wetlands as well as the creation of new
wetlands. For calculating losses, Park used
published vertical accretion rates (see Armentano et
al., 1988), although he allowed for some
acceleration of vertical accretion in areas with
ample supplies of sediment, such as tidal deltas.
Park assumed that dryland would convert to
wetlands within 5 years of being inundated.
For sites in the Southeast, Park also allowed for
the gradual replacement of salt marshes by
mangrove swamps. The upper limit for mangroves
is around Fort Lauderdale. Park used the GISS
transient scenario to determine the year particular
sites would be as warm as Fort Lauderdale is today
and assumed that mangroves would begin to replace
marsh after that year.
Limitations
The greatest uncertainty in Park's analysis is a
poor understanding of the potential rates of vertical
accretion. Although this could substantially affect
the results for low sea level rise scenarios, the
practical significance is small for a rise of 1 meter
because it is generally recognized that wetlands
could not keep pace with the rise of 1 to 2
centimeters per year that such a scenario implies for
the second half of the 21st century.
Errors can be made when determining
vegetation type based on the use of infrared
"signatures" that satellites receive. Park noted, for
example, that in California the redwoods have a
signature similar to that of marsh grass. For only a
few sites, Park was able to corroborate his estimates
of vegetation type.
Park's study did not consider the potential
implications of alternative methods of managing
riverflow. This limitation is particularly serious
regarding application to Louisiana, where widely
varying measures have been proposed to increase
the amount of water and sediment delivered to the
wetlands. Finally, the study makes no attempt to
predict which undeveloped areas might be
developed in the next century.
At the coarse (500-meter) scale Park used, the
assumption of protecting only developed areas
amounts to not protecting a number of mainland
areas where the shoreline is developed but areas
behind the shoreline are not. Therefore, Park's
estimates for protecting developed areas should be
interpreted as applying to the case where only
densely developed areas are protected. Finally,
Park's assumption that dryland would convert to
vegetated wetlands within 5 years of being
inundated probably led him to underestimate the
net loss of wetlands due to sea level rise.
Park's results supported the hypotheses
suggested by previous studies. Figure 7-9 shows
nationwide wetlands loss for various (0- to 3-meter)
sea level rises for the three policy options
investigated. For a 1-meter rise, 66% of all coastal
wetlands would be lost if all shorelines were
protected, 49% would be lost if only developed
132
-------
Sea Level Rise
areas were protected, and 46% would be lost if
shorelines retreated naturally.
As expected, the greatest losses of wetlands
would be hi the Southeast, which currently contains
85% of U.S. coastal wetlands (Figure 7-9). For a 1-
meter sea level rise, 6,000 to 8,600 square miles
(depending on which policy is implemented) of U.S.
wetlands would be lost; 90 to 95% of this area
would be in the Southeast, and 40 to 50% would be
in Louisiana alone. By contrast, neither the
Northeast nor the West would lose more than 10%
of its wetlands if only currently developed areas are
protected.
COMPOSITE FOR UNITED STATES
ALL DRYLAND PROTECTED
0.0 0.1 0.3 0.6 1.0 1.5 2.2 3.0
SEA LEVEL RISE {Meters)
DEVELOPED AREAS PROTECTED
0.0 0.1 0.3 0.6 1.0 1.5 2.2 3.0
SEA LEVEL RISE (Motors)
NO PROTECTION
0.0 0.1 0.3 0.6 1.0 1.5 2.2 3.0
SEA LEVEL RISE (Meters)
Figure 7-9. Nationwide wetlands loss for three
shoreline-protection options. Note: These wetlands
include beaches and flats that are not vegetated
wetlands; however, results cited in the text refer to
vegetated wetlands (Park, Volume B).
Figure 7-10 illustrates Park's estimates of the
inundation of dryland for the seven coastal regions.
If shorelines retreated naturally, a 1-meter rise
would inundate 7,700 square miles of dryland, an
area the size of Massachusetts. Rises of 50 and 200
centimeters would result in losses of 5,000 and
12,000 square miles, respectively. Approximately
70% of the dryland losses would occur in the
Southeast, particularly Florida, Louisiana, and North
Carolina. The eastern shores of the Chesapeake and
Delaware Bays also would lose considerable
acreage.
Costs of Defending Sheltered Shorelines
Study Design
This study began by examining Long Beach
Island in depth. This site and five other sites were
used to develop engineering rules of thumb for the
cost of protecting coastal lowlands from inundation.
Examining the costs of raising barrier islands
required an assessment of two alternatives: (1)
building a levee around the island; and (2) allowing
the island to migrate landward.
After visiting Long Beach Island and the
adjacent mainland, Weggel (Volume B) designed
and estimated costs for an encirclement scheme
consisting of a levee around the island and a
drainage system that included pumping and
underground retention of stormwater. For island
migration, he used the Bruun Rule to estimate
oceanside erosion and navigation charts to calculate
the amount of sand necessary to fill the bay an
equivalent distance landward. For island raising and
island migration, Weggel used the literature to
estimate the costs of elevating and moving houses
and of rebuilding roads and utilities.
Weggel's approach for estimating the nationwide
costs was to examine a number of index sites in
depth and thereby develop generalized cost
estimates for protecting different types of shorelines.
He used the topographic information collected by
Park for a sample of 95 sites to determine the area
and shoreline length that had to be protected. He
then applied the cost estimation factors to each site
and extrapolated the sample to the entire coast.
After assessing Long Beach Island, Weggel
conducted less detailed studies of the following
areas: metropolitan New York; Dividing Creek,
133
-------
Chapter 7
A. DRYLAND LOSS BY 2100 WITHOUT SHORE PROTECTION
Northeast Mtd-
Atlantic
South
Atlantic
South
&West
Florida
Louisiana Other Gulf
B. DRYLAND LOSS BY 2100 WITH PROTECTION OF DEVELOPED AREAS
g 1.0
Northeast Mid- South
Atlantic Atlantic
SEA LEVEL RISE I " I BASELINE
SCENARIO: I J BASELINE
South
&West
Florida
Figure 7-10. Loss of dryland by 2100: (A) if no areas are protected, and (B) if developed areas are protected
with levees (derived from Park, Volume B; see also Titus and Greene, Volume B).
New Jersey; Miami and Miami Beach; the area
around Corpus Christi, Texas; and parts of San
Francisco Bay.
Limitations
The most serious limitation of the Weggel study
is that cruder methods are used for the national
assessment than for the index sites. Even for the
index sites, the cost estimates are based on the
literature, not on site-specific designs that take into
consideration wave data for bulkheads and potential
savings from tolerating substandard roads. Weggel
did not estimate the cost of pumping rainwater out
of areas protected by levees.
Finally, Weggel was able to examine only one
scenario: a 2-meter rise by 2100. This scenario was
chosen over the more likely 1-meter scenario
because an interpolation from 2 meters to 1 meter
would be more reliable than an extrapolation from
1 meter to 2 meters. (See the discussion of Titus
and Greene for results of the interpolation.)
Results
Case Study of Long Beach Island
Weggel's cumulative cost estimates clearly
indicate that raising Long Beach Island would be
much less expensive ($1.7 billion) than allowing it to
134
-------
Sea Level Rise
migrate landward ($7.7 billion). Although the cost
of building a levee around the island ($800 million)
would be less, the "present value" would be greater.
Weggel concluded that the levee would have to be
built in the 2020s, whereas the island could be
raised gradually between 2020 and 2100. Thus, the
(discounted) present value of the levee cost would
be greater, and raising the necessary capital for a
levee at any one time could be more difficult than
gradually rebuilding the roads and elevating houses
as the island was raised. Moreover, a levee would
eliminate the waterfront view. A final disadvantage
of building a levee is that one must design for a
specific magnitude of sea level rise; by contrast, an
island could be raised incrementally.
The Weggel analysis shows that landward
migration is more expensive than island raising,
primarily because of the increased costs of
rebuilding infrastructure. Thus, migration might be
less expensive in the case of a very lightly developed
island. Levees might be more practical for wide
barrier islands where most people do not have a
waterfront view.
Nationwide Costs
Table 7-2 shows WeggePs estimates for the
index sites and his nationwide estimate. The index
sites represent two distinct patterns. Because urban
areas such as New York and Miami would be
entirely protected by levees, the cost of moving
buildings and rebuilding roads and utilities would be
relatively small. On the other hand, Weggel
concluded that in more rural areas such as Dividing
Creek, New Jersey, only the pockets of development
would be protected. The roads that connected them
would have to be elevated or replaced with bridges,
and the small number of isolated buildings would
have to be moved.
Weggel estimates that the nationwide cost of
protecting developed shorelines would be $25
billion, assuming bulkheads are built, and $80 billion
assuming levees are built. Unlike wetlands loss, the
cost of protecting developed areas from the sea
would be concentrated more in the Northeast than
in the Southeast because a much greater portion of
the southeastern coast is undeveloped.
Table 7-1. Total Cost of Protecting Long Beach Island from a 2-Meter Rise in Sea Level (millions of 1986
dollars)
Protective measure
Encirclement
Island
raising
Island
migration
Sand costs:
Beach
Land creation/maintenance
Moving/elevating houses
Roads/utilities
Levee and drainage
Total
290
NA
NA
0
542
"832
290
270
74
1072
0
0
321
37
7352
0
1706
7710
NA = Not applicable.
Source: Leatherman (Volume B); Weggel (Volume B)
135
-------
Chapter 7
Table 7-2. Cumulative Cost of Protecting Sheltered Waters for a 2-Meter Rise in Sea Level (millions of 1986
dollars)
New
bulkhead
Raise old
bulkhead
Move
building
Roads/
utilities
Total
Index sites
New York
Long Beach Island
Dividing Creek
Miami area
Corpus Christi
San Francisco Bay3
Nationwide estimate
57
3
4
11
11
3
Low
205
4
6
111
29
19
0.5
2.7
4.8
0.3
2.8
2.0
His
9.5
3.8
18.2
8.3
40.9
20.0
272.3
13.7
33.0
130.7
83.4
44.0
Northeast
Mid-Atlantic
Southeast
West
Nation
6,932
4,354
9,249
4,097
24,633
.1 o —
23,607
14,603
29,883
12,802
80,176
Site names refer to the name of U.S. Geological Survey quadrant, not to the geographical area of the same
name.
Source: Weggel et al. (Volume B).
Case Study of the Value of Threatened
Coastal Property
Study Design
Yohe's (Volume B) objective was to estimate
the loss of property that would result from not
holding back the sea. Using estimates of erosion
and inundation for Long Beach Island from
Leatherman and Park et al., Yohe determined
which land would be lost from sea level rise for a
sample of strips spanning the island from the ocean
to the bay. He then used the Ocean County, New
Jersey, tax assessor's estimates of the value of the
land and structures that would be lost, assuming
that the premium associated with a view of the bay
or ocean would be transferred to another property
owner and not lost to the community. He estimated
the annual stream of rents that would be lost by
assuming that the required return on real estate is
10% after tax. Yohe assumed that a property on
the bay side was "lost" whenever it was flooded at
high tide, and that property on the ocean side was
"lost" when the house was within 40 feet of the
spring high tide mark. (See Titus and Greene,
Volume B, for discussion.)
Limitations
Yohe's results for a sea level rise of less than 18
inches are sensitive to the assumption regarding
when a property would be lost. On the bay side,
people might learn to tolerate tidal inundation.
Unless a major storm occurred, people 'could
probably occupy oceanfront houses until they were
flooded at high tide. However, the resulting loss of
recreational use of the beach probably would have
a greater impact than abandoning the structure.
Tax maps do not always provide up-to-date
estimates of property values. However, the
distinction between the tax assessor's most recent
estimate of market value and the current market
value is small compared with the possible changes
in property values that will occur over the next
century; hence, Titus and Greene used tax assessors
estimates of market values.
136
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Sea Level Rise
Results
Yohe's results suggest that the cost of gradually
raising Long Beach Island would be far less than
the value of the resources that would be protected.
Figure 7-6 compares Yohe's estimates of the annual
loss in rents resulting from not holding back the sea
with Weggel's estimates of the annual cost of raising
the island for the 2-meter scenario. With the
exception of the 2020s, the annual loss in rents
resulting from not holding back the sea would be
far less than the annual costs of pumping sand and
elevating structures. Titus and Greene point out
that the cost would be approximately $1,000 per
year per house, equivalent to 1 week's rent (peak
season).
Nationwide Cost of Pumping Sand Onto
Recreational Beaches
Leatherman's goal (Volume B) was to estimate
the cost of defending the U.S. ocean coast from a
rise in sea level.
Study Design
Owing to time constraints, it was possible to
consider only one technology. Based on the Long
Beach Island results, Leatherman assumed that the
cost of elevating recreational beaches and coastal
barrier islands by pumping in offshore sand would
provide a more representative cost estimate than
assuming that barrier islands would be abandoned,
would migrate landward, or would be encircled with
dikes and levees.
The first step in Leatherman's analysis was to
estimate the area of (1) the beach system, (2) the
low bayside, and (3) the slightly elevated oceanside
of the island. Given the areas, the volume of sand
was estimated by assuming that the beach system
would be raised by the amount of sea level rise.
The bay and ocean sides of the island would not be
raised until after a sea level rise of 1 and 3 feet,
respectively. Cost estimates for the sand were
derived from inventories conducted by the U.S.
Army Corps of Engineers.
Leatherman applied this method to all
recreational beaches from Delaware Bay to the
mouth of the Rio Grande, as well as California,
which accounts for 80% of the nation's beaches. He
also examined one representative site in each of the
remaining states.
Limitations
Although the samples of sites hi the Northeast
and Northwest are representative, complete
coverage would have been more accurate.
Furthermore, Leatherman used conservative
assumptions in estimating the unit costs of sand.
Generally, a fraction of the sand placed on a beach
washes away because the sand's grain is too small.
Moreover, as dredges have to move farther offshore
to find sand, costs will increase.
For Florida, Leatherman used published
estimates of the percentage of fine-grain sand and
assumed that the dredging cost would rise $1 per
cubic yard for every additional mile offshore the
dredge had to move. For the other states, however,
he assumed that the deposits mined would have no
fine-grain sand and that dredging costs would not
increase. (To test the sensitivity of this assumption,
Titus and Greene developed an increasing-cost
scenario.) Leatherman assumed no storm worse
than the 1-year storm, which underestimates the
sand volumes required.
A final limitation of the Leatherman study is
that it represents the cost of applying a single
technology throughout the ocean coasts of the
United States. Undoubtedly, some communities
(particularly Galveston and other wide barrier
islands in Texas) would find it less expensive to
erect levees and seawalls or to accept a natural
shoreline retreat.
Results
Table 7-3 illustrates Leatherman's estimates. A
total of 1,900 miles of shoreline would be nourished.
Of 746 square miles of coastal barrier islands that
would be raised for a 4-foot sea level rise, 208
square miles would be for a 2-foot rise. As the
table shows, two-thirds of the nationwide costs
would be borne by four southeastern states: Texas,
Louisiana, Florida, and South Carolina.
Figure 7-11 illustrates the cumulative nationwide
costs over time. For the 50- and 200-centimeter
scenarios, the cumulative cost would be $2.3 to $4.4
billion through 2020, $11 to $20 billion through
2060, and $14 to $58 billion through 2100. By
137
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Chapter 7
Table 7-3. Cost of Placing Sand on U.S. Recreational Beaches and Coastal Barrier Islands and Spits
(millions of 1986 dollars)
Sea level rise by 2100
State
Baseline
50cm
100 cm
Nation
3,788.0
14,512.0
26,745.0
200cm
Maine3
New Hampshire3
Massachusetts3
Rhode Island3
Connecticut3
New York3
New Jersey3
Delaware
Maryland
Virginia
North Carolina
South Carolina
Georgia
Florida
(Atlantic coast)
Florida
(gulf coast)
Alabama
Mississippi
Louisiana
Texas
California
Oregon3
Washington State3
Hawaii3^
22.8
8.1
168.4
16.3
101.7
143.6
157.6
4.8
5.7
30.4
137.4
183.5
25.9
120.1
149.4
11.0
13.4
1,955.8
349.6
35.7
21.9
51.6
73.5
119.4
38.9
489.5
92.0
516.4
769.6
902.1
33.6
34.5
200.8
655.7
1,157.9
153.6
786.6
904.3
59.0
71.9
2,623.1
4,188.3
174.1
60.5
143.0
337.6
216.8
73.4
841.6
160.6
944.1
1,373.6
1,733.3
71.1
83.3
386.5
1,271.2
2,147.7
262.6
l,791.0b
l,688.4b
105.3
128.3
3,492.7
8,489.7
324.3
152.5
360.1
646.9
412.2
142.0
1,545.8
298.2
1,799.5
2,581.4
3,492.5
161.8
212.8
798.0
3,240.4
4,347.7
640.3
7,745.5b
4,091.6b
259.6
369.5
5,231.7
17,608.3
625.7
336.3
794.4
1,267.5
58,002.0
Indicates states where estimate was based on extrapolating a representative site to the entke state. All other
states have 100% coverage.
Florida estimates account for the percentage of fine-grain sediment, which generally washes away, and for cost
escalation as least expensive sand deposits are exhausted. All other estimates conservatively ignore this
issue.
Source: Leatherman (Volume B) (baseline derived from Leatherman).
contrast, if current trends continue, the total cost of
sea level rise for beach nourishment would be about
$35 million per year.
Synthesis of the Three National Studies
Study Design
Although Weggel used Park's topographic data,
the analysis in the three nationwide studies
proceeded independently. Titus and Greene's
primary objectives (Volume B) were to combine
various results to estimate the nationwide cost of
holding back the sea for various sea level rise
scenarios and to derive ranges for the specific
impacts. Their objectives were as follows:
1. Use Park's results to weight WeggePs high and
low scenarios according to whether levees or
bulkheads would be necessary, and interpolate
138
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Sea Level Rise
$ Billons
0 V- 001
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s
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t
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s
/
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/
^.-"•'
200 Cm
100 Cm
ED Cm
1B80 2000 2020 2040 3080 2090 2100
Year
Figure 7-11. Nationwide cost of sand for protecting
ocean coast (in 1986 dollars) (Leatherman, Volume
B).
Weggel's cost estimate for the 2-meter rise to
rises of 50 and 100 centimeters;
2.
3.
4.
Use results from Leatherman and Weggel,
along with census data, to estimate the
nationwide cost (other than pumping sand) of
raising barrier islands;
Develop an increasing-cost scenario for the cost
of protecting the open ocean coast; and
Develop statistical confidence intervals for
wetland loss, impacts of the various policy
options, and costs of protecting developed
shores.
Cost of Protecting Sheltered Shores
Titus and Greene developed a single estimate
for protecting each site with bulkheads and levees
by assuming that the portion of developed areas
protected with levees would be equal to the portion
of the lowlands that Park estimated would be
inundated. They interpolated the resulting 2-meter
estimate to 50- and 100-centimeter estimates, based
on Weggel's assumption that the cost of building
bulkheads and levees rises as a function of the
structure's height.
Cost of Raising Barrier Islands Other Than Dredging
Weggel's case study of Long Beach Island
provided cost estimates for elevating structures and
rebuilding roads, while Leatherman estimated the
area that would have to be raised. Many barrier
islands have development densities different from
those of Long Beach Island because they have large
tracts of undeveloped land or larger lot sizes.
Therefore, Titus and Greene used census data to
estimate a confidence interval for the average
building density of barrier islands, and they applied
Weggel's cost factors.
Sensitivity of Sand Costs to Increasing Scarcity of
Sand
Titus and Greene used Leathennan's escalating
cost assumptions for Florida to estimate sand
pumping costs for the rest of the nation.
Confidence Intervals
The Park and Weggel studies involved sampling,
but the researchers did not calculate statistical
confidence intervals. Therefore, Titus and Greene
developed 95% confidence intervals for the cost of
protecting sheltered coasts, the area of wetlands loss
for various scenarios.
Limitations
Besides all of the limitations that apply to the
Park, Leatherman, and Weggel studies, a number of
others apply to Titus and Greene.
Cost of Protecting Sheltered Shores
Titus and Greene assumed that the portion of
the coast requiring levees (instead of bulkheads)
would be equal to the portion of lowlands that
otherwise would be inundated. This assumption
tends to understate the need for levees. For
example, a community that is 75% high ground
often would still have very low land along all of its
shoreline and hence would require a levee along
100% of the shore. But Titus and Greene assume
that only 25% would be protected by levees.
: 139
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Chapter 7
Cost of Raising Barrier Islands
The data provided by Weggel focused only on
elevating roads, buildings, and bulkheads. Thus,
Titus and Greene do not consider the cost of
replacing sewers, water mains, or buried cables. On
the other hand, Weggel's cost factors assume that
rebuilt roads would be up to engineering standards;
it is possible that communities would tolerate
substandard roads. In addition, the census data
Titus and Greene used were only available for
incorporated communities, many of which are part
barrier island and part mainland; thus, the data
provide only a rough measure of typical road
density.
Sensitivity of Sand Costs to Increased Scarcity of
Sand
Finally, Titus and Greene made no attempt to
determine how realistic their assumption was that
sand costs would increase by the same pattern
nationwide as they would in Florida.
Results
Loss of Wetlands and Dryland
Table 7-4 illustrates 95% confidence intervals
for the nationwide losses of wetlands and dryland.
If all shorelines were protected, a 1-meter rise
would result in a loss of 50 to 82% of U.S. coastal
wetlands, and a 2-meter rise would result in a loss
of 66 to 90%. If only the densely developed areas
were protected, the losses would be 29 to 69% and
61 to 80% for the 1- and 2-meter scenarios,
respectively. Except for the Northeast, no
protection results hi only slightly lower wetland loss
than protecting only densely developed areas.
Although the estimates for the Northeast, mid-
Atlantic, the gulf regions outside Louisiana, and the
Florida peninsula are not statistically significant (at
the 95% confidence levels), results suggest that
wetlands loss would be least in the Northeast and
Northwest.
Table 7-4. Nationwide Loss of Wetlands and Dryland3 (95% confidence intervals)
'Square milesp
Baseline
50-cm rise
100-cm rise
200-cm rise
Wetlands
Total protection
Standard
protection
No protection
Dryland
Total protection
Standard
protection
No protection
N.C.
1168-3341
(9-25)
N.C.
1906-3510
N.C.
4944-8077
(38-61)
2591-5934
(20-45)
2216-5592
(17-43)
2180-6147
3315-7311
6503-10843
(50-82)
3813-9068
(29-69)
3388-8703
(26-66)
0
4136-9186
5123-10330
8653-11843
(66-90)
4350-10995
(33-80)
3758-10025
(29-76)
6438-13496
8791-15394
^Wetlands loss refers to vegetative wetlands only.
Numbers in parentheses are percentages.
NC = Not calculated.
Source: Titus and Greene (Volume B).
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Sea Level Rise
Table 7-5. Cumulative Nationwide Cost of Protecting Barrier Islands and Developed Mainland Through the
Year 2100 (billions of 1986 dollars)3
Sea level scenario
Baseline
50-cm rise
100-cm rise
200-cm rise
Open coast
Sand
Raise houses,
roads, utilities
Sheltered shores
Totalb
3.8
0
1.0-2.4
4.8-6.2
15-20
9-13
5-13
32-43
27-41
21-57
11-33
73-111
58-100
75-115
30-101
119-309
aCosts due to sea level rise only.
bRanges for totals are based on the square root of the sum of squared ranges.
Source: Titus and Greene (Volume B).
Costs of Holding Back the Sea
Table 7-5 illustrates the Titus and Greene
estimates of the costs of holding back the sea. The
low range for the sand costs is based on
Leatherman's study, and the high range is based on
the increasing cost scenario Titus and Greene
developed. The uncertainty range for the costs of
elevating structures reflects the uncertainty in census
data regarding the current density of development.
High and low estimates for the cost of protecting
sheltered shorelines are based on the sampling
errors of the estimates for the 46 sites that both
Park et al. and Weggel et al. examined.
Titus and Greene estimated that the cumulative
nationwide cost of protecting currently developed
areas in the face of a 1-meter rise would be from
$73 to 111 billion, with costs for the 50- and 200-
centimeter scenarios ranging from $32 to 309
billion. These costs would imply a severalfold
increase in annual expenditures for coastal defense.
Nevertheless, compared with the value of coastal
property, the costs are small.
POLICY IMPLICATIONS
Wetlands Protection
The nationwide analysis showed that a 50- to
200-centimeter rise in sea level could reduce the
coastal wetlands acreage (outside Louisiana) by 17
to 76% if no mainland areas were protected, by 20
to 80% if only currently developed areas were
protected, and by 38 to 90% if all mainland areas
were protected. These estimates of the areal losses
understate the differences in impacts for the various
land-use options. Although a substantial loss would
occur even with no protection, most of today's
wetland shorelines would still have wetlands; the
strip simply would be narrower. By contrast,
protecting all mainland areas would generally
replace natural shorelines with bulkheads and
levees. This distinction is important because for
many species of fish, the length of a wetland
shoreline is more critical than the total area.
Options for State and Local Governments
Titus (1986) examined three approaches for
maintaining wetland shorelines in the face of a
rising sea: (1) no further development in lowlands;
(2) no action now but a gradual abandonment of
lowlands as sea level rises; and (3) allowing future
development only with a binding agreement to allow
such development to revert to nature if it is
threatened by inundation.
The first option would encounter legal or
financial hurdles. The extent to which the
"due-process" clause of the Constitution would allow
governments to prevent development in anticipation
of sea level rise has not been specifically addressed
141
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Chapter 7
by the courts. Although purchases of land would be
feasible for parks and refuges, the cost of buying
the majority of lowlands would be prohibitive.
Moreover, this approach requires preparation for a
rise in sea level of a given magnitude; if and when
the sea rises beyond that point, the wetlands would
be lost. Finally, preventing future development
would not solve the loss of wetlands resulting from
areas that have already been developed.
Enacting no policy today and addressing the
issue as sea level rises would avoid the costs of
planning for the wrong amount of sea level rise but
would probably result in less wetlands protection.
People are developing coastal properly on the
assumption that they can use the land indefinitely.
It would be difficult for any level of government to
tell property owners that they must abandon their
land with only a few years' notice, and the cost of
purchasing developed areas would be even greater
than the cost of buying undeveloped areas.
Economic theory suggests that under the third
alternative, people would develop a properly only if
the temporary use provided benefits greater than
the costs of writing it off early. This approach
would result in the greatest degree of flexibility,
because it would allow real estate markets to
incorporate sea level rise and to determine the most
efficient use of land as long as it remains dry.
This approach could be implemented by
regulations that prohibit construction of bulkheads
as sea level rises or by the use of conditional long-
term leases that expire when high tide falls above a
property's elevation.
The State of Maine (1987) has implemented
this third approach through its coastal dune
regulations, which state that people building houses
along the shore should assume that they will have to
move their houses if their presence prevents the
natural migration of coastal wetlands, dunes, or
other natural shorelines. A number of states also
have regulations that discourage bulkheads, although
they do not specifically address sea level rise. The
option can be implemented through cooperative
arrangements between developers, conservancy
groups, and local governments. (See Titus and
Greene, Volume B, for additional details.)
The Federal Role
Section 404 of the Clean Water Act discourages
development of existing wetlands, but it does not
address development of areas that might one day be
necessary for wetland migration. This program will
provide lasting benefits, even if most coastal
wetlands are inundated. Although marshes and
swamps would be inundated, the shallow waters that
formed could provide habitat for fish and
submerged aquatic vegetation. No one has assessed
the need for a federal program to protect wetlands
in the face of rising sea level.
Coastal Protection
State and Local Efforts
State and local governments currently decide
which areas would be protected and which would
be allowed to erode. Currently, few localities
contribute more than 10% of the cost of beach
nourishment, with the states taking on an increasing
share from the federal government. However, many
coastal officials doubt that their states could raise
the necessary funds if global warming increased the
costs of coastal protection over the next century by
$50 to $300 billion. If state funds could not be
found, the communities themselves would have to
take on the necessary expenditures or adapt to
erosion.
Long Beach Island, New Jersey, illustrates the
potential difficulties. The annual cost of raising the
island would average $200 to $1,000 per house over
the next century (Titus and Greene, Volume B).
Although this amount is less than one week's rent
during the summer, it would more than double
property taxes, an action that is difficult for local
governments to contemplate. Moreover, the island
is divided into six jurisdictions, all of which would
have to participate.
More lightly developed communities may decide
that the benefits of holding back the sea are not
worthwhile. Sand costs would be much less for an
island that migrated. Although Weggel estimated
that higher costs would be associated with allowing
Long Beach Island to migrate landward than with
raising the island in place, this conclusion resulted
largely from the cost of rebuilding sewers and other
utilities that would still be useful if the island were
raised.
142
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Sea Level Rise
Regardless of how a barrier island community
intends to respond to sea level rise, the eventual
costs can be reduced by deciding on a response well
in advance. The cost of raising an island can be
reduced if roads and utilities are routinely elevated
or if they have to be rebuilt for other reasons (e.g.,
Titus et al., 1987). The cost of a landward
migration also can be reduced by discouraging
reconstruction of oceanfront houses destroyed by
storms (Titus et al., 1984a). The ability to fund the
required measures also would be increased by
fostering the necessary public debate well before
the funds are needed.
Federal Efforts
While state governments generally are
responsible for protecting recreational beaches, the
U.S. Army Corps of Engineers is responsible for
several major federal projects to rebuild beaches
and for efforts to curtail land loss hi Louisiana. The
long-term success of these efforts would be
improved if the corps were authorized to develop
comprehensive long-term plans to address the
impacts of sea level rise.
Beach Erosion
In its erosion-control efforts, the corps has
recently shifted its focus from hard structures (e.g.,
seawalls, bulkheads, and groins) to soft approaches,
such as pumping sand onto beaches. This shift is
consistent with the implications of sea level rise:
groins and seawalls will not prevent loss of beaches
due to sea level rise. Although more sand will have
to be pumped than current analyses suggest, this
approach could ensure the survival of the nation's
beaches.
Nevertheless, consideration of accelerated sea
level rise would change the cost-benefit ratios of
many corps erosion control projects. As with the
operations of reservoirs (discussed in Chapter 16:
Southeast), the corps is authorized to consider flood
protection but not recreation. When they evaluated
the benefits of erosion control at Ocean City,
Maryland, the corps concluded that less than 10%
of the benefits would be for flood control (most
were related to recreation). Had they considered
accelerated sea level rise, however, the estimated
flood protection benefits from having a
protective beach would have constituted a
considerably higher fraction of the total benefits
(Titus, 1985).
Wetlands Loss in Louisiana
By preventing freshwater and sediment from
reaching the coastal wetlands, federal management
of the Mississippi River is increasing the
vulnerability of coastal Louisiana to a sea level rise
(e.g., Houck, 1983). For example, current
navigation routes require the U.S. Army Corps of
Engineers to limit the amount of water flowing
through the Atchafalaya River and to close natural
breaches in the main channel of the Mississippi;
these actions limit the amount of freshwater and
sediment reaching the wetlands. Alternative routes
have been proposed that would enable water and
sediment to reach the wetlands (Louisiana Wetland
Protection Panel, 1987). These include dredging
additional canals parallel to the existing Mississippi
River gulf outlet or constructing a deepwater port
east of the city.
Either of these options would cost a few billion
dollars. By contrast, annual resources for correcting
land loss in Louisiana have been in the tens of
millions of dollars. As a result, mitigation activities
have focused on freshwater diversion structures and
on other strategies that can reduce current wetland
loss attributable to high salinities but that would not
substantially reduce wetlands loss if sea level rises
50 to 200 centimeters (Louisiana Wetland
Protection Panel, 1987).
The prospect of even a 50-centimeter rise in sea
level suggests that solving the Louisiana wetlands
loss problem is much more urgent than is commonly
assumed. Because federal activities are now a
major cause of land loss, and would have to be
modified to enable wetlands to survive a rising sea,
the problem is unlikely to be solved without a
congressional mandate. A recent interagency report
concluded that "no one has systematically
determined what must be done to save 10, 25, or 50
percent of Louisiana's coastal ecosystem" (Louisiana
Wetland Protection Panel, 1987). Until someone
estimates the costs and likely results of strategies
with a chance of protecting a significant fraction of
the wetlands in face of rising sea level, it will be
difficult for Congress to devise a long-term solution.
143
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Chapter 7
Flood Insurance
In 1968, Congress created the National Flood
Insurance Program with the objective of reducing
federal disaster relief resulting from floods. The
Federal Emergency Management Agency (FEMA),
which already had responsibility for administering
disaster relief, was placed in charge of this program
as well.
The National Flood Insurance Program sought
to offer localities an incentive to prevent
flood-prone construction. In return for requiring
that any construction in a floodplain be designed to
withstand a 100-year flood, the federal government
would provide subsidized insurance to existing
homes and a fair-market rate for any new
construction (which was itself a benefit, since private
insurers generally did not offer flood insurance).
Moreover, as long as a community joined the
program, it would continue to be eligible for federal
disaster relief; if it did not join, it would no longer
be eligible. As a result of this program, new coastal
houses are generally elevated on pilings.
Although Congress intended to prevent coastal
disasters, the National Flood Insurance Act does
not require strategic assessments of long-term issues
(see Riebsame, Volume J). Thus, FEMA has not
conducted strategic assessments of how the program
could be managed to minimize flood damage from
shoreline retreat caused by both present and future
rates of sea level rise.
Congress recently enacted the Upton-Jones
Amendment (Public Housing Act of 1988), which
commits the federal government to pay for
rebuilding or relocating houses that are about to
erode into the sea. Although the cost of this
provision is modest today, a sea level rise could
commit the federal government to purchase the
houses on all barrier islands that did not choose to
hold back the sea. Furthermore, this commitment
could increase the number of communities that
decided not to hold back the sea.
The planned implementation of actuarially
sound insurance rates would ensure that as sea level
rise increased property risk, insurance rates would
rise to reflect the risk. This would discourage
construction of vulnerable houses, unless their value
was great enough to outweigh the likely damages
from floods. However, statutes limiting the rate at
which flood insurance rates can increase could keep
rates from rising as rapidly as the risk of flooding,
thereby increasing the federal subsidy.
No assessment of the impacts of sea level rise
on the federal flood insurance program has been
undertaken.
Sewers and Drains
Sea level rise also would have important impacts
on coastal sewage and drainage systems. Wilcoxen
(1986) examined the implications of the failure to
consider accelerated sea level rise in the design of
San Francisco's West Side (sewerage) Transport,
which is a large, steel-reiriforced concrete box
buried under the city's ocean beach. He found that
beach erosion will gradually expose the transport to
the ocean, leaving the system vulnerable to
undermining and eventual collapse. Protection costs
for the $100 million project would likely amount to
an additional $70 million. Wilcoxen concludes that
had sea level rise been considered, the project
probably would have been sited elsewhere.
The impacts of sea level rise on the construction
grants program probably would be less in most
other cases. As sea level rises, larger pumps will
be necessary to transport effluents from settling
ponds to the adjacent body of water. However, sea
level rise would not necessarily require alternative
siting. The projects serving barrier islands often are
located on the mainland, and projects located on
barrier islands are generally elevated well above
flood levels. If barrier islands are raised in
response to sea level as the nationwide analysis
suggests, sewerage treatment plants will be a small
part of the infrastructure that has to be modified.
Engineering assessments have concluded that it
is already cost-beneficial to consider sea level rise
in the construction of coastal drainage systems in
urban areas. For example, the extra cost of
installing the larger pipes necessary to accommodate
a 1-foot rise in sea level would add less than 10% to
the cost of rebuilding a drainage system in
Charleston, South Carolina; however, failure to
consider sea level rise would require premature
rebuilding of the $4 million system (Titus et al.,
1987).
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Sea Level Rise
RESEARCH NEEDS
A much better understanding of erosion
processes is needed to (1) understand how much
erosion will take place if no action is taken; and (2)
help identify the most cost-effective means for
protecting sandy shores. An improved
understanding of how wetland accretion responds
to different temperatures, higher CO2
concentrations, changing mineral content, and the
drowning of adjacent wetlands is needed. This will
refine our ability to project future wetlands loss and,
perhaps, devise measures for artificially enhancing
their vertical growth.
This report did not examine the impacts of
increased flooding because flood models have not
been applied to the large numbers of coastal sites
that would be necessary to conduct a nationwide
assessment. Time-dependent estuarine salinity
models, such as that of the Delaware River Basin
Commission, should be applied to major estuaries
to examine impacts on ecosystems and drinking
water supplies.
Assessments of the impacts of global warming
on coastal environments would be greatly improved
by better estimates of future sea level rise. In
addition to the improved ocean modeling that will
be necessary for better projections of surface air
temperatures (see Chapter 2: Climate Change), this
will also require a substantial increase in the
resources allocated for monitoring and modeling
glacial processes. Finally, this report assumed that
winds, waves, and storms remained constant; future
studies will need estimates of the changes in these
climatic variables.
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the Beach at Ocean City, Maryland. Washington,
DC: U.S. Environmental Protection Agency.
Titus, J.G. 1984a. Planning for sea level rise before
and after a coastal disaster. In: Earth, M.C., and
J.G. Titus, eds. Greenhouse Effect and Sea Level
Rise: A Challenge for This Generation. New York:
Van Nostrand Reinhold Company.
Titus, J.G., M.C. Barth, J.S. Hoffman, M. Gibbs,
and M. Kenney. 1984b. An overview of the causes
and effects of sea level rise. In: Barth, M.C., and
J.G. Titus, eds. Greenhouse Effect and Sea Level
Rise: A Challenge for This Generation. New York:
Van Nostrand Reinhold Company.
Titus, J.G., T. Henderson, and J.M. Teal. 1984.
Sea level rise and wetlands loss in the United States.
National Wetlands Newsletter 6:4.
Titus, J.G., C.Y. Kuo, MJ. Gibbs, T.B. LaRoche,
M.K. Webb, and J.O. Waddell. 1987. Greenhouse
effect, sea level rise, and coastal drainage systems.
Journal of Water Resources Planning and
Management. American Society of Civil Engineers
113(2):216-227.
Wilcoxen, PJ. 1986. Coastal erosion and sea level
rise: implications for ocean beach and San
Francisco's West Side Transport Project. Coastal
Zone Management Journal 14:3.
WMO. 1986. World Meteorological Organization.
Atmospheric ozone 1985. Assessment of our
understanding of the processes controlling its
present distribution and change. Global Ozone
Research and Monitoring Project, Report No. 16.
Geneva, Switzerland: World Meteorological
Organization.
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CHAPTER 8
BIOLOGICAL DIVERSITY
FINDINGS
Unlike most other impacts, loss of species and
reduced biological diversity are irreversible. The
ability of a natural community to adapt to changing
climate conditions will depend on the rate of climate
change, the size of species ranges, the dispersal
rates of the individual species, and whether or not
barriers to species migration are present. If climate
changes rapidly, many species will be lost.
Species Diversity
• The effect of climate change on species and
ecosystems will most likely vary, with some
species benefiting and others facing extinction.
The uncertainties surrounding the rate of
warming, individual species response, and
interspecies dynamics make impacts difficult to
assess. However, climate change would alter
competitive outcomes and destabilize natural
ecosystems in unpredictable ways.
• In many cases, the indirect effects of climate
change on a population, such as changes in
habitat, in food availability, and in
predator/prey relationships, may have a
greater impact than the direct physiological
effects of climate change.
• Natural and manmade barriers, including
roads, cities, mountains, bodies of water,
agricultural land, unsuitable soil types, and
habitat fragmentation, may block migration of
species in response to climate change and
exacerbate losses.
• The areas within the United States that appear
to be most sensitive to changes in climate are
those that have a number of threatened and
endangered species, species especially sensitive
to heat or drought stress, and species
inhabiting coastal areas.
• Rapid climate change would add to the already
existing threats biodiversity faces from
anthropogenic activities, such as deforestation
and habitat fragmentation.
Marine Ecosystems
• The loss of coastal wetlands and coastal
habitat resulting from sea level rise and
saltwater intrusion may profoundly affect the
populations of all inhabitants of these
ecosystems, including mollusks, shellfish,
finfish, and waterfowl. However, there is no
evidence to indicate these species would
become extinct.
Freshwater Ecosystems
• Freshwater fish in large bodies of water, such
as the Great Lakes, may increase in
productivity, but some significant species could
decline. Fish in smaller bodies of water may
be more constrained in their ability to respond
to climate change. They also may be harmed
by reductions in water quality.
Migratory Birds
• Migratory birds are likely to experience mixed
effects from climate change, with some arctic
nesting herbivores benefiting and continental
nesters and shorebirds suffering. The loss of
wintering grounds due to sea level rise and
changing climate could harm many species, as
would the loss of inland prairie potholes due to
potentially increased continental dryness.
Policy Implications
• Existing refuges, sited to protect a species or
ecosystem under current climate, may not be
properly located for this purpose if climate
changes or as species migrate.
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Chapter 8
Wildlife agencies such as the Department of
the Interior, state government agencies, and
conservation organizations may wish to assess
the feasibility of establishing migratory
corridors to facilitate species migration.
Areas that may become suitable future habitat
for threatened and endangered species, such as
lowland areas adjacent to current wetlands,
need to be identified and protected.
The practice of restoration ecology may need
to be broadened to rebuild parts of ecosystems
in new areas as climates shift.
The increase in the number of species at risk
as a result of climate change may require new
strategies for balancing ecosystem level
concerns with single species concerns. Agency
programs such as the Fish and Wildlife
Service's Endangered Species Program, may
wish to assess the relative risk of climate
change and more current stresses on ecological
systems.
VALUE OF BIOLOGICAL
DIVERSITY
Maintaining the biological diversity of our
natural resources is an important goal for the
nation. The preamble to the Endangered Species
Act of 1973 emphasizes the value of individual
species, stating that endangered and threatened
species of fish, wildlife, and plants "are of aesthetic,
ecological, educational, historical, recreational and
scientific value to the Nation and its people." We
depend upon our nation's biological resources for
food, medicine, energy, shelter, and other important
products. In addition to species diversity, the
genetic variability within a species and the wide
variety of ecosystems add to biological diversity.
Reduced biological diversity could have serious
implications for mankind as untapped resources for
research in agriculture, medicine, and industry are
irretrievably lost.
The evolving biological diversity of this planet
is inevitably affected by climate change. Historic
climate changes have resulted in major changes in
species diversity. This has been true for the millions
of years life has existed on Earth. Now our planet
may face a more rapid change in climate that may
have important consequences for biological diversity.
The National Resource
Public and private lands in the United States
provide sanctuary for an abundant diversity of plants
and animals. About 650 species of birds reside in
or pass through the United States annually. Over
400 species of mammals, 460 reptiles, 660
freshwater fishes, and tens of thousands of
invertebrates can be found in this country, in
addition to some 22,000 plants (U.S. Fish and
Wildlife Service, 1981). These species compose a
wide variety of ecosystem types within the United
States, including coniferous and broad-leaf forest,
grassland, desert, freshwater, marine, estuarine,
inland wetland, and agricultural ecosystems. Figure
8-1 shows the major ranges of natural vegetation in
the United States.
The U.S. national parks, forests, wilderness
areas, and fish and wildlife refuges are among the
public lands that provide sanctuary for wildlife
resources, including many endangered species. U.S.
public lands, which encompass over 700 million
acres (about 32% of the land area of the United
States), support about 700 rare species and
communities (Roush, 1986). Over 45% of the lands
held by the Forest Service, Fish and Wildlife
Service, National Park Service, and Bureau of Land
Management are in Alaska, and over 48% are
located in the 11 most western states (U.S.
Department of the Interior, 1987). However, much
of the nation's biological diversity lies outside these
areas.
Private land holdings also account for a great
deal of this nation's biological endowment. Private
groups, such as the Nature Conservancy and the
Audubon Society, manage 500,000 acres and 86,000
acres, respectively, for biological diversity.
GENERAL COMPONENTS OF
BIOLOGICAL DIVERSITY
Biological diversity can be broadly defined as
the full range of variety and variability within and
among living organisms. It includes species
diversity, genetic diversity, and ecosystemic or
community diversity. This report concentrates on
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Biological Diversity
Sf 3 Spruce-fir forest
r * va Transition pine-aspen forest
Ne Northeast hardwood forest
phu Oak-hickory forest
Oak-pine forest
Southeast pine forest
hSWj Southwest broadleaf woodland
p SgJ Short grassland
Mesqulta and desert grassland
r«*TB'd Tall grassland
c Creosote bush shrubland
Pacific coast forest
north: spruce, hemlock
south: douglas fir
I Coast Range-Rocky
•] Mountain conifer forest
* lower: pine, douglas fir
hlghen spruce-fir
summits: alpine meadow
IVPJ Rlverbottom cypress-tupelo-sweetgum
^8%
feM a Mangrove swampland
Figure 8-1. Natural vegetation in the United States (Hunt, 1972).
species diversity, but only because it is better
understood. Genetic and ecosystemic diversity are
equally important.
Species Diversity
Each species occurs in a characteristic range or
geographical area. The factors controlling species
ranges are critical constraints on biological diversity.
The presence of a species in an area suggests that
the species must have successfully achieved the
following: (1) dispersal into an area (no barriers to
dispersal, such as the presense of bodies of water or
unsuitable soil types); (2) survival in that area (the
physical characteristics of the area were suited to
the species' physiology, and food was available); and
(3) establishment in the area (the organism found
an appropriate place in the food web in the absence
of excessive competition and predation, and was
able to reproduce).
The stresses brought about by development,
overuse, and alteration of habitat have fragmented
much of the world's natural habitat and have
created many new barriers. Consequently, for many
species, dispersal has become much more difficult
than it was in the past. For other species, humans
have inadvertently aided dispersal and have caused
rapid spread in recent years. Such practices as
clearcut logging prevent the dispersal of species
adapted to dense forest conditions (e.g., flying
squirrels) and promote the dispersal of species
suited to open areas (e.g., deer).
Currently, 495 species are listed as endangered
within the United States, and over 2,500 species
await consideration for that status by the Fish and
Wildlife Service. The list of endangered species is
dominated by plants, birds, fishes, and mammals but
also includes insects, amphibians, reptiles, mollusks,
and crustaceans (U.S. Fish and Wildlife Service,
1988).
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Chapter 8
New species are created through the
evolutionary process of speciation, whereas existing
species are lost through extinction. Speciation
generally requires at least hundreds of thousands of
years. However, extinction as a result of human
activities, even without climate change, is occurring
rapidly and at an increasing rate. Owing to its
slowness, the process of speciation does little to
offset species' loss to extinction.
Stressed Biological Diversity
Biological diversity continues to erode steadily
around the globe as a result of human activities.
Habitat destruction, degradation, and fragmentation
have resulted in the loss of many species and have
reduced the ranges and populations of others.
These impacts affect all three levels of biological
diversity. Through providing an additional pressure
on ecological systems, climate change will further
reduce the biological diversity in this nation and
around the globe.
It is difficult to determine the exact rate of
species extinction because the number of species on
the Earth is known only to an order of magnitude.
A recent estimate by Wilson (1988) places the total
number of species between 5 and 30 million.
Assuming 10 million species, Wilson made the
rough calculation that one in every 1,000 species is
lost each year. Wilson then compared this to
estimates of extinction rates over geologic time,
which ranged between 1 in every 1 million and 1 in
every 10 million each year. Thus, human activities
may be eliminating species at least 1,000 times
faster than natural forces.
The significance of rare species should not be
underestimated. A narrowly or sparsely distributed
species may be a keystone in an ecosystem,
controlling the structure and functioning of the
community, or it may be a species of great and yet
unknown value to humans.
Genetic Diversity
Each species that persists has a characteristic
genetic diversity. The pool of genetic diversity
within a species constitutes an adaptation to its
present environment as well as a store of adaptive
options for some possible changes in the
environment. The loss of genetic diversity can
contribute to the extinction of a species by reducing
its ability to adapt to changing environmental
conditions.
Generally, species with larger populations have
greater genetic diversity. Species near extinction
represented by few individuals in few populations
have lower genetic diversity, a situation exacerbated
by inbreeding. Additionally, extreme climatic events
may cause bouts of natural selection that reduce
genetic variability (Mayr, 1963).
Community and Ecosystemic Diversity
Ecosystemic diversity is the number, of
distinctive assemblages of species and biotic
processes that occur in different physical settings.
A long-leaf pine forest, a sand dune, and a small
pond are all part of our diversity at this level.
Ecosystems come into existence through complex
physical and biological processes not now well
understood. They may be lost by outright
replacement of one by another (as in the
desertification of a grassland) or by the gradual
merging of two formerly separate ecosystems (as in
the loss of some estuarine systems when they
become saltier and take on more of the
characteristics of a purely saltwater ecosystem).
Ecosystems can also be eliminated because of
human activities (as in the filling in of a wetland).
FACTORS AFFECTING THE
RESPONSE OF BIOLOGICAL
DIVERSITY TO CLIMATE
CHANGE
Species respond to environmental change on a
hierarchy of time scales. For relatively small
changes occurring within the lifetime of an
individual, each member of the species can respond
through a variety of physiological adjustments.
Individual species differ in their ability to adjust to
change. Some can withstand a great deal of climate
change, whereas others are restricted to a narrow
range. Over several generations, natural selection
can cause genetic adaptation and evolution hi
response to the change. Alternatively, a species can
respond to climate change by moving into a new
area through migration and dispersal. This can
occur over a relatively short period of time if the
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Biological Diversity
species has the biological ability to move quickly.
The discussion of response to climate change
centers on migration as the response that could
occur over a relatively short period of time.
The distributions of species are significant
indicators of climate change. Local climate appears
to be the primary factor defining an environmental
setting and determining the species composition and
spatial patterns of communities in terrestrial zones
(Bolin et al., 1986). Temperature means,
temperature extremes, and precipitation are the
factors most often affecting the potential natural
distributional limits of a species (Ford, 1982), while
the actual distribution of a species is also affected
by soil type, soil moisture, ecological dynamics, and
regional isolation.
Rate of Climate Change
Predicting how a species of ecosystem might
respond to a given environmental change is difficult.
Adaptation to climate change will inextricably
depend on the rate of climate change. For some
species, migration rates may be inadequate to keep
up.
The large number of combinations of dispersal
range and age to reproduction make the potential
rate of migration different for every species.
Paleorecords suggest migration rates between 10
and 20 kilometers per century for chestnut, maple,
and balsam fir, and between 30 and 40 kilometers
per century for some oak and pine species (see
Chapter 5: Forests). On the other hand, cattle
egrets have shown a much quicker migration rate by
colonizing all of the North American tropics within
approximately 40 years.
As species .shift at different rates in response
,to climate change, communities may disassociate
into new arrangements of species. Local extinction
can result either directly from physiological
pressures or indirectly from changes in interspecies
dynamics. Hence, the effect of climate change on
an area will be to cause sorting and. separation of
species as a result of the differential rate of
migration and species retreat (Ford, 1982).
Ecosystems, therefore, will not migrate as a unit.
Species do not immediately respond to
changed and changing environmental conditions, A
negative response, such as local extinction in an
area, is usually quicker than the positive response of
new species' colonization of a region (see Chapter
5: Forests). In the Arctics, the lag period between
climate change and species response by migration
and colonization may be several hundred years
(Edlund, 1986). This lag period will leave areas
open for weedy, opportunistic species that can
quickly migrate and propagate in a region.
The rate of climate change will be crucial to
the survival of the species hi an ecosystem. A 3°C
(5°F) increase in temperature, for example, would
effect a several hundred kilometer poleward shift in
the temperate vegetation belts (Frye, 1983). If this
change took place within a century, species would
need to migrate several kilometers each year to
adapt to this warming. Plants have a wide range of
migration rates, and only some may be able to
achieve this rate. Failure of a species to "keep up"
with suitable environmental conditions would
eventually result in extinction.
Many factors make evaluating the impact of
climate change on ecosystems difficult. The great
inter dependencies among species in an ecosystem
add considerable uncertainty to the effect that the
various responses of individual species will have on
the system. An impact upon a single species could
profoundly affect the entire ecosystem. Certain
species are vital to the workings of their ecosystems.
Among them are large carnivores that regulate
predator-prey relationships, large herbivores that
significantly change vegetation, and organisms that
pollinate plants (WEI, 1988). Plants can also be key
species within an ecosystem. For example,
elimination of a tree species in a region could have
a significant effect on the whole forest ecosystem,
including birds, insects, and mammals.
Animal populations are generally much more
mobile than plants. But animal distributions heavily
depend on vegetation for food, protection, and
nesting habitat. Species not directly dependent on
vegetation ultimately depend on some other species
that is. The ranges of the fig wasp and the fig
depend entirely upon one another. In this case, the
plant species depends on a single pollinator, and
the insect species relies upon a single species of
plant for food (Kiester et al., 1984).
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Chapter 8
Effect on Genetic Diversity
With regard to genetic diversity, rapid climate
change would select for those genotypes
(combinations of genes) that were best suited to the
new climate regime and would tend to eliminate
others. This process of natural selection would
usually decrease the genetic variability within a
population. In the long term (evolutionary tune), it
is possible that greater climatic variability could
select for greater genetic variability.
Barriers to Response
The rate of species migration is also affected
by natural and manmade barriers and by
competition. Peters and Darling (1985) examined
the potential responses of species to climate change,
ecological interactions, and barriers to adaptation.
Physical barriers include mountains, bodies of water,
roads, cities, agricultural land, inappropriate soil
type, and habitat heterogeneity (landscape
patchiness). A species whose migration rate is
sufficient to keep up with changing conditions could
become constrained by a physical barrier. Inability
to cross the barrier could result in a reduction of
the range of the species and its eventual extinction.
Reserve and Island Species
Additional constraints on the ability of
populations living on reserves to respond to climate
change frequently result from insufficient habitat
area or isolation from other populations. The
problem of isolation is similar to that of island
species and has become known as the island
dilemma. Species on reserves are often remnants of
larger populations and are more susceptible to
environmental stress and extinction.
Species on reserves are likely to be pressured
from two directions as a result of climate change.
A population isolated on a reserve surrounded by
altered or unsuitable habitat receives little
immigration from populations outside the reserve.
Also, that population may not be able to colonize
areas outside the reserve as these areas become
suitable because of development or other alterations
of habitat.
Even without the added pressure of climate
change, reserve populations are vulnerable because
many reserves are not large enough to support a
self-sustaining population (Lovejoy, 1979). The
predictive theory of island biogeography showed
that, other factors being equal, small islands
accommodate smaller numbers of species than do
large islands (MacArthur and Wilson, 1967). This
held true for other ecological "islands," such as
mountaintops, woodlots, and lakes. Also, when
large ecosystems become smaller through
fragmentation, the number of species always
declines. Figure 8-2 shows how mammalian
extinctions have been inversely related to refuge
area in North American parks.
REFUGE AREA VS. SPECIES LOSS
40-
s
3 35-
i
u_ 30-
o
S 25-
£> "
ui
« 20-
3
•_•
g 15-
a 10-
5
v* S-
2
B B
1 3 5
4 6
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7 B
3
B
9 .
10
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
6 ' 8 ' 10
REFUGE AREA (LOG SQ. Km)
PARK
Bryce Canyon
Lassen Volcano
Zion
Crater Lake
Mount Rainier
Rocky Mountain
Yosemite
Sequoia-Kings Canyon
Glacier-Waterton
Grand Teton-Yellowstone
AREA (km2)'
144
426
588
641
976
1,049
2,083
3,389
4,627
20,736
PERCENT OF ORIGINAL
SPECIES LOST
36
43
36
31
32
31 •
25
23
7
4
Figure 8-2. Habitat area and loss of large animal species in North American parks (1986) (Newmark, 1987)
154
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Biological Diversity
Reserves that originally may have been well
sited to protect a vulnerable population and its
habitat may, after climate change and population
response, exist outside the now suitable range.
Figure 8-3 illustrates this problem. Large reserves
and buffer zones around reserves help to lessen
these problems. Corridors between reserves lessen
the problem of spatial isolation by allowing for
some migration between reserves.
DISTRIBUTION BEFORE MAN
CURRENT DISTRIBUTION
B.
DISTRIBUTION WITH CLIMATE CHANGE
C.l
Figure 8-3. Effect of climate change on biologica
reserves. Hatching indicates the following:
(A) species distribution before human habitation
(SL indicates southern limit of species range);
(B) fragmented species distribution after human
habitation; (C) species distribution after warming
(Peters and Darling, 1985).
Mountain Species
Just as species can migrate latitudinally, they
can respond altitudinally to climate change by
moving up or down a mountain slope. Species can
often respond more easily to changing conditions on
a slope because a shorter distance is required to
migrate to achieve the same temperature change.
Among the problems associated with altitudinal
migration are displacement of the species at the top
(Peters and Darling, 1985). Also, with the increase
in altitude, the area available for colonization
usually becomes smaller, communities become
isolated, and these smaller populations are more
prone to extinction.
CLIMATE EFFECTS RESEARCH
This section reviews some previous studies of
ecological response to past changes in climate,
recent studies of potential response to climate
change, and studies done for this report, which use
climate change scenarios from general circulation
models for a doubled CO9 environment (see Table
8-1).
Forest Ecosystems
The tree species that make up any forest are
major factors in determining the biological diversity
found there. Trees provide a multitude of habitats
and are the basis of much of the food web in a
forest.
Changes in forest composition resulting from
climate change (see Chapter 5: Forests) would have
significant implications for biological diversity.
Potential northerly range shifts of several hundred
to a thousand kilometers may be limited by the tree
species' ability to disperse. One possibility is that
southern pine forests will move farther north into
the regions currently occupied by mixed hardwood
species. Some of these hardwood forests contain
the highest tree species diversity found anywhere in
the United States (Braun, 1950). If they migrated
north, species would inevitably be lost, and overall
biological diversity would substantially decrease.
If forests were disrupted by the extinction of
the dominant tree species, the land would be
invaded by weedy, opportunistic species. This would
create a system with very low diversity, similar to
that following logging. Ultimately, these new
systems would not persist as succession took place,
but the pattern of succession following the removal
of a forest by rapid climate change is unknown.
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Chapter 8
Table 8-1. Studies Conducted for This Report and
Cited in This Chapter
Potential Responses of Great Lakes Fishes and
Their Habitat to Global Climate Warming -
Magnuson, Regier, Shuter, Hill, Holmer, and
Meisner, University of Wisconsin (Volume E)
The Effects of Global Climate Change on the
Water Quality of Mountain Lakes and Streams
- Byron, Jassby, and Goldman, University of
California at Davis (Volume E)
The Effects of Climate Warming on Lake Erie
Water Quality - Blumberg and DiToro,
HydroQual, Inc. (Volume A)
Ecological Effects of Global Climate Change:
Wetland Resources of San Francisco Bay -
Josselyn and Callaway, San Francisco State
University (Volume E)
, Projected Changes in Estuarine Conditions
Based on Models of Long-Term Atmospheric
Alteration - Livingston, Florida State University
(Volume E)
Tropical Forest Ecosystems
The greatest concentration of biological
diversity in the world is in the rain forests of the
Tropics (Wilson, 1988). Besides reducing diversity,
deforestation contributes to disruption of the global
carbon cycle by releasing CO2 into the atmosphere
and will directly affect the rate of climate change
(Prance, 1986). Indeed, on a global scale, the
problems of tropical deforestation, rapid climate
change through (among other factors) increased
CO, production, and the loss of biological diversity
can be seen as aspects of the same problem.
Tropical forests are also important as wintering
grounds for migratory birds coming from the United
States and as sources of new knowledge, because
the patterns of interactions between species and
climate are at their most sensitive and complex
there (Robinson, 1978; Janzen, 1986). The Tropics
may provide important leading indicators of the
ecological effects of climate change.
Freshwater Ecosystems
A study conducted by Magnuson et al.
(Volume E) concludes that in most areas of the
Great Lakes, climate warming would increase the
amount of optimal thermal habitat for warm-, cool-
and coldwater fishes (see Chapter 15: Great Lakes).
Although overall productivity would increase, overall
biological diversity could decrease through
intensified species interactions.
A study by Byron et al. (Volume E) on
mountain lakes suggests that climate change would
cause a range of impacts, including higher
productivity, changes in species composition, and
decreased water quality resulting from an increase
in algal growth (see Chapter 14: California).
Blumberg (Volume A) found that thermal
stratification in Lake Erie could decrease dissolved
oxygen levels.
The combined pressures of warmer waters,
saltwater intrusion, and a rising sea level would
significantly affect estuaries. The regional studies
suggest that coastal estuaries would see a growth in
marine species and a loss of some estuarine species.
A study by Josselyn (Volume E) on the San
Francisco Bay estuary suggests a decline in species
that use the delta for spawning (see Chapter 14:
California). Livingston (Volume E) concluded that
crabs, shrimp, oysters, and flounder in the
Apalachicola estuary could not survive the warming
in the GISS and GFDL scenarios (see Chapter 16:
Southeast).
Saltwater Ecosystems
In general, a warmer global climate would
increase productivity in ocean fisheries, but the
location and relative abundance of species are likely
to change (Sibley and Strickland, 1985). Up to
some threshold temperatures, such as 2°C (4 F),
warmer ocean temperatures would increase ocean
productivity in many species, but beyond that
threshold, productivity could decline (Glantz,
Volume J). It is likely that as productivity decreases,
biological diversity would decrease as well. Warmer
temperatures would most likely cause fish to
migrate poleward, although many other factors, such
as shifts in upwelling, may affect this.
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Biological Diversity
Coral Reef Ecosystems
Coral reefs provide the structural base for the
very biologically diverse reef ecosystems. Coral
reefs in the Caribbean and the Pacific may be
severely stressed as a result of warmer water
temperatures and the rising sea level associated with
climate change. Extensive bleaching of coral (the
expelling of symbiotic algae in response to
environmental stress) occurred in the Pacific after
the 1982-83 El Nino (Glynn, 1984) and in the
Caribbean following a summer of elevated water
temperatures in 1987 (Roberts, 1987). Loss of the
algae, the primary food source of the coral, is
thought to kill coral, making the reef ecosystem
vulnerable to erosion and physical devastation.
Coral reefs also will very likely be affected by
sea level rise. Studies by Buddemeier and Smith
(1988) and Cubit (1985) suggest that vertical
accretion of reef flats eventually may be unable to
keep up with an accelerating rise in sea level. Reef
flats also maybe subject to the stress of increasingly
large waves, erosion, and sedimentation, which can
inhibit coral growth (Buddemeier, 1988).
Arctic Ecosystems
Within the North American Arctics, plant size,
vigor, and reproduction could be expected to
increase with higher temperatures in the near term
(years to decades). Some low-lying plants would
most likely become upright, and there would be a
northerly movement of the tree line and all
vegetative zones (Edlund, 1986).
Over the longer term, however, rising
temperatures may be a mixed blessing. Overall
biological productivity is likely to increase, and some
species may be able to increase their range.
However, some arctic plant species are likely to be
out-competed by invading species, and many others
would face the same type of problem that
mountaintop species face: they would have nowhere
to go once they reach the Arctic Ocean. Thus,
native arctic species may be especially at risk.
Other arctic species may face their own problems.
For example, caribou would be severely harmed if
rivers do not freeze for periods long enough to
allow for migration.
Migratory Birds
Migratory waterfowl are likely to experience
very mixed effects as a result of warmer
temperatures (Boyd, 1988). Herbivorous, arctic
nesting species, such as geese, could benefit from
the shortened winter season and from the increases
in vegetation, in nesting habitat, and in ecosystem
productivity (Harington, 1987). Smaller arctic
nesting shorebirds, on the other hand, would be
harmed by the encroachment of taller vegetation,
potentially eliminating the preferred low-lying
tundra breeding ground. Other effects on
shorebirds could result from changes in ecosystem
predator-competitor relationships and changes in
the seasonal timing of such events as larval blooms,
upon which these birds depend for nourishment
while they are in a flightless stage and during
migration (Myers, 1988).
Waterfowl that breed in the continental interior
may suffer more than arctic nesters. Over half of
all waterfowl in North America originate hi the
prairie pothole region, a large agricultural area
riddled with ecologically productive permanent and
semipermanent wetlands. Increased temperature
and changes in seasonal precipitation could reduce
the highly variable number of potholes (wetlands)
in the area and could significantly impair the
productivity of breeding ducks.
Because of the drought of 1988, over 35% of
the seasonal wetlands within the prairie pothole
region were dry during the breeding season (U.S.
Fish and Wildlife Service, 1988). The Fish and
Wildlife Service forecast that only 66 million ducks
would migrate during the fall of 1988, a total of 8
million fewer than in 1987 and the second-lowest
migration on record (Irion, 1988). The productivity
index for mallards (number of young per adult) was
0.8, which was down by over 20% from the
historical average (U.S. Fish and Wildlife Service,
1988).
Waterfowl and other migratory birds are likely
to be affected on both ends of their migratory
journey and at staging areas along the way. The
loss of coastal wetlands, already an area of great
concern in the United States, reduces the amount of
habitat available to waterfowl, creating population
pressures on a limited resource. Of the 215 million
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Chapter 8
acres of wetlands in the coterminous United States
at the tune of settlement, fewer than 99 million
acres (46%) remain (U.S. Fish and Wildlife Service,
1988). Loss of an additional 26 to 82% of existing
coastal wetlands could occur over the next century
as a result of a 1-meter rise in sea level, saltwater
intrusion, and human development (see Chapter 7:
Sea Level Rise). Loss of wintering habitat along the
Gulf of Mexico would affect many waterfowl,
including mallards, pintails, and snow geese.
The Tropics, the winter home for many species
of migratory birds, may be significantly altered by
rapid climate change. The need to protect a species
in all parts of its range underscores the truly global
nature of the effects of rapid climate change on
biological diversity (Terborgh, 1974).
Endangered Species
Hundreds of species are currently listed as
endangered in the United States, and several
thousand await consideration for that status. These
species are likely to be stressed further as a result
of climate change.
Threatened and endangered species of the
Southeast would be very susceptible to the impacts
of sea level rise. Some species potentially at risk in
that region include the Key deer, manatee, Florida
panther, and Everglades kite (Breckenridge, 1988).
Climate change could also greatly increase the
number of rare, threatened, and endangered species
in the United States.
Other Direct and Indirect Stresses
As plant and animal species experience
increasing pressures from changes in temperature,
precipitation, and soil moisture, so too will
agriculture and urban water supplies. The changes
that result from the human response to climate
change may have the greatest impact on biological
diversity. If the continental interior of North
America dries, for example, wetlands that dry out
may be cultivated, and our current uses of water
resources may change. These secondary effects may
significantly compound the loss of biological
diversity.
NATIONAL POLICY
IMPLICATIONS
Climate change presents new challenges for
policymakers, regulators, and resource managers.
Planning for climate change may help to minimize
the disruption to natural systems and facilitate
adaptation under changing conditions. Decisions
will need to be made in an environment of
increased pressure on many other resources.
Policies regarding rare and endangered species
are likely to change as the number of species at risk
greatly increases. As more species become stressed
and potentially threatened by climate change,
reevaluation of protection policies may be required.
The tradeoffs between protection of individual
species and species' habitats and the broader
protection of biodiversity at the level of ecosystems
may need to be reexamined. As a part of this
question, decisions concerning whether to protect
existing communities or to foster establishment of
new communities may need to be made.
Management Options to Maintain
Biological Diversity
• Only a limited number of techniques are
available for maintaining biological diversity.
However, these techniques can be adapted and
intensified to meet the potentially great impacts of
rapid climate change.
Maintenance of Native Habitats
The most direct way to maintain biological
diversity is to manage land to retain ecosystems,
communities, and habitats. This already has been
successfully undertaken on a broad scale by federal
and state governments and by private organizations.
Ecosystem conservation, especially as represented by
the national parks and other large reserves,
maintains much of our national biological diversity.
These ongoing efforts will be the crucial first step
for maintaining biological diversity in the face of
climate change.
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Biological Diversity
Land acquisition and management policies
should take climate change into account. Climate
change and the future requirements of whole
ecosystems should be considered in siting and
managing reserves. To preserve functioning
ecosystems, large areas of land will be required.
Preserves would need to be at least large enough to
support self-sustaining populations. Lands that
could be more important as future plant and animal
habitats need to be identified and evaluated. Land
managers should consider whether these lands
should be set aside. Although identification of
appropriate future habitats is difficult and highly
dependent on the future rate and extent of climate
change, some areas, such as lowland areas adjacent
to current wetlands, hold good potential for habitat
protection.
To protect a species, alternative sites should
be considered with regard to the ecological needs of
target species under changing conditions. Siting
reserves in mountainous areas is beneficial because
it allows for the shorter-distance altitudinal shifts of
adjustment to changing climate. Stream corridors,
which can be effective avenues of dispersal for
terrestrial as well as aquatic organisms, should be
protected wherever possible. Providing corridors
for migration between reserves also should enhance
the ability of wildlife to adapt to climate change.
Ideally, these corridors should be wide enough to
maintain the ecosystem characteristics of the reserve
in their center. Some species do not find the
habitat conditions of narrow corridors suitable for
migration.
The pressures caused by changing climate are
likely to exacerbate competing land-use demands.
Acquisition of land for preserving biological
diversity will often be difficult, especially in areas
where agriculture or forestry may be expanding.
Flexible management strategies that reserve the
possibility of land management for biological
diversity in the future, while allowing for other use
in the interim, hold potential for reducing resource
conflicts and maintaining biological diversity.
Creative approaches such as encouraging
hedgerows, which may serve as migratory corridors,
should also be considered.
Maintenance of Species in Artificial Conditions
When individual species are threatened with
extinction, a possible option is to ensure that the
species is propagated in captivity. Indeed, some
rare species, such as the Pere David deer and the
California condor, now exist only in captivity. This
technique can be made to work for a variety of
species, depending on their biology and the degree
to which they successfully adapt to captive
conditions. As more species become threatened
with extinction due to climate change, the effort
applied in this area may have to increase
dramatically. However, only a tiny fraction of the
nation's species can be maintained in this way.
Existing seed bank programs also provide an
important method for conserving plant genetic
diversity.
Restoration of Habitat
Restoration ecology is a new discipline whose
goal is to develop methods to restore damaged
ecological communities to their prior unaltered
state. Except in forestry, where reforestation has a
longer tradition, restoration ecology has been in
existence for only a few years. Nonetheless, it offers
some real promise for ameliorating the effects of
rapid climate change.
Normally, restoration is done at the site where
the community previously existed and was altered or
damaged. Historical and baseline information is
used to manage the species in such a way as to
eliminate unwanted new species and to encourage
and possibly reintroduce native species.
Perhaps the theory and practice of restoration
ecology could be expanded to include rebuilding
natural communities on sites where they have not
previously existed. This activity has not yet been
attempted but may be necessary to save
communities displaced by climate change. If the
climate changes so that many of the key species of
a community can no longer survive in their original
range, and if the species are incapable of dispersing
and establishing themselves elsewhere, then the
artificial transplantation of components of entire
communities may become necessary. This
transplantation of communities would be a
monumental task and could help to save much
biological diversity, but it cannot possibly be
undertaken on the scale necessary to preserve all
species threatened by climate change. Restoration
ecology can be useful for extending reserve
boundaries and for providing migratory corridors.
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Chapter 8
Planning Options
While there are only a few management
techniques to maintain biological diversity, many
different groups in our society can implement them.
These groups can be divided into the private and
public sectors.
Many different groups in the private sector,
ranging from private individuals to large
conservation organizations, will have an interest in
maintaining biological diversity. However, all would
need information about the current and probable
future state of biological diversity. The federal
government may be able to play a role here by
providing information on the state of biological
diversity, including the systematics and distribution
of species; on the genetic variability of species; and
on the distribution of communities and ecosystems.
The four major federal land management
agencies develop plans intended to lay out a
comprehensive framework and direction for
managing federal land. Land Resource
Management Plans, required for each national
forest, define the direction of management in the
forest for the next 10 to 15 years. In addition, the
Forest Service prepares 50-year plans, as required
by the Resource Conservation Act. The National
Park Service prepares a General Management Plan
for each unit in the system that defines a strategy
for achieving management objectives within a 10-
year time frame. A Statement for Management is
also prepared for each national park and is
evaluated every 2 years; this includes a
determination of information needs. The Bureau
of Land Management's (BLM) Resource
Management Plans and the Fish and Wildlife
Service's Refuge Master Plans are prepared and
revised as needed for BLM resource areas and
wildlife refuges (U.S. Department of the Interior,
1987). These periodic reviews of the management
plans for public lands should include consideration
of the possible effect of climate change on
biodiversity.
Some federal land management agencies are
beginning to devote resources to the climate change
issue. The Forest Service, for example, has begun
planning the Forest Atmosphere Interaction (FAI),
which will be concerned with the relationship
between the atmosphere and our national forests.
The FAI has been designated a priority research
program for the Forest Service.
The federal government manages an enormous
amount of land and should consider management
options to preserve biological diversity on much of
that land. The major management techniques of
habitat maintenance and restoration ecology could
be applied by the agencies actively responsible for
managing the nation's public lands.
RESEARCH NEEDS
The ability to protect biological diversity is
severely restricted by a lack of knowledge regarding
the rate of climate change, the precise nature of the
change, how individual species will respond, and
how ecological balances will shift. Research should
be expanded in two areas: identification of
biological diversity, and species interactions and
biological diversity. New management options for
biological diversity should be derived from these
studies.
Identification of Biological Diversity
First and most important, an intensified, better
coordinated research effort, involving both
systematics (organism classification) and ecology, is
required to identify the biologically diverse
resources of our country. There should be more
coordination to identify U.S. plants and animals,
range maps, and habitat requirement information
for those species.
The apparently simple task of identifying the
species of plants and animals that exist in a given
area is actually a major barrier to further
understanding. Although common species are
usually easy to identify, serious problems are often
encountered in attempts to determine whether a
widespread group is, for example, one or two
species. For example, there is currently no federally
sponsored Flora (listing of all known plants) of the
United States.
Although it is necessary to describe the genetic
diversity of our nation's species, it is difficult to do
so in a direct fashion. What may be feasible is the
further development of population genetic theory
and of data that would predict the genetic diversity
of a species based on species' properties, such as
population size and habitat range variability.
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Biological Diversity
The challenge in describing ecosystem diversity
is to find the system of classification that best helps
make decisions intended to minimize the loss of
biological diversity. Such a system will most likely
only be found through experience. For now, we
should continue with the many different approaches
of ecosystem classification, and we should look for
the strengths of each.
Species Interactions and Biological
Diversity
The second area to which research should be
devoted is the direct effects of climate on species
and the indirect interactions of species with other
species dependent on climate. Comprehensive
mapping of species' ranges along temperature and
moisture gradients would provide valuable
information. The direct effect of climate change on
vegetation needs to be better assessed, and more
estimates of species' dispersal rates would
significantly improve our ability to identify species
at greatest risk.
A variety of ecosystems within a diversity of
climatic regions and terrains should be intensively
studied using analog climate regions under changed
climate conditions. Although an ecosystem's
response under changing climate conditions will not
be wholly predictable, modeling individual
ecosystemic responses would enhance knowledge of
the likely effects. Further research on how species
interact and how trophic structures might change
with climate would help predictive capabilities.
There should be further study on the question
of the relationship between ecosystem function and
species diversity to resolve the uncertainty in this
area Modeling the effect of climate change on
ecosystem function and its relationship to diversity
would help with predictive capabilities.
It will be impossible to study in detail even a
fraction of the nation's species. The groups chosen
for study either must be representative of many
species or must possess some special properties
(such as extreme sensitivity to climate change). The
method of deciding which group to study is itself a
major outstanding research question.
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CHAPTER 9
WATER RESOURCES
FINDINGS
Higher temperatures will most likely result in
greater evaporation and precipitation; earlier
snowmelt and reduced water availability in summer;
and, during dry periods, more rapid declines in soil
moisture and water levels, volumes, and flows.
Although a general warming and global increase in
precipitation are likely, the distribution of
precipitation is highly uncertain and may change in
unexpected ways. As a result, the frequency,
seasonality, variability, and spatial distribution of
droughts, water availability constraints, floods, and
water quality problems will very likely change.
Some regions could benefit from changing
precipitation patterns, while others could experience
great losses.
Although great uncertainty is associated with the
projection of future hydrologjc conditions and their
water-use implications, we must be most concerned
about current vulnerabilities to climate extremes
that could become exacerbated under climate
change. For instance, certain dry regions could
become more vulnerable to drought as a result of
higher temperatures, earlier snowmelt, and/or shifts
in precipitation.
Impacts on Water Uses
• If climate in a given region were to become
warmer and drier, water availability would
decrease and water demand would increase,
especially demand for irrigation and electric
power production.
• Lower riverflows resulting from drier
conditions could adversely affect instream uses
such as hydropower production, navigation,
aquatic ecosystems, wildlife habitat, and
recreation.
• Lower streamflow and lower lake levels could
cause powerplants to shift from once-through
to evaporative cooling. New plants may also locate
in coastal areas to obtain a water source that is
reliable and that may be used without violation of
thermal restrictions, although sea level rise could be
a problem. This would have important implications
for land use, transmission lines, and the costs of
power.
• Where water availability is reduced, conflicts
among users could increase. These include
conflicts over the use of reservoir systems for
flood control storage, water supply, or flow
regulation; and conflicts over water rights
among agricultural, municipal, and industrial
users of water supply.
• Should extreme flood events become more
frequent in a river basin as a result of earlier
snowmelt and increased precipitation, activities
located in the floodplain would endure more
damages or could require more storage
capacity (whether by construction, reallocation,
or changes in operating procedures), often at
the expense of other water uses.
Policy Implications
Water management responses to current
vulnerabilities are available and in use, and can
appropriately be brought into play to respond to
changing hydrologic conditions. These responses
include the following:
• Build new storage capacity, provided that the
structures show positive net benefits under a
variety of possible climatic conditions;
• Modify water system operations to improve
performance under extreme conditions, to
enhance recovery from extreme conditions,
and to accept greater risk to low-valued uses to
protect high-valued uses; and
• Encourage a reduction in water demand and
an increase in water-use efficiency through
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Chapter 9
conservation, water markets, water quality
control, drought contingency planning, and
coordinated uses of regional and interstate
water resources, provided that such measures
do not reduce the performance and recovery
capabilities of supply systems.
IMPACTS OF CLIMATE CHANGE
ON THE WATER RESOURCES IN
THE UNITED STATES
Current Status of Water Resources
The potential effects of climate change on
water resources must be examined within the
context of the existing and projected supply of, and
demands for, water.
The United States is endowed with a bountiful
supply of water, but the water is not always in the
right place at the right time, or of the right quality.
On the average, 4,200 billion gallons per day (bgd)
of precipitation fall on the lower 48 states.
However, a large portion of this water (66%)
evaporates, leaving 1,435 bgd (34%) for surface
water runoff and groundwater recharge. Largely
owing to weather variability, 675 bgd of the 1,435
bgd of runoff water in the coterminous United
States is considered to be available for use in 95
years out of 100 (Figure 9-1).
Surface and groundwaters are managed by
controlling and diverting flows through
impoundments and aqueducts; by withdrawing water
for such "offstream" applications as irrigation and
municipal use; by regulating flows to maintain
"instream" water quality and such uses as navigation,
hydropower, and recreation; and by controlling
flows under flood conditions to avoid loss of life,
damage to property, or inconvenience to the public.
Water may be "withdrawn" and returned to the
source more than once, or "consumed" and not
returned to the source.
In 1985, freshwater withdrawals for offstream
uses totaled 338 bgd. Of the withdrawals, 92 bgd
were consumed, mostly for irrigation. Withdrawals
and consumption of freshwater by major offstream
uses in 1985 are summarized in Figure 9-1.
Our investment in water infrastructure is
substantial. Water supply for municipal and
industrial use represented a $108 billion national
investment in infrastructure in 1984 (National
Council on Public Works Improvement, 1988).
Government agencies and industries spent $336
WITHDRAWALS
IRRIGATION/LIVESTOCK 140
THERMOELECTRIC POWER 131
DOMESTIC/COMMERCIAL 36
INDUSTRIAL/MINING 31
SURFACE/
GROUND-WATER
FLOWS
1435
CONSUMPTION I RETURN FLOWS
INSTREAM/SUBSURFACE USE
1097
NUMBERS INDICATE BILLIONS OF GALLONS PER DAY
Figure 9-1. Water withdrawals and consumption by offstream uses, coterminous United States. 1985 (Solley et
al., 1988).
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Water Resources
billion (in constant 1982 dollars) from 1972 to 1985
(Farber and Rutledge, 1987) on water pollution
abatement and control activities. In other areas,
excess water periodically floods agricultural and
urban areas, causing annual average damages valued
at $3 billion (in constant 1984 dollars) during the
past decade (National Council on Public Works
Improvement, 1988).
On a national scale, water supplies are
adequate, and water availability exceeds withdrawals
and consumption. However, in some regions, the
gap between demand for water and available supply
is narrow, or the variability in water supply is high,
or both. For example, average surface water
withdrawal exceeds average streamflow in the Great
Basin, Rio Grande, and Colorado River Basins. In
these water-short basins, offstream water uses often
conflict with instream uses, such as recreation and
maintenance of environmental quality. Degraded
water quality further limits water availability in
many regions. Table 9-1 summarizes the current
status of water supply by major river basin. The
regions are delineated in Figure 9-2.
Table 9-1. Current Status of Water Supply
River basin
Average
renewable
supply
(bgd)a
With-
drawals6
(1985)
Consump-
tion"
(1985)
Reservoir
storage1"
Stream-
flow
exceeded
95% of time0
G round -
water
overdraft
(%)
New England 78.4 11.7
Mid-Atlantic 80.7 29.5
South Atlantic-Gulf 233.5 13.5
Great Lakes 74.3 42.9
Ohio (exclusive of 139.5 22.3
Tennessee region)
Tennessee 41.2 22.3
Upper Mississippi (exclusive
0.9
2.1
2.1
2.9
1.5
0.8
15
11
15
8
13
24
62.4
62.2
55.5
62.6
59.0
77.0
0
1.2
6.2
2.2
0
of Missouri region)
Mississippi (entire basin)
Souris-Red Rainy
Missouri
Arkansas-White-Red
Texas -Gulf
Rio Grande
Upper Colorado
Colorado (entire basin)
Great Basin
Pacific Northwest
California
Alaska
Hawaii
Caribbean
77.2
464.3
6.5
62.5
68.6
33.1
5.1
14.7
15.6
9.9
276.2
70.2
975.5
7.4
5.1
21.9
3.7
4.3
55.2
22.3
41.4
109.8
51.4
47.4
81.8
12.9
53.6
0.4
17.2
11.9
2.3
1.2
1.9
20.3
11.7
18.2
43.7
16.3
27.2
36.4
4.5
29.9
0.0
1.8
3.2
14
32
110
120
41
67
182
229
403
30
20
49
0.1
0.1
5
54.0
46.7
32.1
40.7
36.5
27.5
33.3
39.0
75.0
50.0
70.7
44.0
78.5
60.3
35.6
0
0.5
0
24.6
61.7
77.2
28.1
0
48.2
41.5
8.5
11.5
0
0
5.1
"Average renewable supply is defined as the average flow potentially or theoretically available for use in the
region; units = billion gallons per day.
bWithdrawals, consumption, and reservoir storage are expressed as a percentage of the average renewable supply.
cAs a percentage of average streamflow.
Source: U.S. Water Resources Council (1978); U.S. Geological Survey (1984); Solley et al. (1988).
167
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Chapter 9
MISSISSIPPI/ I n,.TH ATLANTIC-GULF
-REGION/ | SOU™«GION 3
Figure 9-2. Water resources regions (U.S. Geological Survey, 1985).
Water supply and use have changed
significantly during the past decade. For the first
time since 1950, when the United States Geological
Survey began recording water withdrawals, national
total fresh and saline water withdrawals dropped
10% from 1980 to 1985 (from 443 billion gallons to
399 billion gallons, of which 338 billion gallons were
freshwater) (Solley et al., 1988). Increased
conservation and water recycling in agriculture,
industry, and energy production, slower growth in
energy demand, and decline in availability of new
water supply reduced or tempered water use in all
sectors (Solley et al., 1988). Withdrawals declined
by 7% in irrigation, by 33% in industry, and by 13%
in thermal power during the same period. Of the
major users, only municipal/domestic water supply
increased (by 7%).
The value of instream uses has risen relative
to that of offstream uses. Navigation and
hydropower have retained their importance as
society has begun to place greater value on
wastewater dilution, ambient water quality, fish and
wildlife habitats, and recreation. Higher values
on instream uses have made diversion of water for
such applications as agriculture in the West and for
powerplant cooling in the East more difficult.
Climate Change, Hydrologic Conditions,
and Water Resources
As shown in Figure 9-3, weather controls
hydrologic conditions through precipitation (mean
and frequency), runoff, snowmelt, transpiration and
evaporation, soil moisture, and the variability of
storms and drought. In turn, the ability to use
water resources is greatly influenced by variability in
hydrologic conditions.
Climate change will affect both the supply of
and demand for water. Figure 9-4 outlines the
major potential impacts of global warming and
changes in precipitation on water resources.
If climate warms in the United States, there
will likely be greater evaporation and, in turn,
greater precipitation; earlier snowmelt and, in turn,
reduced water availability in summer; and, during
168
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Water Resources
EVAPORATION AND TRANSPIRATION FROM
SURFACE-WATER BODIES, UNO SURFACE
AND VEGETATION > l
2.800 bgd
^PRECIPITATION ',
I'J 4 200 Dgd /, i j '
'. ijt&dfTjIti' it
iBECHAR06>s;
'
»S%^^i%.V/'''»
^1SB*iaS&V°.!*« »SAU* n6R«UMOJ(AJ
bgd=bi)lion gallons per day
Figure 9-3. Hydrologic cycle showing the gross water budget of the coterminous United States (Langbein et al.,
1949; Solley et al, 1983).
dry periods, more rapid declines in soil moisture
and water levels, volumes, and flows. Over the very
long term, groundwater availability may be affected
by altered recharge rates. Transpiration may not
increase as much because increased levels of carbon
dioxide may shrink the stoma or pores of plants
(Rosenberg, 1988). Although general warming is
likely to occur, the distribution of precipitation is
highly uncertain and may change in unexpected
ways.
Earlier studies have shown that small changes
in regional temperature, precipitation, and
evaporation patterns can cause significant changes
in water availability, especially in arid areas (see
Nemec and Shaake, 1982; Klemes and Nemec, 1985;
Beran, 1986). Precipitation is more variable in arid
than in humid areas. In addition, each degree of
temperature increase causes a relatively greater
decline in runoff and water availability in arid
regions as compared with humid regions. If
regional climate becomes warmer and drier, more
vulnerability to interruptions hi water availability
may be observed.
As a result, the frequency, seasonally,
variability, and spatial distribution of droughts,
water availability constraints, flodds, and water
quality problems would probably change. In many
locations, extreme events of dryness and flooding
could become more frequent. Some regions may
experience more drought conditions, others more
flooding, others degraded water quality, and others
a combination.
