230989501A
POLICY OPTIONS FOR STABILIZING GLOBAL CLIMATE
\
DRAFT
REPORT TO CONGRESS
Executive Summary
Uafted States Environmental Protection Agency
Office of Policy, Planning, and Evaluation
February 1989
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POLICY OPTIONS FOR STABILIZING GLOBAL CLIMATE
DRAFT
REPORT TO CONGRESS
Executive Summary
Editors: Daniel A. Lashof and Dennis A. Tirpak
United States Environmental Protection Agency
Office of Policy, Planning, and Evaluation
February 1989
„ S Environmental Protection
B^ion 5, IL 1670
230 S.
Chicago
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DISCLAIMER
This draft is being circulated for review and comment and does not
necessarily reflect the official position of the U.S. Environmental Protection
Agency. Mention of trade names does not constitute an endorsement.
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SUMMARY TABLE OF CONTENTS
EXECUTIVE SUMMARY
VOLUME I (Bound under separate cover)
CHAPTER I: INTRODUCTION 1-1
CHAPTER II: GREENHOUSE GAS TRENDS II-l
CHAPTER HI: CLIMATIC CHANGE IIM
CHAPTER IV: HUMAN ACTIVITIES AFFECTING TRACE GASES AND CLIMATE IV-1
CHAPTER V: THINKING ABOUT THE FUTURE V-l
CHAPTER VI: SENSITIVITY ANALYSES VI-1
VOLUME II (Bound under separate cover)
CHAPTER VII: TECHNICAL OPTIONS FOR REDUCING GREENHOUSE GAS EMISSIONS VII-1
CHAPTER VIII: POLICY OPTIONS VIII-1
CHAPTER IX: INTERNATIONAL COOPERATION TO REDUCE GREENHOUSE
GAS EMISSIONS IX-1
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DETAILED TABLE OF CONTENTS
EXECUTIVE SUMMARY
INTRODUCTION 1
Congressional Request for Reports 1
Previous Studies 2
Goals of this Study 4
Approach Used to Prepare this Report 6
Limitations 9
HUMAN IMPACT ON THE CLIMATE SYSTEM 11
The Greenhouse Gas Buildup 11
The Impact of Greenhouse Gases on Global Climate 17
SCENARIOS FOR POLICY ANALYSIS 19
Defining Scenarios 19
Scenarios with Unimpeded Emissions Growth 22
The Impact of Policy Choices 29
Sensitivity of Results to Alternative Assumptions 45
EMISSIONS REDUCTION STRATEGIES BY ACTIVITY 54
Energy Production and Use 56
Industrial Activity 66
Changes in Land Use 71
Agricultural Practices 75
THE NEED FOR POLICY RESPONSES 77
A Wide Range of Policy Choices 78
The Timing of Policy Responses 79
FINDINGS 83
I. Uncertainties regarding climatic change are large, but there is a growing consensus
in the scientific community that significant global warming due to anthropogenic
greenhouse gas emissions is probable over the next century, and that rapid climatic
change is possible 83
II. Measures undertaken to limit greenhouse gas emissions would decrease the magnitude
and speed of global warming, regardless of uncertainties about the response of the
climate system 85
HI. No single country or source will contribute more than a fraction of the greenhouse
gases that will warm the world; any overall solution will require cooperation of many
countries and reductions in many sources 87
IV. A wide range of policy choices is available to reduce greenhouse gas emissions while
promoting economic development, environmental, and social goals 89
111
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DETAILED TABLE OF CONTENTS (Continued)
VOLUME I (Bound under separate cover)
CHAPTER I
INTRODUCTION
INTRODUCTION 1-2
The Earth's Climate and Global Change 1-2
CONGRESSIONAL REQUEST FOR REPORTS 1-3
Goals of this Study 1-4
Report Format 1-5
THE GREENHOUSE GASES 1-8
Carbon dioxide 1-9
Methane 1-9
Nitrous oxide 1-12
Chlorofluorocarbons 1-12
Other gases influencing composition 1-13
PREVIOUS STUDIES 1-13
Estimates of the Climatic Effects of Greenhouse Gas Buildup 1-14
Studies of Future CO2 Emissions 1-15
Studies of the Combined Effects of Greenhouse Gas Buildup 1-20
Major Uncertainties 1-22
Conclusions From Previous Studies 1-23
CURRENT NATIONAL AND INTERNATIONAL ACTIVrnES 1-26
National Research and Policy Activities 1-26
International Activities 1-27
REFERENCES 1-29
CHAPTER II
GREENHOUSE GAS TRENDS
FINDINGS H-2
INTRODUCTION H-5
CARBON DIOXIDE H-7
Concentration History and Geographic Distribution II-7
Mauna Loa n-8
Ice-core Data II-9
GMCC Network 11-10
IV
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DETAILED TABLE OF CONTENTS (Continued)
Sources and Sinks 11-14
Fossil Carbon Dioxide 11-14
Biospheric Cycle 11-16
Ocean Uptake 11-17
Chemical and Radiative Properties/Interactions 11-18
METHANE 11-22
Concentration History and Geographic Distribution 11-22
Sources and Sinks 11-24
Chemical and Radiative Properties/Interactions 11-29
NITROUS OXIDE 11-30
Concentration History and Geographic Distribution 11-30
Sources and Sinks 11-32
Chemical and Radiative Properties/Interactions 11-35
CHLOROFLUOROCARBONS (CFCs) 11-36
Concentration History and Geographic Distribution 11-36
Sources and Sinks 11-37
Chemical and Radiative Properties/Interactions 11-39
OZONE n-40
Concentration History and Geographic Distribution 11-40
Sources and Sinks n-43
Chemical and Radiative Properties/Interactions 11-44
OTHER FACTORS AFFECTING COMPOSITION H-45
Global Tropospheric Chemistry n-46
Carbon Monoxide 11-47
Nitrogen Oxides n-48
Stratospheric Ozone and Circulation 11-49
CONCLUSION H-50
REFERENCES 11-59
CHAPTER III
CLIMATIC CHANGE
FINDINGS m-2
INTRODUCTION IH-4
CLIMATIC CHANGE IN CONTEXT IH-6
CLIMATE FORCINGS ffl-8
Solar Luminosity ffl-12
Orbital Parameters m-13
Volcanoes 111-13
Surface Properties HI-14
The Role of Greenhouse Gases m-14
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DETAILED TABLE OF CONTENTS (Continued)
Internal Variations ............................................... 111-15
PHYSICAL CLIMATE FEEDBACKS ......................................... HI-15
Water Vapor - Greenhouse .......................................... IE- 17
Snow and Ice [[[ ffl-17
Clouds [[[ ffl-19
BIOGEOCHEMICAL CLIMATE FEEDBACKS .................................. ffl-20
Release of Methane Hydrates ........................................ m-20
Oceanic Change ................................................. IH-22
Ocean Chemistry ........................................... HI-23
Mixing ............................................. 111-23
Biology and Circulation .................................. ffl-24
Changes in Terrestrial Biota ......................................... m-25
Vegetation Albedo .......................................... IQ-25
Carbon Storage ............................................ IH-26
Other Terrestrial Biotic Emissions ................................ 111-26
Summary ................................................. 111-27
EQUILIBRIUM CLIMATE SENSITIVITY ..................................... ffl-28
THE RATE OF CLIMATIC CHANGE ....................................... ffl-31
CONCLUSION [[[ ffl-35
REFERENCES [[[ ffl-37
CHAPTER IV
HUMAN ACTIVITIES AFFECTING TRACE GASES
AND CLIMATE
FINDINGS [[[ IV-2
INTRODUCTION [[[ IV-5
HISTORICAL OVERVIEW OF POPULATION TRENDS ............................ IV-5
Global Population Trends ............................................ IV-7
Population Trends by Region .......................................... IV-7
IndustriflligfrH Countries ....................................... IV- 10
Developing Countries ........................................ FV-10
ENERGY CONSUMPTION ............................................... IV-12
History of Fossil-Fuel Use ........................................... IV-13
Current Energy Use Patterns and Greenhouse Gas Emissions .................. IV- 18
Emissions by Sector ......................................... IV-20
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DETAILED TABLE OF CONTENTS (Continued)
INDUSTRIAL PROCESSES IV-31
Chlorofluorocarbons, Halons, and Chlorocarbons IV-33
Historical Development aod Uses FV-33
The Montreal Protocol IV-37
Landfill Waste Disposal IV-40
Cement Manufacture IV-43
LAND USE CHANGE IV-45
Deforestation IV-47
Biomass Burning IV-50
Wetland Loss IV-51
AGRICULTURAL ACTIVITIES IV-55
Enteric Fermentation In Domestic Animals IV-55
Rice Cultivation IV-56
Use of Nitrogenous Fertilizer IV-61
IMPACT OF CLIMATIC CHANGE ON ANTHROPOGENIC EMISSIONS IV-63
REFERENCES IV-67
CHAPTER V
THINKING ABOUT THE FUTURE
FINDINGS V-2
INTRODUCTION V-4
APPROACH TO ANALYZING FUTURE EMISSIONS V-5
Production V-7
Consumption V-ll
SCENARIOS FOR POLICY ANALYSIS V-13
Scenarios with Unimpeded Emissions Growth V-17
Scenarios with Stabilizing Policies V-21
ANALYTICAL FRAMEWORK V-22
Energy Module V-25
Industry Module V-26
Agriculture Module V-26
Land Use and Natural Source Module V-27
Ocean Module V-27
Atmospheric Composition and Temperature Module V-28
Assumptions V-29
Population Growth Rates V-29
Economic Growth Rates V-29
Oil Prices V-30
Limitations V-30
Vll
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DETAILED TABLE OF CONTENTS (Continued)
SCENARIO RESULTS V-33
Energy Sector V-33
End-use Consumption V-33
Primary Energy Supply V-39
Greenhouse Gas Emissions From Energy Production and Use V-44
Comparison to Previous Studies V-45
Industrial Processes V-56
Halocarbon Emissions V-56
Emissions From Landfill? and Cement V-59
Changes in Land Use V-60
Agricultural Activities V-63
Total Emissions V-64
Atmospheric Concentrations V-71
Global Temperature Increases V-76
Comparison with General Circulation Model Results V-81
Relative Effectiveness of Selected Strategies V-82
CONCLUSIONS V-82
REFERENCES V-87
CHAPTER VI
SENSITIVITY ANALYSES
FINDINGS VI-3
INTRODUCTION VI-12
ASSUMPTIONS ABOUT THE MAGNITUDE AND TIMING OF GLOBAL
CLIMATE STABILIZATION STRATEGIES VI-12
No Participation by the Developing Countries VI-13
Delay in Adoption of Policies VI-17
ASSUMPTIONS AFFECTING RATES OF TECHNOLOGICAL CHANGE VI-18
Availability of Non-Fossil Technologies VI-18
Cost and Availability of Fossil Fuels VI-22
High Coal Prices VI-22
Alternative Oil and Natural Gas Supply Assumptions VI-24
Availability of Methanol-Fueled Vehicles VI-29
ATMOSPHERIC COMPOSITION: COMPARISON OF MODEL RESULTS TO ESTIMATES
OF HISTORICAL CONCENTRATIONS VI-30
ASSUMPTIONS ABOUT TRACE-GAS SOURCES AND STRENGTHS VI-34
Methane Sources VI-35
Nitrous Oxide Emissions From Fertilizer VI-38
Aohvdrpus Ammonia VI-38
N-O Inching From Fertilizer VI-39
N2O Emissions From Combustion VI-39
vui
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DETAILED TABLE OF CONTENTS (Continued)
UNCERTAINTIES IN THE GLOBAL CARBON CYCLE VI-41
Unknown Sink In Carbon Cycle VI-43
Amount of CO2 From Deforestation VI-44
Alternative CO2 Models of Ocean Chemistry and Circulation VI-47
ASSUMPTIONS ABOUT CLIMATE SENSITIVITY AND TIMING VI-50
Sensitivity of the Climate System VI-50
Rate of Heat Diffusion VI-53
ASSUMPTIONS ABOUT ATMOSPHERIC CHEMISTRY: A COMPARISON OF MODELS . . . VI-54
Model Descriptions VI-56
Assessment Model for Atmospheric Composition VI-56
Isaksen Model VI-57
Thompson et al. Model VI-58
Results from the Common Scenarios VI-59
EVALUATION OF UNCERTAINTIES USING AMAC VI-67
Atmospheric Lifetime of CFC-11 VI-67
Interaction of Chlorine with Column Ozone VI-69
Sensitivity of Tropospheric Ozone to CH4 Abundance VI-69
Sensitivity of OH to NOX VI-71
BIOGEOCHEMICAL FEEDBACKS VI-72
Ocean Circulation VI-72
Methane Feedbacks VI-73
Combined Feedbacks VI-75
REFERENCES VI-78
VOLUME II (Bound under separate cover)
CHAPTER VII
TECHNICAL OPTIONS FOR REDUCING GREENHOUSE GAS EMISSIONS
PART ONE: ENERGY SERVICES VH-27
TRANSPORTATION SECTOR VII-32
Near-Term Technical Options: Industrialized Countries VII-36
Light-Duty Vehicles VII-38
Freight Transport Vehicles VII-49
Aircraft VII-52
Control of NOX and CO Emissions from Mobile Sources VII-53
Near-Term Technical Options: Developing Countries VII-55
Fuel-Efficiency Improvements VII-57
Improving Existing Vehicles VII-58
Alleviating Congestion ^nd Improving Roads VII-58
Alternative Modes of Transportation VII-59
Alternative Fuels VTI-60
Near-Term Technical Options: Soviet Bloc Countries VII-61
ix
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DETAILED TABLE OF CONTENTS (Continued)
Summary of Near-Term Technical Potential in the Transportation Sector VII-62
Long-Term Potential in the Transportation Sector VII-63
Urban Planning and Mass Transit VII-63
Alternative Fuels VII-65
Expanded Use of Emerging Technologies VII-66
RESIDENTIAL/COMMERCIAL SECTOR VH-67
Near-Term Technical Options: Industrialized Countries VH-71
Improvements in Space Conditioning VH-71
Indoor Air Quality VII-80
Lighting VH-81
Appliances VII-83
Near-Term Technical Options: Developing Countries VII-83
Increasing Efficiency of Fuelwood Use VH-85
Substituting More Efficient Fuels VH-87
Retrofit Efficiency Measures for the Modern Sector VII-88
New Home$ and Commercial Buildings VII-89
Near-Term Technical Options: Soviet Bloc Countries VII-90
Summary of Near-Term Technical Potential in the Residential/Commercial Sector .... VII-91
Long-Term Potential in the Residential/Commercial Sector VII-92
INDUSTRIAL SECTOR VII-93
Near-Term Technical Options: Industrialized Countries VII-98
Accelerated Efficiency Improvements in Energy-Intensive Industries VII-98
Aggreysive Efficiency Improvements of Other Industries VII-100
Cogeneration VH-101
Near-Term Technical Options: Developing Countries VII-102
Technological Leapfrogging VH-103
Alternative Fuels VII-104
Retrofit Energy Efficiency Programs VII-105
Agricultural Energy Use VII-106
Near-Term Technical Options: Soviet Bloc Countries VII-107
Summary of Near-Term Technical Potential in the Industrial Sector VII-111
Long-Term Potential in the Industrial Sector VH-112
Structural Shifts VII-112
Advanced Process Technologies VII-113
Non-fossil Energy VII-115
PART TWO: ENERGY SUPPLY VII-116
FOSSIL FUELS VH-117
Refurbishment of Existing Powerplants VD-121
Clean Coal Technologies and Repowering VII-122
Cogeneration VII-123
Natural Gas Substitution VH-124
Natural Gas Use At Existing Powerplants VII-124
Advanced Gas-Fired Combustion Technologies VII-125
Natural Gas Resource Limitations VII-127
Additional Gas Resources VII-130
Emission Controls VII-132
NO.. Controls VH-132
C02 Controls VII-133
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DETAILED TABLE OF CONTENTS (Continued)
Emerging Electricity Generation Technologies VII-134
Fuel cells VII-134
Mflgnetohydrodynamics (MHD) VII-136
BIOMASS VII-137
Direct Firing of Biomass VII-138
Charcoal Production VII-140
Anaerobic Digestion VII-141
Gasification VII-142
Liquid Fuels From Biomass \H-143
Methanol VH-143
Ethanol VII-145
Other VII-146
SOLAR ENERGY VII-146
Solar Thermal VII-147
Parabolic Troughs VII-147
Parabolic Dishes VII-149
Central Receivers VII-149
Solar Ponds VII-150
Solar photovoltaic VII-150
Crystalline Cells VII-152
Thin-Film Technologies VII-153
Multi-Junction Technologies VII-154
ADDITIONAL PRIMARY RENEWABLE ENERGY OPTIONS VII-155
Hydroelectric Power VII-155
Industrialized Countries VII-155
Developing Countries VII-157
Wind Energy VH-158
Geothermal energy VII-159
Ocean Energy VH-162
NUCLEAR POWER VII-165
Nuclear Fission VII-165
Nuclear Fusion VII-170
ELECTRICAL SYSTEM OPERATION IMPROVEMENTS VII-171
Transmission and Distribution VII-171
Superconductors VII-172
Storage Technologies VII-173
Types of Storage Technologies VH-174
HYDROGEN VH-176
PART THREE: INDUSTRY VII-178
CFCs AND RELATED COMPOUNDS VII-178
Technical Options For Reducing Emissions VII-182
Chemical Substitutes VII-182
Engineering Controls VII-184
Product Substitutes VII-185
xi
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DETAILED TABLE OF CONTENTS (Continued)
Summary of Technical Potential VII-187
METHANE EMISSIONS FROM LANDFILLS VII-187
Methane Recovery VH-190
Recycling and Resource Recovery W-192
CO2 Emissions From Cement Production VII-193
PART FOUR: FORESTRY VII-195
FORESTS AND CARBON EMISSIONS VH-195
DEFORESTATION VH-197
TECHNICAL CONTROL OPTIONS VH-202
Reduce Demand for Forest Land and Products VII-206
Option 1: Slow Deforestation bv Introducing Sustainable Forest Use Systems . . . VII-209
Option 2: Substitute Sustainable Agriculture for Swidden Forest Practices VII-210
Option 3: Reduce Demand For Other Land Uses That Have Deforestation
As A Byproduct VH-217
Option 4: Increase Conversion Efficiencies Of Technologies Using Fuelwood . . . VH-218
Option 5: Decrease Production of Disposable Forest Products Vn-218
Substitute durable wood or non-wood products for high-volume disposable
uses of wood VH-219
Expand recycling programs for forest products VII-220
Increase Supply of Forested Land and Forest Products VII-220
Option 1: Increase Forest Productivity: Manage Temperate Forests For
Higher Yields VII-220
Option 2: Increase Forest Productivity: Improve Natural Forest Management
of Tropical Little-Disturbed And Secondary Forests Vn-222
Option 3: Increase Forest Productivity: Plantation Forests VII-224
Option 4: Improve Forest Harvesting Efficiency VII-228
Option 5: Expand Current Tree Planting Programs in the Temperate Zone .... VII-229
Option 6: Reforest Surplus Agricultural Lands VII-231
Option 7: Reforest Urban Areas VH-234
Option 8: Afforestation for Highway Corridors VQ-235
Option 9: Reforest Tropical Countries VII-236
Obstacles to Large-Scale Reforestation in Industrialized Countries VII-241
Obstacles to Reforestation in Developing Countries VII-243
Summary of Forestry Technical Control Options VII-244
PART FIVE: AGRICULTURE VH-249
RICE CULTIVATION VH-252
Existing Technologies and Management Practices W-253
Emerging Technologies W-257
Research Needs and Economic Considerations W-258
USE OF NITROGENOUS FERTILIZER VH-259
Existing Technologies and Management Practices VQ-260
Management Practices That Affect NgO Production VH-260
Technologies that Improve Fertilization Efficiency VII-262
xii
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DETAILED TABLE OF CONTENTS (Continued)
Emerging Technologies VII-263
Research Needs and Economic Considerations VII-264
ENTERIC FERMENTATION IN DOMESTIC ANIMALS VII-265
Methane Emissions from Livestock VII-268
Existing Technologies and Management Practices VII-269
Emerging Technologies VII-272
Research Needs and Economic Considerations VII-273
CHAPTER VIH
POLICY OPTIONS
FINDINGS Vffl-2
INTRODUCTION YIH-6
INTERNALIZING THE COST OF CLIMATE CHANGE RISKS VHI-8
Evidence of Market Response to Economic Incentives: Energy Pricing VIII-9
Financial Mechanisms to Promote Energy Efficiency VIII-14
Creating Markets for Conservation VDI-16
Limits to Price-Oriented Policies VITJ-IS
REGULATIONS AND STANDARDS VTJI-22
Existing Regulations that Restrict Greenhouse Gas Emissions VHI-23
Regulation of Chlorofluorocarbons Vin-24
Energy Efficiency Standards VTII-25
Air Pollution Regulations VHI-28
Waste Management VTH-29
Utility Regulation Vffl-31
Existing Regulations that Encourage Emissions Reductions VQI-35
RESEARCH AND DEVELOPMENT VHI-39
Energy Research and Development VHI-40
Global Forestry Research & Development Vm-45
Research to Eliminate Emissions of CFCs Vni-46
INFORMATION AND TECHNICAL ASSISTANCE PROGRAMS VHI-47
CONSERVATION EFFORTS BY FEDERAL AGENCIES VIE-SO
STATE AND LOCAL EFFORTS VHI-52
PRIVATE SECTOR EFFORTS VIH-S?
