230989501
POLICY OPTIONS FOR STABILIZING GLOBAL CLIMATE
                                  \
                            DRAFT




                     REPORT TO CONGRESS
                      Volume I: Chapters I-VI
                  United States Environmental Protection Agency




                   Office of Policy, Planning, and Evaluation











                           February 1989

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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 (Bound under separate cover)








VOLUME 1








CHAPTER I:  INTRODUCTION	  1-1



CHAPTER II: GREENHOUSE GAS TRENDS	   IM



CHAPTER HI: CLIMATIC CHANGE	  HI-1



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








CHAPTER VII: TECHNICAL OPTIONS FOR REDUCING GREENHOUSE GAS EMISSIONS .  VIM



CHAPTER VIII: POLICY OPTIONS 	VHI-1



CHAPTER IX: INTERNATIONAL COOPERATION TO REDUCE GREENHOUSE



            GAS EMISSIONS	  IX-1

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                              DETAILED TABLE OF CONTENTS
                                   EXECUTIVE SUMMARY
                                 (Bound under separate cover)


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
                                              111

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                       DETAILED TABLE OF CONTENTS (Continued)


VOLUME 1


                                      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 ACTIVITIES	  1-26
       National Research and Policy Activities	  1-26
       International Activities	  1-27

REFERENCES	  1-29


                                      CHAPTER II

                               GREENHOUSE GAS TRENDS


FINDINGS  	   II-2

INTRODUCTION	   II-5

CARBON DIOXIDE 	   II-7
       Concentration History and Geographic Distribution  	   II-7
              Mauna Loa	   II-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  	   11-40
       Concentration History and Geographic Distribution  	   11-40
       Sources and Sinks	   11-43
       Chemical and Radiative Properties/Interactions	'.	   11-44

OTHER FACTORS AFFECTING COMPOSITION	   11-45
       Global Tropospheric Chemistry	   11-46
              Carbon Monoxide	   11-47
              Nitrogen Oxides	   11-48
       Stratospheric Ozone and Circulation  	   11-49

CONCLUSION	   11-50

REFERENCES	   11-59


                                        CHAPTER III

                                     CLIMATIC CHANGE


FINDINGS  	   III-2

INTRODUCTION	   III-4

CLIMATIC CHANGE IN CONTEXT	   IH-6

CLIMATE FORCINGS  	   III-8
       Solar Luminosity	   Ill-12
       Orbital Parameters  	   111-13
       Volcanoes	   111-13
       Surface Properties	   Ill-14
       The Role of Greenhouse Gases  	   Ill-14

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                        DETAILED TABLE OF CONTENTS (Continued)

       Internal Variations   	   111-15

PHYSICAL CLIMATE FEEDBACKS	   111-15
       Water Vapor - Greenhouse	   Ill-17
       Snow and Ice 	   Ill-17
       Clouds	   111-19

BIOGEOCHEMICAL CLIMATE FEEDBACKS	   111-20
       Release of Methane Hydrates  	   111-20
       Oceanic Change  	   111-22
             Ocean Chemistry 	   111-23
             Ocean Mixing  	   111-23
             Ocean Biology and Circulation  	   HI-24
       Changes in Terrestrial Biota	   111-25
             Vegetation Albedo  	   111-25
             Carbon Storage  	   111-26
             Other Terrestrial Biotic Emissions	   111-26
             Summary	   111-27

EQUILIBRIUM CLIMATE SENSITIVITY  	   111-28

THE RATE OF CLIMATIC CHANGE  	   111-31

CONCLUSION	   111-35

REFERENCES	   111-37


                                       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
             Industrialized Countries	   IV-10
             Developing Countries  	   IV-10

ENERGY CONSUMPTION   	   IV-12
       History of Fossil-Fuel Use	   IV-13
       Current Energy Use  Patterns and Greenhouse Gas Emissions  	   IV-18
             Emissions bv Sector  	   IV-20
             Fuel Production and Conversion 	   IV-25
       Future Trends	   IV-27
             The Fossil-Fuel Supply 	   IV-29
             Future Energy Demand	   IV-29
                                            VI

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                       DETAILED TABLE OF CONTENTS (Continued)


INDUSTRIAL PROCESSES	   IV-31
       Chlorofluorocarbons, Halons, and Chlorocarbons	   IV-33
             Historical Development and Uses  	   IV-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 Landfills 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	  VMS
       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
              Anhydrous Ammonia	  VI-38
              NgO Leaching 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


                                      CHAPTER VII

            TECHNICAL OPTIONS FOR REDUCING GREENHOUSE GAS EMISSIONS


PART ONE: ENERGY SERVICES	  VII-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 NO  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 and Improving Roads	  VII-58
              Alternative Modes of Transportation  	  VII-59
              Alternative Fuels 	  VII-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  	  VII-67
       Near-Term Technical Options:  Industrialized Countries	  VII-71
               Improvements in Space Conditioning  	  VII-71
               Indoor Air Quality  	  VII-80
               Lighting  	  VII-81
               Appliances	  VII-83
       Near-Term Technical Options:  Developing Countries 	  VII-83
               Increasing Efficiency of Fuelwood Use	  VII-85
               Substituting More  Efficient Fuels	  VII-87
               Retrofit  Efficiency Measures for the Modern Sector	  VII-88
               New Homes 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
               Aggressive Efficiency Improvements of Other Industries  	VII-100
               Cogeneration	VII-101
       Near-Term Technical Options:  Developing Countries 	VII-102
               Technological Leapfrogging	VII-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	VII-112
               Structural Shifts  	VII-112
               Advanced Process Technologies	VII-113
               Non-fossil Energy	VII-115


PART TWO:  ENERGY  SUPPLY  	VII-116

FOSSIL FUELS	VII-117
       Refurbishment of Existing Powerplants	VII-121
       Clean Coal  Technologies and Repowering  	VII-122
       Cogeneration	VII-123
       Natural Gas Substitution  	VII-124
               Natural  Gas Use At Easting 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    	VII-132
               C02 Controls	VII-133

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                         DETAILED TABLE OF CONTENTS (Continued)


       Emerging Electricity Generation Technologies  	VII-134
              Fuel cells   	VII-134
              Magnetohydrodynamics (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  	VII-143
              Methanol	VII-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	VII-158
       Geothermal energy  	VII-159
       Ocean Energy	VII-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  	VII-174

HYDROGEN	VII-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	'.	VII-190
       Recycling and Resource Recovery	VII-192
       CO2 Emissions  From Cement Production  	VII-193


PART FOUR:  FORESTRY  	VII-195

FORESTS AND CARBON EMISSIONS	VII-195

DEFORESTATION	VII-197

TECHNICAL CONTROL OPTIONS  	VII-202
       Reduce Demand for Forest Land and Products  	VII-206
              Option  1:  Slow Deforestation by 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  	VII-217
              Option  4:  Increase Conversion Efficiencies  Of Technologies Using Fuelwood .  . . VII-218
              Option  5:  Decrease Production of Disposable Forest Products	VII-218
              Substitute durable wood  or non-wood products for high-volume disposable
                      uses of wood  	VII-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	VII-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  	VII-234
              Option  8:  Afforestation  for Highway Corridors	VII-235
              Option  9:  Reforest Tropical Countries	VII-236
              Obstacles  to Large-Scale Reforestation in Industrialize^ Countries	VII-241
              Obstacles  to Reforestation in Developing Countries  	VII-243
       Summary of Forestry Technical Control Options  	VtI-244


PART FIVE:  AGRICULTURE	VII-249

RICE CULTIVATION	VII-252
       Existing  Technologies and Management Practices	.'	VII-253
       Emerging Technologies	VII-257
       Research Needs and Economic Considerations	VII-258

USE OF  NITROGENOUS FERTILIZER  	VII-259
       Existing  Technologies and Management Practices	VII-260
              Management Practices That Affect NoO Production	VII-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  	VH-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 VIII

                                    POLICY OPTIONS


FINDINGS  	    VIII-2

INTRODUCTION	    VIII-6

INTERNALIZING THE COST OF CLIMATE CHANGE RISKS 	    VIII-8
       Evidence of Market Response to Economic Incentives:  Energy Pricing  	    VIII-9
       Financial Mechanisms to Promote Energy Efficiency	   VIII-14
       Creating Markets for Conservation 	   VIII-16
       Limits to Price-Oriented Policies  	   VIII-18

REGULATIONS AND STANDARDS  	   VIII-22
       Existing Regulations that Restrict Greenhouse Gas Emissions 	   VIII-23
             Regulation of Chlorofluorocarbons	   VIII-24
             Energy Efficiency Standards	   VIII-25
             Air PoUution Regulations	   Vffl-28
             Waste Management	   VIII-29
             Utility Regulation	   VTII-31
       Existing Regulations that Encourage Emissions Reductions  	   VIII-35

RESEARCH AND  DEVELOPMENT   	   VIII-39
       Energy Research and Development	   VIII-40
       Global Forestry Research & Development  	   VIII-45
       Research to Eliminate Emissions  of CFCs	   VIII-46

INFORMATION AND TECHNICAL ASSISTANCE PROGRAMS	   VIII-47

CONSERVATION  EFFORTS BY FEDERAL AGENCIES   	   Vffl-50

STATE AND LOCAL EFFORTS	   VHI-52

PRIVATE SECTOR EFFORTS	   VIII-57

COMPLEMENTARY STRATEGIES TO REDUCE GREENHOUSE GAS EMISSIONS	   VIII-59

IMPLICATIONS OF POLICY CHOICES  AND TIMING	   VIII-63
                                          Xlll

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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 	   VIII-76
       Conclusions From the Sensitivity Tests	   VIII-78

REFERENCES	   VIII-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 	   IX-33

U.S. LEADERSHIP  TO PROMOTE INTERNATIONAL COOPERATION 	   K-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 (bound under separate cover)
                                                                                            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 Warming:  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 Warming  	      55
     16        Primary Energy Supply by Type  	      58
     17        CO2 Emissions From Deforestation	      73
VOLUME I
Chapter I

     1-1

     1-2
Carbon Dioxide Concentrations at Mauna Loa and Fossil Fuel CO2
Emissions  	    1-10
Impact of CO2 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
                                                                             11-20
                                                                             11-23
                                                                             11-25
                                                                             11-31
                                                                             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  	   111-16
     3-6        Equilibrium Temperature Changes from Doubled CO2  	   Ill-18
     3-7        Greenhouse Gas Feedback Processes	   111-21


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        CO, 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 Wanning 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 Warming 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
Chapter VII

     7-1       Current Contribution to Global Warming	  VII-20
     7-2       Global Energy Use by End-Use  	  VD-28
     7-3       Secondary Energy Consumption by Region  	  VII-30
     7-4       End-Use Energy Demand by Sector	  VII-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	  VII-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	VII-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	VII-148
     7-14      Photovoltaic Electricity Costs  	VII-151
     7-15      Nuclear Capital Costs  	VII-167
     7-16      Industrial Process Contribution to Global Warming  	VII-179
     7-17      Emissions of Major CFC's	'	VII-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	VII-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	VIII-21
     8-4       U.S. Carbon Monoxide Emissions  	VIII-30
     8-5       Changes in U.S. Renewable Energy R&D Priorities Over Time  	VIII-42
     8-6       Cost of Potential Residential Electricity Conservation
               in Michigan by 2000  	VIII-55
     8-7       U.S. Energy Consumption By Fuel Share 	VIII-66
     8-8       Atmospheric Response to Emissions Cutoff	VIII-68
     8-9       Actual and Projected U.S. Coal Production	VIII-70
     8-10      Accelerated Emissions Cases: Percent Increase in Equilibrium Warming
               Commitment  	VIII-74
     8-11      Rapid Reduction Strategies: Additional Decrease in Equilibrium Warming
               Commitment  	VIII-79
                                                xvui

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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 (bound under separate cover)
    2
    3
    4
    5
    6
    7
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 COo  	
Major Chlorofluorocarbons,  Halons, and Chlorocarbons:  Statistics and Uses .
                                                                                             Page
15
21
24
33
39
50
61
68
VOLUME I
Chapter II

    2-1         Radiative Forcing for a Uniform Increase in Trace Gases From Current Levels  . .    11-21
    2-2         Trace Gas Data  	    11-51


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 	   IV-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  	   IV-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

Chapter VII

    7-1         Key Technical Options by Region and Time Horizon  	  VII-19
    7-2         High Fuel Economy Prototype Vehicles  	  VII-39
    7-3         Actual New Passenger Car Fuel Efficiency	  VII-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	VII-110
    7-8         Total U.S. Gas Reserves and Resources  	VII-128
    7-9         COo 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	VII-216
    7-17        Natural and Managed Tropical Moist Forest Yields   	VTI-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 .  . VH-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	VII-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  	VII-267

Chapter VIII

    8-1         Energy Intensity of Selected National Economies, 1973-85  	VIII-12
    8-2         Payback Periods in Years for Appliances, 1972-1980  	VIII-20
                                                xxi

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                                  LIST OF TABLES (Continued)

                                                                                              Page
    8-3        Appliance Efficiency Improvements Required by Law  	VIII-26
    8-4        Cogeneration Facilities	VIII-34
    8-5        Erodible Acreage Available to Offset CO2 Emissions From Electricity
              Production	VIII-37
    8-6        Government Efficiency Research and Development Budgets in OECD Member
              Countries, 1986	VIII-41
    8-7        Federal Energy Expenditures and Cost Avoidance, FY1985-FY1987	VIII-51
    8-8        Scenario Results for Realized and Equilibrium Warming	VIH-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)  	   IX-15
    9-6        World Bank Estimate of Capital Requirements for  Commercial Energy in
              Developing  Countries,  1982-1992  	   IX-16
    9-7        U.S. AID Forestry Expenditures by Region	   IX-23
    9-8        World Bank Energy Sector Loans in 1987	   IX-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
                                                xxii

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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
                                           xxm

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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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                                        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 ACTIVITIES	  1-26
       National Research and Policy Activities  	  1-26
       International Activities	  1-27

REFERENCES	  1-29
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Policy Options for Stabilizing Global Climate - Review Draft                          Chapter I








INTRODUCTION








The Earth's Climate and Global Change








    The greenhouse effect is a natural  phenomenon that  plays a central  role in determining the



Earth's climate.  Sunlight passes through the atmosphere and warms the Earth's surface.  The Earth



then radiates infrared energy, some of which escapes back into  space.  But certain gases  (known as



greenhouse gases) that  occur naturally in the atmosphere absorb most of the infrared radiation and



emit some of this  energy back  toward the Earth, warming the surface. This  effect is,  to a great



extent, responsible for  making  the Earth conducive to  life.  In its absence, the Earth would be



approximately 30°C colder.








    Concerns about the greenhouse effect arise out of apprehension that anthropogenic (man-made)



emissions  of greenhouse gases will further warm the Earth.  Greenhouse gases — primarily carbon



dioxide (CO2), methane (CH4),  nitrous oxide (N2O), chlorofluorocarbons (CFCs),  and tropospheric



ozone (O3) — are produced as by-products of human activities.   When these gases are emitted  into



the atmosphere and their concentrations increase, the greenhouse effect is compounded.  The result



is an increase in mean  global temperatures.








    There is scientific  consensus that increases in greenhouse  gas emissions will  result  in climate



change (Bolin et al., 1986; NAS, 1979, 1983,  1987; WMO,  1985).  The Council on  Environmental



Quality concluded in 1981 that the potential long-term risks of societal disruption caused by increased



atmospheric concentrations of CO2 (aside from the  other greenhouse gases) are significant. However,



considerable uncertainty exists with regard to the ultimate magnitude of the warming, its timing, and



the regional patterns of change.  In addition, there is great uncertainty about changes  in climate



variability and regional impacts.
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Policy Options for Stabilizing Global Climate - Review Draft                          Chapter I








CONGRESSIONAL REQUEST FOR REPORTS








    EPA has studied the effects of global warming for several years. The goal of its efforts has been




to use the best available information and models to assess the  effects of climatic change and to



evaluate policy strategies for both  limiting and adapting to such change.








    In 1986, Congress asked EPA to develop two reports on global warming.  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.   Tliis 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




    gases such  as methane and nitrous oxide; as well as the potential for and effects of reducing




    deforestation and increasing reforestation efforts."








    These issues are the focus of this report.








    This report differs from most previous studies of the climate change issue in that  it  is primarily



a policy  assessment.   Although some  aspects  of the relevant scientific  issues are reviewed, this



document is not intended as a comprehensive scientific assessment. A recent review of  the state of



the science is contained in the U.S. Department of Energy's State of the Art series (MacCracken and




Luther, 1985a,  1985b; Strain and Cure,  1985; Trabalka, 1985).








    Congress also asked EPA to prepare a companion report on the health  and environmental effects




of climate change in the U.S., which would examine the impact  of climate change on  agriculture,
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Policy Options for Stabilizing Global Climate ~ Review Draft                         Chapter I








forests,  and water resources, as well as on other ecosystems and society.  In response  to the latter




request, EPA produced its  report entitled,  Tlie Potential Effects of Global Climate Change on the




United States (Smith and  Tirpak, 1989).  That report provides  insights  into the ranges of possible




future effects that may occur under alternative climate change scenarios, and establishes qualitative



sensitivities of different environmental systems and processes to changes  in climate. The report also




examines potential changes  in  hydrology, agriculture,  forestry, and infrastructure in  the Southeast,




Great Lakes, California, and Great Plains regions of the United States.








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




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 for the




scope of this study to be global and the time horizon to be more than a century, because of the long




lags built into both the economic and climatic systems (we chose 1985-2100 as the time frame for



the analysis).  Predictions with such a scope cannot be attempted, 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.
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter I








    •       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 warming.








    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.








Report Format








    The structure of this report is designed to answer the following questions in turn:   What is the



greenhouse  effect?  What evidence is there that  the greenhouse effect is increasing?  How will the




Earth's climate respond to changes in greenhouse gas concentrations?  What activities are responsible




for the greenhouse  gas emissions? How might emissions and climate change in the future?  What
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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter I
                          TERMINOLOGY OF CLIMATE CHANGE
   An attempt has  been made  throughout this  report to avoid  technical jargon, yet some
   specialized terminology is inevitable.  The specialized terms used in this Report are defined
   below.

   Climate System

   The interactive components of our planet  which determine the climate.  This includes the
   atmosphere, oceans, land surface, sea ice, snow, glaciers, and the biosphere.  Climate change
   can be measured  in terms of any part of the system, but it is most convenient to use surface
   air temperature as a measure of climate, since it is the parameter for which we have the best
   record and it is most directly relevant to the component of the biosphere that we know best -
   - humans.

   Radiative Forcing (also called "external forcing," 'forcing," or "perturbation")

   A change imposed on the climate system (as opposed to generated by the internal dynamics
   of the climate system) that modifies the radiative balance of die climate system. Examples
   include:  changes in the output of the sun or the orbit of the Earth about the sun, increased
   concentrations of particles in the atmosphere due to volcanoes or human activity, and increased
   concentrations of greenhouse gases in the atmosphere due to human activity. Radiative forcing
   is often specified as  the net change  in  energy flux  at  the  tropopause (W/m2) or the
   equilibrium change in surface temperature  in the absence of feedbacks (°C).

   Climate Feedbacks

   Processes that alter the response of the climate system to  radiative forcings. We distinguish
   between physical  climate feedbacks and biogeochemical climate feedbacks. Physical climate
   feedbacks are processes of the atmosphere, ocean, and land surface, such as increases  in
   water vapor, changes  in cloudiness, and  decreases in land- and sea-ice accompanying global
   warming.  Biogeochemical feedbacks involve changes in global biology and chemistry, such  as
   the effect of changes in ocean circulation  on  carbon dioxide concentrations and changes  in
   albedo from shifts in ecosystems. The impact of climate feedbacks is generally measured  in
   terms of their effect on climate sensitivity. Positive feedbacks increase climate sensitivity, while
   negative feedbacks reduce it.

   Climate Sensitivity (or equilibrium sensitivity)

   The ultimate change hi climate that can be expected from a given radiative forcing.  Climate
   sensitivity is generally measured as the change in global average surface air temperature when
   equilibrium between incoming  and  outgoing radiation is reestablished following a change  in
   radiative forcing.  A  common benchmark, which  we use in this report,  is the equilibrium
   temperature increase associated with a doubling of the concentration of carbon dioxide front
   preindustrial levels.  The National Academy of Sciences has estimated that this sensitivity is
   in the range of  1_5-4.50C, with a recent analysis suggesting 1.5-5.5°C; a  reasonable central
   uncertainty range is 2-4°C.
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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter I
                         TERMINOLOGY OF CLIMATE CHANGE
                                        (continued)
   Transient Response
   The time-dependent response of climate to radiative forcing.  Climate responds gradually to
   changes in radiative  forcing, primarily because of the heat capacity of the  oceans.  The
   transient mode is characterized by an imbalance between incoming and outgoing radiation,
   Given the changing  concentrations of greenhouse gases the Earth's climate mil  be in a
   transient mode for the foreseeable future.  Most GCMs  (see below), however, have so far
   examined equilibrium conditions because transient effects are much more difficult to analyze.

   Albedo

   The fraction of incoming solar radiation that is reflected back into space.

   Flux

   How per unit time per unit area.  The flow can be of energy (e.g., watts per square meter
   [W/m*|) or mass (e.g.» grams per square meter per day {g m'2
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Policy Options for Stabilizing Global  Climate  -- Review Draft                         Chapter I








technologies  are  available for  limiting  greenhouse  gas emissions?   And what domestic  and




international policy options, if implemented, would help to stabilize global climate?








    This chapter provides a general introduction to the climate change issue and  reviews selected




previous studies.   Chapter II discusses the greenhouse  gases, their  sources and sinks, chemical




properties, current atmospheric concentrations  and distributions, and related uncertainties.  Chapter




III relates the greenhouse gases to the process of climatic change.  Once this link is made, Chapter




IV examines those human activities that affect trace-gas emissions and ultimately influence climate




change.  Chapter V discusses  the scenarios developed for this report to assist us in thinking about




possible future emissions and  climate  change.  Chapter VI then presents sensitivity analyses of the




modeling results.  Chapter VII gives a  detailed description of existing and emerging technologies that




should be considered in the formulation of a comprehensive strategy for mitigating global warming.




Chapter VIII outlines domestic policy options, and the concluding chapter (Chapter DC) discusses




international mechanisms for  responding to climate change.








THE GREENHOUSE GASES








    Congress presented EPA with an  extremely challenging task.  Once emitted, greenhouse gases



remain  in the atmosphere for decades to centuries. 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.  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.   Indeed, in many cases drastic cuts in




emissions would be required  to stabilize atmospheric composition.
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Carbon dioxide








    Carbon dioxide (CO2)  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 show an increase from  315 to 350 parts per  million (ppm)  by volume




(Figure 1-1).  These  data clearly demonstrate that human activities are now of such a magnitude as




to produce global consequences.  Current emissions are estimated at 5.5  billion tons of carbon (Pg




C) from fossil-fuel combustion  and 0.4-2.6 Pg  C from deforestation.1  Most of this CO2  remains in




the atmosphere or is absorbed by the ocean.  Even though only about hah0 of current emissions




remain  in  the atmosphere, currently available models of  CO2 uptake by the  ocean suggest that




substantially more than a 50% cut in emissions is required to stabilize concentrations  at current




levels (Figure  1-2).








Methane








    The concentration of methane (CH4) has more than doubled during the  last three centuries.



Methane, which is currently increasing at a rate of 1% per year, is responsible for about 20% of




current  increases in the greenhouse effect. Of the major greenhouse gases, only CH4 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 the lifetime remains constant, which may  require that  hydrocarbon and carbon




monoxide emissions be stabilized).
    1 One billion tons of carbon  = 1015 grams of carbon =  1 petagram of carbon (Pg C).








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Policy Options for Stabilizing Global Climate -• Review Draft
                                  Chapter I
                                    FIGURE 1-1
      CARBON DIOXIDE CONCENTRATIONS AT MAUNA LOA
                   AND FOSSIL FUEL C02 EMISSIONS
                                                                          2000
      I U 5 0 1900  1963 1964  I860 1961)  1871) 1972 1074  1976 1870  1 0 H 0 1862  I9B4 188C  1808
 Figure 1-1.  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 steadily increasing concentration of
 atmospheric CO? at Mauna Loa since the 1950s is caused primarily by the CO2 inputs from fossil
 fuel combustion (dashed line).  Note that CO2 concentrations have continued to increase since 1979,
 despite relatively constant emissions; this is because emissions have remained substantially larger than
 net removal, which is primarily by ocean uptake.   (Sources: Keeling, 1983, pers. communication;
 Komhyr et al., 1985; NOAA, 1987; Conway et al.,  1988; Rotty, 1987, pers. communication.)
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February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                      Chapter I
                                FIGURE 1-2
            IMPACT OF C02 EMISSIONS REDUCTIONS

              ON ATMOSPHERIC CONCENTRATIONS
                             (Parts Per Million)
       500
       475 \-
       326
         1965   2000
2025       2050

        YEAR
2075
2100
Figure 1-2. The response of atmospheric CO2 concentrations to arbitrary emissions scenarios based
on two one-dimensional models of ocean CO2 uptake. See Chapter VI for a description and models.
(Sources:  Hansen et al, 1984; Lashof, 1988; Siegenthaler, 1983).
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Nitrous oxide








    The  concentration of nitrous oxide (N2O)  has  increased by 5-10% since preindustrial times.



Nitrous  oxide is currently increasing at  a rate of 0.25% per year, which represents an imbalance of




about 30% between sources and sinks.  Assuming that the observed increase in N2O concentrations




is due to anthropogenic sources and that natural emissions have not  changed, then an 80-85% cut



in anthropogenic emissions would be required to stabilize N2O  at current levels.








Chlorofluorocarbons








    Chlorofluorocarbons (CFCs)  were introduced into the atmosphere for the  first time during this




century.   The  most  common species  are  CFC-12 (CFjCy  and  CFC-11  (CFC13),  which had




atmospheric concentrations in 1986  of 392 and 226 parts per trillion  (ppt) by volume, respectively.




While these concentrations are tiny  compared with that of CO2, each additional CFC molecule has




as much as 20,000 times more impact on climate, and CFCs 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 concentrations  of  CFCs also account for about 15% of current  increases in the



greenhouse effect. For CFC-11 and CFC-12, cuts of 75% and 85%,  respectively, of current global



emissions would be required to stabilize concentrations.  However, in order to stabilize stratospheric



chlorine levels ~ of particular  concern for stratospheric ozone depletion ~ a 100% phaseout of fully-



halogenated compounds (those that do not contain  hydrogen)  and a freeze on the use of methyl




chloroform would be required.
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Other gases influencing composition








    Emissions of carbon monoxide  (CO), nitrogen oxides (NOJ, and 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 stabilized, it might only be necessary to freeze emissions of the short-lived gases at current



levels to stabilize atmospheric composition.








PREVIOUS  STUDIES








    Evidence that the composition of the atmosphere  is changing has led to a series of studies



analyzing the potential magnitude of future greenhouse gas emissions. A few of these studies have



carried the analysis further, making projections of the timing and severity of future global warming.



The first generation of these studies focussed principally on energy use and CO2 emissions.  (See,



for example, Arrhennius, 1896; NAS, 1979; Clark et al, 1982; IIASA, 1983; Nordhaus and Yohe, 1983;



Rose et al.,  1983; Seidel and Keyes, 1983; Edmonds and Reilly,  1983b, 1984; Legasov, et al. 1984;



Goldemberg  et al., 1985, 1987; and Keepin et al., 1986).  Subsequent studies have recognized that



other radiatively-active trace gases significantly amplify the effects of CO2.  (See, for example, Lacis



et al., 1981; Ramanathan et al., 1985; Dickinson and Cicerone, 1986; WMO, 1985; and Mintzer, 1987).



In the following sections, some of the most important of these earlier analyses are reviewed in order



to provide a basis for comparison with this study.
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Estimates of the Climatic Effects of Greenhouse Gas  Buildup








     The first serious analysis of the effect of increasing CO2 concentrations on global warming was



conducted by the Swedish chemist Svante Arrhennius (1896).  Arrhennius, concerned  about the



rapidly increasing rate of fossil-fuel use in Europe, recognized that the resulting increase in the



atmospheric concentration of CO2 would alter  the  thermal balance of the atmosphere.  Using a



simplified, one-dimensional model, Arrhennius estimated that if the atmospheric concentration of CO2



doubled, the surface of the planet would warm by about 5°C.   (The expected equilibrium  climate



change associated with a doubling of CO2 has become  a benchmark. That is, many studies examine



the consequences of greenhouse gas increases with a total warming effect equivalent to that  from a



doubling of  the concentration of CO2.)








    In  1979, a study by the U.S. National Academy of Sciences (NAS) evaluated the impact on global



climate of doubling the concentration of  CO2 relative to the preindustrial atmosphere (NAS, 1979).



The NAS study concluded that the planet's surface would be 1.5-4.5°C warmer under such conditions.



Subsequent re-evaluations by NAS  (1983, 1987) as well as the "State-of-the-Art" report issued by the



Department of Energy (MacCracken and Luther, 1985a) have reaffirmed this estimate.







    Recent work by Dickinson (1986) suggests that the  effects of a greenhouse gas buildup radiatively



equivalent to doubling the preindustrial concentration of CO2 might warm the planet to a  greater



extent  than  had  previously been expected.  Focusing on the uncertainties in current understanding



of atmospheric feedback processes, Dickinson estimated that the warming effect of such a buildup



was likely to be between 1.5° and 5.5°C.  Dickinson's "best guess" was that  the actual equilibrium



wanning would be between 2.5° and 45°C.
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Studies  of Future CO2 Emissions








    For the next eighty years after Arrhennius issued his warning, little additional scientific attention



was directed toward understanding the factors that contribute to  future greenhouse gas emissions.



By the mid-1970s, measurements of atmospheric CO2 concentrations at Mauna Loa begun by Keeling



during the International Geophysical Year (1957-1958) provided indisputable evidence of a long-term



increasing trend (see Figure 1-2), while the oil embargo of 1973 and the nuclear power debate



focussed attention on future energy  supplies.   Increasing interest was placed  on the problems of



projecting future global energy use and on estimating the resulting CO2 emissions.








    A major international study of future energy use was conducted by the International Institute for



Applied Systems Analysis (IIASA, 1981 and 1983).  Employing an  international group of almost 200



scientists, the IIASA team developed a set of computer models to estimate regional economic growth,



energy  demand, energy  supply, and future  CO2  emissions.  Although  the  models  were never



completely integrated, the first phase of the IIASA  study produced two complete scenarios of global



energy use.  The IIASA low scenario generated CO2 emissions of about 10 petagrams of carbon per



year (Pg C/yr) in 2030.  The IIASA high scenario projected emissions of about 17 Pg C/yr in 2030.