169
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Chapter 9
Climate Change
1
Temperature Increase in
All Regions
1
Regional Weather Variability
Increased demand
for air conditioning
Greater evapotranspiration
Soil moisture loss
Earlier snowmelt
Less precipitation
Less runoff and
streamflow
Reduced water supply
in hotter, drier
regions
Increased demand for
cooling water for
electric power
production
Increased demand
for irrigation
Increased surface
water withdrawals
Increased water
consumption and
groundwater
mining
1
e effects
water
ality
1
Conflicts between
off-stream and
in-stream uses
Conflicts b
irrigatio
municipal/
use
More precipitation
More runoff and
streamflow
Increased flooding
in hotter, wetter
regions
Increased demand
for flood
control
Conflicts between
flood control and
all other uses
Storage/supply
policy alternatives
Nonstructural/demand
policy alternatives
NOTE: Figure does not trace the impacts of reduced flows and increased evapotranspiration
on navigation, hydropower, and the Great Lakes.
Figure 9-4. National impacts of climate change on water supply and demand.
170
-------
Global warming may have a significant impact
on the demand for water in some regions. Warmer
temperatures may raise the demand for air-
conditioning in the South without a proportionate
decrease in demand for electric heat. Increased
demand for cooling water for electricity powerplants
would result (see Chapter 10: Electricity Demand).
Warmer temperatures may also prompt more
farmers to irrigate crops (see Chapter 6:
Agriculture).
Impacts of Climate Change on Water
Uses
Models of global climate change do not yet
provide reliable data to predict regional changes in
the water supplies; however, we can indicate
possible directions of impacts and the water uses
and sectors affected.
The following sections outline the potential
impacts of climate change on offstream and
instream water uses. The uses most likely to be
affected are those currently vulnerable to water
quantity and quality constraints:
• irrigation, the major source of withdrawals
and consumption in the West;
• thermal power production, a major source
of heat effluent and evaporative
consumption, especially in the East;
Water Resources
• instream uses that depend on levels and
flows; and
• domestic supplies that are vulnerable to
hazardous and toxic substances in ground
and surface water.
Table 9-2 highlights the vulnerability of major
water uses in each region to climate change.
Irrigation
Irrigation accounts for 42% of freshwater
withdrawals and 82% of freshwater consumption in
the United States. Although irrigated land
comprises about 10% of harvested cropland acreage
nationwide, it contributes 30% of the value of
cropland production. Many of these crops are
fruits, vegetables, and specialty crops (U.S. Water
Resources Council, 1978; Bajwa et al., 1987). The
17 western states account for 85% of the irrigated
lands in the country (Bajwa et al., 1987).
Water-short western states are exploring
numerous options for minimizing water
requirements. Because of depleted groundwater
supplies, the rising cost of obtaining groundwater,
and the high cost and limited availability of sites for
new surface water developments, irrigated acreage
has stabilized or is declining in some areas of the
West (Solley et al., 1988). Groundwater pumping
for irrigation has already started to decline in the
Table 9-2. Potential Regional Impacts of Climate Change on Water Uses: Areas of Vulnerability
Use Pacific
Northwest
Irrigation X
Thermal
power
Industrial
Municipal/
domestic
Water quality
Navigation
Flood control X
Hydropower X
Recreation
California
X
X
X
X
X
X
Arid
Western
River
Basins Great Plains Great Lakes Mississippi
X X
X
X
X XX X
X X
x • x
X
X
Southeast
X
X
X
X
X
X
X
Northeast
X
x
171
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Chapter 9
southern Great Plains States and in Arizona,
although the impacts on production have been
mitigated by the adoption of more efficient
irrigation systems and by a switch to crops offering
higher returns to water (Frederick and Kneese,
1989). In contrast, supplemental irrigation is rising
in the Southeast, largely because of expansion in
Georgia (Bajwa et al., 1987).
Climate change may significantly affect
agriculture. Summer drought and earlier runoff are
likely to change agricultural practices and increase
demands for irrigation in most areas east of the
Rocky Mountains.
Thermal Power Generation
Steam electric powerplants withdraw almost as
much freshwater as irrigation but consume much
less than irrigation. Although the freshwater
withdrawn to produce the nation's electricity totals
131 bgd, only 4.35 bgd are actually consumed
(Solley et al., 1988).
Future demand for water for power
production will depend on energy demand,
technology, and on federal and state regulations
governing instream water quality, instream flow, and
thermal pollution. Although a large amount of
installed capacity exists along eastern rivers,
freshwater withdrawals by powerplants hi the East
have decreased, and siting of plants hi coastal areas
has increased, so that by 1987, 30% of installed
capacity in coastal areas used saline surface water
(Solley et al., 1988). In addition, the thermal
regulations have caused a shift in the design of new
cooling systems from once-through cooling, which
discharges heat back into the water sources, to
evaporative cooling with towers and ponds
(Breitstein and Tucker, 1986). Although
evaporative cooling alleviates thermal pollution, it
increases water consumption.
During droughts, federal and state regulations
protecting instream uses and limiting thermal
discharges may constrain withdrawals for
powerplant cooling. In addition, powerplant water
needs on some eastern rivers are so large that
insufficient water may be available to dissipate heat
during low-flow conditions (Hobbs and Meier,
1979).
Demand for electric power and construction of
new generating capacity may increase as warmer
temperatures raise air-conditioning use (see Chapter
10: Electricity Demand). If streamflows are
reduced as a result of climate change, powerplants
using once-through cooling could be adversely
affected. Increased demand for power may
reinforce existing trends in powerplant design
toward evaporative cooling, and hi powerplant siting
toward coastal locations. With less water available,
low-flow conditions may interrupt power production
and may increase power production costs and
consumer electricity prices.
Industrial Uses
Since 1954, self-supplied industry steadily used
less and less water per unit of production (Solley et
al., 1988). This decline was partly due to
efficiencies achieved to comply with federal and
state water pollution legislation that restricts the
discharge of untreated water. The trend toward
more efficient industrial water uses is likely to
continue.
In regions where flows are reduced, there
could be a reduction in both the quantity and the
quality of water available for industrial production.
In addition, if the climate becomes drier, the
potential for interruption of industrial supply will be
increased.
Domestic Water Uses
Domestic uses account for 10% of total water
withdrawn and 11% of consumption. Over the past
20 years, domestic water use has increased from 16
to 25 bgd owing to growth hi the number of
households, with little change hi usage per
household (Solley et al., 1988).
Most municipal water supply systems are
designed to provide reliable water at all tunes (safe
yield). However, urban growth depends upon
developed water supply, which is approaching
exhaustion hi some areas. For instance, hi the
Southeast and parts of the West, a large percentage
of municipal water supply comes from groundwater
(U.S. Water Resources Council, 1978; Solley et al.,
1988). These regions withdraw more groundwater
than can be recharged; consequently, any increased
drought caused by climate change could accelerate
groundwater mining (see Chapter 14: California and
Chapter 16: Southeast).
172
-------
Water Resources
Municipalities in the West are purchasing
irrigators' water rights to ensure adequate water
supplies for urban growth. If climate change results
in reduced municipal supply, this trend will continue
or accelerate, leading to the loss of irrigated
acreage.
In the East, Midwest, and Southeast,
municipalities may be able to increase safe yield by
repairing and replacing existing leaking water
delivery systems and by consolidating fragmented
water supply districts. These actions could provide
the margins of safety necessary to accommodate
climate change.
Navigation
If riverflow and lake levels became lower,
navigation would be impeded. Systems that are
particularly vulnerable are those with unregulated
flows or levels and high traffic, such as the
Mississippi River and the Great Lakes. The effects
of dry conditions and reduced water levels on barge
traffic on the Mississippi in 1988 illustrate the
potential impacts of climate change.
Hvdropower
Because of the decline hi water availability
that could result from climate change, hydropower
output and reliability, which depend on flows, could
decline in the West and the Great Lakes. If the
Southeast became drier, it could face the same
problems unless it sacrificed water supply reliability
to maintain hydropower production.
Recreation
If the Southeast becomes drier, there may be
an increase in the conflict among water uses,
especially over reservoir releases and levels in the
Tennessee Valley and the Lake Lanier, Georgia,
system. The conflicts are among flood control,
which relies on storage; recreation, which depends
' on stable reservoir pool elevations; and downstream
uses and water supply, which depend on flows.
Climate Change and Water Quality
Water quality directly affects the availability of
water for human and environmental uses, since
water of unsuitable quality is not really "available."
Likewise, water quality in the nation's rivers, lakes,
and streams depends in part on water quantity.
Water supply is needed for dilution of wastewaters
that flow into surface and groundwater sources.
Freshwater inflows are needed to repel saline waters
hi estuaries and to regulate water temperatures in
order to forestall changes in the thermal
stratification, aquatic biota, and ecosystems of lakes,
streams, and rivers.
The Federal Clean Water Act of 1972 and
subsequent amendments ushered in a new era of
water pollution control. Massive expenditures for
treatment facilities and changes in water-use
practices by government and industry have
decreased the amount of "conventional" water
pollutants, such as organic waste, sediment, oil,
grease, and heat, that enters water supplies. Total
public and private, point and nonpoint, and capital
and operating water pollution abatement and
control expenditures from 1972 to 1985 totaled $336
billion in 1982 dollars (Farber and Rutledge, 1987).
Nevertheless, serious surface water quality
problems remain. Groundwater pollution problems,
especially toxic contamination and nonpoint source
pollution, are receiving increased recognition (U.S.
EPA, 1987b).
One-third of municipal sewage treatment
plants have yet to complete actions to be hi full
compliance with the provisions of the Clean Water
Act (U.S. EPA, 1987a). Federal and state
regulation of previously unregulated toxic and
hazardous water pollutants has just begun. In the
West, irrigation has increased the salinity levels in
the return water and soils of several river basins
(the lower Colorado, the Rio Grande, and the San
Joaquin) to an extent that threatens the viability of
irrigation (Frederick and Kneese, 1989).
Should climate change involve reduced flows,
less freshwater maybe available in some regions for
diluting wastewater salt and heat, especially in low-
flow periods (Jacoby, 1989). Dissolved oxygen levels
in the water would decline while temperature and
salinity levels would increase, affecting the viability
of existing fish and wildlife. Increased thermal
stratification and enhanced algal production due to
higher temperatures may degrade the water quality
of many lakes (see Chapter 15: Great Lakes;
Blumberg and DiToro, Volume A). Finally, the
combination of declining freshwater availability
173
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Chapter 9
and rising sea level would move salt wedges up
estuaries, changing estuarine ecology and
threatening municipal and industrial water supplies.
On the other hand, should climate change involve
increased flows, greater dilution of pollutants would
be possible in some regions.
Groundwater is the source for over 63% of
domestic and commercial use (Solley et al., 1988).
Although only a small portion of the nation's
groundwater is thought to be contaminated, the
potential consequences may be significant and may
include cancer, damage to human organs, and other
health effects (U.S. Congress, 1984).
Adequate recharge of aquifers is needed not
only to perpetuate supplies but also to flush
contaminants. Should climate change result in
reduced flows and reduced recharge, the quality as
well as the available quantity of groundwater could
be adversely affected.
Climate Change and Flood Hazards
Because of the buffering and redundancy
designed into large structures, major federal flood
control projects may be able to contain or mitigate
the impacts of more frequent severe floods.
However, continued performance for flood control
may come at the expense of other uses. For
example, drawing down the levels of reservoirs to
contain floodwaters from anticipated increases in
precipitation or earlier snowmelt may curtail water
availability for water supply. (This aggravated
conflict is a distinct possibility in California, for
example; see Chapter 14: California.)
The major concern with existing dams and
levees is the consequence of failure under extreme
conditions. For instance, an increased probability of
great floods, whether due to urbanization of
upstream watersheds or to climate change, would
cause dams with inadequate spillways to fail.
(Spillways are designed to prevent dam failure
through overtopping.)
The majority of large dams that provide
substantial flood storage are in good condition. The
National Dam Safety Inventory shows that the
overall condition of the U.S. Army Corps of
Engineers' more than 300 flood control reservoirs is
sound (National Council on Public Works
Improvement, 1988). In addition, the spillways of
many large dams are designed to pass a "probable
maximum flood" (an extreme flood event much
greater than the 100-year flood).
Smaller structures, such as urban drainage
culverts and sewers and local flood protection
projects, are currently more susceptible to failure
and are in poorer condition than large structures
(National Council on Public Works Improvement,
1988). One-third of the non-federal flood control
dams inspected under the national non-federal dam
program were found to be unsafe, mostly owing to
inadequate spillways (National Council on Public
Works Improvement, 1988). The capacity of these
non-federal, smaller, mostly urban flood control and
stormwater structures is more likely to be exceeded.
Urbanization upstream from many dams and water
control structures is already resulting in increased
impervious surfaces (such as pavement) and
increased peak runoff, making some structures
increasingly vulnerable to failure.
Climate Change and Conflicts Among
Water Uses
There is no doubt that climate change has the
potential to exacerbate water availability and quality
problems and to increase conflicts between regional
water uses as a result. The foregoing discussion has
highlighted a number of such conflicts:
• conflicts between instream and offstream
uses;
• conflicts among offstream uses, such as
agriculture, domestic use, and thermal
power production;
• conflicts between water supply and flood
control in the West;
• conflicts between all uses and recreation in
the Southeast; and
• conflicts between thermal power production
and instream uses, especially in the East.
In some areas, increased precipitation due to
climate change could alleviate water quality/quantity
problems and conflicts, but only after water
infrastructure is modified to accommodate the
increased probability of extreme events.
174
-------
Water Resources
REGIONAL IMPACTS OF
CLIMATE CHANGE
Water resources supply and management occurs
at the regional, river basin, state, and local levels.
To be of use to water resources decisionmakers,
climate change models and forecasts need to
address regional impacts.
The regional studies conducted by the U.S.
Environmental Protection Agency for this document
(see Table 9-3) examine the potential regional
impacts of climate change. (With the exception of
Table 9-3. Regional Water Resource Studies
California
« Interpretation of Hvdrologic Effects of Climate Change in the Sacramento-San Joaquin River Basin.
California - Lettenmaier, University of Washington (Volume A)
. Methods for Evaluating the Potential Impact of Global Climate Change - Sheer and Randall, Water
Resources Management, Inc. (Volume A)
. The Impacts of Climate Change on the Salinity of San Francisco Bay - Williams, Philip Williams &
Associates (Volume A)
Great Lakes
. Effects of Climate Changes on the Laurentian Great Lakes Levels - Croley, Great Lakes Environment
Research Laboratory (Volume A)
. Impact of Global Warming on Great Lakes Ice Cycles - Assel, Great Lakes Environment Research
Laboratory (Volume A)
• The Effects of Climate Warming on Lake Erie Water Quality - Blumberg and DiToro, HydroQual, Inc.
(Volume A)
. Potential Climatic Changes to the Lake Michigan Thermal Structure - McCormick. Great Lakes Environment
Research Laboratory (Volume A)
Great Plains
Effects of Projected CO^-Induced Climate Changes on Irrigation Water Requirements in the Great Plains
States - Allen and Gichuki, Utah State University (Volume C)
Southeast
• Potential Impacts of Climatic Change on the Tennessee Valley Authority Reservoir System - Miller and
Brock, Tennessee Valley Authority (Volume A)
• Impacts on Runoff in the Upper Chattahoochee River Basin - Mains, C.F. Hydrologist, Inc. (Volume A)
• Methods for Evaluating the Potential Impact of Global Climate Change - Sheer and Randall, Water
Resources Management, Inc. (Volume A)
175
-------
Chapter 9
Allan and Gichuki (Volume C), all studies listed in
Table 9-3 are found in Volume A.) The studies use
scenarios generated from up to four global
circulation models (GCMs) as thek starting points
(see Chapter 4: Methodology) and match them with
regional or subregional water resource models.
This section reviews the findings from the studies on
California, the Great Plains, the Great Lakes, and
the Southeast; from previous studies of the impacts
of climate change on these and other regions; and
from previous hydrologic studies and models of
individual river basins.
The GCMs do not yet provide definitive
forecasts concerning the frequency, amount, and
seasonality of precipitation and the regional
distribution of these hydrologic effects (see Chapter
2: Climate Change; Chapter 3: Variability; Chapter
4: Methodology; Rind and Lebedeff, 1984; Hansen
et al., 1986; Gleick, 1987; Rosenberg, 1988). The
uncertainty of the forecasts is partially due to the
limitations and simplifications inherent in modeling
complex natural and mamnade phenomena.
Modeling efforts are made more difficult by the
feedbacks and interconnections between changes in
temperature; and the amount and frequency of
precipitation, runoff, carbon dioxide, growth and
transpiration of foliage, cloud cover, ocean
circulation, and windspeed.
However, the regional studies commissioned
for this report are a significant step in the effort to
bring GCM and regional water resources models
together to examine the regional impacts of climate
change.
The West
The arid and semiarid river basins west of the
Mississippi River have significant surface and
groundwater quantity and quality problems and are
vulnerable to restricted water availability. Total
water use exceeds average streamflow in 24 of 53
western water resource regions (U.S. Water
Resources Council, 1978), with the majority of the
West's water withdrawals going to irrigation.
Surface and groundwater quality in the West have
deteriorated as a result of low flow, salts
concentrated by irrigation, and pesticide use. The
West also depends uponnonrenewable groundwater
supplies for irrigation (Solley et al., 1988).
Climate change may exacerbate water shortage
and quality problems in the West. Higher
temperatures could cause earlier snowmelt and
runoff, resulting in lower water availability in the
summer. Some GCM scenarios predict midsummer
drought and heat, less groundwater recharge, and
less groundwater and surface water availability for
irrigation in the middle latitudes of the country.
The sensitivity analyses conducted by Stockton and
Boggess (1979) indicated that a warmer and drier
climate would severely reduce the quantity and
quality of water in arid western river basins (Rio
Grande, Colorado, Missouri, California) by
increasing water shortages. Water shortages and
associated conflicts between instream and offstream
uses, between agricultural and urban/industrial
water uses, and between flood control and other
water uses of reservoirs may be expected under
these scenarios. Hydropower output also would
decline as a result of lower riverflow.
Pacific Northwest
The competition for water for irrigation,
hydropower, and fisheries habitat is increasing in
the Pacific Northwest (Butcher and Whittlesey,
1986). Climate change may alter the seasonality
and volume of precipitation and snowmelt,
increasing the risk of flooding, changing reservoir
management practices, and affecting the output and
reliability of hydroelectric power production and the
availability of water for irrigation.
California
The diversion of water from water-rich northern
California and from the Colorado River to southern
California via federal and state systems of dams,
aqueducts, and pumping stations has transformed
California into the nation's leading agricultural state
and has made possible the urbanization of southern
California. Irrigation accounted for 83% of the
total value of California's agricultural output in 1982
(Bajwa et al., 1987). Because of this high economic
dependence on water in an arid area, southern
California is vulnerable to droughts and any altered
temporal pattern of runoff that may be caused by
atmospheric warming.
Total annual runoff from the mountains
surrounding the Central Valley is estimated to
increase slightly under GCM scenarios, but runoff
in the late spring and summer may be much less
176
-------
Water Resources
than today because higher temperatures cause
earlier snowmelt (Lettenmaier, Volume A). The
volume of water from the State Water Project may
decrease by 7 to 16% (see Chapter 14: California;
Sheer, Volume A). Existing reservoirs do not have
the capacity to increase storage of winter runoff and
at the same tune to retain flood control capabilities.
In addition, flows required to repel saline water
near the major freshwater pumping facilities in the
upper Sacramento-San Joaquin River Delta may
have to be doubled as a result of sea level rise,
further reducing water available to southern
California (Williams, Volume A).
Decreases in water availability may also reduce
hydroelectric power produced in California. In the
1976-77 drought, hydroelectric production in
northern California dropped to less than 50% of
normal, a deficiency relieved by importing surplus
power from the Pacific Northwest and by burning
additional fossil fuels at an approximate cost of $500
million (Gleick, 1989).
Colorado, Rio Grande, and Great Basins
Total consumption is more than 40% of
renewable supply in these river basins. The
Colorado River Basin has huge reservoir storage,
but demand exceeds supply in the lower half of the
basin. Ordinarily all of the Colorado River's water
is consumed before it reaches the Gulf of California
in Mexico. The Colorado River Compact of 1922,
the 1963 Supreme Court decision in Arizona v.
California, the treaties with Mexico of 1944 and
1973, and other agreements allocate Colorado River
water to seven states and Mexico (Dracup, 1977).
Some studies show that the Upper Colorado region
will use all of its allocation by the year 2000,
reducing water hitherto available to lower Colorado
and California (Kneese and Bonem, 1986).
Climate change may further reduce the
availability of water in these basins. A model by
Stockton and Boggess (1979) of a 2°C temperature
increase and a 10% precipitation decrease shows
decreases in the water supply in the upper Colorado
and the Rio Grande of 40 and 76%, respectively.
Great Plains
The southern Great Plains States of Kansas,
Nebraska, Oklahoma, and Texas produce almost
40% of the nation's wheat, 15% of its corn, and
50% of its fattened cattle (see Chapter 17: Great
Plains). The region heavily depends on
groundwater mining (when pumping exceeds aquifer
recharge) for irrigation. The region was severely
affected during the "Dust Bowl" years of the 1930s
and suffered from severe drought in 1988.
Because of the greater reliability in irrigated
yields relative to dryland yields, the demand for
irrigation could rise (Allen and Gichuki, Volume C;
Adams et al., Volume C). Thus, while total
agricultural acreage could decrease, irrigated
acreage and groundwater mining may increase in
the southern Great Plains. Greater demand may be
placed on the Ogallala Aquifer, which underlies
much of the region, causing further mining of the
aquifer.
Great Lakes
Based on analyses for this report (Croley and
Hartmann, Volume A), higher temperatures may
overwhelm any increase hi precipitation and may
evaporate lakes to below the lowest levels on
record. However, changes in Great Lakes
evaporation under climate change are highly
uncertain and depend on such variables as
basinwide precipitation, humidity, cloud cover, and
windspeed. Under a possible set of conditions, lake
levels could rise. The winter ice cover would be
reduced but would still be present, especially in
shallow areas and northern lakes (Assel, Volume
A). Navigation depths, hydropower output, and
water quality all would be adversely affected, but
losses of existing shorelands from erosion would be
reduced as a result of lower lake levels (see Chapter
15: Great Lakes).
Mississippi River
The Mississippi River historically has been
affected by both spring floods and drought. In 1988,
low flows due to drought received national
attention. Low flows disrupt navigation, permit
saltwater intrusion into the drinking water of
southern Louisiana cities, reduce the dilution of
contaminants transported from upstream locations,
and reduce the inflow of water to the vast
Mississippi Delta wetlands (see Glantz, Volume J).
Northeast
Although the Northeast is humid, cities and
powerplants demand large amounts of water at
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Chapter 9
localized points in a watershed, necessitating storage
and interbasin transfers. Because of the small
amount of storage in the Northeast, the region is
vulnerable to prolonged drought. No new major
storage has been built in the Northeast during the
past 20 years, except the Bloomington Dam on the
Potomac River. Water supply in lower New
England, New York, and Pennsylvania, and power
production in the Northeast, remain vulnerable to
drought, which may occur more frequently
(Schwartz, 1977; Kaplan et al., 1981). During
periodic droughts in the Northeast, such as those in
1962-65 and 1980-81, instream flow regulations
ration water and threaten shutdowns of electrical
powerplants (U.S. Army Corps of Engineers, 1977;
Schwartz, 1977; Kaplan et al., 1981).
Southeast
In the Southeast, the experience with drought
in recent years is increasing the use of groundwater
and surface water for irrigation and is prompting
farmers to consider shifting crops. In Georgia, for
instance, the use of groundwater for irrigation has
grown quite rapidly. However, the GCMs disagree
on whether the Southeast may become wetter or
drier (see Haines, Volume A; Miller and Brock,
Volume A). Most reservoirs in the area have
sufficient capacity to retain flood surges and to
maintain navigation, hydropower, water supply, and
instream uses (e.g., dilution, wildlife) under both
wetter and drier conditions (see Chapter 16:
Southeast; Sheer and Randall, Volume A).
However, drier conditions would pose conflicts
between recreational uses (which would be hurt by
changes in reservoir levels) and all other instream
and offstream uses.
Should the Southeast become drier, a decline
in the inflow of freshwater could alter the estuarine
ecology of the gulf coast, which may be most
vulnerable to sea level rise (see Chapter 16:
Southeast).
POLICY IMPLICATIONS
Decreases in water availability and quality,
increased risk of flood damages, and the
exacerbation of conflicts between water users
competing for an increasingly scarce or difficult to
manage resource are the major potential impacts
of a global warming trend on the nation's water
resources. How will we manage water resources
given the possibility of change and uncertainties
about its nature and timing?
Policy approaches to water resources may be
grouped under supply (or structural) approaches
and demand (or nonstructural) approaches. Supply
approaches mitigate hydrologic variability and
climate change; demand approaches modify
behaviors that create vulnerability to such change.
For example, water shortages may be addressed
either by developing surface water storage capacity
and improving the quality of water from available
sources (supply approaches), or by decreasing water
use and consumption (a demand approach).
Many of the policy approaches discussed below
have been recommended by water resource experts
for 20 years and are in use to address existing water
problems and vulnerabilities. The potential of
climate change provides another reason for
expanded use of these approaches.
Supply and Structural Policy Approaches
The supply-related policy approaches to water
resources include design for uncertainty, surface
water development, and optimization of water
resource systems.
Design for Uncertainty
Most water resource decisions in the past have
been based on the assumption that the climate of a
region varies predictably around a stationary mean.
Water managers develop water resources plans
based on statistical analyses of historical
climatological and hydrologic data. However, the
frequency of extreme events, which has been
assumed to be fixed or to be modified only by the
urbanization of watersheds, may be changed
significantly by altered climatic conditions.
In addition to being uncertain about hydrologic
conditions, we are uncertain about future
demographic, economic, and institutional factors
that affect offstream water uses and social and
economic values attached to instream uses. As an
example, water withdrawals in 1985 declined overall
from 1980, falling far short of projections made
starting in 1960 and as recently as 1978 (Solley et
al., 1988).
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Water Resources
Finally, we are uncertain about how our
economic, regulatory, and institutional systems will
respond to climate change in the absence of
concerted governmental action. It would be a
mistake to attempt to project the impacts of climate
change simply by superimposing projected future
hydrologic conditions on today's social systems.
The planners and designers of water resources
must address such uncertainties. Three types of
response are often used to address conditions of
great uncertainty:
• Avoid inflexible, large-scale, irreversible,
and high-cost measures; opt for shorter
term, less capital-intensive, smaller scale,
and incremental measures.
• Conduct sensitivity analysis and risk-cost
exercises in the design of structural and
management systems to address the
potential range of climate change impacts.
Sensitivity analysis describes the sensitivity
of projections to variables affecting their
accuracy; risk-cost analysis identifies the
costs, for various conditions other than
those projected, associated with
underdesign or overdesign of a structure.
The consideration of hydrologic extremes
and the use of risk analysis in the design of
specific projects to mitigate the adverse
consequences of hydrologic variability may
incidentally mitigate many of the physical
impacts of climate change (Hanchey et al.,
1988).
• Design structures and systems for rare
events. Matalas and Fiering (1977) found
that many large systems have substantial
redundancy (margins of safety) and
robustness (ability to perform under a
variety of conditions) that enable them to
adapt technologically and institutionally to
large stresses and uncertain future events.
Although the principle of design for rare
extremes may provide robustness, it has a cost and
may conflict with the principle of maximizing the
economic return from a project. Most public and
private water developers subject projects to "net
present value" or "internal rate or return" analyses.
These analyses discount future benefits relative to
present benefits. If a high discount rate is used in
decisionmaking, conditions beyond 10 or 20 years
may have little impact on design and investment
decisions (see Chapter 19: Preparing for a Global
Warming; Hanchey et al., 1988).
Surface Water Development
Surface water structures increase developed or
available water supply, provide for the regulation of
flows for instream uses, prevent flooding, or
perform some combination of these functions. These
structures include dams, reservoirs, levees, and
aqueducts. Because of high costs of construction,
adverse impacts on the environment, the limited
number of sites available for new structures, and
opposition by citizen groups, the trend during the
past decade has been away from large
excess-capacity, capital-intensive projects. Only the
Central Utah Project and the Central Arizona
Project have gone forward in recent years. Only
one major project in the Northeast has been
completed in past 20 years: the Bloomington Dam
on the Potomac River. In 1982, California citizens
voted down funds for the proposed Peripheral Canal
that would have permitted increased diversion of
water from north to south in the state. In addition,
the national trend toward increased local/state
financing and reduced federal financing for projects
has reduced funds available for large projects
(National Council on Public Works Improvement,
1988).
These current trends in water resources
management may be reevaluated in light of possible
new demands for developed water caused by climate
changes. Pressure to build proposed projects such
as the Narrows Project in Colorado, the Garrison
Diversion in North Dakota, the Peripheral Canal in
California, and structures to divert water from
northern New England to southeastern
Massachusetts may be renewed if droughts reoccur
or demand increases. The pace at which existing
projects are upgraded, modified, or expanded may
also accelerate.
Optimization of Water Resource Systems
Water resources can be managed to maximize
the water availability from a given resource base
such as a dam, watershed, or aquifer. Adoption of
systemwide strategies for a large-scale water system
may allow for substantial operating flexibility related
to releases of stored water. This flexibility can have
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Chapter 9
an enormous influence on the overall performance
and resilience (recovery abilities) of the system, and
may provide additional yields that mitigate the
impacts of climate change. For example, the U.S.
Department of the Interior's Bureau of Reclamation
(1987) is adopting operational, management, or
physical changes to gain more output from the same
resources. Water management agencies nationwide
are implementing methods to protect groundwater
recharge areas and to use ground and surface
waters conjunctively (U-S. EPA, 1987b). Watershed
management practices also affect water supply; for
example, water yields can be significantly affected by
timber harvest practices.
In the East, consolidation of or coordination
among fragmented urban water supply authorities
can achieve economies of scale in water delivery,
decrease the risk of shortage in any one subsystem
within a region, increase yields, and provide
effective drought management procedures. Sheer
(1985) estimated that coordinated water authority
activities in the Potomac River basin eliminated the
need for new reservoirs, saving from $200 million to
$1 billion.
River basin and aquifer boundaries in many
cases traverse or underlie portions of several states.
Regional and interstate cooperation to manage
water resources has a long tradition in some U.S.
river basins. Although numerous opportunities exist
for additional coordination of water management
between states, within basins, or between basins, the
agreements required for regional compacts and
operating procedures and sharing of water supplies
may require substantial and lengthy negotiations.
Several interstate water authorities have
significant water allocation authority. For example,
the Delaware River Basin Commission allocates
water to users in the Delaware Basin and transfers
it to New York City under authority of a 1954
Supreme Court ruling (347 U.S. 995) and federal
legislation, which established the Commission in
1961 and granted it regulatory, licensing, and project
construction powers. Similarly, water authorities in
the Washington, D.C., metropolitan area operate
Potomac River water supply projects as integrated
systems under a 1982 agreement. Both the
Delaware and Potomac regional compacts include
provisions for drought allocations. (See Harkness et
al., 1985, for management actions taken by the
Delaware River Basin Commission during a 1984-85
drought.)
Demand Management and Nonstructural
Policy Approaches
Demand-related adaptations encourage a
reduction in water demand and an increase in water
use efficiency through pricing, market exchange of
water rights, conservation, protection of water
quality, education and extension service assistance,
technological innovation, and drought management
planning. Policies that discourage activities in flood-
prone areas are the nonstructural counterparts for
reducing flood damage.
Water Pricing. Water Markets, and Water
Conservation
In the past, many people considered that water
was too essential a resource or too insensitive to
price to allow market forces to allocate its use,
especially during shortages. Policy took the form of
direct controls and appeals to conserve (Hrezo et
al., 1986). In recent years, greater attention has
been given to market-based policies and
mechanisms that allocate limited water supplies
among competing uses and promote water
conservation.
Water prices that reflect real or replacement
costs and the exchange of water rights by market
mechanisms can promote conservation and efficient
use. Since water use is sensitive to price (Gibbons,
1986) water users faced with higher prices will
conserve water and modify their technologies and
crop selection to use less without substantial
reduction in output. If there is a market for water
rights, those willing to pay more may purchase
rights from those less, willing to pay. As a
consequence, water will be transferred out of
marginal uses and will be conserved.
Three related pricing and conservation
approaches are irrigation conservation, municipal
and industrial water use, and water markets and
transfers.
Irrigation Conservation
Relatively small reductions in irrigation demand
can make large amounts of water available for
urban and industrial uses. For instance, nearly 83%
of the withdrawals and 90% of the consumptive use
of western water is for irrigation. A 10% reduction
in irrigation use would save 20 million acre-feet
(maf) in water withdrawn and 10 maf in water
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Water Resources
consumed annually, effectively doubling the water
available for municipal and industrial uses in the
West (Frederick, 1986). (For comparison, the
average annual flow of the Upper Colorado River
Basin is 15 maf.)
Inexpensive water was a key factor in the
settlement of the West and the expansion of
agriculture (Frederick, 1986). The Bureau of
Reclamation was established early in this century to
promote the development of irrigation hi the West.
The Bureau provides irrigation for about 11 million
acres, more than one-fifth of the total irrigated
acreage. Since the Bureau accounts for nearly
one-third of all surface water deliveries and about
one-fifth of total water deliveries hi the 17 western
states, actions by the Bureau to use this water more
efficiently have an impact throughout the West
(Frederick, 1986).
In the past, demand for Bureau water was not
based on the real cost of the water, because more
than 90% of the Bureau's irrigation projects have
been subsidized, and payments on some projects no
longer even pay for operation and maintenance
(Frederick and Hansen, 1982). Irrigators fortunate
enough to receive such inexpensive water may have
little or no incentive to conserve. However, the
Bureau's more recently stated objectives include
revising their water marketing policy, promoting
conservation, and pricing water to reflect its real
cost (U.S. Department of the Interior, 1987).
Municipal and Industrial Water Use
Municipalities throughout the country are
finding it difficult and expensive to augment their
supplies to meet the demands of population and
economic growth and are finding that users would
rather use less than pay more (Gibbons, 1986).
Traditional average-cost pricing provides adequate
service to customers and adequate returns to water
companies, but is being reevaluated because it tends
to cause overinvestment in system capacity (U.S.
Congress, 1987). Marginal-cost pricing (charging
for the cost of the last-added and most expensive-
increment of supply) or progressive-rate pricing
(charging more per unit to users of large amounts)
can reduce domestic and industrial water
consumption because water use is sensitive to price
(Gibbons, 1986).
Water Markets and Transfers
The "first hi time, first hi right" appropriation
doctrine, which favors the longest standing water
rights, governs much of the West's surface water
and some groundwater. The appropriation doctrine
has the potential to establish clear, transferable
property rights to water — a precondition for
effective operation of water markets. The potential
for water transfers to the highest value users has not
yet been fully realized because the nature and
transferability of the rights are obscured by legal
and administrative factors (Trelease, 1977;
Frederick, 1986; Saliba et al., 1987). Following are
some examples:
• Rather than grant absolute ownership,
states with prior appropriation rules grant
rights to use water for beneficial purposes.
Water rights not put to beneficial use may
be forfeited. This encourages a use-it-or-
lose-it attitude.
• Federal and Native American water rights
remain unquantified hi some areas such as
the Colorado River Basin.
• The emergence hi law of the "public trust
doctrine," which states that all uses are
subject to the public interest, has cast a
cloud over some water rights. This has
been true in California, where the public
interest has driven a reexamination of
withdrawals from Mono Lake, and where
existing permits have been modified to
protect the Sacramento-San Joaquin Delta
from saltwater intrusion. Montana is
increasinglybasing water management plans
on its instream flow requirements and is
exploring ways to have these requirements
for all future beneficial instream uses count
as a bona fide use of the Missouri River to
slow the growth rate of water diversion for
offstream uses (Tarlock, 1987).
• In resolving interstate water disputes, a
federal common law of "equitable
apportionment" has developed under which
an informed judgment, based on
consideration of many factors, secures a
"just and equitable" water allocation (see
Strock, 1987). The Supreme Court
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Chapter 9
decided in Colorado v. New Mexico (456
U.S. 176, 1982) that equitable
apportionment may be used to override
prior appropriation priorities in cases of
major flow reductions. The Supreme Court
specifically mentioned climatic conditions in
ruling that prior appropriation systems
would otherwise protect arguably wasteful
and inefficient uses of water at the expense
of other uses (see Strock, 1987).
• Because of imperfect competition,
third-party effects, uncertainty over
administrative rules, and equity
considerations, water market prices may
not appropriately measure water values
according to economic efficiency criteria
(Gibbons, 1986; Saliba et al., 1987).
• It is possible to control groundwater
withdrawals, but for a number of reasons it
is difficult to establish market mechanisms
for groundwater allocation. Because all
groundwater users essentially draw from a
shared pool, groundwater resources are
treated as "common properly." As a result,
property rights are difficult to define,
third-party impacts of transfers of
groundwater rights are significant, and
interstate agreements concerning allocation
of interstate aquifer water are difficult to
attain (Emel, 1987).
Despite the obstacles, transfer of water rights
among users — especially from irrigators to
municipalities and power companies seeking water
for urban expansion and electricity production — is
becoming common in many western states (Wahl
and Osterhoudt, 1986; Frederick, 1986). Methods
include negotiated purchases, short-term exchanges
during droughts, and water banks and markets
(Wahl and Osterhoudt, 1985; Saliba et al., 1987;
WaM and Davis, 1986).
Legislation in many western states has
facilitated water transfers (Frederick, 1986;
Frederick and Kneese, 1989). For instance,
Arizona's new water law facilitates the purchase of
agricultural land for water rights, and the use of that
water for urban development. Strict technical
standards imposing conservation on municipal and
industrial water uses, such as watering golf courses
with wastewater, are also part of Arizona's laws
(Saliba et al., 1987).
Frederick and Kneese (1989) caution that water
transfers occur gradually and are not likely to affect
more than a small percentage of agricultural water
rights for the foreseeable future. However, legal
and institutional changes facilitating water markets
and demand for water by high-value users may be
accelerated under the stress of climate change
(Trelease, 1977).
Drought Management Policies
Integrating drought planning into water resource
management may assume greater priority if climate
change aggravates water shortages. The Model
Water Use Act (Hrezo et al., 1986) advocates that
states or water supply authorities integrate drought
management and advance planning into their
policies by designating a governmental authority for
drought response and by adopting mechanisms for
automatically implementing and enforcing water-use
restrictions. In 1986, only seven states had
comprehensive management plans for water
shortages (Hrezo et al., 1986). Most states rely on
water rights appropriations, emergency conservation
programs, and litigation to allocate water during
shortages. Improved capabilities in surface
hydrology and in water system modeling and
monitoring would be required to support broadened
drought contingency planning.
Water Quality
Federal and state legislation and regulations for
control of instream water quality have had a
dramatic effect on reducing conventional water
pollutants since the enactment of the 1972 Clean
Water Act. The reduced riverflows and lake levels
that are possible under altered climate conditions
could necessitate more stringent controls on point
and nonpoint sources to meet water quality
standards. Promotion of nonpolluting products,
waste minimization, and agricultural practices that
reduce the application of chemicals will also
enhance water quality, making more water of
suitable quality available for use.
Many states have adopted measures to protect
instream water uses. These include reserving flows
or granting rights for particular instream uses and
directing agencies to review impacts before granting
new rights (U.S. Water Resources Council, 1980;
Frederick and Kneese, 1989). Regulations limiting
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Water Resources
water use may have to be modified where climate
change has resulted in reduced flows during
droughts.
Policies for Floodplains
The National Flood Insurance Program was
enacted in 1968, with major amendments in 1973.
The program provides subsidized flood insurance
for existing structures in flood-prone areas, provided
that the community with jurisdiction regulates the
location and construction of new buildings to
minimize future flood losses. New structures that
comply with the restrictions are eligible for
insurance at full actuarial rates.
In 1979, the program took in $140 million in
premiums and paid $480 million in claims.
Recently, the program was authorized to relocate
structures exposed to repeated flood or erosion
damage rather than pay claims for such structures.
Where rainfall and flooding increase, the
100-year floodplain would expand, and rate maps
would need revision. Premium payments and claims
would rise.
RESEARCH NEEDS
Water is the principal medium by which
changes in atmospheric conditions are transmitted
to the environment, the economy, and society.
Hydrology is the key discipline that enables us to
understand and project these effects. Improvements
in both the GCMs and regional hydrologic models
are needed so that we may understand the impacts
of climate change and devise appropriate water
resources management strategies. Specifically,
GCMs do not yet provide regional forecasts at the
level of certainty and temporal and spatial
resolution required for decisionmakers. To be more
helpful, the GCMs should provide forecasts specific
to individual river basins or demand centers, and
should describe hydrologic conditions over the
typical design-life of water resource structures.
Research activities should include the following:
• Monitor atmospheric, oceanic, and
hydrologic conditions to detect evidence of
water resources impacts of climate change.
• Continue to develop and refine regional
hydrologic models that are capable of
modeling the changes in runoff, water
availability, water use, and evapotran-
spiration induced by changes in
temperature and atmospheric conditions.
This research should focus on vulnerable
river basins where demand approaches or
exceeds safe yield or where hydrologic
variability is high.
• Refine global climate change models and
link them to regional hydrologic models so
that regional water resource planners,
engineers, and managers can use their
projections more confidently.
• Study the sensitivity of existing water
systems to possible changes in climate
conditions.
At the same time, the following research is
needed to identify opportunities for adopting
measures to adjust and adapt to climate change.
• Quantify federal and Native American
water rights in the West.
« Examine how present institutions and
markets can better allocate water among
users and provide incentives to conserve
water.
• Assess the extent to which laws and
regulations may exacerbate the effects of
climate change. (Examples include thermal
controls for rivers and federal pricing and
reallocation policies for irrigation water.)
• Identify, project, and quantify the
demographic and institutional adjustments
that may occur in the absence of public
action in response to climate-induced
impacts on water resources. This research
will reduce uncertainty for policymakers
regarding where concerted public action
may be or not be needed.
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Chapter 9
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the carbon dioxide induced climatic change on water
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Impacts of Increasing Atmosphere CO, With
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Rosenberg, NJ. 1988. Global climate change holds
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Tutwiler, MA., ed. U.S. Agriculture in a Global
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Schwarz, H.E. 1977. Climatic change and water
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National Research Council, ed. Climate, Climatic
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Sheer, D.P. 1985. Managing water supplies to
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United States Water Supply Study, Summary
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U.S. Army Corps of Engineers. 1988. Lessons
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CHAPTER 10
ELECTRICITY DEMAND
FINDINGS
Global warming would increase electricity demand,
generating capacity requirements, annual generation,
and fuel costs nationally. The impacts could be
significant within a few decades and would increase
substantially over time if global warming continues.
• The new generating capacity requirements
induced by climate change effects on electricity
demand estimated for 2010 show an increase of
25 to 55 gigawatts (GW), or 9 to 19% above
estimated new capacity requirements assuming
no change in climate. Between 2010 and 2055,
climate change impacts on electricity demand
could accelerate, increasing new capacity
requirements by 200 to 400 GW (14 to 23%)
above what would be needed in the absence of
climate change. These capacity increases would
require investments of approximately $200 to
$300 billion (in 1986 dollars). In the absence of
climate change, population and economic
growth may require investments of
approximately $2.4 to 3.3 trillion through 2055.
• Estimated increases in annual electricity
generation and fuel use induced by climate
change represent several thousand gigawatt-
hours by 2055. The estimated increases are 1 to
2% in 2010 and 4 to 6% in 2055. Annual fuel,
operation, and maintenance cost to meet
increased electricity demand would be several
hundred million dollars in 2010 and several
billion dollars in 2055. Without climate change,
these annual costs would be $475 to 655 billion
in 2055.
• Estimated regional impacts differ substantially.
The largest increases could occur in the
Southeast and Southwest, where air-conditioning
demands are large relative to heating. Northern
border states may have a net reduction in
electricity generation relative to base case
requirements assuming no change in climate.
These changes could be exacerbated by
reductions in hydropower production and
increases in demand for electricity to run
irrigation equipment.
• These results are sensitive to assumptions about
the rates of economic growth, technological
improvements, and the relationship between
electricity use and climate. The potential savings
in other energy sources (gas and oil) used for
space heating and other end uses sensitive to
climate and the potentially significant impacts on
hydroelectric supplies and other utility
operations were not analyzed.
Policy Implications
• Utility executives and planners should begin to
consider climate change as a factor in planning
new capacity and future operations. The
estimated impacts of climate change in some
regions are similar to the range of other
uncertainties and issues utility planners need to
consider over the 20- to 30-year period.
Additional climate and utility analyses are
needed to develop refined risk assessments and
risk management strategies.
• The increased demand for electricity induced by
climate change also could exacerbate other
environmental problems, such as the
implementation of "acid rain" strategies,
adherence to the international nitrogen oxide
treaty, state implementation plans for ozone
control, and thermal pollution control permit
requirements. The Environmental Protection
Agency should analyze the impacts of climate
change on long-range policies and should
include climate change as an explicit criterion in
making risk management decisions when
appropriate.
• The increased demand for electricity could
make policies to stabilize the atmosphere
through energy conservation more difficult to
achieve. The estimated increases in electricity
generation induced by climate change could
increase annual CCL emissions, depending upon
future utility technology and fuel choice
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Chapter 10
decisions. Assuming no change in efficiency of
energy production and demand, reliance on
coal-based technologies to meet the increased
demands could increase CO2 emissions by 40 to
65 million tons in 2010 and by 250 to 500
million tons in 2055. Use of other, lower CO2-
emitting technologies and fuels (e.g., efficient
conversion technologies and nuclear and
renewable resources) would reduce these
incremental additions. In addition, warmer
winter temperatures could reduce the demand
for oil and gas in end uses such as residential
furnaces for heating, thereby lowering CO2
emissions from these sources. Future analyses
of national and international strategies to limit
greenhouse gases should include the changes in
energy demand created by global warming as a
positive feedback.
CLIMATE CHANGE AND
ELECTRICITY DEMAND
Climate change could affect a wide range of
energy sources and uses. In the near term, policies
aimed at reducing emissions of greenhouse gases
from fossil fuel combustion could affect the level
and mix of fuel consumption in various end-use
technologies and in the generation of electric power.
In the longer term, changes in temperature,
precipitation, and other climatic conditions also
could affect energy resources. For example, warmer
temperatures likely would reduce the demand for
fuels used in the winter for space heating and
increase the demand for fuels used in the summer
for air-conditioning; and reduced precipitation and
soil moisture in some regions could increase the use
of energy to pump water for irrigation. These
effects could be particularly significant for planning
in the electric utility industry based upon the
substantial amount of electric load accounted for by
weather-sensitive end uses, the variety of resources
used to generate electric power, and the capital-
intensivity of the industry. One major consideration
is the potential impact of climate change on the
demand for electricity and the implications of
changes in demand on utility capacity and
generation requirements.
Many electrical end uses vary with weather
conditions. The principal weather-sensitive end uses
are space heating, cooling, and irrigation pumping
and -- to a lesser degree — water heating, cooking,
and refrigeration. These applications of electricity
may account for up to a third of total sales for some
utilities and may contribute an even larger portion
of seasonal and daily peak demands.
Changes in weather-sensitive demands for
electricity can affect both the amount and the
characteristics of generating capacity that a utility
must build and maintain to ensure reliable service.
These changes also can affect fuel requirements and
the characteristics of efficient utility system
operations, particularly the scheduling and
dispatching of the utility's generating capacity. For
example, electric energy used for air-conditioning
exceeds that used for space heating nationwide, and
the temperature sensitivity associated with cooling
is higher than that associated with heating. This
implies not only changes in seasonal electricity
demands but also increases hi annual electricity
demands as a result of higher temperatures.
Similarly, utilities in most regions experience
their peak demands in the summer. A rise in air-
conditioning and other temperature-sensitive
summer loads would significantly increase peak
loads and, as a result, would step up utility
investments in new generating capacity needed to
meet additional demands and to maintain system
reliability.
Examples of other ways in which climate could
affect electric utilities include the following.
Changes in precipitation, evaporation, and runoff
from mountain snowpack as well as changes in
water management practices in response to climate
change could affect the annual and seasonal
availability of streamflow to generate hydropower.
Reductions in hydropower would require utilities to
rely upon other, possibly more costly and less
environmentally benign generation sources to meet
customer needs. Furthermore, reductions in water
resources would adversely affect the availability
and/or cost of water for powerplant cooling.
Other direct impacts of climate change on
electric utilities include the effects of temperatures
on powerplant operating efficiencies, the effects of
sea level rise on the protection and siting of coastal
facilities, and the effects of changes in various
climate conditions on the supply of renewable
energy resources such as solar and wind power.
Also, legislation and regulations designed to limit
greenhouse gas emissions from utility sources could
significantly affect the supply and cost of electricity
generation.
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Although some of these impacts could
significantly affect utility planning and operations
(particularly on a regional basis), they have not been
analyzed in detail and are not addressed in this
report. Further research and analysis are needed to
develop a more complete assessment of utility
impacts.
PREVIOUS CLIMATE CHANGE
STUDIES
A number of utilities conduct analyses relating
short-term variations in weather conditions with a
need to "weather-normalize" historical demand data
and to test the sensitivity of system reliability and
operations to these short-term variations.
Furthermore, some researchers have speculated
regarding the potential effects of longer term
climate changes on electricity demand (e.g., Stokoe
et al., 1987).
However, only one previous study has estimated
the potential implications of longer term, global
warming-associated temperature changes on
electricity demands and the effects of changes in
demand on utility investment and operating plans.
Linder et al. (1987) used general circulation model
(GCM) results to estimate the potential impacts of
temperature change on electricity demand (and on
the supply of hydropower) for selected case study
utility systems in two geographical areas: a utility
located in the southeastern United States and the
major utilities in New York State, disaggregated
into upstate and downstate systems.
Electricity Demand
Linder et al. found that temperature increase
could significantly heighten annual and peak
electricity demands by 2015, and that a temperature
rise would require construction of new generating
capacity and increases in annual generation. The
southeastern utility had higher estimated increases
in electricity demand, generation, and production
costs than the New York utilities because of greater
electricity demands for air-conditioning. In
addition, streamflow used to generate hydropower
in New York could be reduced, requiring increased
use of fossil fuel generation to meet customer
demands for electricity.
CLIMATE CHANGE STUDY IN
THIS REPORT
Study Design
Linder and Inglis (Volume H) expanded the
case studies (Linder et al., 1987) of the sensitivity of-
electricity demand to climate change and conducted
a national analysis of electricity demand. Relevant
regional results from the national studies of Linder
and Inglis are discussed in the regional chapters of
this report.
The analytic approach developed by Linder et
al. (1987) formed the basis for estimating the
regional and national impacts described in this
report. The principal steps in the approach are
summarized in Figure 10-1 (see Volume H for more
details). Estimated impacts were developed for the
relatively near term (from the present to 2010,
Climate
Change
Scenarios
Weather-
Sensitivity of
Electricity Demand
Utility
Planning
Assumptions
Utility
Planning
Model
Impacts on
Utility Investments,
Operations, Costs
Figure 10-1. Analytic approach (Linder and Inglis, Volume H).
189
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Chapter 10
within electric utility long-range resource planning
horizons of 20 to 30 years) and over the longer term
(to 2055), when the magnitude of temperature
changes is expected to approach equilibrium levels
representative of a doubling of atmospheric
concentrations of CO,. Linder and Inglis used
Goddard Institute for Space Studies (GISS) A and
B transient estimates of temperature change in 2010
and GISS A estimates for 2055 in their calculations.
The scenario changes in annual temperatures for
the United States range from about 1.0 to 1.4° C in
2010 and are approximately 3.7°C by 2055.
Regional temperature scenarios show greater
variation.
Linder and Inglis used actual utility demand and
temperature data from the case study utilities, and
from five other large, geographically dispersed utility
systems, to develop a set of weather-sensitivity
parameters for utility areas. On a weighted-average
basis (weighted by electricity sales), utility peak
demands were estimated to increase by about 3.1%
per change in degree Celsius (ranging from -1.35 to
5.40% across utility areas), and annual energy
demands were estimated to increase by about 1.0%
per change in degree Celsius (ranging from -0.54 to
2.70%).
A number of uncertainties associated with the
data and assumptions used to develop these
weather-sensitivity relationships suggested that the
relationships may understate customer response to
climate change, particularly at higher temperature
change levels occurring in the future. For example,
the approach did not explicitly account for probable
increases in the market saturation of air-
conditioning equipment as temperatures rise over
time. To address this possibility, an alternative case
was designed in which the estimated weather-
sensitivity values were increased by 50%. This was
designated as the "higher sensitivity case.
Since this study is focused on estimating how
climate change may affect key utility planning
factors, Linder and Inglis used a planning scenario
assuming no change in climate (a "base case") to
serve as a basis for comparison with planning
scenarios under alternative assumptions of climate
change for 2010 and 2055. Thus, base case utility
plans were developed for 2010 and 2055, using
assumptions regarding future demands for electricity
in the absence of climate change (reflecting
population and economic growth), generating
technology option performance and costs, fuel costs,
and other utility characteristics.1 Linder and Inglis
assumed that future capacity and generation
requirements will be met by investments either in
new coal-fired baseload capacity or in oil- and
natural gas-fired peaking capacity. Other sources,
such as nuclear energy and renewables or innovative
fossil fuel-fired technologies (e.g., fluidized bed
combustion), were not considered (for further
details, see Linder et al., 1987).
Demands for electricity in the absence of
climate change can be related to the overall level of
economic activity as represented by the gross
national product (GNP). Because economic growth
assumptions are critical to estimates of future
electricity demands, alternative GNP growth rates
were assumed in developing the base cases; these
ranged from 1.2 to 2.1% per year.2 These
alternative assumptions are referred to as "lower
growth" and "higher growth," respectively.
These assumptions served as inputs to a regional
planning model called the Coal and Electric Utilities
Model (CEUM). CEUM outputs include the
amount and characteristics of new generating
capacity additions, electricity generation by fuel
type, and electricity production costs.
Limitations
The study extrapolated temperature-sensitivity
findings for some regions and did not include
specific analyses of temperature sensitivity for all
utility regions of the United States. It focused
narrowly on impact pathways, considering only the
potential effects of temperature change on changes
in electricity demand. Neither the potentially
significant impacts of climate change on hydropower
availability nor the impacts of reduced water
supplies for powerplant cooling were included.
Furthermore, the study did not evaluate the
sensitivity of the results to different, doubled-CO2
Note that the development and use of a base case reflecting
changes in non-climate-related conditions over time was
undertaken only for the electricity demand study, not for other
areas in this report. Changes in population and technology are
considered in Chapter 6: Agriculture.
HThese GNP growth rates are relatively conservative, but they
are comparable with GNP growth rates used by EPA in its
report to Congress on Policy Options for Stabilizing Global
Climate.
190
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Electricity Demand
GCM climate scenarios (GFDL and OSU),
although the use of the GISS transient experiment
results for 2010 and 2055 indicates relative
sensitivities to small and large temperature changes.
The study did not consider variations in
temperature changes and the occurrence of extreme
events, which affect powerplant dispatch and
determinations of peak demands, respectively, and
are important for utility planning.
Many uncertainties exist regarding the concepts,
methods, and assumptions involved in developing
and applying estimates of the temperature sensitivity
of demand. For example, a key assumption is that
the estimated sensitivities of demand to historical,
short-term variations in temperature are adequate
representations of future relationships between
electricity demand and long-term changes in mean
temperatures.
Uncertainties also exist regarding market,
regulatory, technological, and other conditions that
will face the utility industry in the future. For
example, technological changes that improve the
energy efficiency of weather-sensitive end-use
equipment or electricity-generating equipment will
continue to evolve. These changes would likely lead
to lower climate change impacts than estimated in
this report. On the other hand, regulatory changes
aimed at reducing the emissions of greenhouse
gases from electricity generation could limit a
utility's future fuel and technology investment
options, leading to higher estimates of cost impacts
than reported here. Because of these limitations, it
is important to recall that the results presented in
the next section should not be considered as
projections of actual powerplant investments and
utility operations, but rather as comparisons
providing estimates of the magnitude of sensitivities
to alternative climate; change assumptions.
Results
The potential national impacts for 2010 and
2055 are summarized in Table 10-1. The table
presents base case values (i.e., assuming no change
in climate) for each year and estimated impacts
represented by changes from the base case values.
The impacts for 2055 are presented for both the
lower growth GNP and the higher growth GNP
cases. Also, where ranges of impacts are presented,
they summarize the estimates under alternative
climate change scenarios (GISS A and GISS B) and
assumptions of the weather sensitivity of demand
("estimated sensitivity' and "higher sensitivity").
Estimated increases in peak demand over the
base case on a national basis range from 2 to 6% by
2010. Changes in estimated annual energy
requirements by 2010 are more modest, ranging
from 1 to 2%. In 2055, peak national demands are
estimated to increase by 13 to 20% above base case
values, and annual energy requirements are
estimated to increase by 4 to 6%.
By 2010, new climate change-induced generating
capacity requirements increase by 6 to 19%, or
about 24 to 55 GW, representing an average
increase of up to 1 GW per state (approximately the
capacity of one to two large nuclear or coal-fired
baseload powerplants). The majority of the capacity
increase is for peaking capacity rather than baseload
capacity. The investment associated with these
capacity increases is several billion dollars (in
constant 1986 dollars). By 2055, the change in new
capacity requirements increases in percentage terms
and represents several hundred GW. Under high
GNP and higher weather-sensitivity assumptions, the
estimated increase attributable to climate change is
almost 400 GW, or 23%. To put these results into
perspective, it should be noted that current
generating capacity in the United States is about 700
GW. The increase in new capacity requirements
under the base case is 1,350 to X780 GW.
Annual generation increases for the United
States are not as large in percentage terms as those
estimated for new generating capacity requirements,
but nonetheless, they account for several hundred
billion kWh by 2055. In the near term (i.e., to
2010), increased. levels and changing patterns of
climate change-induced electricity demand permit
utilities in some areas having excess generating
capacity to serve the growing needs of utilities in
other areas through substitution of lower cost
baseload generation for higher cost peaking
generation. On net, peaking generation would be
lower as a result of climate change in 2010 (see
Under et al., 1987, for further detail). In 2055,
peaking generation is projected to increase along
with baseload generation, because all the excess
capacity that had existed in 2010 either would have
been fully used by growing demands to 2055 or
would have been retired. The estimated impacts of
climate change on national new generating capacity
191
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Chapter 10
Table 10-1. The Potential National Impacts of Climate Change on Electric Utilities
2010
2055
Lower GNP
Peak demand (GW)
New capacity requirements (GW)a
Peaking
Baseload
Total
Annual sales (bkWh)
Annual generation15 (bkWh)
Oil/gas
Coal
Other
Total
Cumulative capital costs°'d
Annual costsd
Base
774
50
226
276
3,847
287
2,798
1,092
4,177
669
162
Increase
20-44
13-33
11-22
24-55
39-67
54-103
43-72
25-48
3-6
Base
1,355
176
1,011
1,187
6,732
221
6,242
846
7,309
1,765
474
Increase
181
118
67
185
281
2
305
(2)
305
173
33
Higher GNP
Base
1,780
254
1,423
1,677
8,848
308
8,295
1,003
9,607
2,650
655
Increase
238-357
182-286
74-98
227-384
370-555
27-51
381-560
(7)-0
401-611
222-328
48-73
^Includes reserve margin requirements; does not include "firm scheduled" capacity.
Includes transmission and distribution losses.
°"Base" values include regional capital expenditures for utility-related equipment hi addition to new generating
capacity (e.g., new transmission facilities).
dln billions of 1986 dollars.
Abbreviations: GW = gigawatts; bkWh = billion kilowatthours.
Source: Linder and Inglis (Volume H).
requirements and annual generation are illustrated
in Figure 10-2.
Table 10-1 also indicates that the increase in
annual costs for capital, fuel, and operation and
maintenance associated with climate change-induced
modifications in utility investments and operations
are a few billion dollars in 2010 and are $33 to $73
billion by 2055, a 7 to 15% increase over base case
values of $475 to $655 billion for 2055.
Figures 10-3 and 10-4 illustrate the diversity of
the estimated results for generating capacity on a
state-by-state basis. The state and regional
differences reflect differences in current climate
conditions (e.g., seasonal temperature patterns),
assumed future climate changes, and electricity end-
use and utility system characteristics (e.g., market
saturation of weather-sensitive appliances and
equipment).
Figure 10-3 shows that estimated reductions in
new capacity requirements induced by climate
change are limited to the whiter-peaking regions of
the extreme Northeast and Northwest. The Great
Lakes, northern Great Plains, and Mountain States
192
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Electricity Demand
Additional Climate Change Impacts:
Higher Sensitivity
Climate Change Impacts:
Base Sensitivity
Base Case (No Climate Change)
2010 2066 2055 2010 2056 2055
Lower Higher Lower Higher
GNP GNP GNP GNP
Assumption Assumption Assumption Assumption
Figure 10-2. Potential impacts of climate change on electric utilities, United States (Linder and Inglis, Volume
H).
Figure 10-3. Changes in electric utility capacity additions by state, induced by climate change in 2055 (derived
from Linder and Inglis, Volume H). '
193
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Chapter 10
are estimated to experience increased new capacity
requirements by 2055 in the range of 0 to 10%.
Increases greater than 20% are concentrated in the
Southeast, southern Great Plains, and Southwest.
Figure 10-4 shows a somewhat similar
geographic pattern of impacts .for electricity
generation in 2055. Reductions in generation are
estimated in the North, and the greatest increases
are concentrated in the Southwest. Despite
substantial use of air-conditioning in the Southeast,
the estimated increases in generation are only in the
5 to 10% range. There is a relatively high market
saturation of electric heat in the region, and the
increase in cooling is partly offset by, a decrease in
heating as a result of warmer winters.
Because regions are affected differently, the
results indicate potential changes in the patterns of
interregional bulk power exchanges and capacity
sales over tune and as climate changes. For
example, under the assumption of increasing
temperatures, some regions may require significant
amounts of additional generating capacity to reliably
meet increased demands during peak (cooling)
seasons, but may experience lower demands in other
(heating) seasons. As a result, the region's needs
may be for powerplants that are utilized heavily
during only part of the year. Low annual utilization
in the region would not justify construction of high-
. capital and low-fuel cost baseload powerplants that
can produce electricity more cheaply (per kWh)
than low-capital and high-fuel-cost peaking units.
However, when considered across several regions,
the least-cost plan may be to construct baseload
powerplants in certain regions, utilize them to an
extent greater than required by the region, and sell
the "excess" electricity from these plants into other
regions. The location and amount of these
interregional sales would be subject to the transfer
capabilities of transmission capacity in place. An
alternative to increased interregional bulk power
sales would be the development and application of
efficient and effective energy storage technologies.
SOCIOECONOMIC AND
ENVIRONMENTAL
IMPLICATIONS
Despite the limitations of the analysis and the
need for more research to refine the data and
methods used, the results are judged to be
Figure 10-4. Changes in electricity generation by state, induced by climate change in 2055 (derived from Linder
and IngUs, Volume H).
194
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Electricity Demand
reasonable estimates of the sensitivity of electricity
demand to potential climate change. Key
socioeconomic and environmental implications of
the: results stem from the increases irt electric
generating capacity and generation requirements
associated with climate-induced changes in demand.
The implications include the following:
• • Climate change could result in overall fuel
mixes for electricity generation that differ
from those expected in the absence of
climate change.
• Climate change would not evenly affect
regional demands for electricity. Greater
impacts would occur in regions where
weather-sensitive end uses (particularly air-
conditioning) are important sources of
electricity demand. Substantially greater
climate change impacts were estimated for
the Southeast and Southwest than for other
regions, especially the northern tier of
states. Other impacts not addressed in this
: study, such as the availability of water for
hydropower generation and powerplant
cooling, also would be more important in
some regions (e.g., the West) than in
others.
• Regional differences in capacity and
generation requirements suggest that
important new opportunities for
interregional bulk power exchanges or
capacity sales may arise as a result of
climate change.
• The impacts of uncertain climate conditions
over the long term could pose significant
planning and economic risks. Because of
long lead times required to plan and build
economic baseload generating capacity, the
ability of utility planners to correctly
anticipate climate change could result in
lower electricity production costs. The
magnitude of these risks in some regions
(e.g., the Southeast and the southern Great
Plains) could be similar to other
uncertainties that utility planners and
decisionmakers must face.
• If the result is confirmed that the majority
of new capacity requirements in response to
climate change are for peaking capacity, a
new technological and market focus would
be directed toward this type of generating
plant. Related to this would be increased
research and development on electricity
storage technologies, which would allow
lower cost, more efficient powerplants to
generate, at off-peak times, electricity for
use during peak periods.
Because increases in customer demands for
electricity may be particularly concentrated
in certain seasons and at peak periods,
conservation and especially load
management programs that improve the
efficiency or change the patterns of
customer uses of electricity could be more
cost-effective when considered in the
context of potential changes in climate.
Increased electricity generation implies the
potential for increased adverse
environmental impacts depending upon
generating technology and fuel-use
assumptions. Potential adverse impacts
compared with the base case are associated
with the following:
air quality (e.g., emissions of sulfur
dioxide, NOX, and other pollutants);
land use for new powerplant sites, fuel
extraction, fuel storage, and solid waste
disposal;
water quality and use (e.g., for
powerplant cooling and fuel
processing); and
resource depletion, especially of
nonrenewable fuels such as natural gas.
Of particular concern would be additional
water withdrawal and consumption
requirements in areas where water supplies
may be reduced by climate change.3
For example, increased electricity generation induced by
climate change in northern California could increase
requirements for water withdrawal by 600 to 1,200 million cubic
feet and for water consumption by 200 to 400 million cubic feet
in 2055. Comparable figures for the southern Great Plains in
2055 would be water withdrawal of 5,800 to 11,500 million cubic
feet and consumption of 1,800 to 3,500 million cubic feet.
195
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Chapter 10
Increased electricity generation also implies
increased emissions of CO« and other
greenhouse gases compared with base case
emissions. For example, if the estimated
increases in climate change-induced
generation reported in Table 10-1 were met
by conventional technologies, CO2
emissions could increase by 40 to 65 million
tons per year by 2010 and by 250 to 500
million tons per year by 2055. Use of
lower CO2-emitting technologies and fuels
— such as efficient conversion technologies
and nuclear or renewable resources —
would lower these estimated impacts.
POLICY IMPLICATIONS
In general, the study results suggest that utility
planners and policymakers should begin now to
assess more fully and to consider climate change as
a factor affecting their planning analyses and
decisions. If more complete and more detailed
analyses support the socioeconomic and
environmental implications of the climate change
effects described above, they should be explicitly
addressed in planning analyses and decisions.
Specific policy implications related to the findings
include the following:
• In formulating future National Energy
Plans, the Department of Energy may wish
to consider the potential impacts of climate
change on utility demands.
• The interactions of climate change and the
current efforts of the Federal Energy
Regulatory Commission (FERC) to
restructure the electric utility industry are
difficult to assess. For example, the
industry's response to FERC policies could
either accelerate or reduce the rate of
emissions of greenhouse gases, depending
upon changes in the mix of generating fuels
and effects on the efficiency of electricity
production. The possible alternative
responses should be assessed, and FERC
Note, however, that these increases in emissions from
electricity production could be offset, at least in part, by
reduced demand for space heating provided by natural gas and
oil furnaces or by other direct uses of fossil fuels.
policies should be considered with respect
to their potential implications related to
climate change issues.
Increases in electricity demands induced by
climate change will make achievement of
energy conservation goals more difficult.
For example, the conference statement
from "The Changing Atmosphere:
Implications for Global Strategy"
(Environment Canada, 1988) calls for
reductions in CO2 emissions to be achieved
in part through increased efforts in energy
efficiency and other conservation measures.
An initial goal for wealthy, industrialized
nations set by the conference is a reduction
in CO, emissions through conservation of
approximately 10% of 1988 emissions levels
by 2005. The impacts of climate change to
increase electricity -demand should be
factored into the policies and plans
designed to achieve this conservation goal.
Similarly, climate change impacts may
exacerbate the difficulties or costs
associated with implementing acid rain
mitigation strategies being considered by
the Congress. However, these strategies
center primarily on near-term solutions
focusing on emissions reductions from
existing powerplants, and the impacts of
climate change may not be large within that
time frame.
Although not addressed directly in the
analyses underlying this report, state and
federal agencies should consider mitigation
strategies that include energy conservation;
increased efficiency in the production,
conversion, and use of energy; and the
development and reliance on fuel sources
with low CO2 emissions.
RESEARCH NEEDS
Important areas for further climate change
research include improved methods for developing
and disseminating climate change scenarios, with
particular emphasis on (1) improved estimates of
climate variables (in addition to temperature)
relevant to utility impact assessment (e.g.,
196
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Electricity Demand
hydrologic factors, winds); (2) estimates of the
possible impacts of global warming on variations in
weather conditions and the occurrence of extreme
events; (3) continued attention to estimates of the
rate of climate change over time; and (4) estimates
of climate change at a more disaggregated regional
or local level.
Follow-on research suggestions on the utility
side include (1) refinement of the analytical
approach, in part through lessons learned from
additional utility-specific analyses; (2) more detailed
and complete analyses of the weather sensitivity of
customer demand for electricity; (3) extension of the
approach to consider other pathways (including
indirect and secondary effects) through which
climate change could affect utility investments and
operations; and (4) an assessment of the value of
improved climate change information to utility
planners and managers.
REFERENCES
Environment Canada. 1988. The Changing
Atmosphere: Implications for Global Security
Conference Statement. Environment Canada,
Government of Canada. Toronto; June 27-30.
Linder, K.P., MJ. Gibbs, and M.R. Inglis. ICF
Incorporated. 1987. Potential Impacts of Climate
Change on Electric Utilities. Report 88-2. Albany,
New York: New York State Energy Research and
Development Authority. (Note: This report was
also published by the Electric Power Research
Institute, Palo Alto, California, in January 1989;
report no. EN-6249.)
Stokoe, P.K., and M. LeBlanc. P. Lane and
Associates, Ltd., and Discovery Consultants, Ltd.
1987. Socio-economic Assessment of the Physical
and Ecological Impacts of Climate Change on the
Marine Environment of the Atlantic Region of
Canada, Phase I. Halifax, Nova Scotia, Canada:
School for Resource and Environmental Studies,
Dalhousie University.
197
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CHAPTER 11
AIR QUALITY
FINDINGS
• Potential changes in regional temperatures,
precipitation patterns, clouds, windspeed and
direction, and atmospheric water vapor that will
accompany global climate change will affect
future air pollution levels and episodes in the
United States.
• While uncertainties remain, it is likely that an
increase in global temperatures would have the
following effects on air quality, if other variables
remain constant. These potential impacts
should be interpreted as relative changes as
compared with air quality levels without climate
change. This chapter does not predict what will
happen to air quality without climate change
and does not consider changes in anthropogenic
emissions or technology.
— Ozone levels in many urban areas would
increase because higher global temperatures
would speed the reaction rates producing
ozone in the atmosphere.
— Natural emissions of hydrocarbons would
increase with a temperature rise. Natural
emissions of sulfur would also change, but
the direction is uncertain. The
hydrocarbons and nitrogen oxides
participate in reactions that produce ozone.
— Manmade emissions of hydrocarbons,
nitrogen oxides, and sulfur oxides may rise
if more fossil fuel is used to meet higher
electricity needs (see Chapter 10: Electricity
Demand) and if technology does not
improve.
— The formation of acidic materials (such as
sulfates) would increase with warmer
temperatures because sulfur and nitrogen
oxides would oxidize more rapidly. The
ultimate effect on acid deposition is difficult to
assess because of changes in clouds, winds, and
precipitation.
- Visibility may decrease because of the
increase in hydrocarbon emissions and the
rate at which sulfur dioxide is oxidized to
sulfate.
— The small increase in temperature will not
significantly affect carbon monoxide
emissions.
Preliminary analyses of the effects of a scenario
of a 4°C temperature increase in the San
Francisco Bay area, with no change in emissions
or other climate variables, on ozone
concentrations suggest that maximum ozone
concentrations could increase by approximately
20%, that the area in which the National
Ambient Air Quality Standard (NAAQS) would
be exceeded would almost double, and that the
number of people-hours of exposure would
triple. The Midwest and Southeast also could
incur high concentrations and an increase in the
area of high ozone by a factor of three.
Increases in ambient ozone levels resulting from
climate change could increase the number of
nonattainment areas and make attainment more
expensive in many regions. Preliminary
estimates suggest that an expenditure of several
million dollars per year may be necessary for
volatile organic compound (VOC) controls
above those needed to meet standards without
climate change. The total costs for additional
air pollution controls that may be needed
because of global warming cannot be estimated
at this time.
Because of the close relationship between air
pollution policies and global climate change, it
is appropriate for EPA to review the impact of
199
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Chapter 11
global climate change on air policies and the
impact of air pollution regulations on global
climate change.
RELATIONSHIP BETWEEN
CLIMATE AND AIR QUALITY
The summer of 1988 provided direct evidence
of the importance of weather to pollution episodes
in the United States. Despite significant progress in
reducing emissions of many pollutants over the last
decade, the extended stagnation periods and high
temperatures caused ozone levels in 76 cities across
the country to exceed the national standard by at
least 25%. Whether this recent summer is an
appropriate analog for the future cannot be
determined with certainty, but scientists have
recognized for some time that air pollution does
vary with seasons and is directly affected by
ventilation, circulation, and precipitation, all of
which could be affected by future global climate
changes.
Ventilation
Two major factors, referred to as "ventilation"
when considered together, control the dilution of
pollutants by the atmosphere: windspeed and the
depth of the atmospheric mixing layer (frequently
called the mixing depth). If windspeed is high,
more air is available to dilute pollutants, thus
lowering pollutant concentrations. The mixing layer
(the distance between the ground and the first
upper-layer inversion) tends to trap pollutants
because the inversion above it acts as a barrier to
vertical pollutant movement. Thus, pollutant
concentrations decrease as mixing depth increases,
providing greater dilution.
The ventilation characteristics of an area
change, depending on whether a high- or low-
pressure system is present. Low-pressure systems
usually produce good ventilation because they
normally have greater mixing depths and
windspeeds, and precipitation is often associated
with them. High-pressure systems, on the other
hand, generally produce poor ventilation conditions
because they frequently have smaller mixing depths
on their western sides and lower windspeeds. They
also tend to move more slowly than lows, so more
emissions can enter their circulation patterns. In
addition, they are frequently free of clouds, resulting
in maximum sunlight and therefore more
photochemical ozone production during the day.
Also, during the evenings, the clear skies allow
surface-based (see below) inversion layers to form,
concentrating pollutants in a small volume of air
and often creating very high air pollution levels.
Climatologically, certain places hi the country,
such as the Great Plains and the Northeast (Figure
11-1A), are frequently windy, and others, such as
the Southwest (Figure 11-1B), frequently have large
mixing depths. These areas will have cleaner-than-
average air if they do not contain too many
pollutant sources. Areas, such as California, that
are frequently affected by high-pressure systems ~
causing lower windspeeds and smaller mixing depths
— will have more major air pollution episodes.
Circulation
Two semipermanent high-pressure systems are
important to the global circulation pattern and
greatly influence U.S. air pollution climatology: the
large Pacific high, which is often situated between
the Hawaiian Islands and the west coast of North
America, and the Bermuda high, located over the
western Atlantic Ocean.
The Pacific high often results in extended
periods of air stagnation over the western United
States from Oregon and California to over the
Rockies, and is responsible for many severe ozone
episodes in southern California. Air stagnation
associated with the westward extension of the
Bermuda high occurs most often during the summer
months and affects the eastern United States from
southern Appalachia northward to New England.
Within the Bermuda high, pollutants are slowly
transported from the industrial areas of the Ohio
River Valley into the populated areas of the
Northeast. The Bermuda high is also responsible
for the general southwest-to-northeast airflow in the
summer, carrying pollutants along the metropolitan
corridor from Richmond to Boston and exacerbating
the ozone problem in the Northeast.
Precipitation
Atmospheric pollutants in both particulate and
gaseous forms are incorporated into clouds and
200
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Air, Quality
B
,789
9—9
Figure 114, (A) Mean annual windspeed averaged through the afternoon mixing layer (speeds are in meters
per second); (B) mean annual afternoon mixing height, in hundreds of meters (adapted from Holzworth, 1972).
precipitation. These pollutants can then be
transported to the ground through rainfall (wet
deposition). Cloud-formation processes and the
consequent type of precipitation, together with the
intensity and duration of precipitation, are
important in determining wet deposition of
pollutants.
PATTERNS AND TRENDS IN AIR
QUALITY
To protect the public health and welfare, the
U,S. EPA has promulgated National Ambient Air
Quality Standards (NAAQS). In 1986, more people
lived in counties with measured air quality levels
that violated the primary NAAQS for ozone (O3)
than for other pollutants (Figure 11-2).
Although millions of people continue to breathe
air that is in violation of the primary NAAQS,
considerable progress is being made in reducing air
pollution levels. Nationally, long-term 10-year (1977-
86) improvements have been seen for
a number of pollutants, including total suspended
particulates (TSP), O,, carbon monoxide (CO),
nitrogen dioxide (NO^), lead, and sulfur dioxide
(SO2). This section does not attempt to predict
future trends in emission levels.
Total Suspended Particulates
Annual average TSP levels decreased by 23%
between 1977 and 1986, and particulate emissions
decreased by 25% for the same period. The more
recent TSP data (1982-86) show that concentrations
are leveling off, with a 3% decrease in ambient TSP
levels and a 4% decrease in estimated emissions
during that time.
In the future, air quality may decrease as the
benefits of current pollution control measures are
affected by increases hi population and economic
growth.
Sulfur Dioxide
Annual average SO2 levels decreased 37% from
1977 to 1986. An even greater improvement
201
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Chapter 11
POLLUT;
TSP
S02
CO
NO 2
Ozone
Pb
C
WT
mmmmmw
|0.9
wmsmmm*\A
^7.5
^^^^^^^^^^^^^^^75
14.5
) 10 20 30 40 50 60 70 80 90
mil lions of persons
Figure 11-2. Number of persons living in counties
with air quality levels above the primary National
Ambient Air Quality Standards in 1986 (based on
1980 population data) (U.S. EPA, 1988).
was observed in the estimated number of violations
of the 24-hour standard for SO, concentration,
which decreased by 98%. These decreases
correspond to a 21% drop in sulfur dioxide
emissions during this 10-year period. However, most
of the violations and the improvements occurred at
source-oriented sites, particularly a few smelter
sites. Additional reductions may be more difficult
to obtain. The higher concentrations were found in
the heavily populated Midwest and Northeast.
Ozone
A national standard for ambient levels of ozone
was established with the original Clean Air Act in
1972, along with standards for five other pollutants.
While headway has been made in meeting all these
national air quality standards, progress in meeting
the ozone standard has been particularly slow and
frustrating for concerned lawmakers and
environmental officials at all levels of government.
At the end of 1987, the date anticipated in the act
for final attainment of the ozone standard, more
than 60 areas had not met the standard. In recent
years, the number of nonattaimnent areas has
fluctuated with meteorology, often overwhelming the
progress being made through reduced emissions.
Thus "bad" weather (summertime conditions
favorable to ozone formation) in 1983 led to an
increased number of nonattainment areas, and
"good" conditions in 1986 led to a decreased number
of areas.
Nationally, between 1979 and 1986, O3 levels
decreased by 13%. Emissions of volatile organic
compounds (VOCs), which are ozone precursors,
decreased by 20% from 1979 to 1986. The
estimated number of violations of the ozone
standard decreased by 38% between 1979 and 1986.
The highest concentrations were in southern
California, but high levels also persisted hi the
Texas gulf coast, the northeast corridor, and other
heavily populated regions.
Acid Deposition
Widespread concern exists concerning the
effects of acid deposition on the environment. With
the present monitoring network density in eastern
North America, it is now possible to quantify
regional patterns of concentration and deposition of
sulfate, nitrate, and hydrogen ions, primary
constituents of acid deposition. In Figures 11-3
through 11-5, isopleth maps show the geographic
pattern of acid deposition, as reflected by the
concentration and deposition of these three species
(Seilkop and Finkelstein, 1987).
For the relatively short period from 1980 and
1984, evidence indicates the total deposition and
average concentration of sulfate, nitrate, and
hydrogen ions in precipitation falling over eastern
North America decreased by 15 to 20%. The
observed decreases correspond with reported
reductions in the U.S. emissions of sulfur oxides
(SOX) and nitrogen oxides (NOX), and sulfate and
nitrate precursors. However, the emission figures
are subject to estimation error and should be used
cautiously (Seilkop and Finkelstein, 1987).
STUDIES OF CLIMATE CHANGE
AND AIR QUALITY
Some of the climate factors that could affect air
quality are listed in Table 11-1. To explain these
relationships, two projects were undertaken for this
report to identify the potential impacts of climate
change on air quality:
1. Climate Change and Its Interactions with
Air Chemistry: Perspectives and Research
Needs - Penner, Connell, Wuebbles, and
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Air Quality
SULFATES
CONCENTRATION
DEPOSITION
1980
1984
Figure 11-3. Isopleth maps of average annual concentrations (mg/liter) and total annual deposition (g/m ) of
sulfates in 1980-84 (Seilkop and Finkelstein, 1987).
NITRATES
CONCENTRATION
DEPOSITION
1980
1984
Figure 11-4. Isopleth maps of average annual concentration (mg/liter) and total annual deposition (g/m ) of
nitrates in 1980-84 (Seilkop and Finkelstein, 1987).
203
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Chapter 11
1980
1984
HYDROGEN IONS
CONCENTRATION DEPOSITION
Figure 11-5. Isopleth maps of average annual concentration (mg/liter) and total annual deposition (g/m^) of
hydrogen ions in 1980-84 (Seilkop and Finkelstein, 1987).
Table 11-1. Climate Change Factors Important for Regional Air Quality
Changes in the following affect air quality:
1. the average maximum or minimum temperature
and/or changes in their spatial distribution
leading to a change in reaction rates and the
solubility of gases in cloud water;
2. stratospheric O3 leading to a change in reaction
rates;
3. the frequency and pattern of cloud cover
leading to a change in reaction rates and rates
of conversion of SO2 to acid deposition;
4. the frequency and intensity of stagnation
episodes or a change in the mixing layer leading
to more or less mixing of polluted air with
background air;
5. background boundary layer concentrations of
water vapor, hydrocarbons, NO , and O,,
leading to more or less dilution ofpolluted air
in the boundary layer and altering the chemical
transformation rates;
6. the vegetative and soil emissions of
hydrocarbons and NOX that are sensitive to
temperature and light levels, leading to changes
in their concentrations;
7. deposition rates to vegetative surfaces whose
absorption of pollutants is a function of
moisture, temperature, light intensity, and other
factors, leading to changes in concentrations;
8. energy usage, leading to a change in energy-
related emissions;
9. aerosol formation, leading to changes in
reaction rates and the planetary albedo
(reflectivity); and
10. circulation and precipitation patterns leading to
a change in the abundance of pollutants
deposited locally versus these exported off the
continent.
Source: Adapted from Penner et al. (Volume F).
204
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Air Quality
Covey - Lawrence Livermore National
Laboratory (Volume F)
2. Examination of the Sensitivity of a Regional
Oxidant Model to Climate Variations -
Morris, Gery, Liu, Moore, Daly, and
Greenfield - Systems Applications, Inc.
(Volume F)
The literature does not contain studies on the
effects of climate change on air quality. Thus, these
studies should be considered as preliminary analyses
of the sensitivity of air quality to climate change.
Climate Change and Its Interactions with
Air Chemistry
Penner et al. conducted a literature review of
studies on the relationship of climate and air quality.
They also organized a workshop on the issue.
Effect of Climate Change on Ozone Formation
Changes in ventilation, circulation, precipitation,
and other aspects of climate affect the concentra-
tions of the ozone precursors (VOCs and NO ).
Climate changes can also increase or decrease the
rates at which these precursors react to form ozone.
The effects of change in global temperature and in
stratospheric ozone concentration on tropospheric
ozone precursor concentrations, reaction rates, and
tropospheric ozone concentrations are discussed
below.
Temperature Change
Studies of the Effects of Temperature on
Ozone. Smog chamber and modeling studies have
shown that ozone levels increase as temperature
increases. Kamens et al. (1982) have shown in an
outdoor smog chamber study that the maximum
ozone concentration increases as the daily maximum
temperature increases (holding light intensity
constant). Their data show that there is no critical
"cut-off temperature that eliminates photochemical
ozone production. Instead, a general gradient is
observed as a function of temperature.
Samson (1988) has recently studied ambient
data for Muskegon, Michigan, and found that the
number of ozone excursions above the standard
(0.12 ppm) is almost linearly related to mean
maximum temperature. In 1988, the mean
maximum temperature was 77°F and there were 12
ozone excursions. In 1984, with a mean
temperature of 73.50°F, there was only one
excursion.
Temperature-dependent modeling studies were
conducted by Gery et al. (1987). For this modeling
effort, Gery et al. used the OZIPM-3 trajectory
model, which is city specific. The scenarios for the
different cities used actual observed mixing heights,
solar radiation and zenith angle, and pollutant
concentrations characteristic for the particular city
considered for June 24, 1980. This base case was
chosen because it was a high-pollution day, and
ambient data were available. The increased
temperature scenarios applied the increase
throughout the day and were added to the base case
scenario. The light intensity increase was achieved
by increasing the photolyses rates for nitrogen
dioxide, formaldehyde, acetaldehyde, hydrogen
peroxide, and ozone. Results for New York in June
1980 are shown in Table 11-2. In general, ozone
concentration increased withincreasing temperature.
The concentration of hydrogen peroxide (H2O2), a
strong oxidant that converts SO2 to sulfunc acid,
was also observed to increase with higher
temperatures. This is compatible with the increase
in ozone because the entire photochemical reaction
process is accelerated when temperature rises. As
a result, cities currently violating the ozone NAAQS
will be in violation to a greater degree in the future,
and cities that are complying with the NAAQS now
could be forced out of compliance just by a
temperature increase. Figure 11-6 shows the
predicted increase in low-level ozone for two
temperature increases in Los Angeles, New York,
Philadelphia, and Washington.
Modeling studies by Penner et al. have shown
that the effect temperature has on ozone formation
also depends on the ratio of volatile organic
compounds to nitrogen oxides, both of which are
ozone precursors. Figure 11-7 shows that ozone
levels will generally go up, except in areas where the
ratio of VOCs to NOX is low.