COMPLEMENTARY STRATEGIES TO REDUCE GREENHOUSE GAS EMISSIONS Vffl-59
IMPLICATIONS OF POLICY CHOICES AND TIMING VIH-63
xui
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DETAILED TABLE OF CONTENTS (Continued)
SENSITIVITY TESTS OF THE EFFECT OF ALTERNATIVE POLICIES ON
GREENHOUSE GAS EMISSIONS: RISK TRADE-OFFS VHI-67
Policies That Increase Greenhouse Gas Emissions VHI-69
Policies Designed to Reduce Greenhouse Gas Emissions Vm-76
Conclusions From the Sensitivity Tests Vffl-78
REFERENCES YIH-83
CHAPTER IX
INTERNATIONAL COOPERATION TO REDUCE GREENHOUSE GAS EMISSIONS
FINDINGS IX-2
INTRODUCTION IX-4
THE CONTEXT FOR POLICIES INFLUENCING GREENHOUSE GAS EMISSIONS IN
DEVELOPING COUNTRIES IX-5
Economic Development and Energy Use IX-7
Oil Imports, Capital Shortages, and Energy Efficiency IX-13
Greenhouse Gas Emissions and Technology Transfer IX-17
STRATEGIES FOR REDUCING GREENHOUSE GAS EMISSIONS IX-18
International Lending and Bilateral Aid IX-20
U.S. Bilateral Assistance Programs IX-21
Policies and Programs of Multilateral Development Banks IX-24
New Directions IX-31
REDUCING GREENHOUSE GAS EMISSIONS IN EASTERN BLOC NATIONS DC-33
US. LEADERSHIP TO PROMOTE INTERNATIONAL COOPERATION IX-36
Restricting CFCs to Protect the Ozone Layer IX-36
International Efforts to Halt Tropical Deforestation IX-38
Ongoing Efforts Toward International Cooperation IX-42
REFERENCES IX-45
XIV
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LIST OF FIGURES
Executive Summary
Page
1 Carbon Dioxide Concentrations at Mauna Loa and Fossil Fuel CO2 Emissions . . 3
2 Structure of the Atmospheric Stabilization Framework 8
3 Greenhouse Gas Contributions to Global Warming 12
4 Impact of CO? Emissions Reductions on Atmospheric Concentrations 14
5 Atmospheric Concentrations 25
6 Realized Wanning: No Response Scenarios 27
7 Realized Warming: No Response and Stabilizing Policy Scenarios 31
8 Stabilizing Policy Strategies: Decrease in Equilibrium Warming
Commitment 34
9 Rapid Reduction Strategies: Additional Decrease in Equilibrium Warming
Commitment 37
10 Share of Greenhouse Gas Emissions by Region 41
11 Increase in Realized Warming When Developing Countries Do Not
Participate 43
12 Increase in Realized Warming Due to Global Delay in Policy Adoption 44
13 Accelerated Emissions Cases: Percent Increase in Equilibrium Warming
Commitment 46
14 Impact of Climate Sensitivity on Realized Warming 48
15 Activities Contributing to Global Wanning 55
16 Primary Energy Supply by Type 58
17 CO2 Emissions From Deforestation 73
VOLUME I (bound under separate cover)
Chapter I
1-1
1-2
Carbon Dioxide Concentrations at Mauna Loa and Fossil Fuel CO2
Emissions 1-10
Impact of CO 2 Emissions Reductions on Atmospheric Concentrations 1-11
Chapter II
2-1 Greenhouse Gas Contributions to Global Warming
2-2 Carbon Dioxide Concentration
2-3 CO2 Atmospheric Concentrations by Latitude
2-4 The Carbon Cycle
2-5 Gas Absorption Bands
2-6 Methane Concentration
2-7 Current Emissions of Methane by Source
2-8 Nitrous Oxide Concentrations
2-9 Temperature Profile and Ozone Distribution in the Atmosphere
II-6
11-11
11-12
11-15
H-20
n-23
11-25
H-31
11-41
xv
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LIST OF FIGURES (Continued)
Page
Chapter III
3-1 Surface Air Temperature III-7
3-2 Oxygen Isotope Record From Greenland Ice Cores III-9
3-3 Carbon Dioxide and Temperatures Records From Antarctic Ice Core 111-10
3-4 Oxygen Isotope Record From Deep Sea Sediment-Cores III-ll
3-5 Global Energy Balance Ill-16
3-6 Equilibrium Temperature Changes from Doubled CO? ID-IS
3-7 Greenhouse Gas Feedback Processes in-21
Chapter IV
4-1 Regional Contribution to Greenhouse Warming ~ 1980s IV-6
4-2 Regional Population Growth - 1750-1985 IV-8
4-3 Global Energy Demand by Type ~ 1950-1985 IV-14
4-4 COo Emissions Due to Fossil Fuel Consumption - 1860-1985 IV-16
4-5 Global Commercial Energy Demand by Region IV-17
4-6 1985 Sectoral Energy Demand by Region IV-19
4-7 Potential Future Energy Demand IV-32
4-8 Historical Production of CFC-11 and CFC-12 IV-36
4-9 CFC-11 and CFC-12 Production/Use for Various Countries IV-39
4-10 CO2 Emissions from Cement Production - 1950-1985 IV-44
4-11 Cement Production in Selected Countries - 1951-1985 IV-46
4-12 Net Release of Carbon from Tropical Deforestation - 1980 IV-48
4-13 Wetland Area and Associated Methane Emissions IV-53
4-14 Trends in Domestic Animal Populations ~ 1890-1985 IV-57
4-15 Rough Rice Production - 1984 IV-59
4-16 Rice Area Harvested ~ 1984 IV-60
4-17 Nitrogen Fertilizer Consumption - 1984/1985 IV-64
Chapter V
5-1 Total U.S. Energy Consumption per GNP Dollar - 1900-1985 V-8
5-2 Consumption of Basic Materials V-10
5-3 Population by Region V-19
5-4 Structure of the Atmospheric Stabilization Framework V-23
5-5 Geopolitical Regions For Climate Analyses V-24
5-6 End-Use Fuel Demand by Region V-34
5-7 End-Use Electricity Demand by Region V-35
5-8 Share of End-Use Energy Demand by Sector V-38
5-9 Primary Energy Supply by Type V-40
5-10 Share of Primary Energy Supply by Type V-41
5-11 Energy Demand for Synthetic Fuel Production V-42
5-12 Emissions of Major CFCs V-58
5-13 CO2 Emissions from Deforestation V-62
5-14 CO2 Emissions by Type V-66
5-15 Share of CO2 Emissions by Region V-68
5-16 CH4 Emissions by Type V-69
xvi
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LIST OF FIGURES (Continued)
Page
5-17 Share of CH4 Emissions by Region V-70
5-18 Atmospheric Concentrations V-72
5-19 Realized and Equilibrium Warming V-77
5-20 Relative Contribution to Warming by 2100 V-80
5-21 Stabilizing Policy Strategies: Decrease in Equilibrium Warming Commitment . . . V-83
Chapter VI
6-1 Increase in Realized Warming When Developing Countries Do Not
Participate VI-16
6-2 Increase in Realized Warming Due to Global Delay in Policy Adoption VI-19
6-3 Availability of Non-Fossil Energy Options VI-21
6-4 Impact of 1% Per Year Real Escalation in Coal Prices VI-23
6-5 Impact of Higher Oil Resources On Total Primary Energy Supply VI-26
6-6 Impact of Higher Natural Gas Resources on Total Primary Energy Supply VI-28
6-7 Realized Warming Through 1985 VI-32
6-8 Increase in Realized Warming Due to Changes in the Methane Budget VI-37
6-9 Change in Atmospheric Concentration of N2O Due to Leaching VI-40
6-10 Change in Atmospheric Concentration of N2O Due to Combustion VI-42
6-11 Impact on Realized Warming Due to Size of Unknown Sink VI-45
6-12 CO2 From Deforestation Assuming High Biomass VI-46
6-13 Impact of High Biomass Assumptions on Atmospheric Concentration of CO2 . . . VI-48
6-14 Comparison of Different Ocean Models VI-51
6-15 Impact of Climate Sensitivity on Realized Warming VI-52
6-16 Change in Realized Warming Due to Rate of Ocean Heat Uptake VI-55
6-17 Regional Differences for Urban Areas With Different Emissions of CO and
NO VI-64
6-18 OH and Ozone Perturbations in the Isaksen and Hov Model VI-66
6-19 Sensitivity of Atmospheric Concentration of CFC-11 to Its Lifetime VI-68
6-20 Change in Realized Warming Due to Rate of Interaction of CLx With
Ozone VI-70
6-21 Increase in Realized Wanning Due to Change in Ocean Circulation VI-74
6-22 Increase in Realized Warming Due to Methane Feedbacks VI-76
6-23 Increase in Realized Warming Due to Change in Combined Feedbacks VI-77
xvu
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LIST OF FIGURES (Continued)
Page
VOLUME II (bound under separate cover)
Chapter VII
7-1 Current Contribution to Global Warming VH-20
7-2 Global Energy Use by End-Use VH-28
7-3 Secondary Energy Consumption by Region Vn-30
7-4 End-Use Energy Demand by Sector VH-33
7-5 Transportation Energy Use by Region VII-35
7-6 Components of Transportation Energy Use in the OECD: 1985 VII-37
7-7 U.S. Residential/Commercial Energy Use VH-68
7-8 Residential/Commercial Energy Use by Region VII-70
7-9 Industrial Energy Use by Region VII-97
7-10 Electricity Utility Demand by Fuel Type VH-118
7-11 Average Fossil Powerplant Efficiency VII-120
7-12 Strategies for Improving Efficiency of Biomass Use VII-139
7-13 Basic Solar Thermal Technologies VH-148
7-14 Photovoltaic Electricity Costs VH-151
7-15 Nuclear Capital Costs VH-167
7-16 Industrial Process Contribution to Global Warming VII-179
7-17 Emissions of Major CFC's VH-180
7-18 CH4 Emissions by Type VII-188
7-19 Movement of Tropical Forest Lands Among Stages of Deforestation and Potential
Technical Response Options W-198
7-20 Population Growth, Road Building, and Deforestation in Amazonia VII-201
7-21 Model Agroforestry Farm Layout, Rwanda VII-214
7-22 Agricultural Practices Contribution to Global Warming VII-250
7-23 Trace Gas Emissions From Agricultural Activities VII-251
Chapter VIII
8-1 Energy Intensity Reductions, 1973-1983 VIII-11
8-2 U.S. Electricity Demand and Price VIII-15
8-3 Cost of Driving Versus Automotive Fuel Economy Vm-21
8-4 U.S. Carbon Monoxide Emissions VHI-30
8-5 Changes in U.S. Renewable Energy R&D Priorities Over Time VIH-42
8-6 Cost of Potential Residential Electricity Conservation
in Michigan by 2000 VHI-55
8-7 U.S. Energy Consumption By Fuel Share Vffl-66
8-8 Atmospheric Response to Emissions Cutoff WI-68
8-9 Actual and Projected U.S. Coal Production Vffl-70
8-10 Accelerated Emissions Cases: Percent Increase in Equilibrium Warming
Commitment Vm-74
8-11 Rapid Reduction Strategies: Additional Decrease in Equilibrium Warming
Commitment Vm-79
XVffl
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LIST OF FIGURES (Continued)
Page
Chapter IX
9-1 Greenhouse Gas Emissions By Region IX-6
xix
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LIST OF TABLES
Executive Summary
2
3
4
5
6
7
8
Approximate Reductions in Anthropogenic Emissions Required to Stabilize
Atmospheric Concentrations at Current Levels
Overview of Scenario Assumptions
Current and Projected Trace Gas Emissions Estimates
Scenario Results for Realized and Equilibrium Warming
Examples of Policy Responses by the Year 2000
Sensitivity Analysis: Impact on Realized Warming and Equilibrium Warming
Key Global Indicators for Energy and CO,
Major Chlorofluorocarbons, Halons, and Chlorocarbons: Statistics and Uses .
Page
15
21
24
33
39
50
61
68
VOLUME I (bound under separate cover)
Chapter II
2-1 Radiative Forcing for a Uniform Increase in Trace Gases From Current Levels . . 11-21
2-2 Trace Gas Data H-51
Chapter IV
4-1 Regional Demographic Indicators IV-9
4-2 Emission Rate Differences by Sector IV-21
4-3 End-Use Energy Consumption Patterns for the Residential/Commercial
Sectors IV-24
4-4 Carbon Dioxide Emission Rates for Conventional and Synthetic Fuels FV-28
4-5 Estimates of Global Fossil-Fuel Resources IV-30
4-6 Major Halocarbons: Statistics and Uses IV-34
4-7 Estimated 1985 World Use of Potential Ozone-Depleting Substances IV-38
4-8 Refuse Generation Rates in Selected Cities .' IV-42
4-9 Land-Use: 1850-1980 FV-49
4-10 Summary Data on Area and Biomass Burned IV-52
4-11 Nitrous Oxide Emissions by Fertilizer Type IV-62
Chapter V
5-1 Overview of Scenario Assumptions V-14
5-2 Economic Growth Assumptions V-18
5-3 Key Global Indicators V-46
5-4 Comparison of No Response Scenarios and NEPP V-48
5-5 Comparison of Stabilizing Policy Scenarios and ESW V-49
5-6 Summary of Various Primary Energy Forecasts for the Year 2050 V-51
5-7 Comparison of Energy-Related Trace-Gas Emissions Scenarios V-55
5-8 Trace Gas Emissions V-65
5-9 Comparison of Estimates of Trace-Gas Concentrations in 2030 and 2050 V-75
xx
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LIST OF TABLES (Continued)
Page
Chapter VI
6-1
6-2
6-3
6-4
6-5
Impact of Sensitivity Analyses on Realized Warming and Equilibrium Warming
Comparison of Model Results to Concentrations in 1986
Low and High Anthropogenic Impact Budgets for Methane
Comparison of Emission Estimates for EPA #2, RCW and SCW Cases
Comparison of Results from Atmospheric Chemistry Models for the Year 2050
Compared to 1985
VI-7
VI-33
VI-36
VI-60
VI-61
VOLUME II (bound under separate cover)
Chapter VII
7-1 Key Technical Options by Region and Time Horizon VTI-19
7-2 High Fuel Economy Prototype Vehicles VII-39
7-3 Actual New Passenger Car Fuel Efficiency VTI-40
7-4 Summary of Energy Consumption and Conservation Potential With
Major Residential Equipment VII-84
7-5 Reduction of Energy Intensity In the Basic Materials Industries VII-95
7-6 Energy Intensities of Selected Economies VII-108
7-7 Innovation in Steel Proudction Technology VH-110
7-8 Total U.S. Gas Reserves and Resources VTI-128
7-9 CO^ Scrubber Costs Compared to SO? Scrubber Costs VII-135
7-10 Estimates of Worldwide Geothermal Electric Power Capacity Potential VII-160
7-11 Capacity of Direct Use Geothermal Plants in Operation - 1984 VII-163
7-12 Geothermal Powerplants On-Line as of 1985 VII-164
7-13 Major Forestry Sector Strategies for Stabilizing Climate Change VII-203
7-14 Potential Forestry Strategies and Technical Options to Slow Climate Change .... VII-207
7-15 Comparison of Land Required for Sustainable Swidden Versus Agricultural
Practices VII-212
7-16 Potential Carbon Fixation and Biomass Production Benefits from Agroforestry
Systems VD-216
7-17 Natural and Managed Tropical Moist Forest Yields VII-223
7-18 Productivity Increases Attributable to Intensive Plantation Management VII-227
7-19 Summary of Major Tree Planting Programs in the U.S VII-230
7-20 Estimates of CRP Program Acreage Necessary to Offset CO? Production from
New Fossil Fuel-Fired Electric Plants, 1987-96, by Tree Species or Forest Type . . VII-233
7-21 Estimates of Forest Acreage Required to Offset Various CO? Emissions Goals . . VII-239
7-22 Comparison of Selected Forest Sector Control Options: Preliminary Estimates . . VII-245
7-23 Overview of Two Social Forestry Projects Proposed to Offset CO2 Emissions of
a 180-MW Electric Plant in Connecticut VH-248
7-24 Water Regime and Modern Variety Adoption for Rice Production in Selected
Asian Countries VII-256
7-25 Average Meat Yield Per Animal VH-267
Chapter VIII
8-1 Energy Intensity of Selected National Economies, 1973-85 Vffl-12
8-2 Payback Periods in Years for Appliances, 1972-1980 Vm-20
xxi
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LIST OF TABLES (Continued)
Page
8-3 Appliance Efficiency Improvements Required by Law Vm-26
8-4 Cogeneration Facilities VIII-34
8-5 Erodible Acreage Available to Offset CO2 Emissions From Electricity
Production Vm-37
8-6 Government Efficiency Research and Development Budgets in OECD Member
Countries, 1986 VHI-41
8-7 Federal Energy Expenditures and Cost Avoidance, FY1985-FY1987 VHI-51
8-8 Scenario Results for Realized and Equilibrium Wanning VIII-82
Chapter IX
9-1 1985 Population and Energy Use Data From Selected Countries IX-8
9-2 Efficiency of Energy Use in Developing Countries: 1984-1985 IX-10
9-3 Potential for Electricity Conservation in Brazil IX-12
9-4 Net Oil Imports and Their Relation to Export Earnings for Eight Developing
Countries, 1973-1984 IX-14
9-5 Annual Investment in Energy Supply as a Percent of Annual Total Public
Investment (Early 1980s) DC-15
9-6 World Bank Estimate of Capital Requirements for Commercial Energy in
Developing Countries, 1982-1992 DC-16
9-7 U.S. AID Forestry Expenditures by Region DC-23
9-8 World Bank Energy Sector Loans in 1987 DC-26
9-9 Expenditures of Multilateral and Bilateral Aid Agencies in the Energy Area .... IX-27
9-10 World Bank Energy Conservation Projects: Energy Sector Management
Assistance Program (ESMAP) Energy Efficiency Initiatives IX-30
9-11 Energy Use in the Soviet Union and Eastern Bloc IX-34
9-12 Countries Responsible for Largest Share of Tropical Deforestation IX-41
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ACKNOWLEDGEMENTS
This report would not have been possible without the tireless efforts of the primary chapter
authors:
Executive Summary Daniel Lashof
Dennis Tirpak
Chapter I. Introduction Joel Scheraga
Irving Mintzer
Chapter II. Greenhouse Gas Trends Inez Fung
Michael Prather
Chapter III. Climatic Change Daniel Lashof
Alan Robock
Chapter IV. Human Activities Affecting Trace Gases and Climate Barbara Braatz
Craig Ebert
Chapter V. Thinking About the Future Daniel Lashof
Leon Schipper
Chapter VI. Sensitivity Analyses Craig Ebert
Chapter VII. Technical Control Options Paul Schwengels (Energy Services)
Michael Adler (Renewable Energy)
Dillip Ahuja (Biomass)
Kenneth Andrasko (Forestry)
Lauretta Burke (Agriculture)
Craig Ebert (Energy Supply)
Joel Scheraga (Energy Supply)
John Wells (Halocarbons)
Chapter VIII. Policy Options Alan Miller
Chapter IX. International Cooperation to Reduce Greenhouse Gas Emissions Alan Miller
Jayant Sathaye
Appendix A. Model Descriptions William Pepper
Appendix B. Scenario Definitions Craig Ebert
Appendix C. Results of Sensitivity Analyses Craig Ebert
xxui
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Model integration was coordinated by William Pepper and Craig Ebert, with assistance from
Rossana Florez. Models and/or analysis were prepared by Irving Mintzer; Jayant Sathaye, Andrea
Ketoff, Leon Schipper, and Sharad Lele; Klaus Frohberg and Phil Vande Kamp; Richard Houghton;
Berrien Moore, Chris Ringo, and William Emmanuel; Michael Prather; Ivar Isaksen, Terje Berntsen,
and Sverre Solberg; and Anne Thompson.
Document integration was coordinated by Craig Ebert and Barbara Braatz. Editorial assistance
was provided by Susan MacMillan. Technical, graphics, and typing assistance was provided by
Courtney Dinsmore, Katey Donaldson, Donald Devost, Michael Green, Karen Zambri, Judy Koput,
Donna Whitlock, Margo Brown, and Cheryl LaBrecque.