In the second phase of the IIASA study  a third scenario was outlined, emphasizing increased use of



natural gas.   In this third scenario, CO2 emissions in 2030 were only about 9.4 Pg C/yr.







    In 1983 Edmonds and Reilly, two U.S. economists,   developed a detailed partial equilibrium



model to investigate the effects of alternative energy policies  and  their implications for future CO2



emissions (Edmonds and Reilly, 1983a).  This model disaggregates the world into nine geopolitical



regions.  It  offers a highly  detailed  picture of the supply side of the world's commercial energy



business but only limited detail on the demand side. It considers nine  primary and four secondary



forms of commercial energy (including biomass grown  on plantations) but ignores non-commercial
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uses of biomass for fuel. Using explicit assumptions about regional population changes and economic




growth and combining them with assumptions about technological change and the costs of extracting




various grades of fuel resources in each region, the model calculates supply and demand schedules



for each type of fuel.








    For their first major report, Edmonds and Reilly (1983b) developed a Base Case energy future




for the period 1975 to 2050.  In this scenario, CO2 emissions in 2050 were approximately 26.3 Pg




C/yr. The authors generated several other scenarios in this study that reflected the effect of various




taxes imposed on fuel supply and use.  These taxes reduced CO2 emissions by varying amounts, with



emissions  in some scenarios falling  as low as 15.7 Pg C/yr in 2050.  In 1984 Edmonds and Reilly




produced a new set of scenarios for  the U.S. Department of Energy by varying other key parameters



in the model (Edmonds and Reilly, 1984).  In these new scenarios, CO2 emissions in 2050 vary from




about 7 to 47 Pg C/yr, with a  new "Base Case" value  of about 15  Pg C/yr.   The principal force




contributing to  the difference between the results  of the two studies conducted by Edmonds and




Reilly is the higher coal price applied in the second study.








    A number of other studies have used the  Edmonds-Reilly (ER) model to project future energy



use  and  CO2 emissions.   The most  important  of these were  studies  conducted  by  the  U.S.



Environmental Protection Agency (Seidel and  Keyes,  1983) and Rose et al. (1983).  The EPA study



used the ER model to generate  13  scenarios for  the period 1975-2100, which were used as a basis



for investigating whether actions taken now to reduce fossil-fuel consumption could significantly delay




a  future global warming.  Six baseline and seven policy-driven  scenarios  were investigated in this




study.  The scenarios generated in the  EPA study projected CO2 emissions in 2050 at levels of 10-




18 Pg C/yr.  The authors concluded from these scenarios that the timing of a 2°C warming is not




very sensitive to the effects of the energy policies they tested.
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    Rose and his colleagues at the Massachusetts Institute of Technology (MIT) also used the ER



model to study the effect of various  energy policy options on the timing and extent of future CO2



emissions (Rose et al., 1983).  Eleven scenarios were investigated, covering the period from 1975 to



2050 and incorporating a much wider  range of assumptions and policies than those tested in the EPA



study. Rose et al. studied the effects of increased energy efficiency, increased fossil-fuel prices, higher



nuclear  energy supply costs and a moratorium on building nuclear plants, lower photovoltaic costs,



higher oil prices, and a cutoff of oil imports from the Middle East.  The MIT  study went beyond the



ER model results to  provide  detailed  estimates of the materials required for construction  and



operation  of energy facilities in each scenario.  In the  MIT scenarios, emissions of CO2 in 2050



ranged from  less than 3 to about 15 Pg C/yr.  The most important new conclusion of Rose et al.



was that a feasible "option space exists in which the CO^climate problem is  much  ameliorated"



through energy policy choices and improvements in technology.








    In 1983  the National Academy  of Sciences completed a Congressionally-mandated study to



evaluate, among other things, the effects of fossil-fuel development activities authorized by the Energy



Security Act of 1980 (NAS, 1983). One of the chapters in this study, authored by energy economists



Nordhaus  and Yohe, used a compact model of global economic  growth and  energy use to analyze



CO2 emissions between 1975 and 2100 (Nordhaus and Yohe, 1983). Unlike the partial equilibrium



approach employed in the ER model, the Nordhaus and Yohe (NY) model used a generalized Cobb-



Douglas production function to estimate future  energy demand.   In this approach global GNP is



estimated  as  a  function  of  assumptions about  average rates  of change  in  labor  productivity,



population, and energy consumption.   Demand for energy is separated into two categories, fossil and



non-fossil.  Projections of CO2 emissions (based on the weighted  average release rate from fossil



fuels)  were used as inputs to a simple airborne fraction model of the carbon cycle.
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Policy Options for Stabilizing Global Climate - Review Draft                          Chapter I



    The NY analysis used an approach called "probabilistic scenario analysis," to evaluate the effects

on CO2 emissions of alternative assumptions used in the model.  The results of 1000 cases were

examined.  The CO2 emissions trajectories in these cases were presented as percentiles in the overall

distribution among the 1000 scenarios.  Using this approach to uncertainty analysis, Nordhaus and

Yohe concluded that the 50th percentile for carbon emissions in 2050 was approximately 15 Pg C/yr.

The 95th percentile case suggested that emissions hi 2050 would likely be less than 26 Pg C/yr, while

the 5th percentile case indicated that emissions would likely be greater than 5 Pg C/yr.



    The probabilistic approach was subsequently applied to the more detailed ER model using Monte

Carlo analysis (Edmonds et al., 1986; Reilly et al., 1987). The results of this analysis suggest  a larger

total range of uncertainty and a substantially lower median emissions estimate compared with  the

Nordhaus and Yohe (1983) results.  When the likely correlations  between model parameters  are

taken into  account Edmonds et al. obtain emissions of 7.7 Pg C/yr  in 2050 for the 50th  percentile

case with 5th and 95th percentile bounds of 2.3 and 58.1 Pg C/yr, respectively. Note that the median

result is about half of the Base  Case scenario obtained in earlier analysis by Edmonds and Reilly

(1984).



    In 1984 Legasov et al. published one of a continuing series of Soviet analyses  of future global

energy use and its environmental implications.  Legasov et al. analyzed two scenarios in which energy

demand reaches 6 and 20 kilowatts per capita by the end of the next century.  Annual per capita

energy consumption  is treated as a logistic function, approaching these levels asymptotically  in 2100.

Assuming a global population of  10 billion persons,  the minimal variant implies  a global energy

demand of 60 terawatts  (TW), about six times the current level by 2100.2  CO2 emissions in this

scenario follow a bell-shaped trajectory, peaking at about  133 Pg C/yr in 2050.
     2 1 terawatt =  1012 watts  = 31.5xl018 joules per year =  31.5  exajoules (EJ) per year =  29.9
Quadrillion British Thermal Units (Quads) per year.
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    Goldemberg and his colleagues have used a completely different approach to projecting future



energy use and its  consequences for CO2  emissions (Goldemberg et al., 1985,  1987, 1988).  The



Goldemberg et al. analysis is based on an end-use oriented approach to evaluating the demand for




energy services, rather than the availability of energy supply.  Based on  detailed studies of energy



demand in four countries (U.S., Sweden, India, and Brazil), Goldemberg and his colleagues developed




a scenario of future energy requirements in both industrialized and developing countries.  Although




the study does not  represent a forecast of future energy demand, it provides an "existence  proof,"




demonstrating the feasibility of a world economy that continues to grow while consuming much less




energy than it would if historical trends continue.








    Emphasizing the potential to improve the efficiency of energy supply and use, per capita energy




demand in the industrialized countries is cut by 50% in the Goldemberg et al. scenarios.  During the




same 40-year period, per capita demand for energy in the developing countries grows by about 10%,




with commercial fuels  displacing traditional biomass fuels at a rapid and increasing rate.   Global




energy demand remains essentially constant in the base case with CO2 emissions in 2020 of 5.9 Pg




C/yr, only about 5% higher than today's level.








    A limitation of the Goldemberg et al. studies is that the impact of market imperfections and the




rate of capital stock turnover are not fully addressed. Nonetheless, these studies, along with the Rose



et al. analysis, demonstrate that economic growth can be decoupled from increases in CO2 emissions.



Experience over  the last 15  years  in the U.S., Western Europe, and Japan  suggests that this



conclusion is correct.








    A study by Keepin  et al. (1986) reviewed and re-evaluated the range of previous energy and CO2




projections, including those summarized here. It concluded that the feasible range for future energy
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in 2050 was somewhere between about 10  and  35 TW, with  CO2 emissions between 2 and 20 Pg



C/yr.








Studies of the Combined Effects of Greenhouse Gas Buildup








    In  the  last  few years  a number of analysts have investigated  the combined effects on global




surface temperature of a buildup of CO2 and other trace gases. Preliminary analysis of the impact




of concentration increases during the 1970s was presented by Lacis et  al. (1981) and  estimates of




future impacts were included in Seidel  and Keyes (1983).  A  seminal article by Ramanathan et al.




(1985) focused attention on the subject. This study used a one-dimensional radiative-convective model




to estimate the impact of a continuation of current trends in  the buildup of more than two dozen




radiatively active trace gases between 1980 and 2030.  Ramanathan and  his colleagues calculated an



expected value for the  equilibrium  warming of about 1.5°C over this period, with a  little less than




hah0 of that amount due to the buildup of CO2 alone. (The Ramanathan et al. analysis included the



effects  of water-vapor feedback, but not the other known feedback mechanisms; see Chapter III.)




The most important conclusion of the analysis by Ramanathan et al. is that, if current trends continue




and uncertainties in the future emissions projections  are accounted for, the warming effects of the



non-CO2 trace gases will  amplify  the warming due  to the buildup of CO2 alone by a  factor of



between  1.5 and 3.








    In  1986, Dickinson and Cicerone extended the work of Ramanathan et al. to evaluate a range



of trace-gas scenarios covering the  period from 1985 to 2050.  Using the radiative-convective model




developed by Ramanathan  et al., and considering a range of emissions growth rates for the  most




important greenhouse gases, Dickinson and Cicerone (1986) estimated that equilibrium global  average




surface temperatures would rise at least 1°C and possibly more than 5°C by 2050, when the full range



of atmospheric feedback processes  was  considered.
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    Each of the analyses described above was based on the assumption that historical trends in the



growth of greenhouse gas emissions continue for the next 40-50 years.  Mintzer (1987) has developed



a model to consider the alternative:  that policy and investment choices  made in the next several




decades  will substantially alter  the growth rates  of future emissions.  Mintzer's  analysis uses a




composite tool called the Model of Wanning Commitment to link future rates of economic growth



to the increasing atmospheric concentrations of carbon dioxide, nitrous oxide, chlorofluorocarbons,




methane, and  tropospheric ozone.  The results are reported as the date of atmospheric commitment




to a  warming  equivalent to doubling preindustrial  CO2 concentrations and as  the magnitude of




warming commitment in 2075.








    Mintzer's  initial  analysis considered four policy-driven  global scenarios, including a Base Case




representing a continuation of current trends.  All four scenarios  support a global population of about



10 billion people and the same levels of regional economic  growth.  Most recent analyses, including




the ones cited above and Mintzer's Base Case, indicate that a continuation of current trends would



lead to a warming commitment equivalent to  doubling the preindustrial concentration of CO2 by




about 2030.  In Mintzer's Base  Case, by 2075, the planet is committed to an eventual warming of



about 3-9°C.   Alternatively, in the  High Emissions  case, policies  that increase  coal use, spur



deforestation,  extend the use  of  the most  dangerous CFCs  and limit  improvements  in energy




efficiency, will accelerate the onset of the "doubled CO2 equivalent" atmosphere to about 2010 and



commit the planet to a warming of about  5-15°C in 2075.  By  contrast, in Mintzer's Slow Buildup



scenario, a warming associated with the doubled CO2 equivalent atmosphere is postponed beyond



the end of the simulation period in 2075.   In the Slow Buildup scenario this  level of risk reduction



is achieved by aggressively pursuing policies to increase energy efficiency, limit tropical deforestation,




reduce the use of the most dangerous CFCs, and shift the fuel  mix from carbon-intensive fuels like



coal to hydrogen-intensive fuels like natural gas, and ultimately,  to energy sources  that emit no CO2.
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    More recently, Rotmans et al. (1988) have used a framework similar to the Model of Warming



Commitment to develop scenarios of greenhouse warming based  on alternative policy assumptions.



Also, Rotmans and Eggink (1988) have analyzed the role of methane in greenhouse wanning.








Major Uncertainties








    Major uncertainties underlie many aspects of our understanding of the climate change problem.



These uncertainties  encompass our  understanding  of the geophysical  processes  underlying  the



sensitivity of the climate to perturbations,  that is, the processes  that control how fast greenhouse



gases flow into  and  out of the atmosphere and biosphere, including feedback processes that may



affect future concentrations of greenhouse gases, and socio-economic uncertainties that are inherent



in any energy/economic  model used to forecast long-term emissions.  The physical uncertainties



include uptake of heat and CO2 by the ocean and any other sinks, geophysical  and  biogeochemical



feedback  mechanisms, and natural rates  of emission of the  greenhouse gases.  The social  and



economic uncertainties include population growth, GNP growth, structural changes in economic



systems, rates of technological change, future reliance on fossil fuels, and future compliance with the



Montreal  Protocol.  Future rates  of greenhouse gas emissions cannot be predicted with certainty.



Future emissions rates will  be  determined by  the emerging  pattern  of  human industrial  and



agricultural activities as well  as by the effects of feedback processes in the Earth's biogeophysical



system whose details are not well  understood at the  present time.








    All existing climate models encompass large uncertainties that limit the  accuracy of the models



and the level of geographic detail  that can be considered.  Even the best General Circulation Models



(GCMs)  are limited by the assumptions necessarily made about the influence of clouds, vegetation,



ice and snow, soil moisture, and terrain, all of which affect the energy balance of the  Earth's surface.
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Two of the largest uncertainties involve our limited understanding of the role that clouds, and ocean



uptake and transport of beat, play in the climate system.








Conclusions From Previous Studies








    Despite the significant uncertainties that underlie our understanding of climate change, several



important conclusions emerge from the existing literature.  First, emissions of a number  of other



trace gases will  amplify  the  future warming  effect of any  further  buildup  in the atmospheric



concentration  of CO2.   Second, it  is too late to prevent all future global  warming.  Trace gases



released  over  the last century have already committed the planet to an ultimate warming (of up to



2°C) that may be greater than any other in the  period of written human  history.  Finally, policy



choices and investment decisions made during the next decade that are designed to increase the



efficiency of energy use and shift the fuel mix away from fossil fuels could slow the rate of buildup



sufficiently to  avoid the most catastrophic potential impacts of rapid climate change.  Alternatively,



decisions to rapidly expand the use of coal, extend the use of the most  dangerous  CFCs, and rapidly



destroy the remaining tropical forests could "push  up  the calendar," accelerating the onset of a



dangerous global warming.








    The  rate at which climate  may change must be of particular concern to policy makers.  The



temperature increases resulting from doubling the concentration of CO2 that are  predicted  by most



GCMs are comparable to the increase that has occurred since the last ice age. The difference is that



the period of tune within which this increase could happen is much shorter. Atmospheric scientists



predict that within approximately  100 years we could experience temperature increases equivalent to



those that have "occurred over the past 18,000 years (about 5°C; see Chapter III).   It is not clear that



our ecosystems and economic systems will be able to adjust to such a  rapid change in global mean
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter I








temperatures.   Increases in world population, coupled with limited environmental and agricultural



resources, increase the vulnerability of social  systems to climatic change.








    The potential impacts of climatic change  are highly uncertain and are beyond the scope of this




report. They are addressed hi the companion  volume, Tlie Potential Effects of Global Climate Change




on the United States (Smith and Tirpak, 1989). The findings of this 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." Although sensitivities



were identified in this report, detailed regional predictions of climate change cannot be made at this




time.  Thus potential responses to the greenhouse gas buildup must  be viewed hi the  context of risk



management, or buying insurance.








    A second major concern is that  the greenhouse gases have very long lifetimes  once they are



introduced into the  atmosphere.  Although  there  is a substantial lag between the time when  a



greenhouse gas  is introduced into the atmosphere and when its full impact on  climate is realized,



once the gases are in the atmosphere they will remain there for a long time. The longer  the delay



before mitigating action is taken, the larger will be  the commitment to further global warming.








    Policy makers must determine how best to minimize the costs of global warming  to the peoples




of the world  and the damage to ecosystems.   But global warming is a complex problem for which




there is no single, simple solution.  No single policy initiative will completely mitigate man-made




climate change.  The sources, sectors, and countries contributing to the emissions of greenhouse gases




are numerous (Chapter IV).
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter I








    Compounding the difficulty  of  identifying  solutions to the greenhouse problem  is  that the



greenhouse gases do not all have the same forcing effect on global temperatures. In fact, CO2 is the



least effective absorbent of infrared radiation of all  of the greenhouse gases per additional molecule



added to the atmosphere.  Because the combined effect of the other greenhouse gases is comparable



to the effect of CO2, mitigatory policies cannot  be  directed  solely at reducing CO2 emissions.  The



sources  of methane,  CFCs, nitrous oxide,  and other gases must therefore be carefully considered.








    As we explore the options for limiting greenhouse gas emissions in this report,  it is important



to remember two salient points:  (1)  Global warming is an international problem whose solution will



require extensive cooperation between both industrialized and developing countries; and (2) No single



economic sector can  be held entirely responsible for the greenhouse effect.  In focusing on strategies



to stabilize climate in this Report, we recognize that the optimal mix of adaptation  and prevention



is uncertain.  The Earth is already committed to some  degree of climatic change, so adaptation  to



some level of change is essential.  On the other hand, the highest rates of potential  change may be



considered unacceptable, requiring some degree of prevention. Stabilizing strategies would require



global cooperation of an unprecedented nature and could be costly for some countries. The activities



responsible for greenhouse gas emissions  are economically valuable, the distribution  of emissions is



large, and the responsible countries reflect diverse economies and a variety of interests.  Adaptation



strategies, on the other hand, can be adopted unilaterally.   They may  also  be  less burdensome



because the costs will  be spread out into the future when countries may be better able to afford



them.  Imposing  climatic change  on our grandchildren, however, raises serious concerns regarding



intergenerational  equity.
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter I








CURRENT NATIONAL AND INTERNATIONAL ACTIVITIES








    Subsequent to the Congressional request to produce this report and the companion document on




potential effects of climate change there have been a wide variety of new domestic and international




initiatives related to climatic change.








National Research and Policy Activities








    The Global Climate Protection Act of 1987 requires  that:








           The  President,  through the  Environmental  Protection Agency,  shall  be




           responsible for developing and proposing to Congress a coordinated national



           policy on global climate change.








This Act is a very broad mandate that will require  close cooperation between  EPA and other




agencies  (including NASA,  NOAA, the Corps  of Engineers, and the Departments  of  Energy,



Agriculture, and the  Interior,  the  National  Climate  Program Office, and  the Domestic Policy



Council).








    The  Global  Climate Protection Act also requires that the Secretary of State  and the EPA



Administrator jointly submit, by the end of 1989, a report analyzing current international scientific



understanding of the greenhouse effect,  assessing U.S. efforts to gain international cooperation in




limiting global climate change, and describing the  U.S. strategy for seeking  further international




cooperation to limit global climate change.  This report, along with those being developed by other




Federal agencies, will provide a foundation upon  which a national policy can be  formulated.
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter I








International Activities








    The greenhouse gas  problem is  an international issue.  In order  to respond effectively to this




problem, the nations of  the  world must act in concert.  Several  international organizations have




recognized the need for multilateral  cooperation and have become involved with the global climate




change issue.  The United Nations Environment Programme (UNEP) is responsible for conducting



climate impact assessments.  The World Meteorological Organization (WMO) is supporting research




on  and  monitoring of atmospheric and physical sciences.  The International  Council  of Scientific




Unions (ICSU) is developing an international geosphere-biosphere program.








    The U.S.  Government is supporting the Intergovernmental Panel on  Climate  Change (IPCC)




established under the auspices  of UNEP and WMO.  The IPCC, which  held its  first meeting in



November 1988, will help ensure an orderly international effort in responding to the threat of global




climate change.  At its first meeting  the IPCC established three working groups: the first, to assess




the state of scientific knowledge on the issue, will be chaired by the United Kingdom; the second,




to assess the potential social and economic effects from a warming, will be chaired by the Soviet




Union; and the third, to examine possible response  strategies, including options for limiting emissions




and adapting to change, will be chaired by the United States.








    In addition, several countries have held or plan to hold international conferences on global



climate change.  These include Canada, The Federal Republic of Germany, Italy, Japan, India, Egypt,



and the Netherlands.  The Netherlands and the Federal Republic of Germany (through  the Enquete



Commission) are undertaking analyses of policy options.








    The efforts of all of these organizations may be hindered if some  countries perceive themselves




as winners instead of losers, as a result of climate change. For example, both Canada and the Soviet
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Policy Options for Stabilizing Global Climate - Review Draft                          Chapter I








Union, which have vast land areas that are currently largely unusable because  of their severe




climates,  could benefit from increased agricultural productivity as those areas become warmer.  But




the notion that a global warming might be beneficial to some may prove fallacious.  Two particular




problems might limit anticipated benefits.   First, if the  shift in climatological zones happens too




quickly,  ecosystems may not be able to keep  up and may be severely disrupted.   Although the




Canadian climate may become more conducive to certain types of forests, if the forests can't migrate




fast enough and therefore die back as  the  climatological zones  shift  northward, benefits to the




Canadians will be reduced.  Second, although shifts  towards more favorable climatic  conditions may




be a necessary condition for increased agricultural productivity, a warmer climate  in itself may not




be sufficient.  For example, the northern areas of Canada might not have the proper soil composition




for high agricultural yields.  The conclusion must therefore be drawn that it is difficult to  predict




what the net  costs and benefits of climate change will be for any one country.








    The  global  warming  issue is  an international concern.   In  order to develop  a  responsible




program, the U.S.  government  must  consider  the  feasibility of  achieving both  domestic  and




international  acceptance  and implementation of policy initiatives.   Otherwise,  the effectiveness of



programs instituted by any one country could be compromised by the lack of participation by other



countries. International collaboration must be pursued.
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter I
                                       REFERENCES


Arrhennius,  S.  1896.  On the influence of carbonic acid in the air  upon the temperature on the
ground. Phil. Mag.   41:237.

Bolin, B.,  J. Jager, and B.R. Doos.  1986. The greenhouse effect,  climatic change, and ecosystems:
A synthesis  of present  knowledge. In Bolin, B.,  B.R. Doos, J. Jager, and RA. Warrick, eds.  The
Greenhouse Effect,  Climatic Change,  and Ecosystems. Scope 29. John Wiley & Sons, Chichester 1-
34.

Clark, W.C., K.H., Cook, G., Marland, A.M. Weinberg, R.M. Rotty, P.R., Bell,  LJ. Allison, and C.L.
Cooper. 1982. The carbon dioxide question:  A perspective  in 1982. In Clark, W.C. ed. Carbon
Dioxide Review  1982. Oxford University Press, New York. 3-43.

Conway, T.J., P. Tans, L.S. Waterman, K.W. Thoning,  KA.  Masarie, and R.H.  Gammon.  1988.
Atmospheric carbon  dioxide measurements in the remote global  troposphere. 1981 -  1984. Tellus
40:81-115.

Council on Environmental Quality. 1981. Global  Energy Futures and the CO2 Problem.  The Council
on Environmental Quality, Washington, D.C.

Dickinson, R. 1986. The Climate System and modelling of future climate. In Bolin, B., B. Doos, J.
Jager, R. Warrick,  eds.  Tlie Greenhouse Effect,  Climatic Change, and Ecosystems.  Scope 29.  John
Wiley & Sons, Chichester.  207-270.

Dickinson, R.E., and R.J. Cicerone. 1986.  Future global warming from atmospheric  trace gases.
Nature 319:109-115.

Edmonds, JA.,  and J.M. Reilly. 1983a. A long-term global energy-economic model of carbon dioxide
release from fossil  fuel use Energy Economics 5:74-88.

Edmonds, JA., and  J.M. Reilly. 1983b. Global Energy and CO2 to the Year 2050.  The Energy
Journal 4:21-47.

Edmonds, JA.,  and J.M. Reilly. 1984. The IEA/ORAU Long-Term Global Energy CO2 Model. Carbon
Dioxide Information  Center, Oak Ridge National Laboratory,  Oak Ridge, Tennessee.

Edmonds, J., J. Reilly,  R. Gardner, and A. Brenhert. 1986.  Uncertainty in future global energy use
and fossil  fuel CO2 emissions 1975-2075. U.S. Department of Energy, Washington, D.C. DOE/NBB-
0081 (TR036).

Goldemberg, J., T.B. Johansson, A.K.N.  Reddy, and R.H. Williams, 1985.  An  end-use oriented
global energy strategy.  Tlie Annual Review of Energy 10:613-688.

Goldemberg, J., T.B. Johansson, A.K.N. Reddy, and R.H. Williams.  1987. Energy for a Sustainable
World.  World Resources Institute, Washington,  D.C.  119 pp.

Goldemberg, J., T.B. Johansson, A.K.N. Reddy, and R.H. Williams.  1988. Energy for a Sustainable
World.  Wiley Eastern Limited, New Delhi, India.  517 pp.
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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter I
Hansen, J.,  A. Laos, D. Rind, G. Russell, P. Stone, I. Fung, R.  Ruedy, and J. Lerner.   1984.
Analysis of  feedback mechanisms.  In J. Hansen, and T.  Takahashi, eds. Climate Processes and
Climate Sensitivity. Geophysical Monograph 29, Maurice Ewing Volume 5.  American Geophysical
Union, Washington, D.C. 130-163.

IIASA (International Institute for Applied Systems Analysis). 1981. Energy in a Finite World.  Hafele,
W., ed. Ballinger, Cambridge.

IIASA (International  Institute  for Applied  Systems Analysis). 1983.   '83  Scenario for Energy
Development:  Summary.  Rogner, H.H., ed.  IIASA, Laxenburg, Austria.

Keeling, CD.  1983. The global carbon cycle:  What  we know and could know from  atmospheric,
biospheric, and oceanic observations.  In Proceedings of the  CO2 Research  Conference:   Carbon
Dioxide, Science and Consensus.  DOE CONF-820970, pp. 11.3-11.62.

Keepin, W.,  I.  Mintzer, and L. Kristoferson.  1986.  Emission of CO2 into the atmosphere. In Bolin,
B., B.R.  Doos, J. Jager, and RA. Warrick, eds.  The Greenhouse Effect, Climatic  Change, and
Ecosystems.  Scope 29.  John Wiley and Sons, Chichester.  35-91.

Komhyr,  W.D., R.H. Gammon,  T.B. Harris, L.S.  Waterman, TJ. Conway, W.R. Taylor, and K.W.
Thoning. 1985. Global atmospheric CO2 distribution and variations from 1968-1982 NOAA/GMCC
CO2 flask sample data. Journal of Geophysical Research 90:5567-55%.

Lacis, A., J. Hansen, P. Lee, T. Mitchell, and S. Lebedeff.  1981. Greenhouse  effect of trace gases,
1970-1980. Geophysical Research Letters 8:1035-1038.

Lashof, D.  1988.   The Dynamic Greenhouse:  Feedback Processes That May  Influence  Future
Concentrations of Atmospheric Trace Gases. U.S. Environmental Protection Agency, Washington, D.C.

Legasov,  VA., I.I. Kuzmin, and  A.I. Chernoplyokov.  1984.  The influence of energetics on climate.
Fizika Atmospheri i Okeana 11:1089-1103.  USSR  Academy of  Sciences.

MacCracken, M. C, and F. M. Luther, eds. 1985a. Projecting the Climatic Effects of Increasing Carbon
Dioxide. U.S. Department of Energy, Washington, D.C.

MacCraken, M.C.  and  F.M.  Luther,  eds. 1985b. Detecting the Effects of Increasing Carbon Dioxide.
U.S. Department of Energy,  Washington, D.C.

Mintzer, I.M.  1987. ,4 Matter of Degrees: The Potential for Controlling the Greenhouse Effect.  World
Resources Institute, Washington, D.C.

NAS (National Academy of  Sciences). 1979. Carbon Dioxide and Climate:  A  Scientific Assessment.
National  Academy Press, Washington, D.C.

NAS (National Academy of Sciences). 1983. Changing Climate. National Academy Press, Washington,
D.C.

NAS (National Academy of Sciences). 1987. Current Issues in Atmospheric Change. National Academy
Press,  Washington, D.C.

NOAA (National Oceanographic and Atmospheric Administration). 1987. Geophysical Monitoring for
Climatic Oiange No. IS, Summary Report 1986.  Schnell, R.C., ed. U.S. Department of Commerce,
NOAA Environmental Research Laboratories, Boulder.  155 pp.
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Policy Options for Stabilizing Global Climate « Review Draft                         Chapter I
Nordhaus, W.D.,  and G. Yohe.  1983.  Future paths of energy and carbon dioxide emissions.  In
Changing Climate. National Academy Press, Washington, D.C.

Ramanathan, V.,  R. J. Cicerone, H. B. Singh, and J. T. Kiehl. 1985. Trace gas trends and their
potential role in climate change.  Journal of Geophysical Research 90:5557-5566.

Reilly, J., J. Edmonds, R. Gardner, and A. Brenkeri. 1987.  Uncertainty analysis of the IEA/ORAU
CO2 emissions model.  Tlie Energy Journal 8:1-29.

Rose, DJ., M.M. Miller, and C. Agnew.  1983.  Global Energy Futures  and CO2-Induced Climate
Change.  MITEL 83-015.   Prepared  for National Science Foundation.  Massachusetts Institute of
Technology,  Cambridge.

Rotmans, J.,  H. de Boois,  and RJ. Swart.  1988.  An integrated model  for the assessment  of the
greenhouse effect:   The Dutch approach. Working paper.  National Institute of Public Health and
Environmental Protection, Bilthoven,  The Netherlands.

Rotmans, J.,  and E. Eggink. 1988.  Methane as a greenhouse gas:  A simulation  model  of the
atmospheric chemistry of the CH4 - CO - OH cycle. Working paper.  National Institute of Public
Health and Environmental protection, Bilthoven, The Netherlands.

Rotty, R.M.  1987.  A look at 1983 CO2 emissions from fossil  fuels (with preliminary data for 1984).
Tellus 396:203-208.