Temperature change has a direct effect on
ozone concentrations because it increases the rates
of ozone-forming reactions. However, a
temperature rise can also affect ozone formation by
altering four other aspects of climate or the
atmosphere: cloud cover, frequency and intensity of
205
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Chapter 11
Table 11-2. Maximum Hourly Concentrations and Percentage Changes for Ozone, H2O2, and PAN for the
Future Sensitivity Tests Using an EKMA Model for the Simulation of June 24,1980, New York
Ozone
Change in Temp (°C)
Stratospheric Ozone3
Base
-16.6%
-33.3%
Concentration fppm)
0 +2 +5
0.125 0.130 0.138
0.150 0.157 0.167
0.165 0.170 0.178
Percent change
(from base)
+2 +5
20
32
4
26
36
10
34
42
Hydrogen Peroxide (H2O2)
Change in Temp (°C)
Stratospheric Ozone3
Base
-16.6%
-33.3%
Concentration fppb)
0.05 0.06 0.08
0.43 0.58 0.84
3.08 3.31 3.60
Percent change
(from base)
20 60
760.0 1060 1580
6060.0 6520 7100
Peroxvacetvl Nitrate (PAN)
Change in Temp (°C)
Stratospheric Ozone3
Concentration (ppb)
Percent change
(from base) .
Base
-16.6%
-33.3%
3.98
5.85
7.59
3.50
5.26
6.73
2.79
4.34
5.49
—
-. 47
91
-12
32
69
-30
9
38
aBase refers to the present stratospheric ozone column. The -16.6 and -33.3% refer to a depletion of the base
value. Ultraviolet light will increase with the depletion (Gery et al., 1987).
stagnation periods, mixing
reactant concentrations.
layer thickness, and
Effect of Changes in Cloud Cover. The
reduction in light intensity caused by increased
cloud cover can reduce ozone production. Penner et
al. (Volume F) calculate that a reduction hi light
intensity of 50% throughout the day will reduce the
ozone formation. However, the magnitude of ozone
reduction depends on the time of day when the
cloud cover occurs. If clouds occur in the afternoon
or evening, little effect is observed in the ozone
production, but if clouds occur during the morning
hours, photochemical reactions are slowed, and less
ozone is produced. Jeffries et al. (1989) suggest
that cloud cover can decrease ultraviolet radiation
by 7 to 14% in their outdoor smog chamber located
in North Carolina. Although a global temperature
change would affect cloud cover, the type and
direction of the change are unknown.
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Air Quality
L.A. N.Y. Phil. Wash.
2'C TEMPERATURE INCREASE
LA. N.Y. Phil. Wash.
5-0 TEMPERATURE INCREASE
Figure 11-6. Percent increase in predicted O3 over
future base case (0.12 ppm) for two temperature
increases in four cities (Gery, 1987).
10
15 20 25 30 35 40
TEMPERATURE (°C)
BL = Boundary Layer
Figure 11-7. The effect of temperature on the peak
O, concentrations predicted in a box model
calculation of urban O3 formation. Calculations are
shown for three hydrocarbon to NOX ratios. The
effect of increasing the boundary layer depth for the
case with a hydrocarbon to NQj ratio of 7 is also
shown (Penner et al., Volume F).
The Penner et al. study assumes that cloud
cover causes an equal decrease in all wavelengths of
solar radiation. However, clouds are not expected
to cause an equal decrease at all wavelengths. Solar
radiation is needed to form ozone. Since Penner et
al. may have underestimated the intensity of some
wavelengths of light, they may have overestimated
the decrease in ozone production.
Effect of Water Vapor. Water vapor is
involved in the formation of free radicals (reactive
compounds) and hydrogen peroxide, which are
necessary for the formation of ozone. Global
increases in temperature are expected to raise
tropospheric water vapor levels.
If sources of water vapor are not perturbed by
vegetative changes, and if global circulation patterns
do not significantly affect precipitation events (an
unlikely assumption), then global water vapor levels
are expected to increase with increasing
temperature. A temperature increase of 2°C could
raise the water vapor concentration by 10 to 30%
(Penner et al., Volume F). This change should
affect both oxidant formation and sulfur dioxide
oxidation (acid deposition).
Smog chamber studies have shown that at high
pollutant levels, increases in water vapor can
significantly accelerate both the reaction rates of
VOCs and the rate of oxidant formation (Altshuller
and Bufalini, 1971). Walcek (1988) has shown with
the use of a regional acid deposition model
(RADM) that the ozone, hydrogen peroxide, and
sulfate production rates in the boundary layer of the
troposphere all increase with increasing water vapor.
Effect of Changes in Frequency and Intensity of
Stagnation Periods. As noted previously, high-
pressure systems significantly enhance ozone
formation potential. During a high-pressure
episode, pollutants are exposed to high
temperatures and prolonged irradiation (Research
Triangle Institute, 1975), resulting in high levels of
ozone. If the intensity and frequency of high-
pressure episodes increase with global warming,
then ozone levels can be expected to be even higher.
Effect of Changes in Mixing Layer Thickness.
As shown in Figure 11-7, increases in the mixing
layer height decrease ozone formation, presumably
because there are less ozone precursors per volume
of atmosphere. An increase of global temperature
207
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Chapter 11
would probably lead to an increase in average
mixing depths as a result of greater convection,
which raises the mixing depth and increases mixing.
Effect of Changes in Reactant Concentrations.
The concentrations of ozone precursor pollutants
(VOCs, NOX) play a large part in determining the
amount of ozone produced. With increasing
temperature, natural hydrocarbon emissions are
expected to increase. Also, unless preventive
measures are taken, manmade emissions would
increase (vapor pressure of VOCs increases with
increasing temperature). If these ozone precursors
increased in concentration, ozone production would
increase.
Lamb et al. (1985) have shown that natural
hydrocarbon (VOC) emissions from deciduous
forests would increase by about a factor of three
with a temperature change from 20 to 30°C.
However, as discussed in Chapter 5: Forests, the
abundance of some deciduous forests could decline
because of global warming. However, grasslands or
shrubs that replace forests would still emit
hydrocarbons. The net effect is probably uncertain.
Emissions of NOX from powerplants would grow
because of a greater demand for electricity during
the summer months. Soil microbial activity is also
expected to increase with increasing temperature.
This will increase natural emissions of Npx.
Evaporative emissions of VOCs from vehicles and
refueling would also be expected to rise with
warmer temperatures. However, exact predictions
of the effects of all these factors on ozone formation
are difficult to make because the relationship
between precursor emissions and ozone is extremely
complex and not fully understood, and because
increases in emissions are difficult to quantify.
An example of this complex relationship
between ozone and its precursors is shown in Figure
11-8 (Dodge, 1977). At high VOC levels and low
NOX, adding or reducing VOCs has very little effect
on ozone formation. Likewise, when NOX
concentrations are high and VOC concentrations
are low, increasing NOX reduces ozone formation
while lowering NO increases ozone formation.
Thus, VOCs and NOX must be examined together
when considering any ozone reduction strategy
based on controlling ozone-forming precursors.
Stratospheric Ozone Change
Changes in stratospheric ozone concentration
can also affect tropospheric ozone formation
•0.2 0.4 O.6 O.8 1.0 1.2 1.4 1.6 I..8
O.O 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
VOC, PPMC
Figure 11-8. Ozone isopleths as a function of NOX
and volatile organic compounds (VOCs) (Dodge,
1977).
because stratospheric ozone regulates the amount of
ultraviolet (UV) radiation available for producing
ozone hi the troposphere. Stratospheric ozone
absorbs UV light from the sun and decreases the
UV energy striking the Earth's surface. When
stratospheric ozone is depleted by the
chlorofluorocarbons (CFCs) generated by human
activity, more UV radiation reaches the Earth's
surface, which increases the photolysis rates1 of
compounds that absorb solar radiation (NO2,
formaldehyde, acetaldehyde, O3, andH2O2). Faster
photolysis produces more free radicals (high-energy
species) that increase the amount of smog. Thus,
less stratospheric ozone will lead to enhanced ozone
formation in the troposphere.
Modeling results for New York from Gery et al.
(1987) show that tropospheric ozone increased when
stratospheric ozone decreased (see Table 11-2).
. They also show that H2O2 and peroxyacetyl nitrate
(PAN) yields increased. ELOj is a strong oxidant
that converts SO2 to sulfunc acid, and PAN is an
air pollutant that damages plants and irritates eyes.
The 16.6 and 33.3% decreases (Table 11-2) in
stratospheric ozone far exceed the expected
decrease resulting from the buildup of CFC
concentrations. This is especially true since the
Photolysis is the breakdown of chemicals as a result of the
absorption of solar radiation.
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Air Quality
Montreal Protocol agreement will limit CFC
production. These high values of stratospheric
ozone depletion are used only for illustrative
purposes.
Changes in Tropospheric Hydroxyl Radicals
Hydroxyl radicals (reactive compounds) are the
most important free radicals found in the
atmosphere. These reactive compounds are
responsible for removing many atmospheric
pollutants (such as CH4, VOCs, methyl chloroform,
CO) from the atmosphere (Penner et al., Volume
F). Without these free radicals, pollutants would
not be removed from the atmosphere and would
build up to higher levels (global heating would be
greater). Hydroxyl radicals in the free troposphere
are produced primarily by the decomposition of
ozone by sunlight and the subsequent reaction of
high-energy oxygen with water. In the urban
atmosphere, hydroxyl radicals are produced through
a complex series of reactions involving VOCs,
nitrogen oxides, and sunlight. The solar photolysis
of hydrogen peroxide also gives rise to hydroxyl
radicals. This occurs in both urban and rural areas.
The effect of global climate changes on
hydroxyl radical abundance is unclear. In urban
areas with increases in VOCs and NO , a
temperature increase will increase hydroxyl radical
concentration. Also, if natural hydrocarbons and
NOX increase in rural areas, hydroxyl radicals are
expected to increase. However, if methane, CO,
and natural hydrocarbons increase without an
additional increase in NOX, then hydroxyl radicals
will be depleted. A definitive prediction on the
effect of increasing temperature on global
concentrations of hydroxyl radicals cannot be made
at this time.
Effect of Climate Change on Acid Deposition
Rainwater and surface waters are more acidic
than natural background levels because of industrial
and mobile emissions of SO2 and MX, which form
sulfuric and nitric acids in the atmosphere. In the
air, sulfuric acid (HgSO,) is produced primarily by
.the reaction of SO2 with hydroxyl radicals (high-
energy species); in clouds, the oxidation of SO2 to
H2SO4 is more complex, involving reactions with
hydrogen peroxide and other dissolved oxidants.
Nitric acid (HNO3) is produced in air by the
reaction of hydroxyl radicals with NOX.
Organic acids, such as formic and acetic acids,
are also formed in the atmosphere. However, their
relative importance to the acid deposition problem
is unknown at present. Because they are weak acids
(compared to H^SO^ and HNO,), their contribution
to the problem is expected to be much less than
that of the inorganic acids (Galloway et al., 1982;
Keene et al., 1983,1984; Norton, 1985).
The acids produced in the atmosphere can be
"dry deposited" to the Earth's surface as gases or
aerosols, or they can be "wet deposited" as acid rain.
Changes in total acid levels depend on changes both
in atmospheric chemistry and changes in
precipitation. Wet deposition is affected most by
the amount, duration, and location of precipitation.
Since the direction of regional precipitation
changes is unknown, it is not known whether acid
fain will increase or decrease in the future.
However, many of the same factors that affect
ozone formation will also affect the total deposition
of acids.
Temperature Change
Higher temperatures accelerate the oxidation
rates of SO, and NOX to sulfuric and nitric acids.
Gery et al. (1987) have shown that a temperature
rise would also speed the formation of H2O2,
increasing the conversion of SO, to sulfuric acid
(see Table 11-2). Hales (1988) studied the
sensitivity to a 10° C temperature rise using the
storm-cloud model PLUVIUS-2. Considering only
the chemistry occurring with a 10°C temperature
rise, sulfate production increased 2.5 times. No
modeling was performed at more modest
temperature increases (e.g., ~4°C); however, it is
likely that oxidation would also increase with a
smaller increase in temperature. The limiting factor
in the oxidation of SO2 appears to be the availability
of H2O2. The model also suggested that a
temperature increase would cause more sulfuric acid
to form near the sources where SO2 is emitted.
Effect of Global Circulation Pattern Changes.
Potential changes in global circulation patterns
would greatly affect local acid deposition, because
they would alter ventilation and precipitation
patterns. Galloway et al. (1984) have calculated that
over 30% of the sulfur emissions from the eastern
United States are transported to the north and
farther east. Changes in circulation patterns would
209
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Chapter 11
affect this transport, although the direction or
magnitude of the effect is unknown. '
Effects of Changes in Emissions. If electricity
demand rises with rising temperatures (see Chapter
10: Electricity Demand), if more fossil fuels are
burned, and if technology is not improved, SO2 and
NOX emissions will increase. An. approximate 10%
growth in use of electricity in the summer could
increase SCL emissions during the summer by
approximately 30% if present-day technology is used
in the future. This, in turn, would increase acid
deposition.
Effects of Reduced Stratospheric Ozone. A
decrease in stratospheric ozone due to CFCs may
increase acid deposition because more UV radiation
would be available to drive the chemical reactions.
As discussed above, a modeling study by Gery et al.
(1987) showed an increase in the yield of H2O2
when stratospheric ozone was reduced by 16 and
33%. Because FJ^Ou is a strong oxidant, SO2 would
probably also be oxidized more quickly into sulfate
aerosols and acid rain, but this depends on the
availability of water vapor (e.g., clouds, rain).
Implementation of the Montreal Protocol should
help reduce CFC emissions.
Reduced Visibility. The growth in natural
organic emissions and increases in sulfates resulting
from warmer temperatures should reduce visibility,
assuming that the frequency of rain events, wind
velocity, and dry deposition rates remain the same.
If rain events increase, washout/rainout should
increase and visibility would be better than
predicted (see Chapter 3: Climate Variability).
MODELING STUDY OF CLIMATE
AND AIR QUALITY
Study Design
Morris et al. (Volume F) applied a regional
transport model RTM-HI to an area covering
central California and a region covering the
midwestern and the southeastern United States.
The model was run for the present-day conditions
and for a future climate. For California, Morris et
al. used input data from August 5-10, 1981; for the
Midwest and the Southeast, they used input data
from July 14-21, 1981. These were periods with
high ozone levels and may be most sensitive to
changes in climate. The scenario assumed that
temperatures would be 4°C warmer than in the base
case, but all other climate variables were held
constant (relative humidity was held constant). The
scenario assumed no change in emission levels, no
change in boundary layer, and no change in wind
velocity.
The RTM-III is a three-dimensional model that
represents point sources embedded in a grid
framework. The model has three prognostic vertical
layers and a diagnostic surface layer. This means
that the surface layer is represented by actual
observations. The other three layers are predicted
by using the surface layer data. The photochemical
reactions are based on the latest parameterized
chemical mechanism.
Limitations
Perhaps the most important limitation is that
emission levels were held constant. It is likely that
future emission levels will be different, although this
study did not estimate how. The results of this
study are useful for indicating the sensitivity of
ozone formation to temperature, but should not be
considered as a prediction of future ozone levels.
The model ignored future increases in emissions
that would occur with increased temperatures. The
estimates for ozone are only coarse approximations.
Morris et al. used the National Acid Precipitation
Assessment Program (NAPAP) emissions data of
1980. These data appear to underestimate actual
ratios of VOCs to NOX as measured in urban areas.
Ching et al. (1986) state that for most cities, the
NAPAP data underestimate VOC emission values
by a factor of three or more. The model simplified
some reactions of the hydrocarbons (VOCs)
because the chemistry is not well known.
This study did not estimate climate-induced
alterations in most meteorological variables, except
temperature and water .vapor, which is an
oversimplification. For example, this study assumed
that the mixing heights remain unchanged for the
temperature increase scenario; in reality, mixing
heights could increase with rising temperature.
Holding the mixing heights constant probably
overemphasized the importance of temperature in
oxidant production, because an increased mixing
layer depth might have had a dilution effect. Also,
as stated earlier, cloud cover will affect ozone
production. If cloud cover increases, then ozone is
expected to decrease. Frequency and intensity of
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Air Quality
stagnation periods can also have profound effects on
ozone formation. This modeling exercise did not
consider these factors.
Results
Central California Study
Table 11-3 summarizes the results from the
base case scenario and a climate sensitivity scenario
that used a 4°C temperature increase and an
attendant increase in water vapor concentration.
All of the days studied show a larger area exposed
to high levels of ozone. An increase in temperature
may lengthen the duration of high ozone levels,
although the maximum levels may be the same.
Figure 11-9 illustrates the August 6 base case and
climate sensitivity case. The temperature change
increased the August 6 maximum ozone
concentration from 15 parts per hundred million
(pphm) to 18 pphm, a 20% increase in ozone. The
area in which the NAAQS was exceeded almost
doubled from 3,700 to 6,600 square kilometers.
The temperature increases in the two main
cities in the San Joaquin Valley (Fresno and
Bakersfield) resulted in an approximate 0.5-pphm
increase (approximately 8%) in maximum daily
ozone concentration. In regions farther away from
the emissions, such as the Sierra Nevada Mountains,
little change in ozone levels was observed with the
increased temperature.
Midwest and Southeast Study . •
The results from applying RTM-in to the
midwestern and southeastern areas are shown in
Table 11-4. On one particular day (July 16), raising
the temperature caused maximum ozone to increase
from 12.5 pphm to 13.0 pphm (Figure 11-10).
Although this is only a slight increase (0.5 pphm),
the predicted area of exceedance of the ozone
NAAQS increased by almost a factor of three, from
9,800 to 27,000 square kilometers. The differences
occurred mainly in the upper Midwest. In general,
the results range from a reduction of 2.4% to an
increase of 8.0% in ozone levels. Although a
temperature increase will generally increase ozone
formation, it is noted in Table 11-4; that on two
days, July 14 and July 21, no ozone increases were
observed. This occurs when there are insufficient
precursors to sustain ozone formation. Under these
conditions, ozone is produced more quickly with
increasing temperature but the total amount
produced need not be greater and could even be
less in some cases.
Both modeling exercises indicate that
temperature change alone could increase ozone
levels over what they would be without climate
change.
Table 11-3. Maximum Daily Ozone Concentrations Predicted by the RTM-III for Each Day of the Central
California Modeling Episodes for the Base Case and the Case of Climate Sensitivity to Increased
Temperature of 4°C
Maximum daily ozone concentrations (pphm)
Date of Episode
(1981)
August 5
August 6
August 7
August 8
August 9
August 10
Base
case
11.8
15.0
11.7
13.5
10.5
9.1
4°C temperature
increase
12.1
18.0
13.1
13.7
11.2
9.18
Percent
increase
3
20
12
2
7
8
Source: Morris et al. (1988)
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Chapter 11
Base Case
August 6, 1981
Exceeds Standard
<6 >6 >8
Climate Sensitivity Scenario No. 1
4°C Temperature Increase
Figure 11-9. Comparison of estimated maximum daily ozone concentrations (pphm) for the base case and
climate sensitivity scenario No. 1 (temperature and water increase) for August 6, 1981 (Morris et al., 1988).
Table 11-4. Maximum Daily Ozone Concentrations Predicted by the RTM-III for Each Day of the
Midwestern/Southeastern Episode for the Base Case and the Case of Increased Temperature of
4°C .•••:'... . . .
Date of Episode
(1981)
July 14
July 15
July 16
July 17
July 18
July 19
July 20
July 21
Base
case
11.3
11.5
12.5
11.7
11.2
13.8
11.1
12.6
Maximum daily ozone concentrations
4°C temperature
increase
, • • . • 5 •. ,.-...••,•
11.3
11.9
1 13.0 •'.•'•
12.0
ill
14.8
' 11.2 .
12.3
(DDTim)
Percent
, increase "".' , ,
. :. 'o'.o ,,.
•:.-.:"•.•; 3.5: '•••" •
4.0
." :.' 2.6 •'; :- ;;. ..
: 8.0
• •"•"•. '72'
0.9
-2.4 V
Source: Morris et al. (1988).
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Air Quality
Base Case
Climate Sensitivity Scenario
Figure 11-10. Comparison of predicted estimated maximum daily ozone concentrations (pphm) for the base case
and climate sensitivity scenario No. 1 (temperature and water increase) for July 16, 1980 (Morris et al., 1988).
Population Exposure
As discussed above, both the California and
Midwest/Southeast studies show a significant
increase in the area that is potentially exposed to
higher levels of ozone when the temperature is
increased as compared with base case conditions.
Data taken from the 1980 census from central
California and the midwestern and southeastern
areas were used to determine the number of people
exposed to ozone for the base case and a 4°C
temperature rise scenario. Table 11-5 presents the
number of people-hours of exposure to ozone
concentrations exceeding 8,12, and 16 pphm. These
estimates of human exposure were generated by
multiplying the number of people in the grid cells by
the total number of hours that the estimated hourly
ozone concentration in those grid cells exceeded the
8-, 12-, or 16-pphm levels. Actual exposure levels
may be less because indoor levels are generally
lower than ambient air levels.
ECONOMIC, ECOLOGICAL,
AND ENVIRONMENTAL
IMPLICATIONS
Ozone
An increase in ozone levels due to climate
change is important for several reasons:
• Ozone itself is a radiatively important gas
and contributes to climate change. Ozone
absorbs infrared energy much like carbon
dioxide. It has been calculated that a 15%
increase in tropospheric ozone could lead to
a 0.1°C rise in global temperature
(Ramanathan et al., 1987).
• Ozone levels in many areas are just below
the current standard. If emissions are not
reduced, any increase in ozone formation
may push levels above the standard.
213
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Chapter 11
Table 11-5. Number of People-Hours of Exposure to Ozone Concentrations in Excess of 8,12, and 16 pphm
for the Base Case and the Case of Climate Sensitivity to Increased Temperature
Scenario
Exposure to Exposure to Exposure to
O3 > 8 pphm O3 > 12 pphm O3 > 16 pphm
Base case
Increased
temperature
Central California Modeling Episode
70,509,216 660,876 0
102,012,064
2,052,143
92,220
Base case
Increased
temperature
Midwestern/Southeastern Modeling Episode
1,722,590,208 29,805,348 0
1,956,205,568
47,528,944
0
Source: Morris et al. (1988).
• Many inexpensive controls for ozone are
already in place in nonattainment areas.
Increases in ozone levels would require
relatively expensive measures to sufficiently
reduce ozone precursors to attain the
standard.
• The standard itself is defined in terms of
the highest levels of ozone experienced in
an area, not average levels. (As a yearly
average, no area of the country would
exceed the standard of 0.12 ppm.) Thus, a
factor such as temperature that may have a
modest effect on average levels of ozone
formation may have a much more significant
effect on peak levels.
A rough estimate of each of these factors can
illustrate the potential policy problems created by
a rising temperature scenario. The data in Figure
11-9 suggest that 4°C degree rise in temperature
may lead to an increase in peak ozone
concentrations of around 10%. A 10% increase in
peak ozone levels could affect a number of potential
ozone violations. In the 1983-85 period for example,
68 areas showed measured exceedances of the
ozone air quality standards (for technical and legal
reasons, not all these areas were officially
designated nonattainment areas). A 10% increase
in ozone levels in that period doubled the number
of nonattainment areas to 136. This would include
41 new metropolitan statistical areas (MSAs) added
to the list and 27 non-MSAs. These new
nonattainment areas would add most midsize and
some small cities in the Midwest, South, and East to
the list of nonattainment areas.
The policy implications of this should be put
into context because the full effect of climate change
may not be felt until well into the next century.
Over the next several decades, various national
measures to reduce ozone precursors, such as a
reduction in the volatility of gasoline, may go into
effect. These would provide a cushion to marginal
areas and could offset a temperature effect.
However, other factors suggest that rising
temperatures could be a problem.
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Air Quality
Ozone levels and ozone precursors are closely
related to economic expansion and population
growth. Consumer solvents (e.g., paints, sprays, and
even deodorants) are a major source of ozone
precursors. These are very difficult to control and
are likely to increase in the future in areas currently
attaining the standards. Growth in other sources
of ozone precursors would bring many areas
relatively close to the limits of the ozone standard.
Gradual increases in temperature would make
remaining in compliance with the standard more
difficult. Although any sudden change in the
number of nonattainment areas as a result of a
secular trend toward increased temperature is
unlikely, a number of small to midsize cities
eventually may be forced to develop new control
programs.
The implications of warmer temperatures for
existing nonattainment areas can also be estimated.
In these areas, existing and planned control
measures may not be adequate to reach the
standard, if additional ozone forms. In the past,
EPA has attempted to project the emission
reductions and costs associated with the attempts
of existing nonattainment areas to reach the ozone
standard. Using the same modeling approach, the
effects of a temperature increase were analyzed to
estimate the additional tons and costs associated
with a projected temperature rise. Extrapolations
of existing inventories to the year 2000 suggest that
higher temperatures could require an additional
reduction of 700,000 tons of VOC from an inventory
of about 6 million tons. Given that most current
nonattainment areas already will have implemented
the most inexpensive measures, these additional
reductions may cost as much as $5,000 per ton per
year. Their aggregate cost could be as much as $3.5
billion each year.
These conclusions should be viewed as
preliminary. Nonetheless, they demonstrate that
the potential economic consequences could be
significant for an already expensive program to
combat ozone.
Acid Rain
The global climate change is likely to affect
acidic deposition in the near future for several
reasons.
First, emissions from fossil fuel powerplants
both influence acid rain and contribute to global
warming. In the future, global warming may
increase energy demand and associated emissions.
Because the growth in demand for electricity in
northern states (see Chapter 10: Electricity
Demand) may be lower than in southern states,
regional shifts in emissions may occur in the future.
Second, global climate change would influence
atmospheric reaction rates and the deposition and
form of acidic material. It is conceivable that
regions of high deposition may shift or that more
acid rain may be transported off the North
American continent. Strategies that seek to control
powerplants in regions near sensitive areas may or
may not be as effective, as global climate change
occurs.
Third, global climate change may alter the
impacts of acid rain on ecological and other systems
in as yet unpredictable ways. For example:
• Changes in the amount of rainfall may dilute
the effect of acid rain on many sensitive
lakes.
• Changes in clouds may alter the fertilization
of high-elevation forests.
• Changes in humidity and frequency of rain
may alter degradation rates for materials.
• Increased midcontinentaldryness would alter
the amount of calcium and magnesium in
dust, neutralizing impacts on soils.
• Increased numbers of days without frost
would decrease forest damage associated
with frost and overfertilization by
atmospheric nitrogen.
• Changes in snowpack and the seasonality of
rainfall would change acid levels in streams
and alter the timing and magnitude of spring
shocks on aquatic species.
Finally, solutions to both problems are
inextricably linked. Some solutions, such as SO2
scrubbers and clean coal technologies, may abate
acid rain levels, but they may do little to improve air
quality or may increase global warming. Other
215
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Chapter 11
solutions, including increased energy efficiency and
switching fuels to natural gas or to renewable
energy sources, may provide positive solutions to
both problems.
In summary, an examination of the time
horizons of importance to both acid rain and global
climate change problems suggests that these two
issues should not be viewed in isolation. Emissions,
atmospheric reaction rates, pollutant transport, and
environmental impacts will likely be altered by
climate change. This suggests that a more holistic
approach must be taken to air pollution problems
and that proposed solutions should be evaluated on
the basis of their contributions to solving both
problems.
POLICY IMPLICATIONS
The Environmental Protection Agency issues
air pollution regulations to improve air quality and
to protect public health and welfare. In general,
current regulations to reduce oxidant levels will also
provide positive benefits toward a goal of limiting
the rate of growth in global warming. Other
programs aimed at reducing carbon monoxide
levels, particularly from mobile sources, or CFCs to
protect the stratospheric ozone layer, also positively
affect greenhouse gases and the rate of global
warming. However, the regulatory activities of the
Agency have not been retrospectively reviewed to
determine their impacts on global warming. In
some cases, there may be important benefits; for
example, current emission standards for automobiles
do not encourage more efficient use of gasoline. A
different form of standard, while potentially
disruptive to air pollution efforts, might produce
positive greenhouse gas benefits via reduced energy
consumption. These issues will have to be analyzed
in the future.
Because of the climate change issue, the
following are some of the more important policy
issues:
• Air pollution control agencies such as EPA
should undertake a broad review to
determine the impact of global climate
change on air pollution policies. In
particular, the cost of added controls
resulting from climate change should be
determined, perhaps as each significant regulation
is proposed or reevaluated.
• The impact of EPA regulations, particularly
the impact on energy use; and greenhouse
gases, should be a more important weight in
future regulatory decisions. Since EPA
regulations often serve as models for other
countries, the cost penalty for better energy
usage, while sometimes small in the United
States, may be important on a global basis.
• Future reports to Congress and major
assessments of ecological effects, e.g., the
1990 Acid Deposition Assessment document,
should include sensitivity analyses of
alternative climates. Risk management
decisions of the Agency could then be made
with improved knowledge of climate impacts.
RESEARCH NEEDS
Some of the key questions that need to be
resolved regarding climate change and air quality
include the following: How important will climate
change be relative to other factors such as
population growth to future air pollution problems?
Is the impact of climate change likely to be
significant enough to require totally different air
pollution strategies? What mix of control strategies
could be most cost effective in reducing acid rain,
global warming, tropospheric ozone, and other
pollution problems? The research elements needed
to address these issues include basic research,
sensitivity analyses, full-scale atmospheric modeling,
and cost-effectiveness studies. Examples are
presented below:
Basic Research - There is an important need to
understand how manmade and natural emissions of
hydrocarbons and other pollutants might change in
the future when temperature, CO2, and UV-B
radiation increase and other climate parameters
vary.
Sensitivity Analyses - Analyses of ozone
concentrations are dependent on boundary layer
height, clouds, water vapor, windspeed, UV-B
radiation, and other parameters. Sensitivity tests
using single models could improve our
understanding of the relative importance of these
216
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Air Quality
variables and could provide important information
for general circulation modelers. ;-, ;
Full-Scale Modeling - Complete understanding of
the interactions of climate change and air quality
will ultimately require that general .circulation
models and mesoscale chemistry models be linked
iri some direct or indirect manner. This will require
the development of innovative approaches between
; the general circulation and air pollution modeling
communities.
Cost-Effectiveness Studies - There are currently a
number of congressional proposals to improve the
Clean Air Act and to reduce global climate change.
To assume that both air quality and global climate
change-goals are achieved, '.analyses, of-the cost-
effectiveness of alternating strategies will be
necessary./, , „ ••.'•••..'.. ., ;; ,
REFERENCES
Altshuller, A.P., and J.J. Bufalini. 1971.
Photochemical aspects < of air pollution.
Environmental Science and Technology 5:39-64.
' . " ' i l . i ,••'.-'."; - \ "
Ching, J.K.S., J.H. Novak, K.L. Schere, and FA.
Schiermeief. 1986. Reconciliation of Urban
Emissions and Corresponding Ambient Air
Concentrations Using Mass'Flow.Rate Technique.
Draft report prepared for EPA/ORD; April.'
Dodge, M.C. 1977. .Effect, of Selected Parameters
oh Predictions of a Photo-Chemical Model. EPA
600/3-77/048. Research Triangle Park, NC: U.S.
Environmental Protection Agency. June. •
Galloway, J.N., G.E. Likens, W.C. Keene, and M.M.
Miller. 1982. The composition of precipitation in
remote areas of the world. Journal of Geophysical
Research 87:8771-8788.
Galloway, J.N., D.M. Whelpdale, and G.T. Wolff.
1984. The flux of sulfur and nitrogen eastward from
North America. Atmospheric Environment
18:2595-2607. . ; -; •..,-.
Gery, M:W., R.D. Edmond, and G.Z. Whitten. 1987.
Tropospheric Ultraviolet Radiation: Assessment of
Existing Data and Effect on Ozone Formation.
EPA Report 600/3-87/047.- Research Triangle
Park, NC: U.S. Environmental Protection Agency.
October.
Hales, J. 1988. In: Sensitivity of Urban/Regional
Chemistry to Climate Change: Report of the
Workshop, Chapel Hill, NC. Wuebbles, D.J., and
J.E. Penner, eds. Livermore, CA: Lawrence
Livermore National Laboratory. Feb. 17-18.
Holzworth, G.C. 1972. Mixing Heights,
Windspeeds and Potential for Urban Air Pollution
Throughout the Contiguous United States. Research
Triangle Park, NC: U.S. Environmental Protection
.Agency, Office of Air Programs. Publication No.
AP-101.
Jeffries, H.E., K.G. Sexton, J.R. Arnold, and T.L.
Kole. 1989. Validation Testing of New
Mechanisms with Outdoor Chamber Data, Volume
4: Appendixes to Photochemical Reaction Photolysis
.Rates in the UNC Outdoor Chamber. EPA/600/3-
89/010d. .Research Triangle Park, NC: U.S.
Environmental Protection Agency.
Kamens; R.M., H.E. Jeffries, K.G. Sexton, and AA.
Gerhardt. 1982. Smog Chamber Experiments to
.Test Oxidant-Related Control Strategy Issues. EPA
600/3-82-014. Research Triangle Park, NC: U.S.
.Environmental Protection Agency. August.
JCeehe, :w.C., J.N. Galloway, and J.D. Holden Jr.
,1983. Measurement of weak organic acidity in
precipitation from remote areas of the world.
Journal of Geophysical Research 88:5122-5130.
Keene; W.C., and J.N. Galloway. 1984. Organic
acidity in precipitation of North America.
Atmospheric Environment 18: 2491-2497.
Lamb B.K., H.H. Westberg, T. Quarles, and D.L.
Flyckt 1985. Natural Hydrocarbon Emission Rate
Measurements From Selected Forest Sites.
EPA-600/3-84-001. Research Triangle Park, NC:
U.S. Environmental Protection Agency. October.
Norton, R.B. 1985. Measurements of Formate and
Acetate in Precipitation at Niwot Ridge and
Boulder, Colorado. Geophysical Research Letters
12:769-772.
Ramanathan, V., L. Callis, R. Cess, J. Hansen, I.
Isaksen, W. Kuhn, A. Lacis, F. Luther, J. Mahlman,
217
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Chapter 11
R. Reck, and M. Schlesinger. 1987. Climate-
chemical interactions and effects of changing
atmospheric trace gases. Review Geophysics
25:1441-1482.
Research Triangle Institute. 1975. Investigation of
Rural Oxidant Levels As Related to Urban
Hydrocarbon Control Strategies. EPA-450/3-75-
036. Research Triangle Park, NC: U.S.
Environmental Protection Agency. March.
Samson, PJ. 1988. Linkages Between Global
Climate Warming and Ambient Air Quality. Paper
presented at the Global Climate Linkages
Conference, Washington, DC; Nov. 15-16.
Seilkop, S.K., and P.L. Finkelstein. 1987. Acid
precipitation patterns and trends in eastern North
America, 1980-84. Journal of Climate and Applied
Meteorology 26(8):980-994.
U.S. EPA. 1988. U.S. Environmental Protection
Agency, Office of Air Quality Planning and
Standards. National Air Quality and Emissions
Trends Report, 1986. Research Triangle Park, NC:
U.S. Environmental Protection Agency. EPA report
No. 45014-88-001. Research Triangle Park, NC:
U.S. Environmental Protection Agency.
Walcek C. 1988. In: Sensitivity of Urban/Regional
Chemistry to Climate Change: Report of Workshop,
Chapel Hill, NC. Wuebbles, DJ. and J.E. Penner,
eds. Livermore, CA: Lawrence Livermore National
Laboratory. Feb. 17-18.
218
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CHAPTER 12
HUMAN HEALTH
FINDINGS
Global warming may lead to increases in human
illness (morbidity) and mortality during summer.
Populations at particular risk are the elderly and
very young (age 1 year and below), particularly
those who are poor and/or homeless. These effects
may be more pronounced in some regions than in
others, with northern regions more vulnerable to
the effects of higher temperature episodes than
southern regions. Milder winters may offset
increases in morbidity and mortality, although net
mortality may increase. Mortality in southern cities
currently shows a lesser effect from heat waves,
presumably because populations have acclimatized.
If northern populations show this same
acclimatization, the impact of global warming on
summer mortality rates may be substantially lower
than estimated. The full scope of the impacts of
climate change on human health remains uncertain
and is a subject for future research.
• Although there may be an increase in weather-
related summer deaths due to respiratory,
cardiovascular, and cerebrovascular diseases,
there may be a decrease in weather-related
winter deaths from the same diseases. In the
United States, however, our studies suggest that
an increase hi weather-related deaths hi
summer would be greater than the decrease in
weather-related deaths in winter. To draw firm
conclusions, however, this area needs additional
study.
• Sudden changes in temperature are correlated
with increases hi deaths. So if climate
variability increases, morbidity and mortality
may also increase. Conversely, a decrease in
, the frequency or intensity of climate extremes
may be associated with a decrease in mortality
and morbidity.
• Seasonal variation hi perinatal mortality and
preterm birth (higher hi the summers, lower
hi the winters) have been observed hi several
areas in the United States. The longer and
hotter summers that may accompany climate
change could increase infant mortality rates,
although changes hi variability may be more
important than average changes in
temperature.
Vector-borne diseases, such as those carried
by ticks, fleas, and mosquitoes, could increase
hi certain regions and decrease hi others. In
addition, climate change may alter habitats.
For example, some forests may become
grasslands, thereby modifying the incidence of
vector-borne diseases.
While uncertainties remain about the
magnitude of other effects, climate change
could have the following impacts:
— If some farmland is abandoned or some
forests become grasslands, a result could be
an increased amount of weeds growing on
cultivated land, and a potential increase hi
the incidence of hay fever and asthma.
— If humidity increases, the incidence and
severity of skin infections and infestations
such as ringworm, candidiasis, and scabies
may also rise.
— Increases hi the persistence and level of air
pollution episodes associated with climate
change may have adverse health effects.
CLIMATE-SENSITIVE ASPECTS
OF HUMAN HEALTH
Human illness and mortality are linked hi
many ways to the environment (Figure 12-1).
Mortality rates, particularly for the aged and very ill,
219
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Chapter 12
Figure 12-1. Schematic showing how climate change can affect human health.
are influenced by the frequency and severity of
extreme temperatures. The life cycles of disease-
carrying insects, such as mosquitoes and ticks, are
affected by changes in temperature and rainfall, as
well as by modifications in habitat that result from
climate change. Air pollution, frequently associated
with climate change, is known to increase the
incidence or severity of respiratory diseases such as
emphysema and asthma A variety of human
illnesses show sensitivity to the changes in
temperature (and/or humidity) that accompany
changes in season. Stroke and heart attacks
increase with very cold or very warm weather.
Allergic diseases such as asthma and hay fever
increase in spring and summer when pollens are
released. Diseases spread by insects such as St.
Louis encephalitis1 increase in the warmth of
StXouis encephalitis is an example of a vector-borne disease.
Such diseases are spread to humans or animals by arthropods
(e.g., mosquitoes or ticks). The disease-causing organism, such
as a virus, is carried and transmitted by the vector, also known
as the agent. Some vectors, such as ticks, live on other animals,
such as deer and birds, which are called intermediate hosts.
For example, Lyme disease is caused by a bacteria (the agent),
which is carried by a certain type of tick (the vector), which
lives on deer and mice (the intermediate hosts).
summer when the mosquitoes that transmit it are
active. In addition, adverse effects on reproduction,
such as increased incidence of premature births,
show a summertime peak in some cities. Table 12-
1 lists the number of deaths and the number of
physician visits (used to estimate the incidence of
illness associated with a given effect) associated with
major causes of mortality and illness in the United
States.
General Mortality and Illness
The relationship between mortality and
weather has been studied for ; over a century
(Kutschenreuter, 1959; Kalkstein, Volume G), with
the relationship between mortality and temperature
receiving the most attention. Kutschenreuter (1959)
observed "mortality is higher during cold winters
and hot summers and lower during warm winters
and cool summers." The people most sensitive to
temperature extremes are the elderly (White and
Hertz-Picciotto, 1985). One explanation is the
increased susceptibility of the elderly is that for
individuals already stressed by the circulatory
problems associated with vascular and heart disease,
heat waves (temperatures above 100°F for 5
220
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Human Health
. Table 12-1. Major Causes of Illness and Mortality in the United States (1984)a
Cause of illness or mortality
Estimated
number of
physician
contacts
Estimated mortality
Number
Rate/100,000
Accidents and adverse effects
Cerebrovascular diseases'5
Chronic liver disease
and cirrhosis
Chronic obstructive pulmonary
diseases and allied conditions
Congenital anomalies
Diabetes mellitus
Heart diseases
Malignant neoplasms
Pneumonia and influenza
Suicides, homicides
Total for potentially weather-
sensitive diseases
• Total all causes
70,000,000
9,100,000
1,400,000
20,500,000
4,300,000
35,600,000
72,400,000
20,300,000
14,500,000
152,100,000
248,100,000-
93,520
154,680
26,690
70,140
12,900
35,900
763,260
453,660
58,800
47,470
1,082,780
1,717,020
39.6
65.5
11.3
29.7
5.5
5.2
323.2
192.1
24.9
20.1
448.5
717.1
^Causes are presented in alphabetical order and therefore are not ranked by severity.
Conditions that can be influenced by changes hi weather and climate are indicated in bold type.
Source: CDC (1986). :: ' r
consecutive days) "overload" the thermoregulatory
system, which is struggling to maintain the
appropriate body temperature. This results in heat
stress, heatstroke, and often mortality as well
(White and Hertz-Piccibtto, 1985).
In addition to the elderly, people working in
hot environments, such as steel mills and
construction sites, are at special risk from heat
waves (Dukes-Dobos, 1981). These workers face
even greater risk if they have underlying medical
problems such as impaired circulation; higher than
normal body temperature due to disease; chronic
diseases such as alcoholism, diabetes, and obesity;
or other problems.
Cardiovascular, Cerebrovascular, and
Respiratory Diseases
.Although much of the earlier information
characterized the relationship between weather and
total mortality from all causes, a growing body of
literature evaluates the relationship of weather to
specific Causes of death. For example, changes in
weather have been associated with mpacts on the
cardiovascular, Cerebrovascular, and respiratory
systems. As previously shown in Table 12-1,
diseases of these three systems cause the majority of
deaths observed on a yearly basis in the United
States, as well as significant illness; Incidences of
these diseases rise as climate extremes increase.
The relationships of weather variables to
diseases of these'.' systems are diverse and
complicated. Weather is 'riot the main causative
factor in these diseases but, rather, changes in
weather have an impact because they add stress to
systems that have already been compromised for
some other reason(s). For example, although it has
been observed that deaths in individuals with
diseases of the cardiovascular system go up with
heat waves, the .precise reason for this relationship
is not known. ' •> ', •.
221
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Chapter 12
To understand the relationship between
weather and these diseases, one must examine the
specific diseases that come under broad categories
such as "cardiovascular disease." For instance, heart
attack, coronary heart disease, and possibly coronary
arteriosclerosis and rheumatic heart disease are
apparently sensitive to changes in temperature
(particularly cold and heat waves), whereas ischemic
heart disease is not (Vuori, 1987).
That these different relationships exist is not
unexpected given that different parts of the system
are compromised (e.g., the arteries in
arteriosclerosis and the heart muscle in rheumatic
heart disease), and that different causes are also
likely (e.g., an infection-related process in rheumatic
heart disease and diet and heredity in
arteriosclerosis). What this information does
indicate, however, is that these relationships are
very complex and that unraveling them to predict
the effects of global warming will require
considerable analysis (Lopez and Salvaggio, 1983).
The relationship between temperature changes
and illness (morbidity) from diseases such as heart
attack and stroke is not as well defined as the
relationship reported for mortality. Mortality has
national reporting procedures, whereas morbidity
must be estimated from such data as hospital
admission figures. A few studies have evaluated the
relationship of weather to hospital admissions from
cardiovascular or cerebrovascular disease. These
have shown a relationship to weather changes, e.g.,
an increase in admissions for cardiovascular effects
with heat waves, similar to that observed for
mortality (Sotaniemi et al., 1970; GUI et al., 1988).
Morbidity from respiratory diseases is
somewhat easier to estimate, principally because
two such diseases, asthma and hay fever, affect as
much as 3 and 6% of the U.S. population,
respectively, causing significant losses of work time.
The most common seasonal pattern for the allergic
type of asthma and for hay fever is an increased
springtime occurrence in response to grass pollens.
A nonseasonal form of allergic asthma may also
occur in response to allergens such as molds, which
are affected by changes in precipitation and
temperature.
Vector-Borne Diseases
Two tick-borne diseases currently posing a
public health problem in the United States, Rocky
Mountain spotted fever and Lyme disease, induce
similar initial symptoms: high fever, chills, headache,
backache, and profound fatigue. Rocky Mountain
spotted fever can eventually result in hemorrhagic
areas that ulcerate, and Lyme disease may cause
permanent neurologic, cardiac, and rheumatologic
abnormalities (APHA, 1985). The ticks that spread
these diseases, and therefore the geographic
distribution of the diseases themselves, are affected
both directly and indirectly by climate variables.
Such environmental factors as temperature,
humidity, and vegetation directly affect tick
populations and the hosts of the tick populations,
e.g., deer, mice, and birds.
Mosquito-borne diseases, such as malaria and
certain types of encephalitis (inflammation of the
brain), are not a major health problem in the
United States today because occurrences are
relatively rare. However, mosquitoes are also
weather-sensitive insects favoring a warm, humid
climate. The spread of mosquito populations and
the diseases they carry depends in part upon such
climate factors as temperature and humidity, and
upon vegetation, which is also influenced by the
climate.
Human Reproduction
Preterm delivery and perinatal mortality (i.e.,
death just before, during, or just after birth) are two
adverse reproductive outcomes that are associated
with particular seasons and, thus, might be affected
by climate change. Statistically significant increases
in preterm births and in perinatal mortality in the
summer months have been documented (Keller and
Nugent, 1983; Copperstock and Wolfe, 1986) (see
Figure 12-2). The data on total perinatal deaths
correspond closely with those on perinatal deaths
associated with infection in the mother or infant,
suggesting that the observed seasonally in perinatal
death is linked to a seasonality of reproductive
infections (Keller and Nugent, 1983).
POTENTIAL HUMAN HEALTH
EFFECTS OF CLIMATE CHANGE
To assess the effects of climate change on
human health, EPA sponsored three studies for this
report (Table 12-2). Longstreth and Wiseman
(Volume G) reviewed the literature on the role of
climate, season, and weather variables in the
222
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Human Health
F M A M
J J A S O N D
Month
Figure 12-2. Probabilities of (A) perinatal death or
(B) preterm delivery (Keller and Nugent, 1983).
Table 12-2. Studies Conducted for This Report
The Impact of C(X. and Trace Gas-Induced
Climate Change Upon Human Mortality -
Kalkstein, University of Delaware (Volume G)
Computer Simulation of the Effects of Changes
in Weather Pattern on Vector-Borne Disease
Transmission - Haile, UJS. Department of
Agriculture (Volume G)
The Potential Impact of Climate Change on
Patterns of Infectious Disease in the United
States - Longstreth and Wiseman,
ICF/Clement Associates, Inc. (Volume G)
incidence of, and mortality due to, vector-borne
diseases. In November 1987, they also conducted a
workshop of scientists to evaluate the potential
impacts of global climate change on vector-borne
infectious diseases in the United States. Following
the workshop, Haile (Volume G) conducted
modeling studies of the potential impact of climate
change on (1) the distribution of the American dog
tick, the vector of Rocky Mountain spotted fever;
and (2) the potential for malaria transmission in the
United States. The third study, by Kalkstein
(Volume G), as an extension of an earlier modeling
study that assessed the potential effects of global
climate change on the elderly and on total mortality
in New York (Kalkstein et al., 1986). Kalkstein
(Volume G) expanded the New York analysis to
include 14 other cities. A detailed review of these
three studies, supplemented with other information
from the literature, is presented in this section.
General Mortality
Preliminary analyses suggest that unless the
U.S. population becomes fully acclimatized2 to
higher temperatures, climate change will be
associated with a sharply rising number of summer
deaths. With full acclimatization to the warmer
summers, heat-related mortality might increase less
dramatically or not at all. In winter, the number of
weather-related deaths will probably decline
regardless of acclimatization. It is not clear what
the net effect of these two offsetting trends may be.
Only a few studies have evaluated the effects of
global climate change on human mortality.
Kalkstein et al. (1986) developed a regression
equation involving nine weather elements, such as
temperature, windspeed, and humidity, to give the
best algorithm for describing the current impact of
weather on mortality. The algorithm used mortality
data from New York City for 1964-66,1972-78, and
1980.
The analysis revealed the existence of a
summertime "threshold temperature" ~ the
maximum temperature above which mortality
increases — for New York City of 92°F for total
deaths. This information was then used to assess
the potential impact of climate change under the
assumption that the population would not
Estimations of the impact of warming on future mortality must
address the question of whether humans will acclimatize
(socially, psychologically, or physiologically adapt) to changing
weather. How quickly humans may become acclimatized is a
topic of considerable controversy, so it is difficult to predict
whether the climate changes due to global warming will occur
slowly enough to permit acclimatization.
223
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Chapter 12
acclimatize, as well as under the assumption that it
would acclimatize. Unacclimatized impacts were
estimated by combining the climate scenarios and
the historical weather algorithm described above,
and acclimatized impacts were estimated by
analyzing analog cities that have values of weather
variables today that look like those New York is
estimated to have under climate change.
Assuming full acclimatization and a scenario
predicting that New York will be 3 to 4°C (5 to 7°F)
warmer than it is today, no additional deaths were
predicted. However, assuming no acclimatization,
the number of summertime deaths attributable to
temperatures above the threshold (hereafter called
suprathreshold summer deaths) increased seven- to
tenfold. Changes in winter weather, i.e., more
subthreshold temperatures, were not estimated to
affect mortality.
For this report, Kalkstein (Volume G)
extended the New York analysis to cover 14
additional metropolitan areas and to evaluate the
impact of two climate scenarios: the GISS doubled
CO2 scenario, and the GISS transient A scenario,
evaluated at 1994 to 2010 and at 2024 to 2040.
Threshold temperatures were calculated for each
city for summer and winter. Historical relationships
between mortality and temperature were derived
independently for each of these 15 cities for both
summer and winter. Table 12-3 summarizes the
results for total mortality, by city and by season
(summer or winter), for the doubled CCv, scenario
with and without acclimatization. The cities
with the highest estimated number of
suprathreshold summer deaths historically were
New York City, Chicago, and Philadelphia; each
averaged over 100. All of the cities with the highest
average number of summer deaths are in the
Table 12-3. Estimated Future Mortality Under Doubled CO2 Climate Conditions without
and with Acclimatization
City
Current
Number of deaths per season
Summer
Without
With
Winter
Current Without
With
Atlanta
Chicago
Cincinnati
Dallas
Detroit
Kansas City
Los Angeles
Memphis
Minneapolis
New Orleans
New York
Oklahoma City
Philadelphia
St. Louis
San Francisco
Total
18
173
42
19
118
31
84
20
46
0
320
0
145
113
27
1,156
159
412
226
309
592
60
1,654
177
142
0
1,743
0
938
744
246
7,402
0
835
116
179
0
138
0
0
235
0
23
47
466
0
159
2,198
2
46
14
16
16
21
0
0
5
0
56
0
10
47
10
243
2
2
6
1
2
5
0
0
1
0
18
0
1
7
7
"52
0
96
0
0
37
0
0
0
0
0
25
0
1
0
0
159"
Source: Kalkstein (Volume G).
224
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Human Health
Midwest or Northeast, and those with the lowest
number are in the South.
As would be expected, generally more deaths
were predicted for populations that do not
acclimatize. However, for certain cities, e.g.,
Chicago, Kansas City, and Minneapolis, more deaths
were predicted with acclimatization than without.
Exactly why this occurred is uncertain. The results
appear to be very sensitive to the choice of the
analog city. For example, Chicago appears to have
more deaths if its population becomes acclimatized
than if it does not. It may be that the analog city
chosen to represent a particular acclimatized city,
Chicago for instance, is more sensitive to weather
effects on mortality than Chicago currently is. More
research is planned to investigate this apparent
anomaly to refine the estimates of what global
warming will mean in terms of mortality. Thus,
Kalkstein's results should not be used as predictions
of individual city behavior, but as illustrations of
sensitivities.
In the absence of any acclimatization,
suprathreshold summer mortality in the United
Stated under conditions of doubled CC^ is
estimated to rise from an estimated current total of
1,156 deaths to 7,402 deaths, with deaths in the
elderly (aged 65 or over) subset contributing about
60% of each figure (727 and 4,605, respectively).
Currently, the percentage of elderly in the U.S.
population is increasing. Thus, the mortality
estimated to result from climate change may be
larger than that found by Kalkstein because his
analysis is predicated on today's age distribution.
Even with full acclimatization, the number of
weather-associated summer deaths almost doubles
to 2,198, possibly because hot weather increases
physiological stress. Kalkstein's analysis also
estimates a drop in the number of subthreshold
winter deaths. Historically, however, the number of
these deaths during the winter in the United States
is much smaller (243) than that observed for the
summer, and subthreshold winter deaths were
estimated to fall to 52 without acclimatization and
to 159 with acclimatization. The net result for the
United States is an increase in yearly mortality
associated with doubled CO2-
This study is exploratory research in the field
of the potential impacts of climate change on
human health. Some aspects of the analyses that
led to these estimates need further investigation;
thus, the estimates should be accepted with caution.
The direction of predicted change, i.e., an increase,
is probably much more solid than the magnitude of
change. In addition, this research has concentrated
on mortality occurring above a particular threshold
temperature for summer or below a particular
threshold temperature for winter. Consideration of
a broader range of temperatures could conceivably
result in different conclusions being drawn.
Cardiovascular, Cerebrovascular,
Respiratory Diseases
and
Overall global warming and climate change
may exacerbate the effects of cardiovascular,
cerebrovascular, and respiratory diseases. Data
from these studies show an inverse relationship
between mortality and temperature (i.e., deaths go
down as temperature goes up) for the range
between -5°C and about +25°C, with sharp
increases at temperatures above and below this
range, particularly for the elderly and for hot
weather (White and Hertz-Picciotto, 1985); the
exact range appears to depend on the city.
Illustrations of this relationship for coronary heart
disease and stroke are shown in Figures 12-3 and
12-4, respectively (Rogot and Padgett, 1976). This
complex relationship precludes simple prediction of
the net effect of climate change. For example, it is
possible that hot weather-associated mortality from
these diseases may increase in some localities, but
this trend may be offset, at least in part, by a
decrease in cold weather-associated mortality.
Just as higher summer temperatures are
associated with increases in mortality from
cardiovascular, cerebrovascular, and respiratory
diseases, they are also likely to be associated with
increases in morbidity from these diseases through
increases in the number or duration of hospital
admissions. Particular stress may be put on the
respiratory system because climate change can
potentially increase pollen, urban smog (discussed
below), and heat stress, all of which have an adverse
effect on the respiratory system.
For example, if, as has been suggested in the
chapter on forests, climate change encourages a
transition from forest to grassland in some areas,
grass pollens could increase. This, hi turn, may
increase cases of pollen-induced hay fever and
allergic asthma. (However, the switch from forest
to grassland would reduce the amount of tree
pollens that also cause allergic responses in some
225
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Chapter 12
100
90
to
70
60
50
I I I I
I I I I III
•20
•28
20
•7
40
4
80
27
100 F
38 C
•18 -7 4 16
AVERAGE TEMPERATURE ON DAY OF DEATH
Figure 12-3. Relationship of temperature to heart
disease mortality (adapted from Rogot and Padgett,
1976).
5. 20
p LOS ANGELES
SAN FRANCISCO
I I I I I I I I I I
-20 0 20 40 60 80 100 F
•29 -18 -7 4 16 27 38 C
AVERAGE TEMPERATURE ON DAY OF DEATH
Figure 12-4. Relationship of temperature to
mortality from stroke (adapted from Rogot and
Padgett, 1976).
individuals.) Rises in humidity also may affect the
incidence of mold-induced asthma and hay fever.
As indicated in Chapter 11: Air Quality, global
warming may modify global and regional air
pollution because it may increase concentrations of
ozone and may also have impacts on acid deposition
and general oxidant formation. The increasing
occurrence of numerous respiratory diseases, such
as lung cancer, emphysema, bronchitis, and asthma,
has been attributed to the pollutants in urban smog
(Lopez and Salvaggio, 1983). Many of the trace
gases implicated in global warming contribute to
these problems; other pollutants are created from
the interaction of ultraviolet light with these and
other chemicals present in the atmosphere.
The component that causes the greatest
concern in urban smog is ozone (Grant, 1988). If
global warming causes an increase in tropospheric
ozone, adverse consequences could result for adult
asthmatics and people who suffer from acute or
chronic bronchitis.
Vector-Borne Diseases
Potential changes in humidity and temperature
could alter the geographic ranges and life cycles of
plants, animals, insects, bacteria, and viruses. (For
further discussion of forestry and agriculture, see
Chapters 5 and 6, respectively.) For example, the
range of many plant pests may move northward by
several hundred miles. Such changes could occur
for insects that spread diseases to both humans and
animals. Vector-borne diseases that affect humans
are relatively rare in the United States. The
incidence of most of those found, however, is
increasing. The incidence of some, such as Lyme
disease, is increasing dramatically (CDC, 1986).
226
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Human Health
Tick-Borne Diseases
Both Rocky Mountain spotted fever and Lyme
disease are considered to be public health problems
in the United States. Although these two diseases
are spread by different species of ticks, some
overlap exists in their geographic distribution
(Figure 12-5). Because tick populations appear to
be limited by the size of their intermediate host
populations (such as white-tailed deer), the spread
of tick-borne diseases may be particularly sensitive
to any change that may affect the geographic range
of these hosts and, consequently, the range of the
vector, or carrier.
In addition to the presence of the host, tick
populations also depend upon the seasonally of
environmental factors such as temperature,
humidity, and vegetation. Optimally, climate must
be warm enough to promote progression through
the life cycles, humid enough to prevent the drying
out of eggs, and cold enough in winter to initiate the
resting stage.
As for many tick-borne diseases, the
opportunity for a tick to acquire the infective agent
from an infected animal is limited to the short
period when the level of the agent in the blood of
the host is high enough for the tick to receive an
infective dose. Higher temperatures may increase
the amount of the agent (the organism that is
transmitted by the carrier, such as a virus) and the
time it remains lodged on the host animal. Both
these mechanisms would increase the rate of
infection of the carrier. However, although higher
temperatures may favor the presence of the agent,
there is some indication that they could disrupt the
life cycle of some tick species. In these cases,
warmer temperatures would reduce both tick
survival and the spread of diseases they carry.
Tick populations also vary with the natural
vegetation of an area. The incidence of Rocky
Mountain spotted fever, in particular, has been
linked to natural vegetation and changes in climate.
In examining the potential impact of climate
change in the United States on Rocky Mountain
spotted fever, Haile (Volume G) used a weather-
based model, ATSIM, to evaluate the impact of the
scenario climate changes on the distribution of the
American dog tick, the primary carrier of this
disease (Haile, Volume G; Mount and Haile, 1988).
The model uses data inputs from the three doubled
CO2 scenarios (GISS, GFDL, and OSU) to estimate
population dynamics, growth rate, and generation
time. Haile assumed that habitats and host density
did not change in response to global wanning.
Sample results for six cities representing the most
southern, the most northern, and the two middle
latitudes are presented in Figure 12-6. The results
indicate that under all scenarios, tick populations
would shift from south to north and would be
virtually eliminated from the most southern
locations (Jacksonville and San Antonio). However,
in the middle latitude cities, the results are mixed
and depend on the scenario evaluated. The model
does not estimate changes in incidence of the
disease.
In this analysis, the only model inputs that
were changed to simulate climate change were the
weather inputs. Other important parameters in the
model are the distribution of habitat between forests
and meadows and the presence of suitable hosts.
Both parameters are likely to be changed relative to
current conditions under climate change. As
indicated in Chapter 5: Forests, a change from
forests to meadows may occur in certain areas of
the country; this would depress the tick population.
However, the distribution of small mammals also
may change. If small mammal populations
increased, tick populations would grow. In addition,
this study did not consider changes in climate
variability, which may have a major effect on the
outbreak of diseases.
In a sensitivity analysis of their model, Mount
and Haile (1988) found that the model predictions
could vary sixteenfold, depending on the inputs used
for host density, whereas the variability conferred by
changes in the weather inputs is about fourfold.
Based on the sensitivity analysis, host densities are
extremely important to these predictions. Keeping
them constant, as was done in this analysis, could
have underestimated or overestimated the impact of
climate change on the density of the American dog
tick.
Mosquito-Borne Diseases
A second category of vector-borne diseases
that can be affected by climate change consists of
diseases carried by mosquitoes. Climate changes
resulting in more days between 16 and 35°C (61 to
95°F), with humidity between 25 and 60%, are likely
to favor the growth of mosquitoes (White and
Hertz-Picciotto, 1985). Mosquito populations are
227
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Chapter 12
LYME DISEASE
ROCKY MOUNTAIN SPOTTED FEVER
States With Highest
Incidence (Cases Per 100K)
NC 3.6, SC 3.2, OK 2.3
Figure 12-5. Geographic distribution of Lyme disease and Rocky Mountain spotted fever (Longstreth and
Wiseman, Volume G).
228
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Human Health
Richmond, VA
Columbus, OH
Jacksonville, FL
San Antonio, TX
Hal fax, N.S.
Missoula, MT
,X\\\\\\\\\\\\\V*I
(XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXxXXXXXXXXXXXI
10
\\ I I I
15 20 25 30 35
DENSITY (ADULT TICKS ON HOSTS/HECTARE)
Figure 12-6. Simulated tick densities for selected cities under various scenarios of climate change (Haile,
Volume G).
also sensitive to the presence of standing water. It
is not clear whether standing water will generally
increase or decrease (see Chapter 9: Water
Resources).
Worldwide, mosquito-borne diseases are
associated with significant illness and mortality. In
the United States, however, vector control programs
and improved hygiene have virtually eliminated
endogenously transmitted cases of these diseases,
with the exception of sporadic outbreaks of
arbovirus-encephalitis. (Imported cases are seen
occasionally.) Numerous mosquito species are
present hi the United States, however. Recent
restrictions on pesticide use, coupled with the influx
of visitors and immigrants who can serve as sources
of infectious agents, as well as the lack of available
vaccines for many of the potential diseases, suggest
the potential for reintroduction and establishment of
these diseases in the United States — particularly if
global warming provides a more suitable climate for
their growth and development (Longstreth and
Wiseman, Volume G).
At a recent workshop, five of the numerous
mosquito-borne diseases were considered to pose a
potential risk to U.S. populations if the status quo
is disturbed by climate change (Longstreth and
Wiseman, Volume G). Malaria, dengue fever, and
arbovirus-induced encephalitides were considered to
be significant risks, and yellow fever and Rift Valley
fever were considered to be possible risks.
Malaria
Malaria is an infectious disease transmitted by
mosquitoes and induced by parasites (Plasrnodia).
The symptoms are highly variable, depending on the
species of the agent. They include chills, sweats,
and headache, and in severe cases, may progress to
liver damage and even liver and renal failure.
As a result of effective vector control and
treatment programs, malaria is no longer indigenous
to the United States. However, imported cases
occur regularly, and occasionally indigenous
transmission has been documented (Longstreth
229
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Chapter 12
and Wiseman, Volume G). Current U.S.
demographic trends, including a large number of
legal and illegal immigrants from locations where
malaria is endemic, could present a pool of infected
individuals that, in conjunction with climate changes,
may create sufficient conditions for increased
disease incidence.
Haile used the weather-dependent model
MALSIM to evaluate the potential impact of
climate change on malaria in an infected population
living in an area where a competent carrier is
present. The model was originally developed to
help predict malaria outbreaks in tropical countries
such as Kenya. This is the first application of the
model to the United States. This analysis did not
consider changes in climate variability, which may
be important for the spread of malaria. The
MALSIM model showed that several cities in the
South (e.g., Miami, Key West, and Orlando), under
current climate conditions, are very favorable for
malaria transmission. Using the climate change
scenarios in MALSIM did little to affect the
estimated transmission potential of malaria in the
United States (Figure 12-7). In a few cities, e.g.,
Richmond, Nashville, and Atlanta, the model
estimated large increases in one scenario relative to
those that would occur normally. However, the
results varied with different climate scenarios, did
not occur at all locations, and should be considered
to be inconclusive.
"jfhe MALSIM estimates of malaria incidence by city under
current conditions were based on two assumptions: that there
were 100,000 female mosquitoes in the vicinity of each city and
that 100 infected people were added to the cities' populations.
Under those assumptions, infection of virtually the entire
population of Miami was predicted to be possible unless
protective measures were taken.
Miami, FL
Key West, FL
Orlando, FL
San Antonio, TX
Atlanta, CA
Nashville, TN
Tulsa, OK
Dallas, TX
Richmond, VA
—
Baltimore, MD
Indianapolis, IN
Boston, MA
0
SSSi^
1
!
1
]
1
1
•a
i
1 l^g^BJaJ!'.. .. s
^ ioswt^'
fESES,"*'
HJqgFDTK'*
;BJP^£/ISE I
1 1 1 1 1 1 1 1 1 1
1000 2000 3000 4000 SOOO 6000 7000 8000 9000 10000
INCIDENCE (CASES/10,000 POPULATION)
Figure 12-7. Simulated incidence of malaria for selected cities under various scenarios of climate change (Haile,
Volume G).
230
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Human Health
Dengue Fever
Dengue fever is an arbovirus-induced illness
characterized by fever, rash, and severe pain in the
joints. The dengue virus has four different types
(DEN 1 through DEN 4). Sequential infection by
different types is possible and has been suggested
to lead to an increased risk of developing a more
severe, hemorrhagic form of the disease that can be
fatal in the very young and the elderly. Like
malaria, it is not currently endemic in the United
States, although potential carriers are present and
the disease is imported here regularly by people
who have traveled abroad.
The ability of the vector to transmit the agent
appears to depend on temperature, and current
conditions do not appear to be favorable for this
process. Climate changes that raise temperatures,
however, may reduce the required incubation period
and increase the infectivity of the carrier, increasing
the potential transmission of the disease.
Arbovirus-Related Encephalitides
Arbovirus-related encephalitides are a group
of acute inflammatory diseases that involve parts of
the brain, spinal cord, and meninges. In mild cases,
these infections result in feverish headaches or
aseptic meningitis; in more severe cases, those
symptoms can be accompanied by stupor, coma,
convulsions (in infants), and occasionally spastic
paralysis (APHA, 1985).
At least seven types of viruses causing
encephalitis are present in the United States. These
include the three forms that also infect horses (the
western, eastern, and Venezuelan equine
encephalitis viruses) as well as four that are named
after the location of their discovery (the La Cross,
St. Louis, Powassan, and California encephalitis
viruses). Cases range in severity depending on the
type of virus, with yearly fatality rates between 0.3
and 60%. These infections are rare. In 1984, 129
cases were reported to the Centers for Disease
Control, which maintains an active surveillance
program for them (CDC, 1986).
An arbovirus is a virus transmitted by an arthropod.
Arthropods are a group of animals that includes insects and
arachnids. Examples of arthropods that transmit disease
include mosquitoes and ticks.
Outbreaks of encephalitis attributable to these
viruses are normally limited to specific geographic
locations and seasons for several reasons. First,
warm temperatures are normally required for the
viruses to multiply and to be transmitted to a new
host. Higher temperatures may quicken the
transmission process and promote epidemic disease.
However, the extent of this effect depends largely
on the particular virus. Some viruses require cooler
weather and higher moisture conditions. Thus,
higher temperatures may reduce their prevalence.
Second, environmental conditions that favor the
presence of carriers and hosts must prevail. For
example, relative humidity may affect plant life
necessary for the feeding of hosts.
Other Diseases
The Incidence of a variety of other U.S.
diseases appears to be sensitive to changes in
weather. If humidity is higher, an increased
incidence and severity of fungal skin diseases (such
as ringworm and athlete's foot) and yeast infections
(such as candidiasis) may be observed. Studies on
soldiers stationed in Vietnam during the war
indicated that outpatient visits for skin diseases (the
largest single cause of outpatient visits) were
directly correlated to increases in humidity but
showed a 4-month lag with relationship to
temperature increases (Figure 12-8). In addition,
excessively high temperatures can lead to such skin
diseases as prickly heat and heat rash, which impair
the ability of the skin to breathe and thus place
additional stress on people already suffering from
overexposure to heat from other causes.
Several diseases appear to be associated with
the acquisition of winter infections. If a reduction
in winter severity is also accompanied by a decrease
hi wintertime Infections, these diseases could be
reduced under global warming.
For example, birth in cold winter months has
been associated with a higher risk of schizophrenia
in individuals whose schizophrenia is without an
apparent genetic component (Kovelman and
Scheibel, 1983). In addition, juvenile-onset diabetes,
which has been reported to be increasing over the
past several decades, has been shown to be
associated with a seasonal variation in that the
month of first admission peaks in the whiter
(Glatthaar et al., 1988; Patterson et al., 1988). It is
a common clinical experience that a minor viral
illness precedes the onset of symptoms.
231
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Chapter 12
JAN
JUN
1967
JAN
JUN
1968
JAN
MONTH AND YEAR
JUN
1969 ,
JAN
JUN
1970
TEMPERATURE (°C) —'
RELATIVE HUMIDITY
74
Figure 12-8. Relationship of skin infections to humidity and temperature (Longstreth and Wiseman, Volume G),
SOCIAL AND ECONOMIC
IMPLICATIONS
Demographic and technological trends (the
aging of the population, an influx of immigrants,
advances in treatment techniques) make it difficult
to analyze the potential impacts of climate change
on human health. Although this chapter attempts
to identify those human health effects at risk from
climate change, the analyses were not designed to
consider adaptive responses and should not be
treated as predictions of what will happen with
climate change but as illustrations of sensitivities.
Rather, the analyses presented here represent
possible scenarios, in the absence of consideration
of demographic trends or adaptive responses, that
may either exacerbate or ameliorate the impact of
climate change on human health. Societies possess
considerable ability to adapt to change. The
potential for climate to affect human health may be
considerably modified by adaptive responses, such
as immunizations, modification of the environmental
temperature (e.g., use of air conditioners), and
control of disease carriers.
Climate change may affect regional and
national health care. For instance, the treatment
requirements for asthma may increase or decrease
as locations experience changes in the distribution
and intensity of pollen concentrations. Increased
resources maybe needed to treat premature infants
if the number of preterm births increases. If heart
attacks, stroke, and respiratory problems increase,
hospitalization costs and costs due to days lost from
work may also increase. Higher health care costs
might be particularly obvious in Medicaid and
Medicare because those below the poverty line
would be less able to take adaptive measures (e.g.,
air-conditioning), and the elderly are more
susceptible to the ill effects of extreme weather
conditions.
The United States is already experiencing an
infant mortality higher than that of any other
industrialized nation (World Bank, 1987). Some
studies have found that perinatal mortality is higher
hi the summer; consequently, the increased
temperatures expected with global wanning may
well exacerbate infant mortality (or at least neonatal
mortality).
232
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Human Health
The need for irrigation may increase in many
regions of the United States (see Chapter 6:
Agriculture). Irrigation may result in greater
amounts of standing water and can therefore
increase mosquito populations. Arbovirus
encephalitis may become a greater problem than at
present, and other mosquito-borne diseases, such
as dengue or yellow fever, could be more easily
spread if introduced.
One health impact of climate change not
assessed in this report is the morbidity and mortality
associated with certain kinds of extreme events, e.g.,
tornadoes and hurricanes. These currently cause
some mortality in the United States; however, it is
difficult to say whether there will be a change in the
mortality induced by these events with global
warming. As indicated in Chapter 3: Variability,
changes in the frequency of such extreme events
cannot be predicted on the basis of an analysis of
the general circulation model (GCM) output,
although an increase in severity of some kinds of
storms, e.g., hurricanes, is not inconsistent with
current theories and more detailed models of storm
behavior.
The impact of global change on human health
will most likely be greater in the lesser-developed
countries (LDCs) that do not have the resources to
take the adaptive or preventative measures available
to the United States. Impacts on agriculture and
water resources in the LDCs could result in poor
nutrition and water shortages that may make
populations more susceptible to disease. Changes
in insect (arthropod) habitats may allow diseases to
flourish where they never have before. Changes in
extreme events such as monsoons or floods could
significantly affect mortality in the developing world.
Such external impacts on health might have an
impact on the United States not only via the
potential for introduction of diseases already
discussed but also via our participation in
international aid and relief programs.
POLICY IMPLICATIONS
The full impacts of climate change on human
health will require more research. Agencies such as
the Department of Health and Human Services
should consider conducting studies on potential
impact.
In the future, a cadre of trained professionals
may be needed to respond to outbreaks of diseases.
A shift in the distribution of carriers of human
disease may necessitate regional shifts in
surveillance and eradication programs. States that
do not have these programs may need to develop
them.
RESEARCH NEEDS
Although information evaluating the
relationship of weather and season to various health
effects is plentiful, research into the significance of
these relationships in the context of global warming
is scarce. A number of areas requiring further
research are described below.
A number of studies have identified
relationships between temperature changes and
mortality from diseases of the heart, respiratory
system, and cerebrovascular system. These studies
show slightly different relationships depending on
the city that provided the data, although some
common elements exist. A statistical analysis of this
information might be warranted to determine if one
general relationship (across the United States, or
perhaps related to latitude) could be developed for
each of these categories. Such a relationship could
then be used to estimate the impact of global
warming by specific disease category.
A companion study to that proposed above
should identify the top 10 causes of deaths
associated with changes in weather in the Kalkstein
study. The results could then be compared with the
information derived above to determine other
causes of mortality that show great sensitivity to the
weather.
The Kalkstein analysis did not look at deaths
occurring in the very young (aged 1 year and
below). Given the seasonality of perinatal mortality
and preterm death observed in several studies, an
investigation of the relationship between
temperature and mortality in the very young
probably would be worthwhile. More baseline
information is needed for the latter study. Related
studies on perinatal mortality could examine the
following:
233
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Chapter 12
• Whether the South has a higher per capita
incidence of perinatal mortality.
• Whether infections, which have been
suggested as a potential cause of the
perinatal mortality observed, show a
seasonality in parallel to perinatal
mortality, and whether more such
infections occur in the South.
• The principal causes (e.g., bacteria,
viruses) for perinatal infections, and
whether they are the same as those for
skin infections that increase with increases
in humidity.
• Whether the incidence of preterm birth or
perinatal mortality is related to weather
parameters such as temperature, humidity,
or high-pressure systems.
The following additional research areas are
suggested:
• Synergism between stratospheric ozone
depletion (due to increases in UV-B
radiation) and global warming. Increased
UV-B radiation and global warming might
be expected to exacerbate infectious
diseases. UV-B radiation may have an
impact on the ability of an individual to
respond to a disease, and global warming
may change the incidence of certain
infectious diseases. For example,
leishmaniasis is an important disease in
many African countries. In animal
models, UV-B irradiation adversely affects
the development of immunity to
Leishmania. If climate change creates
more favorable habitats for the sand-fly
vector of this disease, then a double insult
to the system could occur: a higher
incidence, and a worse prognosis.
• The impacts on LDCs. The Agency for
International Development is supporting
the development of a Famine Early
Warning System (FEWS) that will use a
variety of inputs (many of them weather
related) to help predict when conditions
leading to famine may be occurring.
Appropriate GCM outputs could be input
into this system to evaluate how the
changes associated with global warming
may affect famine development.
Similarly, the Department of Defense is
using a number of models comparable to
those used by Haile to attempt to predict
where infectious diseases are likely to
pose problems for U.S. troops. It might
be interesting to evaluate how the climate
variables from the GCM-generated
scenarios would affect these predictions,
particularly in the LDCs where these
diseases present a very real problem to
the health care systems.
Introduction of infectious diseases into the
United States via immigrants. Anecdotal
information indicates that many
immigrants are not served by the health
care system; consequently, they could
become a population where diseases
might develop into full-blown epidemics
before initiation of treatment.
Determining whether or not global
warming will affect this process, either
directly via the provision of a more
hospitable environment for the disease or
indirectly via an increased number of
immigrants and refugees, will require a
better characterization of the current
situation.
Intermediate hosts and their habitats. In
the models used by Haile, two important
input parameters that were held constant
were the size of the intermediate host
population and the distribution of habitat
between forest and meadow. It is likely
that both of these parameters will
themselves be affected by climate change.
A better grasp of how climate change will
affect these parameters needs to be
developed and integrated into the
infectious disease models.
Irrigation and incidence of vector-borne
disease. An increase hi irrigation is
possible, which could have a significant
impact on mosquito development and
therefore on mosquito-borne diseases.
The importance of such water is time-
dependent, however (i.e., it must occur at
the right moment hi the insect's life-
cycle). Thus an analysis of how the
growing season overlaps transmission of
234
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Human Health
diseases such as La Cross encephalitis
might provide an indication of whether
changes in irrigation practices should be a
concern in terms of public health.
Mortality from extreme events. Another
issue that might warrant investigation is
how climate change may affect the
mortality associated with extreme events,
such as hurricanes and floods.
Air pollution and respiratory disease. Air
pollution is already a major contributing
factor in the incidence and severity of
respiratory disease in the United States.
An analysis of the extent that global
warming will exacerbate air pollution is
critical to an assessment of the potential
health effects of climate change.
REFERENCES
APHA. 1985. American Public Health Association.
In: Berenson, A.S., ed. Control of Communicable
Diseases in Man. Springfield, VA: John D. Lucas
Printing Company.
CDC. 1986. Centers for Disease Control. Annual
Summary 1984. MMWR 33:54.
Cooperstock, M., and RA. Wolfe. 1986. Seasonally
of preterm birth in the collaborative perinatal
project: demographic factors. American Journal of
Epidemiology 124:234-41.
Dukes-Dobos, F., 1981. Hazards of heat exposure.
Scandinavian Journal of Work and Environmental
Health 73-83.
Gill, J.S., P. Davies, S.K. Gill, and D.G. Beevers.
1988. Wind-chill and the seasonal variation of
cerebrovascular disease. Journal of Clinical Epidem-
iology 41:225-230.
Glatthaar, C., P. Whittall, T. Welborn, M. Giboon,
B. Brooks, M.M. Ryan, and G. Byrne. 1988.
Diabetes in Western Australian children:
descriptive epidemiology. Medical Journal of
Australia 148:117-123.
Glenzen, W.P. 1982. Serious illness and mortality
associated with influenza epidemics.
Epidemiological Reviews 4:25-44.
Grant, L.D. 1988. Health effects issues associated
with regional and global air pollution problems.
Prepared for World Conference on the Changing
Atmosphere, Toronto. Draft document.
Harris, R.E., F.E. Harrell, K.D. Patil, and R. Al-
Rashid. 1987. The seasonal risk of pediatric/juvenile
acute lymphocytic leukemia in the Unites States.
Journal of Chronic Diseases 40:915-923.
Kalkstein, L.S., R.E. Davis, JA. Skindlov, and K.M.
Valimont. 1986. The impact of human-induced
climate warming upon human mortality: a New
York case study. Proceedings of the International
Conference on Health and Environmental Effects of
Ozone Modification and Climate Change,
Washington, DC; June.
Kalkstein, L.S., and K.M. Valimont. 1987. Effect
on human health. In: Tirpak, D., ed. Potential
Effects of Future Climate Changes on Forest and
Vegetation, Agriculture, Water Resources, and
Human Health, Vol. V, pp. 122-152. Washington,
DC: U.S. Environmental Protection Agency. EPA
400/1-87/101E.
Keller, CA., and R.P. Nugent. 1983. Seasonal
patterns in perinatal mortality and preterm delivery.
American Journal of Epidemiology 118:689-98.
Kovelman, J., and A. Scheibel. 1986. Biological
substrates of schizophrenia. Acta Neurologica
Scandinavica 73:1-32.
Kutschenreuter, P.H. 1959. A study of the effect of
weather on mortality. New York Academy of
Sciences 22:126-138.
Lopez, M., and J.E. Salvaggio. 1983. Climate-
weather-air pollution. In: Middleton, E., and C.E.
Reed, eds. Allergy, Chapter 54. St. Louis, MO:
C.V. Mosby Company.
Mount, GA., and D.G. Haile. 1988. Computer
simulation of population dynamics of the American
dog tick, Dermacentor variabilis (Acari: ixodidae).
Journal of Medical Entomology. In press.
Patterson, C., P. Smith, J. Webb, M. Heasman, and
J. Mann. 1988. Geographical variation in the
incidence of diabetes mellitus in Scottish children
during the period 1977-1983. Diabetic Medicine
5:160-165.
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Rogot, E., and S J. Padgett. 1976. Associations of
coronary and stroke mortality with temperature and
snowfall in selected areas of the United States 1962-
1966. American Journal of Epidemiology 103:565-
575.
Sontaniemi, E., U. Vuopala, E. Huhta, and J.
Takkunem. 1970. Effect of temperature on hospital
admissions for myocardial infarction in a subarctic
area. British Medical Journal 4:150-1.
Vuori, I. 1987. The heart and the cold. Annals of
Clinical Research 19:156-162.
White, M.R., and I. Hertz-Picciotto. 1985. Human
health: analysis of climate related to health. In:
White, M.R., ed. Characterization of Information
Requirements for Studies of CO2 Effects: Water
Resources, Agriculture, Fisheries, Forests, and
Human Health. Washington, DC: Department of
Energy. DOE/ER/0236.
World Bank. 1987. World Development Report
1987. New York: Oxford University Press.
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CHAPTER 13
URBAN INFRASTRUCTURE
FINDINGS
Global climate change could require U.S. cities to
make major changes in capital investments and
operating budgets. Areas most likely to be affected
include water supplies, roads, and bridges; storm
sewers and flood control levees; and energy demand
in municipal buildings and schools.
• Most urban infrastructure in the United States
will turn over in the next 35 to 50 years. If
potential changes in climate are considered,
this turnover will allow cities to prepare for
climate change at lower costs. In some cases,
the risk of climate change should be
incorporated into decisions beginning today,
such as coastal drainage systems that are likely
to last for 50 to 100 years.
Northern and Southern Cities
• Northern cities, such as Cleveland, may incur
a change in the mix of their expenditures. In
such locations, increased electricity costs for
air-conditioning could be offset by reductions
in expenditures for heating fuel, snow and ice
control, and road maintenance. Southern
cities could see increases in operating budgets
due to the demand for additional air-
conditioning.
Coastal Cities
• Coastal cities, including 12 of the 20 largest
metropolitan areas, may face somewhat larger
impacts, such as the following:
— Sea level rise or more frequent droughts
would increase the salinity of shallow
coastal aquifers and tidal surface waters.
Cities that rely on water from these sources
should examine water supply options. Such
areas as Dade County, Florida, or New
York City would probably be vulnerable.
~ As sea level rises, some coastal cities
would require levees to hold back the sea
or fill to raise the land surface area. In the
case of Miami, the cost of these activities
might exceed $500 million over the next
50 to 75 years, necessitating an average
increase of 1 to 2% in annual capital
spending in Greater Miami.
Water Supply and Demand
• Climate change will influence the supply and
demand for water in many cities. A lengthened
summer season and higher temperatures would
increase the use of water for air conditioners,
lawns, and gardens. Changes in rainfall
patterns, runoff, and flood control measures
may alter water supplies. In the Hudson River
Basin, summer water demand could increase by
5% over the demand for water without climate
change, while supplies might fall. Such a
change would require new institutional and
management approaches for both the Delaware
and Hudson Rivers.
Policy Implications
• Climate change has implications for many
national programs and policies, including the
following:
— The National Flood Insurance Program may
react to climate change by redrawing
floodplain maps and adjusting insurance
rates to account for sea level rise and
changes hi riverflows. This program might
consider discouraging development that
would be vulnerable to sea level rise.
- Because of the key role federal programs
play in the development of cities, the
Department of Housing and Urban
Development should examine the
implications of climate change on long-term
policies. A minimum response might be to
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Chapter 13
provide guidance on the certainties and
uncertainties of climate change to groups
such as the National League of Cities, the
U.S. Conference of Mayors, and the
American Planning Association.
Because water supply infrastructure may last
for several centuries, improved planning is
important. The TJ.S. Geological Survey
should study the probable impacts of global
climate change and sea level rise on the
water supplies of major cities. The U.S.
Army Corps of Engineers should factor
climate change into the design of major
projects.
Given the assumption that modest changes
in the design and location of many
transportation systems may facilitate an
accommodation to climate change, the
Department of Transportation should factor
climate change into the design of roads,
bridges, and mass transit facilities.
Voluntary standards organizations, such as
the American Society of Civil Engineers, the
Building Officials and Code Administrators
International, and the American Society of
Heating and Refrigerating and Air
Conditioning Engineers should examine the
need for changes in existing energy and
safety factors to account for the possibility
of climate change.
RELATIONSHIP BETWEEN
URBAN INFRASTRUCTURE AND
CLIMATE
Three-quarters of the U.S. population is
concentrated in urban areas (Statistical Abstract,
1988). The majority of the nation's investment in
water supply, wastewater transport and treatment
facilities, drainage, roadways, airports, mass transit,
electric power, solid waste disposal sites, and public
buildings serves these urban areas. The current
value of selected infrastructure nationwide,
displayed in Table 13-1, provides insight into the
aggregate investment at stake if climate changes.
Most of these items could be considered part of
urban infrastructure; their locations and designs
have been based on historic meteorologic
information. Annually, governments add an average
of $45 billion to the capital stock (National Council
on Public Works Improvement, 1988).
Of the 20 most populated U.S. urban areas, 18
have access to oceans, major lakes, or rivers and
have invested in infrastructure for port facilities and
flood control. The expenditure required to
construct coastal defense structures — which prevent
inundation by the sea, slow oceanfront erosion,
control storm surges, slow saltwater advance up
rivers, and reduce saltwater intrusion into aquifers
— is now minimal.
Table 13-1. Value of the Nation's Stock of
Selected Infrastructure (billions of
1984 dollars)
Component
Value3
Water supply
Wastewater
Urban drainage
Streets
Public airports
Mass transit
Electric power
(private only)b
$108
136
60
470 .
31
34
266
Public buildings
Total
unknown
$1,105+
Based on a useful life of 35 to 50 years for most
assets, and 10 to 20 years for transit vehicles.
bAbout 77% of electric power is privately produced.
Source: Statistical Abstract (1988); National Council
on Public Works Improvement (1988).
Of the 20 most populated urban areas in the United States, 12
are tidal waterfront cities (Baltimore, Boston, Houston, Los
Angeles, Miami, New York, Philadelphia/Wilmington, San
Francisco/Oakland, San Diego, Seattle, Tampa/St. Petersburg,
and Washington, DC), 3 are located on the Great Lakes
(Chicago, Cleveland, and Detroit), 3 are on navigable rivers
(Minneapolis, Pittsburgh, and St. Louis), and 2 are not on a
navigable waterway (Atlanta and Dallas).
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Urban Infrastructure
Although actual practice varies, the nominal
replacement cycle for most infrastructure is 35 to 50
years (National Council on Public Works
Improvement, 1988). Some water supply
investments have 100-year cycles between planned
replacement; however, sea level rise, temperature
change, and changes in precipitation patterns could
alter the balance between water supply and demand.
The nature and pattern of precipitation could affect
drainage requirements as well as highway design
and maintenance.