Literally hundreds of other people have contributed to this report, including the organizers and
attendants at four workshops sponsored by EPA to gather information and ideas, and dozens of
formal and informal reviewers. We would like to thank this legion for their interest in this project,
and apologize for not doing so individually. Particularly important comments were provided by,
among others, Thomas Bath, Deborah Bleviss, Gary Breitenbeck, William Chandler, Robert Friedman,
Howard Geller, James Hansen, Tony Janetos, Stan Johnson, Julian Jones, Michael Kavanaugh,
Andrew Lacis, Michael MacCracken, Elaine Matthews, William Nordhaus, Steven Piccot, Marc Ross,
Stephen Schneider, Paul Steele, Pieter Tans, Thomas Wigley, Edward Williams, and Robert Williams.
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.
Technical support was provided by the Office of Research and Development, administered by Eric
Brethauer.
xxiv
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Review Draft
POLICY OPTIONS
FOR STABILIZING GLOBAL CLIMATE
Executive Summary
INTRODUCTION 1
Congressional Request for Reports 1
Previous Studies 2
Goals of this Study 4
Approach Used to Prepare this Report 6
Limitations 9
HUMAN IMPACT ON THE CLIMATE SYSTEM 11
The Greenhouse Gas Buildup 11
The Impact of Greenhouse Gases on Global Climate 17
SCENARIOS FOR POLICY ANALYSIS 19
Defining Scenarios 19
Scenarios with Unimpeded Emissions Growth 22
The Impact of Policy Choices 29
Sensitivity of Results to Alternative Assumptions 45
EMISSIONS REDUCTION STRATEGIES BY ACTIVITY 54
Energy Production and Use 56
Industrial Activity 66
Changes in Land Use 71
Agricultural Practices 75
THE NEED FOR POLICY RESPONSES 77
A Wide Range of Policy Choices 78
The Timing of Policy Responses 79
FINDINGS 83
I. Uncertainties regarding climatic change are large, but there is a growing consensus
in the scientific community that significant global warming due to anthropogenic
greenhouse gas emissions is probable over the next century, and that rapid climatic
change is possible 83
II. Measures undertaken to limit greenhouse gas emissions would decrease the magnitude
and speed of global warming, regardless of uncertainties about the response of the
climate system 85
III. No single country or source will contribute more than a fraction of the greenhouse
gases that will warm the world; any overall solution will require cooperation of many
countries and reductions in many sources 87
IV. A wide range of policy choices is available to reduce greenhouse gas emissions while
promoting economic development, environmental, and social goals 89
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INTRODUCTION
The composition of the Earth's atmosphere is changing. There is a growing scientific consensus
that the observed trends and projected increases in the atmospheric concentrations of greenhouse
gases will alter the global climate. "Greenhouse" gases (carbon dioxide, methane,
chlorofluorocarbons, and nitrous oxide, among others) in the atmosphere absorb heat that radiates
from the Earth's surface and emit some of this heat downward, warming the climate. Without this
"greenhouse effect," the Earth would be about 30°C (60°F) colder than it is today. Human activities
are now increasing the atmospheric concentrations of greenhouse gases on a global basis, thus
intensifying the greenhouse effect. Although the specific rate and magnitude of future climate change
is hard to predict, the rate of greenhouse gas buildup during the next century will depend heavily on
future patterns of economic and technological development, which are, in turn, influenced by policies
of local, state, national, and international private and public institutions.
Congressional Request for Reports
To better define the potential effects of global climate change and identify the options that are
available to influence the composition of the atmosphere and the rate of climatic change, Congress
asked the U.S. Environmental Protection Agency to undertake two studies on the greenhouse effect.
In one of these studies Congress directed EPA to include:
"An examination of policy options that if implemented would stabilize current levels of
atmospheric greenhouse gas concentrations. This study should address the need for and
implications of significant changes in energy policy, including energy efficiency and development
of alternatives to fossil fuels; reductions in the use of CFCs; ways to reduce other greenhouse
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gases such as methane and nitrous oxide; as well as the potential for and effects of reducing
deforestation and increasing reforestation efforts."
This report responds to that request. The second study was to focus on "the potential health and
environmental effects of climate change." A companion report, The Potential Effects of Climate
Change on the United States, responds to the second request.
This Executive Summary describes the goals established by EPA for this study, considering
previous work and our Congressional mandate. The analytical framework developed for this study
is briefly described and its limitations are noted. We then summarize current understanding of the
greenhouse gases and their impact on global climate. A description of the scenarios that were
developed to explore the sensitivity of the climate system to policy choices is presented next. The
results of this scenario analysis follows, emphasizing the relative impact of various options. The
technological and policy strategies that appear most promising for reducing greenhouse gas emissions
are then presented by major activity category: energy production and use, other industrial activities,
changes in land use, and agricultural practices. The policy options that are available for promoting
these emission reduction strategies are then reviewed, giving consideration to the timing of policy
responses to the greenhouse gas buildup. Finally, the major findings of this study are summarized.
Previous Studies
Atmospheric measurements indicating that the composition of the atmosphere is changing (e.g.,
Figure 1) have led to many assessments of the potential magnitude of future greenhouse gas
emissions, future greenhouse gas concentrations, and associated climatic changes. A scientific
consensus has emerged from these studies that increased concentrations of greenhouse gases will
result in climate change. Moreover, there is serious risk that, in the absence of policy responses,
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Executive Summary
FIGURE 1
CARBON DIOXIDE CONCENTRATION AT MAUNA LOA
AND FOSSIL FUEL CO2 EMISSIONS
310
i! 5UO O
O
uouo t-
55UO w
Ctf
5000 g
I 5UO _j
UJ
1 QUO Qt,
J
asoo M
OT
OT
3000 O
fa.
2500
1856 I860 1982 1884 1888 1888 1870 1873 1874 1876 1878 1880 1982 1884 1888 1888
Figure 1. The solid line depicts monthly concentrations of atmospheric CO2 at Mauna Loa
Observatory, Hawaii. The yearly oscillation is explained mainly by the annual cycle of photosynthesis
and respiration of plants in the northern hemisphere. The dashed line represents the annual
emissions of CO2, in units of carbon, due to fossil fuel combustion.
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greenhouse gas emissions will continue to increase due to population and economic growth, and that
sometime during the middle of the next century, the buildup of greenhouse gases will have a climatic
effect equivalent to doubling the concentration of carbon dioxide from preindustrial levels.
A study by the U.S. National Academy of Sciences in 1979 concluded that doubling the
concentration of carbon dioxide relative to the preindustrial atmosphere would result in an eventual
(equilibrium) global warming of 1.5-4.5°C. Subsequent re-evaluations by the National Academy of
Sciences (in 1983 and 1987), as well as the "State-of-the-Art" report issued by the U.S. Department
of Energy in 1985, have reaffirmed this estimate. Recent general circulation model results and a
recent review conducted for the international Scientific Committee On Problems of the Environment
(SCOPE) suggest that a warming of 5.5°C as a result of doubling carbon dioxide may be at least as
likely as a warming of 1.50C.
Only a few studies have examined potential policy responses to the greenhouse gas buildup. The
IEA/ORAU Long-Term Global Energy CO2 Model developed for the Department of Energy in 1983
was used in many of these studies, including EPA's 1983 report, Can We Delay a Greenhouse
Warming? This study investigated the extent to which policy measures might influence the timing of
a 2°C global warming. The IEA/ORAU model was also used for important studies conducted at
the Massachusetts Institute of Technology Energy Laboratory (in 1984) and the World Resources
Institute (in 1987). These studies concluded that policy choices could have a major influence on the
total wanning that may be experienced during the next century.
Goals of this Study
Congress presented EPA with a very challenging task. From a policy perspective, it is not
enough to know how emissions would have to change from current levels in order to stabilize the
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atmosphere. Instead, policy options must be evaluated in the context of expected economic and
technological development and the uncertainties that prevent us from knowing precisely how a given
level of emissions will impact the rate and magnitude of climate change. It is also necessary that the
scope of this study be global and the time horizon be more than a century, because of the long lags
built into both the economic and climatic systems (we chose 1985-2100 as the tune frame for the
analysis). We cannot predict what the future will bring, but scenarios can be developed to explore
policy options.
Based on these considerations EPA established four major goals:
• To assemble data on global trends in emissions and concentrations of all
major greenhouse gases and activities that affect these gases.
• To develop an integrated analytical framework to study how different
assumptions about the global economy and the climate system could
influence future greenhouse gas concentrations and global temperatures.
• To identify promising technologies and practices that could limit greenhouse
gas emissions.
• To identify policy options that could influence future greenhouse gas
concentrations and global wanning.
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Approach Used to Prepare this Report
To achieve these goals EPA conducted an extensive literature review and data gathering process.
The Agency held several informal panel meetings, and enlisted the help of leading experts in the
governmental, non-governmental, and academic research communities. EPA also conducted five
workshops, which were attended by over three hundred people, to gather information and ideas
regarding factors affecting atmospheric composition and options related to greenhouse gas emissions
from agriculture and land-use change, electric utilities, end-uses of energy, and developing countries.
Experts in NASA, the Department of Energy, and the Department of Agriculture were actively
engaged.
Based on the outcome of this process, EPA developed an integrated analytical framework to
organize the data and assumptions required to calculate (1) emissions of radiativety and chemically
active gases, (2) concentrations of greenhouse gases, and (3) changes in global temperatures. This
framework is highly simplified, as its primary purpose is to rapidly scan a broad range of policy
options in order to test their general effectiveness in reducing atmospheric concentrations of
greenhouse gases. It is the first attempt to relate the underlying forces (e.g., population growth,
economic growth, and technological change) to the emissions of all the important greenhouse gases.
This framework makes it possible to estimate the impact of changes in these factors on the
composition of the atmosphere and global temperatures. In constructing this framework, we used
the results of more sophisticated models of individual components as a basis for our analysis. While
we believe that this framework generally reflects the current state of scientific knowledge, there are
important limitations (discussed below) that may affect the results of our analysis.
Emissions of the greenhouse gases COj, CH4, N2O, and of a number of halocarbons are explicitly
calculated within the framework based on assumptions about activities that generate these gases, such
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as energy production and consumption, industrial processes, agricultural practices, and deforestation.
Emissions of CO and NO,, which are not themselves greenhouse gases, are also explicitly calculated,
as these gases can significantly alter the chemistry of the atmosphere and thus affect the
concentrations of the greenhouse gases. The four emissions modules (Figure 2) use input data,
including scenario specifications, for population growth, GNP, energy efficiency, agricultural
productivity, and the rate of deforestation. The Energy Module is based on the IEA/ORAU Long-
Term Global Energy CO2 Model developed for the U.S. Department of Energy (modified considerably
for this study), and on analysis of energy end-use patterns conducted by Lawrence Berkeley
Laboratory and the World Resources Institute. EPA's CFC model, developed to assess stratospheric
ozone depletion, forms the primary component of the Industry Module. The Agriculture Module is
based on the Basic Linked System developed at the International Institute of Applied Systems
Analysis and emissions coefficient estimates from the literature; and the Land-Use and Natural
Source Module uses the Terrestrial Carbon Model developed at the Woods Hole Marine Biological
Laboratory for CO2 emissions related to deforestation. Emissions are estimated for nine regions of
the globe and are calculated every 5 years from 1985 to 2025 and then every 25 years through 2100.
In addition to the emissions modules, there are two concentration modules. Together these
concentration modules estimate changes in global atmospheric concentrations of the greenhouse gases
based on the projected emissions and changes in global temperatures that result from the calculated
concentrations. The Atmospheric Composition Module consists of a highly simplified model of global
chemistry developed by NASA and a parameterization of the impact of changes in greenhouse gas
concentrations on the radiation balance of the Earth. The Ocean Module contains a modified
version of the Goddard Institute for Space Studies ocean model that simultaneously calculates carbon
dioxide and heat uptake. The Ocean Module also contains four additional models for carbon dioxide
uptake assembled by the Complex Systems Research Center at the University of New Hampshire.
The calculated atmospheric trace-gas concentrations and temperature changes affect the emissions
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Executive Summary
FIGURE 2
STRUCTURE OF THE ATMOSPHERIC STABILIZATION FRAMEWORK
Inputs
Base case
Assumptions
Resources
Population
Growth
Productivity
Technology
Alternative
Strategies
_fc^^
F
Emissions
orecasting
Modules
Energy
Industry
Agriculture
Concentration
Determination
Modules
Atmospheric
Composition
Ocean
Outputs
Atmospheric
Concentrations
and
Temperature
Change
Feedbacks
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modules in the next time period. The estimates of global temperature change serve as indicators for
the rate and magnitude of global change, but it is important to keep in mind that changes in
precipitation and other factors may be as important as changes in global temperature, and that the
timing and magnitude of climatic changes at a regional level may differ significantly from the global
average.
Limitations
This analytical framework attempts to incorporate some representation of the major processes
that will influence the rate and magnitude of greenhouse wanning during the next century within a
structure that is reasonably transparent and easy to manipulate. In so doing we recognize a number
of major limitations:
• Economic growth rates are difficult to forecast and will strongly influence
future greenhouse gas emissions. Although there are factors cutting in both
directions, emissions can generally be expected to be higher if economic
growth is more rapid. Our alternative assumptions may not adequately
reflect the plausible range of possible growth rates.
• Economic linkages are not fully captured. The type of economic analysis
conducted cannot ensure that the activity levels assumed in each sector are
completely consistent with the aggregate economic assumptions. In addition,
capital markets are not explicitly considered. This is particularly significant
with regard to developing countries, as it is unclear if they will be able to
obtain the capital needed to grow as fast or develop the energy supplies
assumed in some of the scenarios.
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• Technological changes are difficult to forecast. Substantial improvements
in the efficiency of energy-using and energy-producing technologies are
assumed to occur even in the absence of substantial energy price increases
or policy measures. If this assumption proves to be untrue, then greenhouse
gas emissions may be substantially underestimated in the No Response
scenarios (see below for the scenario definitions). Similarly, aggressive
research and development is assumed to substantially reduce the cost of
renewable technologies in the Stabilizing Policy scenarios. The impact of
policies may be overestimated if such improvements fail to materialize or
if they would have materialized as rapidly even without increased government
support.
• Detailed cost analyses have not been conducted. Technological strategies
have been screened based on judgments about their potential to be cost-
effective, but no attempt has been made to rank the cost-effectiveness of
each strategy or to estimate the government expenditures or total social costs
or benefits associated with the stabilizing strategies.
• The modules of the framework are not fully integrated. Existing models of
individual processes that affect greenhouse gas emissions were assembled
within the analytical framework and were used with consistent assumptions.
However, it was not possible to ensure complete consistency of results. For
example, while the biomass energy supplies arrived at in the Energy Module
do not appear to be inconsistent with the land use patterns calculated in the
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Agriculture and Land Use and Natural Source Modules, there is no explicit
coupling among these results.
• The ocean models employed, are highly simplified. The ocean plays an
important role in taking up both CO2 and heat. The one-dimensional
models used to represent this process may not adequately reflect the
underlying physical processes, particularly as climate changes.
• Changes in atmospheric chemistry are calculated in a highly simplified
fashion. Chemical interactions are analyzed based on parameters derived
from detailed chemical models. These parameters may not adequately
reflect the underlying chemistry, particularly as the atmospheric composition
changes significantly from current conditions. Also, it is not possible to
explicitly model the heterogeneous conditions that control, for example,
tropospheric ozone concentrations. In our analysis we also assume that non-
methane hydrocarbon emissions remain constant, which may cause future
.methane and ozone changes to be underestimated.
HUMAN IMPACT ON THE CLIMATE SYSTEM
The Greenhouse Gas Buildup
Many greenhouse gases are currently accumulating in the atmosphere. The most important is
carbon dioxide (CO^, followed by methane (CH4), chlorofluorocarbons (CFCs), and nitrous oxide
(N2O) (Figure 3). Carbon dioxide is a fundamental product of burning fossil fuels (coal, oil, and
gas), and is also released as a result of deforestation (Box 1). The largest methane source is decay
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FIGURE 3
GREENHOUSE GAS CONTRIBUTIONS TO GLOBAL WARMING
1880-1980
Other(8%)
CFC-11&-12
(8%)
N20 (3%
CH4
(15%)
CO2(66%)
1980s
Other(13%)
CFC-11 &-12
(14%)
CO2 (49%)
CH4(18%)
Figure 3. Based on estimates of the increase in the concentration of each gas during the specified
period. Other includes additional CFCs, halons, changes in ozone, and changes in stratospheric water
vapor. The other category is quite uncertain.
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of organic matter in the absence of oxygen, while CFCs are produced only by the chemical industry.
The sources of nitrous oxide are not well characterized, but most are probably related to soil
processes.
Stabilizing emissions of greenhouse gases at current levels will not stabilize
concentrations. Once emitted, greenhouse gases remain in the atmosphere for decades to
centuries. At current emission levels, greenhouse gases are being released into the atmosphere faster
than they are being removed. As a result, if emissions remained constant at 1985 levels, the
greenhouse effect would continue to intensify for more than a century. Carbon dioxide
concentrations would reach 440-500 parts per million (ppm) by 2100, compared with about 350 ppm
today, and about 290 ppm 100 years ago (Figure 4). CFC concentrations would increase by more
than a factor of three from current levels, while nitrous oxide concentrations would increase by about
20%, and methane concentrations might remain roughly constant.
Drastic cuts in emissions would be required to stabilize atmospheric composition as shown in
Table 1 (see also, Box 1), and even if all anthropogenic emissions of COj, CFCs, and N2O were
eliminated the concentrations of these gases would remain elevated for decades. It would take more
than 50 years, and possibly more than a century, for the oceans to absorb enough carbon to reduce
the atmospheric concentration of CO2 half way toward its preindustrial value. It would «lso take
more than 50 years before excess concentrations for CFCs and N2O declined by half after all
anthropogenic emissions were eliminated.
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FIGURE 4
IMPACT OF C02 EMISSIONS REDUCTIONS
ON ATMOSPHERIC CONCENTRATIONS
(Parts Per Million)
500
475 -
450 -
o
_J
^ 425
DC
UJ
Q.
V>
400 -
375 -
350 -„
325
1985 2000
2025
2050
YEAR
2075
2100
Figure 4. The response of atmospheric CO2 concentrations to arbitrary emissions scenarios, based
on two one-dimensional models of ocean CO2 uptake. The emissions scenarios are relative to
estimated 1985 levels of 5.9 billion tons of carbon per year.
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TABLE 1
Approximate Reductions in Anthropogenic Emissions
Required to Stabilize Atmospheric Concentrations at Current Levels
GAS REDUCTION REQUIRED
Carbon Dioxide (CO2) 50-80%
Methane (CH4) 10-20%
Nitrous Oxide (N2O) 80-85%
Chlorofluorocarbons (CFCs) 75-100%
CO, NOs Freeze
BOX1
Greenhouse Gases
Carbon dioxide. Carbon dioxide (CO,) is the most abundant and single most important
greenhouse gas in the atmosphere. Its concentration has increased by about; 25% since the
industrial revolution. Detailed measurements since 1958 snow an increase from 315 to 350
parts per million by volume (Figure 1), Carbon dioxide concentrations ate currently increasing
at a rate of about 0.4% per year, which is responsible lor about itall of current Increases In
commitment to global warming from greenhouse gas buildup (Figure 3). Both deforestation
and fossil-fuel combustion have contributed to this rise. Current emissions are estimated at
5.5 bfllioa tons of carbon (Pg C) from fossil-fuel combustion and 0,4-2,6 Pg C from
deforestation. Most of this carbon dioxide remains in the atmosphere- or is absorbed by the
oceans. Even though only about half of current emissions remain in the atmosphere, available
models of COa uptake by the ocean suggest that substantially more than a 50% cut in
emissions is required to stabilize concentrations at current levels;
Methane. The concentration of methane (CH4) has more titan doubled daring the last
three centuries. Methane, which: is currently increasing at a rate of 1% per year, is
responsible for about T®% of current increases in commitment to global warming. There i&
consider able uncertainty about the sources of methane, and the observed Increase is probably
due to incjteases & a luteW of sources as well as to change* k tropospheric chemistry.
Increases in agricultural sources, particularly rice cultivation and animal husbandry, have
probably been the most significant factor, but emissions from landfills and coal seams could
play an important role in the future. Of the major greenhouse gases only methane
concentrations can be stabilized with modest cuts in anthropogenic emissions: a 10*20% cut
would suffice to stabilize concentrations at current levels due to methane's relatively short
atmospheric lifetime, assuming that this lifetime remains constant and that natural emissions
do not change. Whether this is the case will depend on changes in tropospheric chemistry as
influenced by emissions of hydrocarbons and carbon monoxide, among others, and on whether
global climate change itself affects methane emissions.
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The concentration of nitrous oxide (N2O) has increased by 5-10% since
preindustrial times. The cause of this increase is highly uncertain, but it appears that the use
of nitrogenous fertilizer, land clearing, biomass burning, and fossil-fuel combustion nave all
contributed. Each additional molecule of nitrous oxide has over 200 times as much impact
on climate as additional molecules of carbon dioxide, and nitrous oxide can also contribute to
stratospheric ozone depletion. Nitrous oxide is currently increasing at a rate of 0.25% per
year, which represents an imbalance of about 30% between total emissions and total losses.