Seidel, S., and D.  Keyes.  1983.   Can We  Delay a Greenhouse Warming?   Office of  Policy and
Resources Management, U.S. Environmental Protection Agency, Washington, D.C.

Siegenthaler,  U. 1983.  Uptake of excess CO2 by an outcrop-diffusion model of the ocean. Journal
of Geophysical Research 88:3599-3608.

Smith, J. and D. Tirpak, eds. 1989.  Tlie Potential Effects of Global Climate Change on the  United
States. U.S. Environmental  Protection Agency, Washington, D.C.

Strain, B.R. and J.D. Cure, eds. 1985.  Direct Effects of Increasing Carbon Dioxide on Vegetation. U.S.
Department  of Energy, Washington, D.C.

Trabalka, J.R., ed. 1985. Atmospheric Carbon Dioxide and the Global Carbon Cycle.  U.S. Department
of Energy, Washington, D.C.

WMO (World  Meteorological Organization).  1985. Atmospheric Ozone  1985: Assessment  of Our
Understanding of the Processes Controlling its Present Distribution and Change. Volume  1.  WMO,
Geneva. 392+ pp.
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                                         CHAPTER II

                                 GREENHOUSE GAS TRENDS


FINDINGS  	   11-2

INTRODUCTION	   II-5

CARBON DIOXIDE	   II-7
       Concentration History and Geographic Distribution	   II-7
              Mauna Loa	   II-8
              Ice-core Data   	   II-9
              GMCC Network	   11-10
       Sources and Sinks	   11-14
              Fossil Carbon  Dioxide	   H-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	   II-32
       Chemical and Radiative Properties/Interactions	   11-35

CHLOROFLUOROCARBONS  (CFCs)	   II-36
       Concentration History and Geographic Distribution	   11-36
       Sources and Sinks	   11-37
       Chemical and Radiative Properties/Interactions	   11-39

OZONE  	   11-40
       Concentration History and Geographic Distribution	   11-40
       Sources and Sinks	   11-43
       Chemical and Radiative Properties/Interactions	   11-44

OTHER FACTORS AFFECTING COMPOSITION  	   11-45
       Global Tropospheric Chemistry	   11-46
              Carbon Monoxide	   11-47
              Nitrogen Oxides	   11-48
       Stratospheric Ozone and Circulation 	   11-49

CONCLUSION  	   11-50

REFERENCES	   11-59
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FINDINGS








    The composition of the atmosphere is changing as the result of human  activities.  Increases in




the concentration of carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons (CFCs) are



well documented.   In  addition,  tropospheric  (lower   atmospheric)  and stratospheric  (upper




atmospheric) chemistry are being modified due to the addition of these gases as well as emissions




of carbon monoxide, nitrogen oxides, and other compounds.  Specifically, we find that:








    •       The concentration of carbon dioxide in the atmosphere has increased by 25% since the



            industrial revolution.  Detailed measurements since 1958 show an increase of about 35




            parts per million by volume.   Both land clearing  and fossil  fuel combustion  have




            contributed to this rise,  but the fossil fuel source has dominated in recent years. Carbon



            dioxide is increasing at  a rate of about 0.4% per year and is responsible for about half




            of the current increases in the greenhouse effect. Carbon cycle models indicate that the




            oceans are responsible for the uptake of most of the fossil fuel CO2 that does not remain




            in the atmosphere.    The  total net uptake  of CO2 by  the oceans  and  the net



            uptake/release of CO2 by the terrestrial biosphere cannot be precisely determined at this




            time.








    •       The concentration of methane has more  than doubled during the last  three centuries.




            There is considerable  uncertainty about  the total emissions from  specific sources of




            methane, but the observed increase is probably due to increases  in a number of sources




            as well  as  changes  in  tropospheric chemistry.   Agricultural sources, particularly rice




            cultivation and  animal  husbandry, have probably been the most significant contributor




            to historical increases in concentrations.   But there is the potential for  rapid growth in



            emissions from landfills,  coal seams, permafrost, natural gas exploration and pipeline
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            leakage, and biomass burning associated with forest clearings in the future.  Methane is




            increasing at a rate of 1% per year and is responsible for about 20%  of  the current




            increases in the greenhouse effect.








    •       The concentration of nitrous oxide 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 have all contributed.




            Nitrous oxide is over 200 times more powerful, on  a  per molecule  basis, than carbon




            dioxide as a greenhouse gas,  and  can also contribute to stratospheric ozone depletion.



            Nitrous oxide is currently increasing at a rate of about 0.25% per year, which represents




            an imbalance between sources and sinks of about 30%.  Nitrous oxide is responsible for




            about 6% of the current  increases in the greenhouse effect.








    •       CFCs were introduced  into the atmosphere for the first time during this century; the




            most common  species are CFC-12 and  CFC-11 which  had atmospheric  concentrations




            in  1985  of  380  and 220  parts  per  trillion  by  volume, respectively.   While  these




            concentrations  are tiny compared with  that of carbon  dioxide, these compounds are



            about 30,000 times more powerful, on a per molecule basis, than carbon dioxide as  a



            greenhouse gas and are increasing very  rapidly ~ 5%  per year from 1978 to 1983. Of



            major concern  because of their potential to deplete stratospheric ozone,  the CFCs also



            represent about 15% of the current increases  in the greenhouse effect.








    •       The chemistry  of the atmosphere is changing due to  emissions of carbon monoxide,




            nitrogen oxides, and volatile organic compounds, among other species, in addition to the




            changes in the greenhouse gases just described. This alters the amount and  distribution



            of ozone and the oxidizing power of the atmosphere, which changes the lifetimes of
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           methane and other greenhouse gases. Changes in global ozone are quite uncertain, and




           may have contributed to an increase or decrease in the warming commitment during the




           last decade.
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INTRODUCTION








    The  composition of the Earth's  atmosphere  is changing.   Detailed background  atmospheric




concentration  measurements combined  with  analyses  of ancient  air  trapped in Antarctic and




Greenland ice now give a compelling picture,  not  only of recent trends,  but also of major changes




that have occurred since preindustrial times.  Mounting evidence that the atmosphere is changing has




increased  the urgency of understanding the processes  that control atmospheric composition and the




significance of the changes that are taking place. In this chapter we examine what is known and not




known about the gases expected to be most important  in altering climate during the  coming decades.




For each  gas, we present data regarding its concentration history  and geographic distribution, its




sources and sinks, and its chemical and radiative interactions in the atmosphere.  This information




is summarized at the end of the Chapter in Table 2-2.








    The concentrations of a number of greenhouse gases have already increased substantially over




preindustrial levels.   The estimated relative radiative forcing from the major gases  (excluding water




vapor and clouds)  is illustrated in Figure 2-1 for  the  period  1880-1980 and for the  expected




concentration changes during the 1980s.  Carbon dioxide accounted for about two-thirds of the total



forcing over the last century, but its relative importance has declined to about half the total in recent



years  due  to more  rapid growth in  other  gases  during  the last  few decades  (see Chapter IV).



Particularly important has  been the  recent growth  in chlorofluorocarbon (CFC) concentrations.



Methane (CH4) has remained the second most important greenhouse gas, responsible for 15-20% of



the forcing. With the recent signing of the Montreal Protocol on Substances that Deplete the Ozone



Layer, growth  in CFC concentrations is likely to be substantially restrained  compared with what has




been assumed until recently (e.g., Ramanathan et al.,  1985; see Chapters IV and V).  The relative
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Policy Options for Stabilizing Global Climate - Review Draft
                               Chapter II
                                  FIGURE 2-1
  GREENHOUSE GAS CONTRIBUTIONS TO GLOBAL WARMING
                 Other (8%)
                             CO2(66%)
                                               Other (13V.)
                                                                 CO2 (49%)
                                     CFC-11 &-12
                                        (14%)
    CH4

   (15%)
                                                CH4(18%)
                 1860-1980
                 1980s
Figure 2-1. Based on estimates of the increase in concentration of each gas during the specified
period.  The "Other" category includes other halons, tropospheric ozone, and stratospheric water
vapor.  The contribution to warming of the "Other" category is highly uncertain.  (Sources: 1880-
1980: Ramanathan et al.( 1985; 1980s: Hansen et al., 1988.)
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importance of CO2 is therefore likely to increase again in the future unless these emissions are also




restricted (Chapter V).








    The  radiative  impact  of greenhouse gases is  characterized  here hi terms of the  effect  of




concentration changes  on surface  temperatures  in  the  absence  of climate  feedbacks.   Climate




feedbacks are defined and  discussed  in Chapter III, where the  climatic effects of  changes  in




greenhouse gases are put into the broader context  of other factors that influence climate.  The




human activities that are apparently responsible  for the concentration trends documented in this




chapter are described in Chapter IV.








CARBON DIOXIDE








Concentration History and Geographic Distribution








    Carbon dioxide (CO^ is the most abundant and single  most  important greenhouse gas (other




than water vapor) in the atmosphere. Its role in the radiative balance, and its potential for altering



the climate of the  Earth have been recognized for over a hundred years.  Chemical measurements




of atmospheric CO2 were made in the 19th Century at a few locations (Fraser et al., 1986a; From



and Keeling, 1986). However, the modern high-precision record of CO2 in the atmosphere did not



begin until 1958, the International Geophysical Year (IGY), when C.D. Keeling of Scripps Institution



of Oceanography pioneered  measurements of CO2  using an infrared  gas analyzer at Mauna Loa




Observatory (MLO) in Hawaii and  at the South Pole.   Since 1974, background  measurements  of



atmospheric CO2 have been  made continuously at four stations (Pt. Barrow, Alaska;  Mauna Loa,




Hawaii; American Samoa; and the South Pole) as part of the Geophysical Monitoring for Climatic




Change (GMCC) program of the National Oceanic and Atmospheric Administration  (NOAA) of the
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U.S. Department of Commerce.  In addition to the continuous monitoring stations, NOAA/GMCC




also operates a cooperative sampling network. Flask samples of air are collected weekly from these




sites and are shipped to the GMCC facility in Boulder, Colorado, for analysis.  The sampling network




began before 1970 at a few  initial sites, expanded to a network of 15 stations in 1979, and, as of




1986, consisted of -26 stations (Komhyr et al., 1985; Conway et al., 1988).  In addition  to the U.S.




programs, surface measurements of atmospheric CO2 around the globe are made by many countries




including Australia, Canada,  France, Italy, Japan, New Zealand, West Germany,  and Switzerland.








Mauna Loa








    The MLO CO2 record is shown in Figure 1-2 in Chapter I.  CO2 steadily increased from 315




parts per million by volume  (ppm) in 1958  to 346 ppm in 1986.  This corresponds  to an increase




at the rate of 0.4% per year, or a mean increase of 1.5 ±  0.2 ppm per year. From 1958 to 1986,




CO2 at Mauna Loa increased by 31 ppm; over the same period, fossil fuel combustion (shown also




in Figure 1-2) was a source of 117 petagrams (Pg)1 of carbon (C)  as CO2 to the atmosphere, which




is equivalent to  56 ppm  of  CO2.  The apparent  fraction  of the fossil fuel sources of CO2 that



remained  in  the  atmosphere during  this period  is thus  55%.  As  other net sources of  CO&



particularly deforestation (see below), may have been important during this period, the actual fraction



of anthropogenic carbon emissions remaining in the atmosphere is uncertain. Superimposed on the



increasing secular trend of atmospheric CO2 are regular  seasonal oscillations:   the concentration



peaks  in  May/June,  decreases  steadily through  the  summer, and  reaches  a minimum  in




September/October.  The seasonal peak-to-trough amplitude is ~5.8  ppm.  The seasonal cycle of




CO2 at Mauna Loa and at other northern hemispheric locations is caused primarily by the  natural




dynamics  of  the  terrestrial  biosphere:  There is  net removal of CO2 from the atmosphere via
     1 peta = 1015' giga =  109, 1 ton = 106 grams.  Thus, 1 petagram (Pg) =  1 gigaton (Gt).
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photosynthesis during the growing season, and net return of CO2 to the atmosphere via respiration




and decomposition processes during the rest of  the year.








    Despite its  regular  appearance, there are  interannual variations  in  the  CO2  concentration




measured at MLO.  Annual mean  concentration changes do  not  remain uniform throughout the




duration of the record, but have large  fluctuations  around  the  mean (Keeling,  1983).   These




excursions of atmospheric CO2 from the mean generally occur during El Nino-Southern Oscillation




events,  where the large-scale perturbations  of  atmospheric temperature,  precipitation, and other




circulation statistics also alter the biological, chemical, and physical aspects of carbon cycling between




the atmosphere, land, and ocean reservoirs.  These El Nino excursions highlight the  possibility of




climatic feedbacks in the carbon cycle.  They do  not mask the increasing secular trend,  which mainly




tracks the trend in fossil fuel combustion.








    The seasonal amplitude  also does not  remain constant and has  a  ±10% variation about the




mean.  Recent analysis reveals a statistically significant positive trend in the seasonal amplitude since




1976 (Bacastow et al, 1985;  Enting, 1987).  The causes of  this  amplitude trend have not been




unambiguously identified; hypotheses involve shifts in the seasonality of photosynthesis and respiration,




faster cycling of carbon as a result of climatic warming, and the direct effects of CO2 on plants (also



referred to as the CO2 fertilization effect).








Ice-core Data








    Bubbles in natural ice contain samples of ancient air.  Analysis by gas chromatography and laser




infrared  spectroscopy  of gases occluded  in gas bubbles  in polar  ice  has provided  a  unique




reconstruction of atmospheric CO2 history prior to the modern high-precision instrumental record
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(Oeschger  and Stauffer, 1986).   Deep  ice cores have been drilled from many locations  in both




Greenland  and Antarctica.








    From the  ice-core data, it is deduced that in pre-industrial times, ~ 1800, the CO2 concentration




was 285  ±  10 ppm and has increased at an accelerating rate since the industrial era (Neftel et al.,




1985; Raynaud and Barnola, 1985; Pearman et al., 1986) (Figure 2-2).  The ice-core data reveal the




possible existence of natural fluctuations of the order of ± 10 ppm occurring at decadal time scales




during the  last few thousand years (Delmas et al., 1980;   Neftel et al., 1982;  Stauffer et al., 1985;



Raynaud and Barnola,  1985; Oeschger and Stauffer, 1986).








    Recent analysis of the 2083-meter-deep ice core from  Vostok, East Antarctica, provides for the



first tune information on CO2 variations in the last 160,000  years (Barnola et al.,  1987; Figure 3-3




in Chapter III).   Large CO2 changes  were  associated with the  transitions  between glacial  and




interglacial conditions.  CO2 concentrations were low (~200 ppm) during the two glaciations and high




(~285 ppm) during the two major warm periods.  The Vostok ice-core data also emphasize that



current levels of atmospheric CO2 are higher than they have ever been in the past 160,000 years.



The CO2 increase  since 1958 is larger than the natural CO2  fluctuations seen in the Greenland  and



Antarctic ice-core  record.








GMCC Network








    The CO2 concentrations from the -26 globally distributed sites in the NOAA/GMCC cooperative




flask sampling network  have been reviewed in Komhyr et al. (1985) and Conway et al.  (1988).  The




distribution for 1981-1985 is shown in Figure 2-3.  There are large-scale, coherent, temporal and
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                                                          Chapter II
                                     FIGURE 2-2
                  CARBON DIOXIDE CONCENTRATION

                                   (Parts Per Million)
        o-
        \D
        o-
        CO
        00
        o-
    111
    Q.

    
    H-
    £C


    2   g'
    o
        O
        f--
        CM
          1720
1760
1800
1640
I860
i     r^   i     i
   1920      1960
ZOOO
                                          YEAR
Figure 2-2.  The history of atmospheric CO2  presented here is based on ice core measurements
(open spaces, closed triangles) and atmospheric measurements (crosses).  The data show that CO2
began to increase in the 1800s with the conversion of forests to agricultural land.  The rapid rise
since the 1950s,  due primarily to fossil fuel combustion, is at a rate unprecedented in the ice core
record, (Sources: Neftel et al, 1985; Friedli et al., 1986; Keeling, pers. communication; as cited in:
Siegenthaler and Oeschger, 1987).
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                                  Chapter II
                                   FIGURE 2-3
      C02 ATMOSPHERIC CONCENTRATIONS BY LATITUDE
Figure 2-3.  The distribution of CO2 by latitude from 1981-1985 shows  that CO2 is increasing
globally.   Superimposed on the increasing trend are coherent seasonal oscillations reflective of
seasonal dynamics of terrestrial vegetation. The seasonal cycle is strongest at high Northern latitudes,
and is weak and of opposite phase in  the Southern  Hemisphere, reflecting the distribution of
terrestrial vegetation.  The data are from the NOAA/GMCC flask sampling network. (Sources:
Komhyr et al., 1985; NOAA, 1987; Conway et al., 1988.).
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spatial variations of CO2 in the atmosphere. Concentrations of CO2 at all the stations are increasing



at the rate of -1.5 ppm per year (ppm/yr), similar to the rate of increase at Mauna Loa.








    Annually averaged CO2 concentrations are higher in the Northern  Hemisphere than in  the




Southern Hemisphere.  The interhemispheric difference was ~1 ppm in the 1960s and is ~3.2 ppm




now, reflecting the Northern Hemisphere mid-latitude source (about  90%) of fossil fuel CO2.  This




gradient has remained approximately constant in the past decade. Also evident in the north-south




distribution of atmospheric CO2 is the relative maximum of ~ 1 ppm in the equatorial regions, caused




mainly by the outgassing of CO2 from the super-saturated surface waters of the equatorial oceans.




Although tropical deforestation may also contribute to the equatorial  maximum in atmospheric CO2)




models  of the  global  carbon cycle suggest that the  observations  are  inconsistent with a  net



deforestation source greater than approximately 1.5 Pg C/yr (Pearman et al.,  1983;  Keeling and




Heimann, 1986; Tans et al., 1989).








    There is a coherent seasonal cycle at all the observing stations: the  Northern Hemisphere cycles




resemble that at Mauna Loa.  The seasonal amplitude is  largest, -16  ppm, at  Pt.  Barrow, Alaska,




and decreases toward the  equator to ~6 ppm at Mauna Loa (Figure 2-3). The CO2 concentration




is flat through the year  in the equatorial region and  is  of opposite  seasonality in the Southern



Hemisphere,   The seasonal  cycle in the Northern Hemisphere  is  caused primarily by  seasonal



exchanges with the terrestrial  biosphere  (Fung et al., 1987;  Pearman  and Hyson, 1986), while in  the



Southern Hemisphere, oceanic and  terrestrial exchanges are equally important in  determining  the



seasonal oscillations in the atmosphere (Pearman and Hyson, 1986').  The CO2 seasonal cycle shows



a consistent amplitude increase with time for some sites  (Cleveland et al., 1983; Thompson et  al.,




1986).
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    The geographical variations of CO2 growth  rates at the GMCC sites show more clearly the El



Nino perturbations, as  noted already in the Manna  Loa data.  For  example, the El  Nino-caused



cessation of upwelling that resulted in the devastation of the fishing industry and marine wildlife in



the eastern  equatorial  Pacific is also evidenced by reduced outgassing of CO2 to the atmosphere



(Feely et al., 1987) and a concomitant decrease in the global CO2 growth rate (Conway  et al., 1988).



These variations in the growth rate contain information about the response of the carbon system to



climatic perturbations, some of which are under investigation currently.






Sources and Sinks






    The atmosphere exchanges  CO2 with the terrestrial biosphere and with the oceans.  Averaged



over decades, sources must approximately equal sinks  if the system is to remain in quasi-steady state;



however, the individual flux in each direction may be large (50-100 Pg C/yr).  The fluxes of carbon



to the  atmosphere associated with anthropogenic activities  are roughly ten times smaller than the



natural fluxes of carbon.  However,  the anthropogenic fluxes are unidirectional and are thus net



sources of carbon to the atmosphere (Figure 2-4).






Fossil Carbon Dioxide
                                                            •





    The combustion of fossil fuels, in liquid, solid, or gas forms, is the major  anthropogenic source



of CO2 to the atmosphere.   A recent documentation and summary of the fossil fuel source of CO2



is given by Rotty (1987a, 1987b).  In 1985,  about 5.2 Pg C were released in the form  of CO2 as a



result of fossil fuel combustion.  Of this, the USA, USSR, and China contributed 23%, 19%,  and



10%, respectively (Rotty, pers. communication).  The  emissions for 1987 were 5.5 Pg C.  The history



and mix of activities and fuels giving rise to these emissions are discussed in detail in Chapter  IV.
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                                                    Chapter II
                                    FIGURE 2-4
    (a)
                           THE CARBON CYCLE
               ATMOSPHERE: 770
                                              SEDIMENTS
                                                  orgonic C: 12,000,000
                                                     limestone: 50,000,000
         FOSSIL FUEL:5000
   BIOSPHERE:
living plants: 800
 young soils: 1500
   old soils: 1500
    (b)
                            60
                                                         100
Figure 2-4.  (a) Major reservoirs of the global carbon cycle. Reservoirs (or stocks) are in units of
10T5 grams of carbon (Pg C).

(b) Fluxes of carbon, in 1015 grams of carbon per year (Pg C/yr).

Source: Adapted from Keeling, 1983.
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Biospheric Cycle








    The terrestrial biosphere absorbs CO2 from the atmosphere via photosynthesis on the order of



60  Pg C/yr.   Approximately the same amount  is  returned  to  the atmosphere  annually via



heterotrophic respiration and decomposition processes.  While the net exchange of the unperturbed



biosphere  is close  to zero over a period of one year, the seasonal asynchronicity of the exchange



gives rise to the  regular oscillations seen in the  atmospheric CO2 records.








    In general, land-use modification is a net source of CO2 to  the atmosphere.  CO2 is released



as a result of burning and  decay of dead plant matter and oxidation of soil organic matter.  The



amount of this release exceeds the amount of CO2 absorbed as a result of regrowth of live vegetation



and accumulation of soil organic matter. Recently, Houghton  et al. (1987) and Detwiler and Hall



(1988)  estimated a  net source  of 0.4-2.6 Pg  C/yr to  the  atmosphere  from land-use  changes.



Deforestation in  the tropics accounted for nearly all the flux:  The release of carbon from temperate



and boreal regions was only 0.1 Pg  C/yr.   The  regional and  temporal patterns and causes of



deforestation  are taken up in Chapter IV.







    Natural changes in terrestrial biospheric dynamics may result from climate warming and/or from



increased CO2 concentrations in the atmosphere.  The possibility of such natural changes is suggested



by the increasing amplitude of CO2 oscillations in the atmosphere (Bacastow et al., 1985; Cleveland



et al., 1983; Thompson et al.  1986;  Enting, 1987). The amplitude change may signal a  tendency



towards a biospheric sink of CO2, as photosynthesis responds  to increasing temperatures  and CO2



concentrations (Pearman and Hyson,  1981;  D'Arrigo et al., 1987; Kohlmaier  et al., 1987).  The



amplitude change  can also mean increased sources via respiration and decay, which  are  strongly



temperature-dependent processes (Houghton, 1987). Because growth and decay cycles are intimately
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linked, it is difficult to tell  whether atmosphere-biosphere interactions will  act as a positive or a



negative feedback without further theoretical and field studies (see the discussion of biogeochemical




feedbacks in Chapter III).








Ocean Uptake








    The exchange of CO2 across the air-sea interface depends on the degree of CO2 supersaturation




in the surface waters of the oceans and the  rate at which CO2 is transferred across the interface




itself. Because of the very nature of shipboard measurements, data on oceanic CO2 partial pressure



(pCO2) are sparse, both spatially and temporally.  Most of the data have come from oceanographic




research  programs,  mainly  Scripps  Institution  of  Oceanography in the  1960s (Keeling,  1968),



Geochemical Sections (GEOSECS) in the 1970's (Takahashi et aL, 1980,1981), and Transient Tracers




in the Oceans  (TTO) in the  early 1980s (Brewer et al., 1986) and more recently from NOAA survey




cruises and from ships  of opportunity.








    Depending on the  regional interplay between temperature, carbon supply from upwelling, and




carbon consumption by biological activities, the seasonal cycle of CO2 in surface water may peak at




different  times of the year in different  oceanic regions  (Peng et al., 1987; Takahashi et al., 1986,



1988).  This makes it extremely difficult to interpret the sparse oceanic carbon data in the  context



of the global carbon cycle.  The interpretation is aided by data from carbon-14 and other transient



tracers in the  ocean.








    Based  on  the available data and an understanding of carbon  dynamics in the ocean, it is




estimated that, on an annual basis, about 90 Pg C/yr is exchanged between the atmosphere and  the
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ocean.   This  exchange results in a net  outgassing of approximately 1 Pg C/yr from the equatorial



oceans and a net absorption of about the same  amount by the  middle to high latitude oceans.








    Superimposed on this exchange of 90 Pg C/yr in either direction is the penetration of fossil fuel



CO2 into the  oceans, estimated  to be ~3 Pg C/yr currently.  This oceanic uptake of fossil fuel CO2



is corroborated by the observations of anthropogenic tracers penetrating gradually into the oceanic



thermocline.  These tracers include tritium and carbon-14, by-products of nuclear testing in the 1960s,



and the chlorofluorocarbons, a recent man-made compound. The magnitude of  the oceanic uptake



of fossil fuel CO2  is estimated using  numerical models  calibrated by tracers.  Because of the



variability of the oceanic carbon system and the precision of ocean carbon measurements, the oceanic



signature  of  fossil fuel CO2 has not been  demonstrated  unambiguously.   Takahashi  et  al. have



demonstrated that in  the Atlantic, the oceanic pCO2  increased  by 8 ± 8 microatmospheres (fiatm)



from 1958 to the mid-1970s, an increase that is  consistent with estimates from numerical models.








Chemical and Radiative Properties/Interactions








    Carbon dioxide is chemically inert in the atmosphere, but it has a very important impact on the



Earth's radiation budget and hence on climate  and the  chemistry of the atmosphere.  After water



vapor,  CO2 is the most abundant and most significant infrared (IR) absorbing gas in the atmosphere.



As discussed  in Chapter III, the Earth's climate is determined by the point at which incoming solar



(short-wave) radiation is balanced by IR (long-wave)  emissions  to space from the warm surface and



atmosphere.  Increasing the concentration of CO2 and  other greenhouse gases in the atmosphere



elevates the average surface temperature required to achieve this balance. Doubling the atmospheric



CO2 concentration from 315 to 630 ppm would  produce a radiative forcing (the  equilibrium surface



temperature increase in the  absence of climate  feedbacks)  of 1.2-1.3°C. At current concentrations
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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter II
                   THE RADIATIVE EFFECTS OF GREENHOUSE GASES
       The radiative effects of greenhouse gases have received a great deal of attention over
   the last decade.  Recent reviews are given by Dickinson and Cicerone (1986) and
   Ramanathan et al. (1987).  In the absence of an atmosphere the Earth would radiate energy
   to space as a black body with a temperature of about 250° K (-23°C).  Figure 2-5 shows
   the actual emissions, indicating the absorption bands of the major greenhouse gases.  Not
   shown is water vapor, which has continuous absorption throughout this spectral range and
   dominates all other gases at wavelengths <  8 micrometers Qim) and >  18 /im (Dickinson
   and Cicerone, 1986).  The 15 jUm  band of CO2 dominates absorption in the spectral range
   from 12 to  18 Mm> and its absorption in the other parts of the spectrum amounts to 15% or
   less of its impact in this region.

    The shaded region in Figure 2-5, between about 7 and 13 Jim, is called the atmospheric
   window because it is relatively transparent to outgoing radiation:  70-90% of the  radiation
   emitted by  the surface and clouds in these wavelengths escapes  to space (Ramanathan et al.,
   1987),  Many trace gases happen to have absorption bands in this window region and are
   therefore very effective greenhouse absorbers. For example, CFCs are as much as 20,000
   tunes more effective than CO2 per incremental increase in concentration (see Table 2-1).
CO2 already absorbs most of the radiation emitted from the Earth's surface in the wavelengths where

it is active.  As a result, each additional  molecule of CO2 added to the  atmosphere has a smaller

effect than the previous one.  Hence, radiative forcing scales logarithmically, rather than Linearly, with

increases in  the concentration of atmospheric CO2.   For example, a 50 ppm increase in CO2 from

350 to 400 ppm yields a radiative forcing of 0.23°C, while the same increment from 550 to 600 ppm

yields a radiative forcing of only 0.16°C.   Despite the reduced  greenhouse effectiveness of each

molecule of CO2 as concentrations increase, CO2 will remain the dominant greenhouse gas in the

future, responsible for 50% or more of the increased greenhouse  effect during the next century for

plausible scenarios of future trace gas  emissions (Hansen et al., 1988; Chapter V).
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                                     Chapter II
                                       FIGURE 2-5
        emission
        wavelength  5
                        15   17.5/20
Figure 2-5.  Infrared (long-wave) emissions to space from the Earth.  Many of the absorption bands
of the greenhouse gases fall within the atmospheric window -- a region of the spectrum, between 7
and  13 Jim, in which there is little else to prevent radiation from the Earth escaping directly into
space. (Source:   UNEP, 1987.)
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                                    Chapter II
                                      TABLE 2-1

                             Radiative Forcing for a Uniform
                       Increase in Trace Gases From Current Levels
Compound
CO2
CH<
N2O
CFC-11
CFC-12
CFC-13
Halon 1301
F-116
CC14
CHC13
F-14
HCFC-22
CH2C12
CH3CC13
C2H2
SO2
Radiative Forcing
(No Feedbacks)
(°C/pPb)
.000004
.0001
.001
.07
.08
.10
.10
.08
.05
.04
.04
.03
.02
.01
.01
.01
                     Source:  Adapted from Ramanathan et al., 1985.
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METHANE








Concentration History and Geographic Distribution








    High-precision atmospheric measurements of methane (CH4) have been made in the past decade



at many different locations. The data show clearly that the concentration of methane, 1675 parts per



billion by volume (ppb) in 1987, has been increasing at the rate of about 16 ppb per year (Blake and



Rowland, 1986,  1988) (Figure 2-6).








    Since 1982,  air samples from ~25 globally  distributed sites of the NOAA/GMCC cooperative



network have been analyzed for CH4 (Steele et al., 1987). In addition to  flask sampling, continuous



measurements of atmospheric CH4 are now made at Cape Meares, Oregon (Khalil and Rasmussen,



1983); Pt. Barrow, Alaska; and Mauna Loa,  Hawaii (NOAA, 1987).