The heat wave of 1988 illustrated some of the
potential impacts. Hundred-degree weather
distorted railroad tracks, forcing Amtrak to cut
speeds from 200 to 128 kilometers per hour between
Washington and Philadelphia (Bruske, 1988) and
possibly contributing to a train wreck that injured
160 people on a Chicago-Seattle run (The
Washington Post, 1988). A U.S. Army Corps of
Engineers contractor worked around the clock for
2 weeks to build a 170-meter-wide, 9-meter-high silt
wall across the bottom 40% of the Mississippi River
channel, 48 kilometers below New Orleans
(Sossaman, 1988a,b). This $2 million wall, designed
to wash away when spring snowmelt demands the
full capacity of the channel, slowed an advancing
wedge of saltwater that threatened the water supply
in New Orleans and nearby parishes. In Manhattan,
heat exacerbated the effects of longstanding leaks in
256 kilometers of steam pipes, causing the asphalt
to soften. As vehicles kneaded the soft asphalt,
thousands of bumps formed on city streets,
requiring extensive repairs (Hirsch, 1988). In the
suburbs of Washington, DC, steel expansion joints
bubbled along a 21-kilometer stretch of Interstate
66 (Lewis, 1988).
The following sections of this chapter will
examine such issues as the portions of the
infrastructure that will be significantly affected, and
anticipated costs and who will bear them.
PREVIOUS CLIMATE CHANGE
STUDIES ON URBAN
INFRASTRUCTURE
Available literature on the potential effects of
global climate change on urban infrastructure is
sparse. Rhoads et al. (1987) examined the potential
impacts of sea level rise on water supply and flood
protection in Dade and Broward Counties, Florida,
and concluded that the effects might be substantial.
Linder et al. (1987) estimated that CO2 doubling
might require raising electric capacity by 21% in a
southeastern utility and by 10 to 19% in New York
State. Hull and Titus (1986) analyzed the potential
impact of sea level rise on water supply in the
Philadelphia-Wilmington-Trenton area and found
that a rise of 0.3 meters could require adding 140
million cubic meters of reservoir capacity, about a
12% increase, to prevent saltwater from advancing
past water intakes on the Delaware River.
Additional investment would be required to prevent
or respond to saltwater infiltration into underground
aquifers. Cohen (1987) estimated that large
municipalities along the Great Lakes might increase
water withdrawals by 5.2 to 5.6% during May to
September because of increased lawn watering.
Two recent studies illustrate the importance of
considering sea level rise in urban coastal
infrastructure planning and the uncertain nature of
the decisions involved. Wilcoxen (1986) examined
the impact of sea level rise on a portion of San
Francisco's sewage transport system buried near the
shoreline. The study estimated that if sea level rose
0.6 meters by the year 2100, an expenditure of
roughly $70 million on beach nourishment might be
required to prevent damage to a structure that cost
$100 million to build in the late 1970s. The author
suggested that consideration (at no additional cost)
of sea level rise in siting the structure could have
prevented these expenses. Titus et al. (1987)
examined the impact of sea level rise on a proposed
coastal drainage system in Charleston, South
Carolina, and estimated that a 0.3-meter sea level
rise by 2025 would require almost $2.5 million in
additional investments to maintain the target level
of flood protection. The present value of these
investments is $730,000. In contrast, only about
$260,000, one-third of the cost of responding in
2025, would be required to add this level of
protection at initial construction. Thus, the
investment would be worthwhile if the probability of
sea level rising this rapidly exceeds 35%.
URBAN INFRASTRUCTURE
STUDY IN THIS REPORT
Several studies undertaken for this report
examined some of the implications of climate
change in relationship to urban infrastructure. One
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Chapter 13
study comprehensively examined the impacts on
infrastructure in several cities:
• Impact of Global Climate Change on Urban
Infrastructure - Walker, Miller, Kingsley,
and Hyman, The Urban Institute (Volume
H)
The following studies, referenced in this chapter,
covered issues relating to urban infrastructure:
• The Potential Impacts of Climate Change
on Electric Utilities: Regional and National
Estimates - Linder and Inglis, ICF Inc.
(Volume H)
• Impacts of Extremes in Lake Michigan
Levels Along the Illinois Shoreline: Low
Levels - Changnon, Leffler, and Shealy,
University of Illinois (Volume H)
• Methods for Evaluating the Potential
Impacts of Global Climate Change: Case
Studies of the Water Supply Systems of the
State of California and Atlanta. Georgia^-
Sheer and Randall, Water Resources
Management Inc. (Volume A)
• National Assessment of Beach Nourishment
Requirements Associated with Sea Level
Rise - Leatherman, University of Maryland
(Volume B)
• The Costs of Defending Developed
Shorelines Along Sheltered Waters of the
United States from a Two-Meter Rise in
Mean Sea Level
- Weggel, Brown,
and Doheny, Drexel
Escajadillo, Breen,
University (Volume B)
Effect of Climate Change on Shipping
Within Lake Superior and Lake Erie -
Keith, DeAvila, and Willis, Engineering
Computer Optecnomics (Volume H)
RESULTS OF THE
INFRASTRUCTURE STUDY
Impacts on Miami, Cleveland, and New
York City
Walker et al. examined three cities distinctly
affected by climate change to determine a range of
impacts on urban infrastructure.
Study Design
The study was based on a critical review of
existing infrastructure studies in the three cities,
discussions of likely impacts with local infrastructure
experts, analyses undertaken by these experts, and
preliminary calculations of probable impacts.
Experts were presented with GCM scenarios for
CO2 doubling, and scenarios were used to calculate
effects on energy demand, roadways, and other
systems. The study also derived conclusions based
on experiences in other cities where current
temperatures are analogous to temperatures
projected for the cities under study, using the
analogs identified by Kalkstein (Volume G).
Limitations
The principal limitation of the overall study is
the limited use of hydrologic and other modeling.
In addition, experts were asked to derive
conclusions regarding conditions beyond their
experience. Since only three cities are included, the
full range of effects on urban infrastructure was not
covered. The authors did not perform engineering
analyses of cost-effective responses, and they did not
assess the potential for reducing impacts through
technological change. Thus, these results should be
considered as approximations of the costs of impacts
and as illustrative of the sensitivity of urban
infrastructure to climate change.
Results and Implications
Miami's Infrastructure
Greater Miami is bounded by water on all
sides during the rainy season. An extensive network
of canals and levees has been built to control ocean
and freshwater flooding and to recharge the aquifer
beneath the area. Miami has one of the world's
most porous aquifers, which lies less than 1.5 meters
below the surface in one-third of the developed
area. Federal law requires that roughly 15% of
Miami's freshwater be released into the Everglades
National Park.
The Miami case study examined the probable
impacts of climate change and sea level rise on
Dade County's water supply, water control and
drainage systems, building foundations, roads,
bridges, airports, solid waste disposal sites, and
sewage transport and treatment systems, assuming
that a gradual sea level rise would be managed
through strategies such as raising the land in
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low-lying areas, upgrading levees and dikes with
pumped outflows, retreating selectively from some
areas, and increasing the freshwater head roughly in
proportion to sea level rise to prevent saltwater
infiltration into the aquifer.
As Table 13-2 shows, global climate change
could require more than $500 million in capital
investment in Greater Miami over the next century.
Because needed investments in many systems could
not be estimated and because a complete
engineering analysis was not performed, these
results should be considered only as rough
estimates. They imply an increase of 1% to 2% in
Greater Miami's capital spending for the next 100
years, no more than $20 per household per year at
1985 population levels (Metropolitan Bade County
Planning Department, 1988).
Because the south Florida aquifer extends
under the ocean, the typical urban response to a
rising sea ~ diking the water at the surface and
pumping out the seepage from ditches behind the
dikes ~ appears to be unworkable. Unless the dike
extended downward more than 45 meters, rising
seawater pressure would cause the sea to rush into
the aquifer below the surface and push freshwater
upward, almost to the surface.
The one-time capital costs for upgrading
existing canals and levees in response to a 1-meter
sea level rise could be about $60 million. However,
almost $50 million in new control structures,
including extensive pumping capacity, might be
required for the canals used to maintain the
freshwater head. Large-scale pumping along canals
also could involve substantial operating costs, but
these have not been estimated. Storm sewers and
drainage would need upgrading, requiring invest-
ment of several hundred million dollars above
normal replacement costs.
Building foundations generally should remain
stable if the freshwater head rises 1 meter because
houses are built on concrete slabs, most buildings in
newer areas already are built on raised lots to meet
Dade County's flood control ordinance, and the
foundations of many larger buildings are designed to
extend into the water table.
Conversely, the water table could infiltrate the
base of about a third of Dade County streets, which
Table 13-2. Probable Infrastructure Needs and
, Investment in Miami in Response to a
Doubling of CO2 (millions of 1987
dollars)
Infrastructure need
Cost
Raising canals/levees
Canal control structures
Pumping
Raising streets
Raising yards and houses
Pumped sewer connections
Raising lots at reconstruction
Drainage
Airport
Raising bridges
Sewer pipe corrosion
Water supply
Electric generation
60a
50
not estimated
250 added to
reconstruction
cost
not estimated
not estimated
not estimated
200-300
30
not estimated
not estimated
uncertain
20-30% capacity
increase
aCosts are partially based on Weggel et al.,
Volume B.
Source: Walker et al. (Volume H); Linder and
Inglis (Volume H).
would have to be raised or risk collapse. If sea level
rose gradually, thereby permitting raising of streets
and related sewer mains during scheduled recon-
struction, the added public cost might be
approximately $250 million. Building owners would
incur substantial costs to improve drainage, raise
yards, raise lots at reconstruction, and pump sewage
to mains. Miami's airport also would need better
drainage, requiring an approximately $30 million
investment.
A 1-meter rise in sea level would require
raising most bridges to ensure adequate clearances
and reduce vulnerability to storm surges during
hurricanes.
It is unclear what effect climate change will
have on hurricanes. Without increased hurricane
activity, climate change probably would exacerbate
water shortages that are expected to result from
population growth in Greater Miami. Thus, climate
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Chapter 13
change could accelerate Miami's long-range plan
for large-scale production of desalinated water at
three times current water prices. If hurricanes
increase, Miami's added expense for water supply
might be roughly $100 million to move some wells
farther inland. Conversely, increased hurricane
frequency and intensity could cause billions of
dollars in property damage.
Analysis of Miami's coastal defense and water
supply options provides insight into the impacts of
sea level rise on cities built on coral reefs, but not
into the response of most mainland cities on the
U.S. coastline. Dade County is unusual because
readily extracted fill is extensively available on
public lands having easy access to a canal system
that can be navigated by flat-bottomed barges.
Nevertheless, this case study suggests that global
climate change could cause large coastal cities to
invest billions of dollars over the next 50 to 75 years
to add and upgrade infrastructure.
Cleveland's Infrastructure
The Cleveland case study examined impacts of
climate change on snow and ice control costs, road
construction and maintenance, heating and cooling
costs and equipment needs, water supply, and storm
and wastewater transport. The study also included
a preliminary analysis of the effects of a drop in the
level of Lake Erie as estimated by Croley (see
Chapter 15: Great Lakes). The impact on the snow
and ice control budget was estimated by analogy to
the budget in Nashville, Tennessee.
Results are displayed in Table 13-3, which
shows that the net impact of climate change on
Cleveland's annual infrastructure costs could be
negligible, although expenditures probably would
shift between categories. In addition to the costs
shown in Table 13-3, a one-time capital expenditure
of $68 to $80 million could be required to add air
conditioners in public buildings. Also, many private
residences probably would install air conditioners.
Walker et al. estimated that global climate
change could cause annual snowfall in Cleveland to
drop from 1.25 to roughly 0.2 meters (4.1 to 0.7
feet), reducing annual snow and ice control costs by
about $4.5 million. Decreased frost damage to
roads and bridges could yield further savings
estimated at $700,000 per year. A drop of $2.3
million per year in heating costs for public buildings
also was estimated. Conversely, annual public air-
Table 13-3. Estimated Impacts of a CO2 Doubling
on Cleveland's Annual Infrastructure
Costs (millions of 1987 dollars)
Infrastructure category
Annual
operating costs
Heating
Air-conditioning
Snow and ice control
Frost damage to roads
Road maintenance
Road reconstruction
Mass transit
River dredging
Water supply
Storm water system
Total
-2.3
+ 6.6-9.3
-4.5
-0.7
-0.5
-0.2
summer increase
offsets winter
savings
less than 0.5
negligible
negligible
-1.6 to +$1.1
Source: Walker et al. (Volume H); Keith et al.
(Volume H).
conditioning costs seemed likely to rise by $6.6 to
$9.3 million. The impacts on the transit operating
budget seemed likely to mirror the impacts on the
general budget, with reduced mishaps and traffic
delays in ice and snow offsetting increased fuel costs
for vehicle cooling.
The study suggested Cleveland might spend
about $65 to $80 million to add air-conditioning to
older schools and to large nonoffice spaces such as
gyms and repair garages. Much of this expenditure
would occur as buildings were replaced or
refurbished and might have occurred even without
climate change.
The rise in winter temperatures associated with
a doubling of CO2 might allow Cleveland to use
thinner pavement, resulting in possible savings of
about 3% in road resurfacing costs and 1% in
reconstruction costs. The net savings could average
about $200,000 per year or 1.3% of the city's current
capital budget. Engineering standards (AASHTO,
1987) suggested that the rate of pavement
deterioration probably also should decline as whiter
temperatures rise, saving roughly $500,000 per year.
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Urban Infrastructure
A climate-induced drop in the level of Lake
Erie probably would not adversely affect Cleveland,
although some dredging might be required in the
Cuyahoga River and port area (Keith et al., Volume
H). Upgrading of the city's combined storm and
wastewater collection system appeared to be
unnecessary, although this would depend upon
rainfall variability.
If temperature rises several degrees, most
northern cities probably could anticipate savings in
snow and ice control, heating, and roadway
construction and maintenance costs similar to those
described for Cleveland. These savings might
approximately offset the increase in air-conditioning
costs. More southern cities could experience
modest budget increases.
Cleveland could become a more attractive
location for water-intensive industry if water
supplies in other areas become less reliable.
Resulting in-migration could bring further growth-
related infrastructure costs.. Lower Great Lakes
levels could require dredging, modification to ports,
and relocation of some water intakes. (For a
further discussion of these issues, see Chapter 15:
Great Lakes.)
New York City's Water Supply
New York City's infrastructure maybe affected
in many ways by global climate change.
Temperature change could affect the same capital
expense categories in both New York City and
Cleveland. In addition, the city may have to
gradually raise its dikes and better protect
underground infrastructure from seawater
infiltration. Interpolating from Weggel et al.
(Volume B), approximately $120 million might be
invested to protect shorelines from a sea level rise
of 1 meter. The most pressing, and perhaps largest,
problem facing the city may be the effects of global
climate change on the adequacy of the city's water
supply. The New York City study focused on that
issue. Table 13-4 provides estimates drawn from a
number of studies about possible infrastructure
impacts on New York City.
The New York metropolitan area draws water
from the adjoining Hudson and Delaware River
Basins and from underground aquifers serving
coastal New Jersey and Long Island. Figure 13-1
shows the region and its water supply sources.
Table 13-4. Probable Impacts of a CO, Doubling
on Selected Infrastructure in the New
York Metropolitan Area (millions of
1987 dollars)
Infrastructure
category
Costs
Upgrading levees
Drainage
Sewer outflows
Water supply
Snow and ice control
120
increased flooding in low-
lying areas, minimal
sewer system changes
more frequent inspection
3,000
reduced substantially
Road maintenance and winter savings, offset by
reconstruction melting asphalt in
Manhattan
Mass transit
summer increase offsets
winter savings
Electricity production 65-150
Heating
reduced
NOTE: Impacts on underground infrastructure,
airports, and ports have not been probed,
but a discussion of these impacts among
Port Authority representatives and other
experts at the Second North American
Conference on Preparing for Climate
Change, Washington, DC, December 7,
1988, suggested they might be small.
Source: Walker et al. (Volume H); Weggel et al.
(Volume B); Linder et al. (1987); Schwarz and
Dillard (1989).
The water supply network is in deficit. The
Mayor's Task Force (1987) has recommended
remedying New York City's portion of the deficit
through better management of water demand and
detailed study of the possibility of reactivation of a
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Chapter 13
DELAWARE
SYSTEM
ATLANTIC OCEAN
Figure 13-1. The sources of New York City's water supply (New York City Municipal Water Finance Authority,
1986).
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Urban Infrastructure
water intake at Chelsea, a $223 to $391 million
investment that would yield 375 to 750 million liters
of water daily.
Walker et al. estimated changes in water
demand using design standards for commercial
cooling-tower demand, changes in electricity
demand estimated by Linder et al. (1987), and
historic residential summer water use. The impact
of sea level rise on water supply was estimated by
analogy using Hull and Titus (1986), which analyzes
possible saltwater advance up the Delaware River.
The impact on reservoir supply also was estimated
by analogy, using a Great Lakes water balance
model (Linder et al., 1987). Walker et al. assumed
that baseline demand would not increase above
projected demand in 2030, potentially
underestimating the increased demand for water.
Walker et al. estimated that a rise in
temperatures consistent with the GISS and GFDL
scenarios would mean about a 20% increase in
cooling degree days. In response, average daily
demand for water used in cooling large buildings
could increase by 190 million liters during the
summer, and increased lawn watering could raise
demand by 110 million liters per day, thereby
generating a 5% rise in annual demand.
Higher temperatures could increase
evaporation and evapotranspiration, decreasing the
ability to store water efficiently in surface
impoundments. The water balance model indicated
the supply loss could range from 10 to 24%.
Saltwater infiltration due to rising sea level
would further reduce supply. The study suggested
that a 1-meter sea level rise could place the
proposed $300 million Chelsea intake below the salt
line during the peak summer demand period in mild
drought years, reducing supply another 13%.
Larger sea level rise or greater droughts might
prevent use of the existing Poughkeepsie intake
during severe droughts, further reducing supply. In
addition, subsurface infiltration could reduce the
supply available from the Long Island aquifer.
In summary, a doubled CO2 atmosphere could
produce a shortfall equal to 28 to 42% of planned
supply in the Hudson River Basin.
Implications Arising from Other EPA
Studies in This Report
Linder and Inglis (Volume H; Chapter 10:
Electricity Demand) suggest that increased air-
conditioning use could raise peak electricity demand
by 10 to 30% in the southern half of the United
States. Nationally, utilities supplying the
northernmost cities could experience decreased
demand, while those supplying cities in the
remainder of the country could experience
electricity needs higher than they have anticipated.
Sheer's study of California (see Chapter 14) water
supply suggests that new surface water
impoundments maybe needed to meet urban water
needs and other demands. The coastal defense
strategies suggested hi Chapter 7: Sea Level Rise
would apply to most urban coastal areas, especially
those along the Atlantic and Gulf coasts.
Changnon et al. (Volume H) conclude that a
falling lake level might prompt investment of $200
to $400 million to adapt recreational and
commercial harbors and beach facilities, and an
investment of $20 million to adjust water supply
intakes and sewer outfalls along the Illinois
shoreline of Lake Michigan, with similar costs likely
on the other Great Lakes. The Keith study (see
Chapter 15: Great Lakes) suggests that each
commercial harbor on Great Lakes Erie and
Superior could spend $5 to $30 million on dredging
to maintain harbor access.
RESULTS OF RELATED STUDIES
Metropolitan Water Supply
Schwarz and Dillard (1989) conducted
telephone interviews with local infrastructure
managers to identify the probable impacts of global
climate change on water supply and drainage in
several metropolitan areas. Results from some
cities are discussed here.
Washington. DC
Longer hot spells could warm the Potomac
River and cause trihalomethane formed during
chlorination to rise above allowable limits.
Remedying this could require a capital investment
of roughly $50 to $70 million and could increase
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Chapter 13
treatment costs. Also, lawn watering probably
would increase during long spells of hot, dry
weather. Although a substantial decrease in runoff
could reduce supply in parts of the system, the
availability of additional storage capacity would
make a shortage unlikely.
New Orleans
Sea level rise could necessitate moving the
water intakes considerably farther up the Mississippi
and replacing cast iron water mains that would
corrode if exposed to saltwater. Reduced riverflow
also could increase settling and treatment
requirements. Rising sea level could increase
saltwater infiltration into the water system and could
require increased pumping capacity.
New York City
This study raised many of the same concerns
regarding water supply and demand as the study by
Walker et al. (Volume H) and indicated that even
a 0.25-meter sea level rise would mean the proposed
Chelsea intake was too far downstream. The
sanitary and storm sewage system capacity and
design probably would not need revision.
Nevertheless, in a few low-lying areas, higher sea
level could increase sewer backups, ponding, and
basement flooding when high tides coincided with
high runoffs.
Tucson
Tucson is depleting its aquifer despite substan-
tial conservation efforts and lawn watering with
treated wastewater. Higher temperatures would
increase demand and tighten supply, possibly
jeopardizing the city's ability to draw on water from
the Central Arizona Project on the already strained
Colorado River. While modest savings might be
achieved through stricter conservation measures and
more wastewater use, purchase of water in the
regional market most likely would be the only
practical response to climate-related shortfalls.
IMPLICATIONS FOR URBAN
INFRASTRUCTURE
The implications of climate change for urban
America vary spatially. Some localities, especially
those along the Great Lakes, might experience
roughly offsetting gains and losses. Others
especially those along the coastlines and in water-
short areas, could bear increased infrastructure
costs. The costs would be especially high if changes
came through abrupt "sawtooth" shifts or increases
in extreme events, making it difficult to adapt
infrastructure primarily during normal repair and
replacement. The likely impacts of an effective
doubling of atmospheric CO, could affect a wide
range of infrastructure. Additional climate change
effects beyond doubled CO2 or sea level rise above
1 meter could result in even greater costs.
Water
Hotter temperatures could cause faster
evaporation of groundwater and raise the demand
for water to support commercial air-conditioning
systems and lawn watering. Earlier snowmelt in the
West could force a lowering of dam levels to ensure
availability of enough capacity to control flood
waters. At the same time, sea level rise could cause
saltwater to advance up rivers and to infiltrate into
coastal aquifers. In droughts, many existing water
intakes might deliver brackish water.
The solution to these problems could involve
strong conservation measures, such as miles of
aqueducts from new water intakes at higher river
elevations, new reservoirs, sewage effluent recycling
systems to support commercial cooling or lawn
watering, and perhaps desalinization efforts along
the coasts. The solution for the New York-
Philadelphia corridor alone is likely to cost $3 to $7
billion. Communities in the Delaware River Basin,
northern New Jersey, the lower Hudson, and Long
Island might well form a multistate water supply
and management district of unprecedented size and
complexity to handle financing and capital
construction.
Drainage and Wastewater Systems
Increased storm size and intensity could tax
many storm sewer systems. Sea level rise also could
reduce coastal flood protection levels in low-lying
areas. The resulting increases in flooding and
releases of untreated waste into watercourses from
combined storm and wastewater systems probably
would motivate new sewer investments. In Bade
County alone, costs to maintain flood protection at
existing levels could be $200 to $300 million if sea
level rose 1 meter.
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Urban Infrastructure
Temperature rise could increase hydrogen
sulfide formation in sewer pipes, leading to internal
corrosion and eventual failure. In coastal areas with
increased ocean flooding, storm sewers would carry
corrosive saltwater with increased frequency. Sea
level rise also could cause more pipes in coastal
areas to face the external risk of corrosive seawater.
More frequent inspection and earlier replacement of
much existing pipe, as well as a gradual shift to
more corrosion-resistant pipe with plastic lining,
might be required.
Coastal Defenses
Protection from a rising sea could require
periodic investment in many major coastal
communities. In urban areas, a common approach
might be the New Orleans solution, where
extensively developed coastal areas are protected by
dikes, and covered drainage ditches behind the dikes
are pumped to keep out the saltwater.
Roads
Rising temperatures could reduce the costs of
road construction and maintenance. Snow and ice
control costs might drop dramatically. A decrease
in deep freezes and freeze-thaw cycles also would
mean fewer potholes. Warmer temperatures and
the improved drainage resulting from higher
evaporation rates could permit use of thinner
pavements in many areas, but could require
enhanced expansion capabilities.
Bridges
Sea level rise and increased storm intensity
could require upgrading of many bridges either
through costly retrofit or as part of normal recon-
struction. The range of temperature accommodated
by expansion joints also might need to be increased.
The costs might be modest if bridge planners
upgraded in anticipation of climate change.
Mass Transit
In the North, buses and railcars could
experience fewer snow-related delays. Conversely,
slight increases in fuel costs could result from
increased use of air conditioners.
Electricity and Air-Conditioning
Hotter temperatures could increase air-con-
ditioning use. Consequently, peak load capacity to
generate electric power might have to increase in
response to global climate change. Fortunately, air-
conditioning equipment is replaced frequently, so
increased loads on existing equipment could be
accommodated incrementally. Some houses and
public buildings in northern climates might need to
add air-conditioning, but such retrofitting has been
performed since the first window air conditioners
were introduced.
POLICY IMPLICATIONS
The possibility of global climate change
increases the risks of infrastructure investment.
Application of design standards and extrapolation
from historical data still may not provide reasonable
assurance that water and power supply, dam
strength and capacity, bridge clearances, or storm
sewerage capacity will be adequate for the 35-,
50-, and 100-year design cycles of these facilities.
For example, the National Flood Insurance
Program's maps identifying the historical 100-year
floodplain and 500-year floodway may no longer
provide a reliable basis for local building and zoning
ordinances designed to minimize flood losses to life
and property.
Investment Analysis Methods
Especially in coastal areas, the possibility of
global climate change may soon require careful
decisions regarding how and when to adapt the
infrastructure. A strong emphasis on lifecycle
costing and upgrading during reconstruction in
anticipation of future changes could yield large,
long-term cost savings. To accomplish this goal,
such institutions as the Department of Housing and
Urban Development might work with the American
Public Works Association, the National League of
Cities, the U.S. Conference of Mayors, the
American Planning Association, and similar groups
to educate their constituencies regarding the
uncertainties and ways to incorporate them into the
decisionmaking process.
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Chapter 13
Water Supply
Water supply is of particular concern because
decades are required to plan and complete projects,
which then might last 100 years. Dams, reservoirs,
and water intakes currently being planned and built
could become obsolete or inadequate as a result of
global climate change. Elsewhere, communities
might be allowing development of land needed for
reservoirs to meet the water shortages that would
result from climate change.
Such federal agencies as the U.S. Geological
Survey, U.S. Army Corps of Engineers, and EPA
may wish to work with states and municipalities to
study the possible impacts of climate change on the
water supply of major metropolitan areas.
Water supply investments frequently affect
multistate areas, creating a need for federal
coordination. The Supreme Court has been forced
to settle previous water rights disputes concerning
many major rivers, and global climate change might
well generate new disputes. Cost-effective response
to climate change also might require new multistate
water projects. For example, a major project on the
Hudson River that allowed New York City to
reduce its use of Delaware River water might be the
least costly way to increase water supply in
Philadelphia. The upcoming state debates over
water supply financing should be informed by the
lesson of past infrastructure crises: water piping
and pumping costs resulting from global climate
change should be fully recovered from the water
users to avoid stimulating artificial demand for
bargain water.
Infrastructure Standards
Voluntary standards organizations, such as the
American Society of Civil Engineers, the Building
Officials and Code Administrators International,
and the American Association of State Highway and
Transportation Officials, may wish to educate their
committees on global climate change. Growing
uncertainty concerning future temperature,
precipitation, and sea levels might dictate a
reassessment of existing standards and safety factors
for ventilation, drainage, flood protection, facility
siting, thermal tolerances, resistance to corrosion,
and so forth. Conversely, prompt detection of
lasting changes could allow adjustment of
geographically based standards — for example, on
roadbed depth and home insulation levels -- and
provide significant savings. Thus, the standard-
making organizations might beneficially establish
policies concerning how and when their committees
should account for global climate change or educate
their committees about the prospects.
RESEARCH NEEDS
The following are recommended for further
research:
1. More case studies of urban impacts, with
priority on a west coast city and an inland city.
Issues of particular interest include the effects
on subsidence problems in cities similar to
Phoenix, the implications for sewage treatment
capacity in areas where more frequent and
intense periods of low riverflow could reduce
acceptable effluent discharge rates, the impact
on bridge replacement costs, and the potential
for and probable consequences of saltwater
infiltration into pipes in older coastal
communities.
2. The probable impacts of global climate change
on domestic and international migration flows
and the infrastructure demands these flows
produce. Heat and high water prices might
drive jobs and people away from some regions,
while others might flourish. Infrastructure
investment in new water supply, for example,
might be unnecessary in areas that would lose
population, but extra capacity might be needed
in areas where population would grow.
Similarly, as climate change shifts the best
growing areas for specific crops, new farm-to-
market transportation networks might need to
be developed. Rights-of-way for these systems
might best be set aside now, before land prices
rise in response to climate change.
REFERENCES
AASHTO. 1987. American Association of State
Highway and Transportation Officials.' Manual for
the Design of Permanent Structures, Appendix A.
Treatment of Roadbed Swelling and/or Frost Heave
248
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Urban Infrastructure
in Design. Washington, DC: American Association
of State Highway and Transportation Officials.
Bruske, E. 1988. 104 (phew!) degrees hottest in 52
years. The Washington Post 111(225):A1, A6. July
17.
Cohen, S.J. 1987. Projected increases in municipal
water use in the Great Lakes due to CCyinduced
climatic change. Water Resources Bulletin
Hirsch, J. 1988. As streets melt, cars are
flummoxed by hummocks. The New York Times
137(47599):B1, B5. August 16.
Hull, C.H.J., and J.G. Titus, ed. 1986. Greenhouse
Effect, Sea Level Rise, and Salinity in the Delaware
Estuary. Washington, DC: U.S. Environmental
Protection Agency. Publication No. 230-05-86-010.
Lewis, N. 1988. Two more heat records fall as
summer of 1988 boils on. The Washington Post 111
(257):A1, A10, All. August 18.
Linder, K.P., MJ. Gibbs, and M.R. Inglis. ICF
Incorporated. 1987. Potential Impacts of Global
Climate Change on Electric Utilities. Albany, NY:
New York State Energy Research and Development
Authority. Publication No. 824-CON-AEP-86.
Mayor's Intergovernmental Task Force on New
York City Water Supply Needs. 1987. Managing
for the Present, Planning for the Future; December.
Metropolitan Dade County Planning Department.
1988. Comprehensive Development Master Plan for
Metropolitan Dade County, Florida. July 1979, July
1985, June 1987, and April 1988.
National Council on Public Works Improvement.
1988. Fragile Foundations - Final Report to the
President and Congress, Washington, DC; February.
New York City Municipal Water Finance Authority.
1986. Water and Sewer System Revenue Bonds,
Fiscal 1986, Series A. Prospectus. New York.
Rhoads, P.B., G.C. Shih, and R.L. Hamrick. 1987.
Water resource planning concerns and changing
climate: a Florida perspective. In: Proceedings of
the Symposium on Climate Change in the Southern
United States: Future Impacts and Present Policy
Issues. Norman, OK: University of Oklahoma, pp.
348-363.
Schwarz, H.E., and L. Dillard. 1989. Urban water.
Chapter III-D. In: Waggoner, P.E., ed. Climatic
Variability, Climate Change, and U.S. Water
Resources. New York: John Wiley and Sons. In
press.
Sossaman, BA. 1988a. News release. U.S. Army
Corps of Engineers, New Orleans District. June 28.
Sossaman, BA. 1988b. News release. U.S. Army
Corps of Engineers, New Orleans District. July 15.
Statistical Abstract of the United States. 1988.
Washington, DC: U.S. Government Printing Office.
Titus, J.G., C.Y. Kuo, MJ. Gibbs, T.B. LaRoche,
M.K. Webb, and J.O. Waddell. 1987. Greenhouse
effect, sea level rise, and coastal drainage systems.
Journal of Water Resources Planning and
Management 113(2):216-227.
The Washington Post. 1988. Warped rails checked
in Amtrak wreck. 111(246)A5. August 7.
Wilcoxen, PJ. 1986. Coastal erosion and sea level
rise: implications for Ocean Beach and San
Francisco's Westside Transport Project. Coastal
Zone Management Journal 14(3):173-191.
249
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CHAPTER 14
CALIFORNIA
FINDINGS
Global warming could cause higher winter runoff
and lower spring runoff in California and increase
the difficulty of meeting water supply needs. It
could also increase salinity in the San Francisco Bay
and the Sacramento-San Joaquin Delta and increase
the relative abundance of marine species in the bay;
degrade water quality in subalpine lakes; raise
ambient ozone levels; increase electricity demand;
and raise the demand for water for irrigation.
Water Resources
• Higher temperatures would lead to higher
winter runoff from the mountains surrounding
the Central Valley, because less precipitation
would fall as snow, and the snowpack would
melt earlier. Runoff in the late spring and
summer consequently would be reduced.
• As a result, the amount and reliability of the
water supply from reservoirs in the Central
Valley Basin would decrease. Annual water
deliveries from the State Water Project (SWF)
could be reduced by 200,000 to 400,000 acre-
feet or 7 to 16%. In comparison, the statewide
increase for water from the SWP, due to non-
climate factors such as population growth, may
total 1.4 million acre-feet by 2010. Even if
operating rules were changed, current
reservoirs would not have the capacity to store
the heavier winter runoff and at the same time
retain flood control capabilities.
• Rising sea level could increase the possibility of
levee failure. If the delta and bay levees failed
and sea level rose 1 meter (40 inches) by 2100,
agriculture in the delta region would be almost
eliminated, the pumping of freshwater out of
the delta to users to the south could be
jeopardized by increasing salinity, and the area
and volume of the estuary could triple and
double, respectively. Even if the levees were
maintained, the estuary could still increase in
area and volume by 30 and 15%, respectively,
as a result of a 1-meter sea level rise alone.
• Sea level rise of 1 meter could cause saline
(brackish) water to migrate inland between 4
and 10 kilometers (2.5 and 6 miles,
respectively) if the levees fail and if tidal
channels do not erode. Freshwater releases
into the delta might have to be doubled to
repel saline water near the major freshwater
pumping facilities.
Wetlands and Fisheries
• The wetlands in the San Francisco Bay estuary
would be gradually inundated as sea level rises
faster than the wetlands accrete sediments.
The amount of wetlands lost would be a
function of the rate of sea level rise and of
whether shorelines are protected. If sea level
rises 1 meter by 2100, the rate of rise will be
greater than wetland vertical accretion by the
middle of the next century. If sea level rises 2
to 3 meters by 2100, wetland inundation will
begin early in the 21st century.
• If salinity increases within the San Francisco
Bay estuary, wetland vegetation will shift from
brackish and freshwater species to more salt-
tolerant plants. This shift could severely
reduce waterfowl populations that depend on
freshwater habitats. The timing, magnitude,
and location of phytoplankton production could
shift. Marine fish species could increase in
abundance, while saltwater species that breed
in freshwater areas would most likely decline.
• Higher temperatures in subalpine lakes could
increase annual primary production (such as
algae) by between 16 and 87%, which could
degrade lake water quality and change the
composition of fish species.
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Chapter 14
Agriculture
• The impacts of climate change on agriculture
in California are uncertain. The effects of
changes in temperature and precipitation alone
would most likely reduce yields by 3 to 40%,
depending on the crop. However, with the
combined effects of climate and higher CO2
levels, yields for all modeled crops, except corn
and sugarbeets, might increase.
• The potential growth in irrigation in some
parts of the state may require increased
extraction of groundwater because of current
full use of surface water supplies. This would
decrease water quality and affect water
management options.
• Yields in California may be less adversely
affected than those in most parts of the
country. Crop acreage could increase because
of the shifts in yields and the presence of
irrigation infrastructure.
Natural Vegetation
• Drier climate conditions could reduce forest
density, particularly pine and fir trees, and
timber productivity. (The full impacts on
California forests were not assessed in this
report.)
Air Quality
• If today's emissions exist in a future warmer
climate, ozone levels in central California could
increase and could change location because of
higher temperatures. As a result, the area in
central California with ozone levels exceeding
EPA standards (0.12 parts per hundred million
(pphm)) on a given day could almost double
unless additional steps are taken to control
emissions. These additional controls would
increase the cost of pollution control.
Electricity Demand
• The annual demand for electricity in California
could rise by 3 to 6 billion kilowatthours (kWh)
(1 to 2%) over baseline demand in 2010 and by
21 to 41 billion kWh (3 to 5%) over baseline
demand hi 2055.
By 2010, 2 to 3 gigawatts (GW) would be
needed to meet the increased demand. By
2055,10 to 20 GW would be needed -- a 14 to
20% increase over baseline additions that may
occur without climate change. The additional
capital cost by 2055 would be $10 to $27 billion
(in 1986 dollars).
Policy Implications
• Water management institutions, such as the
U.S. Bureau of Reclamation and the California
Department of Water Resources, should
analyze the potential impacts of climate change
on water management in California. They
should consider whether and how the Central
Valley Project and State Water Project should
be modified to meet increasing demands in the
face of diminishing supplies due to climate
change. They may also consider whether to
change water allocation procedures to
encourage more efficient use of water.
• The California Water Resources Control
Board should consider the impact of climate
change on surface and groundwater quality.
• State and local entities should consider the
impacts of climate change on levee and
wetland management in San Francisco Bay and
the delta.
• The California Air Quality Board should
review the long-term implications of climate
change on air quality management strategies.
• The California Energy Commission should
consider the impacts of climate change on the
energy supply needs for the state.
CLIMATE-SENSITIVE
RESOURCES OF CALIFORNIA
California's Central Valley is the most
productive and diverse agricultural region of its size
in the world. The Central Valley Basin, which
includes the drainages of the Sacramento and San
Joaquin Rivers, encompasses several large
metropolitan areas, dispersed manufacturing, major
port facilities, important timber reserves, heavily
used recreational areas, and diverse ecosystems.
252
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California
Much of the region's economic and social
importance is derived from its water resources.
Over 40% of California's total surface water runoff
drains from the Central Valley Basin into the San
Francisco Bay area (Miller and Hyslop, 1983). The
basin supplies water for irrigated agricultural,
municipal, and industrial uses, and for a host of
other resources and activities.
The Central Valley Basin encompasses
approximately 40% of California's land area (Figure
14-1). Elevations range from just below sea level
on leveed islands in the Sacramento-San Joaquin
River Delta to peaks of over 4,200 meters (14,000
feet) hi the Sierra Nevada (Figures 14-2 and 14-3).
Mountains ring most of the basin: the Sierra
Nevada along the eastern side and the Coast Ranges
on the west. The only outlet to the Pacific Ocean is
via the San Francisco Bay estuary (Figure 14-2).
Current Climate
California's climate is characterized by little, if
any, summer precipitation and by generally wet
winters (Major, 1977). Both temperature and
precipitation vary with elevation and latitude hi the
Central Valley Basin. Extremes in mean annual
precipitation range from about 15 centimeters (6
inches) in the southern San Joaquin River Basin to
about 190 centimeters (75 inches) in the mountains
of the Sacramento River Basra. While almost all
valley floor precipitation falls as rain, winter
precipitation hi the high mountains often falls as
snow. Storage of water hi the snowpack controls
the seasonal timing of runoff in the Central Valley
rivers and has shaped the evolution of strategies for
water management and flood protection. Under
current climatic conditions, peak runoff occurs
between February and May for individual rivers
within the Central Valley Basin (California
Department of Water Resources, 1983; Gleick,
1987b).
Water Resources
Water Distribution
California's water resources are poorly
distributed relative to human settlement patterns in
the state. Over two-thirds of the state's surface
water supply originates north of Sacramento, and
CENTRAL VALLEY
DRAINAGE BASIN
0 40 80 Hiles
0 50 100 Kilometers 34'
• GISS
AfiFOL
• OSU
Figure 14-1. The Central Valley (shaded) and
Central Valley Drainage Basin of California.
Symbols refer to locations of general circulation
model (GCM) gridpoints. (See California Regional
Climate Scenarios section of this chapter for details
on GCMs).
70% of its population and 80% of its total demand
for water lie to the south (California Department of
Water Resources, 1985). In addition, about 85% of
the Central Valley Basin's total annual precipitation
occurs between November and April, whereas peak
water use occurs during the summer.
In working to solve these water distribution
problems, the U.S. Government and California have
built two of the largest and most elaborate water
development projects hi the world: the Federal
Central Valley Project (CVP) and the California
State Water Project (SWP). Both are essentially
designed to move water from water-rich northern
253
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Chapter 14
Delta
Pumping •/ *\
Plant 'Tracy*
Pumping
Plant
SOUTH BAY!
Figure 14-2. The San Francisco Bay estuary and locations of the freshwater pumping plants in the delta. The
numbered bars indicate distance (in miles) from the Golden Gate. The dotted line indicates the maximum area
affected by a 100-year high tide with a 1-meter (40-inch) sea level rise.
254
-------
California
LEGEND
^B Delta Waterways
[ I Above Sea Level
I | Sea Level to —10 Feet
-10 to-15 Feet
|^|^] —15 Foot and Deeper
20246
Scale In Miles
Figure 14-3. The Sacramento-San Joaquin River Delta. Shaded areas indicate land below sea level. See Figure
14-2 for location of the delta in the San Francisco Bay estuary.
255
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Chapter 14
California to the water-poor south, and to supply
water for agricultural, municipal, and industrial
purposes. Currently, the CVP has a water surplus
and the SWP has a shortage, especially in
relationship to users' projected requirements. Thus,
the SWP is particularly susceptible to dry years.
Flood Control and Hydroelectric Power
Another objective of the CVP and SWP is
flood control. By 1984, CVP facilities had
prevented almost $500 million in flood damages
(U.S. Bureau of Reclamation, 1985). Flood control,
however, comes at the expense of water storage
(and hence water deliveries), because reservoir
levels must be kept low to absorb high riverflows
during the rainy season.
Hydroelectric power generation is also an
objective of the CVP and SWP, and surplus power
is sold to utility companies. CVP powerplants
produce an average of 5.5 to 6 billion kWh per year.
In 1976 and 1977, precipitation was 35 and 55%
below normal, respectively, and hydroelectric power
generation fell to 50 and 40%, respectively, of target
production.
Sacramento-San Joaquin River Delta
The delta at the confluence of the Sacramento
and San Joaquin Rivers is the focal point of major
water-related issues in California (Figure 14-3). For
example, most islands in the delta lie below sea
level and are protected by levees, some of which are
made of peat and are relatively fragile. These
islands would be vulnerable to inundation from
rising sea level associated with climate warming.
The deep peat soils on these islands support highly
productive agriculture that would be lost if
inundated.
In addition to agricultural importance, the
delta is also the source of all CVP and SWP water
exports to points farther south, and in this regard
basically functions as a transfer point of water from
the north to the south. The freshwater pumping
plants (see Figure 14-3) in the delta are the largest
freshwater diversions in California (Sudman, 1987).
Delta outflow must be maintained at a required
level to prevent saltwater intrusion into the pumping
plants. The volume of water released from
upstream reservoirs to achieve this level is known as
carriage water.
Commerce
The San Francisco Bay estuary includes the
largest bay on the California coast (see Figure 14-
2). The bay's northern reach between the Golden
Gate and the Sacramento-San Joaquin River Delta
is a brackish estuary dominated by seasonally
varying river inflow (Conomos et al., 1985). The
southern reach between the Golden Gate and the
southern terminus of the bay is a tidally oscillating
lagoon-type estuary. The port facilities of the San
Francisco Bay area are vital to California's internal
trade, to Pacific coast commerce, and to foreign
trade, particularly with Asian countries. The ports
of Oakland and San Francisco, combined, ranked
fourth in the United States in tonnage of
containerized cargo handled in 1983 (U.S. Maritime
Administration, 1985). These facilities and
operations are sensitive, in varying degrees, to both
sea level change and fluctuation in freshwater
runoff.
Agriculture
California annually produces about 10% of the
cash farm receipts in the United States and
produced $14.5 billion in farm income in 1986 (U.S.
Department of Agriculture, 1987). Central Valley
farms make up significant proportions of total U.S.
production of many crops, including cotton, apricots,
grapes, almonds, tomatoes, and lettuce.
Agriculture, the primary land use and the
largest consumer of water hi the Central Valley
Basin, accounts for 87% of total net water use in
the region. Furthermore, the region accounts for
72% of total net water use for the entire state and
almost 80% of net agricultural use (California
Department of Water Resources, 1987a).
Forestry
Silviculture is extensively practiced in
California's mountains. The nine national forests
substantially within the Central Valley Basin
recorded over $88.6 million in timber sales in fiscal
year 1986 (U.S. Department of the Interior, 1986).
Forest productivity is sensitive to climate variation.
For example, the drought of 1976-77 contributed to
significant tree mortality because of large
infestations of bark beetles (California Division of
Forestry and Fire Protection, 1988).
256
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California
Natural Vegetation
Approximately one-fourth of all the threatened
and endangered plants in the United States are
found in California. About 460 species, or about
9% of the California species listed by Munz and
Keck (1959), are either extinct or in danger of
becoming extinct.
California contains about 5,060 native vascular
plant species; of these, about 30% occur only in
California (Munz and Keck, 1959; Raven, 1977).
These species are more numerous than those
present in the entire central and northeastern
United States and adjacent Canada, a region about
eight tunes larger than California (Fernald, 1950).
Within the Central Valley Basin, terrestrial
vegetation may be grouped into the following broad
classes, listed according to decreasing elevation:
alpine, subalpine forest, montane forest, mixed
evergreen forest, chaparral and oak woodland, and
valley grassland (Barbour and Major, 1977).
Wetlands
The San Francisco Bay estuary includes
approximately 90% of the salt marsh area in
California (Macdonald, 1977). Nichols and Wright
(1971) documented a 60% reduction in San
Francisco Bay marsh between 1850 and 1968. This
reduction was largely the result of reclamation for
salt ponds, agriculture, expanding urbanization,
shipping facilities, and marinas. Further loss of
wetlands could result in substantial ecological and
economic losses for the region. For example, the
managed wetlands north of Suisun Bay support a
hunting and fishing industry producing over $150
million annually (Meyer, 1987). Tourism, rare and
endangered species, and heritage values also could
be harmed.
Wildlife and Fisheries
The San Francisco Bay estuary provides vital
habitat for many bird and fish species (California
Department of Water Resources, 1983). The
estuary is an important wintering area for waterfowl
of the Pacific flyway. Important sport fish include
striped bass, chinook salmon, sturgeon, American
shad, and steelhead rainbow trout. These species
are anadromous (i.e., saltwater species that enter
freshwater areas for breeding), and the delta is an
important nursery for these species. Chinook
salmon also constitute an important commercial fish
species, and Central Valley rivers support about
75% of California's chinook salmon catch, valued at
$13.4 million at 1981 prices. The populations of
these species are affected by water quality in the
estuary.
To protect aquatic organisms in the delta, the
State Water Resources Control Board (SWRCB)
adopted water right Decision 1485 in 1978 that sets
water quality standards to protect the delta and
Suisun Marsh. The standards vary from year to
year, with less stringent requirements in dry years.
The standards are achieved by meeting minimum
delta outflow requirements. If delta outflow falls
below the required level, then releases from
upstream state and federal reservoirs must be
increased so that the outflow requirement is met.
The water quality standards take precedence over
water export from the delta.
Recreation and Nature Preservation
Recreation and nature preservation are
important in California. Major recreational areas in
the Central Valley Basin include four national parks
(Lassen Volcanic, Sequoia, Kings Canyon, and
Yosemite) and nine national forests that lie either
completely or largely within its boundaries. Two
national recreation areas and 13 designated wildlife
refuges and management areas also are situated in
the region. Downhill skiing and other winter sports
are economically important in the state. Water
projects throughout the Central Valley Basin
provide significant recreational opportunities.
PREVIOUS CLIMATE CHANGE
STUDIES
Two of the few studies previously undertaken
to assess the potential effects of climate change on
the region are discussed in this section.
Forests
Leverenz and Lev (1987) estimated the
potential range changes, caused by CO2-induced
climate change, for six major commercial tree
species in the western United States. Two of the
257
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Chapter 14
species, ponderosa pine and Douglas-fir, have
significant populations in California. Leverenz and
Lev based their estimates of range changes on the
species' response to increased temperature,
decreased water balance, and higher CO2
concentrations. The scenario of climate change
used was based on a simulation using the
Geophysical Fluid Dynamics Laboratory (GFDL)
model (a different run from that used for this
study), with CO, concentrations double their
present levels. Their results suggest that in
California, ponderosa pine could increase in range
and abundance because of its ability to withstand
long summer drought. Douglas-fir could be
eliminated from coastal lowlands in California but
might occur in coastal areas at higher elevations.
Water Resources
Gleick (1987a,b) applied 18 general circulation
model (GCM)-based and hypothetical scenarios of
climate change to a hydrologic model of the
Sacramento River Basin. He used a two-part water
balance model to estimate monthly runoff and soil
moisture changes in the basin. His results suggest
that winter runoff could increase substantially, and
summer runoff might decrease under most of the
scenarios. Summer soil-moisture levels might also
decrease substantially. These changes are driven by
higher temperatures, which decrease the amount of
winter precipitation falling as snow and cause an
earlier and faster melting of the snowpack that does
form.
CALIFORNIA STUDIES IN THIS
REPORT
Seven studies were completed as part of this
regional study of the possible impacts of climate
warming on California (Figure 14-4). These studies
were quantitatively integrated as much as possible
within the overall timeframe of this report to
Congress to obtain as complete a picture of those
impacts as possible. Also, several of the national
studies have results pertaining to California. At the
outset, it should be emphasized that most of these
studies used existing models, and most evaluated
potential climate change in terms of present
demands, values, and conditions (including the
current population and water delivery system).
Water is a key limiting resource in both
managed and unmanaged ecosystems in the Central
Valley Basin, and freshwater is important in
estuarine ecosystems in the delta region.
Consequently, the California studies were organized
so that the impacts of climate warming on the entire
hydrologic system could be examined, starting at
subalpine lakes in the mountains surrounding the
valley and finishing at the freshwater outflow into
the delta region and estuary (Figure 14-4). The
individual projects examined the potential impacts
of climate change and sea level rise on particular
ecosystems and water-delivery systems in the
Central Valley (see Chapter 4: Methodology). One
of the major goals of this regional study was to
determine how much runoff would flow into the
Central Valley from the surrounding mountains
under different scenarios of climate change, how
much of that runoff would be available for delivery
to the water users in the state, and how much would
reach the delta.
Analyses Performed for This Study
The following analyses were performed for this
study.
• Interpretation of Hvdrologic Effects of
Climate Change in the Sacramento-San
Joaquin River Basin - Lettenmaier and
Gan, University of Washington, and Dawdy,
consultant (Volume A)
The Lettenmaier et al. project is the first of a
series of four projects designed to determine the
impact of climate change on runoff and water
deliveries within the Central Valley Basin (Figures
14-4 and 14-5). Their project was designed to
estimate changes in runoff from the mountains to
the water resource system in the floor of the valley.
Lettenmaier et al. used data from climate scenarios
supplied by EPA as input to their modeling studies.
(See Chapter 4: Methodology, and the following
section, California Regional Climate Change
Scenarios).
• Methods for Evaluating the Potential
Impacts of Global Climate Change: Case
Studies of the Water Supply Systems of the
State of California and Atlanta. Georgia -
Sheer and Randall, Water Resources
Management, Inc. (Volume A)
258
-------
California
Hydrologic
Impacts
(Lettenmaier et al.)
1
Effects on
Water Deliveries
(Sheer and Randall)
i
r
Salinity Effects in
San Francisco
Bay Estuary
(Williams)
i
r
Sensitivity of
San Francisco
Bay Wetlands
(Josselyn and
Callaway)
CLIMATE
SCENARIOS
i r
CALIFORNIA
AGRICULTURAL
EFFECTS
(Dudek)
t
1
1
1
1
SEA LEVEL
RISE
SCENARIOS
Water Quality
of Subalpine Lakes
(Byron et al.)
TERRESTRIAL
VEGETATION
EFFECTS
(Davis)
National Studies:
- Agriculture
- Air Quality
- Electricity
Figure 14-4. Organization of the study, showing paths of data input from scenarios and between projects (solid
lines). Dashed lines indicate some important linakges between projects that were not quantitatively made in this
study.
Sheer and Randall used the projected runoff
from the mountains determined by Lettenmaier et
al. to simulate the response of the Central Valley
and State Water Projects to climate change. Output
from this study includes estimated total water
deliveries to State Water Project users.
• The Impacts of Climate Change on the
Salinity of San Francisco Bay - Williams,
Philip Williams and Associates (Volume A)
The main goal of Williams' project was to
determine the impact of sea level rise and changing
freshwater outflow into the delta on salinity within
the bay. Williams also determined how much
carriage water might be required to hold back
salinity intrusions from the delta pumping plants
after sea level rise. The new carriage water
requirements were then factored into Sheer and
Randall's simulation of the water resource system,
and they represent an important feedback between
the hydrologic effects of climate change and sea
level rise effects in the delta (see Figure 14-3).
• Ecological Effects of Global Climate
Change: Wetland Resources of San
Francisco Bay - Josselyn and Callaway, San
Francisco State University (Volume E)
Josselyn and Callaway used results from
Williams and Park (see Chapter 7: Sea Level Rise)
to assess the impact of changing salinity and sea
level rise on the wetlands within San Francisco Bay.
• Climate Change Impacts upon Agriculture
and Resources: A Case Study of California
- Dudek, Environmental Defense Fund
(Volume C)
Dudek simulated the impact of changing
climate on California agriculture. Besides using the
climate data from the different climate scenarios to
estimate crop productivity impacts, Dudek used
estimates of mean annual water deliveries for
259
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Chapter 14
NORTH FORK
AMERICAN RIVER
BASIN
MERCED RIVER
BASIN
Figure 14-5. The Central Valley Drainage Basin of
California. Shaded areas refer to the four study
catchments used by Lettenmaier et al. Dots
indicate the positions of the Castle Lake study site
(Byron et al., Volume E) and the five fossil pollen
sites (Davis, Volume D).
deliveries for irrigation under the different climate
scenarios as input to a regional economic model to
estimate shifts in land and water use. This
information was qualitatively used to compare
available future water supplies and future water
demand (see Figure 14-4). The ability of water
policy changes to compensate for climate impacts
was also evaluated.
• The Effects of Global Climate Change on
Water Quality of Mountain Lakes and
Streams - Byron, Jassby, and Goldman,
University of California at Davis (Volume
E)
Byron et al. studied the impact of climate
change on the water quality of a subalpine lake in
northern California (see Figure 14-5).
• Ancient Analogs for Greenhouse Warming
of Central California - Davis, University of
Arizona (Volume D)
Davis reconstructed the vegetation present hi
the Sierra Nevada during warm analog periods of
the Holocene to estimate the potential impact of
warming on the present-day vegetation in these
mountains (see Figure 14-5).
National Studies That Included Results for
California
• The Economic Effects of Climate Change
on U.S. Agriculture: A Preliminary
Assessment - Adams and Glyer, Oregon
State University, and McCarl, Texas A&M
University (Volume C)
Adams et al. conducted a national study of
agriculture to estimate shifts in land and water use.
Results pertaining to California are discussed in this
chapter.
• The Potential Impacts of Climate Change
on Electric Utilities: Regional and National
Estimates - Linder and Inglis, ICF, Inc.
(Volume H)
As part of a national study, Linder and Inglis
estimated future California electrical demands in
response to climate change.
• Examination of the Sensitivity of a Regional
Oxidant Model to Climate Variations -
Morris, Gery, Liu, Moore, Daly and
Greenfield, Systems Applications, Inc.
(Volume F)
Morris et al. describe possible interactions of
climate change and air pollution. Results pertaining
to California are discussed in this chapter.
CALIFORNIA REGIONAL
CLIMATE CHANGE SCENARIOS
Results from two GCM gridpoints were used
to drive the effects models used in most of the
260
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California
California studies. (For a discussion of how the
scenarios were developed and applied, see Chapter
4: Methodology.) Both gridpoints lie at 120°W, with
the northern gridpoint near the Oregon-California
border and the southern gridpoint south of
Sacramento (see Figure 14-1). Average
temperature and precipitation changes for both
gridpoints are displayed in Figure 14-6. Generally
large seasonal increases in mean temperature are
projected by the models. Winter temperatures are
between 1.7°C (OSU) and 4.9°C (GISS) warmer,
and summer temperatures are between 2.6° C
(OSU) and 4.8°C (GFDL) warmer. The OSU
model generally projects less warming than the
other two GCM models.
Annual precipitation increases in GISS by 0.28
millimeters per day (4.02 inches per year) and
remains virtually unchanged in the GFDL and OSU
scenarios. Seasonal changes are more varied. For
instance, spring rainfall in GFDL is 0.35 millimeters
per day (0.41 inches per month) lower, while spring
rainfall in the OSU and GISS scenarios is higher.
The scenarios also show a large difference in fall
precipitation (Figure 14-6).
Overall, the OSU scenario represents a smaller
change from the present climate, and GFDL and
GISS show larger temperature changes. The GISS
scenario has higher precipitation than the other two
scenarios. Generally, temperature increases are
larger in the northern gridpoints than in the
southern gridpoints. Changes in annual
precipitation are greater in the north in GISS and
show little regional difference for the other models.
A. Temperature
6 I
| | OSU
Spring
B. Precipitation
f <"
o
1 0.1
UJ 0
< -0.1
§ -0.2
—0.3
ton-
14-6. General circulation model (GCM) scenario results showing seasonal and annual (A) temperature
and (B) precipitation changes between GCM model runs at doubled CO, and current CO2 concentrations. The
values are averages of the two gridpoints used by the water resource modelers. (See Figure 14-1 for the location
of the gridpoints.)
261
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Chapter 14
RESULTS OF THE CALIFORNIA
STUDIES
Hydrology of Catchments in the Central
Valley Basin
Changes in mountain snowpack and runoff
could have a major 'impact on water supply and
quality in the Central Valley Basin. Lettenmaier et
al. used a hydrologic modeling approach to simulate
runoff under different climate scenarios; these
estimates then served as input to the simulation of
the Central Valley Basin water resource system
response to climate change (Sheer and Randall,
Volume A).
Study Design
The approach taken was to model the
hydrologic response of four representative medium-
sized catchments in the Central Valley Basin. Then
streamflows for 13 larger subbasins in the Central
Valley Basin were estimated using the results from
the four catchments. The four catchments chosen
(see Figure 14-5) for modeling range in size from
526 to 927 square kilometers (203 to 358 square
miles). Outflows for each basin were determined
using two hydrologic models that estimate snow
accumulation, ablation, and daily runoff. The
models were calibrated using a subset of the historic
record and were verified using an independent
subset of the data.
Lettenmaier et al. developed an additional
climate scenario besides those specified by EPA to
test the sensitivity of their results to changes in the
scenarios. The scenario they developed Included
only the GISS doubled COg temperature estimates;
precipitation was kept unchanged from the current
values. The purpose of this scenario was to
determine the sensitivity of runoff to temperature
changes alone.
To provide input for the water resource
simulation model of Sheer and Randall (Volume
A), Lettenmaier et al. developed a statistical model
that relates historic flows in the four study
catchments to historic flows in 13 larger subbasins
in the Central Valley Basin. This statistical model
was then used to estimate flows in the 13 subbasins
under the different climate scenarios.
Limitations
Results would be different if geographic and
temporal variability were not held constant within
each grid. Several assumptions made in this study
are important considerations in terms of limitations
of the results. The intensity of rainfall is the same.
Fewer rainfall events of higher intensity could
increase runoff relatively more than a greater
number of rainfall events of lower intensity. One
implicit assumption is that no long-term changes in
vegetation cover and composition would occur,
when in fact such changes are virtually certain (but
their hydrologic manifestations are difficult to
predict). If vegetation cover decreases, runoff could
increase, since less precipitation would be used by
plants.
Lettenmaier et al. assumed that the flows into
the water resource system were adequately
estimated from the study catchment flows using
their statistical model. One limitation of this model
was that the study catchments are at high elevations
and their runoff is strongly affected by changes in
snowfall, whereas some of the areas contributing
runoff to the water resource system are at lower
elevations with runoff driven primarily by rainfall
under present climatic conditions. Since the
principal change under the scenarios was a change
in snowfall accumulation patterns, the statistical
model was biased toward these effects and may have
somewhat overestimated the total effect of snowfall
change on the water resource system. However,
because basins at lower elevations have a relatively
small impact on the total hydrology, this bias
minimally affected the results.
Despite these limitations, the results from this
study are qualitatively robust. Any improvement in
the hydrologic modeling probably would not alter
the general nature of the results, although their
precision probably would increase.
Results
Total annual runoff from the four subbasins
would remain about the same or increase slightly
under the doubled CO2 scenarios, but major
changes occur in the seasonality of the runoff.
Runoff could be higher in the winter months than it
is today, because less of the precipitation would fall
as snow and the snowpack could melt earlier
(Figure 14-7A). As a consequence of higher early
winter snowmelt, spring and summer runoff would
262
-------
California
x. 60 -
Dec
Apr Jun
Month
Aug Oct
Feb Apr Jun
Month
Aug Dot
Figure 14-7. Mean monthly streamflows under difference climate scenarios for the Merced River Basin, one of
the the four study catchments modeled (see Figure 14-5 for locations of the study catchments): (A) results from
the three doubled CO, scenarios; and (B) results from the scenario incorporating only the temperature change
projected in the GISS model run, and from the 1930s analog scenario (Lettenmaier et al., Volume A).
substantially decrease under these scenarios. The
variability of the runoff could substantially increase
in the winter months. Winter soil moisture could
increase; evapotranspiration could increase in the
spring; and late spring, summer, and fall soil
moisture could decrease. A major shift in the
seasonally of runoff could occur in 50 to 75 years,
according to the transient scenario GISS A.
When only temperature changes were
incorporated into the climate scenario and
precipitation was held equal to the base case, total
annual runoff was estimated to be lower hi all four
catchments than in the scenario in which both
temperature and precipitation were changed (Figure
14-7). However, the seasonal shift in runoff, which
is the dominant effect of a general warming, would
be similar.
The scenario producing results that differed
the most from the other scenarios was the 1930s
analog. In this case, runoff was estimated to be
lower in most months in the four subbasins, but the
seasonal distribution of runoff was similar to the
base case (Figure 14-7B). The reason for this
difference is that the 1930s drought was mainly
caused by a reduction in 'precipitation, rather than
by an increase in temperature.
These results are consistent with those of
Gleick (1987b), in that higher temperatures cause a
major change in the seasonally of runoff. Since two
different modeling approaches using many climate
change scenarios produced similar results, these
results can be viewed as relatively robust.
Implications
The potential change in seasonality of runoff
could have significant implications for stream
ecosystems and the water resource system in the
Central Valley Basin. Reduction in streamflows in
the late spring and summer could negatively affect
aquatic organisms simply because of decreased
water volume. Wildlife using streams for food and
water also could be harmed. Water quality
probably could be degraded because pollutants
would become more concentrated in the streams as
263
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Chapter 14
flows decrease. The possible impacts on the water
resource system are discussed in the next section.
The decrease in spring, summer, and fall soil
moisture could have a strong impact on the
vegetation in the basin, with plants adapted to drier
conditions becoming more abundant at the expense
of plants adapted to higher moisture conditions.
These potential vegetation changes also could affect
wildlife, and perhaps water quality, through changes
in the nutrient composition of upland runoff and
changes in erosion rates.
Water Resources in the Central Valley
Basin
Changes in runoff under the different climate
scenarios could have a major impact on water
resources in the Central Valley. The study by Sheer
and Randall (Volume A) used estimates from
Lettenmaier et al. of streamflows into the Central
Valley to simulate how the water resource system
would perform under the various climate scenarios.
Particular emphasis was given to how water
deliveries to users would be affected by climate
change.
Study Design
To estimate the climate scenarios' impact on
water deliveries, Sheer and Randall used an existing
model of the California water resource system
currently used by the southern California
Metropolitan Water District (MWD) (Sheer and
Baeck, 1987). The model emulates the State of
California's Department of Water Resources
Planning Simulation Model (California Department
of Water Resources, 1986). The model used
hydrologic inputs to project water-use demands,
instream and delta outflow requirements, and
reservoir operating policies. Water requirements
were set at levels projected for 1990.
Two different sets of runs were made with the
model. The first involved running the model for
the different climate scenarios using current carriage
water requirements. Williams (see the following
section of this chapter, Salinity in San Francisco
Bay) determined that in response to rising sea level
and levee failure, carriage water might have to be
doubled to maintain the water quality at the delta
pumping plants (see Figure 14-2). Consequently,
Sheer and Randall ran the model a second time to
determine the effects of doubling the carriage water
requirement on water deliveries. Both simulations
were run with a monthly time step, with water
deliveries summarized on a yearly basis.
Interannual variation was used as an indicator of
delivery reliability.
Sheer held a meeting with representatives of
the California Department of Water Resources and
the U.S. Bureau of Reclamation to discuss the
results of his analyses and to obtain their responses
on how the water resource system would handle the
changes in runoff.
Limitations
The limitations to Lettenmaier's study carry
over to this one. Thus, interpretation of the results
of the simulation of the water resource system's
response to climate change should focus on how the
system deals with the change in seasonality of
runoff, rather than on the absolute values of the
model output. Also, the model was run using 1990
conditions, and changes in future management
practices, operating rules, physical facilities, water
marketing, agriculture, and demand were not
considered in the simulation.
Results
The simulation results suggest that both the
amount and reliability of water deliveries could
decrease after global warming. The decreases in
mean annual SWP deliveries were estimated to
range from 7% (OSU) to 14% (GISS) to 16%
(GFDL) (200,000 to 400,000 acre-feet) (Figure 14-
8). In some years, the decreases would be over
20% for all three doubled CO2 scenarios. The
projected decrease in water deliveries occurs despite
a slight increase in precipitation over current levels
in the climate scenarios and greater total outflow
from the delta. Deliveries to the CVP are not
reduced under the scenarios. Average monthly
outflow from the delta increases in the late fall and
whiter under the climate scenarios and is lower in
the spring (Figure 14-9). In comparison, the state
estimates that population growth and other factors
will increase demand for SWP deliveries by 1.4
million acre-feet by 2010 (California DWR, 1983).
The driving factor behind this decrease is the
change in seasonality of runoff. Higher winter
temperatures could lead to more of the winter
264
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California
-500
Figure 14-8. Mean annual change in SWP deliveries
(base case minus scenario). KAF = thousands of
acre-feet (Sheer and Randall, Volume A).
;\
GISS
......... GFDL
osu
Figure 14-9. Projected monthly delta outflows
under different general circulation model climate
scenarios (adapted from Sheer and Randall,
Volume A).
precipitation in the mountains falling as rain rather
than snow, and also to an earlier melt of the
snowpack. Consequently, more water would flow
into the system during the winter, and less during
the spring and summer. Given current operating
rules and storage capacity, much of the higher
winter runoff would be spilled from the reservoirs to
maintain enough storage capacity to capture heavy
runoff later in the rainy season and thus prevent
downstream flooding. When the threat of floods
decreases at the end of the rainy season in the
spring and the reservoirs could be filled, runoff into
the system would be reduced because of the smaller
snowpack. Thus, total storage would be lower at
the end of spring and water deliveries would be
lower during the dry summer months. With system
changes, the extra runoff could be stored. The shift
in the seasonality of runoff and the response of the
water resource system to that shift determine the
changes in monthly delta outflow (Figure 14-9).
Doubling the carriage water requirement in
the model run for the GFDL scenario would only
minimally affect SWP deliveries. This is because
the base period (1951-80) does not include a lengthy
drought period, during which the doubled carriage
water requirement could have a substantial impact
on deliveries.
The consensus of the meeting of the
representatives from the state DWR and the Bureau
of Reclamation concerning the potential changes in
seasonality of runoff was that the magnitude of this
change would be such that operational changes
alone would not markedly improve the system's
performance. One factor limiting the potential for
adjusting the system to the projected changes is the
likely need to provide for additional flood control
storage during the winter months because of higher
peak flows.
Implications
Under the three doubled CO2 climate
scenarios, water deliveries would be less than the
base case and could fall short of 1990 requirements.
Moreover, if carriage water requirements are
doubled, shortages during a prolonged drought
could become more significant. In comparison to
these projected changes, the severe drought of 1977
reduced water deliveries by over 50% from the
previous year. This decrease is over three times
greater than those projected by Sheer and Randall.
However, their study produced estimates of average
changes, while the 1977 value reflects an extreme
event over a short time period, which would have
to be dealt with less frequently and in a potentially
265
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Chapter 14
different manner than a more persistent shortfall in
average supply. Also, Sheer and Randall did not
consider future increases in water requirements
caused by population increases and changes hi the
state's economy, which would exacerbate the
projected water shortages. For instance, users and
managers project a 55% (1.3 million acre-feet)
increase hi water required by SWP users hi 2010
over the amount the system can reliably supply to
them today (California Department of Water
Resources, 1983).
The potential decrease hi water deliveries
could affect urban, agricultural, and industrial water
users hi the state. How the potential decrease
should be managed has many policy implications,
which are discussed at the end of this chapter.
On a positive note, the increase hi delta
outflow shows that more water could flow through
the Central Valley Basin under these scenarios, and
water deliveries could be increased if major new
storage facilities were constructed. However, this
would be an environmentally and politically
controversial option (see Policy Implications section
of this chapter).
Salinity in San Francisco Bay
Climate change could affect the San Francisco
Bay estuary in two ways: first, changes hi
precipitation and temperature could affect the
amount of freshwater runoff that will flow into the
bay; and second, global warming could cause sea
level to rise because of thermal expansion of the
water and glacial melting, which could hi turn affect
a wide range of physical characteristics hi the bay.
The major objective of the study by Williams
(Volume A) was to estimate the implications of
global warming and rising sea level on the size and
shape (morphometry) of the San Francisco Bay
estuary and on salinity hi the estuary.
Study Design
Williams' project was conducted hi three parts,
using two sea level rise scenarios and delta outflows
estimated by Sheer and Randall (Volume A). The
sea level rise scenarios are a 1-meter (40-inch) rise
with the levees hi the Sacramento-San Joaquin
Delta and San Francisco Bay maintained, and a 1-
meter sea level rise with levee failure. The first part
of this study involved estimating how sea level rise
would affect the shape of the bay by establishing the
elevation/area and elevation/volume relationships
for all areas below +3 meters (+10.0 feet)
according to National Geodetic Vertical Datum
(NGVD). In the second part of the study, the bays
tidal exchange characteristics were determined for
its future shape by using a tidal hydrodynamic
model (Fischer, 1970).
Finally hi the third part of Williams' study, the
bay's salinity under the combined impacts of sea
level rise and changing delta outflows was calculated
using a mixing model developed by Denton and
Hunt (1986). This model was first run with nine
different constant delta outflows (all months the
same) to establish new carriage water requirements
after sea level rise. (These requirements will also
meet the state water quality standards for Suisun
Marsh, as detailed in Water Rights Decision 1485.)
Once these were established, and Sheer and Randall
(Volume A) had run their simulation model with
the new requirements, the mixing model was run
again to determine the salinity regime hi the estuary
after climate change. Included in the model output
were average monthly and average annual salinities
hi different parts of the estuary under the different
scenarios.
Limitations
Because of the short time available for
analysis, Williams used some old and inaccurate
surveys hi the morphometric analysis instead of
making new surveys. These could produce errors of
plus or minus 20% hi the estimates of the estuary's
volume. In addition, some levees probably would be
maintained under any delta management plan, and
thus the flooding of the delta islands would not be
as extensive as assumed in the levee failure scenario.
Williams did not consider changes hi siltation and
erosion of sediments that would likely occur under
the different climate change scenarios. However,
erosion would probably have a significant impact on
water flow hi the delta. For instance, deepening of
the tidal channels hi the delta could lead to
intrusion of salinity farther upstream than projected
hi this study. In addition, more sophisticated
models of salinity and tidal ranges and exchanges
might improve the accuracy of the results. Finally,
the new carriage water requirements were based on
a steady-state analysis (e.g., constant delta outflows).
Changes in the hydraulics of the Sacramento-San
Joaquin Delta and Suisun Bay with sea level rise
266
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California
could increase these requirements. Williams' results
should be viewed as a preliminary estimate of
estuarine changes, with emphasis placed on the
direction of change, rather than on the absolute
amount of change.
Results
The morphometric analyses suggested that
given a 1-meter (40-inch) sea level rise and failure
of the levees, the total area of the estuary might
triple, and its volume could double. If the levees
are maintained, the increases hi area and volume
could be about 30 and 15%, respectively. The
amount of sea level rise would be less important to
the physical size of the bay than whether or not the
levees are maintained.
Under the sea level rise scenarios with levees
maintained, tidal ranges would not change
significantly from current conditions. If the levees
failed, downstream constrictions at Carquinez Strait
and to the east of Suisun Bay (see Figure 14-2)
would limit tidal transport and reduce tidal range in
the delta, assuming that erosion does not alter the
tidal characteristics of the delta
The results from the initial application of the
salinity model to constant delta outflows indicate
that monthly carriage water requirements might
have to be doubled to repel saline water from the
upper part of the delta. Also, whether or not the
levees are maintained would have little effect on the
salinity regimes in the bay according to the model's
results. However, because possible scouring of tidal
channels was not incorporated into the model, the
predicted salinity after levee failure is probably
underestimated.
Using Sheer and Randall's estimated delta
outflow with double carriage water, Williams also
estimated annual salinity hi the bay. The results
suggest that after a climate warming, a 1-meter sea
level rise, and failure of the levees, water of a given
average annual salinity could migrate inland
between 4 kilometers (2.5 miles) (GISS scenario)
and 9.6 kilometers (6 miles) (OSU scenario) (Figure
14-10).
Williams also calculated the average monthly
salinity for Suisun Bay for the three climate
scenarios, levee failure, and double carriage water
requirements. Monthly salinities would be higher
Figure 14-10. Movement of mean annual salinity
of 10 parts per thousand under different hydrology
scenarios. Other salinity levels move similar
distances (see Figure 14-2 for location of Suisun
Bay; Williams, Volume A).
for all months as compared with the base case,
except for winter and early spring months in the
GISS scenario. The greatly increased runoff of the
GISS scenario (see Figure 14-9) during these
months kept the salinity at the same level as the
base case. Williams additionally modeled the
frequency of a given salinity value in any month. In
June, for example, salinities that were exceeded in
50% of the years in the base case might be
exceeded hi 80% of the years in both the GISS and
OSU scenarios because of the lower outflows
predicted under these scenarios.
Implications
Rising sea level could place the delta islands
under increased risk of inundation, not only because
of higher water levels but also because the larger
area and volume of the San Francisco Bay estuary
could result hi greater wave energy and higher
erosion rates of the levees. Improving the levees
just to protect them against flooding at the current
sea level could cost at least $4 billion (California
267
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Chapter 14
Department of Water Resources, 1982). With
higher sea levels, the cost of maintaining the levees
would increase.
The large body of water created if all the
levees failed would have a longer water residence
time. This means that any contamination (salt or
other pollutant) would be more difficult to flush out
of the delta region. Also, if saline water fills the
islands when levees fail, significant amounts of
freshwater would be needed to flush out the salt.
Increasing salinity could necessitate increases
in carriage water to maintain freshwater at the
export point in the delta or could require developing
a different method to convey freshwater from
reservoirs to users. Assuming the current water
management system is not expanded, the increase in
carriage water coupled with the decrease in
reservoir storage would most likely mean reduction
in water deliveries to at least some of the system's
users during extended droughts. With higher future
water requirements, shortages caused by the higher
carriage water requirements may not be limited to
extended droughts. An increase in sea level could
make navigation easier, temporarily reducing the
need for dredging of navigation channels. On the
other hand, a rising sea level could threaten fixed
port terminals and piers.
Wetlands in the San Francisco Bay
Estuary
Climate warming could alter two important
physical factors that affect wetland distribution: sea
level and freshwater outflow. Major impacts of sea
level rise could include erosion and marsh
inundation. Changes in freshwater outflow can
change the distribution and productivity of estuarine
plants and animals. Josselyn and Callaway (Volume
E) estimated the possible effects of climatic
warming on deep-water and wetland habitats of the
San Francisco Bay estuary (see Figure 14-2).
Study Design
Josselyn and Callaway examined the impacts of
a 1-, 2-, and 3-meter (40-, 80-, and 120-inch) sea
level rise by the year 2100. Of the three scenarios,
a 1-meter rise by the year 2100 is regarded as the
most probable (NRC, 1987). Models were used to
estimate rates of sea level rise from 1990 through
2100 under these three scenarios. The relationship
between sedimentation rates required for marsh
maintenance and sea level rise rates was examined.
The effects of salinity changes on the distributions
and abundances of organisms were related to
various freshwater outflow scenarios developed by
Sheer and Randall (see Figure 14-9). In the
absence of appropriate quantitative models, biotic
changes in the estuary in response to changing
salinity were qualitatively determined based on
literature review and expert judgment.
Limitations
Circulation and sedimentation in the estuary
could change dramatically as sea level rises and if
levees fail. The specific characteristics of these
biologically important changes are unknown at
present and were not considered in this study. The
sea level rise scenarios did not consider the
possibilities of sudden changes in sea level.
Increased water temperature, which may directly
affect the reproduction, growth, and survival of
estuarine organisms, or may have an indirect effect
through changes in oxygen availability, also was not
considered. Although specific impacts on plant and
animal species in the estuary are difficult to assess,
the general impacts would most likely be similar to
those reported here.
Results
Rates of sea level rise from 1990 to 2040 for
the three scenarios are presented in Figure 14-11.
Once the rate of sea level rise exceeds the rate of
sediment accretion, tidal marsh habitats would
become inundated and erosion of the marsh edge
could increase. For the 1-meter rise scenario, the
rate of rise was not estimated to exceed maximum
accretion rates (7 to 8 millimeters per year) until
about the year 2040. For the 2- and 3-meter (80-
and 120-inch) rise scenarios, the rate of sea level
rise could exceed accretion rates after 2010 and
2000, respectively (Figure 14-11).
Peak primary productivity, at present, occurs in
early spring hi San Pablo Bay and in the summer in
Suisun Bay. These maximum productivity levels
could be substantially reduced, particularly for
brackish and freshwater plant species, under the
higher salinities of the OSU scenario (see Figure
14-10). Peak spring production might also shift
upstream into the delta if levees fail. However,
under the higher freshwater outflows of the GFDL
268
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California
E.
UJ
l-
oc
z
DC
o
o
Q
LU
1990
2000
2010
2020
2030
2040
YEAR
Figure 14-11. Estimated sea level rise at San Francisco for three scenarios by the year 2100 (Josselyn and
Callaway, Volume E).
and GISS scenarios, the locations of maximum
production levels might remain in their present
positions if the levees are maintained. If the levees
fail, primary production could increase in the
extensive shallow water and mudflat areas created.
Since many areas currently protected by levees
are 1 to 2 meters (40 to 80 inches) or more below
sea level, levee failure would cause them to become
deepwater areas rather than marshes (see Figure
14-3). Eventually, enough sediment might be
deposited hi these formerly leveed areas to support
marsh development. Inundation of marshes and
salinity impacts on freshwater and brackish-water
plant species could reduce sources of food and
cover for waterfowl. Loss of emergent vegetation
could significantly reduce the numbers of migratory
waterfowl using the managed wetlands along Suisun
Bay's north shore.
If levees are maintained under conditions of
sea level rise, salt may build up behind them from
the evaporation of standing water. This salt would
cause marsh vegetation to die back and reduce the
value of these wetlands to wildlife.
Freshwater outflows estimated during
springtime under the climate change scenarios (see
Figure 14-9) maybe too low to support anadromous
fish (saltwater fish that enter freshwater areas for
spawning). Lower outflows could result in declines
among these populations (Kjeldson et al., 1981).
If levees failed, a large inland lake with fresh
to brackish water quality could be created in the
delta. Striped bass and shad spawn in essentially
freshwater conditions and their spawning could be
reduced under increased salinity, especially if they
did not move upstream to relatively fresh water.
Marine fish species could increase hi abundance in
the Suisun and San Pablo Bays in response to the
projected higher salinities, and freshwater and
anadromous species could decrease.
Implications
The loss of wetlands could result in substantial
ecological and economic losses for the region. For
example, the managed wetlands north of Suisun Bay
support a hunting and fishing industry valued at
over $150 million annually (Meyer, 1987). Tourism,
hunting, fishing, rare and endangered species, and
heritage values also could suffer.
California Agriculture
California's agricultural production is highly
dependent on irrigation, which accounts for
approximately 80% of the state's net annual water
269
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Chapter 14
use. Dudek (Volume C) used existing
agroecological models to explore potential responses
of California agriculture to climate change.
Study Design
Climate changes from the GISS and GFDL
doubled CO2 scenarios were linked to an
agricultural productivity model adapted from
Doorenbos and Kassam (1979). Growth responses
to both climate change and climate change plus
dkect effects of carbon dioxide were modeled.
These productivity responses were then introduced
into the California Agriculture and Resources
Model (CARM) (Howitt and Mean, 1985), which
estimates the economic and market implications of
such changes. Mean surface water supplies under
the base, GISS, and GFDL scenarios, calculated
from the simulations of Sheer and Randall (Volume
A), were also used as inputs into CARM.
Limitations
The COg direct effects results should be
viewed as preliminary, since they are based on data
from growth chamber experiments that may poorly
represent field conditions. This study did not
consider changes in crop varieties, planting dates,
energy costs, water-use efficiency, changes in the
status of groundwater resources under a changed
climate, or possible changes in delta agricultural
acreage caused by flooding after levee failure. Also,
new crop/location combinations were not
considered, nor were changes in soil quality such as
increases in salinity. The interaction between
climate change and direct CO2 effects on
productivity were not examined but may significantly
limit potential growth increases. The effects of
climate changes on other agricultural production
regions in the nation and the rest of the world were
not considered. These could be major factors in
determining how California farmers respond to
climate change. Given these limitations, realistic
estimates of agricultural responses to climate change
may be difficult to obtain. The results maybe more
valuable as indications of sensitivity than as specific
impacts.
Results
Relative to the 1985 base, yields could be
significantly reduced for California crops in
response to climate changes alone (i.e., without
consideration of the direct effects of CCO.
Generally, the greatest impacts are estimated under
the hotter GISS scenario. Table 14-1 presents
regional yield changes for sugarbeets, corn, cotton,
and tomatoes. These projections were generated by
the agricultural productivity model and did not
consider economic adjustments or water supply
limitations. Tomatoes might suffer the least
damage, with yields reduced by 5 to 16%.
Sugarbeets could be hardest hit, with declines of 21
to 40%. Yield reductions in sugarbeets were
estimated to be greatest in the relatively hot interior
southern regions. Differences in growth response
between the two climate scenarios are greatest for
corn and least for tomatoes.
Without economic adjustments, corn yields are
estimated to decline by 14 to 31%, based on the
agricultural productivity model under the GISS
scenario (Table 14-1). With economic adjustments,
declines of roughly 15% were estimated, a result at
the lower end of the direct productivity impacts.
When the dkect effects of CO2 on crop yields
were considered, yields of cotton and tomatoes
generally increased over the 1985 base (Table 14-
1). Corn and sugarbeets were generally estimated
to be unable to increase growth in response to
increases in CO2 concentration, although yield
reductions were not as great as with climate change
alone (Table 14-1). Cotton could benefit the most
from inadvertent CO2 fertilization, with yields
increasing in most cases by 3 to 41% (although
under the GISS scenarios in the Sacramento Valley,
they were estimated to decrease by 2%).
Potential increases in yields in response to
CO2 fertilization might be achieved only at a cost of
increased groundwater extraction in many areas.
For example, when surface water use was projected
at 100% of capacity, as in the Central Coast regions,
higher water requirements would necessitate
increased groundwater usage (Figure 14-12).
However, increased crop yields may offset increased
economic costs of water.
Regionally, across all scenarios (not
considering potential changes outside California) the
largest reductions in crop acreage were projected in
the Imperial Valley, while the delta region showed
the largest gains in acreage (Figure 14-12). This
expansion of agriculture in the delta region would
270
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California
Table 14-1. Regional and Statewide Percentage Yield Changes (relative to 1985) Under Different
General Circulation Model Climate Scenarios3
Crop
Regionb
South Coast
Los Angeles
North Interior
Red Bluff
Sacramento Valley
Sacramento
Southern San Joaquin
Fresno
Southern Deserts
Blythe
CARM Statewide
Scenario
GISS
GFDL
GISS
GFDL
GISS
GFDL
GISS
GFDL
GISS
GFDL
GISS
GFDL
sugarbeets
CC Net
-27
-21
-34
-26
-29
-24
-34
-32
-40
-39
-31
-25
-3
5
-11
0
-3
3
-14
-13
-2
0
-8
-1
corn
CC
-22
-3
-17
-14
-14
-8
-19
-13
-31
-14
-15
-10
Net
-18
3
-12
-9
-9
0
-14
-7
-27
-8
-10
-4
cotton
CC
-22
-4
-30
-26
-34
-32
-29
-26
-28
-19
-29
-26
Net
11
41
3
9
-2
2
6
11
6
21
6
11
tomatoes
CC Net
-8
-5
-16
-14
-14
-12
-15
-15
-13
-12
-14
-13
17
20
10
12
13
15
10
10
13
15
12
13
aRegional changes were projected by the Doorenbos and Kassam agricultural productivity model, while statewide
production changes were projected by the California Agriculture and Resources Model (CARM). The latter
estimates included economic adjustment. "Net" includes the direct effects of increases in CO2 and climate
change (CC).
bRefer to Figure 14-12 for locations.
Source: Dudek (Volume C).
depend on maintenance of levees protecting the
farmland. Without a consideration of CO2
fertilization, statewide crop acreage was estimated
to be reduced by about 4 to 6% from the 1985 base.
When CO2 direct effects were considered, statewide
crop acreage was estimated to be approximately
equal with 1985 base levels.
Implications
Regional changes in cropping locations and
patterns of water use imply potential exacerbation
of existing nonpoint source pollution and
accelerated rates of groundwater overdraft with
ensuing environmental impacts.
Changing water supply requirements may result
in increased conflicts between water users. In
addition, shifts in the location of agricultural
production could affect the future viability of natural
systems. Such shifts could also have a significant
impact on the economic health of small agricultural
communities.
271
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Chapter 14
crop acreage groundwater surface water
groundwater surface water
Northern San Joaquin
crop acreage groundwater surface water
crop acreage groundwater surface water
Southern San Joaquin
crop acreage groundwater surface water
crop acreage groundwater surface water
LEGEND
GISS Climate Change
GFDL Climate Change
GISS Net Effect
GFDL Net Effect
crop acreage groundwater surface water
Figure 14-12. Regional crop acreage, groundwater use, and surface water use under different GCM climate
scenarios. Net effect includes the direct effects of increases in CO2 and climate change. The resource use
indices represent the ratio (as percentages) of scenario results to the 1985 base period (Dudek, Volume C).