Nitrous oxide increases are responsible for roughly 6% of current increases Jn commitment
to global warming. Assuming that the observed increase in NjO concentrations is due to
anthropogenic sources and that natural emissions have not changed* then aft 80-85% cut in
anthropogenic emissions would be required to stabilize N2O at current levels.
Hajpcarbons. Chlorofluorocarbons (CFCs), currently the most important halocarbons,
were introduced into the atmosphere for the first time during this century. The most common
species are CFC-12 (CCy?^ and CFG-11 (CCIjF)> which had atmospheric concentrations in
1586 of 392 and 225 parts per trillion by volume, respectively. While these concentrations are
tiny compared with that of CO,, CFCs have as much as 20,000 times moire impact oa climate
per additional molecule and are increasing very rapidly-more than 4% per year since 1978.
A focus of attention because of their potential to deplete stratospheric ozone, the increasing
concentration of CFCs also represents about 15% of current increases i» commitment to global
warming* For CFC-11 and CFC-12, cuts of 75% and 85%, respective^, of current global
emissions would be required to stabilize concentrations. However because of growth in other
compounds, in order to stabilize the total greenhouse Warming potential from all halocarbons,
a phaseout of the fully halogenated compounds (those that do not contain hydrogen), a freeze
on the use of methyl chloroform^ and a limit on the emissions of partiafly halogenated
substitutes would be required.
Other gases influencing composition. Emissions of carbon monoxide (CO) and nitrogen.
oxides (NO*), among other species, in addition to the greenhouse gases just described, are also
changing the chemistry of the atmosphere. This change in atmospheric chemistry alters the
distribution of ozone and the oxidizing power of the atmosphere, changing the atmospheric
lifetimes of the greenhouse gases. If the concentrations of the long-lived gases were stabilised,
it might only be necessary to freeze emissions of the short-lived gases at current levels to
atmospheric composition,
In preparing this report, EPA did not develop scenarios that achieve zero change in
concentrations, instead we have focused on promising options that can significantly slow the rate of
greenhouse gas buildup and climatic change.
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The Impact of Greenhouse Gases on Global Climate
Uncertainties about the impact of the greenhouse gas buildup on global climate abound. These
uncertainties are not about whether the greenhouse effect is real or whether increased greenhouse
gas concentrations will raise global temperatures. Rather, the uncertainties concern the ultimate
magnitude and timing of warming and the implications of that warming for the Earth's climate
system, environment, and economies.
The magnitude of future global warming will depend, in part, on how geophysical and biological
feedbacks enhance the warming caused by the additional infrared radiation absorbed by increasing
concentrations of greenhouse gases. The ultimate global average temperature increase that can be
expected from a specific increase in the concentrations of greenhouse gases can be called the "climate
sensitivity." This parameter provides a convenient index for the magnitude of climatic change that
would be associated with different scenarios of greenhouse gas buildup. (In this report we use a
doubling of the concentration of CO2 from preindustrial levels, or the equivalent from increases in
the concentrations of a number of greenhouse gases, as the benchmark case.)
Estimating the impact of increasing greenhouse gas concentrations on global climate has been
a focus of research within the atmospheric science community for more than a decade.
• If nothing else changed in the Earth's climate system except the doubling
of CO2 (or the equivalent in other greenhouse gases), average global
temperature would rise 1.2-1.3°C.
• A strong scientific consensus exists that increased global temperatures would
raise atmospheric levels of water vapor and change the vertical temperature
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profile, raising the ultimate global warming caused by a doubling of CO2 to
1.8-2.5°C, if nothing other than these factors changed in the Earth's climate
system. Changes in snow and ice cover are also expected to enhance
warming, raising the estimate to 2-4°C.
• General Circulation Models now generally project that the global warming
from doubling CO2 would cause changes in clouds that could enhance this
warming to roughly 2.5 to 5.5°C. Uncertainties exist about this feedback,
however. There also exists the possibility that the cloud feedback will be
negative and would diminish the warming somewhat, perhaps to 1.5'C.
• A variety of other geophysical and biogenic feedbacks exist that have
generally been ignored in global climate models. For example, future global
warming has the potential to increase emissions of carbon from northern
latitude reservoirs in the form of both methane and carbon dioxide, and to
alter uptake of CO2 by the biosphere and the oceans. When all such
feedbacks are considered, it is possible that the actual climate sensitivity of
the Earth could exceed 5.5°C for an initial doubling of CO2.
Global wanning of just a few degrees would represent a enormous change in climate. The
difference in mean annual temperature between Boston and Washington is only 33°C, and the
difference between Chicago and Atlanta is 6.7°C. The total global warming since the peak of the
last ice age, 18,000 years ago, was only about 5°C. That change transformed the landscape of North
America; it shifted the Atlantic ocean inland by about one-hundred miles, created the Great Lakes,
and changed the composition of forests throughout the continent.
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The potential future impacts of climatic change are difficult to predict and are beyond the scope
of this report. Sensitivity analyses can be undertaken to estimate potential impacts, as was done in
the companion volume, The Potential Effects of Global Climate Change on the United States. The
findings of that study collectively suggest that the climatic changes associated with a global warming
of roughly 2-4°C would result in "a world that is different from the world that exists today. Global
climate change will have significant implications for natural ecosystems; for when, where, and how
we farm; for the availability of water to drink and water to run our factories; 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."
SCENARIOS FOR POLICY ANALYSIS
Defining Scenarios
Defining scenarios that encompass more than a century is a daunting task. While this is an
eternity for most economists and planners, it is but a moment for geologists. And indeed, decisions
made in the next few decades, about how buildings are constructed, electricity is generated, and cities
are laid out, for example, will have an impact on the climate in 2100 and beyond. Decisions about
what kinds of automobiles and other industrial products to produce and how to produce them will
also have a profound impact. These choices, which will affect the amount and type of fuel we use
to travel, to heat and light our homes and offices, and to run our factories, will influence the
magnitude of greenhouse gas emissions for many years.
To explore the climatic implications of such policy and investment decisions, we have constructed
four scenarios of future patterns of economic development and technological change. These scenarios
start with alternative assumptions about the rate of economic growth and policies that influence
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emissions. These scenarios are intended to be internally consistent pictures of how the world may
evolve in the future. They are not forecasts and they do not bracket the full range of possible
futures. Instead, they were chosen to provide a basis for evaluating strategies for stabilizing the
atmosphere in the context of distinctly different, but plausible, conditions.
Two scenarios explore alternative pictures of how the world may evolve in the future assuming
that policy choices allow unimpeded growth in emissions of greenhouse gases (these are referred to
as the "No Response" scenarios). One of these scenarios, called a Rapidly Changing World (RCW),
assumes rapid economic growth and technical change; the other, called the Slowly Changing World
(SCW), represents a slower evolution of the world's economies. Two additional scenarios (referred
to as the "Stabilizing Policy" scenarios) start with the same economic and demographic assumptions,
but assume a world in which policies to limit anthropogenic emissions have been adopted. These
scenarios are called the Slowly Changing World with Stabilizing Policies (SCWP) and the Rapidly
Changing World with Stabilizing Policies (RCWP). An overview of the scenario assumptions is given
in Table 2. In all of the scenarios it is assumed that the key national and international political
institutions evolve gradually, with no major upheavals.
The various assumptions that go into these scenarios are conceptually consistent, which leads to
partially offsetting impacts on greenhouse gas emissions. For example, more rapid economic growth
in the RCW compared to the SCW scenario is assumed to be associated with more rapid
technological innovation and replacement of older equipment, which has higher greenhouse gas
emissions. Similarly, rapid increases in income are assumed to be associated with more rapid
decreases in population growth rates. In the Stabilizing Policy scenarios it is assumed that more
rapid reductions in greenhouse gas emissions per unit of activity are possible when economic growth
rates are higher. If such offsetting tendencies do not occur, and/or if economic growth is more rapid
than assumed in the RCW and RCWP scenarios, then the rate of greenhouse gas buildup would
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TABLE 2
Overview of Scenario Assumptions
Slowlv Changing World
Raoidlv Chanting World
Slow GNP Growth
Continued Rapid Population Growth
Minimal Energy Price Increases
Slow Technological Change
Carbon-Intensive Fuel Mix
Increasing Deforestation
Montreal Protocol/Low Participation
Rapid GNP Growth
Moderated Population Growth
Modest Energy Price Increases
Rapid Technological Improvements
Very Carbon-Intensive Fuel Mix
Moderate Deforestation
Montreal Protocol/High Participation
Slowly Changing World
with Stabilizing Policies
Rapidly Changing World
with Stabilizing Policies
Slow GNP Growth
Continued Rapid Population Growth
Minimal Energy Price Increases/Taxes
Rapid Efficiency Improvements
Moderate Solar/Biomass Penetration
Rapid Reforestation
CFC Phase-Out
Rapid GNP Growth
Moderated Population Growth
Modest Energy Price Increases/Taxes
Very Rapid Efficiency Improvements
Rapid Solar /Biomass Penetration
Rapid Reforestation
CFC Phase-Out
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probably be higher than what is calculated for these scenarios. Economic growth may also be lower
than is assumed in the SCW.
The analysis for this study included a detailed examination of energy demand for the year 2025.
We chose this date because, although substantial change will have occurred, some infrastructure will
still be in place and much of the technology to be deployed over this period is already under
development. Scenarios extending beyond this date are speculative, but they are included because
they are necessary to evaluate the full implications of more immediate decisions and because
greenhouse gases affect warming for many decades. Projections to 2100 are based on the patterns
and relationships established between 1985 and 2025. Our procedure is to consider the major
economic and social structures that determine the activities that give rise to trace-gas emissions.
Scenarios with Unimpeded Emissions Growth
In "A Slowly Changing World" (SCW) we consider the possibility that the recent experience of
modest growth will continue indefinitely, with no concerted policy response to the risk of climatic
change. In this scenario we assume that the aggregate level of economic activity (as measured by
GNP) increases relatively slowly on a global basis. Per capita income is stagnant for some time in
the developing regions that have very high population growth, with modest increases elsewhere. Per
capita economic growth rates increase slightly over time in all developing regions as population
growth rates gradually decline. The population engaged in traditional agriculture continues to
increase, as does demand for fuelwood and speculative land clearing. These factors lead to
accelerated deforestation until tropical forests are virtually eliminated toward the middle of the next
century. Because of slack demand, real energy prices increase slowly. Correspondingly, existing
capital stocks turn over slowly and production efficiency in agriculture and industry improves at only
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a moderate rate. The energy efficiency of buildings, vehicles, and consumer products also improve
at a slow rate.
In "A Rapidly Changing World" (RCW) rapid economic growth and technological change occurs
with little attention given to the global environment. Per capita income rises rapidly in most regions
and consumers demand increasing energy services, which puts upward pressure on energy prices.
The number of cars increases rapidly in developing countries and air travel increases rapidly in
industrialized countries. Energy efficiency is not much of a consideration in consumer choices, as
income increases faster than real energy prices, but efficiency increases occur due to technological
improvements. Correspondingly, we assume that there is a high rate of innovation in industry and
that capital equipment turns over rapidly, thereby accelerating reductions in energy required per unit
of industrial output. An increasing share of energy is consumed in the form of electricity, which is
produced mostly from coal. The fraction of global economic output produced in the developing
countries increases dramatically as services become more important hi industrialized countries and
as industries such as steel, aluminum, and auto-making grow in developing countries. Population
growth rates decline more rapidly than hi the Slowly Changing World scenario as educational and
income levels rise. Deforestation continues at about current rates, spurred by land speculation and
commercial logging, despite reduced rates of population growth.
The No Response scenarios examined lead to substantial greenhouse gas buildup
and global wanning. The two worlds described above lead to significant increases in carbon
dioxide and trace gas emissions (Table 3), large increases in greenhouse gas concentrations (Figure
5), and substantial global warming. Carbon dioxide concentrations reach twice their preindustrial
levels in about 2080 in the SCW scenario. In the RCW this level is reached by 2055, and
concentrations more than three times preindustrial values are reached by 2100. Methane
concentrations increase by almost a factor of 2 in the SCW and a factor of 2.6 in the RCW, with the
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TABLES
Current and Projected Trace Gas Emissions Estimates
C02 (Pg Q*
sew
RCW
SCWP
RCWP
N20 (Tg N)b
sew
RCW
SCWP
RCWP
CH4 (Tg CH<)
sew
RCW
SCWP
RCWP
NO, (Tg N)
sew
RCW
SCWP
RCWP
CO (Tg C)
sew
RCW
SCWP
RCWP
CFC-12 (Gg)c
sew
RCW
SCWP
RCWP
CFC-22 (Gg)
sew
RCW
SCWP
RCWP
1985
5.9
5.9
5.9
5.9
11.3
11.3
11.3
11.3
514.4
510.5
514.4
510.5
53.3
53.2
53.3
53.2
502.3
502.0
502.3
502.0
363.8
363.8
363.8
363.8
73.8
73.8
73.8
73.8
2025
9.2
11.5
5.1
5.2
13.5
13.0
10.7
10.8
676.4
712.4
545.0
558.7
68.8
72.9
44.8
50.7
842.0
699.1
286.1
290.8
379.7
437.5
54.9
85.9
385.0
829.1
385.0
829.1
2100
11.4
25.5
3.1
4.5
12.1
15.0
10.7
10.9
815.9
1,089.0
484.7
508.0
70.1
118.2
42.6
43.8
603.5
1,207.1
250.9
244.9
410.8
493.1
66.0
86.6
794.8
2,795.6
794.8
2,795.6
1 1 Pg C = 1 billion metric tons of carbon.
b 1 Tg N = 1 million metric tons of nitrogen.
c 1 Gg = 1 thousand metric tons = 1 million kilograms.
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FIGURES
u 600
ATMOSPHERIC CONCENTRATIONS
(3.0 Degree Celsius Climate Sensitivity)
CARBON DIOXIDE METHANE
(Parti P«r Million)
1*86 2000 2025 20EO 207S 2100
VEAR
£ 3000
(P«rt« Per Billion!
1985 2000 2026 2050 2076 2100
VEAR
NITROUS OXIDE
(P«rtf P«r Billion)
1985 2000 2025 2060 2076 2100
VEAR
CHLOROFLUOROCARBONS
(P«rli P«r Trillion o< CFC-12 Equivalent)
I I I I
1986 2000 2025 2060 2076 2100
YEAR
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most rapid growth occurring between 1985 and 2050. The combined greenhouse effect of CFCs
increases to a greater extent, reaching 4.2 times 1985 levek by 2100 in the SCW and 6.5 times 1985
levek in the RCW, despite assuming that at least 65% of developing countries and 95% of
industrialized countries participate in the Montreal Protocol to control emissions of these compounds.
Nitrous oxide concentrations also increase significantly, primarily as a result of the current imbalance
between sources and sinks. When all the trace gases are considered, an increase in the greenhouse
effect equivalent to that which would occur from a doubling of CO2 concentrations is reached by 2040
in the SCW and by 2030 in the RCW. These results are hi good agreement with recent studies that
have made less formal estimates based primarily on current trends in concentrations and/or emissions.
A notable exception is CFCs, for which we expect significantly lower concentrations as a result of the
recent Montreal Protocol to control production of these compounds (see Production and Use of
Halocarbons).
Even the Slowfy Changing World scenario is calculated to produce a 2-3°C
temperature increase during the next century. In the SCW scenario, realized global warming
would increase by 1.0-1.5°C between 2000 and 2050 and by 2-3°C from 2000 to 2100 (temperature
ranges are based on a climate sensitivity of 2-4°C unless otherwise noted; see Box 2; Figure 6). The
maximum realized rate of change associated with this scenario is 0.2-03°C per decade, which occurs
sometime in the middle of the next century. The total equilibrium wanning commitment is
substantially higher, reaching 3-6°C by 2100 relative to preindustrial levels.
Higher rates of economic growth are certainly the goal of most governments and could lead to
higher rates of climatic change as illustrated by the RCW scenario. Compared with the SCW, the
rate of change during the next century would be more than 50% greater in the RCW: In the RCW
realized global warming increases by 1.2-1.9°C between 2000 and 2050, and by 3-5°C between 2000
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FIGURE 6
REALIZED WARMING
NO RESPONSE SCENARIOS
(Degrees Celsius; 2.0 - 4.0 Degree Climate Sensitivity)
5 \-
4 |_
UJ
o 3
v>
UJ
111
cc
2 J_
1 (-
1985 2000
2025
2050
YEAR
2075
2100
Figure 6. Shaded areas represent the range based on an equilibrium climate sensitivity to doubling
C02 of 2-4°C.
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BOX 2
Equilibrium and Realized Warming
Equilibrium Warming Commitment
The equilibrium warming commitment for any given year is the eventual increase in
temperature that would occur at some point in the future if atmospheric concentrations of
greenhouse gases were to remain constant at that year's levels.
Realized Warming
Because the oceans have a large seat capacity the temperature change realized in the
atmosphere lags considerably behind the equilibrium level (the difference between the
equilibrium wanning and the realized warming in any given year is called the unrealized
warming}* Realized warming has been estimated with a simple model of ocean heat uptake.
CBmale Sensitivity :
Because the response of the climate system to changes in greenhouse gas concentrations is
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Policy Options for Stabilizing Global Climate - Review Draft Executive Summary
The Impact of Policy Choices
Government policies could significantly decrease or increase future warming. The
warming suggested by the Slowly Changing and Rapidly Changing World cases is not inevitable; it
is the result of the public and private choices implicit in these scenarios. While some future warming
is locked in, there is a wide range of possibilities. It is prudent to begin to understand what impact
alternative economic development strategies might have on future warming.
Scenarios with Stabilizing Policies
Two alternative scenarios were constructed to explore the impact of policy choices aimed at
reducing the risk of global wanning. These scenarios, labelled Slowly Changing World with
Stabilizing Policies (SCWP) and Rapidly Changing World with Stabilizing Policies (RCWP) start with
the same economic and demographic assumptions used in SCW and RCW scenarios, respectively, but
assume that government leadership is provided to ensure that limiting greenhouse gas emissions
becomes a consideration in investment decisions beginning in the 1990s. We assume that policies to
promote energy efficiency in all sectors succeed in substantially reducing energy demand relative to
the No Response scenarios (which already assume substantial efficiency improvements). We also
assume that efforts to expand the use of natural gas increase its share of primary energy supply
relative to other fossil fuels in the near term. Research and development investments in non-fossil
energy supply options such as photovoltaics (solar cells) and biomass-derived fuels (fuels made from
plant material) assure that these options are available and begin to become competitive after 2000.
As a result, non-fossil energy sources meet a substantial fraction of total demand in later periods.
The existing protocol to reduce CFC and halon emissions is assumed to be strengthened, leading to
a phase-out of fully-halogenated compounds and a freeze on methyl chloroform. A global effort to
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reverse deforestation transforms the biosphere from a source to a sink for carbon by 2000, and
technological innovation and controls reduce agricultural, industrial, and transportation emissions.
While the same general emissions reduction strategies are assumed in both the SCWP and
RCWP cases, the degree and speed of improvement are higher in the RCWP scenario because
technological innovation and capital stock replacement are greater in this case. The policies
considered in these scenarios do not require changes in basic life styles. For example, energy use
in buildings is greatly reduced in the Stabilizing Policy scenarios relative to the No Response
scenarios, but the floor space available per person and the amenity levels provided are assumed to
be the same. Similarly, the automobile efficiency assumptions are not inconsistent with the size
distribution of the current vehicle fleet.
The impact of these policy assumptions is a substantial reduction in the rate of greenhouse gas
buildup, but not a complete stabilization of the atmosphere (Figure 5). Carbon dioxide
concentrations increase gradually throughout the time frame of the analysis despite declining
emissions, reaching a level 65% greater than preindustrial values by 2100, or approximately one-third
higher than current levels. Methane concentrations increase through about 2025, after which they
level off and decline to roughly 1985 levels by 2100. Weighted CFC concentrations also increase
rapidly at first, but they are relatively stable after about 2010. Nitrous oxide concentrations increase
by an amount 40-50% less than the amount of increase in the RCW and SCW cases.
The calculated rate of climatic change in the Stabilizing Policy scenarios is
between 0.6 and 1.4°C per century, or at least 60% less than in the corresponding
worlds without a policy response to potential climatic change. Global temperatures in the
SCWP case increase by 0.4-0.8°C from 2000 to 2050 and 0.6-1.1°C from 2000 to 2100; corresponding
values are 0.5-0.9°C and 0.8-1.4°C in the RCWP case (Figure 7). Total equilibrium warming
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FIGURE 7
REALIZED WARMING:
NO RESPONSE AND STABILIZING POLICY SCENARIOS
(Degrees Celsius; 2.0 - 4.0 Degree Climate Sensitivity)
Slowly Changing Scenarios Rapidly Changing Scenarios
V)
ut
o
w
ut
o
Ul
1985 2000 2025 2050 2075 2100
YEAR
I
J_
1985 2000 2025 2050 2075 2100
YEAR
Figure 7. Shaded areas represent the range based on an equilibrium climate sensitivity to doubling
C02of2-4°C. S
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commitment reaches 1.4-2.8°C by 2100 in the SCWP case and 1.7-3.3°C in the RCWP case, assuming
the climate sensitivity is 2-4°C. Given the possibility that the climate sensitivity could be higher and
that there could be large positive biogeochemical feedbacks that are not included in these calculations,
there is a possibility that even the Stabilizing Policy scenarios could lead to extremely high climatic
change. It is also possible that the policies assumed in these scenarios could limit climatic change
to about 1"C if the true climate sensitivity of the Earth is low.