    The data show that CH4, like COj, exhibits  very coherent spatial and temporal variations. CH4



is approximately uniform from mid- to high latitudes in the Southern Hemisphere, and increases



northward.   The Northern Hemisphere concentration is approximately 140 ppb higher than that in



the Southern Hemisphere.  The seasonal cycle in the Southern Hemisphere shows a minimum in  the



summer, consistent  with  higher   summer abundances  of  the  hydroxyl  radical  (OH)  and



temperature-dependent destruction rates.  In the Northern Hemisphere, the seasonal cycle is more



complex, showing the  interaction  mainly  between  chemical  destruction  and  emissions  from



high-latitude peat bogs.








    Analysis of air bubbles in ice cores shows that in pre-industrial years, CH4 was relatively constant



at ~700 ppb, from 100,000 years before present  (100 kyBP) until the mid-19th century,  and exhibited
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                                                  Chapter II
                                      FIGURE 2-6
                           METHANE CONCENTRATION
           (a)
      Atmospheric Data
          (Parts P«r Million)
                       1.7
                                                         I"1
                  
                  
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Policy Options for Stabilizing Global Climate — Review Draft                         Chapter II



a factor of 2.5 increase to its present value in only the last 300 years (Stauffer et al., 1985; Pearman

et al., 1986)  (Figure 2-6).  The 2083-meter ice core recovered by the Soviet Antarctic Expedition at

Vostok, Antarctica, shows that the CH4 concentration was as low as 340 ppb during the penultimate

ice age  (-155 kyBP) and nearly doubled to 610 ppb in the following interglacial (130 kyBP).  The

trend in CH4 closely followed the trend in air temperature deduced from deuterium, confirming the

role  of CH4  as an important greenhouse gas (Raynaud et al., 1988). These measurements show that

current  concentrations of CH4, like that  of CO^ are higher than they have been in the past 160,000

years.



Sources and Sinks



    Methane is produced  via anaerobic decomposition  in biological systems.  It is also a major

component of natural gas  and of coal gas.  While the major sources of CH4 have been identified,

their individual contributions to the global budget  are highly  uncertain. A recent review of the

sources and  sinks of CH4 is given by Cicerone  and Oremland (1988) (see Figure 2-7).



    The major sink of CH4 is reaction with OH radicals in the atmosphere.2   Based on chemical

considerations, it is estimated that the global sink of methane is ~510 teragrams (Tg) CH4/yr.3 By

inference, the annual global source is the sink  plus the annual  increase, i.e., about 550 Tg CH4/yr.

Cicerone and Oremland (1988)  estimate a range of 400 to 640  Tg/yr for the annual global source.
    2 A radical is an atom or group of atoms with at least one unpaired electron, making it
highly reactive.
      1 Tg = 1 teragram = 1012 grams
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                                           Chapter II
                                      FIGURE 2-7
               CURRENT EMISSIONS OF METHANE BY SOURCE
                                       (Teragrams)
                        Fossil Fuel Production
                              50-95 TG
          Domestic Animals
              65-100 TG
        Biomass Burning
           50-100 TG
                                  Rice Production
                                    60-170 TG
                      Landfills
                      30-70 TG
                               Natural Sources
                                 116-346 TG
           Rice Production
           1. India
           2. China
           3. Bangladesh
TOP THREE PRODUCERS

Domestic Animals
 I.India
 Z. USSR
 3. Brazil
Fossil Fuel Production
 1. United States
 2, USSR
 3. China
Figure 2-7.  Human  activities in  the agricultural sector (domestic animals, rice production and
biomass burning) and the energy sector (fossil fuel production) are the major sources of atmospheric
CH4.  Natural sources,  from  wetlands, oceans, and  lakes, may contribute less than 25% of total
emissions. (Sources: Cicerone and Oremland, 1988; Crutzen et  al., 1986; Lerner et al., 1988; United
Nations, 1987; IRRI, 1986.)
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    Estimates of methane emissions from natural wetlands have  ranged from 11-150 Tg/yr  (e.g.,



Seiler, 1984; Khalil and Rasmussen, 1983). A recent study by Matthews and Fung (1987) estimated



that there are 530 million hectares of natural wetlands that account for a global emission  of  ~110



Tg  CH4/yr.   Of this, about 50% of the CH4 is emitted from productive peat bogs at high  latitudes



in the Northern Hemisphere, a regional emission that is likely to increase with greenhouse wanning.



While this study has employed more extensive field data than earlier estimates (e.g., Sebacher et al.,



1986;   Harriss et al., 1985), uncertainties in the global estimate  remain due to the variability of



natural wetlands and then- CH4 fluxes.








    Rice paddies are environments very similar to natural wetlands in terms of CH4 production and



emission to the atmosphere.  In 1984, there  were 148  million  hectares of rice harvest area  globally,



with ~50% in India  and China.  Methane emission studies have been performed in controlled



mid-latitude environments (Cicerone et al., 1983; Holzapfel-Pschorn and Seiler, 1986).  These studies



have identified factors affecting methane fluxes to the  atmosphere:  inter alia, temperature, soil



properties, fertilizer, and irrigation practices. These factors  make global extrapolation  of  methane



emissions very difficult.  Cicerone and Oremland  (1988) estimate a global emission of 60-170 Tg



CH4/yr.







    Methane is also produced by enteric fermentation in animals, especially ruminants. The amount



of CH4 produced is dependent on enteric ecology, the  composition and quantity of feed, and the



energy  expenditure of  the  individual animal.   Estimates of  emission  rates range from 94 kg



CH4/animal/year from West German dairy  cattle, to -35 kg CH4/animal/year from Indian  cattle



fed on kitchen refuse, to 5-8 kg CH4/animal/year from sheep.  Using these emission coefficients and



population statistics of animals in the world, Crutzen et  al. (1986) obtained a global emission  of 78



Tg CH4 for  1983.  This emission includes  ~5 Tg CH4 from wild animals and  <1  Tg CH4 from
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humans.  About  75% of the emissions are from  cattle and dairy cows.  India, the USSR, Brazil, the



USA, and China are  the five major countries  in  terms of CH4 emission from  domestic animals




(Lerner et al., 1988).








    Other natural sources of CH4 include termites, and exchange with oceans and lakes. The source




from termites is  highly uncertain and controversial.  Estimates of global emissions range from close




to zero (Seiler et al., 1984a) to 20 Tg (Fraser et al.,  1986b), and as high as 200 Tg CH4 (Zimmerman




et al., 1982, 1984), on  the order of half the global emission.   The oceanic source is small, estimated




to be 5-20 Tg CH4/yr (Cicerone and Oremland, 1988).








    There are several anthropogenic  sources of methane.   Methane is produced  by incomplete




combustion during biomass burning. The amount of CH4 produced  depends on the material burned




and  the  degree of combustion.   Estimates range from  50-100 Tg  CH4/yr (see  Cicerone and




Oremland,  1988).  While a few  studies have attempted to  understand and measure CH4 emission




during biomass burning (Crutzen et al., 1979, 1985), extrapolation  to  a global estimate is difficult




because of the lack of global data  on area burned, fire frequency, and characteristics of fires.  The



feasibility of monitoring fires from space (Matson and Holben, 1987; Matson et al., 1987) will improve




this estimate  significantly.








    Methane  is also produced in  large municipal and industrial landfills, where biodegradable carbon



in the refuse  is decomposed to form a mixture of CO2 and CH4. As in the case of many other CH4




sources, the fraction of gas produced that escapes to the atmosphere is debated. Recently, Bingemer



and Crutzen (1987) estimated that this  source produces 45-70 Tg CH4/yr.  These estimates assume




that a large fraction of all organic carbon deposited in landfills eventually is subject to methanogenesis
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and subsequent emission to the atmosphere.  Cicerone and Oremland (1988) adopt a range  of 30-




70 Tg CJVvr.








    Methane is the major component (-90%) of natural gas, and so the leakage of natural gas




from pipelines and the venting of natural gas from oil and gas wells represent sources of CH4  to the



atmosphere.  Although natural gas production and consumption statistics are available globally, the




nature  of this CH4 source makes it difficult  to estimate how much this source contributes  to the



atmospheric  abundance.   From U.S.  and Canadian  natural  gas  statistics  it is  estimated that




approximately 2-2.5%  of  the  marketable gas is unaccounted for.   Assuming that all  of the




unaccounted for gas is  lost to the atmosphere, 25-30 Tg CH4/yr from line loss is obtained globally




(Cicerone and Oremland, 1988).  An additional 15 Tg CH4/yr is estimated from natural gas sources,




assuming that -20% of the gas that is vented and flared at oil and gas wells is not combusted,




escaping to the atmosphere as  CH4 (Darmstadter et al., 1987).  Together these estimates  suggest a




source  of up to  50  Tg  CH4/yr from  natural gas production  and consumption.   Much of the




unaccounted for gas, however, may represent meter discrepancies, and venting of natural gas has been




declining in recent years (Darmstadter et al., 1987).  Thus a reasonable range for these sources may



be 20-50 Tg CH4/yr.








    Methane is also  the major component of gas  trapped  in  coal.   The percentage of the CH4



component increases  with the age and depth of the coal and is released to the atmosphere  during



mining and processing/crushing of coal.   Globally, the amount of CH4  in coal is -0.5% of the mass




of coal  extracted.  This source is estimated  to be  15-45 Tg CH4/yr  in 1980 (Darmstadter  et al.,




1987; Cicerone and Oremland, 1988).
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    A highly uncertain but potentially large source of CH4 is methane hydrates in sediments under




permafrost and on  continental margins (Kvenvolden,  1988).  The magnitude of the current  CH4




release from this source is unknown. Climate warming presents the potential for destabilization of




the hydrates and subsequent release of CH4 to the atmosphere (Chapter III).








Chemical  and Radiative Properties/Interactions








    Methane is the most abundant  trace gas in the atmosphere that is active both radiatively and




chemically.  Although  the abundance of methane is 1/200 that  of CO2, CH4  is a  more efficient




absorber of thermal radiation than is CO2: Donner and Ramanathan (1980) and Lacis et al. (1981)



estimate that at present levels, an additional molecule of CH4 will contribute a radiative forcing that




is  equivalent to that contributed by approximately 25  molecules of CO2.   These radiative transfer




calculations suggest that a doubling of atmospheric CH4 (1.6-3.2  ppm) will contribute a radiative




forcing of 0.16°C (Hansen et al., 1988).








    The destruction rate of CH4 is dependent on the amount of OH (and hence water vapor) in the




atmosphere as well as on temperature.  The lifetime (atmospheric abundance divided by destruction



rate) of CH4 is approximately 10 years,  the lifetime being shorter in the tropics.  Using estimates of



the  average concentration  of  atmospheric  hydroxyl radicals  derived  from  measurements  of



methylchloroform, Prinn et al. (1987) have deduced the average atmospheric lifetime of methane to



be 9.6  (+2.2, -1.5) years.  The reaction between  CH4 and OH eventually  produces  CO; CO itself



reacts  with OH,  producing  CO2 (Thompson and Cicerone,  1986).   Thus,  an  increase in  the



background levels of  either  CH4 or CO can reduce  OH and the  oxidizing power of the entire




atmosphere. It is estimated that increases in CO alone from 1960 to 1985 would have lowered OH




concentrations in the atmosphere, increased the methane lifetime, and resulted in a 15-20% increase
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in CH4 concentrations (Khalil and Rasmussen, 1985; Levine et al., 1985; Thompson and Cicerone,



1986).








    Because of the interactions  between CO,  CH4, and OH  in the atmosphere, it is difficult to



predict the effects of climate change on OH destruction of CH4, as increasing atmospheric water



vapor and  increased  precipitation (and removal  of  OH reservoirs like nitric acid [HNO3] and



hydrogen peroxide [H2OJ) have opposite effects on OH concentrations.  Changes in nitrogen oxides



(NOJ and tropospheric ozone (O3) also strongly affect atmospheric OH (see below).








NITROUS OXIDE








Concentration History and Geographic Distribution








    Nitrous oxide (N2O) is present in minute amounts in the atmosphere but it is nonetheless of



great importance.  Its concentration is three orders  of magnitude less than that  of CO2,  but  its



radiative  forcing per  molecule is 230  times greater.   The first high-precision measurements of



atmospheric N2O in the late 1970s showed  an unambiguous increasing trend in its concentration



(Weiss,  1981).    Continuous  measurements at  four Atmospheric Lifetime Experiment/Global



Atmospheric Gases Experiment (ALE/GAGE) sites have been made since 1979 (Figure 2-8). Flask



samples of air from the globally distributed  cooperative network of NOAA-GMCC are also being



analyzed  for N2O (Thompson et al., 1985; Komhyr et al., 1988).








    The ALE/GAGE data show that the mid-1980s concentration of atmospheric  N2O is 310 ppb



and that  its annual growth rate is -0.8 ppb per year, or 0.2-0.3% per year.  The concentrations at
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Policy Options for Stabilizing Global Climate - Review Draft
                                                        Chapter II
                                     FIGURE 2-8
          z
          o
           CO
           cc
           at
           o.
           a:
           <
           O.
           CO
           ec   300
           Ui
           a.
           cc
           <
           a.
              3 SO -
                      NITROUS OXIDE CONCENTRATIONS


                                     (Parts P«r Billion)



                                Atmospheric Data
                    3 1 0
                         N -, O
308 I-
    i




306 r





304 r


    H ,


302 t-




300
                       1979
                                           1983
                                    Ice Core Data
                                       1986
                    ieoo
                                  i;oo
                                               ieoo
                                                            itoo
                                          YEAR
Figure 2-8.  Concentration of atmospheric N2O has been increasing at the rate of 0.25%/yr in the

last decade (upper panel).  The ice core record shows that N2O was relatively constant from the

1600's to the beginning  of the 20th century, and began increasing rapidly in the last SO years.

(Sources: Khalil and Rasmussen, 1987; Pearman et al., 1986.)
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February 16, 1989

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the two Northern Hemisphere sites are 0.8 ppb higher than those at the Southern Hemisphere sites,



suggesting the dominance of a northern source.








    Ice-core data show that the preindustrial concentration of N2O was 285  ± 10  ppb averaged



between 1600-1800 (Pearman et  al., 1986;  Khalil and Rasmussen, 1987).  Unlike CO2,  whose




concentration  began to increase significantly in  the 1800s, N2O remained fairly  constant until  the




1900s,  and then began increasing more  rapidly in the 1940s (Pearman et al., 1986; Khalil and



Rasmussen, 1987).  (See the ice-core data in Figure 2-8).








Sources and Sinks








    While a lot of progress  has been made during the last five years in quantifying  the sources and




sinks of N2O in the atmosphere, there remain considerable uncertainties in the global budget and




in the  contributions of individual source  terms.   The  uncertainties arise not  just because  of  the




scarcity of measurements of N2O fluxes, but also because of the complexity of the biogeochemical




interactions and heterogeneous landscape  where N2O is produced.








    Nitrous oxide is simultaneously produced and  consumed in soils via the metabolic pathways of



denitrification, nitrification, nitrate dissimilation, and nitrate assimilation. These processes are affected



by various environmental parameters such as temperature, moisture,  the presence of plants, and  the



characteristics and composition of the soils  (e.g., Seiler and Conrad, 1987;  Sahrawat and Keeney,




1986).   The flux of N2O to the atmosphere also depends on the location of the N2O-producing and



N2O consuming microorganisms  and  their  relative activity within the soil column (Conrad and Seiler,




1985).  Because of the complexity of  the N2O production and destruction processes, and the inherent




heterogeneity  of soils, it is  difficult  to estimate the contribution of  natural  soils  to the global N2O
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budget.   Slemr et al. (1984) calculated N2O emissions from natural temperate and subtropical soils




to be 4.5 Tg N/yr. Recent measurements  (Livingston et al., 1988; Matson and Vitousek, 1987) show




that  N2O emission rates from tropical soils are higher than those from temperate soils and that a




relationship exists between the N2O flux and the rate of nutrient  cycling in the tropical forest soils.




However, no budget of N2O  emissions from tropical soils has been attempted.  Seller and  Conrad




(1987) give a very tentative estimate of 6  ± 3 Tg N/yr  from natural soils globally.








    Measurements of  supersaturation of  N2O in  the oceans indicate  that  the oceans  contribute




additional N2O to the atmosphere, though  in smaller quantities  (Seiler and Conrad,  1981; Weiss,




1981).  Seiler  and  Conrad (1987)  estimated the oceanic contribution  to be 2 ± 1 Tg N/yr.








    Little is known about N2O emissions from terrestrial freshwater  systems.  Extrapolating from




measurements in the Netherlands  and in Israel of elevated N2O levels in aquifers contaminated by




the disposal of human or animal waste, cultivation, and fertilization, Ronen et  al.  (1988) estimated




a global  source 0.8-1.7 Tg N/yr from contaminated aquifers.








    Nitrous oxide is also produced during combustion, but the importance of this source is  unclear




at this time.  A recent study  of this N2O source was reported by Hao et al.  (1987) who found that



the amount of N2O in flue gases was correlated with the nitrogen content of fuels.  N2O emission



rates were highest during coal combustion, lower when oil was used as the fuel, and lowest when the




fuel  was  natural gas.  They found  that hi conventional single-stage boilers, on average, 14% of fuel



nitrogen  was converted to N2O during combustion.  Conversion of fuel nitrogen to N2O was much



less  efficient (2-4%) in a two-stage  experimental combuster and in wood fires.  They also found




consumption of N2O in fuel-rich flames with low air-fuel ratios, reducing significantly  the emission




factor.  Using statistics on solid- and liquid-fuel production, they estimated  an emission of 3.2 Tg
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N2O-N in 1982.  Very recent studies, however, suggest that many of the N2O measurements reported




in the literature have been affected by a sampling artifact.  A reaction between water, sulfur dioxide




(SO2),  and  nitrogen  oxides (NOJ generates N2O in sample  cylinders over a  period  of hours,



sometimes increasing  N2O concentrations by more than an order of magnitude unless the samples




are carefully dried or N2O is measured immediately (Muzio and Kramlich,  1988).  Reanalysis of




measurements made  in the U.S.,  excluding those that were apparently affected by this  reaction,




found no significant difference between N2O emissions  from  gas and coal-fired boilers (Piccot, pers.




communication).  Recent measurements conducted by EPA with an on-line analyzer confirm  this




finding:  In both utility and small experimental boilers N2O concentrations in the exhaust gases were



always less than 5 ppm and generally less than 2 ppm (Hall, pers. communication).  This suggests




that the relationship between N2O and fuel-nitrogen found by Hao et al. (1987) may have actually




been due to differences in  SO2 and NOX  emissions.  Emissions of N2O do appear  to  vary  with




combustion technology.  Preliminary measurements suggest that fluidized-bed combusters and catalyst-




equipped automobiles may have substantially elevated N2O emissions (De Soot, pers. communication).




Total N2O emissions  from fossil-fuel combustion cannot be estimated with any confidence  at  this



time, but may be closer to 1 Tg N/yr than to 3 Tg N/yr  (Chapter V).








    The  addition of nitrogenous fertilizers to soils enhances the emission of N2O and other nitrogen



gases to  the atmosphere. This emission depends on temperature,  soil  moisture, rainfall, fertilizer



type, fertilizer amount, and the way the fertilizer is applied. It also depends on the properties of the



soils and the crops grown.  The fraction of fertilizer nitrogen lost to the atmosphere as nitrous oxide




ranges from  -0.001-0.05% for nitrate, -0.01-0.1% for  ammonium fertilizers,  to -0.5->5% for




anhydrous ammonia.   With a  global consumption  of  approximately 705 million tons nitrogen as




nitrogenous fertilizers in 1984,  an N2O contribution of 0.14-2.4 Tg N/yr  is estimated. Although the
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estimated N2O emissions associated with the use of nitrogenous fertilizers are small compared with




those from natural sources, they are, nonetheless, a source subject to rapid growth.








    Land-use  modification in the tropics may also contribute N2O  to  the  atmosphere.  N2O is




produced during biomass burning, but because direct estimates of total N2O emissions are difficult,




N2O emissions are estimated by ratios with  emissions of C02 or  other  nitrogen gases.  Crutzen




(1983)  estimated  this source to be 1-2 Tg N/yr, although the accuracy of this estimate is highly




uncertain.








    Recently,  Bowden and Bormann (1986)  found enhanced N2O  fluxes to  the  atmosphere from




cleared areas in a temperate  forest and  elevated N2O concentration  in ground water adjacent to the




cut watershed.  Similarly, tenfold increases in N2O fluxes are found in pastures  and forest clearings



in the Amazon (Matson, pers. communication).  Robertson and Tiedje (1988) postulate, on the basis




of observations in Central America, that the  loss of primary tropical rain forest may decrease the




emissions of N2O to the  atmosphere. These  studies suggest  that rapid deforestation in the  tropics



may significantly  alter the N2O budget, although an  estimate of its contribution to the global  budget




has not been attempted.








Chemical and Radiative Properties/Interactions








    N2O has a low concentration in the atmosphere, and  its  rate of increase is much smaller than




that of the  other trace gases.   Yet it still plays  an important role in the radiative and chemical




budgets of the atmosphere.  The seemingly small growth rate, ~0.25%/year, is the result of a large




unbalance (-30%) between the sources  and sinks.  The extremely long lifetime of N2O, -160 years,



means  that the system has a  very long memory of its emission history.
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    Nitrous oxide is an effective greenhouse gas.  The radiative forcing of one molecule of N2O is




equivalent to that  of -230 molecules of C02;  a doubling of N2O  and a doubling of CH4 yield




approximately the same radiative forcing, even though the N2O concentration is less, by a factor of



5, than that of CH<.  A 25% increase in the  current burden of N2O in the atmosphere will yield a



radiative  forcing  of 0.07°C.








    Nitrous oxide  is not  chemically reactive  in the troposphere.  However, its destruction in the




stratosphere, by photolysis and by reaction with atomic oxygen in the excited state [OC'D)], makes




N2O the  dominant precursor of odd nitrogen in the stratosphere.  Thus, an increase in N2O would




lead to an increase in  stratospheric  NO^ which  would significantly  influence stratospheric ozone



chemistry.








CHLOROFLUOROCARBONS  (CFCs)








Concentration History and  Geographic  Distribution








    High-precision measurements of CFC-11 (CC13F) and CFC-12 (CC12F2) began in 1971 with the



development of  electron  capture detector/gas chromatograph techniques  (Lovelock, 1971).  Like



CO2 and  CH4, surface measurements have consisted of high-frequency observations at a few dedicated



sites as well as flask samples of air collected from a global network  of stations or from irregular




global transects.








    High-frequency in situ measurements of surface concentrations have been or are currently being




made at the five coastal/island stations of the Atmospheric Lifetime Experiment/Global Atmospheric




Gases Experiment  (ALE/GAGE) (Cunnold et al., 1986; Prinn et al., 1983; Rasmussen and Khalil,
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1986;  Simmonds  et al., 1987).   In addition, analysis of CFC concentrations in the flask samples of




air collected at the NOAA-GMCC globally distributed network of sites have begun at the GMCC




facility hi Boulder (Thompson et al., 1985; NOAA, 1987).








    CFC-12 is  the most  abundant  halocarbon in the atmosphere.   Its  average  tropospheric




concentration in 1986 was 392 parts per trillion by volume (ppt), corresponding to a total burden of




about 7.6 Tg. Its concentration is increasing at 4%/yr.








    With a total burden of about 5.0 Tg, CFC-11 is the second most abundant halocarbon in the




atmosphere.  Its average concentration in 1986 was 226 ppt, and is also increasing at 4%/yr.








    The other important  halocarbons  include  methyl  chloroform  (CH3CC13),  125 ppt  in  1986,




increasing at ~6%/yr; carbon tetrachloride (CC14), 121 ppt in 1982, increasing at 1.3%/yr;  HCFC-




22 (formerly denoted CFC-22; CHC1F2),  -100 ppt in  1986, increasing at  7%/yr; and Halon-1211




(CF2ClBr), -2 ppt in 1986 and increasing at >10%/yr (Prinn, 1988).








Sources and Sinks








    CFCs  are the product solely of the chemical industry.  CFC-11 is used  in blowing plastic foams



and in aerosol cans.   CFC-12  is used primarily in refrigeration and aerosol cans. Comprehensive



data on production of CFC-11 and CFC-12 are published by the Fluorocarbon Program Panel (FPP)



of the Chemical Manufacturers Association (CMA).  The peak year  for CFC production was 1974,



in which a total of 812.5 gigagrams (Gg) of CFC-11 plus CFC-12 was produced.4  The  annual total




CFC production decreased for  a number of years following a ban on non-essential aerosol uses in
    4 1 Gg =  109 grams = 106 Kg
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the United States, Canada, and Sweden.  Non-aerosol uses have continued to increase, however, and



the total has risen rapidly in recent years, reaching 703.2 Gg in 1985. Of this total about 70% was



consumed by the U.S., the European Economic Community, and Japan (see  Figure 4-9 in Chapter


IV).






   The CMA data do not cover the USSR.  The FPP has estimated Soviet production; however,



these estimates are considered unreliable. Data for China and the countries of Eastern Europe are



lacking entirely, rendering large uncertainties in the magnitude of world  emissions.  Cunnold et  al.



(1986) and Fraser et al. (1983) have found the measured trend of CFC-11 and CFC-12 concentrations



is  relatively consistent with the  CMA estimates of CFC-11  release but not CFC-12 release, which



suggests that the USSR and Eastern Europe contribute a substantial amount to CFC-12 emissions.






   Methyl chloroform (CH3CC13) is widely used  in the manufacturing industry  as a  solvent for



degreasing, CFC-113 is used in the electronics industry, mainly for circuit board cleaning, and HCFC-



22 is used mainly in refrigeration.  The sources of these gases have been estimated in various studies,


but a survey of sources-equivalent to that conducted for CFC-11  and CFC-12 ~ has not been done.






    Fully  halogenated CFCs (those  that  contain  no  hydrogen) are  destroyed almost solely  by


photolysis in the stratosphere.  The atmospheric lifetimes of CFCs estimated from  the ALE/GAGE


analyses are 111+22 years for CFC-12, 73+31  years for CFC-11, 6.3+li2 years  for methyl chloroform,
               -44                     -17                      -OS

and  approximately 40 years for  carbon tetrachloride.  Compounds containing hydrogen (HCFCs)



react with OH in the  troposphere and have lifetimes on the order of 20 years or less.
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Chemical and Radiative Properties/Interactions








    CFCs absorb infrared radiation in the window region of the atmospheric spectrum (Figure 2-5).



Although CFCs are  present in minute  amounts in the atmosphere, together they are one  of  the



dominant greenhouse gases. They have the highest annual fractional increase (~5%/yr)  of  all  the



greenhouse gases. Furthermore, the radiative forcing due to each additional molecule of CFC is



equivalent to that due to about 30,000  molecules  of CO2, and at present  levels increases linearly



with the concentration (Ramanathan et  al., 1987).  A 2 ppb increase in both CFC-11 and CFC-12



will contribute  a  radiative forcing of 0.3°C, equivalent to that from a 65 ppm increase in CO2.  In



the 1980s, CFC-11  and CFC-12 together will  contribute about  15%  of  the  increase  in  global



greenhouse forcing.








    Chlorinated  and brominated  compounds  contribute chemically active  halogens  into   the



atmosphere, where they are broken down  by solar ultraviolet radiation or by reaction with OH.  In



addition to  CFC-11  and CFC-12,  these species  include  methyl chloroform (CH3CC13), carbon



tetrachloride (CCIJ,  and methyl halides (CH3C1, CH3Br, and CH3I). Also important are two rapidly



increasing chlorofluorocarbons, CFC-113 (C2C13F3)  and HCFC-22 (CHCIF^.  Halocarbons with at



least one hydrogen, such as methyl chloroform and HCFC-22 are destroyed primarily by reaction with



OH radicals in the troposphere.  Long-lived species survive the 1-3 year transport  time from  the



surface up to stratospheric levels  to play  a  critical role in ozone photochemistry.  All of these species



can contribute  to the stratospheric burden of chlorine, but the longer-lived CFCs can accumulate,



reaching higher concentrations before a  steady state balance is achieved.








    The dissociation  products of  halocarbons are the  dominant sources of chlorine (Cl) and fluorine



(F) for  the stratosphere (WMO, 1985), which are major components in  the catalytic cycles that
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control ozone abundance.  Ground-based data and  aircraft data of trends for  major halocarbon




reservoirs (HC1, HF, CIO) are highly uncertain.  Within the limits of the uncertainties, the estimated




trends in these species were not in disagreement with trends in the source gases  themselves.
OZONE
Concentration History and Geographic Distribution








    Ozone (O3) is both produced and destroyed in situ in the atmosphere.  Unlike the other trace



gases, the vertical distribution of O3 in the atmosphere is of prime importance in determining its




radiative and chemical effects (Figure 2-9).








    Ozone sondes from a diverse and globally distributed network provide our only record of possible




trends in the vertical distribution of tropospheric O3.  A review of ozone sonde and surface data have




been given by Logan  (1985), Tiao et al.  (1986), and more recently by Crutzen (1988).  Since the



1970's, surface  O3 concentrations are measured  routinely  at the four  continuous  monitoring



stations  operated by NOAA-GMCC:  Pt. Barrow, Alaska; Mauna Loa, Hawaii;  American Samoa;



and  the South Pole  (see  e.g.  NOAA,  1987).   NOAA-GMCC also  participates in  international



cooperative ozone sonde profiling activities.








    The O3  data taken near populated and industrial regions in the 1930's to the 1950's generally




showed an annually averaged concentration of 10-20 ppb at  the surface, with a seasonal cycle that




peaked  in summer.   The data showed a generally increasing trend,  especially in the summer, in




surface  concentrations of O3 at sites in western Europe, the USA and northern Japan.  For example,



a factor of two increase, from -30  ppb in 1933 to ~60 ppb in  the 1980s, is found in the summer
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Policy Options for Stabilizing Global Climate - Review Draft
                                 Chapter II
                                   FIGURE 2-9
              OZONE CONCENTRATION (cm'3)
          10
 140
            TEMPERATURE PROFILE
            AND  OZONE
            DISTRIBUTION IN
            THE ATMOSPHERE
 120 -
          100
                    200        300


                     TEMPERATURE IK)
Figure 2-9. On the left, temperature profile and ozone distribution in the atmosphere.  On the right,
sensitivity of global surface temperature to changes in vertical ozone distribution. Ozone increases
in Region I (below -30 km) and ozone decreases in Region II (above ~30 km) warm the surface
temperature.  The results are from a  1-D  radiative transfer model in which 10 Dobson unit ozone
increments are added  to each layer.  The heavy solid line is a least square fit  to step-wise
calculations. (Sources:  Watson et al., 1986; Lacis et al., no date)
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter II








concentrations in south Germany and Switzerland.  Similarly, summertime concentrations of O3 at




the surface in rural areas in the Eastern U.S. have increased by 20%-100% since the 1940s (Logan,




1985).  The surface O3 trend is 1%/yr or more at those sites in close proximity to population and



industrial centers.  At Pt. Barrow and at Mauna Loa, geographically removed from but still under




the influence of  urban centers, surface O3 was about 25 ppb in 1986 with summer values of 35-40




ppb. A small positive trend (0.7±0.5%/yr) is detected at these two sites from 1973-1986.