272
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California
Regional Implications of National
Agriculture Changes
Adams et al. conducted a national agricultural
study that included results relevant to California
(Adams et al., Volume C). The results of the study
are not directly comparable with the results from
Dudek's study (discussed above), since Adams et al.
considered national agricultural impacts and
aggregated California into a Pacific region with
Oregon and Washington. Further, the two studies
did not examine the same set of crops and modeled
productivity differently. (For a description of the
study's design and methodology, see Chapter 6:
Agriculture.)
Adams et al. (Volume C) estimated that
national crop acreage could decline by 2 to 4% in
response to climate change, but Pacific Coast State
acreage could increase by 18 to 20%. This increase
in the Pacific region is attributable to the region's
extensive use of irrigated agriculture. In contrast,
most other regions of the United States
predominantly use dryland fanning, and crop
acreage might decline in response to moisture
stress. The Adams et al. approach was based on
maximizing farmers' profits and indicates that
higher yields associated with direct CO2 effects
might result in further declines in crop acreage (or
in the case of the Pacific Coast States, a smaller
increase), since fewer acres might be required to
produce the necessary crops.
Water Quality of Subalpine Lakes
Subalpine lakes are common hi the California
mountains, and many of these are the source of
streams and rivers flowing down into the lowlands.
Changes in the water quality of these lakes could
significantly alter their species composition and
nutrient dynamics and also could have an impact on
downstream water quality and ecosystems. The
sensitivity of California's subalpine lakes to weather
variability and climate change has not been
extensively studied. Consequently, Byron et al.
studied how climate controls the water quality of
Castle Lake, a subalpine lake in northern California
(see Figure 14-5).
Study Design
Goldman et al. (1989) correlated an index of
water quality, primary production (i.e., the amount
of biomass produced by algae in the lake) with
climate variability at Castle Lake. Subsequently,
Byron et al. (Volume E) were able to develop
empirical models relating primary production with
various climate parameters.
Limitations
Their model was limited to estimating annual
values of primary production; seasonal variability
was not calculated. The model also did not project
changes in species composition and nutrient
dynamics, which could have important consequences
for water quality. Changes in upland vegetation and
nutrient cycling, which could also affect the lake's
water quality, were not part of the model.
The estimates of annual primary production
produced by this model are precise, although the
results are general hi the sense that no species-
specific projections are made.
Results
Byron et al. estimate that mean annual primary
production could increase under all three doubled
CO2 scenarios, with increases ranging from 16%
(OSIT scenario) to 87% (GISS scenario) (Figure 14-
13). The OSU results are within one standard error
of present production. Thus, under this scenario,
there would be no significant decrease in water
quality. The increase in annual primary production
hi the transient scenario was only statistically
significant in the last decade of the transient
scenario (2050-59). Primary production hi the last
decade was estimated to be 25% greater than the
base case.
The increase in annual primary production is
attributed principally to the temperature increase
projected by the scenarios. The higher
temperatures would result in less snow
accumulation, which is correlated with an earlier
melting of the lake ice and a longer growing season.
Implications
Higher primary production could result in
climatic effects being indirectly felt at higher points
273
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Chapter 14
000 -
700-
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5
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£ 300-
| SOO-
100
0M«n
1 9SX Conttdeitea Interval
J
w
I
Meuured
I
Moda
•
•
GFDL GISS OSU
Figure 14-13. Annual primary production estimates
for Castle Lake showing actual and model values
for present conditions and model values for three
GCM climate scenarios (see Figure 14-5 for the
location of Castle Lake). Solid bars show the 95%
confidence interval for each estimate (Byron et al.,
Volume E).
in the Castle Lake food web and could affect the
lake's nutrient dynamics.
Extrapolating these results to other subalpine
lakes suggests their water quality could decrease and
their species composition might change after climate
warming. Increased primary production could
provide additional food for other aquatic organisms,
such as fish, but could also degrade water quality by
ultimately causing a decrease in dissolved oxygen
and by blocking light filtration to lower levels.
Fisheries in unproductive lakes may be enhanced,
although trout populations may suffer in lakes
where temperatures rise past a threshold value and
oxygen levels drop too low.
Changes in production and concomitant
changes in nutrient dynamics could affect
downstream river and reservoir water quality.
However, since the streams draining subalpine lakes
are well oxygenated, the increased biomass entering
them would most likely be rapidly decomposed and
probably would not affect the water quality of lower
reaches of streams and rivers.
Summary of Effects on Water Resources
In terms of economic and social importance,
changes in water resources are among the most
important possible effects of climate change in
California. A wide variety of factors related to
climate change could affect water resources, ranging
from those factors changing water supply to those
affecting water requirements. All the individual
projects discussed above addressed some aspect of
climate impacts on water resources in the state.
However, these studies did not consider all the
major factors that could affect California water
resources in the next century, mainly because of the
complexity and inherent difficulties in forecasting
future requirements for water. This section
discusses other factors that would affect future
water demands not directly considered by the
individual studies, including future changes in
agriculture, population, water-use efficiency, and
sources of water, including groundwater.
Dudek's study used estimates of water
deliveries from Sheer and Randall's study, but
changes in agriculture that he determined, and
hence changes in agricultural demand for water, are
not factored back into the water simulation model.
For instance, Dudek's results indicate that because
of climate conditions, crop acreage in the Imperial
Valley decreases, freeing water used there for
irrigation to be used elsewhere in the state if water
institutions permit such transfers. Also, as cropping
patterns change, so does the pattern of needed
water transfers via the water resource system, thus
affecting water deliveries. Finally, Dudek found that
groundwater usage can increase when the direct
effects of CO2 are included in his model. Estimated
groundwater usage is projected to increase when
full use of surficial water sources does not meet
agricultural demands estimated in the model. Thus,
Dudek's results suggest that agricultural demand for
water could exceed surficial supplies after climate
warming, further exacerbating water shortages.
Not considered in the overall California study,
but critical to determining the magnitude of
potential water shortages in the next century, are
population growth and accompanying changes in
water demands. Projections of population growth
place the state's population at about 35 million in
2010 as compared with 24 million in 1980, an
increase of 45% (California Department of Water
Resources, 1983). As mentioned earlier,
274
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California
requirements for SWP deliveries by urban,
agricultural, and industrial users could increase by
50% over what the system can reliably supply today.
This shortfall by itself is significantly greater than
the decrease in deliveries caused by the climate
scenarios as determined by Sheer and Randall.
If water shortages become more common,
agricultural, industrial, and residential users will
probably change their water-use efficiency. Changes
in efficiency could moderate possible future
shortages. Any change in water pricing or water
law also could affect water demand and supply, but
these changes are very difficult to project far into
the future.
Groundwater usage is discussed by Dudek, but
the overall impacts of climate change on
groundwater are not addressed in this project. As
demand for water increases beyond the capability of
the water resource system to deliver the needed
water, mining of groundwater (as Dudek shows for
agriculture) is one option users could adopt to meet
their demand. Using groundwater could lessen the
severity of water shortages hi the short term but
presents environmental problems, such as land
subsidence, over the long term.
In general, given the current water resource
system, qualitative considerations of future changes
in water requirements suggest that future water
shortages could be significantly greater than
estimated here for climate change alone.
Vegetation of the Sierra Nevada
To better understand the sensitivity of natural
vegetation in California to climate change, Davis
(Volume D) studied changes that have occurred
over the past 12,000 years in terrestrial vegetation
growing in the California Sierra Nevada. Changes
in vegetation that occurred during this period
suggest how the vegetation that currently exists in
the mountains could respond to future climate
changes. The middle latitudes of the Northern
Hemisphere are believed to have been warmest (1
to 3°C warmer than today) about 6,000 years ago
(Budyko, 1982), and parts of western North
America were apparently warmest 9,000 years ago
(Ritchie et al., 1983; Davis et al., 1986). Thus, the
period between 6,000 and 9,000 years ago in
California could present a possible analog to a
warmer future climate.
Study Design
The composition of the vegetation that existed
in the central Sierra Nevada over the last 12,000
years was determined using fossil pollen analysis.
Fossil pollen samples were collected from five lakes
situated along an east-west transect (see Figure 14-
5) passing through the major vegetation zones of the
Sierra Nevada. Dissimilarity values were calculated
between modern and fossil pollen samples to
determine the past vegetation at a particular site.
Limitations
The climate estimated in the three doubled
CO, scenarios is different from the climate that
probably existed between 6,000 and 9,000 years ago
in the Sierra Nevada, according to Davis's
interpretation of the region's vegetation history.
Davis suggests that 9,000 years ago, the climate was
drier than it is today, Whether it was warmer or
cooler is uncertain. The climate 6,000 years ago
was not much different from the modern climate.
Thus, the analog climates are in marked contrast to
the warmer climate estimated by all three GCMs
for the gridpoint closest to the western slope of the
Sierra Nevada. Also, the models suggest that total
annual precipitation will not significantly change.
Consequently, the results of this study do not
provide an indication of how the present-day
vegetation could respond under the climate
scenarios constructed from the GCMs.
Nevertheless, they do present a possible analog for
how Sierra Nevada vegetation could respond to an
overall warmer Northern Hemisphere climate that
produces a drier but not significantly warmer Sierra,
Nevada climate.
Furthermore, the warming 6,000 to 9,000 years
ago occurred over thousands of years, as opposed to
the potential warming within a century. Thus, the
analog does not indicate whether vegetation would
be able to migrate and keep up with a relatively
rapid warming.
Another constraint associated with using the
past as an analog to trace gas-induced warming is
that carbon dioxide levels were lower during the
past 12,000 years than those projected for the next
275
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Chapter 14
century. Higher carbon dioxide concentrations
could partially compensate for adverse effects of
higher temperatures and lower moisture levels on
tree growth. The extent of this compensating effect
is uncertain at this time. Nevertheless, the
possibility exists that the magnitude of the
vegetation change in the past to a warmer
hemispheric climate could have been less if carbon
dioxide concentrations had been higher.
A relatively small set of modern pollen samples
was available for comparison to the fossil samples;
therefore, the precision of the vegetation
reconstruction is uncertain. Also, the precision of
the estimated elevational shifts in the vegetation
zones is low because of the limited number of fossil
sites available for the analysis. Nevertheless, this
study provides a good general summary of the
vegetation changes in the Sierra Nevada during the
past 12,000 years.
Results
The forests existing in the western Sierra
Nevada 9,000 years ago resembled those found east
of the crest today (Figure 14-14), with lower forest
cover and tree density. Pine and fir densities, in
particular, were lower. Between 9,000 and 6,000
years ago, the vegetation gradually became similar
to the modern vegetation in the same area, and by
6,000 years ago the modern vegetation zones were
established on both sides of the Sierra crest. The
vegetation 6,000 years ago was subtly different from
that in the area today, with less fir and more sage.
The forests may have been slightly more open than
today.
Implications
If climate conditions of the Sierra Nevada in
the next century become similar to those that
existed 9,000 years ago, major changes could occur
in forest composition and density. The vegetation
changes could generate significant environmental
impacts, ranging from changes in evapotranspiration
and related hydrogeological feedbacks to changes
in nutrient cycling and soils, which could degrade
the water quality of mountain streams. Fire
frequency could increase as a function of changes in
fuel loads and vegetation. If dead wood rapidly
builds up because of the decline in one or more tree
species, large catastrophic fires could occur.
If future forests west of the Sierra crest
become similar to current forests east of the crest,
timber production could significantly decline. Based
on inventory data from national forests, timberlands
east of the crest currently support only about 60%
of the wood volume of timberlands west of the crest
(U.S. Forest Service, Portland, Oregon, personal
communication, 1988). Different future climates
could also necessitate changes in timber practices
(e.g., reforestation techniques).
Vegetation change in response to climate
change could produce additional stress for
endangered animal species as their preferred
habitats change. Populations of nonendangered
wildlife also could be affected as vegetation changes.
Since the GCMs estimate a different future
climate than the climate reconstructed for the
analog period, it is important to consider how the
vegetation in the Sierra Nevada could respond
under the GCM-based climate scenarios as
compared with the way it responded during the
analog period. Recall that the climate in the GCMs
is estimated to be significantly warmer than today's
climate, with similar amounts of precipitation, while
the analog climate was significantly drier with
similar temperatures. One major difference in the
impact of the two types of climate scenarios could
be in the response of species at higher elevations in
the Sierra Nevada. Since growing season length and
warmth are. generally considered to control the
position of timberline (Wardle, 1974; Daubenmire,
1978), warmer temperatures under the GCM
scenarios could be expected to raise the timberline.
The timberline was not significantly higher during
the analog period. Higher temperatures could also
increase the elevation of other vegetation zones in
the Sierra Nevada.
Another effect of higher temperatures in the
GCM scenarios that would probably affect
vegetation at all elevations is a reduction in effective
moisture during the growing season. Lettenmaier et
al. (Volume A), in fact, estimate such a decrease as
soil moisture decreases in late spring, summer, and
fall compared with the base case. Furthermore, for
lower elevations at least, the growing season could
be effectively shortened because of the earlier onset
of moisture stress after winter rains. One result of
this could be the extension of grasslands and
chaparral higher up the slopes of the Sierra Nevada.
276
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California
4000
3000
2000
1000
0
3000
2000
1000
0
4000 •
3000 -
2000 •
1000 -
0 J
Elev. (m)
MODERN
Tioga Pass Pond a
Starkweather a
Exchequer
Balsam ~
(West)
(East)
Tioga Pass Pond
(East)
Tioga Pass Pond u
(West)
(East)
Figure 14-14. Vegetation zonation in the central Sierra Nevada at present; 6,000 years (6K) before present; and
9,000 years (9K) before present. (See Figure 14-5 for approximate locations of fossil pollen sites.) The dashed
lines indicate uncertainty in the placement of vegetation zone boundaries (Davis, Volume D). SA = subalpine;
UM = upper montane; ES = eastern subalpine; and PF = pine forest.
Also, reduced moisture availability could alter the
outcome of competition between plant species with
different growth forms and longevity, thus changing
the composition of the vegetation zones. Plant
species with drought-resistant characteristics would
probably increase in relative abundance. One
possible consequence of this shift in species
abundance is the formation of plant communities
that resemble in some aspects plant communities
that occurred 9,000 years ago. However, the
complicating factor of more direct effects of higher
temperatures makes such a projection uncertain, as
does the lack of consideration of the direct effects
of increasing concentrations of carbon dioxide.
Electricity Demand
Electric power demand is sensitive to potential
climate change. As part of a national study, Linder
and Inglis estimated California's energy demand for
the years 2010 and 2055. (For a description of the
study's design and methodology, see Chapter 10:
Electricity Demand.)
In California, climate change scenarios result
in only small changes in estimated electrical utility
generation and costs by the year 2010. Annual
277
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Chapter 14
power generation is estimated to increase by 1 to
2% (over the 345 billion kWh estimated to serve the
California population and economy in 2010), and
new generation capacity requirements would be less
than 1% greater than increases without climate
change. By the year 2055, annual power generation
is estimated to increase by 3% under lower growth
of electricity demand (604 billion kWh base) to 5%
under higher growth (794 billion kWh base). New
generation capacity requirements would be 14 to
20% greater than non-climate-induced needs. Then
cumulative investments in new capacity could cost
$10 to $27 billion (in 1986 dollars).
Implications
More powerplants may be required. These
would need more cooling water, further depleting
the water supply. Climate-induced changes in
hydrology may reduce hydropower generation and
increase dependence on fossil fuels and nuclear
power. Increased use of fossil fuels may provide
positive feedback for the greenhouse effect and may
deteriorate local air quality. The increased utility
rates that may be required to pay for new power
generation capacity may limit groundwater pumping
for agriculture.
Air Pollution
Morris et al. (Volume F) studied possible
interactions of climate change and air pollution in
California. They estimated the impacts of climate
change on ozone concentrations using a regional
transport model. The values they calculated should
be viewed as coarse approximations because of the
limitations in the application of the model. For
instance, the study looked only at changes in
temperature and water vapor and kept as
unchanged many other important meteorological
variables. An important unchanged variable was
mixing height. Instead of remaining unchanged,
mixing height could increase with rising
temperatures. This would have a dilution effect on
air pollution. (The study's design limitations and
methodology are discussed in Chapter 11: Air
Quality.)
Morris et al. estimated that ozone
concentrations could increase up to 20% during
some days in August in response toa4°C(7°F)
climate warming in central California. The National
Ambient Air Quality Standard (NAAQS) for ozone
is 12 ppm. Morris et al. estimated that the number
of August days that exceed this standard could
increase by 30%. Furthermore, the area exceeding
the NAAQS could increase by 1,900 square
kilometers (730 square miles), and the number of
people exposed to these elevated ozone levels could
increase by over 275,000.
Implications
Trace gas-induced climate change may
significantly affect the air's chemistry on local and
regional scales. These changes may exacerbate
existing air quality problems around California
metropolitan areas and agricultural areas of the
Central Valley, causing health problems and crop
losses. Increases in air pollution may directly affect
the composition and productivity of natural and
managed ecosystems.
POLICY IMPLICATIONS
An overall question applies to resource
management in general: What is the most efficient
way to manage natural resources? Currently,
management is based on governmental jurisdiction
with, for example, forests managed at the local,
state, or federal level. Management of hydrologic
systems is also based on governmental jurisdiction.
An alternative would be to manage these systems
using natural boundaries as the criteria for
determining management jurisdiction. The pros and
cons of such a management strategy deserve at least
some preliminary research.
Water Supply and Flood Control
Water supply is the basis for most economic
development in California. Yet, almost all the
water available in the SWP is allocated for use. A
major problem is to accommodate rising demand
for water, interannual climate fluctuations, and the
need to export water from northern to southern
California.
In addition, the results from these studies
suggest that climate change over the next 100 years
could cause earlier runoff, thus reducing water
deliveries below their projected 1990 level. This
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situation (together with increasing requirements for
water caused by increasing population) would create
a set of major policy problems for the water
managers and land-use planners in California.
Two major policy questions can be raised
concerning the possible reduction in water
deliveries: How can the water resource system be
changed to prevent a decrease in water deliveries
caused by climate change? If water deliveries fall
short of demand, how should potential water
shortages be allocated?
Approaches for Modifying the Water Resource
System
Several possible approaches can be attempted
to increase water deliveries. First, system
management can be modified. For instance, the
most recent SWP development plan suggests the
possibility of state management of both SWP and
CVP facilities (California Department of Water
Resources, 1987a). Complete joint management
could produce more than 1 million acre-feet (maf)
additional reliable yield in the system. Steps toward
greater cooperation have been taken. The
Coordinated Operating Agreement (H.R. 3113)
between the SWP and the CVP, ratified in 1986,
allows the SWP to purchase water from the CVP.
Using conservation techniques and improving the
efficiency of transfer might also increase water
deliveries.
Operating rules for the reservoirs also could be
modified to increase allowable reservoir storage in
April, which would increase water storage at the
end of the rainy season and deliverable water during
the peak demand season in midsummer. However,
an increase in storage in the late winter and early
spring would likely reduce the amount of flood
protection (increase the risk of flooding) in the
region; this in itself could negatively affect owners
of floodplain property. Floods also place the delta
islands at risk because of higher water levels. The
tradeoff between water supply and flood control in
northern California represents a potentially serious
policy conflict affecting all levels of government in
the region. In fact, the meeting between
representatives of the State DWR and Bureau of
Reclamation, which was held to discuss Sheer and
Randall's results (Volume A), concluded that any
likely changes in reservoir operation that would
avoid a significant loss of flood safety would most
likely bring about little improvement in the system's
performance under the given climatic scenarios.
Detailed study of this point is needed, however.
The second approach to maintain or increase
water deliveries might be to construct new water
management and storage facilities. However, trends
over the past decade have shifted away from
planning large physical facilities (e.g., the Auburn
Dam and Delta Peripheral Canal). Building new
facilities is expensive and raises serious
environmental concerns about such issues as wild
and scenic rivers. Another option is to use smaller
facilities, such as the proposed new offstream
storage facility south of the delta, and to improve
the delta's pumping and conveyance facilities. With
the help of these facilities, the SWP plans to achieve
a 90% firm yield (the amount that can be delivered
in 9 out of 10 years) of about 3.3 maf by 2010
(California Department of Water Resources, 1987a).
Another relatively inexpensive option for off-line
storage is artificial recharge of groundwater during
wet years. The SWP is currently pursuing a proposal
to deliver surplus water to groundwater recharge
areas in the southern Central Valley to provide
stored water for dry years.
The third approach to increase water deliveries
is to turn to other sources of water. For instance,
use of groundwater could be increased. However,
in many metropolitan areas, groundwater bodies are
currently being pumped at their sustainable yields.
Any increase in pumping could result in overdraft.
Furthermore, decisions to use groundwater are
made by local agencies and/or individual property
owners, and groundwater is not managed as part of
an integrated regional water system. Whether or
not to include it in the system is an important policy
issue.
Another option is for southern California to
choose to fully use its allotment of Colorado River
water (which could lead to conflicts between
California and other users of that water, especially
Arizona). Other possibilities include desalinization
plants, cloud seeding over the Sierras, and reuse of
wastewater. However, desalinization plants are
energy intensive and may exacerbate air quality
problems. Also, cloud seeding is controversial, since
downwind users may not be willing to lose some of
their precipitation.
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Options for Allocating Water Shortages
The second major policy question is how best
to allocate potential water shortages. One way
would be to allow greater flexibility in water
marketing. The adverse effects of this policy change
(e.g., perhaps water becoming too expensive for
agriculture and possible speculative price increases)
could be ameliorated through a variety of
governmental policies. Yet, even with regulation,
any changes in the current system along these lines
would most likely be very controversial.
A second way to allocate the shortages is to
rely on mechanisms used in the past to deal with
droughts and water shortages, specifically
governmental restrictions on water use. In the past,
these mechanisms have included increased use
efficiency, transfers of agricultural water to
municipal and industrial uses, and restrictions on
"nonessential" uses of water (e.g., watering of
lawns). Increased efficiency of water usage through
various conservation techniques could effectively
increase the number of water users without actually
increasing the amount of water delivered. If climate
gradually changed and water shortages became
more common, these restrictions could become
virtually permanent.
Sacramento-San Joaquin River Delta
The delta area of the Sacramento and San
Joaquin Rivers in the San Francisco Bay estuary
receives great attention from governmental bodies
at all levels because of its valuable agricultural land,
its crucial role in the state's water resource system,
and its sensitive environment. The results of the
studies in this overall project suggest that this region
could be significantly affected by climate change.
Major changes could occur in delta island land use
and in the water quality of the San Francisco Bay
estuary. The policy implications of these possible
changes are discussed below.
Delta Island Land Use
A critical land use issue is whether to maintain
the levees surrounding islands threatened by
inundation. Much of the land present on these
islands is below sea level and is usable for
agriculture, recreation, and settlement only through
levee protection.
The individual delta islands have a significant
range of values. For example, some islands contain
communities and highways, and others are strictly
agricultural. The property value of the islands is
about $2 billion (California Department of Water
Resources, 1987b). The islands also help repel
saline water from the delta pumping plants (see
Figure 14-2).
The levees have been failing at an increasing
rate in recent years, and further sea level rise could
increase failure probability. Improving the levees to
protect the islands from flooding at the existing sea
level and flood probability would cost approximately
$4 billion (California Department of Water
Resources, 1982).
The issue of levee failure raises three
important policy questions. First, will some or all of
the levees be maintained? The range of options
concerning the levees includes inaction, maintenance
of the status quo, strategic inundation of particular
islands, and construction of polder levees.
Inaction, meaning the levees would not be
improved with time, could eventually lead to the
formation of a large brackish-water bay as all of the
levees failed. Williams (Volume A) suggests that
the area of the San Francisco Bay estuary could
triple if all the levees failed.
Currently, the general policy is to maintain the
delta's configuration. One important policy favoring
the maintenance of the levees is the Delta Levee
Maintenance Subventions Program, in which state
financial assistance is available for maintaining and
improving levees. The value of the islands for
agriculture and maintenance of water quality (see
below) has created additional institutional support
for maintaining the levees, even though the
cumulative cost may exceed the value of the land
protected. Future funding decisions for this and
related programs should consider the possibility of
climate change. If the levees are maintained, an
important policy question must be considered: Who
will pay for the maintenance?
Not all the islands are equal with regard to
their value in protecting the freshwater delivery
system. A possible future policy response to rising
sea level would be to maintain only certain levees
and not reclaim other islands as they became
flooded. In essence, this would be a strategic
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inundation policy. Some precedence exists for this
policy, as Mildred Island was flooded in 1983 and
not reclaimed; the high cost of reclaiming the island
relative to its value was cited as a rationale.
Construction of large levees similar to the
polders in Holland is an option for protecting the
islands and maintaining shipping channels.
However, this approach would be expensive and,
although it has been discussed, has not attracted
much serious attention.
The second policy question concerns failure of
the levees. If all or some levees are allowed to fail,
will landowners be compensated? If so, where will
the money come from? The delta islands contain
some of the most valuable agricultural land in the
state. Loss of this land would be a severe economic
hardship for the local farmers and for the associated
business community. Whether these farmers should
be compensated for their loss is an important public
policy issue.
A final policy question remains: How will
management of the delta islands be coordinated?
Four government bodies have jurisdiction over the
islands at the local, state, and federal levels. These
bodies will need to coordinate activities to reach
decisions regarding the future of individual delta
islands.
Water Quality of the San Francisco Bay Estuary
The intrusion of saline waters into the upper
reaches of the San Francisco Bay estuary could be
a major problem in a warmer climate. Climate
change is projected to cause increased salinity in the
estuary, largely as a result of sea level rise, levee
failure, and the inadequacy of freshwater outflow to
offset the increase in salinity. Furthermore, land
subsidence due to groundwater extraction could
augment sea level rise. In some areas of the
estuary, subsidence up to 1.5 meters (59 inches) has
occurred within the past 40 years (Atwater et al.,
1977).
Maintenance of current salinity levels is
addressed in the water right Decision 1485 (D-1485)
of 1978. This decision requires that water quality
standards in the delta be maintained. If they are
not, additional water must be released from
reservoirs to improve delta water quality, which
could reduce the amount of water available for
delivery. Current policy does not explicitly take into
account the potential for future climate change.
Thus, D-1485 could be interpreted as requiring
maintenance of delta water quality standards even
if sea level rises and causes further penetration of
saline water into the delta. Delta water quality
standards are currently being reviewed at the Bay-
Delta Hearing in Sacramento, which began in mid-
1987 and is expected to continue for 3 years. The
choice of future options will be greatly affected by
decisions made at the hearing.
Possible methods of combating the impacts of
saltwater intrusion include maintaining levees,
increasing freshwater outflows, reducing
withdrawals, enlarging channels, constructing a
barrier in the Carquinez Strait or lower delta,
and/or constructing a canal around the delta's
periphery. Alternatively, the freshwater pumping
plants could be moved to less vulnerable sites.
Decisions regarding response options will not be
easily made. Levee maintenance and construction
are costly. The water delivery agencies might be
reluctant to increase delta outflows or to reduce
withdrawals. Enlargement of delta channels,
construction of saltwater barriers, and construction
of a peripheral canal are extremely controversial
environmental issues. Another possible response to
these climatic impacts would be a gradual, planned
retreat from the delta, devoting resources to options
compatible with the absence of a freshwater delta.
This response would also be very controversial, both
politically and environmentally.
Water Quality of Freshwater Systems
The water quality of lakes, streams, and rivers
could change as climate changes. Results from the
Castle Lake study indicate that primary production
of subalpine lakes could increase, with the potential
for changes in the water quality of mountain
streams (Byron et al., Volume E). Reduction in
summer flows of streams and rivers in the Central
Valley Basin could concentrate pollutants in these
aquatic systems. A major policy question relates to
these potential changes: How will potential
reductions in water quality below levels mandated in
the current Water Quality Act of 1987 (Public Law
100-4) be prevented?
Maintaining water quality despite decreased
summer flows could be difficult and expensive.
Controlling nonpoint source pollution is a goal of
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the Water Quality Act of 1987, and meeting this
goal in the future could be more difficult and
expensive because of the lower summer flows.
Changes in land use near streams and rivers maybe
required to prevent runoff from agricultural land
from reaching them. Reducing herbicide and
pesticide use could also be another response, but
this could harm agricultural production. Another
option for preventing increased concentrations of
pollutants in river reaches below reservoirs is to
increase releases from reservoirs during summer
months; this strategy would dilute the pollutants.
However, this strategy would also have obvious
negative impacts on water deliveries.
Municipalities that release treated sewage into
rivers also could face increased difficulties in
meeting water quality standards. Options include
expanding sewage treatment facilities, which is
expensive; releasing water from reservoirs to dilute
the pollutants, as discussed above; or controlling the
production of wastewater. Any municipalities
planning for new sewage treatment plants should
include climate change as one factor in the design
criteria.
Reductions in summer flows could harm
populations of aquatic organisms and terrestrial
organisms that use riparian habitats. To the extent
that these species become threatened with
extinction, laws requiring preservation of
endangered species (e.g., Endangered Species Act of
1973) may be invoked as a legal basis for increasing
reservoir releases to preserve these species. This
could place into conflict the governmental agencies
and public constituencies concerned with preserving
biodiversity and those concerned with the economic
impacts on agriculture and industry.
Terrestrial Vegetation and Wildlife
Changing species composition and productivity
might alter the character of forestry operations and
the esthetic appeal of currently popular recreational
areas. Climate-induced reductions in growth and
regeneration rates, and increases in losses from
wildfire and insect damage, could decrease the size
and value of industrial forests in the state. How
these changes would be managed is a complex
question involving all levels of government as well as
private landowners.
One major step in response to possible future
climate change is to incorporate climate
considerations into current planning processes.
Federal planning for the effects of climate change
on forests is discussed in Chapter 5: Forestry.
Similar changes in the planning process could be
considered at other levels of government.
Coordinating the actions of government agencies
involved with land management to climate change in
California is another possible response.
The flora and fauna in California are highly
diverse and include many rare and endangered
species. Climate could change faster than some
species could adapt, leading to local extinction of
these species. Species conservation (as mandated by
the Rare and Endangered Species Act of 1973)
might require habitat reconstruction and/or
transplanting in some situations. Monitoring
programs may need to be instituted to track trends
in populations and communities. Extensive
programs have been developed for currently
endangered species in the state (e.g., the California
condor), and similar efforts probably could be
mounted in the future for other highly valued
species.
Agriculture
Changes in water availability and temperature
stresses are projected to affect agricultural
production. How will changes in agricultural
production and crop types be managed, and how
will California agriculture respond in national and
international settings? (For further discussion, see
Chapter 6: Agriculture.)
Historically, agriculture has quickly adapted to
climate fluctuations. New technology and
reallocation of resources might offset the impact of
changed climatic conditions and water availability.
Improved farm irrigation efficiency, such as
extensive use of drip irrigation, could mitigate the
impact of water-delivery shortages. Water
marketing may provide a cost-effective means of
meeting water demands and providing market
opportunities for conserving water (Howitt et al.,
1980). For example, water marketing may provide
rights holders with the financial ability to invest in
water conservation programs to cope with climate
warming impacts on water availability.
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Changes in cropping locations and patterns of
water use could exacerbate nonpoint source
pollution and accelerate rates of groundwater
overdraft. Furthermore, changing water supply
demands may heighten the conflicts between water
allocation strategies and ecosystem and wildlife
values.
It is uncertain how agricultural effects would
be manifest in California's evolving economic and
policy environment. For example, increased
commodity prices could mitigate the financial
impacts of potential reductions in crop acreage and
production.
Wetland Vegetation and Fisheries
Wetland species are valuable ecologically,
esthetically, and economically (photography,
hunting, fishing, etc.). With rising sea level, areas
supporting shallow-water vegetation might be
inundated and converted to deep-water habitats
supporting different species. New shallow-water
sites could be created by artificially adding
sediment. This option features its own
environmental impacts and would most likely be
expensive. However, maintaining shallow-water
vegetation is important not only to the conservation
of plant species but also to migratory birds, which
feed on such vegetation.
Salinity impacts on phytoplankton and fisheries
might be controlled via levee maintenance coupled
with increases in delta outflow.
Shoreline Impacts of Sea Level Rise
The California coast includes a diverse array of
shorelines ranging from cliffs to sandy beaches.
Erosion along these coastlines may increase as a
consequence of sea level rise. Such erosion could
substantially damage shoreline structures and
recreational values. Preventing the erosion would
be very costly. For example, protecting the sewer
culvert of the San Francisco Westside Transport
Project from potential damage caused by sea level
rise may cost over $70 million (Wilcoxen, 1986).
Sound planning for shoreline structures should
consider future erosion that may be caused by sea
level rise. (For further discussion of these issues,
see Chapter 7: Sea Level Rise.)
The accumulation of sediment behind water
project dams and the effects of diversion structures,
dredging operations, and harbor developments have
limited the sources of sediment for beach
maintenance (particularly along the southern
California coast). Individual landowners and
institutions constructing such infrastructures should
consider their effects on sedimentation processes.
Only through artificial deposition of sand (primarily
from offshore sources) have southern California
beaches been maintained. Beaches provide
recreational areas and storm buffers, and their
maintenance will require a major and continued
commitment.
Energy Demand
A warmer climate could affect both energy
demand and supply. For instance, higher
temperatures could cause increased cooling
demands, and changes in runoff could affect
hydroelectric power generation. Institutions in
California that are involved with energy planning,
such as the State Energy Resources Conservation
and Development Commission, should begin to
consider climate change in their planning efforts so
that future energy demands can be met in a timely
and efficient fashion.
Air Quality
Increasing temperatures could exacerbate air
pollution problems in California, increasing the
number of days during which pollutant levels are
higher than the National Ambient Air Quality
Standards. Devising technological and regulatory
approaches to meet ambient air standards is
currently a major challenge in certain regions of the
state, and these efforts must be continued. Under
a warmer climate, achieving air quality standards
may become even more difficult. To ensure that air
quality standards are met under warmer conditions,
policymakers, such as EPA and the California Air
Quality Board, may wish to consider possible
climate changes as they formulate long-term
management options for improving air quality.
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CHAPTER 15
GREAT LAKES
FINDINGS
Global climate change could affect the Great Lakes
by lowering lake levels, reducing ice cover, and
degrading water qualify in rivers and shallow areas
of the lakes. It could also expand agriculture in the
northern states, change forest composition, decrease
regional forest productivity in some areas, increase
open water fish productivity, and alter energy
demand and supply.
Lakes
Average lake levels could fall by 0.5 to 2.5
meters (1.7 to 8.3 feet) because of higher
temperatures under the doubled CO2
scenarios in this report. A drop of 1 meter
would leave average levels below historic lows.
Even if rainfall increases, the levels would fall
because higher temperatures would reduce the
snowpack and accelerate evaporation. The
estimates of lake level drop are sensitive to
assumptions about evaporation; under certain
limited conditions, lake levels could rise.
As a result of higher temperatures, the
duration of ice cover on the lakes would be
reduced by 1 to 3 months. Ice could still form
in near-shore and shallow areas. Changes in
windspeed and storm intensity would affect the
duration of ice cover.
Shoreline communities would have to make
adjustments to lower lake levels over the next
century. Hundreds of millions of dollars may
have to be spent along the Illinois shoreline
alone, dredging ports, harbors, and channels.
Water intake and outflow pipes may have to
be relocated. On the other hand, lower levels
would expose more beaches, which would
enhance shoreline protection and recreation.
Climate change could have both good and bad
effects on shipping. Lower lake levels may
necessitate increased dredging of ports and
channels or reduced cargo loads. Without
dredging, shipping costs could rise 2 to 33% as
a result of reduced cargo capacity. However,
reduced ice cover would lengthen the shipping
season by 1 to 3 months. Under scenarios of
relatively smaller lake level drop (0.7 to 1
meter), the shipping season would be
lengthened sufficiently to allow for the
transport of at least the same amount of cargo.
Under a scenario of larger lake level drops
(1.65 meters) and no dredging, total annual
cargo shipments could be reduced.
Water Quality and Fisheries
• Higher temperatures could change the thermal
structure of the Great Lakes. The result would
be a longer and greater stratification of the
lakes and increased growth of algae. This
result is very sensitive to changes in windspeed
and storm frequency -- two areas of relative
uncertainty. These two factors would combine
to reduce dissolved oxygen levels in shallow
areas of lakes such as Lake Erie. A study of
southern Lake Michigan indicated that annual
turnover of the lakes could be disrupted.
• Climate change could increase concentrations
of pollutants in the Great Lakes Basin.
Dredging of ports could suspend toxic
sediments in near-shore areas. Potential
reductions in riverflow in the basin would
create higher concentrations of pollutants in
streams. The disposal of toxic dredge spoils
was not studied in this report.
• The effects on fisheries would be generally
beneficial. Higher temperatures may expand
fish habitats during fall, winter, and spring, and
accelerate the growth and productivity of fish
such as black basses, lake trout, and yellow
perch. On the other hand, fish populations
could be hurt by decreased habitats and lower
dissolved oxygen levels during the summer.
The effects of potential changes in wetlands
due to lower lake levels, reductions in ice cover,
introduction of new exotic species, and increase
in species interaction were not analyzed,
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Chapter 15
although they could offset the positive results of
these studies.
Forests
• The composition and abundance of forests in
the Great Lakes region could change. Higher
temperatures and lower soil moisture could
reduce forest biomass in dry sites in central
Michigan by 77 to 99%. These mixed
hardwood and oak forests could become oak
savannas or grasslands. In northern areas such
as Minnesota, boreal and cedar bog forests
could change to treeless bogs, and mixed
northern hardwood and boreal forests in
upland areas could become all northern
hardwoods. Productivity could decrease on
dry sites and bogland sites, but it could
increase on some well-drained wet sites.
Softwood species that are currently
commercially important could be eliminated
and replaced by hardwoods, such as oak and
maple, which are useful for different purposes.
• Depending on the scenario, changes in forests
could be evident in 30 to 60 years. These
results do not reflect additional stresses, such
as pests and increased fire frequency, nor do
they reflect the possible beneficial impacts of
increased CO2 levels.
Agriculture
• Considering climate change alone, corn and
soybean yields in northern areas, such as
Minnesota, could increase by 50 to 100% and
could decline in the rest of the region by up to
60%. The combined effects of climate and
higher CCu levels could further increase yields
in the north and result in net increases in the
rest of the region, unless climate change is
severe.
• Agricultural production in the northern part of
the region may expand as a result of declines
elsewhere. However, the presence of glaciated
soils in northern states could limit this
expansion. Acreage in the Corn Belt states
may change little. Wider cultivation in the
north could increase erosion and runoff, and
degrade surface and groundwater quality.
Increased agriculture would require changes in
the infrastructure base, such as in
transportation networks.
Electricity Demand
• There could be little net change in annual
electricity demand. In northern areas, such as
Michigan, reduced heating needs could exceed
increased cooling requirements, while in
southern areas, such as Illinois, cooling needs
may be greater than heating reductions. The
annual demand for electricity in the entire
region could rise by 1 to 2 billion kilowatthours
(kWh) by 2010 and by 8 to 17 billion kWh (less
than 1%) by 2055. This study did not analyze
the reduced use of other fuels such as oil and
gas in the winter, changes in demand due to
higher prices, and the impacts on hydroelectric
supplies. Previous studies have suggested that
reduced lake levels and river flows could lead
to reductions in hydroelectric power production.
• By 2010, approximately 2 to 5 gigawatts (GW)
could be needed to meet the increased demand,
and by 2055, 23 to 48 GW could be needed --
an 8 to 11% increase over baseline additions
that may be needed without climate change.
These additions could cost $23 to $35 billion by
2055.
Policy Implications
• U.S. and Canadian policymakers, through such
institutions as the International Joint
Commission, should consider the implications
of many issues for the region. This study raises
additional issues concerning the following:
~ The water regulation plans for Lake
Ontario and possibly for Lake Superior lake
levels.
— The potential increased demands for
diverting Great Lakes water for uses
outside the basin. Before such a potential
demand could be accommodated, additional
analysis would be required. This is not
currently allowed by federal statutes.
— Long-range industrial, municipal, and
agricultural water pollution control
strategies. Agencies such as EPA may wish
to examine the implications for long-term
point and nonpoint water pollution control
strategies.
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Great Lakes
— The research, planting, and land purchase
decisions in northern forests by federal,
state, and private institutions.
CLIMATE-SENSITIVE NATURAL
RESOURCES IN THE GREAT
LAKES REGION
The Great Lakes region1 is highly developed,
largely because of its natural resources. The steel
industry developed along the southern rim of the
lakes, in part because iron ore from the north could
be inexpensively transported over the lakes. Rich
This chapter will cover only the U.S. side of the Great Lakes
and the eight states bordering them (see Figure 15-1).
soils, moderate temperatures, and abundant rainfall
have made the southern part of the region a major
agricultural producer. Forests are abundant in the
north and support commercial and recreational
uses. The basin has become the home of over 29
million Americans and produces 37% of U.S.
manufacturing output (U.S. EPA and Environment
Canada, 1987; Ray et al., Volume J).
Current Climate
The Great Lakes region has a midlatitude
continental climate. Winter is sufficiently cold to
produce a stable snow cover on land and ice on the
lakes. The average January temperature over Lake
Superior is -15°C (5°F), and the average July
temperature in the southern part of the region is
22°C (72°F). The average rainfall varies from 700
,-f ' j?& Forest Sites
A Compensating Works
• Agriculture Sites
•fa' Shipping Sites
Figure 15-1. Map of the Great Lakes study sites.
289
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Chapter 15
to 1,000 millimeters (27 to 39 inches), depending
on location (Cohen, in Glantz, Volume J).
The Lakes
The Great Lakes consist of a system of five
major lakes that contain approximately 18% of the
world supply of surface freshwater and 95% of the
surface freshwater in the United States (U.S. EPA
and Environment Canada, 1987) (see Figure 15-1,
Map of the Great Lakes). The natural flow of the
lake system begins in Lake Superior, the largest of
the lakes, which drains via the St. Mary's River into
Lakes Michigan and Huron (considered a single
hydrologic unit because they are connected by the
Straits of Mackinac). Water from Lakes Michigan
and Huron flows out through the St. Clair River
into Lake St. Clair. From there, the water flows
through the Detroit River and into Lake Erie, the
shallowest lake. The Niagara River connects Lakes
Erie and Ontario, and the system ultimately empties
into the Atlantic Ocean via the St. Lawrence River
and Seaway.
The greatest influence on lake levels is nature.
Seasonal fluctuations are on the order of 0.3 to 0.5
meter (1 to 1.7 feet), with the lakes peaking in late
summer because of condensation over the northern
lakes and reaching minimum levels in late winter.
Interannual lake level changes have been much
larger, approximately 2 meters (6.6 feet).
Lake Regulation
The flow between the lakes is controlled by
dams at two points: (1) the St. Mary's River to
control levels of Lake Superior; and (2) Iroquois,
Ontario, to control Lake Ontario. The major
diversion out of the lakes is the Chicago diversion,
which transfers water from Lake Michigan through
the Illinois River into the Mississippi River. Human
influence on lake levels is relatively small. Doubling
the flow down the Chicago diversion would lower
lake levels only by 2.5 inches in 15 years ( F. Quinn,
Great Lakes Environmental Research Lab., 1987,
personal communication).
Joint control of lake supply was codified in the
Boundary Waters Treaty of 1909 between Canada
and the United States, which created the
International Joint Commission (UC) consisting of
representatives from both countries. The UC
regulates flow through the control structures and
diversions by balancing the needs of shipping,
hydropower, and consumptive uses among the lakes
and along the St. Lawrence River and Seaway. Two
regulatory plans (Plan 1977 for Superior and Plan
1958D for Ontario) set ranges of levels between
which Lakes Superior and Ontario must be
maintained. Diversion out of the lakes is also
limited by law. Flow through the Chicago diversion
was limited by the Supreme Court to 90 cubic
meters per second (3,200 cubic feet per second)
(Tarlock, 1988), and the 1986 Water Resources
Development Act forbids diversion out of the lakes'
basin without the consent of all Great Lakes
governors (Ray et al., Volume J).
Climate-Sensitive Uses of the Lakes
Shipping
The U.S. Great Lakes fleet, which consists of
approximately 70 ships, transported over 171 million
tons of cargo hi 1987 (The New York Times, 1988).
The tonnage of U.S. shipping consists of iron ore,
coal, and limestone, all primary inputs for steel
(77%); lake grain (13%); and petroleum products,
potash, and cement (10%) (Nekvasil, 1988). Cargo
volumes are displayed in Table 15-1. Most of the
goods are shipped within the Great Lakes, with only
7% of the tonnage (mainly grains) shipped to
overseas markets (Ray et al., Volume J). Although
shipping activity had declined as a result of
reductions in U.S. steel production, recent increases
in steel output have led to additional demand for
shipping (The New York Times, 1988).
Great Lakes ships last over half a century and
are designed to pass within a foot of the bottom of
Table 15-1. 1987 U.S. Great Lakes Shipping Cargo
(thousands of tons)
Cargo
Weight
Percentage
Iron ore
Coal
Stone
Grain
Petroleum
products
Cement
Potash
Total
61,670
37,731
33,164
22,338
11,491
3,806
1.702
171,902
36
22
19
13
7
2
1
100
Source: Nekvasil (Lake Carriers Association, 1988,
personal communication).
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Great Lakes
channels and locks. Cargo capacity is quite sensitive
to lake and channel depth because of this low
clearance. The presence of ice usually shuts down
Great Lakes shipping up to 4 months each year.
Hydropower
The eight Great Lakes States use the
connecting channels and the St. Lawrence River to
obtain 35,435 gigawatt hours of hydropower each
year, which is about 5% of their electricity
generation. About four-fifths of the hydropower is
produced in New York State, which derives over
26% of its electricity from hydropower (Edison
Electric Institute, 1987).
Municipal Consumption
Most water used for the domestic and
industrial consumption in the basin is taken from
the lakes. Surface waters supply 95% of the basin's
water needs. By the year 2000, consumption is
estimated to increase by 50 to 96% (Ray et al.,
Volume J; Cohen, 1987b; UC, 1985).
Fisheries
In 1984, the value of the harvest to the U.S.
commercial fishing industry was approximately $15
million (U.S. EPA and Environment Canada, 1987;
U.S. Department of Commerce, 1987). Although
most fishing in the Great Lakes is for recreation,
fisheries are managed by the states; the Great Lakes
Fishery Commission coordinates activities among
the states.
Tourism
Three national and 67 state parks are located
along the shores of the lakes, as are numerous local
parks. Over 63 million people visited these parks in
1983 (Ray et al., Volume J; Great Lakes Basin
Commission, 1975). In 1984, lake-generated
recreation yielded revenues of $8 to 15 million.
Fishing, boating, and swimming are very popular.
Shoreline Development
Over 80% of the U.S. side of the Great Lakes
shoreline is privately owned. One of the most
developed shorelines is the 101-kilometer Illinois
shoreline, where many parks and residential
structures, including apartment houses, are built
near the water's edge. Shoreline property owners
have riparian rights to use adjoining waters. The
shoreline property owners cannot substantially
diminish the quantity or quality of surface waters
(Ray et al., Volume J).
Climate and Water Quality
Water quality is directly affected by climate.
Lower stream runoff increases concentrations of
pollutants. Every summer, the lakes stratify into a
warmer upper layer and a cooler lower layer. This
stratification can limit biological activity by
restricting the flow of nutrients between layers. In
addition, warm temperatures and an excess supply
of nutrients (phosphorous and other chemicals from
agricultural runoff and sewage effluent) can lead to
algal blooms that decay and cause a loss of oxygen
(eutrophication) and reduction in aquatic life in the
lower layers of lakes such as Lake Erie. Cool
weather and the formation of ice help to deepen the
mixed layer, break up the stratification, and
thoroughly mix the lakes in the winter.
Development, industrialization, and intensive
agriculture in the Great Lakes Basin have created
serious pollution in the lakes, especially Lake Erie.
In the early 1970s, nutrient loadings were so high
that Lake Erie experienced significant
eutrophication problems for several years (DiToro
et al., 1987).
Two measures have helped improve water
quality. The U.S.-Canada Great Lakes Water
Quality Agreement of 1972 called for controlling
nutrient inputs and eliminating the discharge of
toxic chemicals, and the Clean Water Act mandated
construction of sewage treatment plants and
controls on industrial pollutants. The United States
and Canada spent a total of $6.8 billion on sewage
treatment in the Great Lakes. By 1980, nutrient
loadings into Lake Erie had been cut in half (Ray et
al., Volume J; DiToro et al., 1987), and water
quality had markedly improved.
Fluctuating Lake Levels
Recent high and low lake levels have
significantly affected users of the lakes. In 1964,
Lake Michigan was 0.92 meters (3 feet) below
average, making some docks and harbors unusable.
Shipping loads were reduced by 5 to 10% and more
shipments were required, subsequently raising the
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Chapter 15
cost of raw materials and supplies by 10 to 15%. In
addition, many water intakes had to be extended or
lowered (Changnon, Volume H). Flow through the
Niagara hydropower project fell by more than 20%,
with electricity generation off by more than 35%.
Flow through New York's St. Lawrence hydro
project was more than 30% below its mean, with
electricity generation decreased by 20% (Linder,
1987). However, low lake levels also provided
benefits, for example, beaches became larger.
In the mid-1980s, a series of cool and wet
years caused the lakes to rise to record heights.
Apartment houses that were built too close to the
shoreline during the low levels of the 1960s were
flooded, as were roadways built close to the shore.
The low water levels in the 1960s exposed the
supporting structures along Chicago's shoreline to
air, causing dry rot. When lake levels rose, the
wood pilings and sections of the revetment
collapsed. The estimated construction cost for
rebuilding the damaged shoreline protection system
is $843 million (Changnon, Volume H). The last 2
years have been relatively hot and dry, causing lake
levels to recede to average levels. The lower levels
have forced shippers to reduce tonnage just as the
steel industry in the region is undergoing a
resurgence.
Land Around the Lakes
The land in the Great Lakes region is
extensively used for industry, agriculture, and
forestry. Many of the uses are sensitive to climate.
Land Uses
Urban Development
Approximately 29 million people live in the
Great Lakes Basin, mostly in the urban areas
around the cities on the southern edge of the Great
Lakes: Chicago, Detroit, Cleveland, Toledo, and
Buffalo. Many of the residents work in
manufacturing industries, which despite recent
declines, still provide 23% of payroll employment
(Ray et al., Volume J).
Agriculture
Agriculture is the single largest user of land:
42% of all land in the eight Great Lakes States is
devoted to crops, and an additional 10% is used for
pasture. The Great Lakes States encompass most
of the Corn Belt. In 1983, roughly 59% of all U.S.
cash receipts for corn and 40% of the receipts for
soybeans came from this region. Overall, the Great
Lakes States produced 26% of the total U.S.
agricultural output, or $36 billion (Federal Reserve
Bank of Chicago, 1985). Most crops are grown on
dryland, as only about 1% of the region's croplands
were irrigated in 1975 (U.S. Department of
Commerce, 1987).
Livestock are also important to the agricultural
economy of the region. Approximately 18% of U.S.
cattle are raised in these eight states; of these, 52%
are dairy cows (USDA, 1987). (The sensitivity of
livestock to climate change is discussed in Chapter
6: Agriculture.)
Forests
The forests in the region have commercial,
recreational, and conservation uses. The forests in
the south are mainly oak and northern hardwoods,
such as maple. The north has almost 21 million
hectares (52 million acres) of forests consisting
mostly of northern hardwoods, such as maple, birch,
and beech, and boreal forests, such as spruce and fir
trees. The federal and state governments own,
respectively, 11 and 13% of the forests in Michigan,
Minnesota, and Wisconsin, while over half are
privately owned (USDA, 1982). The pulp,
construction, and furniture industries are major
consumers of such species as aspen, pines, balsam
fir, spruce, maples, paper birch, and oak. The
forest industry is a major employer in the northern
part of the region. In Wisconsin, for example,
283,000 jobs are in timber harvesting and
manufacturing related to forestry (Botkin et al.,
Volume D; U.S. EPA and Environment Canada,
1987). Forestry is considered to be a growth
industry in the region, since Michigan has identified
forest products as one of the three key industries
targeted for expansion in the state (Ray et al.,
Volume J).
PREVIOUS CLIMATE CHANGE
STUDIES
The impacts of climate change on many of the
systems in the Great Lakes have been analyzed in
previous studies, mainly by Canadian researchers.
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Great Lakes
These studies are summarized in Cohen and
Allsopp (1988). Several Canadian studies have
examined the potential impacts of climate change on
Great Lakes levels and concluded that levels would
fall. Southam and Dumont (1985) used the
Goddard Institute for Space Studies (GISS) scenario
to estimate that lake levels would fall by 0.2 to 0.6
meters (0.7 to 2 feet). Cohen (1986) used
hydrologic calculations to estimate that the lakes
might fall between 0.2 and 0.8 meters. More
recently, Marchand et al. (1988) also used a
hydrologic model of the lakes to estimate that the
lakes would drop by an average of 0.2 to 0.6 meters.
Cohen (1987a) found that changes in lake levels are
very sensitive to humidity and windspeed. It is not
known how climate change would affect these
parameters on a regional scale. Wall (1985)
concluded that lower lake levels could reduce
ecological diversity and dry up enclosed marshes. In
another study, Cohen (1987b) estimated that
withdrawals of water from the lakes for municipal
consumption would increase by about 2.5% on an
annual basis and would only marginally affect lake
levels.
Assel et al. (1985) studied the extent of ice
cover during the whiter of 1982-83, which had
temperatures 3.3 to 4.4° C warmer than the 30-year
mean. They found that ice cover on Lake Superior
was reduced from a normal 75% coverage to 21%.
On Lake Erie, ice coverage was down to 25% from
the normal 90%. Meisner et al. (1987) conducted
a literature review on the possible effects of global
warming on Great Lakes fish. Results are discussed
in the fisheries section of this chapter.
Marchand et al. (1988) (see also Sanderson,
1987) estimated the combined effects of lower lake
levels and reduced ice cover due to climate change,
and higher water consumption and shipping tonnage
due to population and economic growth of
Canadian shipping and hydropower production.
They found that without economic changes, lower
lake levels would increase shipping costs by 5%.
After consideration of economic growth, lower lake
levels and reduced ice cover could Increase shipping
costs by 12%.
Linder (1987) used the transient scenarios to
estimate impacts on electricity demand and
hydropower generation in 2015 in upstate New
York. He found total energy demand declining by
' 0.21 to 0.27%, but peak demand increasing by 1 to
2%. Meanwhile, hydropower production could
decline between 6 and 8.5% as a result of
reductions in streamflow.
Impacts on managed and unmanaged vegetation
have also been studied. The Land Evaluation
Group examined the potential impacts of climate
change on agriculture in Ontario and found that
yields could decrease hi southern Ontario and
farming could become feasible in northern Ontario.
The study also Indicated that the direction of change
for yields depends on whether rainfall increases or
decreases (Land Evaluation Group, 1986). Solomon
and West (1986) used a stand simulation model (see
this chapter, Forests) to estimate the impacts of
doubling and quadrupling of CO2 levels on a
northwest Michigan coniferous-deciduous
transitional forest. They found that doubled CO,
would lead to an eventual disappearance of boreal
forests and an increase in deciduous trees. Total
biomass would decline at first and rebound in about
two centuries.
Two studies by Canadian researchers examined
the possible impacts of climate change on tourism
and recreation hi Ontario. Both studies used
climate change scenarios based on the GISS and
Geophysical Fluid Dynamics Laboratory (GFDL)
models (although these may have been earlier
model runs). Crowe (1985) estimated that snowfall
would decrease by 25 to 75%, and the ski season
would be cut by 75 to 92% (7 to 12 weeks) in
southern Ontario and by 13 to 31% (2 to 4 weeks)
in northern Ontario. Wall found similar results.
He concluded that reduced snowfall could eliminate
skiing in southern Ontario and would shorten the
northern Ontario ski season by 30 to 44%. A
longer summer season could increase such summer
tourism activities as camping. Wall (1985) also
thought that lower lake levels could decrease
ecological diversity and dry up enclosed marshes.
GREAT LAKES STUDIES IN THIS
REPORT
Unlike previous studies, the studies for this
report used common scenarios to address some of
the potential impacts of climate change on a
number of natural and societal systems hi the Great
Lakes region. The studies address the direct effects
of climate change on the resources and some of the
indirect effects on infrastructure and society. They
focused on the lakes themselves, examining such
293
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Chapter 15
issues as lake levels, ice cover, thermal structure,
and fisheries. They also looked at the effects of
these changes on shipping and shoreline properties,
and examined the sensitivities of agriculture and
forest to climate change. Finally, the studies
examined the implications of climate change for
Great Lakes policies and institutions. Some of the
studies were linked quantitatively, but most were
conducted independently of each other.
The studies involved either new topics or
approaches that were not used in previous studies.
For example, the analysis of lake levels used a more
complex hydrologic model than was used previously.
The agriculture analysis complements the Land
Evaluation Group's study of Ontario by using a
different model to examine impacts on the U.S. side
of the lakes. The potential impacts of climate
change on thermal structure were examined for the
first time. Also for the first time, models were used
to analyze impacts on fisheries. This study
complements previous studies on forests by using a
combination of modeling techniques to test the
similarity of results.
The following analyses were performed for this
report:
Direct Effects on Lakes
• Effects of Climate Changes on the
Laurentian Great Lakes Levels - Croley and
Hartmann, Great Lakes Environmental
Research Laboratory (Volume A)
• Impact of Global Warming on Great Lakes
Ice Cycles - Assel, Great Lakes
Environmental Research Laboratory
(Volume A)
Impacts of Lake Changes on Infrastructure
The results from the first two studies were
used in the following studies:
• Effect of Climatic Change on Shipping
Within Lake Superior and Lake Erie -
Keith, DeAvila, and Willis, Engineering
Computer Optecnomics, Inc. (Volume H)
• Impacts of Extremes in Lake Michigan
Levels Along Illinois Shoreline Part 1: Low
Levels - Changnon, Leffler, and Shealy,
Illinois State Water Survey (Volume H)
Water Quality
The following studies focus on water quality
and the effects on aquatic life in the lakes. The first
two studies examined the direct effects of climate on
the thermal structure of some of the lakes.
• Potential Climatic Changes to the Lake
Michigan Thermal Structure - McCormick,
Great Lakes Environmental Research
Laboratory (Volume A)
• The Effects of Climate Warming on Lake
Erie Water Quality - Blumberg and
DiToro, Hydroqual, Inc. (Volume A)
The results from these studies were used in the
following:
• Potential Responses of Great Lakes Fishes
and Their Habitat to Global Climate
Warming - Magnuson, Regier, Hill,
Holmes, Meisner, and Shuter, Universities
of Wisconsin and Toronto (Volume E)
Forests
A series of studies on forests was commissioned
to examine shifts in ranges, transient impacts, and
the potential for migration of some Great Lakes
forests. Basically, these are different analytic
techniques for understanding how climate change
may affect the composition and abundance of
forests in the region.
• Transient Effects on Great Lakes Forests -
Botkin, Nisbet, and Reynales, University of
California at Santa Barbara (Volume D)
Hard Times Ahead for Great Lakes
Forests: A Climate Threshold Model
Predicts Responses to COo-Induced
Climate Change - Zabinski and Davis,
University of Minnesota (Volume D)
Assessing the Response of Vegetation to
Future Climate Change: Ecological
Response Surfaces and Paleoecological
Model Validation - Overpeck and Bartlein,
Lamont-Doherty (regional results were
taken from this study) (Volume D)
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Great Lakes
Agriculture
The potential changes in agriculture in the
Great Lakes were analyzed by studying changes in
crop yields in the region and integrating the results
in a national analysis of production changes. That
national analysis was used to determine if
production in the region could increase or decrease.
The results of these studies were used to examine
potential farm level adjustments.
. Effect of Global Climate Change on
Agriculture: Great Lakes Region - Ritchie,
Baer, and Chou, Michigan State University
(Volume C)
. Farm Level Adjustments by Illinois Corn
Producers to Climatic Change - Easterling,
Illinois State Water Survey (Volume C)
This chapter will use regional results from the
following:
. The Economic Effects of Climate Change
on U.S. Agriculture: A Preliminary
Assessment - Adams, Glyer and McCarl,
Oregon State University (Volume C)
Energy
This project analyzed potential changes in the
national demand for electricity and estimated
changes in regional demands. Results for the Great
Lakes region are presented in this chapter.
• Electric Utilities - Linder and Inglis, ICF,
Inc. (Volume H)
Policy
The potential policy implications of the
changes indicated by these and previous studies for
local, state, federal, and international
decisionmaking are examined. This project
provided information for the background and policy
implications sections.
. Effects of Global Warming on the Great
Lakes: The Implications for Policies and
Institutions - Ray, Lindland, and Bran, The
Center for the Great Lakes (Volume J)
GREAT LAKES REGIONAL
CLIMATE CHANGE SCENARIOS
All three general circulation models (GCMs)
that provide the basis for the climate change
scenarios show rather large increases in temperature
for the Great Lakes region under the doubled CO,
climate. The seasonal and annual temperatures and
precipitation are displayed in Figure 15-2. The
Oregon State University (OSU) scenario has an
annual temperature rise of 3.5° C, with no change in
seasonal pattern. The Goddard Institute for Space
Studies (GISS) scenario is about a degree warmer
on average and has the largest warming in the
winter and fall. The Geophysical Fluid Dynamics
Laboratory (GFDL) scenario has the largest
warming of the three models, about 6.5° C annually,
with the largest warming in the summer. All three
scenarios have annual increases in precipitation.
OSU has an increase of approximately 0.1
millimeters per day (0.1 inches per year), with
precipitation rising in all seasons. GISS has an
increase of approximately 0.2 millimeters per day
(0.03 inches per year), with precipitation declining
slightly in the fall. GFDL has an annual
precipitation increase of only 0.05 millimeters per
day (0.07 inches per year), but rainfall drops by 0.5
millimeters per day (0.02 inches per day) in the
summer. The large temperature increase and small
rainfall increase combine to make GFDL the most
severe scenario. This is especially true in summer
months, when GFDL has the largest temperature
rise of any scenario and is the only scenario that
reduces rainfall. OSU is the mildest scenario owing
to the smaller temperature increase. (Other runs
of the GFDL model have lower temperature
increases, although they still estimate a decline in
summer rainfall.) GISS is in the middle in terms
of severity, and OSU is the mildest of the three
scenarios.
One limitation related to using the GCMs as a
basis for climate change scenarios for the Great
Lakes region is that the lakes are not well
represented in the GCMs. The relatively large size
of the GCM grid boxes results in little feedback
from the lakes to the regional climate estimates
from the GCMs.
295
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Chapter 15
A. Temperature
B. Precipitation
Annual
NC - No Change
Figure 15-2. Average change in temperature (A) and precipitation (B) over Great Lakes gridpoints in GISS
GFDL, and OSU models (2xCO2 minus IxCCX,).
RESULTS OF THE GREAT
LAKES STUDIES
Lakes
Lake Levels
Geologic records indicate that Great Lakes
levels have fluctuated as paleohistoric climates have
been wetter and drier (Larson, 1985). Recent short-
term variations have been the result of short-term
changes in precipitation patterns. Croley and
Hartmann examined the potential impacts of global
warming on average lake levels.
Study Design
Croley and Hartmann used a water supply and
lake level model of the Great Lakes Basin
developed by the Great Lakes Environmental
Research Laboratory to estimate the potential
impacts of climate change on levels of the Great
Lakes (Croley, 1983a,b; Croley, 1988; Quinn, 1978).
This model is the most detailed hydrologic model of
the Great Lakes Basin and includes a separate
model for each of the 121 watersheds in the basin.
Croley and Hartmann simulated runoff in each of
the subbasins, overtake precipitation, and
evaporation. Lake levels are very sensitive to
evaporation; therefore, Croley and Hartmann ran
each GCM scenario with different assumptions
about evaporation.2 Finally, they used the current
plans (Plan 1977 for Superior and Plan 1958-D for
Ontario) and hydraulic routing models of outlet and
connecting channel flow and estimated water levels
on each of the Great Lakes.
The regulation plan for Lake Superior failed
under the GFDL scenario. To obtain an estimate
of changes in levels for Superior-Huron, St. Clair,
and Erie, Croley and Hartmann assumed that over
a 30-year period, total inflows into Lake Superior
(runoff + overtake precipitation + diversions -
evaporation) would equal total outflows, and Lake
In Volume A, Croley focuses on results from his latest run.
This run includes assumptions that lead to relatively high
amounts of evaporation and larger drops in lake levels. Earlier
runs had less evaporation and larger drops in lake levels.
Results in this chapter include the latest run and an earlier run.
296
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Great Lakes
Superior levels would not change. No figures are
presented for changes in the level of Lake Superior
in the GFDL scenario. The levels of Lake Superior
would probably fall. Only 30-year average lake
levels were calculated for the other lakes.
Limitations
The relationships in this model were
developed for a cool and wet climate. The analysis
did not account for changes in the consumptive uses
of the lakes (due to population and economic
growth or climate change), and it did not consider
changes in the regulation plans, or increases in or
additions to diversions into or out of the lakes. The
analysis also used the difference in vector winds
from the GCMs as a proxy for the difference in
scalar winds because GCM estimates of changes of
scalar winds were not available. Thus, the wind
estimates probably underestimate changes in
windspeed (David Rind, Goddard Institute for
Space Studies, 1988, personal communication). The
uncertainty on winds is complicated by the
uncertainties concerning evaporation. Different
assumptions of evaporation in this analysis affect the
magnitude of lake level drop, but they do not affect
the direction of change - lake levels fall under all
evaporation assumptions. Cohen (1987a) found that
potential changes in Great Lakes levels are very
sensitive to estimates of changes in windspeed and
humidity. He concluded that with the right
combination of conditions, even with higher
temperatures, it is possible for lake levels to rise.
Results
Lake levels were estimated to fall significantly
under all three scenarios (see Table 15-2). The lake
level changes are displayed in ranges from low to
high evaporation.
Average levels for Lake Superior would be
about 0.4 to 0.5 meters (1.3 to 1.7 feet) below
average levels for the 1951-80 period under the
OSU and GISS scenarios. These average levels
would be generally lower than recorded lows of
recent history. The lakes would likely still fluctuate
around these average levels, so levels during some
years would be lower. Even though precipitation
rose in all three scenarios, lake levels were
estimated to fall, primarily as a result of the higher
temperatures. Apparently, only a large increase in
rainfall or humidity or a large decrease in
windspeeds could offset these changes. Lake levels
were estimated to continue fluctuating on an annual
basis. Specific estimates of fluctuation are not
discussed here, since variability was assumed not to
change.
Croley and Hartmann also found that the flow
in the St. Mary's could increase by less than 1% hi
the GISS high rainfall scenario and drop by 13% in
the drier OSU scenario for Lake Superior. The
flow hi the Niagara River was estimated to be 2 to
30% lower. Croley and Hartmann did not estimate
the flow of these rivers for the GFDL scenario.
The lowering of lake levels appears to be
correlated with increased temperatures in the
scenarios. Under all the doubled CO2 scenarios,
there could be declines in runoff to the lakes and
increases in evaporation from the lakes. The
reduction in runoff would be largely the result of
changes in snowpack accumulation and ablation.
Snowpack in the Lake Superior Basin could be
reduced by one-third to two-thirds, and in the other
basins, farther to the south, the snowpack could be
almost entirely absent. The reduction in runoff
would reduce average streamflow in the basin.
These results appear to be driven mainly by the
temperature increase, since precipitation rises in all
scenarios.
Table 15-2. Doubled CO2 Scenarios: Reduction in
Average Great Lakes Levels from 1951
to 1980 (meters)
Scenario Superior Michigan Erie Ontario
GISS -0.43 to -1.25 to -0.95 to NA
-0.47 -1.31 -1.16
GFDL NA -2.48 to -1.65 to NA
-2.52 -1.91
OSU -0.39 to -0.86 to -0.63 to NA
-0.47 -0.99 -0.80
Transient Scenario
(average rate of change per decade 1980-2060)
GISS-A -0.006 -0.055 -0.04 NA
NA = Not applicable.
Source: Croley and Hartmann (Volume A.)
297
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Chapter 15
Evaporation would increase under all three
scenarios. The increase in evaporation varied under
different assumptions about the relationship of
evaporation to change in climate variables and
ranged from 20 to 48%. For a given assumption
about evaporation, higher temperature scenarios
would generally cause more evaporation. Lake level
reductions could also be higher or lower, depending
on these assumptions.
All of these changes could cause a reduction
in net basin supply (the sum of overtake
precipitation and runoff minus evaporation) by 14 to
68%. The exception to this is the GISS scenario for
Lake Superior. In that scenario, annual rainfall
increased by 18%, which could lead to a 1%
increase in net basin supply.
The Ontario regulation plan would fail under
all scenarios, including the transient run. Under
these conditions, the system would not contain
enough water to keep the level of Lake Ontario and
the flow in the St. Lawrence River within ranges
currently specified by the plan. The Lake Superior
regulation plan was estimated to fail under the
GFDL scenario. Although net basin supply hi Lake
Superior increased under GISS, the regulation plan
would require increased flow through the St. Mary's
River to the water-short lower lakes, resulting in a
net drop in Lake Superior levels.
These results are consistent with other studies
done on lake levels and climate change. Both
Cohen and Sanderson agree with Croley and
Hartmann that lake levels would drop under various
climate change scenarios. The other two studies,
however, estimated lake levels would drop less than
1 meter. Croley and Hartmann may have estimated
greater changes because they used a more
sophisticated runoff, evaporation, and routing model
and because of different assumptions made about
evaporation. Croley and Hartmann also used a
more integrated approach and more variables from
the GCMs. The estimates for GFDL may also be
higher because the GFDL scenario used in this
study had a higher temperature rise than the GFDL
scenarios used by Cohen and Sanderson.
The results of the transient run (GISS A) are
expressed as the average change hi lake level per
decade and are not indicative of what would happen
in any particular decade. Lake Superior levels drop
only 0.006 meters (0.2 inches) per decade, while the
other lake levels fall 0.04 to 0.055 meter (1.6 to 2.2
inches) per decade. An extrapolation of the
transient results to the decade of the 2060s (when
the GISS A transient run reaches doubled CO2
climate conditions) results hi lake level reductions
less than for the doubled CO2 GISS scenario. This
is because lake levels may not respond immediately
to climate change, but must catch up. The results
may also be affected by the variability assumptions
hi the transient scenarios (see Chapter 4:
Methodology). By the end of the transient scenario,
the 2050s, lake levels fall at a faster rate -- by more
than 0.05 meters (2.0 inches) per decade. Thus,
these studies do not clearly indicate the length of
tune required for the lakes to drop by the amounts
shown hi Table 15-2.
Croley and Hartmann found that enough heat
could reside hi Lakes Superior, Michigan, Huron,
and Ontario to maintain water surface temperatures
at a sufficiently high level throughout the year, so
that buoyancy-driven turnovers of the water column
may not occur at all. This could significantly affect
lakewater quality and aquatic life (see this chapter,
Thermal Structure of Southern Lake Michigan).
Croley estimated that average surface water
temperatures in the whiter would be above 0°C and
would significantly reduce ice concentrations.
Implications
Hydropower production could be reduced, as
flows through the St. Mary's, the Niagara, and the
St. Lawrence Rivers fall. Losses to hydropower
were not estimated for the EPA study, although
Linder's earlier work on hydropower losses by 2015
hi New York State showed potential loss of 1500 to
2066 gigawatt-hours (6 to 9%) (Linder, 1987).
Sanderson (1987) estimated that under a doubled
CO, scenario, Canadian hydroelectric power
production on the St. Mary's River could rise by
2.5% (because the level of Lakes Michigan-Huron
falls more than that of Lake Superior) and power
production on the Niagara River could fall by 13 to
18% as a result of a drop in flow. The impacts of
lower lake levels on wetlands were not estimated,
and the impacts on shipping and on shoreline
infrastructure are discussed later hi this chapter.
Lower lake levels and reduced riverflow would
likely adversely affect water quality in the basin.
Less water would reduce dilution of pollutants.
Forty-two "hot spots" occupy many bays and harbors
298
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Great Lakes
along the Great Lakes. These are contaminated
with a wide variety of halogenated organics and
heavy metals, as well as remobilizable nutrients.
Lower lakes may cause emergence and near
emergence of these toxic sediments through erosion,
leaching, oxidization, or volatilization.
Higher temperatures may lead to increased
withdrawals of water from lakes for municipal
consumption. Climate change may also result in
more calls for diversion of water out of the Great
Lakes Basin for use elsewhere. However, lake
levels may be lowered even more as a result of
higher demand for withdrawals for use in the basin
as a result of population and economic growth.
Effects of Lower Lake Levels
Coastal infrastructure around the Great Lakes
has generally been built assuming average lake
levels would not change. A drop in levels could
make much of the current infrastructure unusable
and necessitate reconstruction. Changnon et al.
examined the potential impacts and adjustments to
infrastructure along the 101-kilometer (63-mile)
Illinois shoreline. This study and the shipping
analysis used the lower range of the lake level drops
from Table 15-2 because subsequent analyses that
gave different lake levels were performed too late to
be incorporated.
Study Design
Changnon et al. interviewed experts about the
possible impacts and costs of adjustment along the
Illinois shoreline to the lower lake level estimates
described above. Results are expressed in current
dollars.
Limitations
This analysis did not use economic models,
used current prices, and did not consider changes in
population, GNP, or technology. Results are based
on expert judgment. Changnon et al. also assumed
that lakes would reach the levels described above by
2030. The change in lake levels may not be reached
until decades later (by the year 2060 or later) so
costs may be borne over a longer period than
Changnon estimated, allowing for more routine
replacement of infrastructure. This study examined
only the costs of rebuilding infrastructure and did
not examine ecological impacts.
Results
The largest costs appear to accrue to
recreational and commercial harbors (see Table 15-
3). The major expenses are associated with
dredging harbors and lowering bulkheads, which
could cost approximately $200 to $400 million. If
lake levels fall enough, keeping some harbors open
(e.g., Waukegan, Illinois) may not be a cost-effective
choice.
Changnon et al. concluded that slips and docks
would be only slightly affected. Many of these
probably would have been replaced anyway and
could be set at lower levels as the lakes fall. (The
impacts on commercial shipping in Lakes Superior
and Erie are discussed below.)
Intake valves for municipal and industrial
consumption could be exposed and may have to be
lowered or moved farther offshore. Outfalls for
stormwater would have to be extended. Changnon
et al. estimated that extending urban water intakes
and stormwater outfalls could cost $16 to 17 million.
Although the exposure of more land could
present some erosion problems, it could also
enlarge many beaches. An additional 1 to 2.2
square kilometers (0.3 to 0.8 square miles) of
beaches would be added to the Illinois shoreline. In
all, Changnon et al. estimated that the costs of
adjusting to lower levels of 1.25 to 2.5 meters along
the Illinois shoreline, excluding normal replacement
of docks and piers, would be $220 to $430 million.
If normal replacement costs do not account for
lower lake levels, costs could be $30 to $110 million
higher. To put these figures into context, the City
of Chicago may spend over $800 million to repair
shorelines damaged by high water levels in recent
years.
Walker et al. (Volume H; for a discussion of
methodology and results, see Chapter 13: Urban
Infrastructure) examined the potential capacity of
climate change on Cleveland's infrastructure. They
found that savings in such areas as snow removal
and bridge repair could offset increased cooling and
dredging costs. Cities on the Illinois shoreline
would also have savings due to reduced winter
expenditure.
299
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Chapter 15
Table 15-3. Estimated Economic Impacts of Lowerings of the Levels of Lake Michigan Over a 50-Year Period
(1990-2040)
Cost3
Type of expense
1.25 meters lower 2.5 meters lower
Recreational harbors
Dredging
Sheeting
Slips/docks
Commercial harbors
Dredging
Sheeting/bulkheads
Slips/docks
Water supply sources
Extending urban intakes
Wilmette Harbor Intake
Beaches
Facility relocations
Outfalls for stormwater
Extensions and modifications
Totals
30-50
^h
20b
108
38
40b
15
1
1-2
$270-292°
75-100
35
40b
212
38h
90b
15
2
1-2
$512-540
a Costs in millions of 1988 dollars to address future lake levels at indicated depths below average (1951-80)
levels of Lake Michigan.
Some costs could be partly covered by normal replacement expenditures over the period of changing levels.
Source: Changnon et al. (Volume H).
Ice Cover
Warmer winters would reduce ice cover on
the Great Lakes. Some analysts have speculated
that ice would be completely eliminated. Assel used
a model to estimate the potential extent and
duration of ice cover.
Study Design
Assel developed a statistical relationship
between temperature and ice cover for this study.
The models were developed for the three basins of
Lake Erie, for the Lake Superior Western and
Eastern Basins, and for Whitefish Bay in Lake
Superior. Whitefish Bay was included because it
has the longest period of ice cover and acts as a
choke point on shipping in and out of Lake
Superior. Lakes Superior and Erie represent
extremes in terms of air temperature regimes, lake
depth, and heat storage capacity, and bound the
range of potential ice cover changes.
Limitations
Assel's study did not consider the effects of
wind and other variables on ice formation.
Implicitly, the analysis assumed that winds stay the
300
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Great Lakes
same. Stronger winds would make the ice season
shorter than estimated, and weaker winds (and
calmer waters) would make it longer. The three
GCMs estimate that windspeeds over the two lakes
drop by 0.0 to 0.3 meters per second (see Croley,
Volume A). Inclusion of windspeed changes would
have lowered ice cover reduction results. The
model was built based on the relatively cool years of
the 1960s and 1970s; therefore, the doubled CO,,
scenario temperatures are outside the range or
winter temperatures in those years. However, the
model simulated ice duration within 3 weeks of
actual ice duration for the warm winter of 1982-83.
Results
Assel found that although average ice cover
might be significantly reduced, ice would still form
on the lakes (Table 15-4). Results for the central
basin of Lake Erie are displayed in Figure 15-3. It
now averages 83 days of ice cover. In the 1981-2009
transient scenario, ice cover was estimated to be 71
days; in the 2010-2039 scenario, it was estimated to
decline to 41 days. Under the doubled CO2
climate, ice cover could be reduced to a total of 6 to
19 days, and ice formations would be generally
limited to near-shore and shallow areas. Whitefish
Bay in Lake Superior currently averages about 115
days of ice cover. Under the doubled CO-
scenarios, ice duration would be reduced to 69 to 80
days. Also, the maximum percentage of Whitefish
Bay covered by ice would be reduced from close to
100% to 70-20%.
Figure 15-3. Changes in duration and extent of ice
cover in central basin of Lake Erie under transient
and doubled CO2 scenarios (Assel, Volume A).
The temperature rise in the scenarios may not
be warm enough to eliminate ice cover on the Great
Lakes, but many winters could have no ice at all.
The Lake Erie Central Basin is estimated to be ice-
free from 11 to 22 years out of 30 years, rather than
1 out of 30 years, as estimated for base climate
Table 15-4. Reduction in Ice Cover in Lakes Erie and Superior (average annual days of cover)
Lake
Erie West
Erie Cent
Erie East
Supr West
Supr East
Supr WFB
Base
1951-80
93
83
97
112
108
115
GISS Transient A
1981-2009
84
71
82
108
103
109
2010-2039
54
41
43
88
84
92
Doubled CO,,
GISS
26
8
6
46
43
55
GFDL
23
6
5
24
19
26
OSU
35
19
13
75
69
80
Analog
1930s
85
61
70
106
103
112
Abbreviations:
Supr = Superior; WFB = Whitefish Bay; Cent
Source: Assel (Volume A).
Central.
301
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Chapter 15
conditions. This result appears to be sensitive to
depth, as estimates indicate that the deeper Lake
Erie East Basin would be ice-free 60 to 84% of the
time, and the shallow West Basin would be ice-free
in 7 to 17% of the winters. Since it is colder, Lake
Superior would have ice cover in virtually all winters
under the scenarios.
Assel found that ice cover reductions during
the first 30 years of the transient scenario (model
years 1981-2010) may not be significantly different
than under current conditions. The length and
extent of ice cover noticeably decline, beginning in
the second 30 years of the transient scenario (2011-
40). By the last decade of the transient scenario,
the 2050s, the extent of ice cover was almost
identical to the GISS doubled CO2 coverage.
Croley also found that ice cover would be
reduced. His analysis found that average surface
temperatures on all the lakes in the winter could be
above 0°C. Even if average temperatures are that
high, water temperatures in near-shore and shallow
areas, the areas to which Assel said ice would be
limited, would be sufficiently cold to cause ice
formation.
Implications
Ice cover reductions could have positive and
negative effects. On the positive side, the shipping
season would be extended (see below). Water
would flow more freely through rivers and
connecting channels, allowing for more hydropower
production in the winter. On the other hand, ice
protects some aquatic life, such as whitefish, and
protects shorelines against the erosive impact of
high-energy waves (Meisner et al., 1987).
Shipping
With lower lake levels, ships would have to
reduce their cargo, or ports and channels would
have to be dredged. However, the shorter duration
of ice cover would allow for a longer shipping
season. The additional days of transport may make
up for the loss of capacity on each voyage.
Study Design
Keith et al. studied the potential impacts of
changes hi lake levels and ice cover on shipping in
six ports: Two Harbors; Duluth/Superior and
Whitefish Bays hi Lake Superior; and Toledo,
Cleveland, and Buffalo in Lake Erie. They used the
"ECO Great Lakes Shipping Model," which includes
current data on major ports and commercial ships
in the Great Lakes, types of cargo, costs of
transport, and operating costs. Keith et al. used
lake level reductions from Croley and Hartmann to
study the change hi cargo capacity and costs per ton,
and they used the change in cargo capacity to
estimate how many days of shipping would be
needed to transport the same amount of cargo as
transported at present. The latter figure was
compared to ice duration reductions estimated by
Assel to determine whether the shipping season was
sufficiently extended to allow for transport of the
same amount of annual cargo as currently
transported.
Limitations
The analysis did not consider changes in the
composition of the fleet or in the mix and amount
of cargo. It also assumed that demand for shipping
of goods did not change, even in response to
changes in availability of shipping. The analysis did
not examine whether goods would shift to or from
alternate ports or means of transportation and how
changes in the costs of shipping and in the shipping
season would affect users. Keith et al. also assumed
that channels were not dredged to be deeper. Thus,
analysis is useful for estimating the direction and
approximate magnitude of change, but quantitative
results should be interpreted with caution.
Results
The costs of shipping were estimated to
increase as a result of lower lake levels. The effect
on the cargo load for ships using the Port of Buffalo
are displayed hi Figure 15-4. Under drops of 0.7 to
1.0 meter hi Lake Erie, which are the lake level
reductions estimated by Croley for the OSU and
GISS scenarios, cargo capacity would decrease by
about 5 to 13%, and costs per ton would rise by the
same amount. Croley's estimate from the GFDL
scenario was that Lake Erie would fall 1.65 meters
(5.4 feet), but the shipping model does not include
lake level drops of more than 5 feet. A drop of 5
feet would decrease cargo capacity per voyage by
27% and increase costs by 33%. Thus, the drop hi
lake levels estimated under the GFDL scenario
could increase costs by more than 33%. Since lake
levels hi Lake Superior were not estimated to fall as
302
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Great Lakes
Increase in Costs
Reduction in Tonnage/Voyage
Additional Days Required to
Transport Same Amount of Cargo
2 3 4
WATER LEVEL REDUCTION (Feet)
Figure 15-4. Impacts of lower lake levels and reduced ice cover on shipping, cargo capacity, costs,
transport for the Port of Buffalo (Keith et al., Volume H).
and days of
much, the corresponding reduction in cargo capacity
for ships on those ports would be in the range of 2
to 8%.
Sanderson estimated that lake level reduction
of 0.2 to 0.6 meters would increase total Canadian
shipping costs by 5%, assuming the current fleet and
mix stayed the same. Although results are not
directly comparable, since Keith et al. examined
U.S. flagships and ports while Sanderson studied
Canadian ships and ports, the estimates are of the
same magnitude.
Whether the same amount of annual cargo can
be transported, assuming no dredging to deepen
channels, depends mostly on how much lake levels
drop. If the drop is sufficiently large, annual
tonnage could be reduced. The following discussion
assumes that lake level declines occur at the same
time as ice cover reductions. It is not clear from
these studies whether lake levels will respond more
slowly to climate change than ice cover. Figure 15-
4 also displays the additional days needed to
transport the same amount of cargo as is currently
shipped through Buffalo. Under the approximate 2-
to 3-foot drop of the wetter and relatively cooler
OSU and GISS scenarios, another 15 to 40 days of
shipping would be needed. Assel estimated that
under those scenarios, ice duration in eastern Lake
Erie would be reduced by 84 to 91 days. Thus,
under these scenarios, even with reduced capacity
per voyage, there would be enough additional days
of travel to transport even more goods. If lake
levels fell 5 feet, which is less than estimated by
GFDL, an additional 100 days of transport would be
needed to handle the same amount of cargo. Ice
duration in eastern Lake Erie could be reduced by
92 days under this scenario, which would not allow
enough time to transport the same amount of cargo,
assuming the current fleet and demand for
transport. The results appear to be more sensitive
to changes in lake levels than to reductions in ice
cover.
Keith and Willis used current dredging costs to
estimate the cost of dredging the ports to restore
current channel depths. The total costs of dredging
the three ports in Lake Erie range from $7 to $31
million per port (1987 dollars). Current annual
dredging costs for those ports range from $800,000
303
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Chapter 15
per year in Buffalo to $2.5 million per year in
Toledo (J. Hasseler, U.S. Army Corps of Engineers
Buffalo District, 1988, personal communication).
Implications
Reduction in the tonnage per voyage or
increased costs for dredging would raise shipping
costs. However, with a longer shipping season,
users of shipping such as powerplants would not
have to carry large inventories to last through the
winter and own enough land to store those
inventories. Besides reducing costs, this could allow
current lakefront storage areas to be used for other
purposes. Whether these savings would offset
higher shipping costs was not examined.
Dredging the ports and channels could
degrade the water quality of the lakes. The
sediments in many of these ports are toxic, and
disposal of the sediments could be complicated by
their toxicity and by the reduced disposal areas
resulting from lower lake levels.
Water Quality
Two studies estimated the temperatures and
thermal structures of southern Lake Michigan and
the Lake Erie Central Basin. The Lake Erie study
estimated biological activity, such as algal
production and changes in dissolved oxygen levels.
The Michigan and Erie analyses were used by
Magnuson et al. to study changes in the thermal
habitats of fish.
Thermal Structure of Southern Lake Michigan
Study Design
McCormick used a one-dimensional thermal
structure model (Garwood, 1977) to estimate the
heat content and structure of a site in south-central
Lake Michigan. The model has been successfully
applied to oceans and inland seas and was used by
McCormick to analyze a site 150 meters (500 feet)
deep. GCM data for windspeed, temperature,
humidity, solar radiation, and cloud cover were
applied to hourly data from 1981 to 1984.
Limitations
McCormick used the years 1981-84 as his base
case because hourly water temperature data are not
available for 1951-80. Three years provide very
limited baseline climate variability, although these
years include cold and warm periods. The results
are most sensitive to changes in windspeed. Since
the scenario may underestimate reductions in
windspeed from the GCMs (see the discussion of
the limitations of the lake level study), this analysis
may overestimate wind-driven mixing in the upper
layer and underestimate changes in the length of
time and degree of stratification. On the other
hand, if the intensity of summer storm increases,
then stratification may be weakened and shortened.