If the risk of substantial climate change associated with the SCWP and RCWP scenarios is judged
to be unacceptable, more aggressive policies will be required. Therefore we have constructed a Rapid
Reduction case that examines the effect of measures that might be imposed to supplement those
measures already analyzed in the RCWP scenario. This case implies that strategies that rapidly
reduce greenhouse gas emissions are adopted beginning in 1990 (see below). In this scenario realized
wanning is limited to less than 2°C and the warming trend is reversed in the middle of the next
century. All of the scenario estimates for realized and equilibrium wanning are tabulated in Table
4 (including the results of an "Accelerated Emissions" scenario defined below).
The Relative Impact of Various Options On Future Warming
No single activity is the dominant source of greenhouse gases; therefore, no single
measure can stabilize global climate. Many individual components, each having a
modest impact on greenhouse gas emissions, can have a dramatic impact on the rate
of climatic change when combined. This is illustrated in Figures 8 and 9, which show the
impact of the key measures that account for the difference between the RCW, RCWP, and Rapid
Reduction cases. To reduce the amount of global warming to the rates projected in the RCWP and
Rapid Reduction cases, Table 5 lists several policies that might have to be adopted by 2000 to begin
DRAFT - DO NOT QUOTE OR CITE 32 February 21, 1989
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Executive Summary
TABLE 4
Scenario Results For Realized And Equilibrium Warming
(Degrees Centigrade)
Realized Warming - 2°C Sensitivity
Accelerated Emissions
RCW
sew
RCWP
SCWP
Rapid Reduction
Realized Warming - 4°C Sensitivity
Accelerated Emissions
RCW
sew
RCWP
SCWP
Rapid Reduction
Equilibrium Wanning Commitment - 2°C Sensitivity
Accelerated Emissions
RCW
sew
RCWP
SCWP
Rapid Reduction
Equilibrium Warming Commitment - 4°C Sensitivity
Accelerated Emissions
RCW
sew
RCWP
SCWP
Rapid Reduction
1985
0.5°C
0.5
0.5
0.5
0.5
0.5
1985
0.5
0.5
0.5
0.5
0.5
0.5
1985
0.7
0.7
0.7
0.7
0.7
0.7
1985
1.5
1.5
1.5
1.5
1.5
1.5
2000
o.rc
0.7
0.7
0.6
0.6
0.6
2000
1.0
0.9
0.9
0.9
0.9
0.9
2000
1.1
1.1
1.0
1.0
1.0
1.0
2000
2.2
2.1
2.1
2.0
1.9
1.9
2025
1.5°C
1.2
1.1
0.9
0.9
0.8
2025
2.1
1.7
1.7
1.4
13
13
2025
2.4
1.7
1.6
1.3
1.2
1.1
2025
4.7
3.5
3.3
2.5
2.4
2.1
2050
2.8°C
1.9
1.6
1.1
1.0
0.8
2050
4.1
2.8
25
1.8
1.7
1.4
2050
4.3
2.7
2.2
1.5
1.3
1.0
2050
>6
5.4
4.5
2.9
2.7
2.0
2075
45°C
2.7
2.0
1.3
1.2
0.8
2075
>6
4.1
3.2
2.1
1.9
13
2075
>6
3.8
2.7
1.6
1.4
.9
2075
>6
>6
5.4
3.2
2.8
1.7
2100
>6°C*
3.6
2.5
1.4
1.2
0.7
2100
>6
5.6
4.0
2.3
2.0
1.2
2100
>6
4.8
3.1
1.7
1.4
.7
2100
>6
>6
>6
3.3
2.8
1.3
* Estimates of warming greater than 6°C represent extrapolations beyond the range tested in most
climate models.
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STABILIZING POLICY STRATEGIES:
DECREASE IN EQUILIBRIUM WARMING COMMITMENT
a
1. CFC Phaseout
2. Reforestation
3. Improved Transportation
Efficiency0
4. Other Efficiency Gains
5. Energy Emissions Fee9
6. Promote Natural Gas
9
7. Emission Controls
8. Solar Technologies
9. Commercialized Blomass
10. Agriculture, Landfills,
and Cement
11. Promote Nuclear
k
Power
Percent Reduction Relative to RCW Scenario
RCWP (Simultaneous
Implementation of 1-11)
2050
2100
10 15
Percent
20
25
65%
Figure 8. The impact of individual measures on the equilibrium warming commitment in the RCW
scenario The simultaneous implementation of all the measures represents the RCWP scenario.
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FIGURE 8 - NOTES
Impact Of Stabilizing Policies On Global Warming
" A 100% phaseout of CFCs by 2003 and a freeze on methyl chloroform is imposed. There is 100%
participation by industrialized countries and 94% participation in developing countries.
b The terrestrial biosphere becomes a net sink for carbon by 2000 through a rapid reduction in
deforestation and a linear increase in the area of reforested land and biomass plantations. Net CO2
uptake by 2025 is 0.7 Pg C per year.
c The average efficiency of new cars in the U.S. reaches 40 mpg (5.9 liters/100 km) by 2000. Global
fleet-average automobile efficiency reaches 50 mpg by 2025 (4.7 liters/100 km).
d The rate of energy efficiency improvements in the residential, commercial, and industrial sectors
are increased about 0.1-0.2 percentage pobts by 2025 compared to the RCW, and about 03-0.4
percentage points annually from 2025-2100.
' Emission fees are placed on fossil fuels in proportion to carbon content. Maximum production
fees (1985$) were $0.50/GJ for coal, $036/GJ for oil, and S023/GJ for natural gas. Maximum
consumption fees were 28% for coal, 20% for oil, and 13% for natural gas. These fees increased
linearly from zero, with maximum consumption fees charged by 2025 and maximum production fees
charged by 2050.
' Assumes that economic incentives accelerate exploration and production of natural gas, reducing
the cost of locating and producing natural gas by an annual rate of .5% relative to the RCW
scenario. Incentives for gas use for electricity generation increases gas share by 5% in 2025 and
10% thereafter.
1 Assumes more stringent NOX and CO controls on mobile and stationary sources including all gas
vehicles using three-way catalysts in OECD countries by 2000 and in the rest of the world by 2025
(new light duty vehicles in the rest of the world uses oxidation catalysts from 2000 to 2025); from
2000 to 2025 conventional coal boilers used for electricity generation are retrofit with low NO,
burners, with 85% retrofit in the developed countries and 40% in developing countries; starting in
2000 all new combustors used for electricity generation and all new industrial boilers require selective
catalytic reduction in the developed countries and low NOX burners in the developing countries, and
after 2025 all new combustors of these types require selective catalytic reduction; other new industrial
non-boiler combustors such as Kilns and Dryers require low NOX burners after 2000.
h Assumes that low-cost solar technology is available by 2025 for as little as 4.6 cents/kwh.
1 Assumes the cost of producing and converting biomass to modern fuels reaches $4.00/gigajoule
(1985$) for gas and $6.00/gigajoule (1985$) for liquids. The maximum amount of liquid or gaseous
fuel available from biomass is 210 exajoules.
' Assumes that research and improved agricultural practices result in an annual decline of 0.5% in
the emissions from rice production, enteric fermentation, and fertilizer use. CH4 emissions from
landfills are assumed to decline at an annual rate of 2% in developed countries due to policies aimed
at reducing waste and landfill gas recovery; emissions in developing countries continue to grow until
2025 then remain flat due to incorporation of the source policies. Technological improvements reduce
demand for cement by 25%.
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Policy Options for Stabilizing Global Climate •- Review Draft Executive Summary
FIGURE 8 - NOTES (Continued)
Impact Of Stabilizing Policies On Global Wanning
k Assumes that the cost of nuclear technology declines by 0.5% per year.
1 Impact on warming when all the above measures are implemented simultaneously. The sum of
each individual reduction in warming is not precisely equal to the difference between the RCW and
RCWP cases because not all the strategies are strictly additive.
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Executive Summary
RAPID REDUCTION STRATEGIES:
ADDITIONAL DECREASE IN EQUILIBRIUM WARMING COMMITMENT
1. Carbon Fee
2. Consumption Tax
3. High MPG Cars
4. High Efficiency
Buildings d
5. High Efficiency
Powerplants8
6. High Blomass
7. Coal Phaseout
g
8. Rapid Reforestation
Rapid Reduction Scenario
(Simultaneous
Implementation of 1-8)
Additional Percent Reduction
Relative to RCW Scenario
2050
2100
10
15
20
25
Percent
Figure 9. The impact of additional measures applied to the RCWP scenario expressed as percent
change relative to the equilibrium wanning commitment in the RCW scenario. The simultaneous
implementation of all the measures in combination with the measures in the RCWP scenarios
represents the Rapid Reduction scenario.
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FIGURE 9 - NOTES
Impact Of Rapid Reduction Policies On Global Warming
1 High carbon emissions fees are imposed on the production of fossil fuels in proportion to the CO2
emissions potential. In this case, fees of $8.50/GJ were imposed on unconventional oil production,
$5.70/GJ on coal, $2.30/GJ on oil, and $1.10/GJ on natural gas. These fee levels are specified in
1985$ and are phased in over the period between 1985 and 2050.
b A percentage excise tax, proportional to the carbon content of the fuel, was levied on fuel use.
Consumption taxes were also imposed in the RCWP case. In this case, the tax on coal consumption
was increased from 28% of the price to 40%; the tax on oil use was increased from 20% to 30%;
the tax on natural gas use was increased from 13% to 20%; the tax on electricity use was increased
from 0 to 5%. These taxes were phased in and fully applied by 2025.
c Assumes that the average efficiency of new cars in the U.S. reaches 50 mpg (4.7 liters/100 km) in
2000 and that global fleet-average auto efficiencies reach 65 mpg in 2025 (3.6 liters/100 km) and 100
mpg (2.4 liters/100 km) in 2050.
d Assumes that the rate of technical efficiency improvement in the residential and commercial sectors
improves substantially beyond that assumed in the RCWP case. In this case, the rate of efficiency
improvement in the residential and commercial sectors is increased so that a net gain in efficiency
of 50% relative to the RCWP case is achieved in all regions.
" Assumes that, by 2050, average power plant conversion efficiency improves by 50% relative to the
RCWP case. In this scenario the design efficiencies of all types of generating plants improve
significantly. For example, by 2025, oil-fired generating stations achieve an average conversion
efficiency roughly equivalent to that achieved by combined-cycle units today.
' The availability of commercial biomass was doubled relative to the assumptions in the RCWP case.
In this case the rate of increase in biomass productivity is assumed to be at the high end of the range
suggested by the U.S. DOE Biofuels Program. Conversion costs were assumed to fall by half relative
to the assumptions in the RCWP case.
g Environmental fees of about $20/GJ (in 1985$) are phased in by 2050. This has the effect of
gradually making coal uncompetitive in utility markets.
h A rapid rate of global reforestation is assumed. In this case deforestation is halted by 2000 and
the biota become a net sink for CO2 at a rate of about 1 Pg C per year by 2025, about twice the
level of carbon storage assumed in the RCWP case.
1 Impact on warming when all of the above measures are implemented simultaneously. The impact
is much less than the sum of the individual components because many of the measures are not
additive.
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Policy Options for Stabilizing Global Climate - Review Draft Executive Summary
TABLES
Examples Of Policy Responses By The Year 2000
RCWP Case
• New automobiles in the U.S. average 40 mpg
• New automobiles in the OECD use 3-way catalytic converters to reduce CO and NO, (current
U.S. standard); rest of world uses an oxidation catalyst
• Average space heating requirements of new single family homes are 50% below 1980 new home
average
• Net global deforestation stops
• CFCs are phased out; production of methyl chloroform is frozen
• Emission fees are placed on fossil fuels in proportion to carbon content~$2.50/ton on coal,
$0.50/barrel on oil, $0.05/thousand cubic feet on natural gas
• Research and development into solar photovoltaic technology allows solar to compete with oil
and natural gas (DOE long-term policy goals)
• Available municipal solid waste and agricultural wastes are converted to useful energy
• Biomass energy plantations increase current productivity by 65% (to 25 dry tons/hectare
annually)
Rapid Reduction Case
• New automobiles in the U.S. average 50 mpg
• Major retrofit initiatives reduce energy use in existing commercial buildings by 40%
« Average space heating requirements of new single family homes are 90% below 1980 new home
average
• Global deforestation stops; Major reforestation programs undertaken
• CFCs are phased out; production of methyl chloroform is frozen
• Emission fees are placed on fossil fuels in proportion to carbon content~$29/ton on coal,
$3.25/barrel on oil, $0.25/thousand cubic feet on natural gas
• Commercialization incentives lead to significant market penetration for solar technologies
• 250 million hectares globally are committed to biomass energy plantations, i.e., 5% of forest and
woodland area
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Policy Options for Stabilizing Global Climate - Review Draft Executive Summary
reducing greenhouse gas emissions. These policies are meant to illustrate potential policy responses;
a variety of policy combinations might achieve the reductions in global warming estimated in each
case.
This analysis suggests that accelerated energy efficiency improvements, reforestation,
modernization of biomass use, and carbon emissions fees could have the largest impact on the rate
of climatic change over the next few decades. In the long run, advances in solar technology and
biomass plantations also play an essential role. The measures that reduce the wanning to the
greatest extent in the Rapid Reduction case relative to the RCWP case are those that change the fuel
mix For example, imposing stiff carbon fees on the production of fossil fuels, and increasing the
assumed level of biomass availability. Table 4 indicates that only the most aggressive policy case
ensures that the rate of warming will be below a tenth of a degree Celsius per decade. This is still
about twice the average rate of wanning experienced over the last century.
Because of the large potential for growth in their emissions, the participation of
developing countries is crucial for stabilizing greenhouse gases. Increasing the availability
of energy services is a high priority for developing countries attempting to meet basic human needs.
Increased energy use in developing countries could lead to dramatic increases in greenhouse gas
emissions unless stabilizing policies are adopted. The share of greenhouse gas emissions arising from
developing countries (weighted by their estimated impact on global wanning) increases from about
40% currently to 50% by 2025 and almost 60% by 2100 in the RCW scenario; the developing
countries' contributions in greenhouse gas emissions also rise to about 50% in the SCW (Figure 10).
We examined the implications for global warming if industrialized countries adopted climate stabilizing
policies without the participation of developing countries. Stabilizing policies adopted by industrialized
countries, however, are likely to affect the development path of other countries even if these other
countries do not explicitly adopt such policies. Therefore, we assumed that technological diffusion
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Policy Options for Stabilizing Global Climate - Review Draft
Executive Summary
FIGURE 10
SHARE OF GREENHOUSE GAS EMISSIONS BY REGION
sew
SCWP
2026 2060
VEAR
(Percent)
1986 2000 2026 2050 2076 2100
207C 2100
RCW
Other Developing
Chin, k CP Aii»
USSR » CP Europe
Reil of OECD
United Stetes
1986 2000 2025 2050 2075 2100
RCWP
202S 20CO
VEAR
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Policy Options for Stabilizing Global Climate - Review Draft Executive Summary
would result in energy efficiency improvements in developing countries at a rate between the rates
assumed in the No Response and Stabilizing Policy cases. Some other factors, such as when the
cost of solar energy becomes competitive in developing countries, were also assumed to be between
the assumptions in these two scenarios. With these assumptions, equilibrium warming commitment
in 2050 is about 40% higher compared to the scenarios with global cooperation (Figure 11). This
implies that action by industrialized countries on their own can significantly slow the rate and
magnitude of climate change, but that without the participation of the developing countries, the risk
of substantial global warming remains.
Delaying the policy response to the greenhouse gas buildup would substantially
increase the global commitment to future warming. The Stabilizing Policy cases and the
Rapid Reduction case both assume that starting in 1990 action is taken to begin reducing the rate
of greenhouse gas buildup, and that significant policies are in force by 2000. It has been suggested
that any response should be delayed until the current level of scientific uncertainty is substantially
reduced. The impact of such a course was investigated by assuming that industrialized countries delay
action until 2010 and that developing countries delay action until 2025. Once action is initiated,
policies are assumed to be implemented at roughly the same rate as hi the Stabilizing Policy cases.
The result is a significant increase in global warming (Figure 12): The equilibrium warming
commitment in 2050 increases by about 40% compared to the scenarios with policy implementation
beginning in 1990.
Government policies could also significantly exacerbate climate change. Decisions
that will be made in the near future may lead to increased emissions if there is no clear policy goal
to reduce them. This possibility is illustrated by a set of tests that were conducted starting with the
RCW scenario. In this "Accelerated Emissions" case, several key parameters were varied as proxies
DRAFT - DO NOT QUOTE OR CITE 42 February 21, 1989
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Executive Summary
FIGURE 11
INCREASE IN REALIZED WARMING
WHEN DEVELOPING COUNTRIES DO NOT PARTICIPATE
(Degrees Celsius; Based on 3.0 Degree Sensitivity)
SLOWLY CHANGING WORLD
RAPIDLY CHANGING WORLD
2 3
w
UJ
o
M
UJ
UJ
-------
Policy Options for Stabilizing Global Climate - Review Draft
Executive Summary
w
| 3
W
o
V)
5 2
FIGURE 12
INCREASE IN REALIZED WARMING
DUE TO GLOBAL DELAY IN POLICY ADOPTION
(Degrees Celsius; Based on 3.0 Degree Sensitivity)
Slowly Changing World
Rapidly Changing World
SCW
Global Delay
SCWP
4 -
RCW
Global Delay /
RCWP
1985 2000 2025 2050 2075 2100 1985 2000 2025 2050 2075 2100
YEAR YEAR
Figure 12. Assumes that industrialized countries delay action until 2010 and that developing countries
delay action until 2025. Once action is initiated, policies are assumed to be implemented at roughly.
the same rate as in the Stabilizing Policy cases.
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for currently proposed policies (e.g., accelerated development of synfuels) or the possible
consequences of government inaction or failure (e.g., high use of CFCs and deforestation).
Figure 13 summarizes the results of these tests as compared with the RCW scenario. The
results are illustrated in terms of the incremental effect of each policy outcome on the equilibrium
warming commitment in 2050 and 2100. Figure 13 indicates that the measures that amplify the
warming to the greatest extent are those that reduce the rate of efficiency improvement, reduce the
cost of synfuels, and increase the assumed rate of growth in CFC production and use. Policies
leading to accelerated deforestation would have a large impact in the near term, but a relatively small
impact on the result in 2100. The impact of all of these policies in combination could be to increase
the equilibrium warming commitment in 2050 by 60% compared with the RCW scenario.
Sensitivity of Results to Alternative Assumptions
Many factors could increase or decrease future warming. The specific estimates of
climatic change presented above are subject to a variety of uncertainties involving technological and
economic assumptions as well as the response of the Earth-atmosphere system to perturbations.
Many uncertainties regarding the response of the climate system, such as the role of clouds and
sea ice changes, can be reflected by varying the climate sensitivity parameter. The results presented
above were based on a central estimate of 2-4°C for the equilibrium wanning from a doubling of
the concentration of carbon dioxide. Broadening this range to 1.5-5.5°C has one of the largest
impacts on estimates of future warming (Figure 14). In the RCW scenario the range of realized
warming in 2050 increases from 1.9-2.8°C to 1.5-3.2°C; the impact on equilibrium warming is much
greater, increasing the range of the commitment estimated in 2050 from 2.7-5.4°C to 2.0-7.4°C.
DRAFT - DO NOT QUOTE OR CITE 45 February 21, 1989
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Executive Summary
FIGURE 13
ACCELERATED EMISSIONS CASES:
PERCENT INCREASE IN EQUILIBRIUM WARMING COMMITMENT
1. High CFC Emissions'
2. Cheap Coal
3. Cheap Synf uels
4. Slow Efficiency
Improvements'
5. High Deforestation
6. High-Cost Solar
7. High-Cost Nuclear
Accelerated Emissions
(Combination of 1-8)
Percent Increase From RCW Scenario
2050
2100
j i I i I i I i I i | i I i I i
-10 0 10 20 30 40 50 60 70 80
Percent
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Policy Options for Stabilizing Global Climate - Review Draft Executive Summary
FIGURE 13 - NOTES
Impact Of Accelerated Emissions Policies On Global Warming
* Assumes a low level of participation in and compliance with the Montreal Protocol. The
assumptions used in this case are similar to those used in the "Low Case" analysis described in the
EPA's Regulatory Impact Assessment report.
b Assumes that advances in the technology of coal extraction and transport rapidly reduce the market
price of coal at the burner tip. In the RCW scenario, the economic efficiency of coal supply is
assumed to improve at a rate of approximately 0.5% per year. In this case, it is assumed to improve
at a rate of 1% per year.