    Analysis of the ozone sonde data at  these populated sites show a small but significant positive



trend in mid-tropospheric ozone.  In general, the mid-tropospheric trends are smaller than those at




the surface of  the same  O3  profile, and upper-tropospheric and  lower-stratospheric trends  are




negative, —0.5%/yr.








    At remote locations, surface O3 exhibits a behavior very different from that near populated and




industrial regions.  At remote  sites in the Canadian Arctic and in Tasmania, Australia, for example,




the seasonal cycle of surface O3 has a minimum, rather than  a maximum,  in summer or autumn.




Surface O3 at the South Pole  was 20  ppb in 1986, similar to that measured in Western Europe in



the 1930s.   Also,  unlike populated sites in the Northern Hemisphere,  O3  at remote  sites  in the



Northern Hemisphere exhibit no significant trends near the  surface, but significant positive trends at



700 millibars (mb) and 500 mb.  Mid-tropospheric O3  at Resolute, Canada  (75°N), for example, is



found to be increasing at 1%/yr, while there is a negative  trend in  the lower stratosphere.  In the



Southern   Hemisphere,  however,  there  appear  to   be   no  significant  trends  in  surface  or




mid-tropospheric O3,  although O3 in the lower stratosphere has clearly decreased  and the seasonal




cycle at the South Pole has doubled in amplitude.
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter II








    The recent record of O3 concentrations in the upper atmosphere has been reviewed by a NASA



panel of experts (Watson et al.,  1988).  They  report  a general decreasing trend in  the total O3



concentration in the entire  atmospheric column from  1969  to  1986,  the  period  of  examination.



Ground-based Dobson instruments, located  mainly between  30 and 64 degrees  in the Northern



Hemisphere, show a total decrease of 1.7-3.0% in 17 years in the annually averaged O3 concentration



of the entire atmospheric column.   The decrease was more rapid in the winter months,  from



December to March. Satellite data, calibrated by coincident Dobson measurements, show a decrease



of about 2-3% from  October 1978 to October 1985 in  the column O3 concentrations between 53°S



and  53°N.   The observations of stratospheric  O3 in the Northern Hemisphere  indicate  that O3



abundances have declined over the past 20 years.  The rate of decrease in the summer is consistent



with the  predicted  change, due to CFCs.   However, the measured ozone loss poleward of 40°N in



winter is greater than that predicted by theory (Rowland, 1989).  This depletion of O3 in the north



is not associated with the unusual chemistry of the Antarctic ozone hole and may be the beginning



of a truly global decline.








Sources and Sinks








    Ozone  is not directly emitted by human activity, but its  concentration  in the troposphere and



stratosphere is strongly governed by anthropogenic emissions of NOW hydrocarbons, and CFCs, among



others.  Because of the short lifetimes of NOX and many of the other chemical species  important in



tropospheric  O3 chemistry,  O3 concentrations exhibit  large variability horizontally, vertically and



temporally.  Its annual concentration, seasonal  cycle, as well its trend have different  behaviors in



different parts of the globe so that the observations from a few regions cannot be viewed as globally



representative.  Global trends in tropospheric O3 cannot be unambiguously extracted from trends in



column O3  either.  Stratospheric O3 dominates the column abundance and its decreasing trend may
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Policy Options for Stabilizing Global Climate --  Review Draft                        Chapter II








obscure positive or negative trends in tropospheric ozone. The difficulty in determining the globally




representative trend  in tropospheric O3 translates into uncertainties in the  O3 contributions  to the



greenhouse warming.








Chemical and Radiative  Properties/Interactions








    Radiative forcing of O3 is more complex than that of the other greenhouse gases because (1) O3




is the major source of atmospheric heating due to  ultraviolet and visible absorption bands, in addition




to being a greenhouse gas, and  (2) O3 trends are not uniform in the  atmosphere ~ anthropogenic




effects are expected to include upper stratospheric losses, lower tropospheric increases,  and latitude




dependent changes in the lower  stratosphere and upper troposphere.








    Radiative transfer calculations reveal that the climate forcing due to an O3 perturbation changes




sign at 25-30 km altitude  (see Figure 2-9). Ozone increases below this  level lead to surface warming




because  its  greenhouse  effect  dominates its impact  on solar radiation,  while O3 added  to  the




stratosphere above ~30 km increases stratospheric absorption of solar energy at the expense of solar



energy that would otherwise have been absorbed at lower  altitudes.  On a  per  molecule  basis, the



O3 changes with by far the largest net effect on surface temperatures are those near the tropopause



where the temperature contrast between absorbed and  emitted  thermal radiation  is greatest.  O3



changes  near the  surface produce  little greenhouse  forcing since the outgoing thermal  radiation



absorbed is  of nearly the same temperature as the radiation emitted by surface  ozone.








    While the radiative effects of O3 are understood theoretically, quantifying surface  temperature




changes  due to O3 changes is difficult because of the  uneven data and the lack of global coverage




in the observations.  Available ozone trend data are limited to northern mid-latitudes. Based on the
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter II








observed decreases in O3 in the upper troposphere and lower stratosphere, which outweighed the



warming caused by decreases in  the upper  stratosphere  and by increases in O3  in the lower




troposphere, Lacis et al. (no date) find that during the 1970s, surface  cooling resulted from these




O3 changes. This cooling was equal in magnitude to about half of the warming contributed by CO2



increases during the same  time period.   These  results  differ  from  previous  assessments (e.g.,




Ramanathan  et al.,  1985; Wang et al., 1988)  that were based on one-dimensional photochemical




model  results which predict  ozone increases in the lower stratosphere  and  upper troposphere,  and




thus produce surface warming. Predictions of two-dimensional photochemical models for increases




in CFCs suggest that ozone should decrease in the lower stratosphere at middle and high latitudes,




but increase in the tropics (Ko et al., 1984; WMO, 1985).  This implies a strongly latitude-dependent



climate forcing for  O3 distributional changes with surface cooling in the middle and high latitudes and




warming in the tropics.








    The  global nature of O3 changes in the  upper troposphere and lower stratosphere cannot be




deduced, at this point, from current observations.  This makes highly uncertain the evaluation of O3




contributions to  the global greenhouse warming.    Lacis et al. (no  date) note that even the best




sampled  O3 data from mid-latitudes in the northern hemisphere are of  uneven quality, and that the




associated trends have large uncertainties and  may not be globally  representative.








OTHER  FACTORS AFFECTING COMPOSITION








    In addition to those greenhouse gases cited above that have a direct impact on the radiative



balance of the Earth, we must consider those forces that  control the chemical balance of the




atmosphere, in turn controlling the abundance of greenhouse gases.  With  the exception of ozone,




the greenhouse gases are generally not very reactive  in the  atmosphere; they have long chemical
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter II






lifetimes, on the order of 10 to 200 years; and they accumulate in the atmosphere until their rate of



chemical destruction balances their emissions.  The chemistry of the stratosphere and troposphere



provides the oxidizing power to destroy the majority of trace pollutants in the Earth's atmosphere (a



major exception is CO^ see above).  We outline below those primary and secondary components of



the Earth's atmosphere that affect the  chemically reactive gases and note  changes that may have



occurred in the recent past and those possible in the future.






Global Tropospheric Chemistry






    In the troposphere, many species are removed in a chain of reactions beginning with the hydroxyl



radical, OH, and ending with the deposition or rainout of a soluble compound, or with the complete



oxidation of the original compound  (i.e.,  net:  CH4 + 2O2 = = > CO2 + 2H2O).  For CH4, most



hydrocarbons,  and halocarbons containing a hydrogen atom  (e.g., anthropogenic HCFCs such as



CHClFj), the chemical lifetime will vary inversely with the suitably averaged global OH concentration.






    The OH radicals in the troposphere are short-lived (<1 sec) and are produced by sunlight in the



presence of O3  and  H2O; they  are  consumed rapidly  by  reaction with  CO,  CH4, and other



hydrocarbons.  Moderate levels of nitrogen oxides (NOX:  NO and NOj) can play an important role



in recycling the odd-hydrogen (HOJ from HO2 to OH, thus building up the concentrations of OH;



but high levels of NOX can reduce both OH and O3.  The short lifetime of OH means that, when



we integrate the  loss of even a well-mixed gas like CH4 against consumption by reaction with OH,



we are integrating over the myriad of conditions of the troposphere in terms of  sunlight, O3, H2O,
                                                                                  i


CO, CH4, NO,, and others. These tropospheric conditions vary over scales that range from smooth



in latitude and height, to irregular in plumes downwind from metropolitan areas.  At present we do
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter II








not have adequate models for OH that can describe these varied conditions and accurately integrate




the global loss of a greenhouse gas  such as CH4.








    In spite of these problems in modeling the chemically complex, heterogenous conditions of the




global troposphere, we do  understand tropospheric chemistry sufficiently  to make some simple




generalizations:








    •       Most  loss of CH4  occurs in marine  environments,  particularly in  the tropics and



            subtropics, remote from the influence of urban areas and the continental boundary layer,








    •       Increasing concentrations of CO and CH, will reduce global or hemispheric levels of OH,








    •       Large scale perturbations to tropospheric O3 and H2O  (from climate change) may have



            equal impact on OH concentrations,








    •       Changes in anthropogenic emissions of NOX are expected to have only a moderate direct



            impact on globally integrated OH, but may lead to more significant increases in Northern




            Hemispheric O3.








Carbon Monoxide








    Carbon monoxide (CO) has a lifetime of about  one month in the  tropics  that  becomes



indefinitely long in winter at high latitudes.  The globally  averaged destruction of CO corresponds




to an estimated lifetime of 3  months.   Carbon  monoxide is  lost  almost exclusively  through
DRAFT - DO NOT QUOTE OR CITE        II-47                           Februaiy 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter II








tropospheric reactions with OH  (and in this  non-linear system, CO is also a major sink for OH).




There are some estimates of plant/soil uptake of CO, but these are not of major significance.








    Detailed observations of CO concentrations are available over the past decade  (Dianov-Klokov



and Yurganov, 1981; Khalil and Rasmussen, 1988) and there are sporadic measurements since 1950




(Rinsland and Levine, 1985).  These data indicate that CO concentrations have grown modestly, but




consistently  (1-2%/yr) in the northern  mid-latitudes over the  last  few decades.   There  is no




convincing evidence for growth in the Southern Hemisphere (Seiler et al., 1984b).  This pattern is




consistent with  a growing  anthropogenic source,  since  the  short  lifetime precludes  significant



interhemispheric transport.  Since CH< concentrations have also increased similarly (about 1%, as



noted above),  we would expect a similar change  of opposite sign in tropospheric OH.








Nitrogen Oxides








    One form of odd-nitrogen denoted as NOX is defined as the sum of two species, NO  + NO2.




NOX is created in lightning, in natural fires, in fossil fuel combustion, and in the stratosphere from



N2O.  The NOX levels over the  continental boundary layer and  in the aircraft flight lanes of the



Northern Hemisphere are likely  to have increased over the last several decades.  Nevertheless, the



levels of NO, in the  clean marine environment are so low that they might be accounted for entirely



by natural sources (i.e., lightning, fires, stratospheric HNO3).








    The anticipated  changes in  NO, levels over limited regions  of the Northern  Hemisphere are




expected to have only a  small direct effect on the globally integrated  OH concentration. A more



important impact of NO, emissions is likely for tropospheric O3, where a substantial fraction  of the




global tropospheric ozone production is predicted to take place in small regions with elevated levels
DRAFT - DO NOT QUOTE OR CITE       11-48                           February 16, 1989

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Policy Options for Stabilizing Global  Climate - Review Draft                         Chapter II








of NOX and hydrocarbons (Liu et al., 1987). These issues are unresolved and are currently the focus



of photochemical studies with multi-dimensional tracer models.








Stratospheric Ozone and Circulation








    Some species such as N2O and CFCs do not react with OH, and these gases are destroyed only




in the stratosphere by short-wavelength ultraviolet light and by  reactions with the energetic state of




atomic oxygen, O(1D). For CFCs and N2O the abundances will  be perturbed by changes in the rate




of stratosphere-troposphere circulation and changes  in  the stratospheric O3  that  shields  the solar




ultraviolet  radiation.   Major perturbations to stratospheric O3  and  circulation may also alter  the




concentrations of tropospheric O3, since the stratosphere represents a major source for this gas.








    Predictions  have been  made over the past  decade  that stratospheric O3  will change due  to




increasing levels of CFCs, and that the circulation of the stratosphere may be altered in response to




changes in climate  induced by greenhouse gases.  Recent detection of the Antarctic ozone hole has




dramatized the ability of the atmosphere to change rapidly in response to perturbations.  There are




currently underway many theoretical  studies  of  the  impact of  the  ozone hole  on  stratospheric



circulation, O3 fluxes, and the mean chemistry of the stratosphere (e.g., N2O  losses).  As  discussed



above, there are also indications of a declining trend in Northern Hemisphere O3 not associated with



the Antarctic hole.  In summary, we expect stratospheric O3 to change in the next few decades, which




will lead to alterations in the lifetimes of the long-lived greenhouse  gases  and will  also perturb



tropospheric chemistry through the supply of O3 and through the increase  in solar ultraviolet light




available to generate OH.
DRAFT - DO NOT QUOTE OR CITE        H-49                            February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter II








CONCLUSION








    Anthropogenic emissions of both long-lived greenhouse gases  and short-lived highly reactive



species are altering the composition of the atmosphere.  The concentrations of CO2 and CH4 have



increased  dramatically since the preindustrial  era,  and CFCs  have been introduced into the



atmosphere for the first  time.  As  a result of the rapid pace of human-induced change,  neither



atmospheric composition nor climate is currently in equilibrium. Thus, significant global change can



be anticipated over the coming decades, no matter what course is taken in the future.  The rate and



magnitude of change, however, are subject to human control, which serves as the motivation  for this



report.
 DRAFT - DO NOT QUOTE OR CITE        11-50                           February 16, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                       Chapter II



                                        TABLE 2-2

                                      Trace Gas Data

CO2         CARBON DIOXIDE                                       1012 kg C




Atmospheric Burden                                                     720

    348.4 ±0.2 ppm in 1987
    Not  photochemically active


Annual Trend                                                           2.2

    1.15  ppm/yr (0.3%/yr) since 1984


Annual Sources                                                          6-7

    1.  Fossil fuel combustion                                             5.4
       4.5%/yr since 1984

    2.  Land use Modification                                             0.4 - 2.6

    3.  Biosphere -- climate feedback                                      ?
       Enhanced aerobic  decomposition
       of detrital material due to
       more favorable climate


Annual Sinks                                                            ~ 2.5

    1.  Ocean                                                           ~ 2.5
       Ocean's capacity to absorb CO2
       will be  altered by changes in
       temperature, salinity as wells a
       biological activity of ocean.

    2.  Biosphere                                                        ?
       Enhanced photosynthetic uptake of
       CO2 due to more favorable climate
       and/or  due to CO2 fertilization
DRAFT - DO NOT QUOTE OR CITE        II-51                           February 16, 1989

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 Policy Options for Stabilizing Global Climate - Review Draft                        Chapter II



                                  TABLE 2-2 (Continued)


CH,          METHANE                                               109 kg CH4




Atmospheric^ Burden

    1675 ppb in 1987                                                    4600  - 4800
    Lifetime:  5-10 years


Annual Trend

    14 -  16 ppb/yr  (0.8-1%/yr)                                           40 - 46


Annual Sources                                                          500  ± 100

    1. Fossil fuel
       Coal mining                                                     15 - 45
       Natural gas drilling, venting, and transmission loss                   25 - 50

    2. Biomass burning                                                 50 - 100

    3. Natural wetlands                                                 100 - 200

    4. Rice Paddies                                                     60 - 170

    5. Animals - mainly ruminants                                       65 - 100

    6. Termites                                                         10 - 100
       Population unknown

    7. Oceans and freshwater lakes                                       5-45

    8. Landfills                                                         30 - 70

    9. Methane hydrate destabilization                                    0 - 100 (future)


Annual Sinks                                                            495  ± 145

    1. OH destruction                                                  495  ± 145

    2. Dry soils                                                         ?
       absorption by methane -
       oxidizing bacteria in dry soils
DRAFT - DO NOT QUOTE OR CITE       11-52                           February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                                                    Chapter II
                                   TABLE 2-2 (Continued)
N,O
NITROUS OXIDE
109 kg N
Atmospheric Burden

    340 ppb in 1986
    Lifetime:  100 - 175 years
Annual Trend

    0.7  ± 0.1 ppb/yr
    0.2%/yr
Annual Sources

    1. Combustion of coal and oil

    2. Land use modification
       Biomass burning
       Forest clearings

    3. Fertilized agricultural lands

    4. Contaminated aquifers

    5. Tropical and subtropical forests and woodlands

    6. Boreal and temperate forests

    7. Grasslands

    8. Oceans


Annual Sinks

    Stratospheric photolysis and reaction with O(:D)
                                                           1500
                                                          3.5 ± 0.5
                                                           14  ± 3 (inferred)

                                                           1 - 3


                                                           1 - 2
                                                           ?

                                                           0.2 - 2.4

                                                           0.8 - 1.7

                                                           6 ± 3

                                                           0.1 - 0.5

                                                           <0.1

                                                           2 ± 1




                                                           10.5 ±  3
DRAFT - DO NOT QUOTE OR CITE
                              11-53
  February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter II



                                  TABLE 2-2 (Continued)


NOX         NITROGEN OXIDES                                     109 kg N


NOX  =  NO    +   NO2
         nitric      nitrogen
         oxide      dioxide

NOy = NOX + HNO2 + HNO3 + HOzNOa +  NOs + 2N2Os +  PAN + Participate Nitrate


Atmospheric Burden  ~ large variability, lifetime 1-2 days in summer          ?

    Marine air  4 ppt (NO)

    Continental air
       non-urban sites  2-12 ppb
       U.S. & European cities 70 - 150 ppb

    (100 ppt  =  240 x 10' kg  N)


Annual Trend                                                           ?


Annual Sources ~ Spatially and temporally concentrated sources              25 - 99

    1.  Combustion of coal, oil and  gas                                   14 - 28

    2.  Biomass burning                                                 4-24

    3.  Lightning                                                       2 - 20

    4.  Oxidation of ammonia                                            1-10

    5.  Emission from soils (mostly  NO)                                  4-16

    6.  Input from stratosphere (by  reaction of O(JD) with N2O)            ~ 0.5


Sinks

    1.  Wet deposition (precipitation scavenging)                           24-64

       ocean                                                           4-12
       continents                                                       8-30

    2.  Dry deposition                                                  12 - 22
DRAFT -  DO NOT QUOTE OR CITE        11-54                          February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                     Chapter II
                                  TABLE 2-2 (Continued)
CO     CARBON MONOXIDE
                            109 kg CO
Atmospheric Burden                                                    42Q

    ~  90  ppb
    (150 - 200 ppb Northern Hemisphere, 75 ppb Southern Hemisphere)

    Lifetime:  0.4 year
Annual Trend

    1 - 2%/yr Northern Hemisphere
    0 - 1%/yr Southern Hemisphere
Annual Sources                                                         1500 - 4000

    1.  Fossil fuel combustion                                           400 - 1000
       50%  for automobiles
       residential use of coal
       industrial activities, e.g., steel production

    2.  Oxidation of anthropogenic hydrocarbons                          0 - 180
       45%  emissions from  automobiles
       40%  evaporation of fuels and solvents

    3.  Biomass burning
       Wood used as fuel                                               25 - 150
       Forest wildfires                                                  10 - 50
       Forest clearing                                           .       200-800
       Savanna burning                                                100 - 400

    4.  CH< oxidation                                                   400 - 1000

    5.  Oxidation of natural  hydrocarbons (\soprenes and terpenes)          280 - 1200

    6.  Emission by plants                                               50 - 200

    7.  Ocean                                                          20 - 80

Annual Sinks                                                           3420

    1.  Soil uptake                                                     250

    2.  Photochemistry                                                  3170
DRAFT - DO NOT QUOTE OR CITE
11-55
February 16, 1989

-------
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter II
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter II
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Watson, R.T. and  Ozone Trends Panel, MJ. Prather and Ad Hoc  Theory Panel, and  MJ. Kurylo
and  NASA Panel  for Data Evaluation.  1988. Present State of Knowledge of the  Upper Atmosphere
1988: An Assessment Report. NASA Reference Publication 1208. Washington, D.C., 200 pp.

Weiss, R.F. 1981.  The temporal and spatial distribution of tropospheric nitrous oxide.  Journal of
Geophysical Research 86:7185-7195.
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter II
WMO  (World Meteorological Organization).  1985.  Atmospheric Ozone  1985:  Assessment of our
Understanding of the Processes Controlling its Present Distribution and Change.  Volume 1.  WMO,
Geneva, 392+pp.

Zimmerman,  P.R., J.P.  Greenberg, and J.P.E.C.  Darlington. 1984. Response  to:   Termites and
atmospheric gas production (Technical Comment by N.M. Collins, and T.G.  Wood). Science 224:84-86.

Zimmerman, P.R., J.P. Greenberg, S.O. Wandiga,  and PJ. Crutzen. 1982. Termites:  A potentially
large source of atmospheric methane, carbon dioxide and molecular hydrogen. Science 218:563-565.
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                                       CHAPTER III

                                    CLIMATIC CHANGE



FINDINGS  	•	   III-2

INTRODUCTION	   III-4

CLIMATIC CHANGE IN CONTEXT  	   III-6

CLIMATE FORCINGS  	   III-8
       Solar Luminosity  	  111-12
       Orbital Parameters  	  111-13
       Volcanoes	  111-13
       Surface Properties	  111-14
       The Role of Greenhouse Gases  	  111-14
       Internal Variations  	  Ill-15

PHYSICAL CLIMATE FEEDBACKS	  111-15
       Water Vapor - Greenhouse	  Ill-17
       Snow and Ice	  111-17
       Clouds  	  111-19

BIOGEOCHEMICAL CLIMATE FEEDBACKS	  111-20
       Release of Methane Hydrates  	  111-20
       Oceanic Change	  111-22
              Ocean Chemistry  	  111-23
              Ocean Mixing  	  111-23
              Ocean Biology and Circulation	  111-24
       Changes in Terrestrial Biota	  111-25
              Vegetation Albedo  	  111-25
              Carbon Storage 	  111-26
              Other Terrestrial Biotic Emissions	  111-26
              Summary  	  111-27

EQUILIBRIUM CLIMATE SENSITIVITY 	  111-28

THE RATE OF CLIMATIC CHANGE   	  111-31

CONCLUSION  	  111-35

REFERENCES	  111-37
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FINDINGS




    •       Climate  exhibits  natural variability on all time scales, from years to millions of years.

            This variability is caused by a combination of changes in external factors, such as solar

            output, and internal dynamics and feedbacks, such as the redistribution of heat between

            the atmosphere and the oceans.




    •       The ultimate warming that  can  be expected for a given increase  in greenhouse  gas

            concentrations is uncertain  due  to  our inadequate  understanding of  the  feedback

            processes of the  climate system.   For the benchmark case of doubling carbon dioxide

            concentrations, the National Academy of Sciences has estimated that the equilibrium
                                                                                        •>
            increase  in global average temperature would most likely be in  the  range of  1.5-4.5°C;

            recent analyses suggest that  the  warming could  be  as much as 5.5°C;  a reasonable

            central uncertainty range is  2-4°C.




    •       A variety of geophysical and biogenic feedbacks exist that have  generally been ignored

            in quantifying the temperature change that could occur for any given initial increase in

            greenhouse gases.   In particular, the potential of future global warming to increase

            emissions of carbon from northern latitude reservoirs in the form of both methane  and

            carbon dioxide, to alter uptake of CO2 by oceans, and a variety of other temperature

            dependent phenomena indicate that the true  sensitivity of the Earth's climate  system to

            increased greenhouse  gases could exceed 5.5°C for an initial  doubling of CO2.   While

            there  are  biogenic and  geochemical feedbacks that could  decrease greenhouse  gas

            concentrations - enhanced photosynthesis due to higher CO2,  for example ~ it appears

            that  the risk of all  biogenic and  geochemical feedbacks raising the Earth's true
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            temperature sensitivity to anthropogenic emissions of greenhouse gases is greater than



            the possibility of such feedbacks decreasing this sensitivity.








    •       Uncertainties about ocean circulation and heat uptake, and about future internal climate




            oscillations and volcanic eruptions, make  it difficult  to  predict the  time-dependent




            response of climate to changes in greenhouse gas concentrations.  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.  The Earth already is committed to a total warming of about




            0.7-1.5°C (assuming that the climate sensitivity to doubling CO2 is 2-4°C).  The Earth




            has warmed by 0.3-0.7°C during the last century, which is consistent with expectations



            given the uncertain delay caused by ocean  heat  uptake.
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INTRODUCTION








    The increasing concentrations of greenhouse gases documented in the last chapter are expected




to alter significantly the Earth's climate in the coming decades.  The magnitude and timing of actual



climatic change will be determined by future emissions (Chapter  V), by  changes  in other climatic




forcings,  and by the sensitivity of the climate system to perturbations.  Weather  and climate  (the




time-average of weather) are determined by  complex interactions between the atmosphere, land




surface, snow, sea ice,  and oceans, involving radiative and convective exchange of energy within and




among these components.  As is readily  apparent, this system exhibits considerable variability from



day to day, month to month, and year to year.








    Systematic diurnal  (day-night) and seasonal variations are driven by changes in the distribution




and amount of solar energy reaching the top of the  Earth's atmosphere as the Earth rotates on its




axis and orbits around  the sun.  Changes  in the amount of energy emitted by the sun, changes in the




atmospheric composition (due to volcanic eruptions and human input of aerosols and greenhouse




gases), and changes in the earth's surface (such as deforestation) can also affect the earth's energy




balance.  Such factors  are considered "external forcings" because they do not depend on the state of



the climate system itself.








    In contrast, much of the day to  day and  year to year variation results from the  internal dynamics



of the climate system.   For example, the polar front may be unusually far south in North America




during a given year, producing colder than normal weather in the northern Great Plains, but there




can be warmer than  average weather  somewhere  else,  leaving the global average more  or less



unchanged.  Similarly,  upwelh'ng of cold  water off the Pacific Coast of South America may fail for




several years.  This irregularly  recurring event, referred to as  El Nino,  leads to various regional



weather  anomalies, impacts like the collapse  of the Peruvian anchovy fishery, and warmer global
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temperatures.   In this case there is a temporary net release  of heat from the ocean  to the



atmosphere, which is usually followed by a reversal, sometimes referred to as La Nina (Kerr,  1988).




Such  random  variations  of the  atmospheric and oceanic circulation  can produce  anomalous




redistributions of energy in the climate system resulting in random climate variations, with amplitudes




and time  scales which may  be comparable to  climate changes  expected from  past increases in




greenhouse gases (Lorenz, 1968; Hasselmann,  1976; Robock, 1978; Hansen et al., 1988).








    In order to determine precisely the potential effects of the input of greenhouse gases on  future




climate, it would be necessary not only to be able to understand all the physics of the climate system




and the effects of each potential cause of climate change, but also to be able to predict the  future




changes of these forcings.  If we  could do this, we could explain  past climate change and separate




the effects of greenhouse gases from the other factors that  have acted during the past 100 years for




which we  have instrumental  temperature records.   We  could also  use theoretical climate models to




calculate  the  future size  and  timing  of  climate  changes due to greenhouse gases.  Since our




measurements of past climate are incomplete, our understanding of the climate system is incomplete,




and some (not well known) portion of climate change is random and unpredictable, we can only




estimate the impact of greenhouse gas buildup within a broad range of uncertainty.








    In this chapter we discuss in brief the magnitude and rate of past changes in climate and examine



the various  factors influencing  climate in order  to place the potential warming due  to increasing



greenhouse gas concentrations in context. Feedback mechanisms that can amplify or lessen imposed



climate  changes are discussed next.  The overall sensitivity of climate to  changes in forcing is then



considered, followed by a discussion of the time-dependent response of the Earth system. The focus




is on global  temperature as an indicator for the magnitude of climatic change. Regional climate and




the potential impacts of climatic change are not discussed here, but are considered in the companion



report Potential Effects of Global  Climate Change on the United States (Smith and  Tirpak, 1989).
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CLIMATIC CHANGE IN CONTEXT








    The most detailed information  on climate is, of course, from the modern instrumental record,




but even this data set is quite sparse in the Southern Hemisphere and over the oceans.  Wigley et



al. (1986)  reviewed a number of recent analyses, noting that independent groups (including Hansen




et al., 1981 and Vinnikov et al., 1980; more recent publications are Hansen and Lebedeff, 1988 and




Vinnikov et al., 1987), necessarily relying on the  same basic data sources,  but using different data




selection  and  averaging  approaches, have  obtained very  similar  results.   Given  the various




uncertainties due  to factors such  as poor spatial coverage hi some regions,  changes in the number



and location of stations, growth of urban heat islands, and changes in instrumentation, Wigley et al.




conclude that the warming since  1900 has been in the range of 0.3-0.7°C.  The most complete and




up-to-date global  surface air temperature record available  (Jones et al., 1988) is displayed in Figure




3-la, which shows a global warming of  about 0.3°C  from 1900  to 1940, a cooling of about 0.1°C




from 1940 to  1975 and a warming  of about 0.2°C from 1975 to 1987.   The four warmest years in




the record occurred during the 1980s: 1980, 1981,  1983, and 1987.  The overall warming is similar in



the land air temperature record of the Northern and Southern Hemispheres (Figures 3-lb,c), though




the long-term trend is  steadier  in  the Southern  Hemisphere where the 1940-1975 cooling is less



evident.  While the gradual warming seen in Figure 3-1 during the past century is not inconsistent



with the increasing greenhouse gases during this period (Chapter II), the large interannual variations



and the relatively flat curve from 1940 to 1975 show that there are also other important causes of



climate  change.  The differences between the two hemispheres also  show  that there  are regional




differences in the climate response to a global  forcing  (greenhouse gases), that important other




forcings (such as large volcanic eruptions) are not global in their effects,  or that internal climate




variations produce regional differences. Because of past and potential future emissions of greenhouse




gases (see below and Chapter V),  climate changes during the next century may be larger than the




variations shown for the past 100 years.
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                                                    Chapter III
                                    FIGURE 3-1
          (a)
         (b)
         (c)
                  0.5
SURFACE AIR TEMPERATURE
             (Degrees Celsius)
                Global
                 -0.5
                    '900
                            1920
                                     '940
                                              (960
                                                      1980     2000
      Northern Hemisphere
l»0   1870   1890   1910   1930   1350   1970   1990

     Southern Hemisphere
                      1950   1870   1890   1910   1330   1950   1970   1990
Figure 3-1.  (a) Global surface air temperature, 1901-1987.  This record incorporates measurements
made both over land and from ships.  The smooth curve shows 10-year Gaussian filtered values. The
gradual warming during this period is not inconsistent with the increasing greenhouse gases during
this period, but the large interannual variations and the relatively flat curve from 1940 to 1975 show
that there are also other important causes of climate change.  (Source: Jones et al., 1988.)