The analysis assumed there was no change in the
frequency of storms. More summer storms may
weaken stratification, while fewer storms could
strengthen stratification.
Results
McCormick estimated that the length of the
stratified season could increase under all three
scenarios. Figure 15-5 displays the mixed-layer
depth over an average year. The higher heat
content may cause the lake to begin to thermally
stratify, on average, about 2 months earlier than in
the base case (in April as opposed to June). The
stratified layers were estimated to begin to deepen
around late fall, as under current climate conditions.
BASE
GISS
GFDL
OSU
I I I
[ I I
AMJJA SOND
MONTH
Figure 15-5. Average annual mixed-layer depth in
southern Lake Michigan (McCormick, Volume A).
304
-------
Great Lakes
Surface lake temperatures were estimated to
be up to several degrees higher than in the base
case. The increase in surface temperatures was
greater than the increase in subsurface
temperatures. There appears to be a larger
warming of the entire water column in the winter,
about 2 to 3°C, than in the summer, which has a
warming of about 2°C. The wanner lake
temperatures are consistent with the studies of
Croley and Assel, which suggest that midlake water
would generally be ice-free. The earlier onset of
stratification, reduced winds in the scenarios, and
greater temperature differences between lake layers
could yield stronger density differences between
upper and lower layers.
McCormick detected a significant decrease in
the frequency of complete mixing of the lakes. The
surface layer could be warmer and more buoyant,
making it more difficult for entrainment and mixing
to occur. Temperatures were too warm in the
winters of some years to allow the lake to become
isothermal (the mixed layer would stay above the
bottom of the lake all year), leading to a year-long
stratification. This result is consistent with Croley's
analysis.
Implications
Reduced turnover of the lakes could have
serious implications for aquatic species in the lakes.
Mixing of oxygen and nutrients could be disrupted,
possibly affecting the abundance of life in the lower
and upper layers of the lakes.
Eutrophication of the Lake Erie Central Basin
Nutrient loadings have made many areas of
the shallow Lake Erie eutrophic at times. The
shallow western and central basins of the lake are
particularly vulnerable to eutrophication.
Installation of pollution controls in recent years has
improved water quality. Blumberg and DiToro
analyzed whether climate change would have an
effect on eutrophication in the Lake Erie Central
Basin.
Study Design
Blumberg and DiToro modeled the thermal
structure of the Lake Erie Central Basin. They
developed a thermal model for the basin, using a
modeling framework previously designed by
Blumberg (Blumberg and Mellor, 1983). This
model is similar to the one used by McCormick for
southern Lake Michigan.
Blumberg and DiToro then examined the direct
effects of changes in the thermal structure on
aquatic life in the basin. The outputs from the
thermal model were fed into a eutrophication model
that had been previously developed by DiToro
(DiToro and Connolly, 1980). The latter model
estimates what would happen to dissolved oxygen
levels in the lakes by simulating the interactions
between nutrient availability and biological (e.g.,
plankton) activity.
The models were run using only two base years,
1970 and 1975. In 1970, the thermocline (density
gradient between the upper and lower layers) was
deep, and over 60% of the hypolimnion (lower
level) in the Lake Erie Central Basin was anoxic
(depleted of oxygen). In 1975, the thermocline was
shallow, and less than 10% of the lower layer was
anoxic (DiToro et al., 1987).
Limitations
Although the two base years encompass a wide
range of baseline anoxic conditions, they do not
represent a full range of climate variability. In
addition, as in the Lake Michigan study, the
scenario assumed no change in the frequency of
storms. More summer storms would weaken
stratification and increase dissolved oxygen levels,
while fewer storms would have the opposite effect.
The analysis did not incorporate the actual
reduction in nutrient loadings from the base years,
or the estimated drop in lake levels from Croley's
work. Lower lake levels would reduce the volume
of the lower layer in Lake Erie, possibly increasing
eutrophication. The models were not run for the
winter, but Blumberg and DiToro tested the
sensitivity of results to higher water column
temperatures (due to warmer winter air
temperatures) in the spring and found no significant
difference in results. Blumberg and DiToro used
the vector wind estimates from the GCMs, which
may overestimate mixing in the upper layer.
Pollution loadings in 1970 and 1975 were much
higher than they are today. Use of current pollution
loadings would have resulted hi higher estimates of
dissolved oxygen levels and lower estimates of the
area of the basin that could become anoxic. The
305
-------
Chapter 15
direction of change estimated by Blumberg and
DiToro would not have been affected.
Results
Blumberg and DiToro estimated that the Lake
Erie Central Basin could remain stratified about 2
to 4 months longer than under current conditions,
with the stratified season starting 2 to 6 weeks
sooner and ending 2 to 7 weeks later. The
temperature differences between the upper and
lower layers of the basin were estimated to be
greater under all scenarios, leading to less exchange
of nutrients across the thermocline. The depth of
the thermocline appears to be most sensitive to
estimated changes in windspeeds. In two scenarios,
GISS and GFDL, windspeeds were generally lower,
and the thermocline was estimated to be about 2
meters higher than current depths. Under the OSU
scenario, windspeeds were estimated to increase and
the thermocline was estimated to be approximately
1 meter deeper than current levels. A lowering of
the thermocline depth by 2 meters in the 25-meter-
deep Lake Erie Central Basin can reduce the
volume of the lower layer by 20%, limiting total
oxygen availability.
All three scenarios generally led to decreases
in dissolved oxygen levels compared with base case
conditions despite differences in thermocline depth.
The increase in area of the Lake Erie Central Basin
that was estimated to become anoxic is shown in
Figure 15-6. Dissolved oxygen levels were estimated
to increase only in the July 1970 case, and this
occurred because the levels were near zero to begin
with. Blumberg and DiToro concluded that the
difference in oxygen content was caused by warmer
lake temperatures, which raise biological activity
enough to increase oxygen demand. The enhanced
biological activity was combined with a more intense
and longer stratified season to further lower
dissolved oxygen levels. Lower thermocline depths,
such as in the OSU scenario, result in even greater
decreases in dissolved oxygen levels.
The estimated changes in the thermal
structure of Lake Erie are comparable to
McCormick's results for southern Lake Michigan.
Both estimated that average temperatures in the
water column would rise, that there would be
greater differences in temperature between the
epilimnion and hypolimnion, and that stratification
would last longer. One major difference in the
results is that stratification begins earlier and lasts
AUGUST 1970*
BASE CASE
AUGUST 1975*
0.0?
S.9%
28.8*
* Base Casa Years K////I Area That Is Anoxic (Has No Oxygen)
Figure 15-6. Area of central basin of Lake Erie that
becomes anoxic (Slumber and DiToro, Volume A).
longer hi Lake Erie and begins earlier and breaks
up at the same time as the present stratification in
Lake Michigan. It is not clear whether this
difference is attributable to different lake depths, to
surface meteorology used to force the models, or to
surface boundary conditions in the calculations.
Implications
Decreased dissolved oxygen levels could make
the Lake Erie Central Basin less habitable for
finfish and shellfish during the summer. This could
reduce recreational uses of the lake such as
swimming, fishing, and boating. It also could put
more pressure on reducing sources of pollutants,
especially such nutrients as phosphorous, from point
and nonpoint sources.
Fisheries
The Blumberg and McCormick studies show
that climate change would probably raise lake
306
-------
Great Lakes
temperatures and reduce oxygen levels in certain
areas. To get an initial sense of what these changes
might mean for Great Lakes fish, Magnuson et al.
examined the potential ecosystem, organism, and
population responses to warmer temperatures.
Study Design
Magnuson et al. estimated changes in fish
habitat, growth, prey consumption, and population
for sites in Lakes Erie, Michigan, and Superior. The
work used several approaches and models to
examine the following:
• Changes in ecosystem activity, such as
changes in phytoplankton populations, were
estimated by using a community "Q10" rule
(Ruttner, 1931), which approximates the
higher biological activity associated with
higher temperatures.
• Magnuson et al. used the Blumberg and
McCormick thermal structure studies to
estimate the potential effects on thermal
habitats — the niche in which temperatures
are optimum for fish. To estimate changes
in habitats, the study used laboratory
estimates of the temperature regimes
preferred by fish (Magnuson et al., 1979;
Crowder and Magnuson, 1983) and
assumed that the lower layer of the Lake
Erie Central Basin is uninhabitable. In
addition, using a thermal model for streams
(Delay and Seaders, 1966), the study
calculated the change in habitat for brook
trout in a southern Ontario river.
• Magnuson et al. used a food consumption
and conversion model (Kitchell et al., 1977)
to estimate the changes in annual growth
and prey consumption at three near-shore
sites hi Lakes Superior, Michigan, and Erie.
This analysis assumed that consumption
rates increase with climate warming.
Growth simulation for Lake Michigan using
water temperature scenarios from
McCormick assumed that prey availability
did not increase. This study assumed that
fish migrate to habitable sites when inshore
temperatures are too warm.
Limitations
The study did not examine the combined effects
of reduced habitat and greater need for forage in
the summer, which would combine to intensify
species interactions. The analysis did not
incorporate impacts resulting from lower lake levels,
such as possible loss of wetlands, and it did not
analyze the aquatic effects of the potential reduction
hi the frequency of lake turnover or the impacts of
a reduction in ice cover. The introduction of new
species, which could have negative impacts on
existing fish, was not examined.
Any uncertainties associated with the
McCormick and Blumberg studies would be carried
over into the analysis on habitat. These changes in
the lakes and littoral systems may have negative
impacts on Great Lakes fish. These uncertainties
could reverse the direction of results and lead to
more declines in fish populations than indicated
here.
Results
Phytoplankton production, zooplankton
biomass, and maximum fishery yields were
estimated to increase 1.3- to 2.7-fold, with the
largest increase in phytoplankton production (1.6-
to 2.7-fold) (Figure 15-7). The larger increases in
biological activity were generally associated with
larger temperature increases. The increase in
phytoplankton provides more forage for
zooplankton, which, in turn, provides more forage
for fish. The increase hi phytoplankton can also
enhance eutrophication, as was estimated by
Blumberg and DiToro.
Magnuson et al. found that the average annual
thermal habitat for all fishes would increase. This
was especially apparent for lake trout, which is a
coldwater fish with a preference for very cold water,
and which could have more than a 100% increase in
habitat (see Figure 15-8). The major reason for the
increase hi habitat is that more habitable waters
would be found hi the fall, whiter, and spring. On
the other hand, hotter temperatures could decrease
summer habitats for certain species by 2 to 47%,
depending on the temperature rise and species. The
length of stream suitable for brook trout in the
summer could be reduced by 25 to 33% because of
higher temperatures.
307
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Chapter 15
cc
I COLO REGION I I COOL REGION I WARM I
osu
G\SS
GFDL
Figure 15-7. Increases in Great Lakes aquatic
productivity (Magnuson et al., Volume E).
DEC
± 2'C OF OPTIMUM TEMPERATURE
± 5«C OF OPTIMUM TEMPERATURE
Figure 15-8. Increase in lake trout habitat
(Magnuson et al., Volume E).
Fishes were generally estimated to have
increased body size under the scenarios. Cool and
cold coldwater fishes could have 20 to 70% more
growth, and warmwater fishes in warm areas could
have 220 to 470% more growth. This assumes that
prey availability increases. If prey availability does
not increase, fish growth would also decrease owing
to an inability to compensate for the increased
metabolic costs of living in higher temperatures.
Magnuson et al. calculated that if prey availability
does not increase, fish growth in Lake Michigan
could decrease by 10 to 30%. Warmwater fish
would have larger decreases if prey did not increase.
Furthermore, the increased demand for forage may
intensify species' interactions and alter the food web
structure.
The effects of reduced ice cover and possible
reduction in wetlands on Great Lakes fishes was not
investigated, although Freeberg (1985) suggests that
a reduction in ice cover would reduce whitefish
recruitment, and Meisner et al. concluded that loss
of wetlands due to lower lake levels could reduce
spawning, nursery, and feeding grounds for fish in
shallow areas, reducing fish populations (Meisner et
al., 1987).
Implications
Fish populations could increase, with beneficial
implications for commercial and recreational fishing,
although certain species, such as brook trout in
streams, may be reduced. A net increase in
fisheries would lead to more employment in
commercial fishing and tourism industries, but
would increase the need for maintaining water
quality in the lakes. Increased demand on the
forage base by predators and the introduction of
new species and reduced ice cover could have
negative effects, but these cannot be predicted and
must be considered as surprises of unknown
probability.
308
-------
Great Lakes
Forests
Climate change could affect the distribution
and abundance of forests in the Great Lakes region.
Overpeck and Bartlein examined the equilibrium
range shift of forests, Botkin et al. studied
transitional impacts on composition and abundance,
and Zabinski and Davis analyzed the ability of trees
to migrate along with a rapidly changing climate.
Potential Range Shifts
Study Design
Overpeck and Bartlein studied the potential
shifts in ranges of forest types over eastern North
America. This analysis suggests where trees are
likely to grow in equilibrium doubled CO2 climate
conditions after allowing for migration of tree
species to fully catch up with climate change (see
Forest Migration). It indicates only the
approximate abundance of different species within
a range, not what the transitional effects of climate
on forests might be, or how fast trees will be able to
migrate to the new ranges. (For a discussion of the
study's methodology and limitations, see Chapter 5:
Forests.)
Results
Under all three doubled CO2 scenarios, the
range of spruce, a major component of the boreal
forests, could shift almost entirely out of the region.
Northern hardwoods, such as birch and northern
pine species, would shift to the north but may still
be in the region. Oak trees, which are mostly found
in the southern part of the region, would be found
all over the region in the warmer conditions. The
abundance of prairie forbs (shrubs) would increase
in the region, and southern pines could eventually
migrate to the southern part of the region.
Transitional Effects
In contrast to Overpeck and Bartlein, Botkin
et al. examined the transitional effect of climate
change on forests as well as doubled CO2 effects.
Study Design
Botkin et al. used a model of forest species
growth and competition to estimate the effects of
climate change on Great Lakes forests (Botkin et
al., 1972, 1973). This model, which is known as a
stand simulation model, can be used to estimate the
transitional changes in composition and abundance
of forest species in response to environmental
changes such as higher temperature and
precipitation.
Botkin et al. studied two diverse sites in the
Great Lakes region. The first is in Mt. Pleasant,
Michigan, a heavily settled area dominated by
northern hardwoods and oaks, where commercial
forests are an important resource. The other site is
in Virginia, Minnesota, an undeveloped area
dominated by boreal forests that have commercial
and recreational uses.
Limitations
The model includes all dominant tree species
in the northern United States and assumes that
seeds from all these trees are universally available
throughout the region. Species with predominantly
southern distributions are not included; therefore,
the model does not estimate whether they could
grow hi the region under the warmer climate.
(Overpeck found that southern pines may migrate
into the southern part of the region.) Thus, the
stand simulation model does not accurately estimate
migration of trees, either within the region or from
other areas. Furthermore, the results do not assess
whether transplantation by humans of more
southern species would be successful. In addition,
the model does not account for fertilization effects
of CO2, although CO2 may not have positive effects
in the competitive environment of unmanaged
ecosystems (see Botkin et al., Volume D). Botkin
et al.'s analysis did not account for introduction of
new pests into the region, for the possibility of
increased frequency of fires, or for the combined
impact of changes in tropospheric air pollution
levels and UV-B radiation.
Results.
Botkin et al. estimated the doubled CO2
climate would cause major changes in forest
composition throughout the region. Results from
the Mt. Pleasant site indicate that tree biomass at
dry sites, which now have oak and sugar maple,
could be reduced by 73 to 99% and could convert to
oak savannas or even prairies. Relatively wet soil
sites might be converted from sugar maple to mostly
309
-------
Chapter 15
oak woodlands with some red maple. Biomass at
these sites could be reduced by 37 to 77%.
In the Minnesota site, the boreal forests could
be replaced by northern hardwood forests, now
characteristic of areas to the south (see Figure 15-
9). Relatively dry areas, such as the Boundary
Waters Canoe Area where balsam fir dominates,
and upland areas where white birch and quaking
aspen dominate, could be replaced by forests
consisting mainly of sugar maples. Where currently
saturated soils in these upland areas become drier
and better sites for tree growth, wood production
may increase. However, bogs that now contain
white cedar could become treeless. This is because
species that could tolerate warmer bog
no
conditions are currently in the region. It is possible
NORTHERN MINNESOTA IN 1980
While Birch Balsam Fir
NORTHERN MINNESOTA 2xCO2
Sugar Maple
^^Ba^^oll^^-^
•^^-^>xJ^Bedrock
Figure 15-9. Changes in composition of northern
Minnesota forests (Virginia, Minnesota; soil depth
= 1.0 meter; water table depth = 0.8 meter)
(Botkin et al., Volume D).
that more southern species could be transplanted to
these sites, although this was not studied.
In both sites, the biggest decline is seen in the
hotter and drier GFDL scenario. Decreased soil
moisture, which is a result of higher temperatures
and reduced rainfall, appears to be the most
significant factor reducing biomass.
Botkin et al. found that the abundance of
species could significantly change in three to six
decades. Figure 15-10 displays results from the
transient scenarios for balsam fir and sugar maple
at the Minnesota site. The basal area of balsam fir
could start to decline in three to six decades.
Potential declines in several decades are also seen
in simulations of white cedar and white birch in the
BALSAM FIR
%
E 6000
o
o
s
I 4000
a
5 2000
m
GISS A
GISS B
.
X>-0^^-__ ,
X "" "•"»•..
* r~~—--s-i^=»_ i
1980 2000 2020 2040 2060 2080
YEAR
SUGAR MAPLE
ET
E 6000
S
f. 4000
S 2000
19
GISS A /
GISS B /
/'
/
0 2000 2020 2040 2060 2080
YEAR
Figure 15-10. Change in forest composition during
the next century for a deep, wet, sandy soil in
northern Minnesota (Botkin et al., Volume D).
310
-------
Great Lakes
Minnesota site. Sugar maple, which has negligible
basal area in the current climate, was estimated to
start to exhibit significant growth within three
decades in both transient scenarios.
Forest Migration
Both Overpeck and Botkin assumed that trees
would be able to migrate to new locations (although
Botkin did not assume southern species would be
able to migrate into the Great Lakes region).
Zabinski and Davis examined the potential range
shifts of sugar maple, yellow birch, hemlock, and
beech currently found in the Great Lakes region
and compared that shift with potential rates of
migration.
Study Design
Zabinski and Davis assumed that tree species
grow only in climates with temperatures and
precipitation identical to their current range. They
determined the location of potential species ranges
under the GISS and GFDL scenarios. The climate
values were determined by extrapolating between
gridpoints. Zabinski and Davis examined the
potential migration of the species by assuming that
the doubled CO2 climate would not occur until
2090, and that these species could migrate into new
regions at the rate of 100 kilometers (62 miles) per
century.
Limitations
The study did not consider human
transplantation of seedlings to speed migration.
The analysis did not consider competition among
species or whether migratory routes would be
blocked. It also did not analyze whether species
could survive in the soil conditions, nutrient
availability, sunlight, and other relevant factors in
northern areas. Doubled CO^ climate conditions
could occur sooner than 2090, resulting in greater
range reductions. The rate of forest migration used
is double the maximum rate ever recorded for
temperate trees. A faster warming and slower
migration would make it more difficult for forests to
keep up with shifts in range attributable to climate
change. Zabinski and Davis did not consider
whether higher atmospheric CO2 concentrations
would mitigate the decline of forests along southern
boundaries of their ranges.
Results
Under the wetter GISS scenario, the potential
ranges of sugar maple, yellow birch, hemlock, and
beech move markedly northward to central Canada.
The results for hemlock and sugar maple are
displayed in Figure 15-11. The stippled area shows
the potential range, and the black area shows how
far the trees could migrate by 2090. Zabinski and
Davis found that hemlock, yellow birch, and sugar
maple could become much less abundant hi the
parts of Wisconsin and Michigan where they
currently grow. Beech may be completely
eliminated from the lower peninsula of Michigan
where it is presently abundant. In addition, the rate
of migration would be slower than the climate
change. The trees would not migrate as far as the
northern boundary of the climate range (the
stippled area). The southern boundary would be
driven northward by climate change. Since the shift
in climate zones is faster than the assumed rate of
migration, the southern boundary would move north
faster than the northern migration rates. The total
range of all four species would be reduced.
Under the GFDL scenario, which is the hottest
and driest, all four species are eliminated from the
Great Lakes region. Northern hardwood tree
species might be replaced by trees characteristic of
more southern latitudes or by prairie or scrubland.
Since the southern range of the trees moves farther
north than in GISS, the inhabited range would be
much smaller than under GISS. Zabinski and Davis
found that all four tree species would be confined to
an area in eastern Canada having a diameter of only
several hundred kilometers.
The ability of the four species to survive in
more northern latitudes may depend on whether
they could adapt to different day lengths and soils.
Implications of Forest Studies
All three studies, through different analytic
approaches, agree that the scenarios of climate
change would produce major shifts hi forest
composition and abundance. Boreal forests would
most likely no longer exist hi the region. Northern
hardwood forests might still be present, especially in
the north. Uncertainty exists concerning whether
forests in the southern part of the region will die
back leaving grasslands or whether new species will
be able to migrate or will be transplanted and
flourish.
311
-------
Chapter 15
Hemlock
Present Range
Range After 2050: GISS
Range After 2050: GFDL
Sugar Maple
Present Range
HJ Potential Range
• Inhabited Range
Range After 2050: GISS
Range After 2050: GFDL
Scale 0 400Km
Figure 15-11. Shifts in range of hemlock and sugar maple (Zabinski and Davis, Volume D).
The rapid rate of climate change, coupled with the
presence of urban areas and extensive farmland in
the southern Great Lakes States, may impede
migration of southern species into the region. Such
a shift could result in increased soil erosion and
decreased water quality. In addition, higher tree
mortality and drier soils could increase fire
frequency. There also may be an increase in
pathogen-related mortality in trees. Shifts in forest
composition and abundance may have implications
for wildlife in the region.
This shift in species also could have significant
impacts on the commercial forest industry in the
region. The industry currently harvests softwoods
for production of pulp, paper, and construction
materials. These species would decline and would
be replaced by oaks and maples, which are useful
for furniture but take longer to become fully grown.
Red maple, which may be more abundant in the
southern area, is not currently used commercially.
Changes in forest abundance may also affect
tourism and recreation.
Agriculture
The agriculture studies combined analyses of
impacts on the region and across the country.
Ritchie et al. studied the potential impacts of
climate change on crop yields in the region. Adams
312
-------
Great Lakes
et al. then used the results from this study and other
regional crop yield analyses to estimate economic
adjustments by farmers. Easterling studied how a
typical Illinois corn farmer would try to adapt to
climate change.
Crop Yields ,
Study Design
Ritchie et al. used crop growth models to
estimate the impacts of climate change on yields for
corn and soybeans in the Great Lakes States (Jones
and Kiniry, 1986; Wilkerson, 1983). The two
physiological models examine the direct effects of
temperature and precipitation on crop yields.
Ritchie et al. also used simple estimates of
.increased photosynthesis and decreased
transpiration to conduct a sensitivity analysis of the
combined impacts of change in weather and CO2
fertilization on crop yields. In addition, they studied
whether crop varieties currently in southern areas
• may mitigate climate effects.
Limitations
The direct effects of CO2 in the crop modeling
study results maybe overestimated for two reasons.
First, experimental results from controlled
environments may show more positive effects of
y than would actually occur in variable, windy,
ana pest-infested (weeds, insects, and diseases) field
conditions. Second, because other radiatively active
trace gases, such as methane (CH.) also are
increasing, the equivalent warming of a doubled
CO2 climate may occur somewhat before an actual
douoling of atmospheric CO2- A level of 660 ppm
CO2 was assumed for the crop modeling
experiments, while the CO2 concentration in 2060 is
estimated to be 555 ppm (Hansen et al., 1988).
All the scenarios assumed that by having low
salinity and no compaction, soils would be relatively
favorable for crops, and there were would be no
limits on the supply of all nutrients. In addition, the
analysis assumed farmers would make no
technological adjustments to improve crop yields or
introduce new crops. Possible negative impacts due
to changes in storm frequency, droughts, and pests
and pathogens were not factored into this study.
The results could be significantly affected by such
changes. The percentage changes for Duluthare
very large because current yields are very low
relative to other sites.
Results
Ritchie et al. found that temperature and
precipitation changes alone could reduce crop yields
everywhere in the region, except in the
northernmost latitudes, such as Duluth, where yields
could increase depending on rainfall availability.
Results from selected sites are displayed in Table
15-5. Corn yields could decrease from 3 to 60%,
depending on climate and water regime (dryland or
irrigated). However, Duluth, the most northern
site, could see increases of 49 to 86%. Current
dryland and irrigated corn yields are lower in
Duluth than in the more southern sites. Dryland
yields in Duluth under climate change could be
equal to other sites, and irrigated yields could
exceed the other locations.
Dryland soybean yields are estimated to drop
by 3 to 65% in the region, except in the north.
There, dryland yields may decrease by 6% under
GFDL but increase by 109% under the wetter GISS.
Under irrigated scenarios, soybean yields in the
north increase by 96 to 153%. Even with the
increase in output, the soybean yields in Duluth may
still be lower than in areas to the south.
The reduction in yields in the south would be
due mainly to the shorter growing period resulting
from extreme summer heat. Production in the
north is currently limited by the long winter, so a
longer frost-free season results in increased yields.
Ritchie found that the demand for irrigation
would rise between 20 and 173% under the GFDL
scenario and up to 82% under GISS, although some
sites under GISS were estimated to have reductions
in demand of up to 21%.
The combined effects of higher concentrations
of CO2 and climate change could increase yields if
sufficient rainfall is available. If it is not, yields
could rise or fall. Dryland corn and soybean yields
may rise up to 135% under the GISS scenario and
up to 390% in Duluth. In the dry GFDL scenario,
however, yields could fall up to 30% or rise up to
17%, again except for Duluth, which has an increase
of 66 to 163%. Irrigated yields for corn rise and fall
under both scenarios, but irrigated soybean yields
313
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Chapter 15
Table 15-5. Effects of Climate Change Alone on Corn and Soybean Yields for Selected Sites in Great
Lakes States (ranges are GISS-GFDL and are % change from base)
Site
Corn
Soybeans
Dryland
Irrigated
Dryland
Source: Ritchie et al. (Volume C).
Irrigated
Duluth, MN
Green Bay, WI
Flint, MI
Buffalo, NY
Fort Wayne, IN
Cleveland, OH
Pittsburgh, PA
+49 to -30
-7 to -60
-17 to -48
-26 to -47
-11 to -51
-26 to -50
-22 to -55
+86 to +36
-3 to -44
-14 to -38
-18 to -38
-15 to -48
-19 to -43
-19 to -45
+ 109 to -6
-3 to -65
-6 to -51
-21 to -53
-2 to -58
-16 to -59
-13 to -59
+ 153 to +96
+3 to -26
+ 6 to -11
+ 6 to -6
0 to -19
-1 to -14
0 to -13
could rise 43 to 72% in the south and up to 465%
in Duluth. The combined effects lead to an
estimated reduction in demand for irrigation for
corn of 26 to 100% under both scenarios, whereas
irrigation needs for soybeans under GFDL rise by
65 to 207% and range in GISS from a reduction of
10% to an increase of 32%.
Ritchie found that use of a longer season corn
variety could reduce the negative effects of climate
alone, under the GFDL scenario, but would still
result in net losses.
It is not clear whether crop yields would rise
or fall in the region. Among other factors, this will
depend upon how CC*2 and climate change combine
to affect crop growth and on how hot and dry the
climate becomes. Yields and the potential demand
for irrigation appear to be quite sensitive to rainfall,
being higher under relatively drier scenarios. If
climate change is severe enough, as under the
GFDL scenario, yields could fall. In general,
irrigation demand would rise, but some significant
exceptions exist.
Implications
The potential shifts of agriculture northward
are discussed below. Since the demand for
irrigation is generally higher, it could become a
more attractive option for farmers in the region.
Whether more irrigation is actually used will depend
on its costs and the price of crops.
Regional Shifts
Ritchie et al.'s analysis only estimates changes
in potential yields for the Great Lakes region. How
much farmers actually grow will depend in part on
what happens elsewhere. If the relative productivity
of agriculture rises, farmers will probably increase
output. If relative productivity falls, they would
most likely cut back. Adams et al. examined how
different regions of the United States may react to
potential productivity changes. Results are
presented here for the Great Lakes region only.
Adams et al. modeled potential nationwide
shifts in crops using the Great Lakes analysis and
analyses of shifts in other regional crop yields. He
did the analysis for yields attributable to climate
change alone, and for the combined effects of
climate and enhanced CO2 concentrations. Adams
et al.'s analysis did not account for the effects of
climate on agriculture in other countries. How U.S.
and regional agriculture respond to climate change
may be strongly influenced by changes in relative
global productivity and demand. The study did not
consider introduction of new crops such as citrus.
(For a discussion of the study's design and
limitations, see Chapter 6: Agriculture.)
Results
Adams et al.'s estimates of acreage changes for
the Great Lakes States are shown in Table 15-6. It
appears that land devoted to agriculture in the
314
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Great Lakes region would not change significantly
in response to climate change. The results indicate
a slight tendency to increase acreage in the northern
Great Lakes States, although only by small amounts.
Results for the Corn Belt States are inconclusive.
Table 15-6. Percentage Change in Acreage for
Great Lakes States After Doubled
CO2 Climate Change (Corn Belt
States include Iowa and Missouri)
Climate change
alone
Area GISS GFDL
Lake States +3 0
Corn Belt +2 -6
Climate and
CO.
GISS 6FDL
+r +10
-1 -6
Implications
The results of Adams et al. and Ritchie et al.
suggest that northern regions could become more
attractive for agriculture, although more extensive
analysis is needed to confirm this result. The
presence of thin, glaciated soils may limit this
expansion. If it occurs, such an expansion could
have significant implications for development of the
north. Additional acreage could be converted from
current uses, such as forests, to agriculture.
Increased erosion and runoff from this additional
acreage would pollute groundwater and streams and
lakes in relatively pristine areas. Enhanced
agriculture may increase the need for more shipping
as lower lake levels raise shipping costs.
Adjustments by Illinois Corn Producers
Farmers may make many adjustments to
climate change such as planting different crop
varieties, planting earlier in the season, irrigating,
and using different fertilizers. Easterling examined
how a typical corn farmer in Illinois would react to
climate change.
Study Design-
Easterling presented several professional crop
consultants with the GISS and GFDL climate
Great Lakes
change scenarios and with estimates of corn yields
and prices for climate effects alone from the Ritchie
et al. and Adams et al. studies. Based on the
interviews, a set of decision rules was established to
estimate how a typical Illinois corn farmer would
alter farming practices in response to the climate
and agriculture scenarios.
Limitations
The climate change scenarios involve climate
conditions not experienced by the experts. Their
estimates of how farmers would respond are not
based on experience with similar conditions but on
speculation. The results of the combined climate
and CO2 sensitivity analyses were not presented to
the experts. The analysis is specifically for Illinois
corn farmers and cannot be extrapolated to other
areas or crops.
Results
Easterling found that the degree of adjustment
depends on how much climate changes. Under the
wetter GISS scenario, farmers could make
adjustments to help mitigate the impacts of higher
temperatures. Such adjustments could include
planting earlier in the spring to avoid low soil
moisture levels in the summer, using full-season
corn varieties for earlier planting, and changing
tillage practices and lowering planting densities to
better conserve soil moisture. Under the hotter and
drier GFDL scenario, corn production might not be
feasible. Farmers would likely install irrigation
systems; switch to short-season corn, soybeans, and
grain sorghum; and perhaps remove marginal lands
from production. This last conclusion is consistent
with the Adams et al. study.
Implications
Although farmers have a variety of adjustment
options to help cope with climate change, they may
have great difficulty coping with extreme changes*
such as the dry climate implied by the GFDL
scenario. Use of more irrigation would have
negative implications for water quality, although this
would be partly counterbalanced by any retirement
of marginal lands.
315
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Chapter 15
Electricity Demand
Study Design
Linder and Inglis used the GISS transient
scenarios to estimate the national changes in
demand for electricity for the years 2010 and 2055.
The temperature change for 2055 is almost as high
as the GISS doubled CO2 estimate of 4.2° C. They
first estimated the change in electricity demand due
to gross national product (GNP) and population
growth, and then factored hi demand changes based
on change in climate. The results for the Great
Lakes States are displayed here in terms of the
percentage change from the non-climate-related
growth. The Great Lakes analysis did not consider
any reductions in hydropower production resulting
from drops hi lake levels. (For a description of the
study's design and limitations, see Chapter 10:
Electricity Demand.)
Results
Estimates of changes in annual demand
induced by climate change are displayed hi Table
15-7. The results for 2010 are a range based on
GISS transient scenarios A and B, and the results
for 2055 are just for GISS A. A latitudinal
difference exists within the Great Lakes region. In
the northern states of Minnesota, Wisconsin,
Michigan, northern Ohio, and upstate New York,
annual demand falls. The reduced demand for
winter heating apparently offsets the increased
demand for summer cooling. This is true in 2010
and 2055, when scenario temperatures are,
respectively, 1 and 4°C higher than the base case.
Annual demand hi the southern part of the region
(in Illinois, Indiana, southern Ohio, and
Pennsylvania) was estimated to rise because
increased cooling needs are apparently greater than
reductions in heating.
Although annual demand could fall in some
' areas, new generation capacity requirements for all
utilities hi the region would be higher than they are
now because of increased summer cooling needs.
New generation capacity requirements needs are
estimated to rise by 3 to 8% hi 2010 and by 8 to
11% in 2055. Whether costs would rise in the next
two decades is not clear. Linder and Inglis
estimated that under the gradual warming of GISS
B, cumulative capital costs hi the region would be
reduced by $1.3 billion, while under the more rapid
warming of GISS A, costs would increase by $300
Table 15-7. Estimated Changes in Electricity
Demand Induced by Transient
Climate Change Scenarios
for Great Lakes Utilities (%)
Utility
Annual (2010) Annual (2055)
Minnesota
Wisconsin
Michigan
Upstate
New York
Ohio, north
Ohio, south
Pennsylvania
Illinois
Indiana
-0.2 to -0.3
0.4 to -0.5
-0.2 to -0.3
-0.2 to -0.5
-0.2 to -0.3
0.4 to -0.5
0.4 to -0.5
0.5
0.4
-1.2
-2.3
-1.2
-1.3
-1.3
2.1
2.2
2.0
1.9
Total Negligible
<1
Source: Linder and Inglis (Volume H).
million. By 2055, costs would rise to $23 to $35
billion under GISS A. However, Linder and Inglis
estimated that the cost to build additional capacity
to meet GNP and population growth without
climate change would be $488 to $715 billion.
Implications
Increased capacity requirements could place
additional stress on the region. Fossil fuel plants
could add more pollutants to the air. The lake level
analysis indicates that hydropower production from
the lakes would be reduced, further increasing the
demand for energy from other sources.
POLICY IMPLICATIONS
Climate change could raise many issues to be
addressed by policymakers in the region.
Fundamentally, decisionmakers may have to cope
with water use, water quality, and land management
issues. They could have to respond to a decline in
water availability, increased demand for water,
poorer water quality, and shifts in land use,
including the possibility of expanded agriculture in
the north.
316
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Great Lakes
Most likely, many of the decisions in response
to climate change, especially issues concerning water
management, would be made on an international
basis. Both Canada and the United States oversee
the regulation of the lakes, water quality, and
diversions of water out of the basin.
Water Supply Issues
Lake Regulation
One important issue to be faced by both
countries may be regulation of the lakes. Lower
lake levels may require altering regulation plans for
Lakes Superior and Ontario. This would involve
tradeoffs among the needs of shippers, hydropower,
shoreline property owners, and infrastructure, and
downstream needs, in deciding how high to keep the
lakes and rivers. For example, maintaining
highwater levels in the lakes to support shipping,
hydropower, consumption, and improved water
quality would be at the expense of shipping,
hydropower, municipal and industrial consumption,
and water quality in the St. Lawrence River.
Additional structures to control the flow on the
lakes may be an option. The International Joint
Commission should begin to consider in its long-
term planning the potential impacts of climate
change on lake regulations.
Withdrawals
Even without climate change, population
growth would increase demand for water for
municipal and industrial consumption and power
generation. Climate change would most likely
intensify the demand for withdrawals from the lakes
for even more uses within and outside the basin.
Municipal consumption would rise (Cohen, 1987b),
and farmers in the region may need more water for
irrigation.
Others outside the Great Lakes may demand
diversion of water from the basin. The 1986 Water
Resources Development Act prohibits such
diversion without the agreement of all Great Lakes
governors and prohibits the federal government
from studying this issue. Increased diversion
through the Chicago Ship Canal was requested in
the summer of 1988 to raise water levels on the
drought-starved Mississippi River. The U.S. Army
Corps of Engineers rejected the request. Policy-
makers will have to balance these demands with the
needs of people in the basin.
Shipping
Any response to .the potential impacts on the
shipping industry may be costly. Possibilities
include dredging of both ports and connecting
channels. Dredging could cost tens, if not hundreds,
of millions of dollars. In addition to the high capital
costs of dredging, substantial environmental costs
could be incurred in disposing of dredge soils
contaminated with toxic chemicals. If dredging were
not undertaken, cargo loads would be lower and
would possibly impair Great Lakes commerce.
Pollution Control
Climate change could lead to stricter pollution
control to maintain water quality. Reduced
riverflow, lower lake levels, changed thermal
structure, and potentially reduced groundwater
supplies may necessitate stricter standards and
additional controls on sources of pollution. A need
may exist for better management of nutrient runoff
from farms into shallow areas, such as the Lake
Erie Western and Central Basins. Many pollution
control institutions, such as EPA and state and local
water quality agencies, would have the authority to
impose appropriate controls on polluters.
The water quality problems directly caused by
climate change could be exacerbated by other
responses to climate change. Intensified agriculture
in the region could increase runoff, necessitating
more control of noripoint sources of pollution. If
agriculture in northern areas expands, surface and
groundwater quality in relatively pristine areas may
be degraded. Pollution control authorities such as
the U.S. EPA may need to impose more
comprehensive controls for those areas and should
consider this in their long-term planning.
Fisheries
Although the analysis on fisheries indicates that
fish populations in the Great Lakes would generally
increase, maintaining fisheries may require intensive
management. In productive areas, the possibility of
introduction of new species could mean major
changes in aquatic ecosystems. Fisheries
management may be needed to maintain
commercially and recreationally valuable species.
317
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Chapter 15
The Great Lakes FisheryrCommission may wish to
consider the possible implications of climate change
on valuable fisheries and management strategies to
handle these possible changes. Additional pollution
controls maybe needed to help maintain fisheries in
such areas as western and central Lake Erie.
Land Use
Shorelines
The potential changes in land availability and
uses present opportunities and challenges. Lower
lake levels would open up new beaches and
potential areas for recreation and development,
although high capital costs may be associated with
developing them. These lands could be kept
undeveloped to serve as recreational areas and as
protection against fluctuating lake levels and
erosion. Conversely, they could be developed to
provide more housing and commercial uses.
Building structures closer to the shorelines would
make them more vulnerable to short-term rises in
lake levels.
How these lands will be used will be decided
by local and state governments as well as private
shoreline property owners. Under the Coastal Zone
Management Act, states may identify coastal zone
boundaries and define permissible land (and water)
uses (Baldwin, 1984). Thus, the act could be used
to help manage the use of exposed shorelines.
Lower lake levels and less ice cover may also
increase shoreline erosion, decreasing the value of
shorelines and degrading water quality. The Great
Lakes Basin is not included in the U.S. coastal
barrier system, a program that denies federal funds
for development of designated erosion or flood-
prone coastal barriers (Ray et al., Volume J).
Forestry
The potential decline hi forests and northward
shift in Great Lakes agriculture raise many land-use
issues. One important issue may be how to manage
potentially large and rapid shifts hi forest
composition. To speed northward colonization,
plantings of the species might be recommended
along the advancing front of suitable climate.
However, unsuitable soils and day lengths shorter
than the species can tolerate might limit the success
of such plantings. The forestry industry may
consider growing different types of species and
producing wood for different uses, such as for
furniture rather than for pulp and paper.
Agriculture
Although forests may decline, demand for more
land for agriculture in northern areas may grow;
however, Adams et al. indicated this demand may
be small and will depend on market forces and
policies. Federal and state land managers as well as
local zoning laws may need to consider that the
demand for land use may change. Rules on these
lands could have a major influence on how, if at all,
the north is developed.
Demographic Shifts
This report did not study the demographics
associated with climate change and cannot say
whether people will migrate north along with
warmer climates. A workshop on climate change
and the Great Lakes region, conducted by Ray et al.
and attended by government representatives,
academics, and citizens group representatives who
have studied climate-related Great Lakes resources,
concluded that populations from other regions of
the United States could migrate to the Great Lakes.
The region could have a more favorable climate
than more southern areas. Although lake levels
may fall, the lakes will still contain a large amount
of freshwater while other areas have more severe
water availability problems. Consequently, the
Great Lakes region may be relatively more
attractive than other regions.
Like lower lake levels, an in-migration could
present opportunities and challenges. Such a
migration could revitalize the region, reversing
population and economic losses of recent decades.
However, it also could exacerbate some of the
problems associated with climate change. More
people and industries would require more water and
add more pollution, further stressing water supplies
and quality. Population growth could increase
pressure to develop exposed shorelines along the
lakes.
318
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Great Lakes
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321
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CHAPTER 16
SOUTHEAST
FINDINGS
Global climate change could diminish the extent of
the region's forests, reduce agricultural productivity
and increase the abandonment of farms, diminish
fish and shellfish populations, and increase
electricity demand. Approximately 90% of the
national coastal wetland loss and two-thirds of the
national shoreline protection costs from sea level
rise could occur in the Southeast. The impacts on
rivers and water supplies are uncertain.
Agriculture
« Southeastern agriculture is generally more
vulnerable to heat stress than to freezing, so
the adverse impacts of more hot days would
more than offset the beneficial impact of a
longer growing season.
• As a result of climate change alone, yields of
soybeans and corn would vary from no change
in the cooler regions to up to a 91% decrease
in warmer areas, even if rainfall increases.
• A preliminary assessment suggests that when
the direct effects of CO, are included, yields
might increase in parts of the region if climate
also becomes wetter. If climate becomes drier,
yields could decrease everywhere in the region.
However, our understanding of the direct
effects of CO2 fertilization is less certain than
our understanding of the impacts of climate
change. Increased CO2 could also affect
weeds, but these impacts were not analyzed.
• If rainfall decreases, irrigation will become
necessary for farming to remain viable in much
of the region.
• The range of such agricultural pests as potato
leafhoppers, sunflower moths, and black
cutworms could move north by a few hundred
kilometers. This would most likely result in
increased use of pesticides.
• Considering various scenarios of climate
change and CO2, the productivity of
southeastern agriculture could decline relative
to northern areas, and 10 to 57% of the
region's farmland could be withdrawn from
cultivation. This analysis did not consider
whether new crops would be introduced. The
decline in cultivated acreage may tend to be
concentrated in areas where farming is only
marginally profitable today. A reduction in
agriculture could hurt farm-related
employment and the regional economy.
Forests
• There may be a significant dieback in southern
forests. Higher temperatures and drier soils
may make it impossible for most species to
regenerate naturally and may cause forests to
convert to shrub terrain or grassland. The
decline in the forests could be noticeable in 30
to 80 years, depending on the site and scenario.
Southern noncoastal areas, such as Atlanta and
Vicksburg, may have particularly large
reductions. The moist coastal forests and the
relatively cool northern forests may survive,
although with some losses.
• The forest industry, which is structured around
currently valuable tree species, would have to
either relocate or modify its planting strategies.
• Historically, abandoned farms have generally
converted to forests. If large portions of the
Southeast lose the ability to naturally generate
forests, much of the region's landscape may
gradually come to resemble that of the Great
Plains.
Water Supplies
Because the winter accumulation of snow plays
a negligible role in determining riverflow, our
inability to predict whether rainfall will increase or
323
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Chapter 16
decrease makes it difficult to say whether riverflows
will increase or decrease.
• The limited number of hydrologic studies
conducted in the Southeast further prevents us
from making any definitive statement about the
regionwide implications for rivers.
• Decreases in rainfall could disrupt navigation,
drinking water availability, recreation,
hydropower, powerplant cooling, and dilution
of effluent, while increased rainfall could
exacerbate the risk of flooding.
• For the scenarios used in this report, changes
in operating rules for managed water systems
would allow current water demands to be met
in most instances.
• The Southeast generally has ample
groundwater supplies. The potential
implications of increased irrigation on
groundwater need to be examined.
Sea Level Rise
• A 1-meter rise in sea level by the year 2100
would inundate 30 to 90% of the region's
coastal wetlands and flood 2,600 to 4,600
square miles of dryland, depending on the
extent to which people erect levees to protect
dryland from inundation. If current river
management practices continue, Louisiana
alone would account for 40% of national
wetland loss, and developed areas could be
threatened as soon as 2025.
• Holding back the sea by pumping sand or
other measures to raise barrier islands, and
protecting mainland areas with bulkheads and
levees, would cost approximately $42 to $75
billion through the year 2100 for a 1-meter
rise.
Marine Fisheries
• Gulf coast fisheries could be negatively affected
by climate change. A loss of coastal wetlands
due to sea level rise could eliminate critical
habitats for shrimp, crab, and other
commercially important species. Temperatures
in the gulf coast estuaries may exceed the
thermal tolerances for commercially important
finfish and shellfish, such as shrimp, flounder, and
oysters. Oysters and other species could be
threatened by the increased salinity that will
accompany sea level rise. Some species, such as
pink shrimp and rock lobster, could increase in
abundance.
Electricity Demand
• The annual demand for electricity in the
Southeast could rise by 14 to 22 billion
kilowatthours (kWh), or 2 to 3%, by 2010 and
by 100 to 197 billion kWh, or 7 to 11%, by
2055 as a result of increased temperature.
• By 2010, approximately 7 to 16 gigawatts (GW)
could be needed to meet the increased
demand, and by 2055, 56 to 115 GW could be
needed — a 24 to 34% increase over baseline
additions that may be needed without climate
change. The cumulative costs could be $77 to
$110 billion by 2055.
Policy Implications
• Federal laws constrain the U.S. Army Corps
of Engineers and other water resource
managers from rigorously considering tradeoffs
between many nonstatutory objectives of
federal dams in the Southeast, including
recreation, water supply, and environmental
quality. Increased flexibility would improve the
ability of these agencies to respond to and
prepare for climate change.
• Given the potential withdrawals of acreage
from agriculture, the potential for growing
tropical crops needs to be examined.
• Strategies now being evaluated by the
Louisiana Geological Survey and the U.S.
Army Corps of Engineers to address coastal
wetland loss in Louisiana should consider a
possible sea level rise of 0.5 to 2.0 meters.
Measures that would enable this ecosystem to
survive would require major public works and
changes hi federal navigation and riverflow
policies. Because of the decades required to
implement necessary projects and the prospect
that much of the ecosystem would be lost by
2030 even without climate change, these
programs need to proceed expeditiously.
324
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Southeast
Given the potentially important impacts on
forests, private companies as well as agencies
such as the U.S. Forest Service and state
agencies may wish to assess the potential for
large losses of southern forests and the
implications for research and management
strategies.
CLIMATE AND THE SOUTHEAST
The climate and the coastal zone of the
Southeast are among the chief factors that
distinguish the southeastern United States from the
rest of the nation.1 The warm temperatures,
Except for the discussion of the economic implications for
agriculture, the term "Southeast" refers to the study area shown
in Figure 16-1: North Carolina, South Carolina, Georgia,
Florida, Alabama, Mississippi, Tennessee, and the coastal zones
of Louisiana and Texas.
abundant rainfall, and generally flat terrain gave rise
in the 17th century to a strong agricultural economy
with a distinctive regional culture. The combination
of a benign climate and 60% of the nation's ocean
beaches continues to attract both tourists and new
residents to the southeastern coastal plain. Florida,
for example, is the nation's fastest growing state and
will be the third largest by the year 2000 (Meo et
al., Volume J).
CLIMATE-SENSITIVE
RESOURCES OF THE
SOUTHEAST
Water Resources
When statewide averages are considered, each
of the seven states in the Southeast receives more
rainfall than any other state in the continental
MIAMI
Figure 16-1. Southeast region.
325
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Chapter 16
United States (although parts of some western
states receive more). Moreover, the rivers of the
Southeast drain over 62% of the nation's lands; the
Mississippi River alone drains 38% of the nation
(Geraghty et al., 1973).
The Southeast supports 50,000 square miles of
bottomland hardwood forests (Mitch and Gosselink,
1986),2 which are periodically flooded areas that
offer winter habitat for migratory birds such as
ducks, geese, and songbirds. Bass, catfish, and
panfish are found in the slow-moving rivers, and
trout inhabit the fast-moving mountain streams.
Dams have been constructed along most of the
region's major rivers. Although private parties have
built a few dams, most of the major projects were
built by the U.S. Army Corps of Engineers, the
Tennessee Valley Authority, and other federal
agencies. In general, the statutory purposes of these
reservoirs have been to ensure a sufficient flow of
water during droughts, to prevent floods, and to
generate electricity. The nonstatutory objectives of
environmental quality, recreation, and water supply
also are considered in the operation of dams.
Dam construction has created large lakes along
which people have built houses, hotels, and marinas.
These dams generate 22.2 billion kilowatthours
(kWh) per year, approximately 7% of the region's
power requirements (Edison Electric Institute,
1985). In general, the reservoirs have sufficient
capacity to retain flood surges and to maintain
navigation flows during the dry season. The one
notable exception is the Mississippi River: levees
and land-use regulations are the main tools for
preventing flood damages; although the Mississippi's
base flow usually is sufficient to support navigation,
boats ran aground on many stretches of the river
during the drought of 1988.
In Florida, which accounts for 45% of water
consumption in the Southeast, groundwater supplies
about half the water used by farms and 85% of the
water used for residential and industrial purposes.
For the rest of the Southeast, groundwater supplies
most water for agricultural and rural uses
HThis measure includes Mississippi, Arkansas, Louisiana, Texas
and Virginia.
but only 30% for public supplies (see Meo et al.,
Volume J).
Atlanta and some other metropolitan areas
obtain their water supplies from federal reservoirs;
however, even the many cities that do not still may
benefit from federal and federal/state water
management. For example, New Orleans obtains its
water from the Mississippi River. Without the Old
River Control Structure in Simmesport, Louisiana,
which prevents the river from changing its course to
the Atchafalaya River, the New Orleans water
supply would be salty during droughts. Although
Miami obtains its water from the Biscayne Aquifer,
some coastal wells would be salty without the efforts
of the U.S. Army Corps of Engineers and the South
Florida Water Management District to recharge the
aquifer with supplemental freshwater from canals
and Lake Okeechobee.
The various uses of water often conflict with
each other. Hydroelectric power generators,
lakefront residents, and boat owners benefit when
water levels are maintained at high levels. However,
high water levels make flood control more difficult,
and municipal uses, navigation, hydropower, and
environmental quality require that water be released
during the dry season, which adversely affects
recreation.
Estuaries
Over 43% of the fish and 70% of the shellfish
harvested in U.S. waters are caught in the Southeast
(NOAA, 1987). Commercially important fishes are
abundant largely because the region has over 85%
of the nation's coastal wetlands; over 40% are in
Louisiana alone.
Most of the wetlands in the Southeast are less
than 1 meter above sea level. The wetlands in
Louisiana are already being lost to the sea at a rate
of 50 square miles per year because of the
interaction of human activities and current rates of
relative sea level rise resulting from the delta's
tendency to subside 1 centimeter per year. (This
problem is discussed in greater detail below.)
Summer temperatures in many of the gulf
coast estuaries are almost as warm as crabs, shrimp,
oysters, and other commercially important fishes can
tolerate (Livingston, Volume E). Winter
326
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Southeast
temperatures along the gulf coast are almost warm
enough to support mangrove swamps, which
generally replace marshes once they are established;
mangroves already dominate the Florida coast south
of Fort Lauderdale.
Beach Erosion and Coastal Flooding
The Southeast has 1,100 miles of sandy ocean
beaches, many of which are found on low and
narrow barrier islands. The Atlantic coast is heavily
developed, while much of the gulf coast is only now
being developed. In part because of their
vulnerability to hurricanes, none of Mississippi's
barrier islands has been developed, and only one of
Louisiana's barrier islands is developed at present.
Because much of Florida's gulf coast is marsh, it is
still largely undeveloped.
All eight coastal states are experiencing coastal
erosion. Along developed coasts, recreational
beaches have narrowed, increasing the vulnerability
of shorefront structures to storms. In Louisiana,
some undeveloped barrier islands are eroding and
breaking up. Elsewhere, narrow barrier islands are
keeping pace with sea level rise by "overwashing"
(i.e., rolling over like a rug) in a landward direction,
while wide islands and mainland coasts have simply
eroded. The coastal states of the Southeast are
responding by holding back the sea in some areas
arid by adapting to erosion in others.
The two greatest natural disasters hi U.S.
history resulted from floods associated with
hurricanes in Galveston, Texas, and Lake
Okeechobee, Florida, in which over 8,000 people
drowned. After the Mississippi River overflowed
its banks and inundated most of coastal Louisiana
in the 1930s, Congress directed the U.S. Army
Corps of Engineers to initiate a major federal
program of flood control centered around the
Southeast. Nevertheless, flood waters often remain
over some low areas hi Louisiana and Florida for
several days after a major rainstorm.
Hurricanes continue to destroy recreational
development in at least a few ocean beach
communities almost every year hi the Southeast.
The region presently experiences the majority of
U.S. coastal flooding and probably would sustain
the worst Increases in flooding as a result of global
warming. Unlike the Northeast and Pacific
coasts, this region has wide low-lying coastal plains
and experiences several hurricanes annually.
Florida, Texas, and Louisiana account for 62% of
the $144 billion of private property Insured by the
Federal Flood Insurance Program (see Riebsame,
Volume J).
Agriculture
In the last few years, droughts and heat waves
have caused crop failures in many parts of the
Southeast. Unlike much of the nation, cold weather
generally is not a major constraint to agricultural
production, except for Florida's citrus Industry.
Although cotton and tobacco were once the
mainstays of the Southeast's economy, agriculture
now accounts for only 1% of the region's income
(U.S. Department of Commerce, 1986). Since
World War II, substantial amounts of farmland have
been withdrawn from agriculture, and much of this
land has been converted to forest. The cotton crop
has been largely lost to the irrigated Southwest, and
although tobacco remains profitable, it is grown on
only 500,000 acres. However, in the last few
decades, southeastern farmers have found soybeans
to be profitable; this crop now accounts for 45% of
all cultivated land in the Southeast. Corn continues
to account for 5% of southeastern agriculture (U.S.
Department of Commerce, 1982). Table 16-1
compares annual revenues by state for various
crops.
Forests
The commercial viability of southeastern
forests has increased greatly since World War II,
primarily as a result of the increased use of
softwoods, such as pines and firs, for plywood and
for applications that once required hardwood.
Because this transition coincided with lower farm
prices and declining soils in the piedmont foothills
of the Southeast, many mountain farms have been
converted to forests. However, hi the last 10 years,
7 million acres of coastal plain forests have been
converted to agriculture (Healy, 1985).
Approximately 45% of the nation's softwood
(mostly loblolly pine) and 50% of its hardwood are
grown in the region. Forests cover 60% of the
Southeast, and 90% of forests are logged.
Oak-hickory covers 35%, and pine covers another
327
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Chapter 16
Table 16-1. Annual Revenues by State for
Various Crops (thousands of 1986
dollars)
Crop
Value
Corn for grain
Alabama
Florida
Georgia
Mississippi
North Carolina
South Carolina
Tennessee
Cotton
Alabama
Florida
Georgia
Mississippi
North Carolina
Tennessee
Sugarcane for suear and seed
Florida
Tobacco
Florida
Georgia
North Carolina
South Carolina
Tennessee
Peanuts for nuts
Alabama
Florida
Georgia
North Carolina
South Carolina
Soybeans
Alabama
Florida
Georgia
Mississippi
North Carolina
South Carolina
Tennessee
856,550
31,493
203,931
22,600
324,789
104,333
193,687
145,540
8,112
97,325
449,630
30,944
109,610
369,899
NA
NA
NA
NA
NA
133,930
48,600
472,645
122,941
5,882
140,719
31,036
179,676
365,018
196,673
125,214
230,373
NA » Not available.
Source: U.S. Department of Agriculture (1987).
33% of commercial forests. Only 9% of the
southeastern forests are owned by federal and state
governments, and 18% are owned by the forest
industry. In contrast, 73% of the forests are owned
by farmers and other private parties (Healy, 1985).
Indoor and Outdoor Comfort
The Southeast is one of the few areas that
spends as much money on air-conditioning as on
heating. Figure 16-2 shows temperatures
throughout the Southeast for the months of January
and July. Even in January, about half the region
experiences average temperatures above 50°F, and
almost the entire region has a typical daily high
above 50°F. Thus, with the possible exception of
the cool mountains of Tennessee and North
Carolina, a global warming would increase the
number of days during which outdoor temperatures
would be unpleasantly hot much more than it would
reduce the number of unpleasantly cold days.
PREVIOUS STUDIES OF THE
IMPACTS OF CLIMATE CHANGE
ON THE SOUTHEAST
Most studies examining the impact of global
warming on the Southeast have focused on sea level
rise. Recent efforts have addressed other topics.
Several dozen researchers presented papers on
other global warming impacts on the Southeast at a
1987 EPA conference held in New Orleans (Meo,
1987). Their papers suggested that agricultural
yields would decline, forest species would shift, and
that coastal and water supply officials should start to
plan for the consequences of global warming.
Flooding
Leatherman (1984) and Kana et al. (1984)
applied flood-forecasting models to assess the
potential increases in flooding in Galveston, Texas,
and Charleston, South Carolina. For the Galveston
area, a 90-centimeter (3-foot) rise would increase
the 100-year floodplain by 50%, while a 160-
centimeter (5.2-foot) rise would enable the 100-year
storm to overtop the seawall erected after the
disaster of 1900. For the Charleston area, a 160-
centimeter rise would increase the 10-year
328
-------
Southeast
JANUARY
Figure 16-2. Typical temperatures in the Southeast: (A) January, (B) July.
floodplain to the area currently covered by the 100-
year floodplain.
Gibbs (1984) estimated that the economic
impact of a 90-centimeter rise by 2075 could be as
great as $500 million for Galveston and over $1
billion for Charleston. However, he also estimated
that the adverse impacts of flooding and land loss
could be cut in half if the communities adopted
measures in anticipation of sea level rise. Titus
(1984) focused on decisions facing Sullivans Island,
South Carolina, in the aftermath of a storm. He
concluded that rebuilding $15 million in oceanfront
houses after a storm would not be economically
sound if future sea level rise is anticipated, unless
the community is prepared to continuously nourish
its beaches.
Wetlands
Kana et al. (1986) surveyed marsh transects
and estimated that 90- and 160-centimeter (3.0- and
5.2-foot) rises in sea level would drown 50 and 90%,
respectively, of the marsh around Charleston, South
Carolina. Armentano et al. (1988) estimated the
Southeast would lose 35 and 70% of its coastal
wetlands for respective rises of 1.4 and 2.1 meters,
assuming that developed areas are not protected.
Infrastructure
The Louisiana Wetland Protection Panel
(1987) concluded that a rise in sea level might
necessitate substantial changes in the ports and
shipping lanes of the Mississippi River to prevent
the loss of several thousand square miles of coastal
wetlands. Titus et al. (1987) showed that a
reconstructed coastal drainage system in Charleston
should be designed for a 1-foot rise in sea level if
the probability of such a rise is greater than 30%.
Linder et al. (1988) found that warmer temperatures
would require an electric utility company to
substantially increase its generating capacity.
CLIMATE CHANGE STUDIES IN
THIS REPORT
Table 16-2 and Figure 16-3 illustrate the
studies undertaken as part of this effort. Few
resources had previously been applied to examining
the various impacts of climate change for the
Southeast. Models of coastal erosion, coastal
wetland loss, agricultural yields, forest dynamics,
and electricity consumption were sufficiently refined,
so that it was possible to inexpensively apply them
to numerous sites and develop regional assessments.
Louisiana, which accounts for half of the region's
wetlands, has been the subject of previous studies.
It is discussed following the studies for this report.
By contrast, the impacts on water resources
and ecosystems required more detailed site-specific
studies, and it was not possible to undertake such
case studies for a large number of watersheds or
329
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Chapter 16
Table 16-2. Studies of the Southeast
Regional Studies
• Impacts on Runoff in the Upper Chattahoochee River Basin - Hains, C.F. Haines, Hydrologist, Inc.
(Volume A)
• Projected Changes in Estuarine Conditions Based on Models of Long-Term Atmospheric Alteration
- Livingston, Florida State University (Volume E)
• Policy Implications of Global Climatic Change Impacts Upon the Tennessee Valley Authority
Reservoir System. Apalachicola River. Estuary, and Bay and South Florida - Meo, Ballard, Deyle,
James, Malysa, and Wilson, University of Oklahoma (Volume J)
• Potential Impacts on Climatic Change on the Tennessee Valley Authority Reservoir System -
Miller and Brock, Tennessee Valley Authority (Volume A)
• Impact of Climate Change on Crop Yield in the Southeastern U.SA. - Peart, Jones, and Curry,
University of Florida (Volume C)
Methods for Evaluating the Potential Impacts of Global Climate Change - Sheer and Randall,
Water Resources Management, Inc. (Volume A)
• Forest Response to Climate Change: A Simulation Study for Southeastern Forests - Urban and
Shugart, University of Virginia (Volume D)
National Studies That Included Southeast Results
The Economic Effects of Climate Change on U.S. Agriculture: A Preliminary Assessment - Adams.
Glyer, and McCarl, Oregon State University (Volume C)
• National Assessment of Beach Nourishment Requirements Associated with Accelerated Sea Level
Rise - Leatherman, University of Maryland (Volume B)
The Potential Impacts of Climate Change on Electric Utilities: Regional and National Estimates -
Linder and Inglis, ICF Inc. (Volume H)
The Effects of Sea Level Rise on U.S. Coastal Wetlands -Park and Trehan, Butler University and
Mausel and Howe, Indiana State University (Volume B)
Potential Effects of Climatic Change on Plant-Pest Interactions - Stinner, Rodenhouse, Taylor,
Hammond, Purrington, McCartney, and Barrett, Ohio Agricultural Research and Development
Center (Volume C)
• Assessing the Responses of Vegetation to Future Climate Change: Ecological Response Surfaces
and Faleological Model Validation - Overpeck and Bartlein, Lamont-Doherty Geological
Observatory (Volume D)
* An Overview of the Nationwide Impacts of Rising Sea Level - Titus and Greene, U.S.
Environmental Protection Agency (Volume B)
The Cost of Defending Developed Shorelines Along Sheltered Waters of the United States from
a Two Meter Rise in Mean Sea Level - Weggel, Brown, Escajadillo, Breen, and Doheny, Drexel
University (Volume B)
330
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Southeast
Region and Coastal Studies of Wetland
' Loss and Cost of Holding Back the Sea
Forest Study Sites
Agriculture Study Sites
I TVA, Apalachlcola, and South
I Florida Watersheds
Figure 16-3. Overview of studies of the Southeast.
ecosystems. Therefore, our analysis was limited to
representative case studies. For water resources, we
picked (1) the Tennessee Valley, because it is the
largest managed watershed in the region; and (2)
Lake Lanier, because it serves Atlanta, the region's
second largest city. In both cases, we were able to
identify researchers who were already familiar with
the area. The sole aquatic ecosystem studied hi
depth was Apalachicola Bay, picked because the
estuary had already been the subject of the most
comprehensive data collection effort in the
Southeast.
SOUTHEAST REGIONAL
CLIMATE CHANGE SCENARIOS
Figure 16-4 illustrates the scenarios of future
climate change from general circulation models.
Table 16-3 shows the more detailed seasonal
changes.
Table 16-3 illustrates how the frequency of
mild days during the winter and the frequency of
very hot days during the summer might change
under the Goddard Institute for Space Studies
(GISS) doubled CO2 scenario. As explained in
Chapter 4: Methodology, these estimates used
average monthly changes in temperature and
assumed no change in variability. Under this
scenario, the number of days per year in which the
mercury would fall below freezing would decrease
from 34 to 6 hi Jackson, Mississippi; from 39 to 20
hi Atlanta; and from 41 to 8 hi Memphis. The
number of whiter days above 70°F would increase
from 15 to 44 hi Jackson, from 4 to 14 hi Atlanta,
and from 5 to 24 hi Memphis.
Of the nine cities shown, only Nashville has
summer temperatures that currently do not
regularly exceed 80°F. However, the number of
days with highs below SOT would decline from 60
to 34. Elsewhere, the heat would be worse. The
331
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Chapter 16
Table 16-3. The GISS Doubled CO2 Scenario: Frequency of Hot and Cold Days (°F)
number of winter days with: Number of summer days with;
Daily Low <32 Daily high >70 Daily high <80 Daily high >90 Daily high >100
Location
HIST3
2xC02
HIST3
2xCO,
HISTa 2XCO,
HIST8
2xC02
HIST*
2XCO,
Atlanta, GA 38.3 20.5 4.2 13.6 10.0 2.2 17.1 53.3 0.6 4.2
Birmingham, AL 35.5 8.1 7.1 30.7 4.5 0.4 34.1 72.5 1.5 10.7
Charlotte, NC 42.1 23.8 3.4 9.9 11.9 3.7 23.1 56.5 6.1 5.9
Jackson, HS 33.5 5.9 15.3 43.5 0.8 0.2 55.1 83.1 2.0 19.5
Jacksonville, FL 9.3 1.7 34.6 49.6 2.3 0.3 46.4 81.3 0.6 14.1
Memphis, TN 41.2 8.1 5.2 23.6 4.9 0.7 50.5 74.8 2.6 19.1
Miami, FL 0.2 0.0 72.9 82.7 0.6 0.0 29.8 83.5 0.0 2.5
Nashville, TN 42.5 15.4 0.3 8.6 60.4 33.7 10.5 20.2 0.3 3.5
New Orleans, LA 14.9 3.5 24.9 39.5 0.9 0.1 55.4 84.9 0.3 13.5
"HIST « Historic. "
Source: Kalkstein (Volume G).
A. Temperature
61
UJ
1 »
X
o
Spiing
B. Precipitation
Spring Summer
Figure 16-4. 2xCO2 less lxCO2 climate scenarios for the Southeast: (A) temperature, and (B) precipitation.
332
-------
Southeast
number of days per year above 90°F would increase
from 30 to 84 in Miami, from 17 to 53 in Atlanta,
and from 55 to 85 in New Orleans. Memphis,
Jackson, New Orleans, and Jacksonville, which
currently experience 0 to 3 days per year above
100T, would have 13 to 20 such days (Kalkstein,
Volume G).
RESULTS OF SOUTHEASTERN
STUDIES
Coastal Impacts
A number of national studies for the report
presented results for the effects of climate change
on the southeastern coast. Leatherman estimated
the cost of maintaining recreational beaches. Park
et al. and Weggel et al. examined the impacts on
wetland loss and shoreline defense, and used their
results to estimate the regionwide cost of raising
barrier islands. The projected rise in sea level
would cause shorelines to retreat, exacerbate coastal
flooding, and increase the salinity of estuaries,
wetlands, and aquifers. (For a discussion of the
rationale, methods, and nationwide results of these
studies, see Chapter 7: Sea Level Rise.)
Coastal Wetlands
Park et al. (Volume B) examined 29
southeastern sites to estimate the regionwide loss
of coastal wetlands for a variety of scenarios of
future sea level rise. Their analyses included such
societal responses as providing structural protection
for all shorelines (total protection), protecting areas
that are densely developed today (standard
protection), and allowing shorelines to adjust
naturally without coastal protection (no protection).
Figure 16-5 illustrates their estimates for the
year 2100 for the various scenarios of sea level rise
and coastal defense. Even if current sea level
trends continue, 25% of the Southeast's coastal
wetlands will be lost, mostly in Louisiana.
Excluding Louisiana:
« current trends imply a loss of 15%;
• a 50-centimeter rise could result in a loss of
35 to 50%, .depending on how shorelines
are managed;
ALL DRYLAND PROTECTED
MANGROVE
!&»:•:&&!
FRESH MARSH
j^§!£
SWAMP
0.0 0.1 0.3 0.6 1.0 1.5 2.2 3.0
SEA LEVEL RISE (Meters)
DEVELOPED AREAS PROTECTED
0.0 0.1 0.3 0.6 1.0 1.5 2.2 3.0
SEA LEVEL RISE (Meters)
NO PROTECTION
SEA LEVEL RISE (Meters)
Figure 16-5. Wetlands loss in the Southeast for
three shoreline protection options (Park et al.,
Volume B). (NOTE: These numbers are different
from those in Table 16-4 because they include
nonvegetated wetlands, i.e., beaches and flats.)
• a 100-centimeter rise could result in losses
of 45 to 68%; and
• a 200-centimeter rise implies losses of 63 to
80%.
Park et al. estimated losses of 50, 75, and 98%
for Louisiana under the three scenarios. However,
they did not consider the potential for mitigating the
333
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Chapter 16
loss by restoring the flow of river water into these
wetlands; no model exists that could do so
(Louisiana Wetland Protection Panel, 1987). Titus
and Greene estimated statistical confidence intervals
illustrated hi Table 16-4.
Total Coastal Land Loss
Park et al. also estimated total land loss,
including both wetlands and dryland. Most of the
land loss from a rise in sea level would occur in
Louisiana. A 50-centimeter (20-inch) sea level rise
would result in the loss of 1,900 to 5,900 square
miles of land, while a 200-centimeter rise would
inundate 10,000 to 11,000 square miles.
Cost of Protecting Recreational Beaches
In Volume B, Leatherman notes that the
projected rise in sea level would threaten all
developed recreational beaches. Even a 1-foot sea
level rise would erode shorelines over 100 feet
throughout the Southeast. Along the coasts of
North Carolina and Louisiana, the erosion would be
considerably greater. Because the distance from the
high tide line to the first building is rarely more
than 100 feet, most recreational beaches would be
lost, unless either the buildings were removed or
coastal protection measures were undertaken.
Table 16-4 illustrates Leatherman's estimates
of the cost of protecting recreational beaches by
Table 16-4. Summary of Results of Sea Level Rise Studies for the Southeast (billions of dollars)
Response
Baseline
50-cm rise
100-cm rise
200-cm rise
Developed areas are
protected
Land lost
Dryland lost (mi2)
Wetlands lost (%)a
Cost of coastal defense
Open coast
Sand
Elevated structures
Sheltered shores
All shores are
protected
Land lost
Dryland lost (mi2)
Wetlands lost (%)a
No shores are
protected
Land lost
Dryland lost (mi2)
Wetlands lost (%)a
1,300-3,700
11-22
negligible
negligible*3
0
0
1,900-5,500
24-50
19-28
10-15
5-9
2-5
0
38-61
N/A
N/A
2,300-5,900
22-48
2,600-6,900
34-77
42-75
19-30
10-40
5-13
4,200-10,100
40-90
127-174
44-74
60-75
9-41
0
47-90
0
68-93
3,200-7,600
30-75
4,800-10,800
37-88
^"Wetlands" refers to vegetated wetlands only; it does not include beaches or tidal waves.
Costs due to sea level rise are negligible.
Source: Titus and Greene (Volume B).
334
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Southeast
pumping sand from offshore locations. (See Table
7-3 for state-by-state results). A 1-meter rise in sea
level could imply almost $20 billion in dredging
costs, with Texas spending $8.5 billion and Florida
and Louisiana each spending over $3 billion.
Using constant unit costs (except for Florida),
Leatherman estimated that a 2-meter rise could only
double the total cost to $43 billion. Titus and
Greene estimated that if the unit costs of sand
increased, 1- and 2-meter rises could cost $30 and
$74 billion, respectively. They also estimated that
the respective costs of rebuilding roads and utilities
on barrier islands could be $5 to 9 billion, $10 to 40
billion, and $60 to 75 billion for the three scenarios.
Cost of Protecting Calm-Water Shorelines
While Leatherman focused only on the open
ocean coast, Weggel et al. estimated the regionwide
costs of holding back the sea in developed sheltered
and calm-water areas. Weggel et al. estimate that
about $2 billion would be spent to raise roads and
to move structures, and $23 billion would be spent
to erect the necessary levees and bulkheads for a 2-
meter rise. Table 16-4 shows confidence intervals
estimated by Titus and Greene, which imply a total
cost of $42 to 75 billion for a 1-meter rise. The
combined cost is $68 to 83 billion. These estimates
do not include the costs of preventing flooding or of
protecting water supplies.
Tennessee Valley Authority Studies
The Tennessee Valley Authority (TVA) was
created in 1933 to spur economic growth in an area
previously considered to be one of the nation's
poorest. Geographically isolated by the
Appalachian Mountains, the region lacked electricity
and roads, and the Tennessee River could not
provide reliable transportation because it flooded in
the spring and dried to a trickle during the summer.
By creating the TVA, Congress sought to remedy
this situation by harnessing the river to provide
electricity, to prevent the flooding that had plagued
Chattanooga, and to ensure sufficiently stable
riverflows that would permit maintenance of a 9-
foot-deep navigation channel.
The region administered by the TVA covers
40,000 square miles and includes parts of seven
states. In the last half century, the TVA has
coordinated the construction of 43 major dams
along the river and its tributaries, many of which are
shown in Figure 16-6. The system provides power
to over 7 million people and contains 675 miles of
navigable waterways with annual commercial freight
of 28 million tons. The lakes created by the dams
have over 10,000 miles of shorelines, which generate
75 million visits each year and along which people
have invested $630 million, boosting the region's
annual economy by $400 million (Miller and Brock,
Volume A).
To assess the potential impacts of climate
change, Miller and Brock conducted a modeling
study of the water resource implications, and Meo
et al. examined the policy implications for the TVA.
TVA Modeling Study
Methods
Miller and Brock used the TVA's "Weekly
Scheduling Model," which the Agency currently uses
in setting the guidelines for its operations, to assess
the impacts of climate change. This linear
programming model selects a weekly schedule for
managing each reservoir in the TVA system by
sequentially satisfying the objectives of flood control,
navigation, water supply, power generation, water
quality, and recreation. Miller and Brock used this
model to simulate reservoir levels, riverflows, and
hydropower generation for wet and dry scenarios,
derived from the runoff estimates from the GISS
doubled CO2 model run.
TVA was unable to use a hydrologic model to
estimate runoff for this study. Instead, they sought
to use the runoff estimates from general circulation
models. Unfortunately, the OSU and GFDL
models estimate that there is no runoff today, which
would not permit derivation of a scenario.
Therefore, the GISS runoff estimates were used as
the "wet scenarios." Based on Rind (1988), the dry
scenario simply assumed that the change in runoff
would be the inverse of the change assumed in the
wet scenario. Therefore, a TVA study should be
viewed as an assessment of the system's sensitivity
to climate change, not as the literal implications of
particular general circulation models.
Miller and Brock assessed the potential
impacts of climate change on flood levels in
Chattanooga, Tennessee, using a model that had
been developed to estimate the constraints on
weekly tributary releases. They also estimated the
potential implications for water quality in the Upper
Holston Basin of the valley, using a reservoir water
quality model, a riverflow model, and a water
335
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Chapter 16
A.
LEGEND:
- TVA POWER SERVICE AREA
- TENNESSEE RIVER WATERSHED
Figure 16-6. (A) Map of the TVA region, and (B) schematic of the TVA reservoir system (Miller and Brock,
Volume A).
336
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Southeast
quality model that TVA has used in the past to
determine the environmental constraints affecting
riverflow.
Limitations
Because the riverflow scenarios were not based
on hydrologic analysis, conclusions cannot be drawn
regarding the sensitivity of riverflow to climate
change; a more thorough study should apply a
basinwide hydrologic model to the region. A key
limitation for the flood analysis was that EPA
assumed that every storm in a given month would
result in a change in riverflow proportional to the
change in monthly runoff rather than incorporating
potential changes in flood frequency and intensity.
(For climate change scenarios, see Chapter 4:
Methodology.) Finally, the study assumed that TVA
would not mitigate impacts by changing its
operating rules for the reservoirs in response to
climate change.
Reservoir levels
Figure 16-7 shows the estimates of the changes
in reservoir levels in the Norris Reservoir for the
wet and dry scenarios. Currently, water levels are
typically above 1,010 feet (NGVD) from early May
to early August. Under the wet scenario, the water
would generally be above this level from early April
to early September; during the driest years (1%),
the water levels would be similar to the current
normal level between May and October. In the dry
scenario, water levels would never exceed 1,005 feet
in a typical year, and even during the wettest years
(1%) they would barely exceed the current normal
condition between April and September.
Changes in lake levels of this magnitude would
have important implications for recreation in the
Tennessee Valley, which is supported by facilities
worth over $600 million. Even today, recreation
proponents are concerned with reservoir levels
dropping during some summers. Miller and Brock
found that the wet scenario would largely eliminate
current problems with low lake levels; in contrast,
the dry scenario would make these problems the
norm.
Water Quality
Miller and Brock found that a drier climate
could also create environmental problems. Lower
I'-'--..
IMAAAMMJJJJAASSSOONMDD
Figure 16-7. Water levels hi Norris Reservoir under
climate scenarios: (A) 10% wettest years; (B)
median; and (C) 10% driest years (adapted from
Miller and Brock, Volume A).
flows would reduce the dilution of municipal and
industrial effluents discharged into the river and its
tributaries. Moreover, because water would
generally remain at the bottom of reservoirs for a
longer period of time, the amount of dissolved
oxygen could decline; this would directly harm fish
and reduce the ability of streams to assimilate
wastes. Miller and Brock concluded that the water
supplies from TVA would probably be sufficient,
but that TVA could experience operational
difficulties and customer dissatisfaction due to
337
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Chapter 16
degraded water quality. During extended low-flow
conditions, wastes would have increased
opportunities to backflow upstream to water supply
intakes.
Flooding
Although a drier climate could exacerbate
many current problems facing TVA, a wetter
climate could create difficulties, particularly the risk
of flooding, in matters that are currently under
control. Miller and Brock found that in the wet
scenario, during exceptionally wet years, storage
would be inadequate at the tributary reservoirs; this
condition could result hi uncontrolled spillage over
dams. A high probability of flooding would also
exist at Chattanooga. Miller and Brock examined
the levels of the five worst floods of the last 50
years at Chattanooga, which did not overflow the
banks of the Tennessee River or flood the city.
However, under the wet scenario, two of the floods
would overtop the banks. The worst flood could
reach a level of 56.3 feet and cause over $1 billion
in damages; the second worst could reach a level of
46 feet and cause over $200 million hi damages (see
Figure 16-8).
Flooding could be reduced if operating rules
were modified to keep water levels lower in
reservoirs on tributaries (although this would
diminish the hydropower benefits from a wetter
climate). However, changes in operating rules
would not be sufficient to protect Chattanooga from
being flooded during a repeat of the worst storm,
because rainfall would be largely concentrated over
the "mainstem" reservoirs, which do not have
substantial flood-control storage.
Power Generation
Miller and Brock calculated that the wet and
dry scenarios imply, respectively, an annual increase
of 3.2 megawatt-hours (16%, $54 million per year)
and a decrease of 4.6 megawatt-hours (24%, $87
million per year), given current capacity and
operating rules.
Climate change could also have an impact on
fossil-fuel powerplants. If river temperatures
become warmer, they will require additional dilution
water. Although sufficient water would be available
if the climate became wetter, meeting minimum
flow requirements would be more difficult if climate
became drier. Miller suggested that the most
feasible operational change would be to cut back
power generation at fossil-fuel powerplants during
periods of low flow. However, hydropower
production would also be reduced during periods of
low flow, so cutting back production might not be
acceptable. One alternative would be to construct
cooling towers, which would eliminate discharges of
hot water, at a capital cost of approximately $75
million.
Tennessee Valley Policy Study
Meo et al. (Volume J) analyzed the history,
statutory authority, and institutional structure of the
TVA to assess the ability of the organization to
respond to climate change. Their analysis relied
both on the available literature and on interviews
with a few dozen officials of TVA and states within
the region. They divided the possible responses of
TVA into two broad categories: (1) continuing the
current policy of maximizing the value of
hydroelectric power, subject to the constraints of
flood control and navigation; and (2) modifying
priorities so that power generation would be
subordinated to other objectives if doing so would
yield a greater benefit to the region. They
concluded that if the climate became wetter, current
policies would probably be adequate to address
climate change because the only adverse effect
would be the risk of additional flooding, which is
already a top priority of the system.
If climate became drier, on the other hand,
existing policies might be inadequate, because they
require power generation to take precedence over
many of the resources that would be hardest hit.
Although they expect that the TVA will be more
successful at addressing future droughts, Meo et al.
found that during the 1985-86 drought, falling lake
levels impaired recreation and reduced hydropower
generation, forcing the region to import power while
five powerplants sat idle.
Meo et al. point out that groundwater tables
are falling in parts of the region, hi part because
numerous tributaries recharge the aquifers
whenever water is flowing but are allowed to run
dry when water is not being released for
hydropower. They suggest that even without climate
change, the deteriorating groundwater quality and
availability are likely to lead a number of
communities to shift to surface water supplies in the
coming decades, adding another use that must
compete for the water that is left over when the
338
-------
Southeast
Figure 16-8. Chattanooga was vulnerable to flooding until the TVA system of dams was constructed. The upper
photo shows the 1867 Flood, with water levels similar to those projected by the Miller and Brock under the wet
scenario (Miller and Brock, Volume A).
demands for power have been met. Even with
current climate, they contend, the TVA should
assess whether other uses of the region's water
resources would benefit the economy more. If
climate becomes drier, the need for such a
reevaluation will be even more necessary.
Studies of the Impacts on Lake Lanier
and Apalachicola Bay
Figure 16-9 shows the boundaries of the
19,800-square-mile Chattahoochee-Flint-
Apalachicola River Basin. The U.S. Army Corps
of Engineers and others who manage the
339
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Chapter 16
PEACHTREE CREEK
Figure 16-9. Drainage area of the Apalachicola-
Chattahoochee-Flint River system.
Chattahoochee River as it passes through Lake
Lanier on its way to the Apalachicola estuary and
the Gulf of Mexico face many of the same issues as
those faced by the TVA. However, they also are
managing the water supply of Atlanta, the second
largest city in the Southeast, and the flow of water
into an estuary that supports the most productive
fishery in Florida (U.S. Department of Commerce,
1988).
A number of researchers were involved in
EPA's assessment of the potential implications of
climate change for this watershed. A study of Lake
Lanier and a study of the implications for the fish in
Apalachicola Bay are discussed in the following
sections of this chapter.
Lake Lanier
Lake Lanier, located 30 miles northeast of
Atlanta, is a source of water for the city and nearby
jurisdictions. Federal statutes require the U.S.
Army Corps of Engineers to manage Lake Lanier to
provide flood control, navigation, and hydropower.
Nevertheless, the lake is also managed to meet
nonstatutory objections such as recreation, minimum
flows for environmental dilution, and water supply.
Since Lake Lanier was dammed in 1957, the
statutory objectives of flooding and navigation have
been met; annual hydropower generation has been
134 MWH , equal to 2% of today's power
requirements for Atlanta; and the releases of water
have fulfilled the additional minimum flow needed
to dilute the effluents from sewage treatment plants.
During the last two decades, the lake's
shoreline has been substantially developed with
marinas, houses, and hotels. To a large degree, the
residents have become accustomed to the higher
water levels that prevailed from the 1970s through
1984. Droughts from 1985 to the present, however,
have lowered lake levels, disrupting recreation. In
the summer of 1986, navigation for recreational
boats located downstream of the lake was curtailed
because of minimal releases from the lake. In 1988,
Atlanta imposed water-use restrictions, with the
objective of cutting consumption by 10 to 20%. A
bill has been introduced to add recreation to the list
of statutory purposes (HR-4257).
Runoff in the Chattahoochee River Basin
Study Design. Hains estimated runoff in the
Chattahoochee River Basin and the flow of water
into Lake Lanier for the three scenarios. He
calibrated the Sacramento hydrology model
developed by the National Weather Service
(Burnash et al., 1973) to the conditions found in
the watershed of the upper Chattahoochee River.
He then generated scenarios of riverflow for the
baseline climate and the GCM scenarios.
Limitations. The Sacramento model was
designed primarily for flood forecasting, not base
flow. In addition, the model was calibrated using
the data on evaporation of water from pans, which
Personal communication from Harold Jones, Systems
Engineer, Southeast Power Administration, Department of
Energy, September 12, 1988.
340
-------
Southeast
is not perfectly correlated with evapotranspiration,
and these data came from a nearby watershed.
Since the analysis was based on scenarios of
average monthly change, it did not consider
potential changes in variability of events such as
floods. The analysis did not incorporate changes in
vegetation, which could affect runoff.
Results. As with the Tennessee River, the
major climate models disagree on whether the
Chattahoochee watershed would become wetter or
drier with an effective doubling of greenhouse gases.
Hains estimated that under the wetter GISS
scenario, the average annual riverflow of the
Chattahoochee River would increase by 13%; the
drier OSU and GFDL models imply declines of 19
and 27%, respectively, as shown in Figure 16-10.
The GISS scenario implies slight decreases in winter
flow and increases the rest of the year. Under the
GFDL scenario, these substantial decreases were
estimated throughout the year, with almost no flow
in late summer. The OSU scenario also shows
reductions, but the reduction is greatest during the
flood season (February to May) and negligible
during the dry season (late summer/early fall).
Management of Lake Lanier
Study Design. Sheer and Randall (Volume A)
examined the implications for water management of
the riverflow changes estimated by Hains. They
SEASONAL FLOW RATIOS
I ,.,
GFDL
OSU
GISS
^— OBSERVED
/
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
MONTH
Figure 16-10. Ratios of flow under doubled CO2
scenarios to base case in Upper Chattahoochee
River.
modified a monthly water balance model/operations
model previously applied in southern California for
the lake, based on current operating rules for the
reservoir. For the first set of runs, the model
assumes that (1) minimum flows are maintained for
navigation and environmental dilution at all times,
(2) lake levels are kept low enough to prevent
flooding, (3) historic rates of consumption continue,
and (4) peak hydropower generation is maximized.
To ensure that the assumptions adequately reflect
the actual decision rules used by water managers,
Sheer and Randall reviewed the rules with local
officials from the U.S. Army Corps of Engineers,
the Atlanta Regional Council, and others
responsible for managing the water supply. In a
second set of runs, they examined the impacts of
climate change under alternative operating rules
that assume recreation is also a statutory objective.