0 Assumes that the price of synthetic oil and gas could be reduced by 50% and commercialization
rapidly accelerated relative to the RCW case. This case assumes that the minimal production price
for synfuels can be achieved in 20 years rather than the 30 years assumed in the RCW case.
d Assumes that technical gains in the engineering efficiency of energy use occurs only half as rapidly
as assumed in the RCW case. In the RCW case it is assumed that efficiency improves at rates of
approximately 1-2% per year. In the Slow Improvement case the assumed rates were reduced to
only 05-1.0% per year. The lower rate of improvement is similar to the assumptions in recent
projections for the Department of Energy's National Energy Policy Plan.
' Assumes annual deforestation increases at a rate equal to the rate of growth in population.
( Assumes that solar energy remains so expensive that the possibility of its making any significant
contribution to global energy supply is precluded.
* Assumes that the cost of electricity from fission electric systems becomes so high that their
contribution to global energy supply is permanently limited. In this case, an environmental tax of
about $40 (1985$) per gigajoule (GJ) on the price of electricity supplied by nuclear power plants was
phased in by 2050.
h All of the above assumptions were combined in one scenario. The result is not equal to the sum
of the warming in the RCW and the eight individual cases because of interactions among the
assumptions.
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Executive Summary
FIGURE 14
IMPACT OF CLIMATE SENSITIVITY ON
REALIZED WARMING
(Degrees Celsius; 1.5-5.5 Degree Climate Sensitivity)
Slowly Changing World Scenario
Rapidly Changing World Scenario
I
I
I
5.5
4.0
2.0
1.5
1985 2000 2025 2050 2075 2100 1985 2000 2025 2050 2075 2100
YEAR YEAR
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There is a similar impact on warming estimates in the SCW. The sensitivity of the results from the
RCW scenario to a wide range of other assumptions has been tested; the results are summarized in
Table 6.
A variety of factors related to technology, resources, and emissions factors could significantly
influence the projected warming. Of these factors, the largest impacts are due to assumptions that
affect the relative price of coal and non-fossil fuels in the future. If, in the absence of policies, non-
fossil technology decreased in price much faster than we assumed in the RCW, or coal prices
increased much faster than we assumed in the RCW, then warming in 2100 could be as much as one-
fourth lower than calculated for this scenario. The impact of increasing the assumed availability of
oil and gas was surprisingly low. Larger supplies led to greater total demand and reductions in the
share of energy supplied by coal and non-fossil fuels; these factors in combination left greenhouse
gas emissions and estimated wanning almost unchanged. Had the assumed increase in gas availability
been coupled with policies intended to encourage its use as a transition fuel to a non-fossil world,
then a much larger impact may have been seen. Current sources of methane and nitrous oxide are
quite uncertain, but these uncertainties appear to have only a modest impact on projected warming:
up to 5% in the case of methane.
The oceans and biosphere play a major and highly uncertain role in the climate
system. Their ability to absorb CO2 and heat is a key determinant of the rate and magnitude of
climatic change (Table 6). Alternative formulations of carbon dioxide absorption by the ocean and
any other carbon sinks have a significant impact on estimated climatic change. A variety of ocean
models with very different structure produced similar estimates of future carbon dioxide
concentrations, with the exception of the outcrop (Siegenthaler) model, which calculated lower
concentrations in 2100; if this model were correct, the equilibrium warming commitment in 2100
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Policy Options for Stabilizing Global Climate ~ Review Draft
TABLE 6
Sensitivity Analysis: Impact on Realized Warming
and Equilibrium Warming
(Percent change from RCW scenario)*
Executive Summary
Sensitivity Case
Assumptions
2050
2100
Realized
Equilibrium
Realized
Equilibrium
TECHNOLOGY, RESOURCES, AND EMISSION FACTORS
-6 to -13% -9 to -17%
Low Cost Non-Fossil
Technology"
-10
1
-3 to 4
Fossil Resources
High Coal Price6
High Oil Supply"1
High Gas Supply*
Alternative Starting
Methane Budgets
N2O From Fertilizer
High Emissions From
Anhydrous Ammonia8
High Emissions From
Fertilizer Leaching"
High N2O From
Combustion1
High Initial Biomass
On Cleared Land"
OCEAN COZ AND HEAT UPTAKE
Alternative CO2 Modelsk
Oeschger et al.1
Bolin et al.m
Bjorkstrom"
Siegenthaler0
-16 to -25%
-3 to 5
-3 to 5
-3
-3
-3
-3
-19 to -26%
-14
<-l to 1
1
-23
-1
-26
-2
-3 to 5
0 to
-0.1
0
-0.1
to 0
2
0
0 to -0.1
0 to 0.1
2
0
0
0
1
0
0
0
1
-4
-4
-4
-12
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TABLE 6 (continued)
Sensitivity Analysis: Impact on Realized Warming
and Equilibrium Warming
(Percent change from RCW scenario)*
Executive Summary
Sensitivity Case
Assumptions
Alternative Unknown
Sink Assumptions'9
Heat Diffusion Rateq
2°C Sensitivity
4°C Sensitivity
Realized
-7 to 3
-17 to 11
-23 to 17
ATMOSPHERIC CHEMISTRY MODEL
CFC-11 Lifetime'
Chlorine/Col O3
Parameter"
Trop O3/CH4
Parameter'
OH/NO, Parameter"
FEEDBACKS
Ocean Circulation
Surprise"
2°C Sensitivity
4°C Sensitivity
CH< Hydrate and Wetland
Emissions*
2°C Sensitivity
4°C Sensitivity
Ocean Mixing, CH4
Emissions, Terrestrial
Biota"
2°C Sensitivity
4°C Sensitivity
-0.1 to 0.1
-4
1
-1 to 1
0
49
10
15
19
33
2050
Equilibrium
-8 to 3
0
0
ASSUMPTIONS
-0.1 to 0.1
-6
1
-2 to 1
0
4
11
16
14
31
Realized
-13 to 3
-14 to 9
-21 to 16
-0.1 to 0.1
-8
1
-2 to 1
35
62
12
18
22
43
2100
Equilibrium
-14 to 3
0
0
-0.1 to 0.1
-8
1
-2 to 1
4
11
12
19
15
33
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TABLE 6 - NOTES
* The percent changes are independent of the assumed climate sensitivity except where noted.
b These ranges represent modest to optimistic assumptions about future commercial availability of
non-fossil technologies, e.g., solar photovoltaics, advanced nuclear power designs, and synthetic
fuel production from biomass. Solar photovoltaic costs decline to 4.6 cents/kwh (1985$) by 2020
in the optimistic scenario and by 2050 in the modest assumptions. Nuclear costs decline at an
annual rate of 0.5% in the optimistic assumptions and remain relatively flat in the modest
assumptions compared to an overall growth of 1.5 cents/kwh assumed in the RCW scenario.
Assumes that the cost of producing and converting biomass to modern fuels reaches
$4.00/gigajoule for gas and $6.00 (gigajoule) for liquids by 2020 in the optimistic assumptions and
by 2050 in the modest assumptions. The total amount of fuel available from biomass is 210
exajoules.
0 The impact of an escalation hi coal prices above the RCW case by about 1% annually from 1985
to 2100.
d The impact of an increase in global oil resources to 25,000 exajoules, more than double the
estimate in the RCW case, assuming proportionate increases in resource availability at each cost
level.
" The impact of an increase in global natural gas resources to 27,000 exajoules, more than 25
times the estimate in the RCW case, assuming proportionate increases in resource availability at
each cost level.
' These ranges represent assumptions about the relative sizes of anthropogenic versus non-
anthropogenic sources of methane emissions thereby affecting growth in emissions over time, i.e.,
high emission levels (373 Tg CH4) from anthropogenic activities such as fuel production and
landfilling with low emission levels (137 Tg CH4) from natural processes such as oceans and
wetlands, versus low anthropogenic emissions (245 Tg CH4) with high natural emissions (265 Tg
CH4).
8 The impact of elevating the emission coefficient for the anhydrous ammonia fertilizer type (the
percent of N evolved as N2O) from 0.5% to 2.0%.
h The impact of assuming additional N2O emissions from fertilizer leaching into surface water and
ground water, modeled by increasing all the fertilizer emission coefficients by 1 percentage point.
1 The impact of higher emission coefficients for N2O from combustion; assumes that N2O emissions
are about 25% of NO, emissions, thus the N2O emissions from combustion sources in 1985
equaled 2.3 Tg N, over two times the level assumed in the RCW case.
J The impact of assuming a higher estimate for the amount of carbon initially contained in forest
vegetation and soils (roughly a 50-100% increase) and a more rapid rate of change in land use,
resulting hi carbon emissions of 281 Pg from 1980 to 2100 compared with 188 Pg C in the RCW
scenario.
k Realized warming was not calculated in these tests.
1 This box-diffusion model represents the turnover of carbon below 75 meters as a purely diffusive
process.
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TABLE 6 - NOTES (continued)
m This is a 12-compartment regional model which divides the Atlantic and Pacific-Indian Oceans
into surface-, intermediate-, deep-, and bottom-water compartments and divides the Arctic and
Antarctic Oceans into surface- and deep-water compartments.
" This is an advective-diffusive model that divides the ocean into cold and warm compartments;
water downwells directly from the cold surface compartment into intermediate and deep layers.
0 An outcrop-diffusion model that allows direct ventilation of the intermediate and deep oceans
in high latitudes by incorporating an outcrop connecting all sublayers to the atmosphere.
p These ranges represent the impact of alternative assumptions about the "unknown carbon sink"
that absorbs the unaccounted-for carbon in the carbon cycle. Two sensitivities were analyzed:
1) a high case, where the size of the unknown sink increases at the same rate as atmospheric
CO2 levels compared with preindustrial levels; and 2) a low case, where the size decreases to
zero exponentially at 2% per year.
q Heat diffusion in the oceans is modeled as a purely diffusive process. To capture some of the
uncertainty regarding actual heat uptake, the base case eddy-diffusion coefficient of 0.55x10"*
m2/sec was increased to 2x10"* and decreased to 2xlO"5 m /sec. Climate sensitivity had a
measurable effect on these results, so this impact is illustrated as well.
' The atmospheric lifetime of CFC-11, 65 years b the RCW case, was varied from 55 to 75 years.
Increases or decreases in the atmospheric concentration of CFC-11, however, tend to be offset
by corresponding decreases or increases in atmospheric concentrations of other trace gases, such
as other CFCs and CH4.
' The amount of stratospheric ozone depletion due to the chlorine contained in CFCs was
increased from 0.03% to 0.20% decline in total column ozone/(ppb)2 of stratospheric chlorine.
' The rate at which tropospheric ozone forms as a result of CH4 abundance is estimated with a
parameter in the atmospheric composition model. In the RCW case, this variable for the
Northern Hemisphere is a 2% change in tropospheric ozone for each percentage change in CH4
concentration; it was changed to 0.4% in the sensitivity analysis.
u Tropospheric OH formation is affected by the level of NOX emissions. A 0.1% OH change for
every 1% change in NO, emissions for the Northern Hemisphere was assumed in the RCW case;
in the sensitivity analysis, a range of 0.05% to 0.2% was evaluated.
v For this analysis we assumed that a 2°C increase in realized warming would alter ocean
circulation patterns sufficiently to shut off net uptake of CO2 and heat by the oceans.
w We assumed that with each 1°C increase in temperature, an additional 110 Tg CH4 from methane
hydrates, 12 Tg CH4 from bogs, and 7 Tg CH4 from rice cultivation would be released annually.
* This case illustrates the combined impact of several types of biogeochemical feedbacks: 1)
methane emissions from hydrates, bogs, and rice cultivation (see footnote above); 2) increased
stability of the thermodine, thereby slowing the rate of heat and CO2 uptake of the deep ocean
by 30% due to less mixing; 3) vegetation albedo, which is a decrease in global albedo as a result
of changes in the distribution of terrestrial ecosystems by 0.06% per 1°C warming; 4) disruption
of existing ecosystems, resulting in transient reductions in biomass and soil carbon at the rate of
0.5 Pg C per year per 1°C warming; and 5) CO2 fertilization, which is an increase in the amount
of carbon stored in the biosphere in response to higher CO2 concentrations by 0.3 Pg C per ppm.
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would be 12% lower than the estimate for the RCW scenario. If higher CO2 concentrations greatly
fertilize the biosphere (removing some CO2 from the atmosphere), the equilibrium warming
commitment in 2100 could be reduced by as much as 14%. In our highly simplified model of the
ocean, heat uptake is controlled by a single diffusion parameter. Adjusting this parameter over a
wide but plausible range of values has a large impact on the rate of warming, decreasing the warming
realized in 2100 in the RCW scenario by 14-21% or increasing it by 9-16% (for a climate sensitivity
to doubled CO2 of 2-4°C).
A speculative, but potentially important suggestion, is that the role of the oceans could change
suddenly as one consequence of climatic change. To provide a preliminary indication of the
importance of this potential feedback process we have examined a hypothetical case in which warming
by 2°C triggers a change in ocean circulation that prevents the ocean from absorbing any additional
CO2 or heat. The result is a dramatic increase in realized wanning by 40 to 60% in 2100. Also
quite uncertain, but potentially important, are a number of other biogeochemical feedback processes,
such as release of methane contained in near-shore ocean sediments, changes in surface reflectivity
due to shifts in vegetation zones, and changes in biospheric carbon storage. Taken together, these
feedback processes could strongly amplify climatic change, increasing realized warming in 2100 by 20-
40% (assuming the climate sensitivity to doubled CO2 is 2-4°C) (Table 5).
EMISSIONS REDUCTION STRATEGIES BY ACTIVITY
Many individually modest sources are in combination responsible for the
greenhouse gas buildup. Anthropogenic emissions of greenhouse gases can be categorized as
arising from energy production and use, industrial activity (including the use of CFCs), agricultural
practices, and changes in land-use patterns (including deforestation) (Figure 15). It is useful to
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FIGURE 15
ACTIVITIES CONTRIBUTING TO GLOBAL WARMING
Energy Use
and Production
(57%)
CFCs
(17%)
Other Industrial
(3%)
Agricultural
Practices
(14%)
Land Use
Modification
(9%)
Figure 15. Estimated contribution to greenhouse warming for the 1980s, based upon each activity's
share of greenhouse gas emissions, weighted by the greenhouse gas contributions to global warming
shown in Figure 3.
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examine current and potential future emissions and technical and policy options available for reducing
emissions in each of these sectors individually.
Energy Production and Use
Past. Present, and Future Emissions
The largest single factor affecting greenhouse gas emissions is the consumption of energy from
carbon-based fossil fuels. Between 1950 and 1985 annual global primary energy consumption grew
from 80 to 290 exajoules (EJ),2 and annual CO2 emissions grew from 1.6 to 5.2 petagrams of carbon
(Pg C).3 These CO2 emissions are the dominant reason for the increasing atmospheric concentrations
shown in Figure 1. Even though emissions have been relatively stable during the last decade,
atmospheric concentrations have continued their steady rise because CO2 emissions remain
substantially greater than uptake by the oceans and any other sinks.
The almost four-fold increase in energy consumption during the last 35 years was accompanied
by a significant shift in its global distribution. In 1950 countries belonging to the Organization for
Economic Cooperation and Development (OECD) consumed about three-fourths of all commercial
energy supplies, the centrally-planned economies of Europe and Asia, 19 percent, and developing
countries, 6 percent. By 1985 OECD countries consumed just over one-half of all commercial energy
globally, while the European and Asian centrally-planned economies and the developing countries had
increased their relative share to 32 percent and 15 percent, respectively.
2 One exajoule = 1018 joules = 0.95 quadrillion British Thermal Units = 0.95 Quad.
3 One petagram = 1015 grams.
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Developing and Eastern Bloc Countries are potentially large sources of future
emissions. Growth in energy use is driven almost entirely by countries outside the OECD in all
of the scenarios developed for this study. The OECD share of primary energy consumption falls to
25% by 2100 in the SCW and to as little as 17% in the RCW.4 Growth in demand outside the
OECD nonetheless drives up global energy demand significantly in these scenarios. Total end-use
energy demand increases from 220 EJ in 1985 to 320 EJ in 2025 in the SCW versus 420 EJ in the
RCW.5
Greater improvements in energy efficiency in the SCWP and RCWP cases reduce end-use
demand in 2025 by 13% and 15%, respectively, relative to the No Response scenarios. End-use
demand in the Rapid Reduction scenario is 20% lower than in the RCW by 2025. Increases in
energy efficiency account for about one-fourth of the wanning reduction in the RCWP versus the
RCW case in 2050.
While policies affecting demand will have the largest impact on near-term
greenhouse gas emissions, changes in the supply mix are also critical in influencing
emissions over the long term. Global primary energy supply is shown by source for the four
scenarios in Figure 16. Growth in primary energy consumption is substantially higher than growth
in end-use energy demand because of increased requirements for electricity and synthetic fuel
production, which involve substantial conversion losses. This is most dramatic in the RCW, where
4 Primary energy includes conversion losses, such as in electricity and synfuels production. The
primary energy equivalent of nuclear, hydro, and solar electricity is calculated on the basis of the
average efficiency of fossil-fuel-fired power plants.
5 End-use energy is based on final consumption, with electricity valued at 3.6 megajoules per
kilowatt-hour.
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FIGURE 16
PRIMARY ENERGY SUPPLY BY TYPE
(Exajoules)
SCW RCW
1986 2000 2025 20EO 2075 2100
198S 2000 2026 20SO 2076 2100
202E 20EO 207S 2100
RCWP
Reduction From
No A**pons«
Scenario
2076 2100
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primary energy consumption increases from 290 EJ in 1985 to 580 EJ in 2025 and 1410 EJ in 2100;
a 100% and 380% increase, respectively, compared with 90% and 260% increases in end-use demand.
Carbon dioxide emissions could grow by a factor of 2 to 5 during the next century
if Stabilizing policies are not adopted. Heavy reliance on coal in both the SCW and RCW
scenarios leads to large increases in both CO2 and CH4 emissions. In the SCW, energy-related
emissions of CO2 increase from 5.1 petagrams of carbon (Pg C) in 1985 to 7.2 Pg C in 2025 and 10.8
Pg C in 2100. Emissions reach more than twice this level in the RCW scenario: 10.1 and 24 Pg C
in 2025 and 2100, respectively. Emissions of CH4 from fuel production, predominantly coal mining,
grow even more dramatically. The estimated emissions from fuel production in 1985 are 60
teragrams of CH4 (Tg CH4) or just over 10% of the total.6 In the SCW this source increases to
86 Tg CH4 in 2025 and 160 Tg CH4 in 2100. The corresponding values for the RCW are 130 Tg
CH4 in 2025 and 360 Tg CH4 in 2100, about 20 and 30% of the total, respectively.
Technical options are available that, if adopted, could stabilize carbon dioxide
emissions. The combination of higher efficiency and greater reliance on non-fossil fuels assumed
in the Stabilizing Policy scenarios substantially curtails CO2 and CH4 emissions. In both the SCWP
and RCWP cases, CO2 emissions from energy use reach only 5.5 Pg C in 2025, after which time they
decrease, reaching 3.2 and 4.3 Pg C by 2100 in the two cases, respectively. Similarly, CH4 emissions
from fuel production remain relatively constant in both of these scenarios. Increased reliance on non-
fossil fuels in the RCWP is responsible for about one-fourth of the reduction in warming in this
scenario relative to the RCW in 2050.
6 1 teragram = 1012 grams.
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Despite the large range of outcomes illustrated by the four scenarios discussed here, none of the
global rates of change are unprecedented (Table 7). Global reductions in aggregate energy intensity
generally fall within the range of 1-2% per year; the lower value is consistent with long-term trends
and the higher value is consistent with recent experience. Reductions in the amount of carbon
emitted per unit of energy consumed (carbon intensity) varies from 0.0 to 1.3% per year with
significant declines only apparent in the Stabilizing Policy cases. These values are not unprecedented,
as carbon intensity declined by an average of 1.5% per year between 1925 and 1985 due to increased
reliance on oil and gas in preference to coal (but coal is expected to regain market share in the
future in the absence of policy changes).
Energy-related emissions, other than of CO2 and CH4, are strongly affected by the type of control
technology employed in addition to the total amount and type of energy used. Emissions of CO and
NOZ associated with energy use can be expected to increase almost as rapidly as primary energy
consumption in the absence of new policies. On the other hand, in the Stabilizing Policy scenarios,
NOX emissions are roughly constant and CO emissions are cut by more than half. This assumes that
the rest of the world gradually adopts control technology similar to that required of new mobile and
stationary sources in the United States today and that industrialized countries adopt standards
consistent with the use of Selective Catalytic Reduction or Inter-cooled Steam-Injected Gas Turbine
technology in utility and industrial applications after 2000, with developing countries following after
2025. Emission controls account for about 4% of the 2050 warming reduction in the RCWP relative
to the RCW.