(b,c) Land surface air temperatures, 1851-1987  for the Northern Hemisphere (NH) and 1857-1987
for the  Southern Hemisphere (SH).  Note the larger interannual variability before 1900, when data
coverage was much more sparse.  (Source:  Jones, 1988.)
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    Recent climate variations are put in a longer-term perspective in Figures 3-2 through 3-4.  The



amplitude of climatic change over the last millennium (Figure 3-2) is similar to what has been seen



during the last century.  The Medieval Warm Epoch (800-1200 AD) may have been restricted to the



North Atlantic Basin (Wigley et al., 1986), and in any case appears to have been about as warm as



the present. The Little Ice Age (1430-1850; Robock, 1979) appears to have been as cool as the early



20th Century in parts of Europe.  The peak of the most  recent glaciation is generally given as 18



thousand years before the present  (kyBP) (Figures 3-3, 3-4) with globally averaged temperatures



about 5°C cooler than today (Hansen et al.,  1984) between 15 and 20 kyBP. Even over the 700,000



year period illustrated in Figure 3-4 the maximum  global  temperature swing appears to have been



no greater than about 5°C, with the periods of greatest warmth being the present and the interglacial



peaks which occurred approximately every 100,000 years for the past million years (Figure 3-4).  The



temperature change shown in  Figure 3-3 is  for Antarctica  and is substantially greater than what is



believed to represent the globe as a whole. (Such high-latitude amplification of temperature increases



can be expected for greenhouse-induced warming in the future).  The CO2 variations are, in general,



in step with  the temperature  variations  deduced from deuterium variations in the  same ice  core



(Jouzel et al., 1987), demonstrating the importance  of CO2 in amplifying the relatively weak orbital



forcings during past  climate variations (Genthon et al., 1987; see Orbital Parameters).  While it is



difficult to assign a  cause for these past changes,  it is reasonable to  conclude that, given current



greenhouse  gas  concentrations, global temperatures  will  soon equal  or exceed  the maximum



temperatures of the past million years.








CLIMATE FORCINGS








    The patterns of  climate variations discussed in  the last section are the result of a combination



of external  forcings, internal  feedbacks,  and unforced internal  fluctuations.  The  strictly external



forcings are changes in  solar output and  variations  in the Earth's orbital parameters,  while changes
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                                    Chapter III
                                       FIGURE 3-2
X J
03
"o
 ' » I > ' v / V r- ' h /
\r \ / w - \ / v V
w w
400 r,oj HT) 100Q 1?00 MOO 1600 1HOO
AD
Figure 3-2.  Oxygen isotope (6  O) variations from ice cores in Greenland.  This is an index of
Northern Hemisphere temperature, with the maximum range equal to about 1°C. (Source: record
of Dansgaard as given by Lamb, 1977.)
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                                     Chapter III
                                       FIGURE 3-3
     u
     o
    2.5


      0


  -2.5


  -5.0


  - 7.5


 -10.0
Figure 3-3. Carbon dioxide levels and temperatures over the last 160,000 years from Vostok 5 Ice
Core in Antarctica.  The temperature scale is for Antarctica; the corresponding amplitude of global
temperatures swings is thought to be about 5°C.  (Source:  Barnola et al., 1987.)
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                                                  Chapter HI
                                       FIGURE 3-4
 STAGES
                   100
200         300        400

  AGE IN THOUSANDS OF YEAUS
                                                              500
600
Figure 3-4. Composite 618O record of Emiliani (1978) as given by Berger (1982). This comes from
deep sea sediment cores and is an index of global temperature, with the temperature range from
stage 1 (present) to stage 2 (18,000 years ago) equal to about 5°C.
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in aerosols  and greenhouse gas concentrations may be  viewed as  external forcings  or  internal




feedbacks, depending on the time scale  and processes  considered.  The sensitivity  of  the climate




system is determined by the feedbacks  that modify the extent to which climate must change to




restore the overall energy balance of the Earth as  external forcings change.








Solar Luminosity








    The  solar luminosity (or total energy output from the sun) has an obvious and direct influence




on climate by determining the total energy reaching the top of the Earth's atmosphere.  Theories of




stellar evolution suggest that solar output  was 25% lower early in Earth history, but geologic evidence




and the fact that life was able to evolve on Earth shows that the Earth was not an inhospitable ice-




covered planet. An important part of the explanation for this "faint young sun paradox" now appears




to be that the  CO2 content of the atmosphere was many times higher than it is  at present.  The



enhanced greenhouse effect from CO2 was probably the main  factor in counteracting the lower solar




luminosity (see below). Geochemical models  suggest that over millions of years CO2 has acted as



an internal feedback  that has kept the Earth's climate  in a habitable range (Walker et. al.,  1981;




Berner and  Lasaga, 1988; Figure 3-2b).








    Solar luminosity also varies by small  but significant amounts over shorter time periods.  Various



attempts have  been  made  to  explain past climate variations by  assuming a link  between  solar



luminosity and observed  parameters,  such as sunspot activity, solar diameter, and the  umbral-




penumbral ratio (Wigley  et al., 1986).  Unfortunately, measurements with sufficient precision to




detect solar luminosity changes have  only been available sbce 1979  - too short a time period  to be




able to definitively confirm  or refute the proposed relationships.  These measurements show a decline




in solar  luminosity between 1980 and  1986; whereas the most recent data  show a reversal of this



trend (Willson and Hudson 1988; Willson et al., 1986).  The luminosity data are positively correlated
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with sunspot number and suggest an 11-year cycle with an amplitude of 0.04% or 0.1 W/m2 at the




top of the atmosphere (Willson and Hudson, 1988).








Orbital Parameters








     Cyclic changes in Earth orbital characteristics are now widely accepted as the dominant trigger




behind the glacial/interglacial variations evident in Figure 3-3 and  extending back  to at least  1.7




million years before  present (e.g., Wigley et al., 1986;  COHMAP, 1988).  While causing  only small



changes in the total radiation received by the Earth, the orbital  changes (known as the Milankovitch




cycles) significantly alter the latitudbal and seasonal distribution of insolation. For example, Northern




Hemisphere summer insolation was about 8% greater 9 kyBP than it  is now, but winter insolation




was 8% lower. Changes of this type, in combination with internal feedbacks as discussed  below, are




presumed to have determined the pattern of glaciations and deglaciations revealed in the geologic




record.  Attempts have been made to compare model predictions with paleoclimatic data.  There has




been  reasonably good agreement between the two, given specified ice  sheet extent and sea surface




temperatures  (COHMAP, 1988; Hansen  et  al.,  1984).  To  the  extent  that  the Milankovitch




explanation of ice ages is correct, one would expect the  Earth to be heading toward a new ice age




over the next 5000 years, but the very gradual changes in orbital forcings expected in this  period will




be overwhelmed if current trends in greenhouse gas concentrations continue (Wigley et al., 1986).








Volcanoes








    Large volcanoes  can significantly increase the stratospheric aerosol concentration, increasing the




planetary  albedo and reducing surface temperatures by  several tenths of degree for several years




(Hansen et al., 1978, 1988; Robock, 1978, 1979, 1981, 1984).  Because  of the thermal inertia of the




climate system, discussed below, volcanoes can even be responsible for climate changes over decades,
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 and in fact the warming shown in Figure 3-1 from 1920 to 1940 can be attributed to a period with



 very few volcanic eruptions (Robock, 1979).  Since large eruptions occur fairly frequently and cannot



 now be predicted, this component of climate change will have to be considered when searching past



 climate for a greenhouse signal and when projecting future climate change.








 Surface Properties








     The Earth's  radiative balance can also be changed by variations of surface properties.  While



 interactions with the ocean, which covers 70% of the Earth's surface, are considered internal to the



 climate system and are discussed below, land surfaces also exert a strong influence  on the  climate.



 Human  activities,  such as  deforestation, not  only provide a  source  of CO2 and  CH4 to  the



 atmosphere, but also change the surface albedo and moisture flux into the atmosphere.  Detailed



 land surface models,  incorporating the effects of plants,  are now being developed and incorporated



 into GCM studies of climate change (Dickinson, 1984; Sellers et al., 1986).








 The Role of Greenhouse Gases








     The greenhouse effect does not increase the total energy received by the Earth, but it does alter



 the distribution of energy in the climate system by increasing the absorption of infrared (IR) radiation



 by  the atmosphere.  If the Earth  had  no  atmosphere,  its surface temperature  would  be strictly



 determined by the balance between solar radiation absorbed at the surface and emitted IR.  The



• amount of IR emitted by any body  is proportional to the fourth power of its absolute temperature,



 so that an increase  in  absorbed solar radiation  (due to increased solar luminosity  or decreased



 albedo, for example) would  be balanced  by a small increase in the surface temperature, increasing



 IR  emissions until they are  again  equal  to  the absorbed  solar radiation.  The role of greenhouse



 gases can be understood by thinking about the atmosphere as a thin layer that absorbs some fraction
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of the IR emitted by the surface (analogous to the glass in a greenhouse).  The energy absorbed by



the atmosphere is then remitted in all directions, and the downward half of this energy flux warms



the surface (Figure 3-5).  Higher concentrations of greenhouse gases increase the IR absorption in



the atmosphere,  raising surface temperatures.








    Changes in  the atmosphere's radiative properties can result from external perturbations  (such



as anthropogenic emissions of CO2) or from internal adjustments to climatic change.  The amount



of water vapor, the dominant greenhouse gas, is directly determined by climate and contributes the



largest positive feedback to climatic change (Hansen et  al., 1984; Dickinson, 1986).  Similarly, clouds



are an  internal  part of the  climate system that strongly influence  the Earth's  radiative balance



(Ramanathan et  al., 1989).  Changes in the concentrations of other greenhouse gases may be imposed



by human activity or may result from changes in their sources and sinks induced by climatic change.



Such feedbacks are discussed below.








Internal Variations








    As discussed in the introduction,  even with  no changes in external forcings, climate still exhibits



variations due  to internal rearrangements  of  energy within  the  atmosphere  and between  the



atmosphere and  the ocean. The total amplitude and time scales of these internal  stochastic climate



variations are not well known; these variations therefore pose an additional difficulty in interpreting



the past record and projecting the level of future climate change.








PHYSICAL CLIMATE FEEDBACKS








    Any imposed  imbalance in  the Earth's radiative  budget,  such  as discussed above, will be



translated into a changed climate through feedback mechanisms which can act to amplify or decrease
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                                                                 Chapter III
                                      FIGURE 3-5
                                         GLOBAL ENERGY BALANCE
                                                  (Watts/Square Meter)
                                    Solar
                   340
                                  100
                                               90
                                                  150
                      86
                                                                                   154
  Atmosphere
                                                    300
                                                            308
                                                                            2XC02
                           \
                 240
390
                 160
                                                       394
I
                                                                       154
  Earth's  Surface
  (b)
SPACE
               INCOMING
                SOLAR
               RADIATION

                  340
                                               OUTGOING RAC'IATION
                                           Short wdve         Longwave
                                          27  66  20  31
                                                           136
                                                                     68
            ATMOSPHERE
               Absorbed by
               Water Vapor.
                 Dusi, 0,
          Net Emission
             by
          Water Vapor.
            co2.o3
            Absorption
            by Clouds
            Water Vapor,
         ^35)C°2'°3
                                                       Emission
                                                       by Clouds
                                              LONGWAVE RADIATION
                                                                       Ldtent
                                                                      Heat Flux
                                                                 Sensible
                                                                 Heat Flux
            OCEAN, LAND
                              166
                                                     380
                                                               340  24
                                                                         62
Figure 3-5.  (a) Highly simplified schematic of the global energy balance illustrating the mechanism
by which increased greenhouse gas concentrations warm the Earth's surface.  The atmosphere is
treated as a thin layer that does not absorb solar radiation; the role of convective and latent heat
transfer is also neglected. Doubling the concentration of CO2 increases the absorption and emission
of infrared radiation by the atmosphere, increasing the total energy absorbed at the surface.  In the
equilibrium  depicted, total emissions to space remain unchanged.

(b) A more realistic schematic of the global energy balance for current conditions. (Source: adapted
from MacCracken, 1985.)
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Policy Options for Stabilizing Global Climate - Review Draft                       Chapter HI








the initial imposed forcing.  In this section, several of these mechanisms which are internal to the



physical climate system are discussed.  In the next section, several recently quantified mechanisms




involving the planet's biology and chemistry are described.








    By no means do  we understand  or even know about all the mechanisms involved  in climate




feedbacks.  Figure 3-6 shows some of the physical  climate feedbacks involved in  changing surface




temperature. Current state-of-the-art climate models attempt to incorporate most of the physical




feedbacks that have been identified, but are forced, for example, to provide a very crude treatment




for one of the most important — changes in clouds — because of inadequate understanding of cloud




physics and because of the small spatial scale on which clouds form compared to  the resolution of




climate models.








Water Vapor - Greenhouse








    When the climate warms,  the atmosphere  can hold more water vapor.   This  enhances the




warming   because  it  increases the  greenhouse effect  from water  vapor,  producing  still  more




evaporation from the warmed surface. This positive feedback acts to approximately double imposed




forcings.








Snow and Ice








    When climate  warms, snow and ice cover  are reduced, exposing land or ocean with a  lower




albedo than the snow  or ice.  In addition, the albedo of the remaining snow and ice is reduced due



to meltwater puddles  and debris on  the surface.  This acts to absorb more  energy at the surface,




further enhancing the warming.  This albedo feedback was  originally thought to  be  the  dominant




positive feedback effect of snow and  ice, but we now understand that the thermal  inertia feedback
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                                                           Chapter III
                                    FIGURE 3-6
 EQUILIBRIUM TEMPERATURE CHANGES FROM DOUBLED C02
                (Degrees Celsius; Based on 1.5-5.5 Degree Sensitivity)
      5.5
      5.0
      4.5
      4.0
  CO
  2  3.5
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Policy Options for Stabilizing Global Climate - Review Draft                       Chapter III








of sea  ice plays a much more important role (Manabe and Stouffer,  1980; Robock, 1983).   The



albedo feedback requires that the sun be shining, and since the maximum ice and snow extent  is in




the winter, it plays a small role in influencing the albedo except in the spring, when the snow and




ice are present along with high insolation.








    The  thermal inertia feedback  acts to increase the thermal inertia of the oceans when climate



warms by melting sea ice, reducing its insulating effect and increasing the transfer of heat from the




ocean  to the  atmosphere  at high latitudes.   This  acts to  reduce the seasonal cycle  of surface




temperature and is the prime reason for the enhancement of imposed climate change in the polar




regions in the winter (Robock, 1983).  If sea ice retained its current seasonal cycle, there would be




no preferential latitude or time of year for climate change.
Clouds
    Clouds  respond directly and immediately to changes  in climate and may represent the most



important uncertainty in determining  the sensitivity of  the  climate system to  the buildup  of



greenhouse gases.  Fractional cloud cover, cloud altitude and cloud optical depth can all change when



climate changes (Schlesinger,  1985).  It has not been possible to calculate the net effect of cloud



feedbacks because all these properties  of clouds can change simultaneously, because clouds affect



long-wave radiation, short-wave radiation, and precipitation (which affects soil moisture and hence



albedo, thermal inertia,  and moisture  flux of land), and  because the net effect  depends on the



location of the cloud  (in  3 dimensions), the underlying surface albedo,  and the time of day and year



of the changes.  The  current net effect of clouds has only  recently been measured  (Ramanathan  et



al., 1989).   Current climate models include crude calculations of  clouds and have difficulty even



reproducing the current cloud distribution.
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter III








BIOGEOCHEMICAL CLIMATE FEEDBACKS








    In  addition to the climatic processes discussed above, a number of biogeochemical feedback




processes will influence future concentrations of greenhouse gases and climatic change.  Increased




greenhouse gas concentrations will alter not only the climate, but also biogeochemical processes that




affect sources and sinks of radiatively important gases.   Climatically important surface properties,



such as albedo and  evapotranspiration,  will also be modified by vegetation  changes.   The major




biogeochemical  feedback links, illustrated in Figure 3-7, can be categorized as follows:  physical




effects  of climatic change, changes in marine biology, and changes in terrestrial biology. Potential




physical effects of climatic  change  include release of methane hydrates and  changes in ocean



chemistry, circulation, and mixing.  Changes in marine biology may alter  the pumping of carbon




dioxide from the ocean surface to deeper waters and the  abundance of biogenic cloud condensation




nuclei.   Potential  biological responses on land include changes  in surface albedo, increased flux of



CO2 and CH4 from soil organic matter to the atmosphere due to higher rates of microbial activity,




increased sequestering of CO2 by the biosphere due to CO2 fertilization, and changes in moisture




flux to the atmosphere.








Release of Methane  Hydrates








    Potentially the most important biogeochemical feedback is the release of CH4  from near-shore



ocean sediments.   Methane  hydrates are formed  when  a  methane molecule is included within a



lattice of water molecules; the ratio can be as small as 1:6, that is, one methane molecule for every




six water molecules  (Bell, 1982).  The hydrate structure is stable under temperature and pressure




conditions that  are typically found under a water column of a few hundred meters or more in the




Arctic  and closer to  a thousand meters in warmer waters; the region where hydrates are found can




start at the  sea floor and extend up to a few hundred meters into the sediment,  depending on the
DRAFT - DO NOT QUOTE OR CITE        111-20                           February 16, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft
                                  Chapter HI
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 DRAFT - DO NOT QUOTE OR CITE
111-21
February 16, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter HI








geothermal temperature gradient  (Kvenvolden and Barnard, 1984).  Estimates of the total quantity




of CH4 contained in hydrates range from 2x10* to 5xl06 Pg (Kvenvolden, 1988).  Given the climatic




change associated with a doubling of CO2) Bell (1982; as corrected by Revelle, 1983) estimated that




there could be a release of -120  Tg CH4/yr from Arctic Ocean sediments, and Revelle  (1983)




calculated global emissions of ~640 Tg CH4/yr from continental slope hydrates.  These estimates




are,  however,  highly uncertain both because  the total  quantity of hydrates  potentially subject  to




destabilization is not known and because bottom water may be insulated from surface  temperature




increases throughout much of the ocean (Kvenvolden, 1988).   Nonetheless, a very strong positive




feedback from this source cannot be excluded at this time.








Oceanic Change








    The oceans are the dominant factor in the Earth's thermal inertia to climate change as well as



the dominant sink for anthropogenic CO2 emissions.  The mixed layer (approximately the top 75 m)




alone contains about as much carbon  (in  the form of H2CO3, HCO3", and CO3")   as does  the




atmosphere (see Chapter II).  Furthermore,  the ocean biota  play  an  important  role in carrying




carbon (as organic debris) from the mixed layer to deeper  portions of the ocean (see, for example,



Sarmiento and Toggweiler, 1984).  Thus, changes in ocean chemistry, biology, mixing, and large-scale



circulation  have the potential to substantially alter the rate of CO2 accumulation in the atmosphere



and the rate of global warming.








    Because the oceans are such an integral part of the climate  system, significant changes in the




oceans are likely to  accompany a change in climate.  For  example, the oceans are responsible for




about 50% of heat transport from the equator toward the poles (Dickinson, 1986), surface mixing is




driven by winds, and deep circulation is driven by  thermal and salinity gradients.  The feedbacks




involving the  ocean can be  divided  into three categories:  the direct effect of temperature  on
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter III



carbonate chemistry, reduced mixing due to increased stability of the thermocline, and the possibility

of large-scale reorganization of ocean circulation and biological activity1.
Ocean Chemistry



    The most straightforward feedback is on ocean carbonate chemistry. As the ocean warms, the

solubility of CO2 decreases and the carbonate  equilibrium shifts toward carbonic acid; these effects

combine  to increase the  partial  pressure of  CO2  (pCO2) in the ocean by 4-5%/°C  for a  fixed

alkalinity and  total carbon content.  Because the total carbon content would only have  to decrease

by about one-tenth this amount to restore pCO2 to  its previous level, the impact of this feedback is

to increase atmospheric CO2 by about 1%/°C  for a typical scenario (Lashof, 1989; Chapter VI).
Ocean Mixing



    As heat penetrates from the mixed layer of the ocean into the thermocline the stratification of

the ocean will increase and mixing can be expected to decrease, resulting in slower uptake of both

CO2 and heat.  This feedback raises the surface temperature that can be expected in any given year

for two reasons:  First, the atmospheric CO2 concentration will be higher because the oceans will

take up less CO2.   Second, the realized temperature will be closer to  the equilibrium temperature

due to reduced heat transport into the deep ocean (see the  discussion of the transient response

below).
     1  The thermocline starts at the base of the mixed layer and extends to a depth of about 1000m.
It is characterized by a rapid decrease in temperature with increasing depth, which inhibits mixing
in the  water column because the colder deeper water is denser than the warmer overlying  water.
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter III








Ocean Biology and Circulation








    A more speculative, but potentially more significant,  feedback involves the possibility of large-




scale  changes  in the circulation of the atmosphere-ocean system as suggested by Broecker  (1987).




This  possibility is illustrated by the apparently very  rapid  changes in the  CO2  content  of the




atmosphere during glacial-interglacial transitions as revealed by ice-core  measurements (e.g., Jouzel



et al., 1987; Figure 3-2a).  Only shifts in carbon cycling in the ocean are thought to be capable of




producing such large, rapid, and sustained  changes  in atmospheric  CO2.  A number of papers have




attempted  to  model the  changes  in ocean  circulation and/or  biological  productivity required to




account for the change in pCO2, emphasizing the importance of high-latitude processes (Kerr, 1988;



Sarmiento  and Toggweiler,  1984; Siegenthaler and  Wenk, 1984; Knox and McElroy, 1984).   Given




that continuation of current  trends could lead to a climate change during the next century of the




same  magnitude as  that  which occurred between  glacial and interglacial periods,  one must take




seriously the possibility of sudden changes hi ocean circulation. Should this happen, the oceans could




even  become  a CO2 source  rather than a sink -  significantly accelerating climatic change.  Such




changes in circulation could also cause abrupt changes  in climate, a scenario that conflicts with the




general assumption that the warming will be gradual (Broecker, 1987).








    A different feedback  involving  ocean biology has been proposed by Charlson et al. (1987).  It



is  also  uncertain,  but  potentially significant.    Dimethyl  sulfide (DMS)  emitted  by  marine



phytoplankton may act as cloud condensation nuclei in remote marine environments, affecting cloud




reflectivity  and therefore  climate (Charlson  et al.,  1987;  Bates  et  al., 1987).  Climate  presumably




affects biogenic DMS production but the relationship is complex and poorly understood  at this tune




(Charlson  et  al., 1987).  While  this mechanism was  originally proposed  as  a potential negative




feedback consistent with the Gaia  Hypothesis  (Lovelock, 1988;  Lovelock and  Margulis, 1973), ice-




core  data indicate that  aerosol levels were higher during the last glacial maximum, suggesting that
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Policy Options for Stabilizing Global  Climate -- Review Draft                        Chapter III








biogenic DMS production may act instead as a positive feedback (Legrand et al., 1988).  This is only



one  possible cloud  optical property  feedback (discussed  above),  and  the  net effect  cannot be



determined because other cloud properties (amount, elevation) would also change in a complex way.








Changes in  Terrestrial Biota








    The terrestrial biota interact with climate in a wide variety of important ways (Figure 3-7).  The




most significant effects on climate may result from large-scale reorganization of terrestrial ecosystems




as well as the direct effects of temperature and CO2 increases on carbon storage.








Vegetation Albedo








    Probably the most significant  global feedback produced by the terrestrial biota, on a  decades-




to-centuries time scale is due to changes in surface albedo (reflectivity) as a result of changes in the




distribution of terrestrial ecosystems.  Changes in moisture flux patterns are probably also important.




Cess (1978) argued that vegetation albedo feedback could have played a major role in explaining the




glacial-interglacial temperature change. Dickinson and Hanson (1984) reanalyzed this problem and



found  a much smaller, but still significant effect, i.e., that the planetary albedo was 0.0022 higher at




the glacial maximum due  to differences in mean annual vegetation albedo.   A similar result was



obtained by Hansen  et al.  (1984) using a prescriptive scheme to relate vegetation type to climate in



GCM  simulations for current and glacial times.  (The much larger effect found by Cess was due to



differences in the albedo assigned to similar vegetation  types for  18 kyBP  versus the  present



[Dickinson and Hanson, 1984].)  This feedback may be less important in the future than it was during




the last deglaciation  because  of direct human effects on  the  surface, such as  deforestation, and




because the pattern of vegetation change will be different.
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Policy Options for Stabilizing Global  Climate -- Review Draft                       Chapter III








Carbon  Storage








    Other significant feedbacks are related to  the role  of the terrestrial biosphere as a source and




sink for CO2 and CH4. The carbon stored in live biomass and soils is roughly twice the amount in




atmospheric CO2, and global net primary production (NPP) by terrestrial plants absorbs about 10%



of the carbon held in the atmosphere each year.  On  average this is nearly balanced by  decay of




organic  matter, about  0.5-1%  of which is  anaerobic and thus produces CH4 rather than CO2. Small




shifts in the balance between NPP and respiration,  and/or changes  in the fraction of NPP routed to




CH4 rather than CO2, could therefore have a substantial impact on the  overall greenhouse forcing,



because CH4 has a much larger greenhouse effect than CO2 per molecule. Both NPP and respiration




rates are largely determined by climate and NPP is directly affected by the CO2  partial pressure of



the atmosphere.   Thus the potential for  a substantial feedback exists.








Other Terrestrial Biotic Emissions








    The biosphere plays  an important role in the frequency and quantity  of emissions of various




other  atmospheric trace  gases, which are also  likely  to be influenced by climatic change.  For



example, as much as half of nitrous oxide (N2O) emissions are attributed to microbial processes in



natural  soils (Bolle et al., 1986). Emissions of N2O tend to be episodic, depending strongly on the



pattern  of precipitation events in addition to temperature and soil properties (Sahrawat and Keeney,



1986). Thus, climatic change could be  accompanied by significant changes in N2O emissions, although




there is not sufficient understanding of the microbiology to  predict these changes at present.  The




biosphere is also a key source of atmospheric  non-methane hydrocarbons (NMHCs), which play an




important role in global  tropospheric chemistry; the oxidation of  NMHCs generates a substantial




share of global carbon monoxide and  therefore influences the concentration of OH and the lifetime




of CH4  (Mooney et al., 1987;  Thompson and Cicerone,  1986).  As much as 0.5-1% of photosynthate
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Policy Options for Stabilizing Global Climate -- Review Draft                       Chapter HI








is lost as isoprene and terpene (Mooney et al., 1987).  Lamb et al. (1987) found that the volume of



biogenic NMHC emissions in the United States is greater than anthropogenic emissions by about a



factor of two.  The ratio for the globe is probably greater.  Emissions, at least for isoprene and tt-



pinene are exponentially related to temperature (Lamb et al., 1987; Mooney et al., 1987).  The first-



order impact of climatic change, then, would be to increase NMHC  emissions, producing  a positive



feedback through the CO-OH-CH4 link.  The actual impact when changes in ecosystem distribution



are considered is  uncertain, however,  as different species have very different emissions (Lamb et al.,



1987).








Summary








    Of the feedbacks that will come into play during the next century, the physical climate  feedbacks



discussed earlier (water vapor, clouds, ice cover, and ice and snow albedo) will almost certainly have



the greatest impact.  In comparison, the potential individual impacts of the biogeochemical  feedbacks



discussed here are rather modest. If the physical climate feedbacks  approach the strongly positive



end of their ranges, then the overall sensitivity of the climate system would be substantially increased



by even small additional feedbacks. However, since both the internal and biogeochemical  feedbacks



are presently so  poorly understood, and  since other feedbacks  may be  discovered,  the overall



equilibrium response of the climate system (discussed below) can only be specified with a fairly wide



range.








    The perturbations to global biogeochemical cycles reflected in the feedback processes discussed



here are of great importance in their own right in addition to whatever warming they may produce.



The vegetation albedo feedback, for example, contributed only 03°C  out of the 3.6°C global cooling



in the ice-age analysis of Hansen et al. (1984), but this represented  a massive change  in  terrestrial



ecosystems. A better assessment of both the impact of climatic change on biogeochemical cycles and
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Policy Options for Stabilizing Global Climate ~ Review Draft                        Chapter III








the associated feedbacks is needed.    Several aspects of  the  impact  of  climatic change on



biogeochemical processes are discussed in the companion report Potential Effects of Global Climate




Change on the United States (Smith and Tirpak, 1989).  A quantitative estimate of the impact of some




of the  feedbacks discussed here is presented  in Chapter VI based on incorporating them in the



Atmospheric Stabilization Framework developed for this study.








EQUILIBRIUM CLIMATE SENSITIVITY








    When any forcing, such as an increase in the concentration of greenhouse gases, is applied to




the climate system, the climate will start to change.  Since both the imposed forcings and the climatic



response are time-dependent, and since the climate system has inertia due to the response times of




the ocean, the exact relationship between the timing of the forcings and the timing of the response




is  complex.   In an attempt to simplify the  problem of understanding the  sensitivity of the climate




system to forcings, it  has become  a standard experiment to  ask the question,  "What would be the




change in global average surface air temperature if the CO2 concentration in the atmosphere were




doubled from the preindustrial level, all other climate forcings were held constant, and the climate




became completely adjusted to the new radiative forcing?"  This quantity is called the  "equilibrium



climate sensitivity to doubled CO2" and is indicated as AT^ (see Box 3-1).