Limitations. Sheer and Randall did not
consider changes hi demand for water due to
climate change or population growth; thus, it
produces high estimates of future water availability
under all scenarios. Moreover, the results were not
compared with historic lake levels.
Results. Figure 16-11 shows the Sheer and
Randall estimates of lake levels; Figure 16-12 shows
quarterly hydropower production. Under the
relatively wet GISS scenario, annual power
production could increase by 9%. The higher
streamflows in this scenario would still be well
below those that occasionally occurred before Lake
Lanier was closed; hence, no significant threat of
flooding would exist for a repeat of the climate of
1951-80. Under the relatively dry GFDL scenario,
however, power production could drop 47%, and
lake levels would be likely to drop enough to
substantially disrupt recreation. This scenario
assumes that Atlanta would continue to take as
much water as it does currently (allowing for growth
would increase water supply problems).
Sheer and Randall also examined the
implications of making recreation a statutory
objective. Although it would be possible to
maintain lake levels, Atlanta's water supply would
be threatened. With the current climate, strict
enforcement of such a policy would result in Lake
Lanier supplying no water to metropolitan Atlanta
for 8 months of every 30 years. Although under the
GISS scenario this would be reduced to 1 month,
under the dry GFDL scenario, Atlanta would have
to use an alternative source of water 1 to 3 months
each summer.
341
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Chapter 16
BASE GISS GFDL-
Figure 16-11. Lake Lanier elevation (September) under doubled CO2 scenarios (Sheer and Randall,
Volume A).
BASE GISS- GFDt—
I
' i
i i
65
YEAR
Figure 16-12. Lake Lanier power generation under doubled CO2 scenarios (Sheer and Randall, Volume A).
Implications. Climate change combined with
population growth may require water managers to
reexamine the tradeoffs between the various uses of
the Chattahoochee River and Lake Lanier. A
number of local water officials who met with Sheer
suggested that an appropriate response to changing
water availability might be to relax minimum flow
requirements for navigation and environmental
quality. They reasoned that minimum flows for
environmental purposes are based on the
assumption that sewage treatment plants are
discharging at their maximum rates and that
temperatures are high, conditions that are usually
not met. They also argued that little is
accomplished by maintaining minimum flows for
navigation because ship traffic is light in the lower
Chattahoochee. Others argued, however, that it
would be unwise to assume that minimum flows
could be decreased because future growth may
increase the need for dilution of effluents, and
warmer temperatures would speed biological
activity. The likely impacts of climate change on
Apalachicola Bay may also increase the need to
maintain minimum flows.
Apalachicola Bay
Apalachicola Bay supports hundreds of
commercial fishermen; over 80% of Franklin
County earns a livelihood from the bay (Meo et al.
Volume J). The contribution of fishing to the area
was estimated at $20 million for 1980, representing
90% of Florida's oyster harvest and 10% of its
shrimp harvest. This figure is projected to grow to
$30 to $60 million by 2000.
342
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Southeast
Although the state has purchased most of the
land that is not part of a commercial forest,
economic pressures on forestry companies to sell
land for coastal development are increasing. In
1979, the National Oceanic and Atmospheric
Administration created the Apalachicola National
Estuarine Sanctuary to prevent development from
encroaching into this relatively pristine estuarine
environment.
The biology of the Apalachicola Bay estuary
may be affected by higher temperatures, higher sea
levels, and different flows of water into the
Apalachicola River. Mains estimated the flow of the
Apalachicola River, and Park et al. estimated
wetland loss due to sea level rise. Livingston used
both of these results and the temperature change
scenarios to evaluate the potential impacts on the
bay's fish populations.
Sea Level Rise
The methods of Park et al. for estimating
wetland loss are described in Chapter 7: Sea Level
Rise. They estimated that a 1-meter rise in sea
level would inundate approximately 60% of the salt
marshes in Apalachicola Bay, and that mangrove
swamps, which are rarely found outside southern
Florida today, would replace the remaining salt
marsh. Table 16-5 illustrates their estimates.
Apalachicola River/low
Study Design. Hains estimated the impact of
climate change on riverflow, using a regression
model, which is simpler than the Sacramento model
he used for the Chattahoochee River analysis. The
regression expressed the logarithm of riverflow as a
function of the logarithms of precipitation and
evapotranspiration for a few weather stations
located in the basin.
Limitations. Hains' procedure greatly
oversimplified the relationships between the causal
variables and riverflow, ignoring the impacts of
reservoir releases and the failure of the relationships
to fit the simple log-linear form. These results
should be interpreted as an indication of the
potential direction of change.
Results. Figure 16-13 illustrates Hains'
estimates of average monthly flows for the
Apalachicola estuary. Annual riverflow would
SEASONAL FLOW
osu
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG
MONTH
Figure 16-13. Doubled CO2 flow into Apalachicola
Bay (Hains, Volume A).
Table 16-5. Remaining Coastal Wetlands in Apalachicola Bay in the Year 2100 (hectares)
Area
1987
Current sea
level rise
50-cm
rise
100-cm
rise
200-cm
rise
Swamps
Fresh marsh
High marsh
Low marsh
Mangrove
Total wetlands
9.46
1.46
1.19
3.42
0
15.53
6.71
1.27
0.37
2.33
0
10.68
6.26
1.17
0.04
0.39
3.06
10.92
5.47
1.00
0.04
0.06
2.13
8.70
4.16
0.25
0.02
0.03
1.80
6.26
Source: Park et al. (Volume B).
343
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Chapter 16
decrease under all scenarios, although it would
increase in the summer and fall for the GISS and
OSU scenarios, respectively.
/
Fish Populations in Apalachicola Bay
Study Design. Using data from the literature
on the tolerance of various species to warmer
temperatures, Livingston estimated the number of
months in a typical 30-year period during which the
estuary would be too hot for these species and
extrapolated this information to estimate reductions
in populations.
Hydrologic modeling was not used to estimate
the combined impacts of sea level rise and changing
riverflow on salinity. Instead Livingston used
historic data to estimate regression equations
relating riverflow to salinity and salinity to
populations of some commercially important
seafood species.
Limitations. There is no historical record by
which to estimate the impact of warmer
temperatures on the Apalachicola (or any other)
estuary. Livingston did not model the relationships
between various aquatic species or how they would
change. He did not consider how finfish and
shellfish might adapt to climate change, and he was
unable to estimate the impact of wetland loss on
populations of finfish and shellfish.
The limitations in Hains' estimates of riverflow
do not significantly affect the results of Livingston's
study because riverflow was only one of several
variables to be considered. The uncertainties
surrounding changes in rainfall probably dwarf any
errors due to Hains' simplified hydrology, and
higher temperatures and sea level rise appear to be
more important.
Results. The results of this study suggest a
dramatic transformation of the estuary from
subtropical to tropical conditions.
Warmer temperatures. Livingston concluded
that warmer temperatures would have a profound
effect on seafood species in the estuary because
many species cannot tolerate temperatures much
above those that currently prevail. Figure 16-14
compares the number of months in a 6-year period
(based on 1971-76) in which temperatures exceed a
particular level for the current climate and the
GISS and GFDL scenarios, with known thresholds
for major commercial species.
Livingston concluded that crabs, shrimp,
oysters, and flounder could not survive in the
25-
o 15
10 •
Base
GISS
GFDL
Blue Crab Blue Crab Oyster Larvae
Larvae (30°) Juvenile (33°) Spotted Sea Trout
Plnflsh
Flounder
(35°)
Croaker
(36°)
Redflsh
(37.5°)
White Shrimp
(42°)
Figure 16-14. Months in a 6-year period during which temperatures (°C) would be too high for selected species
under doubled CO2 scenarios (Livingston, Volume E).
344
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Southeast
estuary with the warming estimated in the GISS and
GFDL scenarios, which imply close to 100%
mortality for blue crab larvae and juveniles. The
GFDL scenario could cause over 90% mortality for
spotted sea trout, oyster larvae, panfish, and
flounder. The mortality under the milder GISS
scenario would be only 60%.
Although Livingston concludes that the oysters
would probably be eliminated, he cautions that
shrimp and other mobile species might adapt by
fleeing the estuary for cooler gulf waters during the
summer. However, such a flight would leave them
vulnerable to predators.
Increased salinity. Although sea level rise and
warmer temperatures seem likely to substantially
reduce the productivity of the estuary, the probable
impact of precipitation changes is less clear. If
riverflow in the Chattahbochee declines, it would
combine with sea level rise to increase salinity
concentrations in the estuary. Livingston concluded
that oysters are the most vulnerable to increases in
salinity because oyster drill and other predators, as
well as the disease MSX, generally require high
salinities. Livingston estimated losses of 10 to 35%
for oysters, blue crabs, finfish, and white shrimp
under the GFDL scenario because of salinity
increases alone.
Sea level rise. Livingston also concluded that
the loss of wetland acreage would have important
impacts on the estuary. Table 16-6 shows
Livingston's estimates of losses in particulate
organic carbon, the basic source of food for fish in
the estuary. Sea level rise between 50 and 200
centimeters would reduce available food by 42 to
78%. A proportionate loss in seafood populations
would not necessarily occur, since organic carbon
food supplies are not currently the constraining
factor for estuarine populations. However, wetlands
also are important to larvae and small shrimp,
crabs, and other species, serving as a refuge from
predators. A rise in sea level of a meter or more
could lead to a major loss of fisheries.
Despite the adverse impacts on shellfish and
flounder, a number of species might benefit from
global warming. For example, Livingston points out
that pink shrimp could become more prevalent.
Moreover, some finfish spend their winters in
Apalachicola Bay and occasionally find the estuary
too cold. Other species such as rock lobster that
generally find the waters too cold at present may
also be found in the estuary in the future.
Implications. Based on Livingston's
projections, Meo et al. (Volume J) used current
retail prices of fish to estimate that the annual net
economic loss to Franklin County could be $5 to
$15 million under the GFDL scenario, $1 to $4
million under GISS, and $4 to $12 million under the
OSU scenario.
Table 16-6. Projected Changes of the Net Input of Organic Carbon (metric tons per year)
to the Apalachicola Bay System for Various Scenarios of Sea Level Rise
Factor
Fresh
wetlands
Sea-
grass
Salt
marshes
Phyto-
plankton
Total
Current scenario
for 2100
30,000
27,200
46,905
233,280
Source: Livingston (Volume E).
337,385
Baseline
sea level rise
0.5-meter rise
1.0-meter rise
2.0-meter rise
26,100
24,000
21,300
4,980
28,700
28,800
30,100
31,035
23,500
4,690
940
780
144,640
71,450
58,790
15,160
222,940
128,940
111,130
51,955
345
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Chapter 16
Livingston's results should not be interpreted
to mean that fishing will be eliminated from
Apalachicola Bay. The extent to which
commercially viable tropical species could replace
the species that are lost was not estimated.
Agriculture
Agriculture in the Southeast will be affected
directly by changes in climate and indirectly by
changes in economic conditions and pests. This
section presents results from a crop modeling study
of yield changes by Peart et al., and regional results
from national studies of agricultural production
shifts by Adams et al. (Volume C) and of impacts of
changes in pest populations by Stinner et al.
(Volume C).
Crop Modeling Study
Study Design
Peart et al. (Volume C) used the crop models
CERES-Maize (Jones and Kiniry, 1986) and
SOYGRO (Wilkerson et al., 1985) to estimate the
impacts of climate change on yields of corn and
soybeans for 19 sites throughout the Southeast and
adjacent states. Agricultural scientists have used
these models for several years to project the impacts
of short-term climatic variations. They incorporate
the responses of crops to solar radiation,
temperature, precipitation, and soil type, and they
have been validated over a large range of climate
and soil conditions in the United States and other
countries.
The major variable not considered by these
and other existing agricultural models is the direct
"fertilization effect" of increased levels of
atmospheric carbon dioxide. Peart etal., therefore,
modified their models to consider both the
increased rate of photosynthesis and the increased
water-use efficiency that com and soybeans have
exhibited in field experiments (see Chapter 6:
Agriculture).
Limitations
The analysis of combined effects is new
research and will need further development and
refinement. The model runs use simple parameters
for CO2 effects, assume higher atmospheric
concentration of CO, than are predicted, and
probably overestimate the beneficial impact on crop
yields. The direct effects of CO2 in the crop
modeling study results may be overestimated for
two reasons. First, experimental results from
controlled environments may show more positive
effects of CO2 than would actually occur in variable,
windy, and pest-infested (weeds, insects, and
diseases) field conditions. Second, because other
radiatively active trace gases, such as methane, also
are increasing, the equivalent warming of a doubled
CO2 climate may occur somewhat before an actual
doubling of atmospheric CO2. A level of 660 ppm
CO2 was assumed for the crop modeling
experiments, while the CO, concentration in 2060 is
estimated to be 555 ppm (Hansen et al., 1988) (see
Chapter 6: Agriculture).
The study assumed that soils were relatively
favorable for crops, with low salinity or compaction,
and assumed no limits on the supply of all nutrients,
except nitrogen. The analysis considers neither
change in technology nor adverse impacts due to
changes in storm frequency, droughts, and pests and
pathogens.
Results
Soybean Yields. Table 16-7 illustrates the
results of the soybean model for 13 nonirrigated
sites in the study area, as well as Lynchburg,
Virginia, a colder site included for comparison
purposes.
The relatively wet GISS and relatively dry
GFDL scenarios imply very different impacts on
yields. In the GISS scenario, the cooler sites in
Georgia and the Carolinas mostly show declines in
soybeans yields of 3 to 25%, and the other sites
show declines of 20 to 39%, ignoring CO2
fertilization. When the latter effect is included, the
Atlantic Coast States were estimated to experience
gains of 11 to 39%, and the other .states could vary
from a 13% drop in Memphis to a 15% gain in
Tallahassee. (Tennessee fares worse than the North
Carolina sites at similar latitudes because its grid
cell does not receive as favorable an increase in
water availability.)
By contrast, the dry GFDL scenario results in
very large drops in soybean productivity, with all but
one site experiencing declines greater than 50% and
eight sites losing over 75%, considering only the
impact of climate change. Even when CO2
fertilization is considered, all but four sites
experience losses greater than 50%.
346
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Southeast
Table 16-7. Impacts of Doubled CO2 Climate Change on Soybean Yields for Selected Southeastern Sites
for Climate Change Alone and for Climate Change and CO2 Fertilization (percentage change
in yield)3
Site
Climate change
only
GISS
GFDL
Climate change
and COo fertilization
GISS GFDL
Memphis, TN
Nashville, TN
Charlotte, NC
Raleigh, NC
Columbia, SC
Wilmington, NC
Atlanta, GA
Macon, GA
Tallahassee, FL
Birmingham, AL
Mobile, AL
Montgomery, AL
Meridian, MS
Lynchburg, VAb
-38
-30
-7
-3
-20
-11
-11
-25
-20
-31
-34
-39
-37
+ 1
-88
-52
-92
-87
-78
-62
-78
-91
-51
-54
-43
-84
-78
-74
-13
+4
+32
+39
+ 18
+25
+27
+ 11
+ 15
0
-8
-10
-9
+49
-70
-81
-88
-76
-62
-41
-67
-82
-17
-29
error
-68
-66
-55
aThe impacts of CCv, fertilization cannot be quantified as accurately as climate change only. The climates
shown here overstate the beneficial impact of CO, because Peart et al. assume that CO2 has doubled.
Because other gases contribute to the global warming, CO2 will have increased by a smaller fraction.
bPeart et al. investigated a number of sites in states adjacent to the Southeast. Lynchburg is included to permit
comparison of results for the Southeast with a colder site.
Source: Peart et al. (Volume C).
Corn Yields. The two scenarios differ in a
similar fashion for nonirrigated corn. However, in
the case of irrigated corn, where the analysis
primarily reflects the impact of temperature
increases, the two scenarios show more agreement.
When CO2 fertilization was not considered, drops of
13 to 20% were estimated in the GISS scenario, and
drops of 20 to 35% were calculated for the GFDL
scenario. When CO2 fertilization was included, the
GISS scenario implied declines of less than 8% for
all sites, and the GFDL model showed similar
declines for two sites and respective declines of 17
and 27% for Charlotte, North Carolina, and Macon,
Georgia.
Irrigation. The two scenarios show more
agreement for agricultural fields that are already
irrigated. Since the changes in water availability are
irrelevant here, the impacts are dominated by the
increased frequency of very hot days.
The results are mixed on whether currently dry
land areas would be shifted to irrigation. Table 16-
8 shows the percentage increases in yields that
would result from adding irrigation for particular
scenarios. All but four sites could increase yields
today by 50 to 75% by irrigating. Under the wetter
GISS scenario, irrigation would increase yields only
7 to 53% (compared with not irrigating under the
GISS scenario). However, under the dry GFDL
scenario, irrigation would increase yields by 50 to
493% ~ that is, it would mean the difference
between crop failure and a harvest slightly above
today's levels in most years. Even without CO2
fertilization, 75% of the nonirrigated southeastern
sites could gain more from irrigation than they
would lose from the change in climate resulting
from the GFDL scenario.
A farmer's decision to irrigate, shift to other
crops, or remove land from production would
depend to a large degree on what happens to prices
347
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Chapter 16
Table 16-8. Increases in Corn Yields from a Shift
to Irrigation (percent, assuming no
CO2 fertilization)3
Current
Site climate
Memphis, TN
Nashville, TN
Charlotte, NC
Raleigh, NC
Columbia, SC
Wilmington, NC
Atlanta, GA
Macon, GA
Birmingham, AL
Mobile, AL
Montgomery, AL
Meridian, MS
Lynchburg, VAb
70
65
64
51
58
16
15
61
6
36
72
62
56
GISS
50
49
43
28
47
8
7
33
9
41
39
53
37
GFDL
270
205
486
444
386
50
79
489
61
91
493
323
361
aEstimates represent the change in yields, given
a particular scenario, from shifting to irrigation.
kpeart et al. investigated a number of sites in states
adjacent to the Southeast. Lynchburg is included
to permit comparison of Southeast results with
those for a colder site.
Source: Column 1 from Peart et al. (Volume C);
Columns 2 and 3 derived from Peart et al.
and Column 1.
of both crops and water. Even though water is
plentiful today, the capital costs of irrigation prevent
most farmers in the Southeast from taking
advantage of the potential 50% increases in yields.
But if crop failures due to drought became as
commonplace as Peart et al. project for the dry
GFDL scenario, a major increase in irrigation
probably would be necessary. Although
groundwater is currently plentiful in the Southeast,
no one has assessed whether there would still be
enough water if the climate became drier and
irrigation increased. Furthermore, climate change
may increase the demand for water for
nonagricultural uses.
Shifts in Production
Adams et al. (Volume C) examined the
impacts of changes in crop yields on farm
profitability and cultivated acreage in various
regions of the United States. (The methods for this
study are discussed in Chapter 6: Agriculture.)
Their results suggest that the impact of climate
change on southeastern agriculture would not be
directly proportional to the impact on crop yields
(Table 16-9).
Considering only the impact of climate change,
Adams et al. found that the GISS and GFDL
scenarios would reduce crop acreage by 10 and
16%, respectively. When CO2 fertilization is
considered, however, Adams et al. project respective
declines in farm acreage of 57 and 33% for the
GISS and GFDL scenarios. As yields increase,
prices decline. Adams et al. estimate that most
areas of the nation would lose farm acreage.
However, they estimate that the Southeast would
experience the worst losses: while the Southeast has
only 13% of the cultivated acreage, it would account
for 60 to 70% of the nationwide decline in farm
acreage. This result is driven by the increased
yields that the rest of the nation would experience
relative to the Southeast.
When the CO2 fertilization effect is ignored,
the reductions in acreage would be much smaller,
although the Southeast would still account for 40 to
75% of the nationwide loss. The general decline in
yields would boost prices, which could make it
economical for many farmers to irrigate and thereby
avoid the large losses associated with a warmer and
possibly drier climate.
Agricultural Pests
The modeling and economic studies of
agriculture do not consider the impact of pests on
crop yields. However, Stinner et al. (Volume C)
suggest that global warming would increase the
range of several agricultural pests that plague
southeastern agriculture. (For details on the
methods of this nationwide study, see Chapter 6:
Agriculture.) They point out that the northern
ranges of potato leafhoppers, sunflower moths,
black cutworms, and several other southeastern
pests are limited by their inability to survive a cold
winter. Thus, milder winters would enable them to
move farther north, as illustrated in Figure 16-15.
Stinner et al. also note that increased drought
frequency could increase the frequency of pest
infestations.
Implications of Agriculture Studies
Agriculture appears to be at least as vulnerable
to a potential change in climate in the Southeast
348
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Southeast
Table 16-9. Impact of Climate Change on Cultivated Acreage in the Southeast? (figures in parentheses
are percentage losses)
Region
Baseline
With Direct
GISS
GFD
Without Direct CCL
GISS
GFDL
Acreage (millions)
SE coast 12.5
Appalachia 15.5
Delta 19.9
Total 47.9
8.7(30) 7.8(38)
2.8(82) 7.4(52)
9.3(53) 16.7(16)
20.8(57) 31.9(33)
11.5(8) 11.2(10)
14.1(9) 12.9(17)
17.7(11) 16.2(19)
43.3(10) 40.3(16)
aSE coast includes Florida, South Carolina, Georgia, Alabama. Appalachia includes North Carolina, Tennessee,
Virginia, West Virginia, Kentucky. Delta includes Mississippi, Louisiana, Arkansas.
Source: Adams et aL (Volume C).
SUNFLOWER MOTH
GREEN CLOVERWORM
GISS PRESENT
POTATO LEAFHOPPER
BLACK CUTWORM
Figure 16-15. Present and predicted northern ranges of various agricultural pests (Stinner et al., Volume C).
as in any other section of the country. Unlike many
of the colder regions, the benefits of a longer
growing season would not appreciably offset the
adverse impacts of warmer temperatures in the
Southeast, where cold weather generally is not a
major constraint to agricultural production.
Florida may present an important exception to
the generally unfavorable implications of climate
change for crop yields. Although Florida is the
warmest state in the Southeast, its agriculture
appears to be harmed by cold temperatures more
than the agriculture of other states in the region. In
349
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Chapter 16
recent years, hard freezes have destroyed a large
fraction of the citrus harvest several times. As a
result, the industry is moving south into areas near
the Everglades, and sugarcane, which also thrives in
warm temperatures, is expanding into the
Everglades themselves. Global warming could
enable the citrus and sugarcane areas to include
most of the state. Warmer temperatures also would
help coffee and other tropical crops that are
beginning to gain a foothold in the state. This
study, however, did not examine how the frequency
of extreme events, such as the number of days
below freezing in Florida, would change.
Although Florida's relative abundance of water
may make it the exception, the current situation
there highlights an important aspect of climate
change: Within the context of current prices and
crop patterns, the impact of climate change appears
to be unfavorable. However, warmer temperatures
may present farmers with opportunities to grow
different crops whose prices would justify irrigation
or whose seasonal cycles would conform more
closely to future rainfall patterns.
Forests
Potential Range Shifts
Study Desigfi
Overpeck and Bartlein (Volume D) used two
independent methods to study the potential shifts in
ranges of forest types over eastern North America.
These analyses suggest where trees are likely to
grow in equilibrium doubled CO2 climate conditions
after allowing for migration of tree species to fully
catch up with climate change. The study only
indicates the approximate abundance of different
species within a range, not what the transitional
effects of climate on forests might be, or how fast
trees will be able to migrate to the new ranges.
(For a discussion of the study's methodology and
limitations, see Chapter 5: Forests.)
Results
Three GCM scenarios and two vegetation
models yielded similar results. The abundance of
deciduous hardwood populations (e.g., oak), which
currently occupy the entire modeled eastern region
from the Great Lakes region to the gulf coast,
would shift northward away from the gulf coast and
almost entirely out of the study region. Because
the stand simulation model did not include sub-
tropical species, it was unable to simulate any
vegetation along the gulf coast under the very warm
doubled CO2 climate. The results for southern pine
were less conclusive but generally show the upper
border of the species range moving northward while
the southern border remains stable. Growing
conditions along the gulf coastal region, however,
would also be favorable to subtropical species in a
doubled CO2 environment, but since the models
used in the study had no data on such species, it is
unclear how southern pine might fare under
competition with subtropical varieties.
Transitional Effects
Study Desigp
Urban and Shugart (Volume D) applied a
forest simulation model to a bottomland hardwood
forest along the Chattahoochee River in Georgia
and to upland sites near Knoxville, Tennessee,
Macon, Georgia, Florence, South Carolina, and
Vicksburg, Mississippi. Their study considered the
OSU, GFDL, and GISS scenarios for doubled CO2,
as well as the GISS transient A scenario through the
year 2060.
The model these researchers used was derived
from FORET, the "gap" model originally developed
by Shugart and West (1977). The model simulates
forest dynamics by modeling the growth of each tree
in a representative plot of forest land. It keeps
track of forest dynamics by assigning each of 45 tree
species optimal growth rates, seeding rates, and
survival probabilities, and by subsequently adjusting
these measures downward to account for less than
optimal light availability, temperature, soil moisture,
and soil fertility. In the case of the bottomland
hardwood site, the model also considers changes in
river flooding, based on the flows in the lower
Chattahoochee calculated in the Lake Lanier study.
The researchers applied the model to both mature
forests and the formation of a new forest from bare
ground.
Limitations
The results should not be taken literally owing
to a number of simplifying assumptions that Urban
and Shugart had to make. First, they assumed that
certain major species, such as loblolly pine, could
not tolerate more than 6,000 (cooling) degree-days
per year. These species are not currently found in
warmer areas, but the southern limits of their
350
-------
Southeast
range are also limited by factors other than
temperature, such as the Gulf of Mexico and the
dry climate of Texas and Mexico. Although the
6,000 degree-day line coincides with these species'
southern boundary across Florida, the peculiar
environmental conditions of that state make it
impossible to confidently attribute an estimate of
thermal tolerance to that observation alone. This
caveat does not apply to most of the oaks, hickories,
and other species found in the cooler areas of the
Southeast.
Another important caveat is that the model
does not consider the potentially beneficial impact
of CO2 fertilization on photosynthesis, changes in
water-use efficiency, or leaf area. Nor did the
analysis consider introduction of new species into
the region. Thus, there is more confidence about
the fate of species currently in the region than about
what may replace those species.
Results
The simulations by Urban and Shugart call
into question the ability of southeastern forests to
be generated from bare ground, particularly if the
climate becomes drier as well as warmer. For the
Knoxville site, the dry GFDL scenario implies that
a forest could not be started from bare ground,
while the GISS and OSU doubled CO2 scenarios
estimate reductions in biomass of 10 to 25%. For
the South Carolina site, only the GISS climate
would support a forest, albeit at less than 50% of
today's productivity. The Georgia and Mississippi
sites could not generate a forest from bare ground
for any of the scenarios. Thus, even with increased
rainfall, some sites would have difficulty supporting
regeneration.
The transient analyses suggest that mature
forests could also be lost — not merely converted to
a different type — if climate changes. Figure 16-16
shows that none of the forests would decline
significantly within 50 years; however, all would
decline substantially before the end of the transient
run in 80 years. The Mississippi forest would
mostly die within 60 years, and the South Carolina
and Georgia forests within 80 years. Only the
relatively cool Tennessee site would remain
80-
60-
J 40-
t.
a 20~
1 00"
° So-
li 60-
S 40-
20-
19
180-
_. 160-
s
£ 140-
S 120-
1 100-
1 <>oJ
| 60-
40-
20-
19
MISSISSIPPI TRANSIENT
Dynamics of Mature Forest
^ .^^^^^^
N
\
\
\
Woody Biomass \
Control \
Transient \
70 1980 1990 2000 2010 2020 2030 2040 2050 20
Simulation Year
SOUTH CAROLINA TRANSIENT
Dynamics of Mature Forest
-^ HXV ^
^^^
\
\
Woody Biomass \
Control
— — Transient
70 1 980 1 990 2000 2010 2020 2030 2040 2050 2(
Simulation Year
160-
140-
f
|120-
8 100-
I 8°-
f 60-
^
5 40-
20-
60 19
180-
_ 16°"
| 140-
-------
Chapter 16
somewhat healthy, although biomass would decline
35%.
Although the simulation results suggest that
southeastern forests are unlikely to benefit from the
global wanning, the impact on forests may not be as
bad as the model suggests, if new species move in
or if loblolly pine can tolerate more than 6,000
degree days per year. Nevertheless, major shifts in
forest types are almost certain to occur from the
warmer temperatures alone.
Electric Utilities
Linder and Inglis (Volume H) examined the
impact of global warming on the demand for
electricity throughout the Southeast for the two
GISS transient scenarios. (For additional details on
the methods and limitations of this study, see
Chapter 10: Electricity Demand.) Because their
study was limited to electricity, it did not consider
the reduced consumption of oil and gas for space
heating that would result from warmer
temperatures.
Table 16-10 shows the percentage changes hi
electric power requirements for various areas in the
Southeast. Along the gulf coast, annual power
requirements could increase 3 to 4% by 2010 and 10
to 14% by 2055; elsewhere, the increases could be
somewhat less. Because peak demand for electricity
generally occurs during extremely hot weather, peak
demand would rise more than annual demand. (This
result is also sensitive to changes in variability.)
Linder and Inglis compared increases in
electric capacity required by climate change with
those necessitated by economic growth. They
estimated that through 2010, climate change could
increase the expected capital costs of $137 billion by
6 to 9%; through 2055, it could increase expected
requirements of $350 to $500 billion by as much as
20%.
COASTAL LOUISIANA
The sediment washing down the Mississippi
River has formed the nation's largest delta at the
river's mouth, almost all of which is hi Louisiana.
Composed mostly of marsh, cypress swamps, and
small "distributary channels that carry water,
sediment, and nutrients from the river to these
marshes and swamps, Louisiana's wetlands support
half of the nation's shellfish, one-fourth of its fishing
industry, and a large trapping industry. They also
provide flood protection for metropolitan New
Orleans and critical habitats for bald eagles and
other migratory birds.
Water management and other human activities
of the last 50 years are now causing this delta to
disintegrate at a rate of about 100 square kilometers
per year. Sediment that used to replenish the
Table 16-10. Percentage Increases in Peak and Annual Demand for Electricity by 2010 and 2055 as a Result of
Climate Change
Area
GISS A (2010)
Annual Peak
GISS B (2010)
Annual Peak
GISS A (2055)
Annual Peak
North Carolina,
South Carolina,
Georgia
Florida
Eastern Tennessee
Alabama, Western
Tennessee
Mississippi
Louisiana
East Texas
1.6
2.7
1.6
1.9
3.8
2.9
3.1
7.3
4.9
3.7
3.8
7.6
7.6
7.9
1.3
2.7
1.3
2.2
4.4
2.7
2.8
2.4
3.6
1.2
5.7
11.4
6.6
6.6
5.9
9.3
5.9
6.8
13.6
10.2
11.3
24.4
20.0
12.2
13.5
6.9
23.4
25.3
Source: Linder and Inglis (Volume H).
352
-------
Southeast
delta now largely washes into the deep waters of the
gulf because flood-control and navigation guide
levees confine the flow of the river. Thus, the delta
is gradually being submerged, and cypress swamps
are converting to open-water lakes as saltwater
penetrates inland. If current trends continue,
almost all the wetlands will be lost in the next
century.
A rise in sea level would further accelerate the
rate of land loss in coastal Louisiana As shown in
Figure 16-17, even a 50-centimeter rise in sea level
(in combination with land subsidence) would
inundate almost all of the delta and would leave
New Orleans, most of which is below sea level and
only protected with earthen levees, vulnerable to a
hurricane.
Strictly speaking, the entire loss of coastal
Louisiana's estuaries should not be attributed to
global warming because the ecosystem is already
being lost. However, major efforts are being
initiated by the U.S. Army Corps of Engineers, the
U.S. Fish and Wildlife Service, the Louisiana
Geological Survey, several local governments, and
other federal and state agencies to curtail the loss,
generally by erecting structures to provide
freshwater and sediment to the wetlands. Technical
staff responsible for developing these solutions
generally fear, however, that a 1-meter rise in sea
level could overwhelm current efforts, and that if
such a rise is ultimately going to take place, they
already should be planning and implementing a
much broader effort (Louisiana Wetland Protection
Panel, 1987).
Figure 16-17. Projected future coastline of Louisiana for the year 2033, given a rise in sea level of 55 cm as
predicted in the high scenario (Louisiana Wetland Protection Panel, 1987).
353
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Chapter 16
POLICY IMPLICATIONS
Agriculture and Forests
Climate change could have a major impact on
land use in the Southeast. The estimated
abandonment of 10 to 50% of the farmland in the
Southeast and large declines in forests raise the an
important question: How will this land be used?
In the past, forests have been cleared for
agriculture, and when abandoned, they have been
converted to forest again. But the forest models
suggest that the impact of climate change on the
generation of new forests from bare ground would
be even more adverse than the impact on existing
forests. If the forest simulations are correct, the
abandoned fields would become grasslands or would
become overgrown with weeds, and the Southeast
could gradually come to resemble the scenery found
today in the Great Plains. However, no one has
systematically investigated the extent to which
human infrastructure might stabilize these changes.
Changes in crops might enable more farms to stay
in business than Adams et al. project, and new
varieties of trees may find the region more
hospitable. Because the commercial forests in the
Southeast generally have short rotation cycles, it
may be easier to respond to climate change there
than in other regions. To a large degree, the ability
of human intervention to maintain the present
landscape would depend on international prices of
agricultural and forest products, estimation of which
is outside the scope of this report.
Water Resources
The water resource problems faced by the
Southeast are not likely to be as severe as the
problems faced by other regions of the country.
Rainfall and runoff were estimated to increase in
the GISS scenario. Although most other
assessments suggest that runoff would decline, the
magnitude of the decline does not appear to
threaten the availability of water for municipal,
industrial, or residential use. However, the
nonconsumptive uses for hydropower, navigation,
environmental quality, and recreation could be
threatened. Although sufficient time exists to
develop rational strategies to implement the
necessary tradeoffs, current federal statutes
constrain the ability of water managers to do so.
Impacts of Wetter Climate
Although most water resource problems have
been associated with too little water, it does not
necessarily follow that a wetter climate would be
generally beneficial. The designs of water
management infrastructure and the location of
development along lakes and rivers have been based
on current climate. Hence, shifts in either direction
would create problems.
The chief problem from a wetter climate would
be more flooding, particularly in southern Florida
and coastal Louisiana, where water often lingers for
days and even weeks after severe rainstorms and
river surges. Inland communities, such as
Chattanooga, also might face flooding if wetter
periods exceed the ability of dams to prevent
flooding.
Impacts of Drier Climate
A drier climate, on the other hand, would
exacerbate current conflicts over water use during
dry periods. Hydropower would decline, increasing
the need to use fossil or nuclear power, both of
which, would require more water for cooling.
Conflicts between municipal water users and
recreational interests also would intensify. Lake
levels could drop more during the summer, even if
municipal use of water did not grow. However,
warmer temperatures probably would increase
municipal water demand for cooling buildings and
watering lawns.
These conflicts could be further exacerbated
if farmers increase the use of irrigation.
Groundwater is available in reasonably shallow
aquifers that drain into rivers. Any consumptive use
of water from these aquifers would reduce, and in
some cases reverse, the base flow of water from
aquifers into these rivers. Water also could be
drawn directly from rivers for irrigation in some
areas.
A decline in riverflows could be important for
both navigation and environmental quality. For the
Tennessee, as well as the Chattahoochee and other
small rivers, adequate reservoir capacity exists to
maintain flows for navigation, if this use continues
to take precedence over water supply and
recreation. However, the 1988 drought has
354
-------
Southeast
graphically demonstrated that there are not enough
dams to guarantee navigation in the Mississippi. If
this situation became more commonplace, the
economic impact on New Orleans could be severe.
On the other hand, traffic on the Tennessee and
Ohio Rivers might use the Tennessee-Tombigbee
Canal as an alternative, which would benefit the
Port of Mobile.
Lower flows also would reduce the dilution of
municipal and industrial effluents discharged into
rivers and would decrease the level of dissolved
oxygen. This would directly harm fish populations
and would cause indirect harm by reducing the
abilities of streams to assimilate wastes. Reduced
flows also would threaten bottomland hardwood and
estuarine ecosystems. To prevent these problems,
factories and powerplants might have to erect
cooling towers or curtail their operations more
frequently.
Is Current Legislation Adequate?
The same issues that face the TVA and Lake
Lanier would likely face decisionmakers hi other
areas. Federal laws discourage water managers in
the Southeast from rigorously evaluating the
tradeoffs between the various uses of water. Most
dams are more than sufficient to meet the statutory
requirements for navigation and flood safety and to
continue generating substantial hydropower on
demand. Consequently, there has been little need
to analyze the tradeoffs between these factors. For
example, a literal application of the law would not
allow the U.S. Army Corps of Engineers to cut
hydropower production or navigation releases to
ensure a supply of water for Atlanta. Therefore,
agencies have not analyzed the allocation of water
that best serves the public for various levels of water
availability (although the TVA is beginning to do
so).
At a practical level, federal water managers
have shown flexibility, as hi the case of cutting
navigation along the Chattahoochee instead of
further cutting Atlanta's water supply. If climate
changes and more than a modest level of flexibility
is necessary, water resource laws could be changed;
the physical infrastructure is largely hi place to
address water problems of the Southeast. But until
the laws are changed, the federal agencies in the
Southeast often would be forced to allocate water
inefficiently. Moreover, people making decisions
concerning siting of recreational and industrial
development, long-term water supply sources,
powerplant construction, and other activities
sensitive to the availability of water would risk
basing their decisions on incorrect assumptions
regarding the future allocation of water.
Estuaries
Coastal plants and animals across the
Southeast may have difficulty surviving warmer
temperatures. For example, along the northern
coast of the Gulf of Mexico, several types of fish
spend at least part of their lifetimes in estuaries that
are already as hot as they can tolerate. If climate
became warmer, however, migrating north would
not be feasible. While these species could escape
the summer heat by fleeing to the cooler waters of
the gulf, such a flight would make them vulnerable
to larger fish.
In addition to the direct effect of climate
change on estuaries, human responses to climate
change and sea level rise also could hurt coastal
estuaries. Besides the impacts of flood control,
increased reservoir construction would decrease the
amount of sediment flowing down the river and
nourishing the wetlands. If the climate becomes
drier, irrigation could further reduce freshwater flow
into estuaries.
To a large extent, the policy implications for
wetland loss in the Southeast are similar to those
facing the rest of the U.S. coastal zone. Previous
studies have identified several measures to reduce
the loss of coastal wetlands in response to sea level
rise (e.g., Titus, 1988). These measures include the
following:
• increase the ability of wetlands to keep
pace with sea level;
• remove impediments to landward creation
of new wetlands; and
• dike the wetlands and artificially maintain
water levels.
All these measures are being employed or actively
considered.
Congress has authorized a number of
freshwater and sediment diversion structures to
assist the ability of Louisiana's wetlands to keep up
with relative sea level rise. These structures are
355
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Chapter 16
engineered breaches in river levees that act as
spillways into the wetlands when water levels in the
river are high. Although decisions on where to
build diversion structures are being based on
current climate and sea level, consideration of
global warming would substantially change the
assumptions on which current analyses are being
based and the relative merits of alternative options.
More frequent or higher surges in the Mississippi
River would increase the amount of water delivered
to the wetlands. And if climate change resulted in
more soil erosion, more sediment might also reach
the wetlands; lower flows could have the opposite
effect. Sea level rise might shorten the useful
lifetimes of these projects, but because the
flood-protection benefits of protecting coastal
wetlands would be greater with a higher sea level
(Louisiana Wetland Protection Panel, 1987).
Artificially managing water levels also has been
proposed for Louisiana, particularly by Terrebonne
Parish, whose eastern wetlands are far removed
from a potential source of sediment. Such an
approach also might be possible for parts of Florida,
where wetlands already are confined by a system of
dikes and canals, and water levels already are
managed. Although no one has yet devised a
practical means by which shrimp and other fish
could migrate between ocean and estuary, other
species spend their entire lifetimes within the
estuary, and freshwater species could remain in
artificially maintained freshwater wetlands.
A final response would be to accept the loss
of existing wetlands, but to take measures to prevent
development from blocking the landward creation of
new wetlands. This approach has been enacted by
the State of Maine (1987) and would be consistent
with the proposals to discourage bulkheads that
have been widely discussed by coastal zone
managers and enacted by the State of South
Carolina. Titus and Greene estimate that 1,800
square miles of wetlands in the Southeast could be
created if developed areas were not protected.
Although this area represents a small fraction of the
potential loss, it would increase the remaining areas
of wetlands by 30 to 90%, and it would maintain
and perhaps increase the proportion of shorelines
on which at least some wetlands could be found.
Beach Erosion
The implications of sea level rise for
recreational beaches in the Southeast are similar to
the implications for the mid-Atlantic and the
Northeast. If shore-protection measures are not
taken, the majority of resorts will have no beach at
high tide by 2025 under the midrange scenario of
future sea level rise. The cost of undertaking the
necessary measures through 2025 probably would be
economically justified for most resorts (see Chapter
7: Sea Level Rise). However, the cost of protecting
all recreational beaches through 2100 would be $100
to $150 billion, which would probably lead some of
the more vulnerable areas to accept a landward
migration much as areas on North Carolina's Outer
Banks are facing today, particularly if warmer
temperatures also lead to more hurricanes.
The potential responses to global warming
should be viewed within the context of current
responses to erosion flooding. Florida has a trust
fund to nourish its beaches and has received federal
assistance for pumping sand onto the shores of
Miami Beach. Mississippi has nourished the
beaches of Biloxi, Gulfport, and other resort
communities that lie on the mainland along the
protected waters behind the barriers. Louisiana is
rebuilding its undeveloped barrier islands because
they protect the mainland from storms. Most states
are moving toward "soft engineering" solutions, such
as beach nourishment, because of doubts about the
effectiveness of hard structures in universal erosion
and their interference with recreational uses of the
beach.
Land-use measures also have been employed
to adapt to erosion. Because of unusually high
erosion rates on the Outer Banks, houses along the
coast are regularly moved landward. North
Carolina requires houses, hotels, and condominiums
to be set back from the shore by the distance of a
100-year storm plus 30 years' worth of erosion on
the assumption that after 30 years, the house could
be moved back. Texas requires that any house left
standing in front of the vegetation line after the
shore erodes must be torn down.
If a global warming increases the frequency of
hurricanes, a number of southeastern communities
will be devastated. However, the overall impact of
increased hurricane frequency would be small
compared with the impact of sea level rise. While
a doubling of hurricanes would convert 100-year
floodplains to 50-year floodplains throughout much
of the Southeast, a 1-meter rise would convert them
to 15-year floodplains.
356
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Southeast
Because the open-coast areas most vulnerable
to sea level rise are generally recreational beach
resorts, the costs of erosion and flooding should be
viewed within the larger context of why people go to
the beach. People from the north visit southeastern
beaches to escape winter, and residents of the
region go to escape the summer heat. As
temperatures become warmer, Georgia and the
Carolinas may be able to compete with Florida for
northerners. Hotter temperatures also may increase
the desire of the region's residents to visit the
beach.
Thus, it is possible that the cooler communities
will reap benefits from a longer and stronger tourist
season that are greater than the increased costs for
erosion control. Areas that already have a
year-round season are less likely to benefit, and in
a few areas like Miami Beach, the off-season may
be extended.
REFERENCES
Armentano, T.V., RA. Park, and C.L. Cloonan.
1988. Impacts on coastal wetlands throughout the
United States. In: Titus, J.G., ed. Greenhouse
Effect, Sea Level Rise, and Coastal Wetlands.
Washington, DC: U.S. Environmental Protection
Agency.
Earth, M.C., and J.G. Titus. 1984. Greenhouse
Effect and Sea Level Rise: A Challenge for This
Generation. New York: Van Nostrand Reinhold
Company.
Burnash Robert J.C., R.L. Ferral, and RA.
Mcguire. 1973. A Generalized Streamflow
Simulation System, Conceptual Modeling for Digital
Computers. Sacramento, CA: National Weather
Service and California Department of Water
Resources.
Edison Electric Institute. 1985. Statistical
Yearbook of the Electric Utility Industry.
Washington, DC: Edison Electric Institute.
Geraghty, J., D. Miller, F. Van Der Leeden, and F.
Troise. 1973. Water Atlas of the United States.
Port Washington, NY: Water Information Center.
Gibbs, M. 1984. Economic analysis of sea level
rise: methods and results. In: Barth, M.C., and
J.G. Titus, eds. Greenhouse Effect and Sea Level
Rise: A Challenge for This Generation. New York:
Van Nostrand Reinhold Company.
Hansen, J., I. Fung, A. Lacis, D. Rind, G. Russell,
S. Lebedeff, R. Ruedy, and P. Stone. 1988. Global
climate change as forecast by the GISS 3-D model.
Journal of Geophysical Research 93(D8):9341-9364.
Healy, R.G. 1985. Competition for Land in the
American South. Washington, DC: The
Conservation Foundation.
Jones, CA., and J.R. Kiniry. 1986. CERES-Maize:
A Simulation Model of Maize Growth and
Development. College Station, TX: Texas A&M
Press.
Kana, T.W., J. Michel, M.O. Hayes, and J,R.
Jensen. 1984. The physical impact of sea level rise
in the area of Charleston, South Carolina. In:
Barth, M.C., and J.G. Titus, eds. Greenhouse
Effect and Sea Level Rise: A Challenge for This
Generation. New York: Van Nostrand Reinhold
Company.
Leatherman, S.P. 1984. Coastal geomorphic
responses to sea level rise: Galveston Bay, Texas.
In: Barth, M.C., and J.G. Titus, eds. Greenhouse
Effect and Sea Level Rise: A Challenge for This
Generation. New York: Van Nostrand Reinhold
Company.
Linder, K.P., MJ. Gibbs, and M.R. Inglis. 1988.
Potential Impacts of Climate Change on Electric
Utilities. New York: New York State Energy
Research and Development Authority.
Louisiana Wetland Protection Panel. 1987. Saving
Louisiana's Coastal Wetlands: The Need for a
Long-Term Plan of Action. Washington, DC: U.S.
Environmental Protection Agency/Louisiana
Geological Survey. EPA-230-02-87-026.
Meo, M. 1987. Proceedings of the Symposium on
Climate Change in the Southern United States.
Norman, OK: University of Oklahoma.
Mitch, W., and J. Gosselink. 1986. Wetlands. New
York: Van Nostrand Reinhold Company.
357
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Chapter 16
NOAA. 1987. National Oceanic and Atmospheric
Administration. Fisheries Statistics Division,
National Marine Fisheries Service. 1987 Preliminary
Statistics for United States Domestic Catch.
Washington, DC: Unpublished data
Rind, D. 1988. The doubled CO2 climate and the
sensitivity of the modelled hydrologic cycle. Journal
of Geophysical Research.
Shugart, H.H., and D.C. West. 1977. Development
of an Appalachian deciduous forest succession
model and its application to assessment of the
impact of the chestnut blight. Journal of
Environmental Management 5:161-179.
State of Maine. 1987. Dune Rule 355. Augusta,
ME: Maine Department of Environmental
Protection.
Titus, J.G. 1987. The greenhouse effect, rising sea
level, and society's response. In: Devoy, R J.N., ed.
Sea Surface Studies. New York: Croom Helm.
Titus, J.G. 1988. Greenhouse Effect, Sea Level
Rise, and Coastal Wetlands. Washington, DC: US.
Environmental Protection Agency.
Titus, J.G. 1988. Sea level rise and wetland loss:
an overview. In: Titus, J.G., ed. Greenhouse
Effect, Sea Level Rise, and Coastal Wetlands.
Washington, DC: US. Environmental Protection
Agency.
Titus, J.G., C.Y. Kuo, MJ. Gibbs, T.B. LaRoche,
M.K. Welts, and J.O. Waddell. 1987. Greenhouse
effect, sea level rise, and coastal drainage systems.
Journal of Water Resource Planning and
Management ASCE 113(2):216-227.
Titus, J.G. 1984. Planning for sea level rise before
and after a coastal disaster. In: Barth, M.C., and
J.G. Titus, eds. Greenhouse Effect and Sea Level
Rise: A Challenge for This Generation. New York:
Van Nostrand Reinhold Company.
U.S. Department of Agriculture. 1987. Agricultural
Statistics: 1987. Washington, DC: U.S. Department
of Agriculture.
US. Department of Commerce. 1988. U.S.
Department of Commerce, Bureau of the Census.
Statistical Abstract of the United States: 1988.
Washington, DC: Government Printing Office.
U.S. Department of Commerce. 1986. U.S.
Department of Commerce, Bureau of Economic
Analysis.
U.S. Department of Commerce. 1982. U.S.
Department of Commerce, Bureau of the Census.
Census of Agriculture. Vol. 1. Geographic Area
Series. Washington, DC: Government Printing
Office.
U.S. Department of Energy. 1988. US.
Department of Energy, Energy Information
Administration. Electric Power Monthly; May.
U.S. House of Representatives. Rep. Jenkins, Rep.
Barnard, Rep. Darden. HR-4254. Georgia
Reservoir Management Improvement Act of 1988.
100th Congress, 20th Session.
Wilkerson, G.G..
Mishoe. 1985.
Growth and
Documentation.
Florida.
J.W. Jones, KJ. Boote, and J.W.
SOYGRO V5.0: Soybean Crop
Yield Model. Technical
Gainesville, FL: University of
358
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CHAPTER 17
GREAT PLAINS
FINDINGS
Agriculture in the Great Plains (this study focused
on Nebraska, Kansas, Oklahoma, and Texas) is
sensitive to climate fluctuations and would be at risk
from global warming. Although uncertainties
remain regarding the rate and magnitude of global
climate change and the models used to estimate
impacts, results indicate that climate change would
cause reductions in regional agricultural production.
Demand for irrigation is likely to increase, and
quality of water may diminish. Regional electricity
use may increase.
Agriculture
• The effects of a warmer climate alone would
generally reduce wheat and corn yields. Yield
changes range from +15 to -90%. The direct
effects of CO2 on crop photosynthesis and water
use may mitigate these effects, but the extent to
which the beneficial effects of CO2 on crop
yields would be seen with climate change is
uncertain.
Crop yields in Texas and Oklahoma may decline
relative to northern areas of the United States.
This change in productivity could lead to a 4 to
22% reduction of cultivated acreage in these
states.
• Because of increased reliability of yields from
irrigated lands relative to dryland yields, and
because of potentially higher crop prices,
demand for irrigation water on remaining farms
would probably increase as global warming
proceeds. The number of acres irrigated may
increase by 5 to 30%.
Ogallala Aquifer
• Warming and/or drying in the Great Plains may
place greater demand on regional groundwater
resources. Many of the problems associated
with intense groundwater use — water
depletion,soil damage, altered farm and rural
economics, and potential reversion to dryland
farming — could be exacerbated by global
warming.
Water Quality
• It is not clear how climate change would affect
water quality in the Great Plains. Groundwater
quality may be less at risk than surface water
quality because of increased evaporation and
less leaching. These results are very sensitive
to changes in the amounts and frequency of
rainfall, and groundwater impacts will be
affected by total acres under production, by
application rates, by soil type under cultivation,
and by changes in irrigated versus dryland
acres.
Electricity Demand
• Climate warming could cause the annual
demand for electricity hi Kansas, Nebraska,
Oklahoma, and West Texas to rise by an
additional 5 to 9 billion kilowatthours (kWh) (2
to 4%) by 2010, and by an additional 37 to 73
billion kWh (10 to 14%) by 2055. Summertime
use for air-conditioning and irrigation pumping
could increase and outpace reductions in winter
demand for space heating.
• Approximately 3 to 6 gigawatts (GW) of
generating capacity would be needed by 2010 to
meet the additional increased demand, and 22
to 45 GW would be needed by 2055 -- a 27 to
39% increase over baseline additions that may
be needed without climate change. The
cumulative cost of these additions by 2055
would be $24 to $60 billion.
Policy Implications
• Agencies with responsibility for agricultural
land use, such as the U.S. Department of
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Chapter 17
Agriculture (USDA) Agricultural Stabilization and
Conservation Service and the Soil Conservation
Service, should begin to analyze how their missions
may be affected by climate change and to consider
development of flexible strategies to deal with
potential impacts. Water resource managers, such
as those on river basin commissions and in state
natural resource agencies, may wish to factor the
potential effects of climate change into planning of
land use, long-term water supply, irrigation,
drainage, and water-transfer systems.
CLIMATE-SENSITIVE
RESOURCES IN THE GREAT
PLAINS
The Great Plains consists of a predominantly
treeless region of relatively flat topography between
the Rocky Mountains and the Mississippi lowlands
of central North America. Although very
productive, the region (Figure 17-1) is sensitive to
climate fluctuations, a fact that has been made
apparent in several major droughts over the last few
decades.
Despite this climate sensitivity, dryland
agriculture provides the chief economic base for this
thinly populated region with few cities. The region
was first settled by farmers in the late 1800s under
the Homestead Act, which created the family-farm
system in place today in the Plains (Bowden et al.,
1981).
The Great Plains, including portions of
Nebraska, Kansas, Oklahoma, and Texas, constitutes
a vital part of the United States' agricultural base
and is the focus of this report. Nearly 100,000
farms encompassing over 111 million acres produce
an important array of dryland and irrigated crops.
Major dryland crops include winter wheat and grain
sorghum, and key irrigated grains include corn and
rice. In all, the four states have a combined
production of over 80, 30, and 25% of the nation's
grain sorghum, wheat, and cotton, respectively
(Table 17-1).
Exploitation of water from the Ogallala Aquifer
has supported significant irrigated agricultural
production in the Great Plains during the last two
decades. In many areas, irrigated farming of corn,
Figure 17-1. Boundaries of the Ogallala Aquifer
and dryland wheat production in the Great Plains
(Science of Food and Agriculture, 1987, 1988).
rice, and cotton has replaced dryland wheat
production, especially in western Kansas and the
Texas Panhandle (Figure 17-1). However, the
region's groundwater resources have been
overexploited in some areas, leading to some
reversion to dryland cropping.
Livestock constitute another important
agricultural commodity in the region. Almost 50%
of all cattle fattened in the country are raised in the
four states, accounting for 40% of the total U.S.
value of marketed livestock.
In addition to contributing substantially to
national food supplies, the four states are also major
exporters of agricultural products. Foreign exports
of grain and animal products are especially notable
360
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Great Plains
Table 17-1. U.S. Agricultural Ranking of Great Plains States and Percent of U.S. Total
(for the four states combined) for Selected Products, 1982
Product Kansas
Sorghum harvested 2
Cattle fattened on 2
grain and concen-
trates sold
Value of cattle 2
and calves sold
Wheat harvested 1
Cotton harvested
Hay harvested 9
Market value of 6
all agricultural
products
Source: USDA (1983).
Table 17-2. Agricultural Exports from
(millions of dollars)
Exports U.S. Kansas
Feed grains and 7,585 372
byproducts
Wheat and 4,526 797
byproducts
Live animal and 1,161 130
meats
All agricultural 31,187 1,719
products
U.S. total
(all four
Nebraska Oklahoma Texas states) (%)
3 5 1 80.5
3 91 46.7
3 7 1 40.7
9 3 6 31.8
9 2 25.8
2 16 7 15.9
5 20 3 18.5
Selected Great Plains States, Fiscal Year 1984
U.S. total
Nebraska Oklahoma Texas (%)
903 - 385 22
150 353 276 35
134 18 161 38
1,762 1,471 2,031 19
Source: USDA (1985).
361
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Chapter 17
(Table 17-2). In total, these four states provide
approximately one-fifth of the dollar value of all
TLS. agricultural exports. Yet, dependence on
foreign markets puts Great Plains farmers at high
risk. While large historical fluctuations in grain and
livestock production levels are partly related to
climatic variability, changing international demand,
and its effects on price, play an important role in
the region's continuing economic and social
instability.
The Great Plains is also a major source of coal
and oil, though such extractive industries vary more
with international energy markets than with climate.
Otherwise, the area exhibits little economic
diversity, a pattern that has led to a net
outmigration, especially of younger segments of the
population. Regional population is growing slowly
mostly in the fringe cities (e.g., Omaha), while rural
population and the total number of farms are slowly
decreasing. The region's economy remains
inexorably linked to the fortunes of agriculture and,
thus, to the climate.
Dryland Agriculture
The dryland farming area of the Great Plains
is one of the most marginally productive agricultural
regions in the United States. Some observers have
stated that the southern Plains are simply too
sensitive to climate swings and that intensive dryland
farming should be abandoned (Worster, 1979;
Popper and Popper, 1987). Yet in many years, the
Plains produce bumper crops of small grains that
add significantly to the nation's export trade
balance.
Dryland farmers in the Great Plains are
particularly vulnerable to climate variability. The
Great Plains States of Nebraska, Kansas, Oklahoma,
and Texas were the hardest hit during the Dust
Bowl of the 1930s (Worster, 1979; Hurt, 1981).
Yields of wheat and corn dropped as much as 50%
below normal, causing the failure of about 200,000
farms and migration of more than 300,000 people
from the region.
The Dust Bowl, other droughts, and the desire
for continued expansion and intensification of
dryland farming have led to numerous technological
and social adjustments to climate and market
fluctuations. Especially critical, from a dryland
farming perspective, has been the improvement of
conservation tillage practices like summer fallowing
(Warrick and Bowden, 1981; Riebsame, 1983).
These practices are designed to conserve moisture,
reduce energy input, and minimize erosion, and
thus, to increase yields and profits. Nevertheless,
dryland crop yields still fluctuate widely with
temperature and precipitation variations between
years. The coefficient of variation of wheat yields is
close to 50% over much of the region, and
approximately 30-40% of the planted acreage is
abandoned every year because of poor crops,
especially on the western fringes of agriculture
where the dominant crop is dryland wheat grown on
summer fallow (Michaels, 1985).
In addition to the developments in cropping
systems, government policies and programs have
also been devised to absorb or mitigate the impacts
of climate stresses in the Great Plains and
elsewhere. These include federal programs for crop
insurance, disaster grants and low-interest loans to
farmers, and government-sponsored drought
research (Warrick, 1975). Such programs can be
costly. For example, the projected cost of the 1988
Drought Relief is about $3.9 billion nationally
(Schneider, 1988).
Despite the adoption of conservation tillage
techniques, drought-resistant cultivars, and risk
management programs, some analysts argue that
the region remains particularly vulnerable to
climate-induced reductions in crop yields and will be
one of the first U.S. agricultural regions to exhibit
impacts of climate change (e.g., Lockeretz, 1978;
Warrick, 1984). Rapid acreage increases in the
1970s, destruction of windbreaks for larger fields to
accommodate bigger machinery, and speculative
farm expansion all raise the possibility of renewed
land degradation and economic losses similar to
those of the Dust Bowl period, if climate change
creates an increased frequency of heat waves and
droughts hi the region. Most climate models
indicate that the region would become drier as
global warming proceeds, suggesting potentially
severe impacts on dryland farming.
Irrigated Agriculture
One response to the semiarid .and highly
variable climate of the Great Plains has been
exploitation of surface and groundwater resources
for irrigation to replace dryland farming. In 1982,
19 million acres, or 12% of all Great Plains
cropland, mostly in the southern Plains, were
irrigated. Groundwater provides most of the water
362
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Great Plains
for irrigation: 61 to 86% of the water used in
Nebraska, Oklahoma, and Kansas as compared with
only 20% nationally. In this respect, irrigation
farmers in the Great Plains are less sensitive to
climate change relative to dryland farmers.
However, the demand for irrigation water
throughout the region is very sensitive to climate.
The improvement and application of well
drilling and pumping technology after World War II
permitted the use of water from the immense
Ogallala Aquifer (Figure 17-1). Today, the aquifer
supplies irrigation for approximately 14 million acres
in the Great Plains States of Colorado, Nebraska,
Kansas, Oklahoma, New Mexico, and Texas (High
Plains Associates, 1982). Use of the aquifer allows
the irrigation of terrain too far from surface
supplies. The aquifer also provides water for
municipal and industrial purposes.
Farmers in Nebraska recently began to use the
aquifer to irrigate corn, which is grown mostly for
livestock feed. Corn, wheat, and some sugarbeets
are irrigated farther south, while in Texas the
Ogallala is tapped chiefly for cotton. The aquifer
varies in depth from the land surface, in rate of
natural discharge, and in saturated thickness across
the region. In Nebraska, the aquifer has a higher
recharge rate (i.e., the rate at which the aquifer is
replenished) than in the other Great Plains States,
and significant drawdown problems have not yet
occurred. In Texas and other states, high
withdrawal and low recharge rates of the aquifer
have already resulted in "mining" of the resource
(i.e., the rate of water withdrawal is greater than
rate of recharge) and in the abandonment of
thousands of irrigated acres (see Glantz et al.,
Volume J).
Water Quality
Nonpoint pollution (runoff and leaching) is the
main contributor to water quality problems in the
Great Plains. Many of the groundwater supplies in
the region contain elevated levels of fertilizer and
pesticide-derived pollutants.
Electricity Demand
Electricity use hi the region is sensitive to
climate fluctuations in terms of space heating,
cooling, and agricultural operations such as
irrigation and livestock management (heating,
cooling, etc.). Other types of energy are also
sensitive to climate, but this study addresses only
electricity.
PREVIOUS CLIMATE IMPACT
STUDIES
Many studies of climate impacts on agriculture
in the Great Plains have been performed using a
variety of approaches and models. Dozens of
climate impact studies have focused specifically on
the 1930s drought (e.g., Lockeretz, 1978; Bowden
et al., 1981) and, more generally, on Great Plains
droughts (Warrick, 1975). Many recent studies have
used crop-climate models to estimate impacts of
climate on yields. Warrick (1984) analyzed the
vulnerability of the region to a possible recurrence
of the 1930s drought by running a dryland crop yield
model tuned to 1975 technology with 1934 and 1936
temperature and precipitation conditions. He found
that recurrence of 1930s conditions in the region
would result in wheat yield reductions of over 50%.
Terjung et al. (1984) used a crop water demand and
yield model to investigate irrigated corn production
sensitivity to differing temperature, precipitation,
and solar radiation fluctuations. They found that in
the central Great Plains, evapotranspiration and
total water applied for irrigation were very sensitive
to climate variations. Overman et al. (1986)
continued this modeling and found that the lowest
irrigated yields occurred under cloudy, hot, and very
dry climate scenarios. Under dryland cropping,
minimum yields occurred under sunny-hot and
sunny-warm scenarios with very dry conditions.
Using an agroclimatic approach, Rosenzweig
(1985) found that lack of cold winter temperatures
in the southern Great Plains may necessitate a
change from whiter to spring wheat cultivars with
climate change projected for a doubling of CO2-
Changes in temperature, precipitation, and solar
radiation were considered. Decreased water
availability may also increase demand for irrigation.
In a later study, Rosenzweig (1987) showed that
although the combined impact of doubled CO,
climate change (temperature, precipitation, and
solar radiation changes) and the direct effects of
elevated CO2 (increased photosynthesis and
improved water use) compensated for the negative
effects of climate change in years with adequate
rainfall, this compensation did not reduce crop
failures in dry years.
363
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Chapter 17
Robertson et al. (1987) estimated the combined
impact of temperature and precipitation changes
due to doubled CO, climate change and the direct
effects of increased CO2 on rainfed corn and wheat
yields and erosion using the Erosion Productivity
Impact Calculator (EPIC). Results showed that
modeled wheat yields in Texas decreased and
modeled corn yields increased slightly. Such
changes in productivity could result in long-term
changes in cropping patterns.
Glantz and Ausubel (1984) suggested that the
Great Plains' mining of the Ogallala Aquifer and its
susceptibility to future incidence of drought
projected by global climate models be combined in
analyses of the region, since both are critical to the
habitability of the area.
GREAT PLAINS STUDIES IN
THIS REPORT
The studies for this report examine the
implications of climate change for several important
activities in the region: agricultural production and
economics, demand for irrigation water, and water
quality. Climate change impact research on
livestock, electricity use, and resource management
policy relevant to the Great Plains is also described.
The individual studies performed for this report are
listed in Table 17-3.
The Great Plains studies explore the sensitivities
of regional activities to climate change scenarios.
The results are not meant to be predictions of what
will happen; rather the studies aim to define the
ranges and magnitudes of potential responses of
critical regional systems to the predicted climate
changes.
GREAT PLAINS REGIONAL
CLEMATE CHANGE SCENARIOS
The estimated changes in seasonal and annual
temperatures and precipitation for the scenarios are
shown hi Figure 17-2. For a description of the
global climate models, climate scenarios, and a
discussion of the likelihood of these changes, see
Chapter 2: Climate Change, and Chapter 4:
Methodology. All three scenarios show large
Table 17-3. Great Plains Studies for EPA
Report to Congress on the Effects
of Global Climate Change
Analyses Performed for This Case Study
• Potential Effects of Climate Change on
Agricultural Production in the Great Plains: A
Simulation Study - Rosenzweig, Columbia
University, NASA/Goddard Institute for Space
Studies (Volume C)
• Effects of Protected CO2-Induced Climatic
Changes on Irrigation Water Requirements in
the Great Plains States - Allen and Gichuki,
Utah State University (Volume C)
National Studies That Included Great Plains
Results
• Economic Effects of Climate Change on U.S.
Agriculture: A Preliminary Assessment -
Adams, Oregon State University and Glyer and
McCarl, Texas A&M University (Volume C)
• Impacts of Climate Change on the Movement
of Agricultural Chemicals Across the U.S.
Great Plains and Central Prairie -Johnson,
Cooter, and Sladewski, Oklahoma
Climatological Survey, University of Oklahoma
(Volume C)
• Changing Animal Disease Patterns Induced bv
the Greenhouse Effect - Stem, Mertz, Stryker,
and Huppi, Tufts University (Volume C)
• Effect of Climatic Warming on Populations of
the Horn Fly, with Associated Impact on
Weight Gain and Milk Production in Cattle -
Schmidtmann and Miller, U.S. Department of
Agriculture, Agricultural Research Service
(Volume C)
• The Potential Impacts of Climate Change on
Electric Utilities: Regional and National
Estimates - Linder and Inglis, ICF Incorporated
(Volume H)
• Climate Change and Natural Resources
Management in the United States -Riebsame,
University of Colorado (Volume J)
364
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Great Plains
A. Temperature
5
CHANGE ('C)
77,
\
8
w
-
Winter Spring
B. Precipitation
0.4
0.3
._. 0.2
1 "
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•« -0.2
-0.3
-0.5
-
-
-
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1
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Yt
K
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i
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W nter Spring
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^
1
^
i
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1L
Summer Fa 1
p
«f
Annual
^
|
pr
Annual
|%%] GISS
wtm
tw!fW3 GFDt-
1 l°su
Figure 17-2. Average change in (A) temperature,
and (B) precipitation over Great Plains gridpoints in
GISS, GFDL, and OSU global climate models
(2XCO2 run less 1XCO2 run).
increases in temperature for the Great Plains States
under a doubled CO2 climate. The GISS scenario
has an annual warming of 4.5° C, the GFDL scenario
has an annual warming of 5.0° C, and OSU has an
annual warming of 3.3°C. In general, winter
temperatures increase more than summer
temperatures in the GISS model, and summer
temperature changes are greater than winter
temperature changes in the GFDL and OSU
scenarios. The differences between the models
range from 0.2 to 1.5°C. The impact studies used
only the GISS and GFDL climate change scenarios
because of time limitations.
Average annual precipitation decreases by 0.26
millimeters per day (3.7 inches per year) in the
GISS scenario, while GFDL and OSU have slight
increases. However, these annual values mask a
pronounced reduction in rainfall in Nebraska and
Kansas in the GFDL scenario (see Figure 17-3).
The large temperature increase and pronounced
summer drying combine to make the GFDL
scenario severe in these states, and the most severe
case among the climate change scenarios.
The magnitudes of climate changes in the
spring and summer from the GFDL scenario and
the climate of the 1930s drought in Nebraska and
Kansas are compared in Figure 17-3. While the
scenario decreases in growing season precipitation
are about the same as those during the most severe
drought years (1934 and 1936) in the area, the
climate change scenario temperatures are about
3°C higher than the Dust Bowl temperatures.
y
8
7
6
g 5
CD
S 3
2
1
0
0.4
0.2
0.0
•a '°'2
I -0'4
| -0.6
CO
o -°-8
-1.0
-1.2
•1.4
\. Temperature
-
-
J
m
-
-
1934+1936 GFDL
3. Precipitation
-
-
1
-
'ww
-
1934+1936 GFDL
UJ Spring
^ Summer
Figure 17-3. Comparison of observed drought (iy«
and 1936) and GFDL climate change in Nebraska
and Kansas for (A) temperature, and (B)
precipitation (Rosenzweig, Volume C).
365
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Chapter 17
RESULTS OF THE GREAT
PLAINS STUDIES
Crop Production
To better understand the potential physical
impact of climate change on crops, Rosenzweig
modeled changes in corn and wheat yields in the
Great Plains using crop growth models.
Study Design
Two crop growth models, CERES-Wheat
(Ritchie and Otter, 1985) and CERES-Maize (Jones
and Kiniry, 1986) were used to test the sensitivity of
crop yields to the GISS and GFDL climate change
scenarios. These models are designed for large-area
yield prediction and for farm decisionmaking and
have been validated for a wide range of conditions
(Otter-Nacke et al., 1986). The CERES models
simulate crop responses to the major factors that
affect crop yields: climate, soils, and management.
The models employ simplified functions to predict
crop growth stages; development of vegetative and
reproductive structures; growth of leaves and stems;
dieback of leaves; biomass production and use; root
system dynamics; and the effects of soil-water deficit
on photosynthesis and biomass use in the plant.
At each of 14 locations, the crop models were
run with three soils present in the region
representing low, medium, and high productive
capacity. Model results were generated for changes
in yield, water used for irrigation (if crop is
irrigated), crop evapotranspiration, and planting and
maturity dates for both dryland and irrigated cases.
The direct effects of CO2 (i.e., increased
photosynthesis and decreased transpiration per unit-
leaf area) were simulated with the climate change
scenarios in another set of runs. A method for
approximating the direct effects in the CERES
models was developed by computing ratios of daily
photosynthesis and evapotranspiration rates for a
canopy exposed to elevated (660 ppm) CO2 to those
rates for the same canopy exposed to current (330
ppm) CO2 conditions (see Peart et al., Volume C).
Daily photosynthesis rates of wheat and corn
canopies were increased 25 and 10%, respectively,
based on published results of controlled
environmental experiments with crops growing in air
with increased CO2 levels.
Limitations
This work does not consider changes in
frequencies of extreme events, even though
extremes of climatic variables, particularly runs of
extremes, are critical to crop productivity (see
Chapter 3: Variability). Development of the
CERES models was based on current climate; the
relationships in the models may or may not hold
under differing climate conditions, particularly the
high temperatures predicted for greenhouse
warming.
The direct effects of CO2 are only
approximated in the crop modeling study, because
the models do not include a detailed simulation of
photosynthesis. Also, experimental results from
controlled environments may show more positive
effects of CO2 than would actually occur in variable,
windy, and pest-infested (e.g., weeds, insects, and
diseases) field conditions; thus, this study probably
overestimated the beneficial effects of increased
C02.
Results
Climate change scenarios cause simulated
wheat (Figure 17-4) and corn (Figure 17-5) yields to
decrease hi the southern and central Great Plains.
Results shown are means of modeled yields at study
sites grouped by latitude for 30 years of baseline
and climate change scenarios. With climate change
alone, decreases in modeled yields appear to be
caused primarily by increases hi temperature, which
would shorten the duration of crop life cycle (the
period during which a crop grows to maturity). This
results in reduced yields. When the direct effects
of CO2 on crop photosynthesis and transpiration are
included in the climate change simulations, modeled
crop yields overcome the negative effects of climate
change in some cases, but not in others. In general,
the more severe the climate change scenario, the
less compensation provided by direct effects of CO2.
Corn and wheat yields were estimated to
respond differently to dryland and irrigated climate
change conditions and to the direct effects of CO2.
Dryland corn yield decreases were very high in the
hotter and drier GFDL scenario, particularly at
higher latitudes. These decreases were caused by
the combined effects of high temperatures
366
-------
Great Plains
(A) DRYLAND
5
1
36-38 N
LATITUDE
(B) IRRIGATED
I
I 4
38-40 N
36-38 N
LATITUDE
<34N
g^GISS lU GISS + DE fill GFDL f] GFDL + DE
D6 = Direct Effects of CO2
Figure 17-4. CERES-Wheat yields in the Great Plains with GISS and GFDL climate change scenarios with anc
without the direct effects of CO2: (A) dryland, (B) irrigated (Rosenzweig, Volume C).
shortening the grain-filling period and increased
moisture stress. The GFDL scenario has
pronounced reductions in summer precipitation
(decreases of about 30 mm per month) in the two
northern gridboxes of the study area, which occur
during critical growth stages of corn. Irrigated corn
was more negatively affected than irrigated wheat in
the combined climate and direct effects runs
because of the lower photosynthetic response of
corn to CO2-
In general, the amount of water needed for
irrigation in the crop models is estimated to
increase in the areas where precipitation decreases
and irrigation reduces interannual variability in
yields. These results suggest an increased demand
for irrigation in the region.
Adjusting the planting date of wheat to later in
the fall, one potential farmer adjustment to a
warmer climate, was not estimated to significantly
ameliorate the effects of the GISS climate change
scenario on CERES-Wheat yields. Changing to
varieties with lower vernalization requirements
(need for a period of cold weather for reproduction)
and lower photoperiod sensitivity (sensitivity to
daylength), in addition to delaying planting dates,
overcomes yield decreases at some sites but not at
others.
367
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Chapter 17
(A) DRYLAND
8,
i4
> 2
-m
40-42 N
38-40 N
36-38 N
LATITUDE
34-36 N
(B) IRRIGATED
\s
38-40 N 36-38 N
LATITUDE
3 GISS lH GISS + DE Q GFDL
DE = Direct Ellectsof CO2
QGFDL+DE
Figure 17-5. CERES-Maize yields in the Great Plains with GISS and GFDL climate change scenarios with and
without the direct effects of CO2: (A) dryland, (B) irrigated (Rosenzweig, Volume C).
Implications
There is potential for climate change to cause
decreased crop yields in the southern Great Plains.
Farmers would need varieties of corn and wheat
that are better acclimated to hotter and possibly
drier conditions to substitute for present varieties,
and adjustment strategies tailored for each crop and
location.
Pressure for increased irrigation may grow in
the region, particularly with more severe climate
changes. This would occur for two reasons: first,
crops currently irrigated would require more water
where precipitation decreases; and second, more
acreage would be irrigated as high temperatures
increase the risk of crop failures. Increased
irrigation would be needed to ensure acceptable and
stable yield levels. However, availability of and
competition for water supplies also may change with
climate change, and defining the extent to which
irrigation can provide an economic buffer against
climate change requires further study.
Agricultural Economics
Many economic consequences are likely to
result from the physical changes in crop yields and
water availability caused by climate change.
Decreased yields will further stress farmers already
368
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Great Plains
affected by marginal productivity and economic
fluctuations. Additional irrigation needs could place
greater demand on the Ogallala Aquifer and other
water resources in the region. To examine the
agricultural implications of climate change more
closely, Adams et al. introduced yield changes from
the Great Plains and other regional crop modeling
studies, and changes in crop water use and water
availability from the GISS and GFDL scenarios into
an economic model to translate the physical effects
of climate change into economic consequences. (For
study design and limitations, see Chapter 6:
Agriculture.) Analyses were done both for climate
change alone and for the combined effects of
climate change and enhanced CO, concentrations to
explore the sensitivity of the agricultural system to
the projected changes. The economic study did not
address the issues of whether the physical and
institutional changes required to accommodate
increased demand for irrigated acreage are feasible
or whether new crops would be introduced. The
study did not consider changes in global agriculture.
Results
The estimates of Adams et al. (see Volume C)
for total agricultural and irrigated acreage changes
in the southern Great Plains States (Oklahoma and
Texas only) are shown in Table 17-4. Agricultural
land is estimated to decrease in the southern Great
Plains in all scenarios, with and without the direct
effects of CO2. Decreases range from 4 to 22%.
Irrigated acreage, on the other hand, increases in all
scenarios, from 9 to 30%. This is because of
increased stability of irrigated yields relative to
dryland yields, and because of a rise in commodity
prices that makes expansion of irrigation production
economically feasible.
Implications
The results of the agricultural economics study
imply that wheat and corn production may shift
away from the southern Great Plains. This may
weaken the economic base of many rural
Table 17-4. Estimated Changes in Agricultural Land Usage in Oklahoma and Texas (millions of acres)
Usage
Base
acreage
GISS
GFDL
Acreage
Change
% Change Acreage Change % Change
Agricultural land
Without direct
effects 54.7
With direct
effects 54.7
42.6
48.8
-12.1
-10.9
-22.1
-19.9
52.0
52.7
-2.7
-2.0
-4.9
-3.8
Irrigated acreage
Without direct
effects 5.3
With direct
effects 5.3
6.9
5.8
1.6
0.5
29.6
9.4
5.6
6.1
0.3
4.9
0.8 15.3
Source: Adams et al. (Volume C).
369
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Chapter 17
communities in the region and cause dislocations of
rural populations. Uncertainties exist about
adaptation in the region, such as substitution of
more heat- and drought-tolerant varieties and crops.
If irrigated acreage expands as predicted in the
economic analysis, changes in capital requirements
for agriculture would also occur.
If irrigated acreage does increase in the area,
groundwater overdrafts also would be likely, along
with associated increases in surface and
groundwater pollution and other forms of
environmental degradation. The current analysis
did not address the issue of whether the physical
and institutional changes required to accommodate
such an increase in irrigated acreage are feasible.
Irrigation
Higher air temperatures cause increased
evaporative demands, which largely govern crop
water use and irrigation water requirements. The
climate and crop production changes that might be
associated with global warming in the southern
Great Plains are likely to heighten farmer interest
in irrigation, both because evapotranspiration may
increase and because irrigated crops might obtain a
larger economic advantage in a less favorable
climate. Therefore, climate change impacts on
irrigation water requirements were analyzed hi more
detail.
Study Design
Allen and Gichuki (see Volume C) evaluated
the effects of climate -change and reduced
transpiration due to enhanced CO, on crop
irrigation water requirements in the Great Plains.
They used an irrigation water requirement model to
calculate daily soil moisture balances,
evapotranspiration, and irrigation water
requirements for corn, wheat, and alfalfa. The
model employed the Penman-Monteith combination
method to estimate crop evapotranspiration
(Monteith, 1965). Four levels of potential direct
effects of CO2 on transpiration were simulated.
Limitations
Some uncertainty is embedded in the
evapotranspiration and irrigation water requirement
estimates owing to mismatching of weather profiles
and crop characteristics. Also, this study assumed
that alfalfa, corn, and wheat all would respond
similarly to increased CO2 (which may reduce
transpiration), although published reports of
experimental results show different responses
among crops (see Rose, Volume C). The majority
of results presented in this study assumed that crop
varieties would not change, even though farmers
may shift to crops more adapted to the changed
climate.
In general, modeled results showed that
seasonal irrigation requirements for an area growing
alfalfa, corn, and winter wheat in the Great Plains
would increase by about 15% under the doubled
CO, scenario. These results are based on averages
of the two GCM doubled CO, scenarios and the
likely occurrence of only moderate CO2-induced
decreases in transpiration.
Irrigation requirements were estimated to vary
depending on the type of crop, changes in climatic
factors, and variations in response to CO2. The
perennial crop alfalfa showed persistent increases in
seasonal net irrigation water requirements (see
Figure 17-6). These increases are driven primarily
by higher temperatures, with less influence from
stronger winds, greater solar radiation, and a longer
growing season.
Figure 17-6. Seasonal irrigation water requirement
for alfalfa for GISS and GFDL climate change
scenarios and a moderate CO2-induced decrease in
transpiration (Allen and Gichuki, Volume C).
370
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Great Plains
On the other hand, decreases in seasonal net
irrigation requirements were estimated for the
region's two most important crops, winter wheat
and corn, in most areas, depending on the projected
direct effects of CO, on transpiration. These water
need decreases would be generally due to shorter
crop growing periods caused by higher
temperatures, which accelerate crop maturity.
When crop varieties appropriate to the longer
growing season were modeled, irrigation
requirements for winter wheat were estimated to
increase. Water requirements during peak irrigation
periods (when plant growth and temperatures are
greatest) increased in almost all cases (Figure 17-
7). These results are consistent with results from
the crop modeling study.
Plant canopy (leaf) temperatures were
estimated to increase above current baseline values
for all crops and sites studied. Increases hi leaf
temperatures may reduce photosynthetic activity and
crop yields. They also would make crops more
sensitive to moisture stress. (See discussion on
direct effects of CO2 in Chapter 6: Agriculture.)
Implications
Any reduction in irrigation requirements for
corn and winter wheat would be beneficial in the
Great Plains because less water and energy would
be required to produce the crops. However, the
shortened crop growth periods might allow for
double-cropping (planting two crops in one season),
thus increasing total irrigation requirements.
Farmers may shift to longer-season varieties, which
would also increase water needs.
Expanded farm irrigation systems will require
increased capital investments and larger peak drafts
on groundwater systems and on energy supplies.
Increased groundwater extraction could pose
environmental and economic problems, especially
where "water mining" is currently a major problem.
Any action of irrigators to increase irrigation
efficiency as an attempt to cope with projected
water shortages, while economically beneficial, may
lead to increased salinity problems if sufficient water
is not applied to meet soil leaching requirements.
40
20
0
HI
3 100
?
uj 80
13
UJ
w 60
CD
| 40
LL.
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O 20
<
I °
UJ
8 50
UJ
n_
40
30
20
10
0
-10
(A) ALFALFA
JL
(B) CORN
(C) WINTER WHEAT
GISS GFDL GISS GFDL GISS GFDL. GISS GFDL
NEBRASKA KANSAS OKLAHOMA TEXAS
180%
Figure 17-7. Percent change in net peak monthly
irrigation requirement from baseline values for
alfalfa, corn, and winter wheat for GISS and GFDL
climate change scenarios and five levels of CO2-
induced decreases in transpiration (Allen and
Gichuki, Volume C).
Water Quality
Agricultural pesticides are a high-priority
pollution problem in at least half of the states within
the U.S. Great Plains and Central Prairie.
371
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Chapter 17
Potentially toxic agricultural chemicals can be
removed from farmers' fields through degradation,
surface runoff, sediment transport, and downward
percolation. An understanding of potential climate
change effects on the movements of agricultural
chemicals is needed to identify potential changes in
drinking water quality.
Study Design
Johnson et al. used the Pesticide Root Zone
Model (PRZM) (Carsel et al., 1984) to simulate the
partitioning of pesticides between plant uptake,
chemical degradation, surface runoff, surface
erosion, and soil leaching in the Great Plains under
baseline climate and climate change scenarios. The
locations modeled were representative of cropping
practices for winter wheat and cotton in the region.
The interactions among soil, tillage, management
systems, pesticide transport, and climate change
were studied. (For further discussion of the study's
design and limitations, see Chapter 6: Agriculture.)
Results
As Figure 17-8 shows, surface runoff and
surface erosion of agricultural pesticides increased
under the GISS scenario for the winter wheat
regions of the Great Plains. In the southern Great
Plains cotton simulations, both the GISS and GFDL
scenarios produced increases in surface pesticide
losses with runoff and eroded soils.
The quantity of pesticides leached below the
crop root zone is estimated to decrease everywhere
except on silty soils in the cotton region. This
overall decline most likely results from higher
evaporative demands in response to temperature
increases and to less available moisture for
infiltration and deep percolation.
Implications
Results of the modeling imply that water quality
in the southern Great Plains may be affected by
climate change. However, because these results are
highly dependent on the frequency and intensity of
precipitation events, directions of change are
uncertain. Surface water appears to be vulnerable
to deterioration under climate change conditions,
although the result does not hold for all cases.
Groundwater quality in some areas appears to be
less at risk than surface water quality. However,
A. PESTICIDE RUNOFF LOSSES
g 150
U-
O
LU
£ 100
WINTER WHEAT COTTON
CROP REGION
B. PESTICIDE EROSION LOSSES
WINTER WHEAT COTTON
CROP REGION
C. PESTICIDE LEACHING
WINTER WHEAT COTTON
CROP REGION
Figure 17-8. Regional summary of surface and
subsurface pesticide loss as a percentage of the base
climate scenario losses (Johnson et al., Volume C).
groundwater impacts will depend on total acres
under production, application rates, soil type under
cultivation, and changes in irrigated versus dryland
acres.
From a water quality perspective, decreased
pesticide leaching may be advantageous. From a
water quantity perspective, these results could be
cause for concern. Less leaching can imply less
water movement through soil profiles and less water
372
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Great Plains
availability for aquifer recharge. If water demands
were to increase (as suggested by the crop
production, economic, and irrigation analyses) at the
same time that recharge rate decreased, competition
for scarce water resources could increase
dramatically in the region.
Livestock
Livestock production is a critical agricultural
activity in the Great Plains and may be sensitive to
climate fluctuations in several ways. The warming
in the climate change scenarios may alleviate cold
stress conditions in the winter but would exacerbate
heat stress in the summer. Warmer summers are
likely to necessitate more hours of indoor cooling.
Reproductive capabilities have been shown to
decline as a result of higher temperatures. Higher
temperatures also may enable tropical diseases and
pests to extend their ranges northward into the
southern Great Plains. High temperatures also may
reduce insect pest activities in some locations and
increase them in others. (For a discussion of
livestock issues, see Chapter 6: Agriculture.)
Schmidtmann and Miller (see Volume C)
modeled the effect of climate warming on the horn
fly, a common pest of pastured cattle that causes
reductions in weight gain and milk production. (For
a description of study design and limitations, see
Chapter 6: Agriculture.) This study used only the
GFDL scenario; since it had the highest
temperatures, results should be considered as an
extreme case. In Texas, horn fly populations were
estimated to become lower in summer than they are
currently because high temperatures are lethal to
the insects when they are immature. Thus, weight
gains of calves and feeder/stocker cattle could
increase relative to current rates in Texas. In
Nebraska, however, temperatures in the GFDL
scenario would not reach lethal levels, and increases
of 225 to 250 horn flies per head were estimated.
This would result in greater weight reductions than
those currently observed. These results suggest that
greater stress may occur in livestock production in
the northern part of the Great Plains, and that
stress may be alleviated in Texas.
Stem et al. (see Volume C) studied the effects
of climate change on animal disease patterns. (For
study design and limitations, see Chapter 6:
Agriculture.) The ranges of some diseases may be
extended as habitats of disease vectors enlarge or as
warmer environments permit longer seasonality of
diseases currently present. Stem et al. calculated
that the ranges of bluetongue and Rift Valley fever
(both serious or potentially serious diseases of
cattle) could be extended northward from Texas to
Kansas and Nebraska with climate warming.
Climate change thus has the potential to cause
increased incidence of animal disease and to
increase stress on livestock production in the Great
Plains.