Energy Technologies to Reduce Greenhouse Gas Emissions
The introduction of technologies and practices that use less energy to accomplish
a given task will have the largest impact on global wanning in the near term. We
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TABLE 7
Key Global Indicators for Energy and CO2
Parameter
GNP/capita
(1000 1988$)
Primary Energy
(EJ)
Fossil Fuel CO2
(PgC)
GNP/capita
(%/yr)
Energy/GNP
(%/yr)
Fossil Fuel COj/Energy
(%/yr)
Scenario 1985
SCW, SCWP 3.0
RCW, RCWP
SCW 290
RCW
SCWP
RCWP
SCW 5.1
RCW
SCWP
RCWP
SCW, SCWP
RCW, RCWP
SCW
RCW
SCWP
RCWP
SCW
RCW
SCWP
RCWP
2025
3.7
6.7
430
580
380
520
7.2
103
55
1985-2025
0.5
2.0
-1.1
-1.6
-13
-1.9
-0.1
0.0
-05
-1.3
2100
7.1
35.6
680
1410
550
940
11.1
24.4
32
4.3
2025-2100
0.9
2.3
-0.8
-1.4
-1.0
-1.8
-0.0
-0.0
-1.2
-1.1
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estimate that accelerated improvements in energy efficiency account for about 25% of the difference
between the RCWP and the RCW cases in 2050 (we note that this occurs even though fairly rapid
improvements are already assumed in the RCW case). We list below examples of potential efficiency
improvements that can be made in the various sectors of the economy.
Transportation - A number of technologies have already been demonstrated that could
increase automobile fuel efficiency from current levels for new cars (25-33 mpg or 9.4-7.1
liters/100 km) to better than 50 mpg (4.7 liters/100 km); these technologies may pay for
themselves hi fuel savings over the lifetime of the vehicle. Further improvements can
increase fuel efficiency to more than 80 mpg (less than 3 liters/100 km), although they do
not appear to be cost effective at current U.S. gasoline prices. The RCWP scenario assumes
that new cars in the industrialized countries achieve an average of 40 mpg (5.9 liters/100 km)
by 2000. Global fleet average fuel efficiency reaches 50 mpg (4.7 liters/100 km) in 2025 and
75 mpg (3.1 liters/100 km) in 2050 (somewhat lower rates of efficiency improvement are
assumed in the SCWP scenario). In addition, major fuel efficiency improvements in diesel
trucks and aircraft are possible. The Rapid Reduction case assumes more aggressive
measures to improve efficiency: new vehicles achieve an average of 50 mpg (4.7 liters/100
km) by 2000.
Residential and Commercial - Improved building shells, lighting, heating and cooling
equipment, and appliances are currently commercially available. The most efficient new
homes currently being built use only 30% as much heating energy per unit of floor area as
the average existing house in the United States. Advanced prototypes and design calculations
indicate that new homes could technically be built that use only 10% of current average
energy requirements. About 20% of U.S. electricity is consumed for lighting, mainly in
residential and commercial buildings. A combination of currently available advanced
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technology and careful design has been shown to cost-effectively reduce energy requirements
for lighting by more than 75%. The RCWP scenario assumes that the average reduction in
energy use per unit of residential and commercial floor space by 2025 is as much as 75%
for fuel and 50% for electricity in the U.S. Smaller improvements are assumed in other
regions and in the SCWP scenario.
Industrial Energy - Advanced industrial processes are available that can significantly reduce
the energy required to produce basic materials. This is especially true when combined with
recycling. For example, new technology developed in Sweden uses about half as much energy
per unit of steel production as the current U.S. average. Electric motors are estimated to
account for about 70% of U.S. industrial electricity use. Several case studies show that
improved motors and motor controls are commercially available, which could reduce energy
consumption by electric motors by at least 15% relative to current averages.
Developing countries can also significantly improve energy efficiency. Per capita
energy consumption is very low in developing countries, but there is a large potential to increase
efficiency because energy use per unit of GNP is often extremely high. Indeed, the imperative for
energy efficiency may be even stronger in developing countries to the extent that expending scarce
capital on expanding energy supply systems can be avoided. Some of the technical options described
above may be directly applicable in developing as well as industrialized countries, while alternative
approaches suited to available resources will often be needed. In many cases improved management
of existing facilities could have large payoffs.
Research on non-fossil energy technologies is a critical need. The development of
attractive non-fossil energy sources is critical to the success of any climate stabilization strategy over
the long term. Increased penetration of solar and advanced biomass technologies contribute little to
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reduced wanning in 2025, but they are responsible for 24% of the difference between the RCWP and
the RCW case in 2050, and over 30% of this difference in 2100. The exact mix of non-fossil
technologies assumed in the policy scenarios is rather arbitrary, but makes little difference to
greenhouse gas emissions. Some particularly promising non-fossil technologies are described below.
Hydro and Geothennal Power - Hydroelectric power is already contributing the equivalent
of about 7% of global primary energy production and geothermal power is making a small
(less than 1%) but important contribution. There is potential to expand the contribution of
these sources, although good sites are limited and environmental and social impacts of large-
scale projects must be considered carefully. Hydroelectric and geothermal power expands
to 12% of global primary energy production in the SCWP scenario, but only maintains a
roughly constant share of the higher level of production in the RCWP case.
Biomass Energy - Biomass is currently being extensively utilized, accounting for roughly 10%
of global energy consumption, primarily in traditional applications (e.g., cooking), which are
not included in most accounts of commercial energy use. Current and emerging technologies
could vastly improve the efficiency of biomass use. In the near term there is a substantial
potential to obtain more useful energy from municipal and agricultural wastes. More
advanced technologies for producing, collecting, and converting biomass to gaseous and liquid
fuels and electricity could become economically competitive within a decade. The prospects
for integrating biomass gasification with advanced combustion turbines is particularly
promising. Environmental and societal impacts related to large-scale biomass use, which
would have to be addressed, include competition with food production, ecological impacts,
and emissions of volatile organic compounds. In the SCWP scenario biomass energy supplies
21% of primary energy needs in 2050 and 35% in 2100. Biomass supplies about 30% of
primary energy by 2050 in the RCWP scenario.
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Solar Energy - There is a large range of solar options. Direct use of solar thermal energy,
either passively or in active systems, is already commercial for many water and space heating
applications. Wind energy systems are also currently commercial for some applications in
some locations. In recent years engineering advances have resulted in significant cost
reductions and performance improvements. Solar photovoltaic (PV) cells are currently
competitive for many remote power generation needs, especially in developing countries.
Dramatic progress has been made recently in reducing the costs of producing PV systems,
particularly with thin-film amorphous silicon technology. If current research and
manufacturing development efforts reach their objectives, PV could play a major role in
meeting energy needs in the next century. In the SCWP scenario solar sources of electricity
are equivalent to 9% of primary energy supply from 2050 onward. A larger contribution is
envisioned in the RCWP scenario: 15% in 2050, increasing to almost 20% in 2100.
Nuclear Power • Nuclear fission produces about 5% of global primary energy supplies and
its share is currently growing due to the completion of powerplants ordered during the 1970s.
High cost and concerns about safety, nuclear proliferation, and radioactive waste disposal,
however, have brought new orders to a halt in many countries. Advanced designs, in
particular the Modular High Temperature Gas-cooled Reactor, have recently been proposed
in an attempt to overcome some of these problems. The role of nuclear power could be
significantly expanded in the future if these efforts are successful in restoring public
confidence in this energy source. Nuclear power's contribution to primary energy supply
increases to 8% in 2050 and 14% in 2100 in the SCWP case and 13% in 2050 and 20% in
2100 in the RCWP case.
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Energy Policy Options
No single policy approach by itself is likely to be both effective and acceptable as a means of
achieving substantial reductions in greenhouse gas emissions from energy production and use.
Strategies appropriate for developing countries, for example, may be quite different from those that
are appropriate for the United States. However, many complementary policy options are available
that offer differing relative advantages for reducing emissions.
Proper pricing of energy services may be most important. It is critical to encourage both
increases in end-use efficiency and the development of energy sources that emit no CO2. Current
market prices of fossil fuels do not reflect the risk of climatic change and provide no assurance that
limiting greenhouse gas emissions will be a consideration in purchase and investment decisions. A
direct means of providing incentives to reduce emissions is to impose a fee on fossil fuels in
proportion to their relative contribution to global wanning. Regulatory programs may be an
important complement when pricing strategies are not effective, either because of market failures or
because of inequitable impacts on some regions or income groups. Directing research and
development priorities toward energy sources that emit no CO2 is essential to assure the availability
of attractive options over the longer term. Other important policy options include the selective use
of government procurement to stimulate markets and promote technological alternatives, and technical
assistance and information programs.
Industrial Activity
Three significant non-energy sources of greenhouse gases are associated with industrial activity:
the release of halocarbons during their production and use; methane emissions from waste disposal
in landfills; and carbon dioxide emissions from cement manufacture.
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Production and Use of Halocarbons
Chlorofluorocarbons, halons, and chlorocarbons (collectively, halocarbons) are man-made
chemicals containing carbon, chlorine, fluorine, and bromine (HCFCs contain hydrogen as well).
Table 8 lists the major halocarbons with their chemical formulae and major uses. CFCs were
originally commercialized in the 1930s as non-toxic, non-flammable, and highly stable coolants for
refrigerators. They were first used as propellants during World War n, and as blowing agents for
foam products during the 1950s. CFCs are also used in gas sterilization of medical equipment and
instruments, solvent cleaning of manufactured parts, and miscellaneous other processes and products
such as liquid food freezing. Halons were developed in the 1970s and are used primarily as fire
extinguishants. Chlorocarbons are used primarily as solvents and chemical intermediates. The
primary chlorocarbons are carbon tetrachloride and methyl chloroform. Production of halocarbons
has grown rapidly as new uses have developed.
Halocarbons have been identified as a serious threat to the stratospheric ozone layer.
International negotiations to protect the stratosphere began in 1981 under the auspices of the United
Nations Environment Programme (UNEP). These negotiations culminated in September 1987 when
"The Montreal Protocol on Substances That Deplete the Ozone Layer" (or the Montreal Protocol)
to reduce the use of CFCs and halons was initialed. The Montreal Protocol came into force on
January 1, 1989, and has been ratified by 31 countries, representing over 90% of current world
consumption of these chemicals (as of January 11, 1989).
Further reductions in CFCs would be needed to stabilize concentrations. The major
provisions of the Montreal Protocol include a 50% reduction from 1986 levels in the use of CFC-
11, -12, -113, -114, and -115 by 1998; a freeze on the use of Halon-1211, -1301, and -2402 at 1986
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Executive Summary
TABLES
Major Chlorofluorocarbons, Halons, And Chlorocarbons:
Statistics And Uses
Chemical
Chlorofluorocarbons
CFC-11 (CFC13)
CFC-12 (CF2Clj)
HCFC-22 (CHClFj)
CFC-113 (CjCljFj)
1986
Atmospheric
Concentration
(pptv)
226
392
-100
30-70
Atmospheric
Lifetime
(Years)
+32
75
-17
+289
111
-46
20
90
Current Annual
Atmospheric
Concentration
Growth Rates Major
(%/yr) Uses
4 Aerosols,
Foams
4 Aerosols,
Refrigeration
7 Refrigeration
11 Solvents
Halons (Bromofluorocarbons)
Halon-1211 (CBrCtty
Halon-1301 (CBrF3)
Chlorocarbons
Carbon tetrachloride
(ecu
Methyl chloroform
—2
—2
75-100
125
25
110
-50
5.5-10
> 10 Fire
extinguisher
> 10 Fire
extinguisher
1 Production of
CFC-11 and
CFC-12
7 Solvents
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levels starting in approximately 1992; and a delay of up to 10 years in compliance with the protocol
for developing countries with low levels of use per capita. As a result of this historic agreement, the
very high growth rates in CFC concentrations assumed in some previous studies are unlikely to occur.
However, because of the long atmospheric lifetimes of CFCs, the probability that not all countries
will participate in the agreement, and the provision for increased use in developing countries, CFC
concentrations will still rise significantly in the future unless the protocol is strengthened (see Figure
5). Despite assuming that at least 65% of developing countries and 95% of industrialized countries
participate in the agreement, the total contribution of halocarbons to the greenhouse effect increases
by more than a factor of 4 in the SCW and by a factor of 6.5 in the RCW scenario by 2100.
Promising chemical substitutes, engineering controls, and process modifications have now been
identified that could eliminate most uses of CFCs. In the policy scenarios we assume that the use
of CFCs and Halons is phased out and that emissions of methyl chloroform are frozen (no additional
growth in CFC substitutes is assumed as a result of the phaseout). Even under these assumptions
total weighted halocarbon concentrations increase significantly from 1985 levels in part because the
chemical substitutes contribute significantly to greenhouse forcing, but the final concentrations are
about one-third of the level in the corresponding No Response scenarios. The greenhouse forcing
potential of CFC substitutes will have to be carefully evaluated to improve estimates of their potential
role in climate change. In our analysis, phasing out CFCs was responsible for 6% of the decrease
in wanning in the RCWP compared with the RCW in 2050.
Waste Disposal
Landfills are a small but potentially controllable source of methane. Waste disposal in landfills
and open dumps generates methane when decomposition of the organic material becomes anaerobic;
approximately 80 percent of urban solid wastes is currently disposed of in one of these ways.
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Landfilling (compaction of wastes, followed by daily capping with a layer of clean earth) is most
common in industrialized countries, while open pit dumping is the most common "managed" disposal
method in developing countries (30-50% of solid wastes generated in cities in developing countries
is currently uncollected). Most of the decomposition in landfills and some of the decomposition in
open pits is anaerobic, resulting in annual methane emissions of 30-70 Tg CH4, about 10% of the
total source.
Disposal of municipal solid waste in industrialized nations increased by 5% per year during the
1960s, and by 2% per year in the 1970s. Landfilling is not expected to increase very much in
industrialized countries in the future, but it can be expected to increase dramatically in developing
countries as population growth, urbanization, and economic growth all imply increased disposal of
municipal solid waste. The growth of landfill methane emissions in developing countries is assumed
to be related to per capita income in a simple fashion, although growth is curtailed as current per
capita levels in industrialized countries are approached. The result is a three- and five-fold increase
in methane emissions in the SCW and RCW scenarios, respectively, reaching 13-15% of the total
methane budget by 2100. The Stabilizing Policy scenarios assume that gas recovery systems and waste
reduction policies will be adopted, resulting in roughly constant global emissions from landfills.
Cement Making
Carbon dioxide is emitted in the calcining phase of the cement-making process when calcium
carbonate (CaCO3) is converted to lime (CaO). For every ton of cement produced 0.14 tons of
carbon are emitted as CO2 from this reaction. Generally, even more CO2 is emitted from the fuel
used to drive the process (these combustion emissions are accounted for as part of industrial energy-
use emissions). World cement production has increased at an average annual rate of approximately
6% since the 1950s, from 130 million tons in 1950 to about one billion tons currently. Thus, current
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CO2 emissions from calcining are 0.14 billion tons of carbon (0.14 Pg C). The share of global
production in industrialized countries has declined during this period, and this trend is expected to
continue because demand in these countries is saturating. Emissions of CO2 from cement making,
projected using the per capita income approach described in the Waste Disposal section, increase by
two- to three-fold in the SCW and RCW scenarios by the year 2100. (Emissions remain less than
0.5 Pg C/yr in all cases.) In the Stabilizing Policy scenarios, advanced materials are assumed to
reduce the demand for cement (relative to the No Response scenarios), but emissions still grow by
about a factor of 2.
Changes in Land Use
Deforestation and biomass burning are significant sources of COj, CO, CH4, NOC and N2O.
Globally, the world's forest and woodland areas have been reduced by about 15% since 1850,
primarily to accommodate the expansion of cultivated lands. The largest decreases in forest area
during this period have occurred in Africa, Asia, and Latin America; Europe is the only region that
has experienced a net increase. It is generally estimated that approximately 11 million hectares
(Mha) of tropical forests are currently lost each year, while only 1.1 Mha are reforested per year.
Recent analysis of remote sensing data from Brazil, however, suggest that in 1987, 8 Mha were
cleared in the Brazilian Amazon alone. Estimates of net emissions of CO2 to the atmosphere due
to changes in land use (deforestation, reforestation, logging, and changes in agricultural area) in 1980
range from 0.4-2.6 Pg C, almost entirely from tropical countries. This accounts for approximately 10-
30% of annual anthropogenic CO2 emissions to the atmosphere. Of the estimated net release of
carbon from tropical deforestation in 1980 about half was from Brazil, Indonesia, Colombia, the
Ivory Coast, Thailand, and Laos.
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Biomass burning, related to deforestation, shifting cultivation, burning agricultural waste, and
fuelwood use, contributes roughly 10-25% of total annual CH< emissions, 5-15% of N2O emissions,
15-30% of NOX emissions, and 20-35% of the CO emissions. In addition, biomass burning and land
clearing results in elevated biogenic emissions of NO, and N2O from the soil for an extended period
after the burn.
Most tropical forests could be lost during the next century. The causes of deforestation
are complex and vary from country to country, making it difficult to directly tie assumptions about
deforestation rates to the economic and demographic assumptions of the general scenarios.
Qualitatively, we assume that in a Slowly Changing World continued poverty, unsustainable
agricultural practices, and rapid population growth lead to continuously increasing pressure on
remaining forests. The rate of deforestation is assumed to increase from current levels at the rate
of population growth for this scenario. Under this assumption the rate of tropical deforestation
increases from 11 million hectares per year (Mha/yr) in 1980 to 34 Mha/yr in 2047, when the
available area of forests in Asia is exhausted. As a result, CO2 emissions from deforestation increase
rapidly from 0.7 Pg C/yr to more than 2 Pg C/yr in 2047 before the Asian forests are exhausted.
Latin American and African forests are exhausted by 2075, reducing emissions drastically (Figure 17).
In a Rapidly Changing World improved agricultural practices and the substitution of modern fuels
for traditional uses of wood could ease the pressure on forests. Nonetheless, clearing of forest lands
for agriculture, pasture, logging, and speculation could continue apace, even if small areas are set
aside as biological preserves. In this scenario tropical deforestation is assumed to increase very
gradually, reaching 15 Mha/yr in 2097, before the unprotected forest areas of Latin America are
exhausted. Total emissions are almost the same as in the SCW, but they are spread out over a
longer period. Emissions are close to 1 Pg C/yr from 2000 to 2100.
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CO2 EMISSIONS FROM DEFORESTATION
C02 From Deforestation
(Petagrams Carbon)
- (a)
o
m
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Reforestation is a potentially cost-effective means of reducing net carbon dioxide emissions. In
the Stabilizing Policy scenarios it is assumed that the biosphere is transformed from a source to a
sink for carbon by 2000. A combination of policies succeed in stopping deforestation by 2025 while
up to 1000 Mha is reforested by 2100. Forests reach their peak absorption of 0.7 Pg C/yr before
2025. (The land area required depends on the productivity of the reforested land. We have used
a conservative estimate; if the productivity were higher, then less than 1000 Mha would be required
or the maximum sink would be more than 0.7 Pg C/y.) The size of this sink declines gradually after
2025 as forests reach their maximum size and extent. Only land that once supported forests and is
not intensively cultivated is assumed to be available for reforestation. These lands include 85% of
the area currently involved in shifting cultivation (370 Mha) under the assumption that this practice
is replaced by sustainable low input agriculture. In addition, some fraction of the fallow agricultural
land in the temperate zone (250 Mha), planted pasture in Latin America (100 Mha), and degraded
land in Africa and Asia (400 Mha) is assumed to be reforested. Of the reforested land, about 380
Mha is assumed to be in plantations, which is sufficient to produce the biomass energy requirements
of the RCWP case with the productivity goals established by the Department of Energy.
Reversing deforestation could be a very cost-effective policy response to potential
climatic change. Although a vast area of land would have to be involved to make a significant
contribution to reducing net CO2 emissions, preliminary estimates suggest that the cost of absorbed
or conserved carbon could be extremely low in comparison to other options. Furthermore, a
reforestation strategy could offer a stream of valuable ecological and economic benefits in addition
to reducing CO2 concentrations, such as forest products, maintenance of biodiversity, watershed
protection, nonpoint pollution reduction, and recreation. Devising successful forestry programs
presents unique challenges to scientists and policy makers because of the vast and heterogeneous
landscape, uncertain ownership, lack of data, and the need for more research and field trials.
Investments that would be small by the standards of the energy industry, however, could make an
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enormous impact on forestry. Reforestation accounts for almost one-fifth of the decrease in warming
by 2050 in the RCWP versus the RCW scenarios.
Agricultural Practices
Three agricultural activities contribute to atmospheric concentrations of greenhouse gases in
addition to those that have been discussed regarding changes in land use: enteric fermentation in
domestic animals; rice cultivation; and nitrogenous fertilizer use.