    The actual path that the climate system would take to approach the equilibrium climate would



be  determined by the time scales  of the forcings and the various elements of the  climate system.




This is called the "transient  response" and is discussed in the next section.  Because the climate




system response always lags the forcing, there will always be a built-in unrealized warming that will




occur in the future, even if no more forcing occurs. Thus, there is certain to be some future climate




response to  greenhouse gases that were put into the atmosphere in the past, even  if no more are put



in starting today. Another way of saying this is that  societal responses to  the  greenhouse problem
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Policy Options for Stabilizing Global Climate - Review Draft                       Chapter HI
               BOX 3-1.  SIMPLIFIED MODELING FRAMEWORK

            The  concepts  discussed in  this chapter can be summarized b a  simple  zero-
      dimensional or  one-box model of  climate as discussed by Dickinson (1986):

      (1)                          C(dAT/dt) + AAT = AQ

      where AQ is the climate forcing and could be due to changes in solar output, volcanoes,
      surface properties, stochastic processes or greenhouse gases (as discussed under Climate
      Forcings and Feedbacks); AT is the change in tropospheric/mixed-layer temperature from
      the preindustrial equilibrium climate; the factor A, called the "feedback parameter" by
      Dickinson,  gives the  change in  upward energy flux resulting from a change in surface
      temperature, AT, and is the net result of all the climate  feedbacks (as discussed in the
      section on  Climate Sensitivity); t  is time; and C  is the  effective heat capacity  of the
      Earth, which is determined by the rate  of heat uptake by the  ocean (C must be a
      function of time to account for the gradual penetration of heat into an increasing volume
      of the deep ocean and  changing sea ice cover). In equilibrium the first term in (1)  is
      zero,  so the equilibrium climate sensitivity is simply given by

      (2)                                AT = AQ/X

      For a doubling  of CO2, AQ is about 43 W/m2, so the range 1.5-5.5°C  of A-T^ discussed
      above corresponds to a range of 2.9-0.8 W m"2 "C1 in X.  This conceptual model, with
      AQ calculated from changes in  greenhouse gases and C  replaced by a diffusive  model
      of the ocean, is incorporated into the Integrating Framework used  in  the  modeling
      exercises for this report (see Chapter V and Appendix A).
that are undertaken now will be felt for decades in the future, and lack of action now will similarly

bequeath climate change to future generations.



    Analysis of past climate change, and model calculations of future climate change can both be

used to determine AT^.  Unfortunately,  our  knowledge  of both  past climate change and  the

responsible forcings are too poor  to reliably determine AT^ from  past data.   Wigley  and Raper

(1987)  estimate that if all of the warming of the past 100 years was  due to greenhouse  gases, then

ATjx would be  approximately 2°C.  If however, one  allows for other possible  forcings, natural

variability, uncertainties hi ocean heat uptake and the  transient response,  and for uncertainties hi
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Policy Options for Stabilizing Global Climate -  Review Draft                        Chapter III








preindustrial greenhouse gas concentrations (see below, Hansen et al., 1985; Wigley and Schlesinger,



1985; Wigley et al., 1986), then the climate record of the last 100 years is consistent with any ATjx



between 0 and 6°C (Wigley, personal communication).








    Due to the various problems with direct  empirical  approaches, mathematical  models of  the



climate  system are the primary tool for  estimating climate  sensitivity.  While  they have  inherent



errors, they can isolate the greenhouse forcing, and many theoretical calculations can be made to test



the importance of various assumptions  and various proposed feedback mechanisms.  The simplest



climate model is the zero-dimensional global average model described in the box below. Models that



are one-dimensional in the vertical,  often called "radiative-convective" models, and that are one-



dimensional in the horizontal, often  called "energy-balance" models, are very useful for quickly and



inexpensively testing various components  of the climate  system.  In order to calculate the location



of future climate change, however, and in order to incorporate ah1 the important physical interactions,



especially with atmospheric circulation, fully three-dimensional general circulation models (GCMs) are



necessary.  These sophisticated models solve  simultaneous equations for the conservation of energy,



momentum, mass, and the equation  of state on grids with horizontal resolution ranging from 3 to 8



degrees of latitude by 3 to 10 degrees of longitude and with varying vertical resolution.  The radiation



schemes attempt to account  for the radiatively significant gases, aerosols and clouds.  They generally



use different schemes for computing cloud height, cover and optical properties.  The models also



differ in their treatment of ground hydrology, sea  ice, surface  albedo, and diurnal and seasonal cycles



(Schlesinger and  Mitchell, 1988).  Perhaps the most important differences  lie in the  treatment of



oceans, ranging from prescribed  sea surface temperatures,  to "swamp" oceans with mixed layer



thermal capacity but no heat transport,  to mixed  layers with specified heat transport, to full oceanic



GCMs.
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Policy Options for Stabilizing Global Climate ~ Review Draft                        Chapter HI








    A series of reviews by the National Academy of Sciences (NAS, 1979, 1983, 1987) as well as




the "State-of-the-Art" report  of the Department of Energy (MacCracken and  Luther, 1985)  have




concluded that the equilibrium sensitivity  of climate to a 2xCO2  forcing (ATjx) is probably in the




range of 1.5 to 4.5°C.  An independent review by Dickinson (1986) attempts to quantitatively combine




the uncertainties indicated by the range of recent GCM results and concludes that the range should



be broadened  to  1.5-5.5°C.  The GCM result of Wilson and Mitchell (1987) giving AT^ = 5.2°C




was published  after all of the reviews cited here.  Dickinson's estimates of the  contributions of the




individual factors to climate sensitivity are shown in Figure 3-6. The largest positive feedback is  from



changes in  the amount and distribution of water vapor.  Substantial  positive feedback may also be




contributed by changes in sea ice  and surface albedo and clouds, although the uncertainty range




includes the possibility that clouds  contribute significant negative feedback.  The differences in the




strength of these feedbacks between models is the result of different parameterizations of the relevant




processes as well as differences in the control (lxCO2) simulation (Cess and Potter, 1988).  Even




though the  exact value of AT^ is not known, we can study the potential impact  of climatic warming




caused by greenhouse gases by choosing scenarios  that span the range of theoretical  calculations.




Thus, we adopt 2-4°C as a putative one standard deviation (1(7) confidence interval about the center



of the range proposed by  the National Academy of Sciences,  and the range  proposed by Dickinson




(1.5  to  5.5°C) as 20 bounds for  subsequent  modeling  (Chapter V).  When  the  biogeochemical



feedbacks discussed  above are also considered, a  &TK as great as 8-10°C cannot be  ruled out



(Lashof, 1989).








THE RATE OF CLIMATIC CHANGE








    The Earth's surface does not immediately come  to  an  equilibrium  following  an increase in




radiative forcing.  Excess radiation  captured by the Earth heats the land surface, the ocean, and the




atmosphere. The effective heat capacity of the oceanic part of the climate system, in particular, is
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter HI








enormous.  The result is that the warming realized in any given year may be substantially less than



the warming that would occur  in equilibrium if greenhouse gas concentrations were  fixed at their



levels in that year. Hundreds of years would be required for the entire ocean to equilibrate with the



atmosphere, but only the surface layer (about 100 m) is well mixed by winds and therefore  tightly



linked to climate in the short term.  The heat capacity  of the surface layer  is about l/40th  that of



the entire ocean and  this layer by itself would equilibrate with a response time  (the time required



to reach 1 - 1/e, or 63%, of  the equilibrium response) of 2-15 years, depending on the climate



sensitivity and assumed mixed layer depth.  The equilibration tune is longer if the climate sensitivity



is  greater because the feedback processes that increase climate sensitivity respond to the realized



changes in  climate, not to the initial change in forcing (Hansen et al., 1985). When the transfer of



heat from  the mixed layer into the  deep ocean is considered, it is impossible to characterize the



oceanic response with a single  time constant (Harvey and Schneider, 1985; Wigley and Schlesinger,



1985).








    While  the main  features of ocean circulation  and mixing,  and  therefore the rate of  heat and



carbon uptake, have  been identified, they are not well defined  or modeled on a global scale.  The



theory  and modeling of ocean  circulation are currently limited  by  the  inadequacy of the database



(Woods, 1985).  The development of Ocean General Circulation Models (OGCMs) lags significantly



behind their atmospheric counterparts, mainly because it  is difficult and expensive to obtain the



necessary data with sufficient temporal and spatial coverage, because fewer scientists have addressed



this problem, and because a large amount of computer power is needed to resolve the necessary time



and space scales. Due to these  problems it may be a decade or more before OGCMs reach the state



of development achieved by current atmospheric GCMs.








    Lacking well-tested OGCMs, the main tools used so far to investigate ocean heat uptake have



been highly parameterized  models, very  similar to those used for carbon (see Chapter II).   These
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Policy Options for Stabilizing Global Climate -- Review Draft                       Chapter HI








models are calibrated with data on the penetration of tracers such as tritium and 14C produced by



atmospheric nuclear weapons tests during the 1950s and early '60s and/or with  the steady-state




profiles  of various ocean parameters, such as natural WC and temperature.  The simplest models




that yield a plausible time-dependence for heat (and carbon) uptake lump the entire ocean into two



compartments:   A  well-mixed surface layer  and a deep ocean compartment in which  mixing is




parameterized as a  diffusive process (Box-Diffusion or BD model).  This approach was introduced




by Oeschger et al. (1975) for modeling carbon uptake, and has been applied to ocean heat absorption




by Hansen et al. (1985) and Wigley and Schlesinger (1985), among others.  A more elaborate version




of this model which  includes a representation of upwelling implicitly balanced by high-latitude bottom-



water formation (UpweUing-Diffusion or UD model), has  been used by Hoffert et al. (1980), Harvey




and Schneider (1985), and Wigley and Raper  (1987).  The addition of an upwelling term allows the




observed mean thermal structure of the ocean to be  approximated (Hoffert et al., 1980),  but given




the highly parameterized nature of both of these models,  there is no convincing reason to  favor one




approach over the other for modeling small perturbations to heat flows.
    The  response  tune, T, of Box-Diffusion models  is proportional  to  ^(ATjJ2,  where K  is the




diffusion constant  used to  characterize deep  ocean  mixing  (Hansen et al., 1985; Wigley  and




Schlesinger, 1985).  Data on the penetration of tracers into the ocean suggests that K = 1-2 cm2/s



(Hansen et al., 1985).  Hoffert  and Hannery (1985)  have argued that mixing rates derived from



tracers may be too high for heat because mixing rates are highest along constant density surfaces,



which are nearly parallel to ocean isotherms. On the other hand, in a preliminary coupled GCM-



OGCM run, Bryan and Manabe (1985) found  that heat  was  taken up more rapidly than with a



passive tracer because of reduced upward heat convection.  Using a range of 0.5-2 cm2/s for K and




the la range for AT& given above (2-4°C) in the equation derived by Wigley and Schlesinger (with
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Policy Options for Stabilizing Global Climate -• Review Draft                        Chapter HI



their recommended values for other  parameters)  yields 7  = 6-95 years.2   Correspondingly, the

warming expected by now, based  on  past  increases in greenhouse gases and assuming no other

climate forcings, is roughly 40-80% of the equilibrium warming (Wigley and Schlesinger, 1985).  In

other words, even if greenhouse gas concentrations could be fixed at today's level, the Earth would

still be  subject to significant climatic change that has yet to  materialize.  The large uncertainty

surrounding ocean heat uptake, combined with uncertainty about potential climate forcings other than

those from greenhouse gases, also implies that it is not possible to obtain a useful constraint on AT^

from the observed temperature record as discussed above (see also Hansen et al, 1985; Wigley and

Schlesinger, 1985).



    Experiments with Upwelling-Diffusion models demonstrate the importance of the bottom water

formation process for the rate of ocean heat uptake.  The  impact  of using an Upwelling-Diffusion

ocean model  rather than  a  Box-Diffusion  ocean  model is that  the heat that diffuses into the

thermocline is pushed back toward the mixed layer, which decreases the effective heat capacity of the

ocean and the time constant for tropospheric temperature adjustment, assuming that the upwelling rate

and the temperature  at which bottom water is formed do not change.  If the initial temperature of the

downwelling water is assumed  to warm as much as the  mixed layer,  however, then a UD  model

actually takes up more heat in the ocean than a BD model,  leading  to a  larger disequilibrium

between  a given  radiative  forcing  scenario and  the  expected realized warming.  While there are

reasons to think that the temperature of Antarctic Bottom Water will not increase as climate changes,

the temperature of  North Atlantic Deep Water could increase or decrease (Harvey  and Schneider,

1985).   Furthermore, there is no reason to assume that the rate of  bottom-water formation will

remain constant as climate changes.  The tropospheric temperature could even  overshoot equilibrium
     2  It is important to note that the actual response does not correspond to exponential decay with
a single  time  constant, so  that while T gives tie time required for  one e-folding and is a useful
measure, it would not apply to subsequent e-foldings (the time constant would be substantially longer)
and must be interpreted with care.
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if the average bottom-water temperature cools as the surface temperature warms or if the upwelling



rate  increases with warming (Harvey and Schneider, 1985).  One must also recognize the potential




for sudden reorganizations  of the ocean-atmosphere circulation  system as suggested by Broecker




(1987), which could lead to discontinuous, and perhaps unpredictable, changes in climate that cannot




be included in the models used in this report.








    Another  major limitation of the BD and UD models generally used to  analyze the climate




transient problem is that they have limited or no  spatial resolution (at best hemispheric, land-sea)




and  thus cannot consider spatial  heterogeneity in  either the magnitude or rate of climatic change.




Work at the Goddard Institute for Space Studies (Hansen et al., 1988) has  produced one of the few




three-dimensional time-dependent analyses of climatic change that have been published to  date.  This




study employed  three  simple,  but reasonably  realistic,  scenarios  of  future  greenhouse  gas




concentrations and volcanic  eruptions.  The results suggest that the areas where warming is initially




most prominent relative  to  interannual  variability  are  not necessarily those where  the equilibrium




warming is greatest.   For example, low-latitude ocean regions warm quickly  because  ocean heat




uptake is limited by strong stratification in these regions.  Warming is also prominent in high-latitude



ocean areas where a large equilibrium warming is expected  due to increased thermal  inertia as sea




ice melts.  Global  average  temperatures are used in this report as an indicator of the rate and




magnitude  of global  change but, as these  results emphasize, it must be recognized  that major



variations among regions are a certainty.








CONCLUSION








    The changing composition of  the atmosphere will in turn drive significant changes in the Earth's




climate.  These  changes  may have already begun, but because of the uncertainties in temperature




data sets and the complexity of the interaction between climate sensitivity and the transient response,
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definitive predictions are subject to a good deal of controversy at this time.  Whether next year is



warmer or cooler than this year, however, has  no direct bearing on how the greenhouse effect should



be viewed.  Internal fluctuations or countervailing forcings may temporarily mask the warming due



to increasing concentrations of greenhouse gases or make the  climate warmer than expected solely



from greenhouse warming.  Therefore, to derive our estimates  of the magnitude and rate of change



that can be expected during the next century we must  continue to rely on model  calculations, which



indicate that by early in the next century the Earth could be warmer than at any time during the last



million years or more, and that the rate of change could be unprecedented in Earth history.
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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter III
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                                      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
       Industrialized Countries  	  IV-10
       Developing Countries	  IV-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
       Fuel Production and Conversion  	  IV-25
    Future Trends	  IV-27
       The Fossil-Fuel Supply	  IV-29
       Future Energy Demand  	  IV-29

INDUSTRIAL PROCESSES	  IV-31
    Chlorofluorocarbons, Halons, and Chlorocarbons 	  IV-33
       Historical Development and Uses	  IV-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
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter IV








FINDINGS








    Various human activities affect the Earth's climate by altering the level of trace gases in the




atmosphere.   These  activities include energy consumption, particularly  fossil-fuel consumption;



industrial  processes; land use change,  particularly deforestation; and agricultural practices  such  as




waste burning, fertilizer usage, rice production, and animal husbandry. Economic development and




population growth are key factors  affecting the level of each  activity.








•   Population levels  and growth  rates have  increased tremendously over the last 200 years.




    Between 1650 and 1980,  the global population doubling time shrunk from  200  to 35 years.



    At the beginning of this century, global population was about 1.6 billion; in 1987, it  reached




    5 billion.  By the  early part of the next century total population is likely to reach 8 billion.




    The rate of population increase is  most acute in the developing regions, particularly Africa



    and Asia where annual rates of growth  exceed 2%.








•   Fossil fuel combustion emits carbon dioxide and other radiatively important gases and is the




    primary cause of atmospheric warming. Energy consumption currently accounts for more than



    five of the six to eight billion tons of carbon dioxide  emitted  to the  atmosphere annually



    from anthropogenic sources. Between 1950 and 1986, annual global fossil fuel consumption



    grew 3.6-fold and annual carbon dioxide emissions grew 3.4-fold.








•   Emissions  of other  trace gases  due  to fossil  fuel consumption are more uncertain.




    Approximately 0  to  2 million tons nitrogen  as  nitrous oxide,  20 million tons nitrogen as



    nitrogen oxides, and 180 million tons carbon as carbon monoxide are emitted annually from




    fossil  fuel combustion. Leaking and venting of natural gas contributes approximately 20 to
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    50  million  tons  methane annually to  the atmosphere,  and  coal mining contributes



    approximately 25 to 45 million tons methane.








•   Three significant  non-energy sources of greenhouse gases are  associated with  industrial




    activity.  Production and use of chlorofluorocarbons (CFCs), halons, and chlorocarbons; waste




    disposal in landfills; and cement manufacture. Production of CFC-11 and CFC-12 grew 4.7-




    fold between 1960 and 1985.  Consumption of major CFCs and halons reached nearly one




    million tons in 1985.   An  international  agreement (the  Montreal Protocol), however, came




    into force on January 1,  1989  to  reduce future production of certain CFCs  and halons.




    Anaerobic  decay  of  organic wastes in landfills currently contributes  approximately 30-70




    million  tons  of methane  to  the atmosphere annually.   Cement production, which has




    increased sevenfold since the 1950s, contributed approximately 134 million tons carbon as CO2




    to the atmosphere in 1985.








•   Land use change has resulted in  substantial emissions of greenhouse gases to the atmosphere.




    Since 1850, approximately 15% of the world's forests have been converted to agricultural and




    other land uses. Currently, deforestation contributes between one-tenth and one-third of the



    total anthropogenic carbon dioxide emissions to the atmosphere, i.e., between 0.4 to 2.6




    billion tons of carbon. Between  one-quarter and one-half of the world's swamps and marshes



    also have been destroyed by man.  Wetlands currently contribute  approximately one-fifth  of



    the  total  methane emissions to  the  atmosphere; continued changes to wetlands could



    significantly alter the global methane budget. Biomass  burning, in addition to contributing




    to the atmospheric concentrations of carbon dioxide, contributes approximately 10  to 20%




    of total  annual methane emissions, 5 to 15% of the nitrous oxide emissions, 10 to  35%  of




    the  nitrogen oxide emissions, and 20 to 40% of the carbon monoxide emissions.
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•   Three agricultural activities directly result in major contributions to  atmospheric emissions



    of  greenhouse gases:  animal  husbandry,  rice cultivation, and nitrogenous  fertilizer  use.



    Domestic animals, which produce methane as a by-product of enteric fermentation, currently



    contribute approximately 65 to 85 million tons of methane annually.  Over the past several



    decades, domestic animal populations have grown by up to 2%  annually.  Methane is also



    produced by anaerobic decomposition in rice paddies.  Currently, about one-fifth of annual



    methane emissions,  or between 60 and 170 million tons, comes from rice  cultivation.  Rice



    production has grown rapidly since the mid-1900s due to bcreases in crop acreage, double



    cropping,   and higher yields.  Between 1950 and 1984 rice  production  increased nearly



    threefold,  and harvested area grew by about 70%.  Use of nitrogenous fertilizers results in



    nitrous oxide  emissions, either directly from the soil, or indirectly from groundwater.  Global



    use of organic and inorganic fertilizers has risen markedly, and nitrogen-based fertilizers



    increased their market share  of total inorganic fertilizer consumption from 28% in  1950 to



    64% in 1981.  Nitrogenous fertilizer use may contribute between 0.14 and 2.4 million  tons



    nitrogen as nitrous oxide per year to the atmosphere.








•   In  addition  to  the  human activities  that  directly affect  trace gas  emissions,  future



    concentrations of greenhouse gases will be influenced by feedback processes resulting from



    humans living in a world that has undergone climatic change.   Two potential feedbacks of



    increased  temperatures, which  may  counteract each other to  some  extent,  are increased



    energy demand for air conditioning in the summer, and decreased energy demand for heating



    in the winter.
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INTRODUCTION








    As  discussed in Chapter III, the Earth's climate has been in a  constant state of change



throughout geologic time due to natural perturbations in the global geobiosphere.  However, various



human activities  have the potential to cause future global warming over a relatively short amount of



time.  These activities, which affect the Earth's climate by altering the concentrations of trace gases



in the  atmosphere,  include energy  consumption,  particularly fossil-fuel  consumption;  industrial



processes (production and use of chlorofluorocarbons, halons, and chlorocarbons, landfilling of wastes,



and cement manufacture);  changes  in land  use patterns, particularly  deforestation  and biomass



burning; and agricultural practices (waste burning, fertilizer  usage,  rice production, and animal



husbandry). Population growth is an important underlying factor affecting the level of growth in each



activity.








    This chapter describes how the human activities listed above contribute to atmospheric change,



the current pattern of each activity, and how levels of each activity have changed since the early part



of this century.  Figure 4-1  illustrates the current contributions to the  greenhouse  gas buildup by



region.  Almost 50% of the warming is attributable to activities in the United States, the USSR, and



the European Economic  Community.  As background  to the discussion of trace-gas  producing



activities, we first provide an overview of population trends. This historical perspective is meant to



serve as a framework for the discussion of possible future scenarios of trace-gas emissions in Chapter



V.








HISTORICAL OVERVIEW  OF POPULATION TRENDS








    One of the major factors affecting trends in greenhouse gas emissions is the increase in human



population.  As  population  levels  rise, increasing pressures are placed  on the  environment as the



larger population strives to feed  and clothe itself  and achieve a higher standard of living.  Without









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Policy Options for Stabilizing Global Climate - Review Draft
                                Chapter IV
                                  FIGURE 4-1
     REGIONAL CONTRIBUTION TO GREENHOUSE WARMING

                                   1980s

                                   (Percent)
   Rest of the World (36%)
                                                           United States (21%)
                                                                  USSR(14%)
                   China (7%)
                                                 EEC(14%)
Figure 4-1.  Estimated regional contribution to greenhouse  wanning for the 1980s, based upon
regional shares of current levels of human activities that contribute to greenhouse gas emissions.
(Sources:  U.S. EPA, 1988a; United Nations, 1987; U.S. BOM, 1985; IRRI, 1986; FAO, 1986a, 1987;
Bolle et al., 1986; Rotty, 1987; Lerner et al., 1988; Seiler, 1984; WMO, 1985; Hansen et al., 1988;
Houghton et al., 1987;  Matthews and Fung, 1987.)
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changes in the methods used to meet people's  needs, higher population levels invariably lead to




increased  emissions of greenhouse gases.








Global Population Trends








    Not only has global population grown rapidly over the past few centuries, but the rate of growth




has also increased (see Figure 4-2).  World population hi the year 1 A.D.,  approximately 0.25 billion,




doubled by 1650 (Wagner,  1971).  By 1850 (i.e., 200 years later), global population had roughly




doubled again to 1.1  billion.  The global population doubling time has continued to decline — 80



years later, in 1930, world population was 2 billion.  By 1975 global population had reached 4 billion,




and  according  to some  estimates the  population will double once  again within 35 years  (world




population reached 5  billion  in  1987).  Moreover, despite recent declines  in  the world's  annual



population growth rate (IIED and WRI,  1987),  world population is  expected to  continue to grow




rapidly.  Several studies estimate  that world population will exceed 8 billion by 2025 (Zachariah and




Vu, 1988;  U.S. Bureau of the Census, 1987). Such rapid population growth can be expected to result




in increasing pressure  on the  global environment, particularly as the  burgeoning human population




strives to  improve its  living  standards through economic growth.








Population Trends by  Region








    The rapid population growth in recent decades has not occurred uniformly around the world (see



Figure 4-2).  Between 1950 and 1985, population in developed countries increased by 41%, compared



to 117% in developing countries (IIED and WRI,  1987). Recent trends indicate these differences will




continue:  Annual growth rates in the developed countries are generally less than 1%,  while many




developing countries continue to experience rates  of growth  between 2  and 3% (see  Table 4-1).




These higher growth rates in the 20th century in developing countries have been due primarily to the



combined  effects of declining death rates and  continued high birth rates.









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Policy Options for Stabilizing Global Climate - Review Draft
                                 Chapter IV
                                   FIGURE 4-2
                REGIONAL POPULATION GROWTH

                                  1750-1985
                                      (Billions)
    z
    o
    CD
                                                                  North America
                                                                    & Oceania

                                                                  Latin America

                                                                  Africa
                                                                  Europe & USSR
                                                                  Asia
         1750
                         1985
Figure 4-2. Since about 1850, global population has grown at increasingly rapid rates. In 1850, the
population doubling time was approximately 200 years; by 1975, the doubling time had declined to
approximately 45 years. Most of the growth has occurred in the developing world, particularly Asia.
(Sources:  Matras, 1973; Hoffman, 1987.)
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                                            Chapter IV
                                         TABLE 4-1

                              Regional Demographic Indicators




Region
North America
Europe
East Asia
Oceania
Caribbean
Southeastern Asia
Latin America
Southern Asia
Western Asia
Africa
•

Total
Fertility4
1980-85
1.83
1.88
2.34
2.65
3.34
4.11
4.17
4.72
5.22
6.34


Infant
Mortality"
1980-85
11
15
36
31
65
73
61
115
81
112
Annual
Population
Growth Rate
1980-85
(percent)
0.90
0.30
1.22
1.51
1.53
2.05
2.34
2.14
2.79 .
2.92
        World Average
3.52
60
1.67
        a The total fertility rate is the average number of children that a woman bears in a
         lifetime.
         The infant mortality rate is the average number of infant deaths (deaths before the first
         birthday) per 1,000 live births.
        Source:  Adapted from IIED and WRI, 1987.
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Industrialized Countries








    Population growth rates in the industrialized  countries are substantially lower compared with




growth rates in the developing world.  For example, while most developing countries contend with




growth rates that will double their populations within  20-40 years,  current growth rates in North




America and Europe will lead to a doubling within about 100 years and 250 years, respectively (IIED




and WRI, 1987). This trend toward lower growth rates  is due to many complex economic and social




factors, including the  changing role of women in the labor force, the higher economic costs of child




rearing, and the reduced need for children as a labor pool.








Developing Countries








    The  highest rates of population growth are in the developing  countries:  From  1950 to 1985



developing countries increased their share of the world's population from 66.8% to 75.6% (IIED and




WRI,  1987).  During  this time Asia's population grew from 1.3 to 2.7 billion, Africa's from  224  to



555 million, and Latin America from 165 to 405 million.  Key trends are  summarized below.








    Africa.  Africa currently has the highest fertility rates and population growth rates in the world.



Its growth rate has increased recently:  Between 1955 and 1985, Africa's average annual growth rate



increased from 2.3% to 2.9%. The total fertility rate (i.e., average  number of children that a woman



bears in  a lifetime) is  six or higher in 38 African countries, most of which have experienced declining




infant mortality rates  (infant deaths per thousand live births) over the past 20  years (IIED and WRI,




1987). For example,  in Kenya, where the total  fertility rate is 7.8,  the infant mortality rate fell from




112 to 91 between 1965 and 1985. Between 1965 and 1985, the  crude birth rate (births per thousand



population) for Kenya grew by 4.7%, while the crude death rate fell  by 37.7%.  The average  annual




growth rate reached 4.1% in the 1980s  (World Bank, 1987).  The United Nations expects the African
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population to continue to  grow rapidly, with the average annual growth rate increasing to 3% in




1990 (United Nations, 1986).








    Asia..   From 1850  to  1950, Asia experienced the largest increase in population in  the world




(Ehrlich and Ehrlich, 1972).  Rates of growth have continued at high levels ~ annual growth rates




since 1960 have exceeded 2%.  These rates are likely to remain high in  several Asian countries in



future years (United Nations, 1986).  For example, China currently is the most populous  country in




the world, with 22% of the world's total (Ignatius, 1988).  Although its strong population policy of




one  child  per family helped  to halve the 2% annual growth rates of the 1960s, growth rates have



recently turned upward, approaching 1.5% annually.   This trend of growth could lead to population




levels in China in excess of 1.7 billion by 2025.








     India's population has also been rapidly expanding.  It is the second most populous  country hi




the world (United Nations, 1986), with 765 million people as of  1985.  India's rate of growth has




been relatively high this century,  although it has declined in recent years; in 1960 its annual rate of




growth was 2.3%, but has since dropped to 1.7% (IIED and WRI, 1987). Despite this recent decline,




its population is  expected  to grow for many years; e.g., the United Nations estimates that India's



population will be over 1.2 billion by 2025 (United Nations, 1986).








    Latin  America.  Latin  America currently has one of the highest population growth rates hi the



world: From 1980 to 1985 the annual rate of growth  averaged 2.3% for the region (IIED and WRI,



1987), although these rates of growth varied substantially between countries.  Argentina, Chile, and



Uruguay have the lowest growth within Latin America, while countries such as Bolivia,  Ecuador, El




Salvador, Guatemala, Honduras, Nicaragua, Paraguay, and Venezuela have annual population growth




rates that exceed  2.5%.   Fertility  rates have  been  declining  throughout the  region  due to




industrialization, urbanization, rising incomes, and official population policies, although one source
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estimates that Latin America's share of world population will nonetheless increase from 8.4 to 9.5%

between 1985 and 2025 (IIED and WRI, 1987).  The two population projection sources used in this

report (U.S. Bureau of the Census, 1987, and Zachariah and Vu, 1988; see Chapter V) project that

by 2025, Latin America's share of world population will grow to 9.1  and 8.7%, respectively.