Electricity Demand
Linder and Inglis (see Volume H) estimated
the changes in demand for electricity for the years
2010 and 2055. (For a description of the study's
design and methodology, see Chapter 10: Electricity
Demand.) In each case, they first estimated the
change in electricity demand due to projected
regional economic and population growth, and then
factored in changes in demand based on the GISS
transient climate change scenarios A and B. The
results for the southern and central Great Plains are
discussed here.
Results
Estimates of changes in peak demand, capacity
requirements, and cumulative and annual costs
projected for the climate change scenarios in the
Great Plains are shown in Table 17-5. The results
are driven by seasonal changes in weather-sensitive
demands for electricity: summertime use for air-
conditioning and irrigation-pumping increases and
outpaces reductions hi demand for space heating in
the winter. Electricity demand grows by 2 to 4% by
2010, and new capacity requirements are estimated
to increase by 15 to 28% by 2010 for the climate
change scenarios as compared with the base case
(i.e., economic growth without climate change). By
2010, additional cumulative capital costs induced by
climate change may be $3.7 to $6.7 billion, and
annual costs of generating power may rise by 3 to
6%.
In 2055, new capacity generating requirements
are estimated to increase by 22 to 45 gigawatts or 27
to 39%. Annual electricity demand in the region
increased an additional 10 to 14% by 2055 under
the climate change scenarios. New capacity
requirements without climate change are estimated
to be 20 GW by 2010 and 112 to 134 GW by 2055.
373
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Chapter 17
Table 17-5. Estimated Change in Peak Demand and Annual Energy Requirements Induced by Climate
Change (%)
Utility area
2010
2055
GISS A
GISSB
GISS A
Ann.
Peak
Ann.
Peak
Ann.
Peak
Kansas/Nebraska
Oklahoma
Texas, east
Texas, south
Texas, west
1.7
3.0
3.0
3.3
3.1
6.8
7.9
7.9
10.0
8.6
1.3
2.8
2.8
1.7
2.4
5.2
6.6
6.6
5.1
6.1
5.7
11.3
11.3
10.6
11.1
22.1
25.3
25.3
24.6
25.1
Source: Linder and Inglis (Volume C).
Linder and Inglis calculated that cumulative
capital costs for electricity in the region would
increase from $20 to $53 billion by 2055 with
climate change. The estimated changes in annual
costs induced by climate change range from $5 to
$10 billion.
Implications
Increased electrical capacity requirements and
the need to maintain the reliability of utility systems
could place additional stress on the Great Plains.
This is especially important if climate change
increases the demand for irrigation, which is an
important consumer of electricity in the region.
Also, the potential exists for conflicts between
power production and agriculture over the use of
scarce resources such as water. Powerplants may
take the cooling water they need from rivers or
from the already overused Ogallala Aquifer, and
increased coal and oil production in the region
would utilize land that might be farmed. However,
energy production may provide alternative income
sources in an area whose economy is poorly
diversified.
CLIMATE CHANGE AND THE
OGALLALA AQUIFER
Warming and/or drying in the Great Plains may
place greater demand on regional groundwater
resources. Although the Ogallala Aquifer has come
under close scrutiny in the past, it is important to
note that previous studies have not addressed
potential climate change impacts on this resource.
Many of the problems associated with intense
groundwater use (water depletion, soil damage,
altered rural and farm economics, and potential
reversion to dryland farming) could be exacerbated
by global warming. This study shows that irrigated
acreage in the Great Plains could increase and that
the demand on the aquifer could rise by up to 15%.
These potential adjustments to climate change
should be studied to understand their implications
for land use, resource conservation, regional
economics, and community issues in the Ogallala
area.
POLICY IMPLICATIONS
The policy options for responding, either in
anticipation or in reaction, to climate change in the
Great Plains range from noninterference, in which
agricultural, water, and other resource systems are
left to adjust without assistance, to a more active
approach in which federal, state, and local
government agencies plan for and assist in the
process of adaptation.
Given the historical government involvement in
agriculture, especially in this marginal region where
support programs may mean the difference between
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Great Plains
farm survival and failure, it is likely that an active
adjustment process will be called for. Policymakers
in the Great Plains may have to respond to
decreased agricultural production in the area,
increased demand for water and electricity, poorer
water quality, and changes in livestock production.
The major issues that policymakers should address
include land-use management, water resource
management, and agricultural risk management (see
Riebsame, Volume J). Regional utility planners and
policymakers should also begin to consider climate
change as a factor — along with other uncertainties
— affecting their resource availability analyses and
planning decisions.
Of course, uncertain and limited impact
assessments such as those described above cannot
be used to create and implement detailed policy.
Rather, they should be viewed as scenarios that
suggest the types of policies and the range of policy
mechanisms and flexibilities that could alleviate
potentially disruptive impacts from climate change.
The eventual problem for the policymaker, of
course, is deciding when to switch from scenario
analysis to actual policy formulation and
implementation. The last few sections of this
chapter suggest some of the policy implications
raised by the impacts described earlier.
Land-Use Management
Land managers should analyze how their
missions and holdings may be affected by climate
change and should develop flexible strategies to deal
with potential impacts. Federal agencies, such as
the Department of Agriculture, the Forest Service,
the Fish and Wildlife Service, and the Department
of Interior, should work with state agriculture,
forest, and park agencies on such plans.
Climate change may cause agriculture and other
land uses to become more environmentally and
economically marginal in the Great Plains.
Consequently, land uses may shift in intensity, type,
and location. Indeed, locational shifts may involve
several states or multiple regions. This adjustment
process can be made more efficient and less
disruptive if individual jurisdictions, such as
municipalities, states, and federal regions, respond
in a coordinated manner. Decisions made by
managers of agriculture will affect forests, wildlife,
and water resources. Decisionmakers should begin
now to work together to develop a sound and
flexible repertoire of anticipatory strategies; new
institutional arrangements may be needed.
Some programs already in place can help to
lessen the negative effects of climate change on the
Great Plains. Federal legislation such as the "Sod-
Buster Bill" and programs such as the Conservation
Reserve Program are examples of new policies
designed to reduce the use of marginal lands for
agriculture. The basic goals of these laws are to
protect the most erodible farmlands by removing
them from crop production, and to use conservation
as a tool for reducing overproduction. Such
programs are prudent now for reducing erosion and
may become even more important for protecting
soil and water quality in a changing climate.
However, protection of marginal lands may have to
be weighed against the need for greater crop
production if climate change lowers yields. For
example, the government's response to the 1988
drought was to release some conservation land for
cropping in 1989. This would help replenish food
stocks but also would place a greater amount of
marginal land at risk of erosion.
Water Resource Management
If GCM projections of climate change are
qualitatively correct, parts of the Great Plains are
likely to suffer increasing aridity. Farmers may
demand more water for irrigation, although
groundwater sources are already taxed.
Competition for water resources between
agricultural and nonagricultural demands may be
exacerbated. Water managers need to factor the
potential effects of climate change into their
decisions on irrigation, drainage, and water transfer
systems, and they should consider potential climate
change as they formulate supply allocation rules,
reservoir operating criteria, safety protocols, and
plans for long-term water development. Water
conservation techniques, water reallocation between
competing uses, water transfers and marketing, and
land-use adjustments should be evaluated for their
ability to absorb the effects of a range of future
climate changes. The goal at this point may not be
to formulate detailed policy, but rather to test the
climate sensitivity and feasibility of alternative water
management policies and practices.
Decisionmakers should also consider the
potential effects of climate change on water quality
and the use of pesticides. They should examine
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Chapter 17
alternative pest control strategies, such as Integrated
Pest Management, which use biological control,
genetic resistance, and innovative cropping systems
to reduce pesticide applications.
Risk Management
Several government, semiprivate, and private
institutions have a large financial stake in Great
Plains agriculture through land credit, commodity
and equipment loans, and insurance. Additionally,
the federal government provides disaster relief for
climate extremes "affecting regional agriculture.
Climate warming poses a potential long-term risk to
the financial institutions supporting agriculture, to
the resources available for emergency relief, and to
individual farmers. This possibility should be
carefully assessed, and plans should be made now to
monitor risk as climate changes.
REFERENCES
Bowden, MJ., R.W. Kates, PA. Kay, WE.
Riebsame, D. Johnson, H. Gould, and D. Weiner.
1981. The effect of climate fluctuations on human
populations: two hypotheses. In: Wigley, T.M.L.,
MJ. Ingram, and G. Farmer, eds. Climate and
History. Cambridge, United Kingdom: Cambridge
University Press, pp. 479-513.
Carsel, R.F., C.N. Smith, LA. Mulkey, J.D. Dean,
and P. Jowise. 1984. Users' Manual for Pesticide
Root Zone Model: PRZM. USEPA/ERL Report
EPA-600-3-84-109. Washington, DC: U.S.
Government Printing Office.
Dregne, H.E., W.O. Willis, and M.K. Adams. 1988.
The metamorphosis of the "Great American
Desert." Science of Food and Agriculture 6(11):2-
7.
Glantz, M.H., and Ausubel, J.H. 1984. The Ogallala
Aquifer and carbon dioxide: comparison and
convergence. Environ. Conser. 11(2):123-31.
High Plains Associates. 1982. Six-State High Plains-
Ogallala Aquifer Regional Resources Study. Austin,
TX.
Hurt, R.D. 1981. The Dust Bowl. Chicago: Nelson-
Hall.
Jones, CA., and J.R. Kiniry. 1986. CERES-Maize:
A Simulation Model of Maize Growth and
Development. College Station, TX: Texas A&M
Press.
Liverman, D.M., W.H. Terjung, J.T. Hayes, and
L.O. Mearns. 1986. Climatic change and grain corn
yields in the North American Great Plains. Climatic
Change 9:327-347.
Lockeretz, W. 1978. The lessons of the Dust Bowl.
American Scientist 66:560-569.
Michaels, PJ. 1985. Economic and climatic factors
in "acreage abandonment" over marginal cropland.
Climatic Change 7:185-202.
Monteith, J.L. 1965. Radiation and crops.
Experimental Agriculture Review 1(4):241-251.
Otter-Nacke, S., D.C. Goodwin, and J.T. Ritchie.
1986. Testing and Validating the CERES-Wheat
Model in Diverse Environments. Houston, TX:
Lyndon B. Johnson Space Center. AgRISTARS
YM-15-00407. JSC 20244.
Popper, D.E., and FJ. Popper. 1987. The Great
Plains: from dust to dust. Planning (December):13-
18.
Powers, W.L. 1987. The Ogallala's bounty
evaporates. Science of Food and Agriculture 5(3):2-
5.
Riebsame, W.E. 1983. Managing agricultural
drought: the Great Plains experience. In: Platt, R.,
and G. Macinko, eds. Beyond the Urban Fringe:
Land Use Issues in Non-Metropolitan America.
Minneapolis: University of Minnesota Press, pp.
257-270.
Riebsame, W.E. 1987. Human Transformation of
the United States Great Plains: Patterns and
Causes. Proc. Symp. on the Earth as Transformed
by Human Action, Clark University.
Ritchie, J.T., and S. Otter. 1985. Description and
performance of CERES-Wheat: user-oriented wheat
yield model. In: Willis, W.O., ed. ARS Wheat Yield
Project. USDA-ARS. ARS-38. pp. 159-175.
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Robertson, T., V.W. Benson, J.R. Williams, CA.
Jones, and J.R. Kiniry. 1987. Impacts of climate
change on yields and erosion for selected crops in
the southern United States. In: Meo, M., ed. Proc.
Symp. on Climate Change in the Southern U.S.:
Impacts and Present Policy Issues, Science and
Public Prog., Univ. of Oklahoma, Norman, OK.
Rosenzweig, C. 1985. Potential CO2-induced climate
effects on North American wheat-producing regions.
Climatic Change 7:367-389.
Rosenzweig, C. 1987. Climate change impact on
wheat: the case of the High Plains. In: Meo, M., ed.
Proc. Symp. on Climate Change in the Southern
U.S.: Impacts and Present Policy Issues, Science and
Public Prog., Univ. of Oklahoma, Norman, OK.
Schneider, K. 1988. Drought cutting US. grain
crop 31% this year. The New York Times August
Terjung, W.H., D.M. Liverman, and J.T. Hayes.
1984. Climatic change and water requirements for
grain corn in the North American Great Plains.
Climatic Change 6:193-220.
USDA. 1983. UJS. Department of Agriculture, U.S.
Bureau of the Census. 1982 Census of Agriculture.
Washington, DC: U.S. Government Printing Office.
USDA. 1985. U.S. Department of Agriculture,
Economic Research Service. Foreign Agricultural
Trade of the United States. Washington, DC: U.S.
Government Printing Office.
Warrick, R A. 1984. The possible impacts on wheat
production of a recurrence of the 1930s drought in
the U.S. Great Plains. Climatic Change 6:5-26.
Warrick, RA. 1975. Assessment of Research on the
Drought Hazard in the United States. Monograph
No. 4. Boulder, CO: Natural Hazards Research and
Applications Information Center, University of
Colorado.
Warrick, RA., and MJ. Bowden. 1981. The
changing impacts of drought in the Great Plains. In:
Lawson, M.P., and M.E. Baker, eds. The Great
Plains: Perspectives and Prospects. Lincoln:
University of Nebraska Press, pp. 111-137.
Worster, D. 1979. Dust Bowl: The Southern Great
Plains in the 1930s. New York: Oxford University
Press.
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CHAPTER 18
RESEARCH NEEDS
This report has suggested that concerns over
the adaptability and fate of both natural and
managed ecosystems in a changed climate are well
founded. Natural forested ecosystems, aquatic and
marine biota, wildlife in refuges, water quality in
small lakes, and other resources may be vulnerable
to rapid climate change. Strategies for mitigating
changes hi these systems are likely to be complex
and difficult to implement. While it may be difficult
to quantify the consequences, climate change may
have large effects on biodiversity, primary
productivity, and cycling of nutrients, and it may be
difficult, if not impossible, to reverse these impacts.
This report has also shown that while
intensively managed ecosystems, especially
agroecosystems, may also be affected by a climate
change, there seem to be more opportunities for
human intervention to mitigate or adapt to their
responses. Thus, the critically important question is
whether the capacity for human intervention can
keep pace with the rate of change induced by
changing climate. Areas of major concern are the
interactive effects of climate change and carbon
dioxide increases on crop yields, and the adaptation
rate of management practices.
Although it is clearly not possible to study all
the potential effects of a change in the climate
system, or to consider all the possible social or
political ramifications of responding to climate
change, there will be a continuing need to
understand better the possible consequences of
climate change because adaptation to different
climates will be a necessary part of any complete
societal strategies to cope with the greenhouse
effect. Therefore, it is important to have in place a
research framework for both the natural and the
social sciences that will provide the information
required to allow societies to respond to the
challenge of large-scale, rapid changes in the
climate system. This research should be undertaken
simultaneously and in coordination with programs
directed at establishing a broad consensus for
governmental actions, both domestic and
international, that address energy, land use, and
other social policies that might lead to reduced
emissions of greenhouse gases.
Research in the natural and social sciences
must have an important role in developing well-
reasoned adaptation strategies because it will
provide the data and understanding of processes
necessary to design efficient responses to a new
climate, and better management techniques for the
resources that must be conserved.
The needs of U.S. and international
policymakers for information on the possible
environmental effects of climate change and the
processes that control them should not be
underestimated, especially since the task of
attempting to mitigate emissions of greenhouse
gases is so large and complex. This chapter
identifies some of the major topics for research in
the natural and social sciences that should be
pursued to help policy analysis and development in
this area.
The scope of this chapter is necessarily broad.
It addresses both the research proposed by EPA
and the research recommendations of the scientific
research community from a perspective that the
development of sound environmental policy, both
for mitigation and adaptation, depends on the
capability of the scientific research community to
respond to increasingly specific demands for
information from policymakers.
RELATIONSHIP BETWEEN
POLICY AND SCIENCE
Secretary of State James Baker and EPA
Administrator William Reilly recently set forward
four principles to guide policy development:
The first is that we can probably not
afford to wait until all of the uncertainties
have been resolved before we do act.
Time will not make the problem go away.
The second is that while scientists refine
the state of our knowledge, we should
focus immediately on prudent steps that
are already justified on grounds other
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Chapter 18
than climate change. These include
reducing CFC emissions, greater energy
efficiency, and reforestation.
The third is that whatever global solutions
to global climate change are considered,
they should be as specific and cost-effective
as they can possibly be.
The fourth is that those solutions will be
most effective if they transcend the great
fault line of our times, the need to
reconcile the transcendent requirements for
both economic development and a safe
environment.
These four principles establish a framework
within which both domestic and international
programs will develop. They balance the needs for
both scientific research and policy development,
while clearly recognizing the international scope of
the issue. In doing so, these four principles will act
as the basis for U.S. participation in international
assessment activities, as well as for domestic policy
development.
The Global Climate Protection Act of 1987
directs EPA and the State Department to
coordinate the development of national policy for
global climate change. This coordination involves
many other agencies with essential policy roles, such
as the Department of Energy.
In addition, the Global Climate Protection Act
directs EPA, in cooperation with other agencies, to
prepare a scientific assessment of climate change.
This assessment is now being coordinated through
the Intergovernmental Panel on Climate Change, an
organization created under the joint auspices of the
United Nations Environment Programme and the
World Meteorological Organization (WMO). It will
be developed by a work group with extensive U.S.
participation coordinated through the Federal
Coordinating Committee on Science and
Engineering Technology Committee on Earth
Sciences. A second work group will analyze climate
change impacts, and a third work group is
responsible for examining response strategies. Each
work group has approximately 18 months to develop
an interim report. Reports from these three work
groups will be critical to the development of
international scientific and policy consensus on
greenhouse issues.
EPA's domestic responsibilities, and the
research reported on in this document, have led us
to formulate several important questions that should
be thought of as overriding themes, rather than as
a list of all the potential issues:
• How rapidly might climate change as a
result of future manmade emissions?
• What are the likely regional atmospheric
manifestations of such global atmospheric
changes?
• What are the likely extent and magnitude of
ecological, environmental, and societal
changes associated with a given change in
regional atmospheres?
• What technologies and policy options exist
to reduce the rate of growth in greenhouse
gas emissions, and how much would they
cost?
• What are the cultural and institutional
barriers that might limit the implementation
of such options?
• What are the likely consequences of
proposed mitigative or adaptive policies?
These questions are viewed as the foundation
for analyzing possible environmental changes due to
climate change, and eventually for analyzing possible
approaches to managing risks. They begin to match
needs for policy development with scientific needs
for understanding the functioning of the Earth as an
integrated system. By doing so, they define the
specific areas in which scientific research is
necessary: biogeochemical dynamics, physical
climate and the hydrologic cycle, ecosystem
dynamics, Earth system history, and human
interactions with the geosphere-biosphere. Indeed,
they justify an overall program of research, with one
of the main goals being to "establish the scientific
basis for national and international policymaking
related to natural and human-induced changes in
the global earth system" (Federal Coordinating
Committee on Science and Engineering
Technology).
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Research Needs
RESEARCH AND ASSESSMENT
NEEDS IN THE SOCIAL
SCIENCES
This report has identified many important issues
that policy analysts and decisionmakers must begin
or have begun to address. It is apparent that even
for the heavily managed environmental resources
such as agriculture and water supply, an existing
range of concerns makes the response of resource
managers to climate change difficult to predict.
Even current climate variability is not always
accounted for in resource management. Yet it is
the response of resource managers and
environmental policymakers to climate change that
will ultimately determine how society responds to a
changed climate both for managed and natural
resources. The inadequacy of our current
knowledge regarding how their decisions are made
demands closer attention from the social science
research community.
Institutional Response to Climate
Variability and Climate Change
One of the major issues identified in this report
is how institutions respond to current variability in
climate. It is well known that current climate
variability, represented by such episodes as the
recurrence of the El Nino and periodic droughts,
can have catastrophic effects on major regional
industries, that in turn have larger, sometimes global
consequences on supply and processing of resources.
It is also well known that in both the relatively
distant and relatively recent past, variability in
climate has led to severe regional economic
dislocation and subsequent migration of large
numbers of people, even in industrialized societies
such as the United States. What is not as well
known is how the U.S. institutions responsible for
managing agriculture, forestry, and water resources
will be able to respond to future climate variability,
especially if that variability increases. The drought
of the summer of 1988 clearly illustrates that U.S.
farms are still susceptible to severe weather
conditions; it does not, however, answer the
question of whether a succession of such droughts,
as might be expected in future scenarios of a
warmer, drier Grain Belt, could be accommodated
by the existing government programs.
Water resource managers face similar
problems. In California, all the scenarios indicated
that large changes in the management of water
might need to be considered if the snowpack were
smaller and melted earlier. In the Great Lakes,
lower water levels may necessitate changes in
management. While changes in precipitation
remain the most uncertain of the outputs from
GCMs, the lessons for research in water
management are relatively clear. We need to
understand the degree to which there is flexibility in
water allocation decisions, and to develop the
information needed by water managers to evaluate
possible changes in allocation under climate change.
In each of these cases, both the institutional
and historical factors that affect the decisionmaking
process must be analyzed and understood, as must
local, regional, and national political influences. In
particular, the problems of designing resource
management systems for flexible response need to
be addressed as institutional and investment
questions. While the need for flexible resource
management is clear, the reality of maintaining
flexibility while still making decisions regarding
large capital expenditures, such as building
powerplants and dams, may be quite difficult.
There will be a continued need to conduct targeted
case studies of how resource managers currently
consider climate variability and to address potential
future changes in variability (see Chapter 19:
Preparing for Climate Change).
In addition, while climate change may
ultimately be one of the most important variables
that managers must consider in the decisionmaking
process, it may not be the most immediate.
Research is necessary to show how devoting
attention and resources to a developing issue such
as climate change makes sense from a management
and policy standpoint. • Research is also necessary to
examine the differences in how a wealthy, highly
industrialized society, such as the United States,
makes decisions about responding to climate
variability and change and how other societies,
especially lesser developed countries, make such
decisions. Since climate change is intrinsically a
global issue, such studies will be necessary to form
a consensus regarding the need for coordinated
responses and management strategies.
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Chapter 18
RESEARCH AND ASSESSMENT
NEEDS IN THE NATURAL
SCIENCES
As reviewed by the National Academy of
Sciences Committee on Global Change (NRC,
1988), in order to be responsive to policy concerns,
the primary scientific research needs are in those
phenomena and processes that occur on global
scales, or that occur on regional scales but will have
global consequences over the next few decades to a
few centuries. Therefore, research and assessment
activities must examine global scale questions of
emissions and atmospheric chemistry as well as the
regional consequences of global atmospheric
change. The transition from traditional disciplinary
investigations of processes to interdisciplinary
investigations of the links between processes on
such large spatial scales will demand new
approaches from the scientific research community.
Figure 18-1 represents in schematic fashion the
information flow that must occur among scientific
disciplines while explicitly taking into account the
transitions between spatial scales. It indicates that
the purpose of conducting research in emissions of
trace gases, inventorying and evaluating the emission
factors of anthropogenic and biogenic sources of
trace gases, evaluating possible technological
Global Emissions
Global Concentrations
Global
& Models
1
CO,
CH,
NOx
NMHC
Global
Atmospheric
& Scenarios
CO,
CH4 '
N,O
CFC's
c°6
NOx
NMHC
Impacts
Figure 18-1. Relationship between global and regional information flow.
382
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Research Needs
controls, investigating the possibility of positive
feedbacks, and attempting to realistically simulate
the emissions of trace gases is to provide
information for understanding the composition of
the atmosphere. Models can then be used to create
estimates of atmospheric composition on
approximately the same temporal and spatial scales.
Climate System
The scientific research community should fully
investigate the dynamic consequences of different
compositions of the atmosphere, including the
dynamics of the ocean as it influences both
atmospheric composition and heat transfer. The
derivation of regional climate scenarios from either
modeling output or analog methods and scientific
understanding are then necessary to link the
processes on global scales with environmental and
ecological research questions on regional and local
scales. The climate system modeling community, as
well as the statistical climatology community, must
devote significant effort to improving the ability of
the atmospheric sciences to make predictions on
relatively small regional scales, so that policymakers
can begin to have some quantitative confidence in
the results from environmental and ecological
modeling.
Research Scales
A further critical link identified in Figure 18-1
is that estimates of environmental changes will be
needed on spatial scales that are larger than
ecologists and environmental scientists have
traditionally used in their research (e.g., ecoregions
to biomes). While initially qualitative, as in much of
this report, these estimates will be used both as
input for assessments and as a way to formulate
series of testable hypotheses concerning the
processes that control projected ecological changes.
The ecological and environmental research
community must, therefore, define those
atmospheric variables that control the growth and
distribution of major vegetation types, including
crops, and must explore the physical and biological
processes that control the distribution of water and
nutrients in natural and managed landscapes. These
definitions and processes must be those that affect
the characteristics and dynamics of ecosystems on
spatial scales commensurate with the atmospheric
scales defined above.
Socioeconomic Impacts
The final major link is between the ecological
and environmental consequences of climate change
and emissions of greenhouse gases. This link must
include the interaction between societal impacts,
such as changes in energy demand and end-use, and
changes in emissions. It will be critical to establish
interdisciplinary communication because of
feedbacks between the biosphere and the
atmosphere. Clearly, changes in the growth and
distribution of major terrestrial vegetation types, as
well as changes in ocean chemistry and biology, will
alter biogenic emissions of trace gases. Of critical
importance is the possibility that these biogenic
emission changes may lead to even greater
temperature changes (positive feedbacks), as has
been hypothesized for methane. How climate
change will affect anthropogenic emissions, and
whether changes would be positive or negative
feedbacks, is largely unexplored.
Data
Underlying all these concerns for the
interaction among processes in the natural world is
a critical need for long time-series of data on Earth
system processes, and the information systems
necessary to manage the data. No amount of
modeling or experimentation of processes will
replace actual observations of how the Earth system
responds to changes in climate forcing and the
degree and characteristics of its natural variability.
Objectives of Federal Global Change
Program
Both the NAS (NRC, 1988) and the Federal
Global Change Program (CES, 1989) have identified
the scientific elements intrinsic to understanding the
Earth's behavior as an integrated system, and
especially its response to global atmospheric change.
The section below summarizes the scientific
elements and then: rationale, and presents the broad
scientific objectives of the research to be sponsored
in the Federal Global Change Program. These
scientific elements refer directly back to the needs
for information identified in Figure 18-1, as shown
in Figure 18-2.
• Biogeochemical dynamics include (1) the
sources, sinks, fluxes, and interactions
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Chapter 18
Scenario
Assessment
Emissions
Global
Atmospheric
Chemistry
Atmospheric
Dynamics
Scenario
Assessment
Figure 18-2. Two-stage scenario approach to integration.
betweenbiogeochemical constituents within
the Earth system; (2) the cycling of
biogeochemical elements in the atmosphere,
oceans, terrestrial regions, biota, and
sediments over Earth's history; and (3) the
influence of biogeochemical elements on
the regulation of ecological systems and
contribution to potential greenhouse
constituents (CO2, CH4, N-O, CFCs) that
have a direct influence on climate.
Ecological systems and dynamics would
involve the responses of ecological systems,
both aquatic and terrestrial, to changes in
global environmental conditions and of the
influence of biological systems on the
atmospheric, climatic, and oceanic systems.
This includes studies of plant succession,
terrestrial and aquatic biodiversity,
extinctions, and relationships with
geological substrate. Monitoring and
specific ecosystem experiments can provide
information on stresses influencing the
biota and on the biotic response to natural
and societal environmental stresses. Such
information is needed to achieve the basic
understandingrequiredfor the development
of models. Identification and study of
particularly sensitive ecosystems will be
especially informative.
Climatic and hydrologic systems would
involve the study of the physical processes
that govern the atmosphere, hydrosphere
(oceans, surface and groundwaters, etc.),
cryosphere (i.e., glaciers, snow), land
surface, and biosphere.
These are clearly central to the description,
understanding, and prediction of global climate
change, particularly in terms of impacts on global
climate conditions and the hydrologic system.
• Human interactions has been defined as the
study of the impacts of changing global
conditions on human activities. The global
environment is a crucial determinant of
humanity's capacity for continued and
sustained development. Research should
focus on the interface between human
activities and natural processes.
• Earth system history is the study of the
natural record of environmental change that
is contained in the rocks, terrestrial and
marine sediments, glaciers and ground ice,
tree rings, eumorphic features (including
the record of eustatic changes in sea level),
and other direct or proxy documentation of
past environmental conditions. These
archive the Earth's history and document
the evolution of life, past ecosystems, and
human societies. Past ecological epochs
with warmer or cooler climates relative to
the present climate are of particular
scientific interest.
• Solid-earth processes include the study of
certain processes that affect the life-
supporting characteristics of the global
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Research Needs
environment, and especially the processes
that take place at the interfaces between
the Earth's surface and the atmosphere,
hydrosphere, cryosphere, and biosphere.
Solid-earth processes that directly affect the
environment are of primary interest;
processes that have only indirect effects are
excluded.
• The solar influence is the study of the
variability in solar radiation and its impact
on atmospheric density, chemistry,
dynamics, ionization, and climate.
Research on the effects of solar variability
on biogeochemical cycles as well as the
impact of ultraviolet light on biology and
chemistry would be particularly important
here.
Of these scientific elements, studies of
biogeochemical dynamics, climate and hydrologic
systems, ecosystem dynamics, Earth system history,
human interactions, and to a lesser extent, solar
influences, are the most important from the
standpoint of developing a policy-oriented research
program. The degree to which the solid-earth
processes are important depends entirely on their
contribution to global change over the time-scale of
a few decades to a few centuries. A better
understanding of these processes remains an
important scientific aspect of a Federal Global
Change Program but can be anticipated to have less
value from a public policy perspective.
Three Major Scientific Objectives
The scientific elements relevant to the
development of well-informed public policy must be
structured in a way that permits the overall
objectives of the U.S. program to contribute to both
scientific and policy communities. To accomplish
this, the Federal Global Change Program has
outlined three major objectives in its Strategy
Document (CES, 1989).
1. Establish an integrated, comprehensive
program for Earth system measurements on
a global scale.
2. Conduct a program of focused studies to
improve our understanding of the physical,
chemical, and biological processes that
influence Earth system changes and trends
on global and regional scales.
3. Develop integrated conceptual
predictive Earth system models.
and
Each of these objectives simultaneously leads
toward improving the monitoring, understanding,
and predicting of global change. They aim to
provide, by the year 2000, detailed assessments of
the state of the knowledge of natural and human-
induced changes in the global Earth system and
appropriate predictions on time scales 20 to 40 years
into the future. Assessments of uncertainties hi
model outputs will be an integral part of these
predictions.
THE ROLE OF EPA IN POLICY
AND SCIENTIFIC RESEARCH
EPA's own activities have been structured to
provide leadership in both policy analysis and
development, as required by the Global Climate
Protection Act, and in scientific research, especially
on the consequences of changes in the climate
system. The development of a broad-based,
interdisciplinary scientific research program that
responds to the policy-oriented questions identified
earlier in this chapter has depended strongly on
concurrent scientific planning efforts by the National
Academy of Sciences and the Federal Global
Climate Change Program.
Specifically, the goals and objectives of the
EPA Global Climate Change Research Program
have been structured to respond both to the policy-
oriented questions, and to the scientific needs
identified by NAS hi the U.S. proposal for the
International Geosphere Biosphere Program and as
adopted by the Federal Global Change Program.
The program is designed to provide information on
the biosphere and its response to climate change
and technical information to develop policy options
to limit and adapt to climate change. EPA's
proposed research has two goals:
1. To assess the probability and magnitude of
changes in the composition of the global
atmosphere, the anthropogenic
contributions to those changes, and the
magnitude of subsequent impacts on the
environment and society.
2. To assess the likely extent, magnitude, and
rate of regional environmental effects as a
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Chapter 18
function of changes and variability in
climate, for the purpose of evaluating the
risks associated with changes in the climate
system.
Eight associated scientific and institutional
objectives have been identified:
1. To develop improved estimates for both
anthropogenic and natural sources of
radiatively important trace gases, and to
investigate the feedback processes by which
climate variability influences the sources of
these gases.
2. To develop techniques for estimating
current and future emissions of radiatively
important trace gases.
3. To improve understanding of global
atmospheric chemistry in order to project
future concentrations of trace gases,
including tropospheric ozone.
4. To relate global changes in climate to
regional changes by constructing a series of
regional atmospheric scenarios.
5. To predict ecosystems' responses to climate
change and to test the processes that
control those responses.
6. To document the spatial covariation of
regional climate change with regional
ecological change in order to establish
comprehensive ecological monitoring hi
selected locations, cooperatively with EPA
and other federal programs.
7. To develop information on technologies and
practices that could limit greenhouse gases
and to adapt to climate change.
8. To produce periodic scientific assessments
in conjunction with other federal agencies
and international research organizations,
and to perform research to evaluate the
consequences of adaptation and mitigation
policies.
While defining the framework for EPA's own
scientific research, these goals and objectives also
assume that all federal agencies with significant
policy responsibilities in issues of global climate
change are going to be able to take advantage of
developments in all areas previously discussed.
Many of the developmental needs in the
atmospheric and space sciences, and many of the
global monitoring needs, will be beyond the
capability of any one federal agency and will require
the cooperation of all.
The goals and objectives of proposed policy
research and activities in EPA closely follow the
previously listed recommendations. The main foci
will be on the development and coordination of a
national policy, as called for in the Global Climate
Protection Act, and the coordination and
implementation of the International Response
Strategies Assessment of the IPCC. Both mitigation
and adaptation policies will be investigated, as
outlined in the following chapter.
IMPACT ASSESSMENT
METHODOLOGY
Continued efforts at assessing the causes and
consequences of climate change are clearly needed.
This report has illustrated one potentially valuable
method for conducting such an assessment.
However, because the need will continue, there is a
corresponding need to consider how best to do
assessments in a way that preserves both the
understanding of what may happen and the certainty
with which we know it. This .section outlines the
approach that will be taken hi future impact
assessment efforts led by EPA.
Integrated modeling of large-scale
environmental issues has been attempted many
tunes before and may be useful for policy analysis
or for heuristic purposes. However, there is general
agreement within the scientific community that a
model adequate to simulate the dynamics of
geophysical, chemical, and biological processes on
global scales will be developed only after decades of
research (ESSC, 1988).
Although achieving such a goal lies so far in
the future, the question of how to deal with
integrating diverse aspects of science in global
climate change and its potential effects in the nearer
term remains. One promising approach for
integrating research results is to treat the entire
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Research Needs
Scenario
Scenario
Assessment
Atmospheric
Dynamics
Regional
Atmospheres
Scenario
\
Human &
Industrial Effects
Environmental &
Ecological
Effects
Assessment
Emissions
Assessment
Figure 18-3. Three-stage approach to integration.
cycle of information flow (Figure 18-1) as a series of
two-stage processes (Figures 18-2 and 18-3).
Within each two-stage process, research results
should be treated as follows: The first part of the
process is the creation of a set of scenarios, where
a scenario is defined as a plausible combination of
variables derived from a set of internally consistent
assumptions. The second part of the process will
evaluate the range of changes that are potentially
attributable to each scenario and will evaluate the
sensitivity of the underlying systems to different
aspects of the scenarios. Thus, scenarios of changes
in land use could be used to evaluate possible
changes in emissions; scenarios of emissions could
be used to evaluate the possible changes in
atmospheric composition; scenarios of atmospheric
composition could be used to evaluate changes in
climate; climate scenarios could be used to evaluate
the possible changes hi ecosystems; and scenarios of
ecosystem and land-use changes can in turn be used
to evaluate possible changes in emissions.
The use of a scenario-assessment approach for
impact assessments has several advantages. It could
provide clear priorities for research on the
sensitivities of important environmental processes in
each scientific area It maintains a realistically
holistic view of the problems of global change, and
it preserves information on the uncertainty of model
results and data, hi both qualitative and potentially
quantitative fashion.
Each pair of scenario-response steps is
explicitly decoupled from other pairs, while
remaining consistent with them. Thus, such an
approach can indicate both ranges and sensitivities
of responses hi potentially verifiable fashion within
each pair, but does not attempt the premature task
of modeling uncertainty all the way through the
global system.
The use of scenarios as assessment and
integrative tools is not part of the traditional
scientific approach toward prediction and validation.
Nevertheless, it is important from three standpoints:
1. For scientific information to be of use to
policymakers, a continued iterative process
of evaluating the state of knowledge in the
suite of sciences relevant to global change
must be maintained. An iterative process
of using and analyzing scenario-based
assessments can provide such information
in a usable and informative way.
2. To achieve the multidisciplinary syntheses
needed to make scientific advances in
problems of global climate change,
evaluation of the methods by which
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Chapter 18
predictions are made and by which
scenarios of change can be composed, and
evaluation of the sensitivities of affected
processes must continue. The scenario-
based assessment approach provides a
ready-made integrating framework for such
continual evaluations.
3. Because of the importance of this proposed
research in public policy arenas, it is critical
not to lose sight of what is and is not
predictable. By distinguishing between a
set of scenarios and actual verifiable
predictions, the scenario-based approach
can best illustrate the difference without
becoming a morass of hedged bets.
REFERENCES
CES. 1989. Committee on Earth Sciences. Our
Changing Planet: The FY 1990 Research Plan.
The U.S. Global Change Research Program. A
Report by the Committee on Earth Sciences. July
1989. Washington, DC: Executive Office of the
President, Office of Science and Technology Policy.
July.
ESSC. 1988. Earth Systems Science Committee.
A Program for Global Change: Earth Systems
Science a Closer View. Report of the Earth
Systems Science Committee. Washington, DC:
NASA Advisory Council. January.
IGBP. 1988. International Geosphere-Biosphere
Program. Toward an Understanding of Global
Change: Initial Priorities for the U.S. Contribution
to the International Geosphere-Biosphere Program.
Washington, DC: National Research Council,
Committee on Global Change, National Academy
Press.
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CHAPTER 19
PREPARING FOR CLIMATE CHANGE
The preceding chapters suggest that a global
warming could have significant impacts on farms
and forests, rivers and lakes, fish and wildlife, and
many practical aspects of everyday life. This issue
is very different from other environmental problems.
It is global in scope: all nations emit greenhouse
gases and all will experience the impacts.
Moreover, the changes are likely to last for
centuries and could shape the very nature of society.
Although many of the possible consequences may
not occur for decades, it is important that we begin
now to examine how we might respond.
The potential responses fall broadly into two
categories: (1) limiting the change in climate; and
(2) adapting to it. These two responses are
complementary, not mutually exclusive. Because
past emissions of greenhouse gases may eventually
warm the Earth one degree Celsius, some
adaptation will be necessary, and efforts to prepare
for global warming can contribute information to
the process of deciding whether, when, and how to
limit it. On the other hand, slowing the rate of
global warming would make it easier for humans
and other species to adapt.
Although limiting climate change would
require worldwide cooperation, responding to its
consequences would not. Private citizens and
companies can relocate or modify their operations.
Communities and states can undertake public works
or enact planning measures. Charitable foundations
and profit-making corporations can support
research to develop better response strategies.
National governments can support all of these
activities.
Preparing for global warming raises three
challenges. First, the uncertainties make it difficult
to be sure that we are employing the correct
response: the climate may change more (or less)
than anticipated; in the case of precipitation, we do
not even know the direction of change. Second, the
long-term nature increases the difficulty of
forecasting the impacts and gaining the attention of
decisionmakers more accustomed to focusing on
near-term problems. Finally, adaptation would
require thousands, perhaps millions, of
decisionmakers to consciously consider global
warming as they plan their activities.
These differences need not thwart the process
of preparing for global warming. First, many types
of institutions already cope with equally long-term
and uncertain trends; transportation planners, for
example, routinely consider economic growth over
30- to 50-year periods when picking routes for
highways and urban rail systems. Second, reaching
a consensus on what is fair would be easiest when
no one feels immediately threatened. Finally, the
decentralized nature of adaptation would enable the
communities and corporations most sensitive to
climate change to respond quickly, rather than
having to await a national consensus on the most
appropriate response.
Because a companion report ("Policy Options
for Stabilizing Global Climate") examines options
for limiting future global warming, this chapter
focuses on adaptation strategies. We briefly discuss
the process of choosing such strategies, then present
several examples.
WHEN IS A RESPONSE
WARRANTED?
Strategic Assessments
One of the most fundamental issues facing
decisionmakers is whether to implement responses
today or to defer preparation until the timing and
magnitude of future climate change are more
certain and the potential impacts are more
imminent. Although global warming might
eventually require particular actions, such actions
need not necessarily be taken today. On the other
hand, the likelihood of at least some global warming
is sufficiently well established and the time required
to develop a response sufficiently long that deferring
all preparation could lead us to miss opportunities
to substantially reduce the eventual economic and
environmental costs of the greenhouse effect.
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Chapter 19
Individual organizations must decide for
themselves whether or not to prepare for the
greenhouse effect. The first question is whether
global warming is likely to alter the success of
current activities or projects now being planned. If
not, preparing for the impacts of climate change
usually would be unnecessary; if so, the next
question is whether doing something today would be
worthwhile.
We use the term "strategic assessment" to
refer to the process by which people and
organizations examine whether, when, and how to
respond to global warming, based on what people
know today. In some cases, these assessments
formally consider the costs and benefits of
alternative responses; in others, a qualitative analysis
is sufficient to reach a conclusion.
Strategic assessments would be good
investments for almost any organization whose
activities are sensitive to climate or sea level and
whose decisions have outcomes stretching over
periods of 30 years or longer. In many cases, these
studies can use existing analytical tools and
consequently be relatively inexpensive. If they
reveal that action today is worthwhile, the savings
from such action may be orders of magnitude
greater than the cost of the studies. Even if they
show that no action is necessary, many organizations
will find it useful to know that their projects are not
vulnerable, and the studies would contribute to
society's understanding of the impacts of global
warming.
These assessments can be conducted as
decision-oriented analyses (e.g., supplements to
ongoing evaluations of proposed projects) or as
special studies focusing on particular programs or
particular problems; Table 19-1 lists examples of
each type.
Decision-Oriented Assessments
The most cost-effective strategic assessments
are those conducted as a routine part of the
evaluation of ongoing projects. Because they are
oriented toward a specific near-term decision, they
are not likely to be ignored. Moreover, their cost is
often minimal because they supplement existing
studies and therefore have little overhead. For
example, once a consultant has developed a
hydrologic model for a levee or dam, examining the
potential implications of climate change may require
little more than a few additional computer
simulations.
The Council on Environmental Quality has held
public meetings on the possibility of requiring
federal agencies to consider climate change in
environmental impact statements. The rationale is
that (1) if climate changes, the environmental
impact of some federal projects may be different
than the impact if the climate does not change; and
(2) these assessments are an inexpensive way to
increase our understanding of the potential
implications of global warming. The Corps of
Engineers has recently announced that it intends to
estimate the impacts of sea level rise in future
feasibility studies and environmental impact
statements for coastal projects. (Baldwin, Volume
J, discusses including climate change as a
consideration in environmental impact statements.)
Program-Oriented Assessments
Agencies with many potentially vulnerable
activities may need programwide assessments. In
some cases, the combined impact of climate change
can be summarized by a single variable, such as
flood insurance claims. On the other hand, many
agencies, such as the TVA, the Corps of Engineers,
and EPA, have programs that face several impacts,
each of which must be examined separately.
Problem-Oriented Assessments
These studies are sometimes necessary because
project-oriented studies lack a mandate to examine
broader implications. Utility companies, for
example, may want to consider the implications of
increased demand due to warmer temperatures.
Moreover, problems that are explicitly the
responsibility of no one while implicitly the
responsibility of several different groups could be
beyond the scope of program-oriented assessments.
For example, the combined impact of farm closures
and forest dieback raises land-use questions that
would be outside the responsibility of any single
organization.
Criteria for Choosing a Strategy
Strategic assessments can objectively identify
the implications of climate change and possible
responses, but picking the "best" response will
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Preparing for Climate Change
Table 19-1. Examples of Strategic Assessments
Decisionmaker
Question
Decision-Oriented
Home buyers
Forestry companies
Farmers
Utility companies
City engineers
Water resource agencies
Federal agencies
developing environmental
impact statements
Is the buyer willing to accept long-term risk of erosion and flooding?
Are appropriate species being planted? If so, when would a shift be
necessary?
Would a new well be even more useful if climate changed?
Is the size of a proposed powerplant optimal given projected climate
change?
Should new drainage faculties be designed with extra margin for sea level
rise and possibly increased rainfall?
Is the dam designed properly? Would its benefits be different?
Would sea level rise or climate change significantly alter the environmental
impacts of a project?
Program-Oriented
Research directors
Utility companies
Flood insurance programs
Agricultural planners
Public health agencies
Air pollution regulatory
agencies
For which impacts can we develop a solution? What would be the costs
of the research and the potential benefits of anticipated solutions?
Does system capacity need to be expanded? If not, when would expansion
be necessary?
By how much would insurance claims increase? Does expanding the
program to include erosion increase the impact of climate change?
Do current farm programs help or hinder the adjustments climate change
might require?
Would climate change increase the incidence of malaria and other tropical
diseases in the United States?
Should current regulatory approaches be supplemented with incentive
systems, new chemicals, or relocation policies?
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Chapter 19
Table 19-1. Examples of Strategic Assessments (continued)
Decisionmaker
Question
Problem-Oriented
Natural resource
agencies
Federal and state
agencies
Wetland protection
agencies
Canada and the
United States
State coastal zone
agencies and barrier
island communities
Water resource
agencies
Air pollution
agencies
Publicutility
commissions
Do we need a program to aid the survival of forests and other terrestrial
ecosystems?
Which options would ensure long-term survival of Louisiana's coastal
wetlands?
How do we ensure that wetlands can migrate as sea level rises?
How do we manage changes in levels of the Mississippi River and Great
Lakes?
Would the state provide necessary funds to hold back the sea on barrier
islands? If not, would the town bear the cost of retreat? Are current
erosion and flood programs consistent with long-term response?
What should be done to address increased salinity in estuaries?
Will climate change alter the results of current air-pollution strategies?
Should power companies be building extra capacity for increasing demand?
sometimes be a subjective decision based on a
number of criteria:
• Flexibility; Is the strategy reasonable for the
entire range of possible changes (including no
change) in temperature, precipitation, and sea
level?
• Urgency: Would the strategy be successful if
implemented today but fail if implementation
were delayed 10 or 20 years?
• Low Cost: Can the strategy be implemented
with a negligible investment today?
• Irreversibilitv: Would failure to adopt a
strategy result in irreversible loss of a
resource?
• Consistency; Does the policy support other
national, state, community, or private goals?
Economic Efficiency: Are the benefits greater
than the costs?
Profitability: Does the investment provide a
return greater than alternative investments,
i.e., greater than the "discount rate"?
Political Feasibility; Is the strategy acceptable
to the public?
Health and Safety: Would the proposed
strategy increase or decrease the risk of
disease or injury?
Legal and Administrative Feasibility: Can
existing organizations implement the strategy
under existing law?
Equity: Would implementing (or failing to
implement) the strategy impose unfair costs on
some regions or on a future generation?
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Preparing for Climate Change
. Environmental Quality: Would the strategy
maintain clean air and water or help natural
systems survive?
. Private versus Public Sector: Does the
strategy minimize governmental interference
with decisions best made by the private
sector?
. Unique or Critical Resources: Would the
strategy protect against the risk of losing
unique environmental or cultural resources?
The highest priorities would generally be
actions that meet the criteria of flexibility, urgency,
irreversibility, and low cost, because they inherently
address the major obstacles encountered in
preparing for global warming: (1) flexible policies
meet the challenge of uncertainty because they are
appropriate regardless of how the climate eventually
changes; (2) although analytical techniques
substantially discount the benefits of taking action
sooner rather than later, delaying action is not a
viable option when the urgency criterion is met; (3)
irreversible losses can be avoided only by
anticipating a problem; and (4) low-cost options are
always easiest to implement.
Nevertheless, these responses would not
always be sufficient to address the implications of
climate change. More comprehensive solutions
would often involve measures with more significant
costs that might prove, in retrospect, to have been
unnecessary if climate does not change as projected.
The costs of not acting may still be great enough to
justify such actions, but decisionmakers would have
to carefully weigh the various tradeoffs.
To a large degree, the procedures for doing
so have already been developed and applied. Most
corporations and many government agencies
conduct profitability or cost-benefit analyses. If the
principal costs and benefits of a strategy can be
quantified in monetary terms, economic theory
provides a rigorous procedure for making tradeoffs
between present and future costs, and for
considering uncertainty, profitability, and most of
the other criteria.
Nevertheless, subjective assessments are
necessary when the impacts cannot be readily valued
in monetary terms. Many decisionmakers do not
feel comfortable with economic estimates of the
value of a lost human life, unique cultural resource,
or endangered species. Although economic theory
provides a procedure (discounting) for comparing
present and future costs, it provides less guidance
on how much wealth and how many unsolved
problems one generation should pass along to future
generations. Although it provides tools for assessing
risk and uncertainty, economic theory does not
specify the extent to which society should be risk-
averse. Because there is no objective formula for
addressing these types of issues, responses are more
likely to be based on intuitive judgment and on what
is broadly acceptable to the public.
EXAMPLE RESPONSES FOR
ADAPTING TO GLOBAL
WARMING
This chapter presents a variety of example
responses rather than a single integrated strategy
because the process of adapting to climate change
would be relatively decentralized. Although the
various impacts would not be completely
independent of each other, responses to one type of
impact in one region generally could be
implemented regardless of whether strategies are
implemented to address other types of impacts in
other regions. The need to protect California's
water supplies, for example, would be largely
independent of the impact of global warming on
southeastern forests, midwestern agriculture,
mid-Atlantic barrier islands, and the level of the
Great Lakes.
For purposes of this discussion, approaches for
adapting to global warming can be broadly divided
into four categories, three of which require a
response before the climate changes:
. No immediate action is necessary if least-cost
solutions could be implemented using existing
technology and institutions as the problem
emerges.
• Anticipatory action is appropriate where taking
concrete actions today would avert irreversible
and expensive costs.
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Chapter 19
• Planning is appropriate where we do not need
to physically change what we are doing
immediately, but where we need to change the
"rules of the game" now, so that people can
respond to new information in a way that
furthers social goals.
• Research and education are appropriate in
cases where decades would be required to
develop solutions and to train people to
implement them, or where uncertainties must
be reduced before the appropriate action can
be identified.
We discuss each of these categories in turn.
No Immediate Action
The urgency of responding to climate change
depends not only on the severity of a potential
impact but also on the extent to which taking action
today would diminish the ultimate cost of adaptation
or allow us to avoid problems that would be
unavoidable if we waited before taking action. Even
where the impacts of climate change would be
severe, if the solution to a problem is well defined
and can be implemented quickly, or if no known
solution would substantially mitigate the problem,
immediate action is not necessary (although in the
latter case, research may be appropriate). Two
examples follow.
Reservoir Operating Rules
The decision rules that govern the timing and
magnitudes of water releases are generally based
on historic climate variability. For example, if the
flood season is March to May and droughts are
from July to September, reservoir managers
typically lower the water levels by the end of
February to ensure adequate flood control capacity,
and they allow the levels to rise in June to ensure
adequate water in case of a drought. If global
warming advanced the flood season by one month,
managers could eventually shift the schedule of
water releases. But since such modifications could
be implemented quickly, there is no advantage in
modifying the schedule until the climate changes.
Choice of Crops
The differences among crops grown in various
regions of the country result largely from differences
in temperature and water availability. If the climate
of one state gradually comes to resemble the
climate currently experienced in another state,
farmers in the former state may gradually begin to
plant the crops currently grown in the latter. But
there is no advantage in switching crops today.
Anticipatory Action
Although many responses will not be necessary
for a few decades, studies have identified a number
of instances in which physical responses to global
warming are appropriate even today. These
circumstances fall broadly into two categories: (1)
incorporating awareness of global warming into
long-term projects that are already under way,
where climate change must be addressed either now
or not at all; and (2) taking actions today that,
without climate change, would not be necessary
until later, if at all.
Modifying Ongoing Projects to Consider Climate
Change
The rationale for incorporating global warming
into current decisions is that the outcome of
projects initiated today will be altered by changes
in temperature, rainfall, sea level, or other impacts
of global warming. For many long-term projects,
factoring climate change into the initial design is
economically efficient because the failure to do so
would risk premature failure of the project, while
the cost of doing so would be only a few percent of
the total project cost. Because consideration of
global warming would also ensure that projects are
adequate to address current climate variability and
trends in sea level, such modifications may prove to
be worthwhile investments even if the anticipated
climate change does not occur, as described in the
following examples. Thus, these actions can satisfy
the criteria of flexibility, urgency, irreversibiliry, and
low cost.
Street Drains
Consider the replacement of a century-old
street drain. If designed for the current 5-year
storm, such a system might be insufficient with a
10% increase in the severity of the design storm or
a 1-foot rise in sea level, necessitating a completely
new system long before the end of the project's
useful life. On the other hand, installing slightly
larger pipes to accommodate climate change might
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Preparing for Climate Change
cost only an additional 5%. In such a case,
designing for changes in climate might prove to be
worthwhile if these changes occurred; even if they
did not occur, benefits would be realized because
the system would provide additional protection
during the more severe 10-year storm. (For
additional examples, see Chapter 7: Sea Level Rise,
and Chapter 13: Urban Infrastructure.)
Commercial Forests
Because some commercial tree species live as
long as 70 years before being harvested,
consideration should be given to modifying the
locations of commercial forests and types of species
planted to account for global warming. For
example, some types of Douglas-firs need at least a
few weeks of cold winter temperatures to produce
seeds. Forestry companies currently concentrate
planting efforts at the mountain bases, from which
logs can be most readily transported. However, if
temperatures rise, the forests there may no longer
produce young firs to replace the old. Thus, it
might be reasonable to begin planting farther up the
mountain or in a colder region of the country.
A shift from long-lived species vulnerable to
climate change to species having less vulnerability or
shorter growing cycles may also be appropriate. If
two species are equally profitable today but one
would fare much better if climate changed, shifting
to the latter species would involve little risk and
might substantially help long-term profits. Shifting
to a species whose life cycle is only 20 years would
enable harvests to take place before the climate
changes enough to adversely affect growth, and
would make it easier to respond to climate change
as it occurs (see Chapter 5: Forests).
Undertaking New Projects Primarily Because of
Future Climate Change
In a few cases, where authorities are already
contemplating public works for which the economic
justification is marginal, the prospect of climate
change might encourage decisionmakers to proceed
today with such projects. For example, a storm
surge that almost flooded London during the 1950s
led the Greater London Council to develop plans to
build a movable barrier across the Thames River.
Although many questioned whether the barrier was
worth building, steadily rising flood levels (1 foot
every 50 years for the past 5 centuries) convinced
the technical advisory panel that the barrier would
become necessary; once that eventuality was
generally recognized, the consensus was that the
project should go forward.
Constructing a project today solely because of
the greenhouse effect requires more certainty than
incorporating climate change into the design of a
project that would be undertaken anyway, primarily
for two reasons: (1) undertaking a new project
requires the legislature or the board of directors to
initiate major appropriations rather than approve
small increases in the cost of a project already
approved; and (2) because it is not motivated by the
need to address current problems, the project can
be delayed until there is more certainty. Even if
decisionmakers are sufficiently certain of future
impacts, they do not have to initiate the project
today unless the time expected to pass before the
impacts occur is not much greater than the time
required to design, approve, and build the project
intended to prevent those impacts. Thus, only near-
term impacts of global warming and those whose
solution would take several decades to implement
require remedial action today. Two examples
follow.
River Deltas
The loss of wet and dry land in the Mississippi
River Delta in coastal Louisiana is one example of
how global warming could alter the tuning of a
project (see Chapter 16: Southeast). If current
trends continue, most of the delta will be lost by
2100. But if sea level rise accelerates, this can occur
as soon as 2050. The immediacy of the problem is
greater than these years suggest, because the loss of
land is steady. Assuming the additional loss of land
to be proportional to sea level rise, half the delta
could be lost by 2030, with some population centers
threatened before then.
Whether or not sea level rise accelerates, the
majority of the delta can survive in the long run
only if society restores the natural process by which
the Mississippi River once deposited almost all of its
sediment in the wetlands. Because billions of
dollars have been invested over the last 50 years in
flood-control and navigation-maintenance projects
that could be rendered Ineffective, restoring natural
sedimentation would cost billions of dollars and
could take 20 years or longer. Because of the wide
variety of interests that would be affected and the
395
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Chapter 19
large number of options from which to choose,
another 10 to 20 years could pass from the time the
project was authorized until construction began.
Thus, if sea level rise accelerates according to
current projections and a project were initiated
today, about half of the delta would remain when
the project was complete; however, if the project
were authorized in the year 2000, 60 to 70% might
be lost before it was complete. By contrast, if sea
level rise does not accelerate, the two
implementation dates might imply 25% and 35%
losses of coastal wetlands.
Undertaking a project today satisfies the
flexibility criterion, because even current trends
imply that something eventually must be done.
Because a failure to act soon could result in an
irreversible loss of much of the delta, it also satisfies
the urgency criterion.
Purchase of Land
Purchasing land could keep options open for
water resource management and wetlands
protection. In regions where climate becomes
drier, additional reservoirs may become necessary.
However, because accurate forecasts of regional
climate change are not yet possible, water managers
in most areas cannot yet be certain that they will
need more dams. Even in areas such as California
where dams will probably be required, these will not
have to be built for decades. Nevertheless, it may
make sense to purchase the necessary land today.
Otherwise, the most suitable sites may be
developed, making future reservoir construction
more expensive and perhaps infeasible. A number
of potential reservoir sites have been protected by
creation of parks and recreation areas, such as
Tocks Island National Park on the Delaware River.
Federal, state, and local governments often
purchase land to prevent development from
encroaching on important ecosystems. Particularly
in cases where ecosystem shifts are predictable, such
as the landward migration of coastal wetlands, it
may be worthwhile to purchase today the land onto
which threatened ecosystems are likely to migrate.
Even where the shifts are not predictable, expanding
the size of refuges could limit their vulnerability
(see Chapter 8: Biodiversity).
Land purchases for protecting ecosystems have
two important limitations. First, they would almost
certainly be inadequate to address all the species
migration that might be required by climate change:
protecting coastal wetlands would require
purchasing most of the nation's coastal lowlands,
and many types of terrestrial species would have to
shift by hundreds of miles. Second, land purchases
do not handle uncertainty well: if temperatures,
rainfall, or sea level change more than anticipated,
the land purchased will eventually prove to be
insufficient.
Planning: Changing the Rules of the
Game
Although concrete action in response to
climate change is necessary today for only a few
types of problems, defining the "rules of the game"
may now be appropriate for a much wider class of
problems. Doing so increases flexibility: if climate
changes, we are better prepared; if it does not
change, preparation has cost us nothing. Another
advantage of this type of long-range planning is
that reaching a consensus on what is fair is easier
when no one is immediately threatened. Moreover,
such planning reduces risk to investors: although
they still face uncertainty regarding the timing and
magnitude of climate change, planning can prevent
that uncertainty from being compounded by
uncertainty regarding how the government will
respond. Two examples in which changing the rules
of the game might be appropriate follow.
Land Use
The potential consequences of global warming
suggest that it may already be appropriate to guide
development away from areas where it could
conflict with future environmental quality or public
safety. This can be done through master plans, laws
and regulations, and revisions of ownership rights.
Land use is generally regulated by local
governments and planning commissions, with state
governments also playing a role hi some areas.
A primary rationale for most local land-use
planning is that by themselves, real-estate markets
do not always produce economically efficient or
socially desirable outcomes, because people do not
bear all the costs or reap all the benefits from their
actions. The uses to which people put their
396
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Preparing for Climate Change
property often can have significant impacts on other
property owners and the environment. Because
zoning and other land-use restrictions are usually
implemented long before anyone would want to
undertake the prohibited activities, people have time
to plan their activities around the constraints. If
people know the rules of the game well in advance,
those who want the option of subdividing their
property or clearing a forest buy land where these
activities are permissible, and those who want
property in an area where such activities will not
take place buy land where the activities are
prohibited. Thus, in the long run, planning helps
maintain environmental quality while imposing few
costs that individuals could not avoid by buying
property elsewhere.
The institutional capabilities of planning are
well suited for addressing environmental impacts of
climate change when the direction of the impact is
known. The example of coastal wetland loss
(outside Louisiana) has been extensively examined
in the literature; many of the same principles would
also apply to shifts in forests, interior wetlands,
changing water levels in the Great Lakes, and
keeping land vacant for reservoirs.
A possible goal of land-use planning would be
to ensure that development does not block
migration of ecosystems or preclude construction of
a dam. Without planning, the land could be vacated
only by requiring abandonment with relatively little
advance notice, which would require compensation
(except for the case of coastal wetlands in states
where property owners do not currently have the
right to erect shore-protection structures). Planning
measures can either prevent development through
zoning (or purchase of land, discussed above), or set
the basic social constraint that ecosystems will be
able to migrate, while allowing the market to decide
whether or not development should proceed given
this constraint.
Preventing Development: Zoning
The most common tools for directing land use
are master plans and the zoning that results from
them. Zoning to ensure that land is available for a
dam would be similar to zoning to keep land
available for a freeway. For protecting ecosystems,
however, zoning has the same problem as land
purchases: it has to be based on a particular
assumption regarding how far the ecosystem will
need to migrate; if temperature, rainfall, or sea level
change more than expected, zoning provides only
temporary protection.
Flexible Planning: Allowing the Market to Decide
The rationale for these mechanisms is that
preventing development is inefficient; in some cases
developing a property might be worthwhile even if
it would subsequently have to be abandoned.
Flexible planning has the desirable feature of
minimizing governmental interference with private
decisions. For example, the overall constraint of
keeping natural shorelines is set by the government,
but the market decides whether nearby property is
still worth developing given that constraint. If the
effects of climate change do not materialize, the
government has not unnecessarily prevented
development (satisfying the low-cost criterion).
Most importantly, these measures do not require a
precise determination of how much climate will
change, and thus satisfy the flexibility criterion.
With this situation in mind, the State of Maine
has recently issued regulations stating that structures
would have to be removed to allow wetlands to
migrate inland in response to sea level rise. South
Carolina has recently enacted legislation to
substantially curtail construction of bulkheads.
Because these rules do not interfere with the use of
property for the next several decades, they have a
minimal impact on property values, and thus do not
deprive people of their property. The major
limitation of this approach is that it may be too
flexible: if sea level rise begins to require a
large-scale abandonment, a state or local
government may find it difficult to resist pressure
to repeal the rule.
An alternative that avoids the risk of
backsliding is to modify conventions of property
ownership. One example would be long-term leases
that expire 50 to 100 years hence or when high tide
rises above a property's elevation. This approach,
which has been applied to Long Island, allows the
market to explicitly incorporate its assessment of sea
level rise into its valuation of the leases. Although
leaseholders have requested no-cost extensions on
their leases when they expire, local governments
generally have found enforcing the provisions of
leases easier than enforcing regulations requiring
people to abandon property. Moreover, this
approach can be implemented by the private sector;
397
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Chapter 19
for example, a conservancy willing to lease the land
back to developers for 99 years might be able to buy
lowlands inexpensively (see Chapter 7: Sea Level
Rise).
Water Allocation
Particularly hi the Southwest, the nation's
water supply infrastructure is guided by policies
embedded in contracts and laws that prescribe who
gets how much water. Many of these rules are not
economically efficient; water is wasted because of
rules that do not allow people with too much water
to sell it to people with too little. The equity of
these formulas is often sensitive to climate; during
wet periods, everyone may receive plenty, but hi dry
periods some get enough while others get none.
To a large degree, the means by which the
impact of climate change might be reduced are
already being advocated to address current climate
variability and potential supply shortages due to
population growth. These measures include
legalizing water markets; curtailing federal subsidies,
which lead to waste by keeping prices artificially
low; and modifying allocation formulas (see Chapter
9: Water Resources).
Nevertheless, the changes required by global
warming may be different in one crucial aspect: the
effective date of any rule changes. Because the
most severe changes in rainfall from the greenhouse
effect may still be decades hi the future, the
problem can be addressed even if the effective date
is not until 2020. This situation, however, may
enhance the political feasibility of instituting a
rational response today, since no one need be
immediately threatened. By contrast, if planning is
deferred another 20 years, the impacts of climate
change may become too imminent for potential
losers to agree to the necessary changes.
Research and Education: Increasing Our
Understanding
Although a particular problem may not
require solutions for a few decades, society should
begin preparing now. In some cases, we are
decades away from having viable solutions or the
public awareness necessary to reach a consensus.
We now examine two vehicles for expanding our
knowledge: research and education.
Research and Development
Research and development expenditures can
often be economically justified hi cases where other
responses cannot. Most of the impacts of climate
change at least theoretically could be mitigated, but
hi many cases, effective solutions have not yet been
developed. Like strategic assessments, research is
as valuable as the savings it makes possible.
Research is also one of the major vehicles by
which one generation improves life for succeeding
generations. Even if the economic efficiency of
taking action to mitigate impacts of climate change
cannot be demonstrated, some policymakers might
find it equitable for this generation to provide
solutions to accompany the problems we pass on to
the next generation.
Table 19-2 lists a number of research questions
and applications that would assist adaptation.
However, for the most part, strategic assessments
have not been undertaken to determine the cost and
probability of developing solutions or the magnitude
of potential savings that might result, so it is difficult
to be certain that the research would benefit society.
The most notable exception is improvement hi
estimates of future climate change; for virtually
every impact examined hi this report, the relevant
decisionmakers have told EPA that improved
climate projections are critical for developing
responses. (For more details on necessary research,
see Chapter 18: Research Needs.)
Education
Efforts to prepare for climate change can be
only as enlightened as the people who must carry
them out. Education will be a critical component
of any effort to address the greenhouse effect
because (1) decisionmakers hi various professions
will need to routinely consider the implications of
global warming; and (2) an informed citizenry will
be necessary for the public to support the public
policy and institutional changes that may be
required. Governments will almost certainly have a
major role.
To factor global warming into their decision
processes, people will need information about
changes hi climate variables, the resulting effects,
and techniques for mitigating the impacts. Federal
398
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Preparing for Climate Change
Table 19-2. Example Research Problems and Applications
Research problem
Application
Synergistic impacts of CO2, climate change,
and air pollution on plants
Shifts in habitats of birds, fish, and
land animals
Ability of wetlands and coral reefs to
keep up with sea level changes
Erosion of beaches due to climatology and
sea level changes
Ability of alternative plant strains to
tolerate harsh climate
Magnitude of changes in global sea level
and regional climate
Shifts in pests due to climate change
Shifts in microorganisms that currently
diminish water quality in tropical areas
Shifts in mix of trees and crops, drought-tolerant crops
Restoration ecology: rebuilding ecosystems that are lost
Mechanisms to accelerate vertical growth
More efficient placement of sand when beaches are restored
Development of heat- and drought-resistant crops
All responses to global warming
Development of integrated pest management programs and
better background data for groundwater protection policies
Long-term water supply planning
and state agencies have already sponsored large
conferences on sea level rise each year since 1983;
coastal engineers and policymakers are increasingly
considering accelerated sea level rise in land-use
decisions and the design of public works. This
process is now beginning to unfold in the fields of
utility planning and water-resource management,
and may emerge in other areas.
Because climate change could require major
public policy initiatives, governments must explain
the issue to the public at large so that the various
options can be fully considered. To a large degree,
the news media and school systems will be
responsible for explaining the issue to people.
Nevertheless, governments can support these
institutions by sponsoring public meetings, issuing
press releases, and perhaps most important,
translating the results of its technical studies into
brochures and reports that are accessible to
reporters, teachers, and the general public.
399
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AUTHORS
Joseph J. Bufalini
Lauretta M. Burke
Margaret M. Daniel
Robert L. DeVelice
Eugene C. Durman
Peter L. Finkelstein
Anthony Janetos
Roy Jenne
Ross A. Kiester
George A. King
Kenneth P. Linder
Janice A. Longstreth
Linda O. Mearns
Ted R. Miller
Mark W. Mugler
Ronald P. Neilson
Alan Robock
Cynthia Rosenzweig
William E. Riebsame
Michael C. Rubino
Joel B. Smith
USEPA - Atmospheric Research and Exposure
Assessment Laboratory - Research Triangle Park,
North Carolina
The Bruce Company
The Bruce Company
USEPA - Environmental Research Laboratory -
Corvallis, Oregon
USEPA Office of Policy, Planning and Evaluation
USEPA - Atmospheric Research and Exposure
Assessment Laboratory - Research Triangle Park,
North Carolina
USEPA - Office of Research and Development
National Center for Atmospheric Research
USEPA - Environmental Research Laboratory -
Corvallis, Oregon
USEPA - Environmental Research Laboratory -
Corvallis, Oregon
ICF, Inc.
ICF, Inc.
National Center for Atmospheric Research
The Urban Institute
Apogee Research, Inc.
USEPA - Environmental Research Laboratory -
Corvallis, Oregon
University of Maryland
Columbia University/Goddard Institute for Space
Studies
University of Colorado
Apogee Research, Inc.
USEPA Office of Policy, Planning and Evaluation
401
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Dennis A. Tirpak
James G. Titus
Jack K. Winjum
Robert C. Worrest
USEPA Office of Policy, Planning and Evaluation
USEPA Office of Policy, Planning and Evaluation
USEPA - Environmental Research Laboratory -
Corvallis, Oregon
USEPA - Environmental Research Laboratory -
Corvallis, Oregon
402
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CONTRIBUTING INVESTIGATORS AND PROJECTS
Authors: Adams, Richard M., J. David Glyer, and Bruce A. McCarl
Institution: Oregon State University and Texas A & M University
Title: The Economic Effects of Climate Change on UJS. Agriculture: A Preliminary Assessment.
Appendix: Volume C - Agriculture
Authors: Allen, Richard C., and Francis N. Gichuki
Institution: Utah State University
Title: Effects of Projected CO2-Induced Climate Changes on Irrigation Water Requirements in the
Great Plains States (Texas, Oklahoma, Kansas, and Nebraska).
Appendix: Volume C - Agriculture
Author: Assel, Raymond, A.
Institution: Great Lakes Environment Research Laboratory
Title: Impact of Global Wanning on Great Lakes Ice Cycles.
Appendix: Volume A - Water Resources
Author: Baldwin, Malcolm F.
Institution: Environmental Management Support, Inc.
Title: Applicability of Federal Long-Range Planning and Environmental Impact Statement Processes
to Global Climate Change Issues.
Appendix: Volume J - Policy
Authors: Blumberg, Alan F., and Dominic M. DiToro
Institution: HydroQual, Inc.
Title: The Effects of Climate Warming on Lake Erie Water Quality.
Appendix: Volume A - Water Resources
Authors: Botkin, Daniel B., Robert A. Nisbet, and Tad E. Reynales
Institution: University of California, Santa Barbara
Title: Effects of Climate Change on Forests of the Great Lake States.
Appendix: Volume D - Forests
Authors: Byron, Earl R., Alan Jassby, and Charles R. Goldman
Institution: University of California, Davis
Title: The Effects of Global Climate Change on the Water Quality of Mountain Lakes and Streams.
Appendix: Volume E - Aquatic Resources
Authors: Changnon, Stanley A., Jr., Steven Leffler, and Robin Shealy
Institution: Illinois State Water Survey and University of Illinois
Title: Impacts of Extremes in Lake Michigan Levels Along Illinois Shorelines: Low Levels.
Appendix: Volume H - Infrastructure
403
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Authors: Croley, Thomas E., II, and Holly C. Hartmann
Institution: Great Lakes Environment Research Laboratory
Title: Effects of Climate Changes on the Laurentian Great Lakes Levels.
Appendix: Volume A - Water Resources
Author: Davis, Owen K.
Institution: University of Arizona
Title: Ancient Analogs for Greenhouse Warming of Central California.
Appendix: Volume D - Forests
Author: Dudek, Daniel J.
Institution: Environmental Defense Fund
Title: Climate Change Impacts upon Agriculture and Resources: A Case Study of California.
Appendix: Volume C - Agriculture
Author: Easterling, William E.
Institution: Resources for the Future
Title: Farm-Level Adjustments by Illinois Corn Producers to Climate Change.
Appendix: Volume C - Agriculture
Authors: Glantz, Michael H., Barbara G. Brown, and Maria E. Krenz
Institution: National Center for Atmospheric Research
Title: Societal Responses to Regional Climate Change: Forecasting by Analogy.
Appendix: Volume J - Policy
Author: Haile, Daniel G.
Institution: U.S. Department of Agriculture, Agriculture Research Service - Gainesville
Title: Computer Simulation of the Effects of Changes in Weather Patterns on Vector-Borne Disease
Transmission.
Appendix: Volume G - Health
Author: Hains, David K.
Institution: C.F. Hains, Hydrologist, Inc.
Title: Impacts of Global Warming on Runoff in the Upper Chattahoochee River Basin.
Appendix: Volume A - Water Resources
Authors: Johnson, Howard L., Ellen J. Cooter, and Robert J. Sladewski
Institution: University of Oklahoma
Title: Impacts of Climate Change on the Transport of Agricultural Chemicals Across the USA Great
Plains and Central Prairie.
Appendix: Volume C - Agriculture
Authors: Josselyn, Michael, and John Callaway
Institution: San Francisco State University
Title: Ecological Effects of Global Climate Change: Wetland Resources of San Francisco Bay.
Appendix: Volume E - Aquatic Resources ,
404
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Author:
Institution:
Title:
Appendix:
Kalkstein, Laurence S.
University of Delaware
The Impact of CO, and Trace Gas-Induced Climate Changes upon Human Mortality.
Volume G - Health
Authors: Keith, Virgil R, J. Carlos DeAvila, and Richard M. Willis
Institution: Engineering Computer Optecnomics, Inc.
Title: Effect of Climatic Change on Shipping within Lake Superior and Lake Erie.
Appendix: Volume H - Infrastructure
Author: Leatherman, Stephen P.
Institution: University of Maryland
Title: National Assessment of Beach Nourishment Requirements Associated with Accelerated Sea
Level Rise.
Appendix: Volume B - Sea Level Rise
Authors: Lettenmaier, Dennis P., Thian Yew Gan, and David R. Dawdy
Institution: University of Washington
Title: Interpretation of Hydrologic Effects of Climate Change in the Sacramento-San Joaquin River
Basin, California.
Appendix: Volume A - Water Resources
Authors: Linder, Kenneth P., and Mark R. Inglis
Institution: ICF, Inc.
Title: The Potential Impacts of Climate Change on Regional and National Demands for Electricity.
Appendix: Volume H - Infrastructure
Author: Livingston, Robert J.
Institution: Florida State University
Title: Projected Changes in Estuarine Conditions Based on Models of Long-Term Atmospheric
Alteration.
Appendix: Volume E - Aquatic Resources
Authors: Longstreth, Janice, and Joseph Wiseman
Institution: ICF/Clement Associates, Inc.
Title: The Potential Impact of Climate Change on Patterns of Infectious Disease in the United States.
Appendix: Volume G - Health
Authors: Magnuson, John J., David K. Hill, Henry A. Regier, John A. Holmes, J. Donald Meisner, and
Brian J. Shuter
Institution: University of Wisconsin, University of Toronto, and Ontario Ministry of Natural Resources
Title: Potential Responses of Great Lakes Fishes and their Habitat to Global Climate Warming.
Appendix: Volume E - Aquatic Resources
Author: McCprmick, Michael J.
Institution: Great Lakes Environment Research Laboratory
Title: Potential Climate Changes to the Lake Michigan Thermal Structure.
Appendix: Volume A - Water Resources
405
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Authors: Mearns, Linda O., S.H. Schneider, S.L. Thompson, and L.R. McDaniel
Institution: National Center for Atmospheric Research
Title: Analysis of Climate Variability in General Circulation Models: Comparison with Observations
and Changes in Variability in 2xCO2 Experiments.
Appendix: Volume I - Variability
Authors: Meo, Mark, Thomas E. James, Jr., Steve Ballard, Lani L. Malysa, Robert E. Deyle, and Laura
A. Wilson
Institution: University of Oklahoma
Title: Policy Implications of Global Climate Change Impacts upon the Tennessee Valley Authority
Reservoir System, Apalachicola River, Estuary, and Bay, and South Florida.
Appendix: Volume J - Policy
Authors: Miller, Barbara A., and W. Gary Brock
Institution: Tennessee Valley Authority
Title: Potential Impacts of Climate Change on the Tennessee Valley Authority Reservoir System.
Appendix: Volume A - Water Resources
Authors: Morris, Ralph E., Mike W. Gery, Mei-Kao Liu, Gary E. Moore, Christopher Daly, and Stanley
M. Greenfield
Institution: Systems Applications, Inc.
Title: Sensitivity of a Regional Oxidant Model to Variations in Climate Parameters.
Appendix: Volume F - Air Quality
Authors: Overpeck, Jonathan T., and Patrick J. Bartlein
Institution: Lamont-Doherty Geological Observatory and University of Oregon
Title: Assessing the Response of Vegetation to Future Climate Change: Ecological Response Surfaces
and Paleoecological Model Validation.
Appendix: Volume D - Forests
Authors: Park, Richard A., Manjit S. Trehan, Paul W. Mausel, and Robert C. Howe
Institution: Butler University and Indiana State University
Title: The Effects of Sea Level Rise on U.S. Coastal Wetlands.
Appendix: Volume B - Sea Level Rise
Authors: Peart, Robert M., James W. Jones, R. Bruce Curry, Ken Boote, and L. Hartwell Allen Jr.
Institution: University of Florida
Title: Impact of Climate Change on Crop Yield hi the Southeastern USA: A Simulation Study.
Appendix: Volume C - Agriculture
Authors: Penner, Joyce E., Peter S. Connell, Donald J. Wuebbles, and Curtis C. Covey
Institution: Lawrence Livennore National Laboratory
Title: Climate Change and Its Interactions with Air Chemistry: Perspective and Research Needs.
Appendix: Volume F - Air Quality
406
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Authors: Ray, Daniel K., Kurt N. Lindland, and William J. Brah
Institution: The Center for the Great Lakes
Title: Effects of Global Warming on the Great Lakes: The Implications for Policies and Institutions.
Appendix: Volume J - Policy
Author: Riebsame, William E.
Institution: University of Colorado
Title: Climate Change Perceptions Among Natural Resource Decision-Makers: The Case of Water
Supply Managers.
Appendix: Volume J - Policy
Authors: Riebsame, William E., and Jeffrey W. Jacobs
Institution: University of Colorado
Title: Climate Change and Water Resources in the Sacramento-San Joaquin Region of California:
Policy Adjustment Options.
Appendix: Volume J - Policy
Authors: Rind, David, R. Goldberg, and R. Ruedy
Institution: Goddard Institute for Space Studies, Columbia University, and Sigma Data Service Corporation
Title: Change in Climate Variability in the 21st Century.
Appendix: Volume I - Variability
Authors: Ritchie, Joe T., B.D. Baer, and T.Y. Chou
Institution: Michigan State University
Title: Effect of Global Climate Change on Agriculture: Great Lakes Region.
Appendix: Volume C - Agriculture
Author:
Institution:
Title:
Appendix:
Rose, Elise
Consultant
Direct (Physiological) Effects of Increasing CO2 on Crop Plants and Their Interactions with
Indirect (Climatic) Effects.
Volume C - Agriculture
Author: Rosenzweig, Cynthia
Institution: Columbia University/Goddard Institute for Space Studies
Title: Potential Effects of Climate Change on Agricultural Production in the Great Plains: A
Simulation Study.
Appendix: Volume C - Agriculture
Authors: Schmidtmann, Edward T., and JA. Miller
Institution: U.S. Department of Agriculture, Agriculture Research Service - Beltsville, Maryland
Title: Effect of Climatic Warming on Populations of the Horn Fly, with Associated Impact on Weight
Gain and Milk Production in Cattle.
Appendix: Volume C - Agriculture
407
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Author: Schuh, G. Edward
Institution: University of Minnesota
Title: Agricultural Policies for Climate Changes Induced by Greenhouse Gases.
Appendix: Volume C - Agriculture
Authors: Sheer, Daniel P., and Dean Randall
Institution: Water Resources Management Inc.
Title: Methods for Evaluating the Potential Impacts of Global Climate Change: Case Studies of the
State of California and Atlanta, Georgia.
Appendix: Volume A - Water Resources
Authors: Stem, Edgar, Gregory A. Mertz, J. Dirck Strycker, and Monica Huppi
Institution: Tufts University
Title: Changing Animal Disease Patterns Induced by the Greenhouse Effect.
Appendix: Volume C - Agriculture
Authors: Stinner, Benjamin R., Robin AJ. Taylor, Ronald B. Hammond, Foster F. Purrington,
David A. McCartney, Nick Rodenhouse, and Gary Barrett
Institution: Ohio Agricultural Research and Development Center and Ohio State University
Title: Potential Effects of Climate Change on Plant-Pest Interactions.
Appendix: Volume C - Agriculture .
Authors: Titus, James G., and Michael S. Greene
Institution: U.S. Environmental Protection Agency
Title: An Overview of the Nationwide Impacts of Sea Level Rise.
Appendix: Volume B - Sea Level Rise
Authors: Urban, Dean L., and Herman H. Sheer
Institution: University of Virginia
Title: Forest Response to Climate Change: A Simulation Study for Southeastern Forests.
Appendix: Volume D - Forests
Authors: Walker, Christopher J., Ted R. Miller, G. Thomas Kingsley, and William A. Hyman
Institution: The Urban Institute
Title: Impact of Global Climate Change on Urban Infrastructure.
Appendix: Volume H - Infrastructure
Authors: Weggel, J. Richard, Scott Brown, Juan Carlos Escajadillo, Patrick Breen, and Edward L.
Doheny
Institution: Drexel University
Title: The Cost of Defending Developed Shorelines Along Sheltered Waters of the United States from
a Two Meter Rise in Mean Sea Level.
Appendix: Volume B - Sea Level Rise
Author: Williams, Philip B.
Institution: Philip Williams & Associates
Title: The Impacts of Climate Change on the Salinity of San Francisco Bay.
Appendix: Volume A - Water Resources
408
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Authors: Woodman, James N., and Cari L. Sasser
Institution: North Carolina State University
Title: Potential Effects of Climate Change on UJS. Forests: Case Studies of California and the
Southeast.
Appendix: Volume D - Forests
Author: Yohe, Gary W,
Institution: Wesleyan University
Title: The Cost of Not Holding Back the Sea: Phase 1, Economic Vulnerability.
Appendix: Volume B - Sea Level Rise
Authors: Zabinski, Catherine and Margaret B. Davis
Institution: University of Minnesota
Title: Hard Times Ahead for Great Lakes Forests: A Climate Threshold Model Predicts
Responses to CO2-Induced Climate Change.
Appendix: Volume D - Forests
409
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ROBERT T STAFFORD, VERMONT, CHAIRMAN
JOHN H. CHAFEE. RW50E BLAND U.OYO BENTSEN. TEXAS
ALAN K. SIMPSON. WYOMWO OUENTIN H. BUflOKX NORTH DAKOTA
JAMES ABONOR. SOUTH DAKOTA GARY HART. COLORADO
STEVE SYMMS. IDAHO OANIEL PATRICK MOYNMAN. NEW YORK
CORDON HUMPHREY. NEW HAMPSHIRE CEORGE J. MITCHEU. MAINE
PETE V DOMENKI. NEW MEXICO MAX BAUCUS. MONTANA
DAVE OURENBERGEft. MINNESOTA FRANK R. tAUTENBERG. NEW JERSEY
BAILEY GUARD. STAFF DIRECTOR
UE O. FUU.ER. MINORITY STAFF DIRECTOR
United States
COMMITTEE ON ENVIRONMENT AND PUBLIC WORKS
WASHINGTON. DC 20610
September 12, 1986
Mr. Lee Thomas
Administrator
Environmental Protection Agency
Washington, D.C. 20460
Dear Mr. Thomas:
The purpose of this letter is to formally request that
EPA undertake two studies on climate change due to the greenhouse
effect and submit them to Congress no later than March 31, 1988.
At the outset, we want to thank you for appearing
before the Subcommittee on Environmental Pollution at hearings
last June on the problems of global climate change and
stratospheric ozone depletion. Your testimony showed a
refreshing appreciation for the magnitude of the environmental
risks presented by these problems and the need to be exploring
incremental actions that can be taken to reduce these risks.
As summarized at those hearings and elsewhere, the
scientific community appears to have reached agreement that
substantial ozone depletion may result from continued use of
chlorofluorcarbons (CFC's) and that increases in CFC's and other
greenhouse gases are like to produce global climate changes
greater than any in man's history. There is a very real
possibility that man - through ignorance or indifference, or both
- is irreversibly altering the ability of our atmosphere to
perform basic life support functions.
What is urgently needed now is for us to begin to deal
with these issues. They can no longer be treated solely as
important scientific questions. First, some actions including
limits on CFC's appear warranted in the near term. Second, we
need to expand efforts to more fully understand the effects that
atmospheric pollution has on the environment and to develop
an extensive range of policy options for dealing with the serious
global problem of climate change due to the greenhouse effect.
This second need has led to our request for two EPA studies.
One of the studies we are requesting should examine the
health and environmental effects of climate change. This study
should include, but not be limited to, the potential impacts on
agriculture, forests, wetlands, human health, rivers, lakes and
estuaries as well as other ecosystems and societal impacts. This
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Mr. Lee Thomas
September 9, 1986
Page 2
study should be designed to include original analyses to identify
and fill in where important research gaps exist, and to solicit
the opinions of knowledgeable people throughout the country
through a process of public hearings and meetings.
The other study should include an examination of the
policy options that, if implemented, would stabilize current
levels of atmospheric greenhouse gas emissions. This study
should address: the need for and implications of significant
changes in energy policy, including energy efficiency and
development of alternatives to fossil fuel; reductions in the use
of CFC's; ways to reduce other greenhouse gases such as methane
and nitrous oxides; as well as the potential for and effects of
reducing deforestation and increasing reforestation efforts. It
should include a series of policy options and recommendations for
concrete steps to be taken along with a discussion of the
potential effectiveness of each for limiting climate change.
Since the United States must take a leadership role in addressing
these global problems, the policy options that you develop should
include a specific plan for what the United States can do to
stabilize its share of greenhouse gas emissions as well as a plan
for helping other nations to achieve comparable levels of
control.
We realize that undertaking this project will be a _
significant challenge and will require substantial resources. We
therefore urge you to immediately direct the necessary funds in
both FY.-87 and FY-88 to assure that you can comply with our
request to promptly conduct these studies.
Many of us believe that these are among the most
important environmental problems of the next decade. The sooner
you can provide recommendations to Congress, the sooner we will
be able to provide leadership throughout the world to prevent a
pending environmental disaster.
Your personal attention and prompt reply to this
request will be greatly appreciated. We look forward to-working
with you on these important environmental problems. Please do
not hesitate to contact us for additional guidance and
assistance.
Sincerely,
e*.
Geocge J. Mitchell
John H. Chafee
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Mr. Lee Thomas
September 9, 1986
Page 3
Max Baucus
Patrick J. Leahy
ert T. Staffer
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