Methane emissions from animals may increase significantly over the next century.
Methane is produced as a by-product of enteric fermentation in herbivores, a digestive process by
which carbohydrates are broken down by microorganisms into simple molecules for absorption into
the bloodstream. The highest CH4 losses are reported for ruminants (e.g., cattle, dairy cows, sheep,
buffalo, and goats) in which 4-9% of total energy intake is released as methane. Of the annual
global source of 400 to 600 Tg CH4, domestic animals contribute approximately 65-85 Tg. Of these
emissions approximately 57% comes from cattle and 19% from dairy cows. The domestic animal
population has increased considerably during the last century. Between the early 1940s and 1960s,
increases in global cattle populations averaged 2% per year. Since the 1960s, the rate of increase
has slowed somewhat, to 1.2%. By comparison, the average annual increase in global human
population since the 1960s has been about 1.8%. Future demand for agricultural products will
depend more on population than on income levels. Based on a global agriculture model, methane
emissions from enteric fermentation are estimated to increase by about 125% from 1985 to 2100 in
both the SCW and the RCW scenarios as the much higher incomes in the RCW largely offset the
somewhat higher populations in the SCW.
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Methane emissions from rice cultivation are likely to increase more slowly. Methane produced
by anaerobic decomposition in flooded rice fields escapes to the atmosphere by bubbling up through
the water column, diffusing across the water/air interface, and transport through the rice plants. The
amount of CH4 released to the atmosphere is a complex function of rice species, number and
duration of harvests, temperature, irrigation practices, and fertilizer use. Rice fields are estimated
to contribute 60-170 Tg CH4 per year to the atmosphere, or approximately 10-30% of the global flux.
This large range reflects a paucity of data, particularly from Asia, where 90% of rice cultivation
occurs. From 1950 to 1984, harvested rice paddy area increased approximately 40%, from 103 to 148
Mha, and average global yields doubled, from 1.6 to 3.2 tons per hectare. Methane emissions are
probably primarily a function of area under cultivation rather than yield, although yield could
influence emissions, particularly if more organic matter is incorporated into the paddy soil The land
area used for rice production, and thus the CH4 emissions from this source increases by only about
50% by 2100 in both the SCW and RCW scenarios (production per hectare increases by 80-100%).
Nitrous oxide is released through microbial processes in soils, both through denitrification and
nitrification. The use of nitrogenous fertilizer enhances N2O fluxes since some of the applied N is
converted to N2O and released to the atmosphere. The amount of N2O released varies greatly and
depends on rainfall, temperature, the type of fertilizer applied, mode of application, and soil
conditions. Approximately 70 million tons (70 Tg) of nitrogen were applied in the form of
nitrogenous fertilizers worldwide in 1984-85. A preliminary estimate suggests that this produced N2O
emissions of 0.14-2.4 Tg N out of the global source of 11-17 Tg N per year. Satisfying the demands
of increasing populations with a finite amount of land requires more intensive cultivation resulting
in a 160% increase in fertilizer use between 1985 and 2100 in both the SCW and RCW scenarios.
Future research and technological changes could reduce agricultural emissions. In
the policy scenarios we do not assume changes in the demand for agricultural commodities, but rather
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changes in production systems that could reduce greenhouse gas emissions per unit of product.
Although the impact of specific approaches cannot be quantified at present, a number of techniques,
such as feed additives for cattle, changes in water management in rice production, and fertilizer
coatings, have been identified for reducing methane and nitrous oxide emissions from agricultural
sources. The implementation of these options depends on further research and demonstrations. For
simplicity we have assumed that methane emissions per unit of rice, meat, and milk production
decrease by 0.5% per year (emissions from animals not used in commercial meat or milk production
are assumed to be constant). Emissions of nitrous oxide per unit of nitrogen fertilizer applied are
also assumed to decrease by 0.5% per year for each fertilizer type. In addition, fertilizer use is
assumed to shift away from those types with the highest emissions after 2000. The result of these
assumptions is substantially lower agricultural emissions in the policy scenarios relative to the No
Response scenarios. Emissions grow by less than a factor of 2 in all cases, and methane emissions
from rice remain roughly constant until 2075, after which time they fall by about 20% as the global
population stabilizes. Reduced emissions from agriculture, landfills, and cement manufacture accounts
for 10% of the reduced warming in the RCWP compared with the RCW scenario in 2050.
THE NEED FOR POLICY RESPONSES
The prospect of global climate change presents policy makers with a unique challenge. The
potential scale of the problem is unprecedented. Many choices are available and the consequences
of these choices will be profound.
If limiting U.S. and global emissions of greenhouse gases is desired, government
action will be necessary. Market prices of energy from fossil fuels, products made with CFCs,
forest and agricultural products, and other commodities responsible for greenhouse gas emissions do
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not reflect the risks of climate change. As a result, increases in population and economic activity will
cause emissions to grow in the absence of countervailing government policies.
A Wide Range of Policy Choices
A wide range of policy choices is available for reducing greenhouse gas emissions.
There is an important distinction between short-term and long-term policy options. In the short-
term, the most effective means of reducing emissions is through strategies that rely on pricing and
regulation. In the long-term, policies to increase research and development of new technologies and
to enhance markets through information programs, government purchases, and other means could also
make a major contribution.
• The most direct means of allowing markets to incorporate the risk of
climatic change is to assure that the prices of fossil fuels and other sources
of greenhouse gases reflect their full social costs. It may be necessary to
impose emission fees on these sources according to their relative
contribution to global warming in order to accomplish this goal. This would
also raise revenues that could finance other programs. The degree to which
such fees are accepted will vary among countries, but acceptability would be
enhanced if fees were equitably structured.
• Regulatory programs would be a necessary complement when pricing
strategies are not effective or produce undesirable impacts. In the U.S.,
greenhouse gas emissions are influenced by existing federal regulatory
programs to control air pollution, increase energy efficiency, and recycle solid
waste. Reducing greenhouse gas emissions could be incorporated into the
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goals of these programs. New programs could focus directly on reducing
greenhouse gas emissions through requirements such as emissions offsets
(e.g., tree-planting), performance standards, or marketable permits.
• State and local government policies in such areas as utility regulation,
building codes, waste management, transportation planning, and urban
forestry could make an important contribution to reducing greenhouse gas
emissions.
• Voluntary private efforts to reduce greenhouse gas emissions have already
provided significant precedents for wider action and could play a larger role
in the future.
• Over the long term, other policies will be needed to reduce emissions and
can complement pricing and regulatory strategies. Other policy options
include redirecting research and development priorities in favor of
technologies that could reduce greenhouse gas emissions, information
programs to build understanding of the problems and solutions, and the
selective use of government procurement to promote markets for
technological alternatives.
The Timing of Policy Responses
The costs and benefits of actions taken to reduce greenhouse gas emissions are difficult to
evaluate because of the many uncertainties associated with estimates of the magnitude, timing, and
consequences of global climate change, as well as the difficulty of assessing the net social costs of
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strategies that involve widespread and long-term shifts in technological development. In this situation
it may appear to be prudent to delay action to stabilize greenhouse gas concentrations until the
magnitude of the problem and the costs of responses are better established. The potential benefits
of delay, however, must be balanced against the potential increased risks.
Policy development and implementation can be a lengthy process, particularly at
the international level Any decision to respond to the greenhouse gas buildup cannot be
translated immediately into action. Roughly a decade was required for the process that led to
international agreement to reduce emissions of CFCs, embodied in the Montreal Protocol, and it will
take another decade to implement the agreed-upon reductions. Agreements to reduce other
greenhouse gas emissions could take much longer to achieve and implement.
The development of technologies to reduce greenhouse gas emissions will take
many years. The majority of emissions are associated with fundamental components of the global
economy (transportation, heating and cooling buildings, industrial production, land clearing, etc.), such
that reducing emissions by curtailing these activities would be highly disruptive and undesirable.
While a large menu of promising technologies have been identified that can meet our needs for
goods and services while generating much lower emissions of greenhouse gases, many require
additional research and development to become economically competitive. The time required for
innovative technologies to be brought to market is unpredictable, but is usually many years. And
once a technology is cost-effective, it may take years before it achieves a large market share and
decades more for the existing capital stock to be replaced. Depending on the sector, it may take 20-
50 years or more to substantially alter the technological base of industrial societies, and the cost of
reducing emissions could rise dramatically as the time allowed for achieving these reductions is
decreased. While the rate of change can be higher in rapidly developing countries, and may be
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influenced by government policies, once industrial infrastructure is built, it will be many years before
it is replaced.
Industrialized and developing countries could limit the buildup of greenhouse gases
in a manner consistent with economic development and other environmental and
social goals. The justification for policies that reduce greenhouse gas emissions may be much
greater than it would appear from a narrow examination of costs and climatic benefits. Most of the
measures proposed to reduce emissions ~ increasing energy efficiency, reversing deforestation, and
reducing use of CFCs, for example -- are already of substantial public interest; global wanning is
often simply another reason for promoting these policies. Many energy efficiency measures are cost-
effective, but a number of institutional barriers and market failures would need to be overcome to
facilitate their adoption. Benefits include reductions in conventional pollutants, increased energy
security, and reductions in the balance of payments deficit, as well as reduced risk of wanning.
Similarly, reversing deforestation has a wide range of benefits, including maintenance of biological
diversity, reduction in soil erosion and reservoir siltation, and local climatic amelioration. Reductions
in CFC production beyond those called for in the Montreal Protocol would probably be most
significant in reducing the risk of stratospheric ozone depletion, and would also make an important
contribution to reducing the risk of climatic change. Some of the options discussed here, such as
reduced agricultural emissions, improved biomass production, and heavy reliance on photovoltaics
would require further research and development to assure their availability. Relatively small
investments in such research could yield important payoffs. The incremental cost of taking actions
to limit global warming today may therefore be modest.
The OECD countries can play a leadership role in bringing about reductions in
emissions by Other countries. Despite great differences between the OECD countries and other
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countries in sources of emissions and the economic and social constraints on policies to limit them,
initiatives by the U.S. and OECD countries can have a significant global impact. U.S. leadership has
made important contributions to recent international environmental agreements such as the Montreal
Protocol on substances that deplete the ozone layer and the Tropical Forest Action Plan. The U.S.
is committed to playing a leadership role in the Intergovernmental Panel on Climate Change recently
organized by the World Meteorological Organization and the United Nations Environment
Programme. Finally, the U.S. can use its bilateral aid and its influence in multilateral development
banks to encourage economic development consistent with reducing the buildup of greenhouse gases.
In contrast to the common notion that limiting global wanning would require great sacrifices, we
find that many of the policy options that are available for reducing greenhouse gas emissions appear
to be attractive in many respects. Policies to begin reducing greenhouse gas emissions must be
carefully considered now, notwithstanding the many uncertainties, because the risks of delaying action
appear to be large, and the costs of reducing emissions are likely to increase as the time allowed for
these reductions is shortened.
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FINDINGS
I. Uncertainties regarding climatic change are large, but there is a growing
consensus in the scientific community that significant global warming due to
anthropogenic greenhouse gas emissions is probable over the next century, and
that rapid climatic change is possible.
• A scientific consensus has emerged that greenhouse gases are increasing in
concentration in the atmosphere, that, even with a freeze in emissions
concentrations will continue to increase, and that, as a result, warming and
climate change are likely to occur.
• Uncertainties about global warming abound. The greatest uncertainties
concern the ultimate magnitude and timing of wanning and the implications
of that warming for the Earth's climate system, environment, and economies.
The warming that can be expected for a given increase in greenhouse gas
concentrations is uncertain due to our inadequate understanding of the
climate system. For the benchmark case of doubling carbon dioxide
concentrations from preindustrial levels, the equilibrium increase in global
average temperature would most likely be in the range of 2-4°C, and could
be as little as 1.5°C or as much as 5.5°C.
• A variety of geochemical and biogenic processes that could significantly
affect the response of the climate system to greenhouse gas increases have
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generally been neglected in estimating potential future wanning. When all
such feedbacks are considered, it is possible that the actual sensitivity of the
Earth's climate system to increased greenhouse gases could exceed S.5°C
for an initial doubling of CO2.
• Because the oceans delay the full global warming that would be associated
with any increase in greenhouse gases, significant climatic change could
continue for decades after the composition of the atmosphere were
stabilized. Assuming that the climate sensitivity to doubling CO2 is 2-4°C,
the Earth is already committed to a total warming of about 0.7-1.50C
relative to the preindustrial era. The Earth has wanned by 03-0.7°C during
the last century, which is consistent with expectations given the uncertain
delay caused by ocean heat uptake.
• Global warming of just a few degrees would represent an enormous change
in climate. The difference in mean annual temperature between Boston and
Washington is only 33°C, and the total global wanning since the peak of
the last ice age, 18,000 years ago, was only about 5°C.
• Global temperature change estimates are only indicators for the rate and
magnitude of climatic change. Climatic changes at the regional level
associated with global wanning will vary in both magnitude and timing and
changes in precipitation and other factors will be as important as changes
in temperature.
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II. Measures undertaken to limit greenhouse gas emissions would decrease the
magnitude and speed of global warming, regardless of uncertainties about the
response of the climate system.
• Scenario analyses indicates that greenhouse gas concentrations will show
large increases whether the rate of future economic growth and technological
change is rapid (the "Rapidly Changing World") or slow (the "Slowly
Changing World"). Fossil fuel would play a relatively larger role in raising
greenhouse gases in a Rapidly Changing World while agricultural activities
and deforestation would play a relatively larger role for the Slowly Changing
World.
• If no policies to limit greenhouse gas emissions are undertaken, the
equivalent of a doubling of CO2 occurs between 2030 and 2040 in these
scenarios.
• The equilibrium warming commitment for a Rapidly Changing World
without policies to limit greenhouse gas emissions is estimated to be 1-2°C
by 2000, 3-5°C by 2050, and 5-10°C by 2100 (assuming that the climate
sensitivity to doubling CO2 is 2-4°C). For a Slowly Changing World the
equilibrium warming commitment is estimated to be 1-2°C by 2000, 2-4°C
by 2050, and 3-6°C by 2100. Estimated warming commitments greater than
5°C may not be fully realized because the strength of some positive
feedback mechanisms may decline as the Earth warms.
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• The realized warming in a Rapidly Changing World, without policies to limit
greenhouse gas emissions, is estimated to be 2-3°C by 2050, and 4-6°C by
2100 (assuming that the climate sensitivity to doubling CO2 is 2-4°C). In
a Slowly Changing World realized warming is estimated to be about 2°C
by 2050 and 3-4°C by 2100.
• The early application of existing and emerging technologies included in this
study could lower the commitment to global wanning in 2025 by about one-
fourth, and the rate of climatic change during the next century could be
reduced by at least 60%.
• Although delaying action would allow time to increase knowledge of risks
and refine the choice of policies, it could reduce the effectiveness of policy
responses. If industrialized countries delay implementation of any response
to global warming until 2010 and developing countries delay until 2025, the
equilibrium warming commitment in 2050 could increase by 30-40%.
• Stabilizing the commitment to global warming would require cuts in
emissions from present levels so significant that currently available and
emerging technologies are insufficient to achieve this goal. Consequently,
stabilization would require very rapid introduction of existing and emerging
technologies and very significant investments in research and development
for advanced technologies that reduce greenhouse gas emissions. With such
action, equilibrium wanning commitment might peak at 1-2°C in 2025 and
realized warming may not exceed 1.4"C if the climate sensitivity to doubling
CO2 is 2-4°C.
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• If the climate sensitivity of the Earth to increases in greenhouse gases is
low, then early application of existing and emerging technologies to limit
greenhouse gases could prevent an equilibrium warming commitment of
greater than 2°C within a century. If, on the other hand, the true
temperature sensitivity of the Earth to doubling CO2 is 5.5°C or even
greater, then without very rapid application of existing and emerging
technologies and development of new technologies, the Earth could be
committed to a global wanning of more than 3°C by as early as 2010 even
with application of many existing and emerging technologies to limit
greenhouse gases.
III. No single country or source will contribute more than a fraction of the
greenhouse gases that will warm the world; any overall solution will require
cooperation of many countries and reductions in many sources.
• The U.S. is currently the largest contributor to the greenhouse gas buildup,
but its share of global emissions is only about one-fifth of the total. The
rest of the OECD and the East Bloc each contribute a similar amount.
The relative contribution of the U.S. and OECD countries to total global
emissions is likely to decrease over the next century.
• Per capita emissions in developing countries are currently very low, but the
share of total emissions contributed by developing countries is expected to
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increase significantly in the future, and becomes more than 50% by 2025 in
the scenarios analyzed.
• All nations will need to adopt measures to slow the buildup of greenhouse
gases, if climate change is to be effectively limited. If developing countries
do not adopt climate stabilizing policies, then the equilibrium warming
commitment in 2050 could increase by about 40% compared to scenarios in
which there is global cooperation.
• Technologies developed in the OECD nations could enhance the ability of
developing nations to reduce emissions. Efforts to develop technologies that
are more efficient and that produce energy from sources other than fossil
fuel can make a significant difference in ultimate greenhouse gas emissions
throughout the world.
• Energy production and use is currently responsible for almost 60% of
increases in the greenhouse effect, followed by chlorofluorocarbons (about
20%), and agricultural practices and deforestation (roughly 10% each).
Even the largest source categories, such as automobiles or utilities, however,
represent less than 30% each of total greenhouse gas emissions.
• In the immediate term the most effective options to reduce commitments
to greenhouse warming are to further reduce chlorofluorocarbons, apply
already attractive energy-efficiency technologies, and reduce and then reverse
deforestation. Longer-term approaches for reducing the warming
commitment would emerge from immediate investments to develop
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technologies that lower the cost of producing goods and services without
producing as high levels of greenhouse gas emissions. Promising
technologies include advanced materials, thin-film photovoltaics, and biomass-
fired turbines.
• Neither energy efficiency nor non-fossil fuels alone would be sufficient to
greatly limit greenhouse gas emissions in the long term; both will be
necessary.
IV. A wide range of policy choices is available to reduce greenhouse gas
emissions while promoting economic development, environmental, and social goals.
• Industrialized and developing countries could limit the buildup of greenhouse
gases in a manner consistent with economic development and other
environmental and social goals. In industrialized countries, acid rain, urban
ozone, and dependence on imported energy could be reduced as part of an
overall strategy that reduces greenhouse gas emissions. Energy efficiency
improvements are already essential in developing countries to reduce capital
requirements for the power sector, and efforts to halt deforestation will
provide many long-run economic and environmental benefits.
• If limiting the greenhouse gas buildup is desired, government action will be
necessary. Market prices of energy from fossil fuels, products made with
CFCs, forest and agricultural products, and other commodities responsible
for greenhouse gas emissions do not reflect the risks of climate change.
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• The most direct means of allowing markets to incorporate the risk of
climatic change is to assure that the prices of fossil fuels and other sources
of greenhouse gases reflect their full social costs. It may be necessary to
impose emission fees on these sources according to their relative
contribution to global warming in order to accomplish this goal. This would
also raise revenues that could finance other programs. The degree to which
such fees are accepted will vary among countries, but acceptability would be
enhanced if fees were equitably structured.
• Regulatory programs would be a necessary complement when pricing
strategies are not effective or produce undesirable impacts. In the U.S.,
greenhouse gas emissions are influenced by existing federal regulatory
programs such as those designed to control air pollution, increase energy
efficiency, and recycle solid waste. Reducing greenhouse gas emissions could
be incorporated into the goals of these programs. New programs could
focus directly on reducing greenhouse gas emissions through requirements
such as emissions offsets (e.g., tree-planting), performance standards, or
marketable permits.
• The best ways to avoid producing greenhouse gases cannot be anticipated;
accelerated investment in a range of options is necessary if policy makers
want to assure that better and less costly options will be available in the
future.
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• Government policy is already exerting considerable influence on the rate of
growth in greenhouse gases. Policies adopted to reduce CFC production will
reduce the rate of greenhouse gas buildup. Policies that have been adopted
or are under consideration to promote greater use of coal, reduce required
improvements in automobile efficiency, and subsidize electricity consumption,
may significantly accelerate the rate of greenhouse gas emissions. A
combination of factors that increase greenhouse gas emissions could
accelerate commitments to global warming by as much as 60% in 2050
relative to the Rapidly Changing World scenario.
• U.S. leadership has made important contributions to recent international
environmental agreements, such as the Montreal Protocol on Substances that
Deplete the Ozone Layer and the Tropical Forest Action Plan. The U.S.
government is committed to playing a key role in the Intergovernmental
Panel on Climatic Change (IPCC) established under UNEP and WMO
auspices. The U.S. can also promote desirable changes in energy and
environmental policy in developing countries through judicious use of its
bilateral aid programs and its influence on loans extended by multilateral
development banks. Finally, domestic initiatives could foster international
cooperation by demonstrating a commitment to respond to global climatic
change.
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"U.S.GOWERNBOT PRINTING OFF ICE H989-620-710 ,00960
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