ENERGY CONSUMPTION



    The major human activity affecting trace-gas emissions is the consumption of energy, particularly

energy from  carbon-based fossil  fuels.  As discussed in Chapter  II, global carbon dioxide (COj)

emissions from anthropogenic sources currently range from 6  to 8  petagrams (Pg) of carbon (C)

annually, with commercial energy consumption accounting for approximately 65-85% of this total.1

Non-commercial (biomass) energy consumption accounts for approximately 7%. Energy consumption

and  production also  produce  substantial amounts of other  greenhouse gases,  including carbon

monoxide (CO), methane (CH4),  nitrogen oxides (NOX, or NO and NOj), and  nitrous oxide (N2O).2



    This  section explores the role of energy consumption in climate change.   We  first discuss the

world's increasing reliance on fossil fuels, the roles that fossil-fuel production (e.g., coal mining and

oil drilling) and fossil-fuel combustion play in the emission of trace gases to the atmosphere, and the

implications of the continuation of current energy consumption patterns on future global warming.
     1 Anthropogenic sources of trace gases are those resulting from human activities, e.g.,
combustion of fossil fuels.  These sources are distinguished from natural sources, since emissions
from anthropogenic sources result in unbalanced trace-gas budgets and accumulation of gases in
the atmosphere.

     1 Throughout the report these gases are often referred to as greenhouse gases, although
strictly speaking, CO and NO, are not greenhouse gases since they do not directly affect radiative
forcing (see Chapter II). These two gases indirectly affect global wanning due to their chemical
interactions with other gases in the troposphere.  As a result,  for simplicity, we shall refer to
them as greenhouse gases.
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History of Fossil-Fuel Use



    Prior to the discovery and development of fossil fuels (coal, oil, and natural gas), people relied

on readily-available energy resources such as wood and other forms of biomass (i.e., living matter),

as well  as water and wind,  to satisfy their basic energy  needs.  Since the beginning of the 19th

century, fossil fuels have played an increasingly important role in the world economy, particularly for

developed countries, by providing the energy  required for industrial development, residential and

commercial heating, cooling, and lighting, and transportation services.  Fossil fuels now provide about

85% of the world's total energy requirements.   This  dependence  on fossil  fuels is  greatest  in

industrialized countries, where over 95% of all energy needs are provided by fossil fuels, compared

with about 55%  in developing countries (Hall et al., 1982) .3



    Global consumption of  fossil  fuels has  increased  rapidly  over the past  century as  human

populations and their economic activities have grown, resulting in the development  of additional

fossil-fuel resources. Since 1950, global primary energy consumption has  increased nearly fourfold

(Figure 4-3), with energy consumption per capita approximately doubling.  In 1985, 42%  of global

energy demand was supplied by liquid fossil fuels (primarily petroleum); solid fuels (coal) supplied

31%, natural gas, 22%,  and other fuels combined accounted for 5%  of the market share.4  These

relative proportions have  changed  considerably since  1950, when  coal  supplied  59% of  total

commercial energy requirements, liquids, 30%, natural gas, 9%, and other fuels, 2%.



    The increase hi fossil fuel consumption over the last  century has caused a substantial increase

in the amount of CO2 emitted to the atmosphere.  Carbon dioxide emissions from fossil fuels grew
    3 In some developing countries, the dependence on biomass can approach 95 percent of total
energy requirements.

    4 Non-commercial biomass estimates are not included in these figures.



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                                                            Chapter IV
                                 FIGURE 4-3
               GLOBAL ENERGY DEMAND BY TYPE *
                               1950 - 1985
                                  (Exajoules)
       300
       250  -
       200  -
    V)
    Ul
    _1
    o
    <
    X
    OJ
150  -
        100  -
        50
                                                               Other
                                                                Natural Gas
                                                               Liquid Fuels
                                                                Solid Fuels
          1950    1955    1960   1965   1970   1975   1980   1985
                                   YEAR
     * Data is for commercial energy only; biomass Is not included
Figure 4-3.  Global demand for fossil fuels has more than tripled since 1950. Today, about 85% of
the world's energy needs are met by fossil fuels. (Sources:  United Nations, 1976, 1982, 1983, 1987.)
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Policy Options for Stabilizing Global Climate ~ Review Draft                        Chapter IV



from less than 0.1 Pg C annually in the mid-nineteenth century, to about 5.4 Pg C in 1986 (see

Figure 4-4).5  This rate of increase is about 3.6% per year and is the major reason why atmospheric

CO2 concentrations increased from about 290 ppm in 1860 to about 348 ppm as of 1987 (Farman et

al, 1985).  Currently fossil fuel combustion also contributes  approximately 0-2 Tg N as  N2O, 20 Tg

N as NOX and 180 Tg C as CO annually to the atmosphere.



    In recent decades there has also been a significant shift  hi global energy use patterns.  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%, and developing countries, 6% (United Nations, 1976,  1983).6  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 shares

to 32% and 15%, respectively (see Figure 4-5).  Between 1950 and 1985,  commercial energy use per

capita in  the OECD grew from 93 to 189 gigajoules per capita (GJ/cap) (103%), in centrally-planned

economies from  16 to 59  GJ/cap (269%), and in  the developing countries from 3 to 18 GJ/cap

(500%).7   The proportion of energy consumed by the  OECD is expected to decline further as the

developing world continues to experience population growth and economic  development and, thus,

significantly expands their energy requirements  (Chapter V).
    5 In 1986 CO2 emissions from fossil fuels were approximately 5370 million metric tons C, or
5.37 Pg C.  1 billion metric tons = 1 gigaton  = 1 Pg = 1015 grams.

    6 The OECD countries include the U.S., Canada, Japan, Australia, New Zealand, the United
Kingdom, France, Spain, Portugal, the German Federal Republic, Belgium, the Netherlands,
Sweden, Norway, Finland, Italy, Ireland, Iceland, Denmark, Austria and Switzerland.

    7 1 GJ = 1 gigajoule =  109 joules.  1055 joules = 1 Btu.
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Policy Options for Stabilizing Global Climate ~ Review Draft
                                Chapter IV
                                  FIGURE 4-4
      C02 EMISSIONS DUE TO FOSSIL FUEL CONSUMPTION

                                 1860-1985
                                 (Petagrams Carbon)

        6
   o
   GO
   
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Policy Options for Stabilizing Global Climate -- Review Draft
                                    Chapter IV
                                  FIGURE 4-5
      GLOBAL COMMERCIAL ENERGY DEMAND BY REGION


                                  (Exajoules)


        350
    CO
    111
    O
    -5
    
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter IV








Current Energy Use' Patterns and Greenhouse Gas Emissions








    The allocation of energy consumption among sectors varies considerably from one region to the



next. Figure 4-6 summarizes 1985 end-use energy demand (for both commercial and non-commercial,



or biomass, fuels) by sector for the OECD countries, the centrally-planned economies of Asia and



Europe  (including China and the USSR), and the developing countries.  Whereas the OECD  split



is approximately one-third industrial, one-third transportation, and one-third residential/commercial,



centrally-planned economies of Asia and Europe consume more than 50%  of  their energy in the



industrial sector.








    These energy  consumption patterns partly reflect the  basic differences in  the structure of



economic activity at the current stage of each region's economic development.  The centrally-planned



economies and the developing countries  devote a greater share of their energy requirements to the



industrial sector because they are at a stage of economic development where energy-intensive basic



industries  account  for a large share of total output, while infrastructure in  the transportation and



commercial sectors has not been extensively developed.  In the  OECD, transportation consumes a



larger share of total energy compared with other regions, primarily because of the large number of



automobiles in the OECD.  For example, in the U.S. there are 550 cars and light trucks/1000 people,



compared with 60 cars and light trucks/1000 people in the USSR, and 6  cars and light trucks/1000



people in China.   Also, biomass  is very important to the residential energy requirements of the



developing economies compared with  those of industrialized countries; the  industrial sector is the



major consumer of fossil fuels in most developing countries.
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Policy Options for Stabilizing Global Climate - Review Draft
                                        Chapter IV
                                   FIGURE 4-6
           1985 SECTORAL ENERGY DEMAND BY REGION
                         COMMERCIAL AND NON-COMMERCIAL FUELS
                                       (Exajoules)
  42.6,
                    33.4
                               29.3
                   39.7
                                                           19.0
                                            27.0
        OECD
                 8.4

CENTRALLY PLANNED
                                    Residential/Commercial

                                    Industrial

                                    Transportation
10.0
                                                                DEVELOPING
Figure 4-6. End-use energy demand by sector for three global regions. While energy demand in the
OECD  countries is split almost equally between the three sectors, over 50% of the energy b the
centrally planned countries is consumed by the industrial sector, and almost 50% of the energy in the
developing countries is consumed by the residential/commercial sector.  (Sources:  Sathaye et al.,
1988; Mintzer,  1988.)
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter IV








Emissions by Sector








    The differences among regions in terms of the share of energy consumed by each sector and the



types  of applications for which the energy within each sector is used can have a major impact on the



amount and types of greenhouse gases emitted. This section discusses how emissions of greenhouse



gases  vary as a result of differences in type of fossil energy consumed and combustion technology



used.








    Electric Utility Sector.  Energy is increasingly desired in the form of electricity.  The amount  of



greenhouse gases produced from electricity generation is a function of the type of primary energy



used to produce the electricity and the production technology.  For example, nuclear, hydroelectric,



or solar  primary energy sources emit little  or no greenhouse  gases, while  fossil fuels  generate



substantial quantities of CO2,  as well as other gases (see Table 4-2).  The amount of greenhouse gas



emissions varies according to the type of fossil fuel  used because of inherent differences in the



chemical structure of the fuels. Additionally, the level of emissions varies as a function of production



efficiency.  For example -








    •       Coal-fired power plants  produce  about two to three  times as much CO2 as natural



            gas-fired units per unit of electricity generated (330 kg CO2/GJ for  a pulverized coal



            wall-fired unit  compared with 120 kg CO2/GJ for a combined cycle gas-fired unit).



            Oil-fired units produce more CO2 than natural gas units produce, but less CO2 than



            coal-fired units produce.  Within fuel types the emission levels may vary.  For ex-



            ample, when natural gas is used as the fuel, combined cycle or ISTIG units  produce



            about 40% lower CO2 emissions  than simple cycle units (see Chapter VII)  because



            of the greater generating efficiency obtained through the use of these technologies.
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    Policy Options for Stabilizing Global Climate -- Review Draft
                                           Chapter IV
                                                  TABLE 4-2

                                    Emission Rate Differences by Sector
                                            (grams per gigajoule)'
Source
Electric Utility (g/GJ delivered
Gas Turbine Comb. Cycle
Gas Turbine Simp. Cycle
Residual Oil Boilers
Coal - F. Bed Comb. Cycle
Coal - PC Wall Fired
Coal - PC Cyclone
Coal - Integrated Gas
Efficiency
(%)
electricity)
42.0
26.4
32.4
35.0
31.3
313
27.3
C02

120,300
191,400
230,000
290,000
330,000
330,000
253,600
Industrial (g/GJ delivered steam for boilers; energy output for
Boilers
Coal-Fired
Residual Oil-Fired
Natural Gas-Fired
Kilns - Coal
Dryer - Natural Gas
Dryer - Oil
Dryer - Coal
Residential /Commercial (g/GJ
Wood Stoves
Coal Stoves
Distillate Oil Furnaces
Gas Heaters
Wood Boilers
Gas Boilers
Residual Oil Boilers
Coal Boilers

80
85
85
65-75
30-65
30-65
30-65
energy output)
50
50
75
70
67.5
80.9
84.9
75.9

130,000
88,000
57,000
300-350,000
75-170,000
100-240,000
155-340,000

[150,000]
198,000
111,000
101,000
[138,0001
61,800
86,000
135,000
CO

70
110
43
NA
42
42
222
others)

110
17
18
75
10
15
170

17,600
3,400
17
13
280
10.6
19
244
CH4

13
20
2.2
1.8
2.0
2.0
NA


2.9
3.3
1.5
1
1
1
1

70
NA
7
1
21
1.4
1.8
13
N2O

20
30
44
40
45
45
51


18
16
35
2
NA
NA
NA

NA
NA
NA
NA
6
2.7
14
16
NOX

400
640
590
690
1,400
2,600
760


390
180
71
500
52
160
215

190
170
65
61
47
53
183
295
Total
Carbon

32,850
52,060
62,750
79,090
90,020
90,020
69,260


35,510
24,010
15,550
81-95,490
20-46,370
27-65,460
42-92,800

48,500
55,460
30,290
27,550
37,770
16,860
23,460
36,930
Transportation (g/GJ energy input)
Rail
Jet Aircraft
Ships
Light Duty Gasoline Vehicle
Light Duty Diesel Vehicle
Light Duty Compressed
N. Gas Vehicle
NA
NA
NA
NA
NA
NA

69,900
72,800
70,000
54,900
73,750
50,200

570
120
320
10,400
340
4

13
2
20
36
2
120

NA
NA
NA
0.5
20
7

1,640
290
830
400
300
140

19,320
19,910
19,240
19,460
20,260
13,780

a  All emission rates, except for the total carbon estimates in the last column, are based on total molecular weight.
   Total carbon estimates refer only to the total amount of carbon emitted.

NA - Not Available
[ ] = No Net CO2 if based on sustainable yield

Source:  Radian, 1988; except N2O data, which is based on unpublished EPA data.  N2O emission coefficients are highly
uncertain and currently undergoing further testing and review.
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter IV



            Similarly, coal-fired fluidized bed units produce less NOX emissions than do coal-

            fired cyclone units because  the  higher operating temperatures typical of cyclone-

            units are more conducive to NOX formation.



    Industrial Sector.  The industrial sector includes mining, construction, and manufacturing, which

are some of the most energy-intensive economic activities.  Energy consumption in this sector can

be subdivided into four categories:



    •       Boilers — Boilers produce steam for many different purposes, including mach-

            ine drive, on-site  electricity production, high-pressure cleaning, and process

            requirements.  Virtually any  fuel  can be consumed to produce steam (e.g., fossil

            fuels, biomass, hazardous wastes, by-product wastes, etc.).  In the U.S., boilers

            consume about 30%  of all industrial energy.



    •       Process Heat — Many industrial processes that do not use steam require the use

            of some form of heat during production.  Examples of process heat applications

            include  ovens, furnaces, dryers, melters, and kilns. The degree of flexibility in

            fuel choice a consumer may have depends on  the process heat application —

            some applications may use technologies or production  processes that require a

            particular fuel.8  Process heat applications consume about 40% of the energy in

            the U.S. industrial sector.
     8 For example, some food production processes use natural gas because its relatively clean-
burning characteristic allows it to be used when product contamination may be an issue.
Similarly, melters in the glass industry are often designed to burn natural gas because of the
flame characteristics of this fuel. Use of other fuels would tend to produce an inferior product
and likely require the redesign of equipment.
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    •       Feedstocks - Fuels may be used as a raw material for the production process.



            Examples of such  applications include the  conversion of  metallurgical coal to




            coke for use in the manufacture of steel, natural gas for  fertilizer  production,



            and petroleum for asphalt.   It is  usually very difficult to  switch to alternative




            fuels with these  applications.  In  the  U.S., feedstocks consume about 15% of




            industrial energy.








    •       Other  - This category  consists  primarily  of  industrial activities  requiring




            electricity, e.g., lighting, motor drive, etc.  These  applications account for 15%




            of all energy consumed by U.S. industry.








    The amount of greenhouse gas  emissions generated from industrial energy  consumption is a




function of fuel type and the process in which it is consumed (see Table 4-2  for emissions from




selected industrial applications).








    Residential and  Commercial Sectors.  In the residential and  commercial sectors  the main end-



use applications for energy are heating,  cooling, cooking,  and lighting.  The form and amount of




energy  used  to meet  these  needs varies,  as  summarized  in  Table  4-3  for  the  U.S.  and




South/Southeast Asia. In developing countries, most of the energy in these two sectors is consumed



for cooking purposes, with consumers relying on  biomass or kerosene for fuel.  In industrialized



countries, however,  space heating and water heating consume the most  energy, which is supplied



primarily by fossil fuels  and, to some extent, electricity; gas and electricity are  the primary energy,




forms for cooking in industrialized countries.  Because  of the wide variety of end-use applications,




types of energy consumed, and conversion efficiencies in the residential and commercial sectors it is




difficult to  generalize about emission trends  in these  sectors; for  illustrative  purposes,  emission




coefficients  for several major applications in industrialized  countries  are listed in Table 4-2.
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    Policy Options for Stabilizing Global Climate - Review Draft
                                                      Chapter IV
                                           TABLE 4-3

                             End-Use Energy Consumption Patterns for
                                the Residential/Commercial Sectors

                                       (% of Total Energy)
  End-Use
                                           Type of Energy
Biomass
Fossil Fuels
Electricity
Total
South /Southeast Asia
Heating
Cooling
Cooking
Lighting
TOTAL
United States
Heating
Cooling
Cooking
Lighting
Other
TOTAL

0
0
75
o
75%

<1
0
0
0
-°-
<1%

16
0
3
1
20%

59
0
7
0
-Q-
66%

NA
NA
NA
NA
5%

8
6
3
7
IQ
34%

NA
NA
NA
NA
100%

67
6
10
7
^Q
100%
Sources:  Sathaye et al., 1988; Mintzer, 1988; U.S. DOE, 1987; Leon Schipper, pers. communication.
    DRAFT - DO NOT QUOTE OR CITE
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    Transportation Sector.  As consumers become wealthier, the absolute quantity and share  of



energy used  in  the  transportation sector  increases.   For example, as  discussed earlier, in  many




developing countries, such as China, the transportation sector consumes a much smaller portion  of




the country's  energy requirements than the portion consumed by this sector in industrialized countries,




such as the United States. Energy requirements in the transportation sector are typically met with




fossil fuels, particularly petroleum-based products such as gasoline,  diesel, or jet fuel. For example,



in 1985  countries belonging to the OECD met 91% of their transportation energy requirements with




oil-derived products, 8% with electricity, and the remaining 1% with natural gas and coal (OECD




1987).  As countries  become wealthier, increased use of petroleum to meet transportation needs can




significantly increase greenhouse gas emissions to the atmosphere (see Table 4-2).








    The amount and type of greenhouse gases emitted can  also be affected by the transportation




technology.  For example, gasoline vehicles produce about 25% less CO2 on an energy input basis




than do diesel vehicles, while  producing  substantially more  CO.   However, the CO is  eventually




oxidized to CO2, so  the CO2 emissions  attributable to gasoline vehicles are comparable to those  of




diesel vehicles.  Also, the efficiencies of diesel engines are generally greater than those of gasoline



engines for a similar vehicle, implying that diesel vehicles would actually have lower effective CO2




emissions per mile travelled.  Similarly, vehicles powered with compressed natural gas would emit




CO2 and CO  at lower levels than would either  gasoline or diesel vehicles, although CH4 emissions



might be higher.








Fuel Production and Conversion








    Significant quantities of greenhouse gases are emitted during the production of energy and its




conversion to end-use energy  forms.  Several major components of these fuel  production and




conversion processes are discussed below.
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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter IV



    Natural Gas Flaring. Venting, and Leaking. During the production of oil and natural gas, some

portion  of natural gas, which is mostly methane, is typically vented to the atmosphere (as CH4) or

flared (thereby producing CO2) rather than produced for commercial use.  Venting typically occurs

during natural gas drilling and well maintenance operations to avoid pressure buildup, to test well

drawdown,  and during required maintenance at existing production wells.  Flaring is most common

in conjunction with oil production when no market can be found for the natural gas associated with

oil reservoirs.  In some circumstances, the gas may be vented rather than flared.  On average, the

amount  of  natural gas flared and vented amounts  to about 2-3%  of global  natural gas production,

although in some regions virtually all of  the  natural gas  may be vented or flared,  while in other

regions  (like the U. S.) the total amount flared or vented is less than 0.5% of total production (U.S.

DOE, 1986).'  Currently, approximately 50 teragrams (Tg) of CO2 are released to the atmosphere

from  flaring of natural gas (Rotty, 1987).10



    Leaks  of natural gas also occur during the refining, transmission, and  distribution of the  gas.

These leaks  may occur at the refinery as the gas  is cleaned for market, from the pipeline system

during transportation to the  end-user, or during liquefaction and regasification if liquified natural gas

(LNG) is produced.  About  20-50 Tg of CH4 are released to the atmosphere each year from leaking

and venting of natural gas (Crutzen, 1987; Cicerone and  Oremland, 1989).



    Coal Mining. As coal forms, CH4 produced by the decomposition of organic material, becomes

trapped in  the coal seam. This CH4  is released to  the atmosphere during coal extraction operations.

The amount of CH4 released by coal mining varies depending on factors such as depth of the  coal

seam, quality of the coal, and  characteristics of  the  geologic strata surrounding the seam.   The
     9 U.S. regulations strictly govern the flaring and venting of natural gas.  In other parts of the
world, however, insufficient data exists to determine whether the natural gas is flared or vented,
although safety precautions would strongly encourage flaring rather than venting.

     10 1 Tg  = 1 teragram =  million metric tons =  1012 grams.



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amount of CH4 emitted as a result of coal mining is highly uncertain, with estimates ranging from



25 to  45  Tg per  year (Cicerone  and Oremland, 1989).   If coal mining  operations intensify, the



quantity of methane  released as an indirect result of mining is expected to increase at a comparable



rate.








    Synthetic Fuel Production.  As conventional petroleum resources are depleted, some of the



demand for liquid (oil and natural gas liquids) and gaseous  (natural gas) fuels may be met by



synthetic fuels.  Although there is currently little  synthetic fuel produced in the world, processes have



been  developed to convert relatively abundant solid energy resources such as coal, oil shale, and tar



sands  to liquid  or gaseous products that could  be consumed in the same  end-use  applications as



conventional oil and gas.








    Significant  amounts of energy are typically required to produce synthetic fuels.  The conversion



process produces greenhouse gas emissions, particularly CO2,  so that the net emissions per unit of



energy for synthetic fuels are greater than those  for conventional fossil fuels.  For example, the CO2



emissions from production and consumption  of synthetic liquid fuels from coal are  about 1.8 times



the amount from conventional liquid fuels from  crude oil (Marland, 1982).  Table 4-4 lists emission



rates  for both conventional fossil fuels and synthetic fuels produced from coal and shale oil.







Future Trends








    As shown  in  Figure 4-4,  the  quantity of CO2 emitted to  the atmosphere as  a result of the



combustion of fossil fuels has increased dramatically in the last century. This increase in fossil-fuel-



produced  CO2  emissions is  the  main factor  that  has led to an  increase in  atmospheric CO2



concentrations - from about 280 ppm in preindustrial periods to about 345 ppm  today. As discussed



in Chapter II, future CO2 concentrations will depend on many factors, but most important will be
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    Policy Options for Stabilizing Global Climate -- Review Draft
                                                   Chapter IV
                                            TABLE 4-4

                          Carbon Dioxide Emission Rates for Conventional
                                        and Synthetic Fuels
             Fuel
CO2 Emission Rate
    (g C/109J)
                   Notes
Conventional Fossil Fuels (rates for consumption)

  Natural Gas                        13.5-14.2

  Liquid Fuels from Crude Oil         18.2-20.6

  Bituminous Coal                    23.7-23.9

Synthetic Fuels (rates for production and consumption)
   Shale Oil
   Liquids from Coal
   High-Btu gas from coal
    104.3
     66.4
     47.6
     28.4

     51.3

     41.8
     39.9
     38.6
     37.2
     31.9
     30.5

     40.7
     40.1
     36.2
     32.7
                       Differences are partly attributable to product
                       mix, i.e., gasoline versus fuel oil and gasoline.
High temperature, 10 gal/ton shale
High temperature, 25 gal/ton shale
Modified in situ, 28 gal/ton shale
Low temperature retorting

Gasoline from methanol using Mobil MTG
    process
Sasol-type technology, Eastern coal
FHP process
Exxon-Donor Solvent, Eastern coal
H-coal
Generic 75% thermal efficiency
SRC-II, liquid and gas products

Lurgi
Hygas
Generic 66% thermal efficiency
Via synthesis gas with by-product credits
Source:  Marland, 1982.
    DRAFT - DO NOT QUOTE OR CITE
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the rate of growth in energy demand and the type of energy that is consumed hi order to satisfy this



demand.








The Fossil-Fuel Supply








    Higher levels of energy demand will produce  higher levels of greenhouse gas emissions if the




demand is satisfied with fossil fuels. As indicated above, fossil fuels  currently supply a majority  of




the world's energy needs,  and it seems likely that fossil fuels will continue to play a key role in the




world's  energy supply picture  for  decades to come.   However, supplies  of fossil fuels are not




unlimited.  Resource and reserve estimates for coal, oil, and gas are listed in Table 4-5.  A resource




is any presently or potentially extractable mineral supply, a reserve is  a presently extractable supply.




A resource that is not presently economic to extract, may become economic in the future and  then




be called a reserve.  The estimates of the lifetimes of fossil-fuel reserves are based on current (1985)




rates  of production.   The lifetime estimates of  fossil-fuel  resources  are based  on  linear  and




exponential extrapolations of current energy demand (described below).  Despite uncertainties about




the size of the resource base and the rate at which the resource base may be depleted, it is clear




from  a technical standpoint that the consumption of fossil fuels could continue for a very longtime.




As will be discussed in Chapter V, if the world continues to rely on fossil fuels to meet the majority




of its  energy needs, the amount of carbon emitted to the atmosphere may be many times greater  than



current  levels.








Future Energy Demand








    The future rate of energy demand depends on many variables,  including the rate of population




growth,  the rate  of  economic  growth,  energy prices,  the types of energy services demanded by




consumers, the type and efficiency of technology used,  and the type and  amount of  energy supplies
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      Policy Options for Stabilizing Global Climate ~ Review Draft
                                     Chapter IV
                                              TABLE 4-5

                                Estimates of Global Fossil-Fuel Resources"

                                              (Exajoules)

Coal
Oil
Gas
Geological
Resources
(exajoules)
315,800
12,800
10,100
Reserves/ Reserves Resource Lifetime (Years)
Reserves . Resources Lifetime11 Linear
(exajoules) (%) (Years) Extrapolation
20,400 6 229 524
4,300 34 41 69
3,700C 37 61 86
Exponential
Extrapolation
103
39
44
1      Resources estimates, as of 1985,  are  from the World Energy Conference  (1980), adjusted  for global
       production from 1979-85.  Reserve estimates are from DOE/EIA (1986):   oil and gas estimates as of
       January 1, 1986; coal estimates as  of 1981.

b      Based on 1985 rates of production.

e      Includes estimates for the Middle  East and USSR.


Sources:  World Energy Conference,  1980; United Nations, 1983, 1987; U.S. DOE, 1986.
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Policy Options for Stabilizing Global Climate - Review Draft                       Chapter IV



available (Chapter V).  Two hypothetical cases based on crude  extrapolations illustrate potential

upper and lower bounds on future energy demand (see Figure 4-7) and the  lifetime of fossil fuel

resources  (Table 4-5).  For example, from 1950 to 1973, the average annual growth rate in energy

demand was  5.2%.   If this rate of growth were exponentially extrapolated to 2050, global energy

demand would be about 254 TW (or equivalently about 8,000 EJ), almost 30 times the 1985 level.11

This amount  of energy demand  could lead to an increase in annual CO2 emissions from the current

5.2 Pg C to about 140 Pg C in 2050, assuming that this demand is met by consumption of fossil fuels.

Cumulative energy demand for  1985  through 2050 based on this  extrapolation represents over five

times the amount of fossil fuels  in proven reserves and about 45%  of the resource estimate. On the

other hand, the average annual  growth rate in  energy demand from 1973 to 1985 was  much lower:

about 2.2%.  If this rate were linearly extrapolated to 2050, global energy demand would be about

23 TW (720 EJ) - almost 150% greater than the demand in 1985 - which could increase annual CO2

emissions  from fossil  fuels  to nearly  13 Pg C.   Cumulative energy demand for 1985 through 2050

based on the  linear extrapolation represents about 115% of proven  fossil fuel reserves, or nearly 10%

of estimated  resources.



INDUSTRIAL PROCESSES



    There are three significant  non-energy sources  of greenhouse gases  associated with  industrial

activity: the use of chlorofluorocarbons (CFCs), halons, and chlorocarbons (collectively, halocarbons);

cement  manufacture; and waste disposal in landfills.  The use of  CFCs, halons, and chlorocarbons,

which  are man-made chemicals  with  a variety of  applications, results  in  their release  to the

atmosphere.  Certain uses,  such as aerosol propellants and  solvents, result in  instantaneous release

(when the product is used), while others, such  as foam-blowing agents and refrigerants, result in a
     11 TW = Terawatt-years per year =  1012 watt-years per year; 1 TW =  31.53 EJ; 1 EJ =  1
Exajoule = 1018 joules; 1055 joules =  1 Btu.
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Policy Options for Stabilizing Global Climate - Review Draft
                                  Chapter IV
                                    FIGURE 4-7
                  POTENTIAL FUTURE ENERGY DEMAND

                                      (Exajoules)
       8000
       7000  -
       6000  -
       5000  -
    oo
    LU  4000

    O
    -3
    
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter IV








delayed release. Cement manufacture results in CO2 emissions, and waste disposal in landfills results



in CO2  and CH4 emissions, although only the  CH4 emissions are significant in terms of the  total




global source.








Chlorofluorocarbons, Halons, and Chlorocarbons








Historical Development and Uses








    Chlorofluorocarbons are man-made chemicals containing chlorine, fluorine, and carbon, hence the




name CFCs (HCFCs contain hydrogen as well).  Table 4-6  lists the major CFCs with their chemical




formulae.  CFCs were developed in the late 1920s  in the United States as a substitute for the toxic,




flammable, refrigerator coolants in use at that time.  The chemicals, which are noncorrosive, nontoxic,



nonflammable, and highly stable in the  lower atmosphere, provided the refrigerator industry with  a




safe,  efficient  coolant  that soon  proved  to  have numerous  other uses as  well.    Commercial




development of CFCs began in 1931.   During World War II, CFCs were  used as  propellants in




pesticides  against  malaria-carrying mosquitos.   Since then, CFCs  have been used  as  aerosol




propellants hi a wide  range of substances, from hairsprays to spray  paints.  In the 1950s, industries



began using CFCs as blowing agents for plastic foam and foam insulation products.  Chillers,  used




for cooling large commercial and industrial buildings,  as well as cold storage  units for produce and



other perishable goods, became feasible at this tune with the  use of CFCs.  Mobile air conditioners



(in automobiles, trucks, and buses) currently constitute the largest single use  of CFCs in the United



States.   CFCs are also  used in gas  sterilization  of  medical equipment and instruments, solvent




cleaning of manufactured parts, especially electronic components and metal parts, and miscellaneous




other processes and products such as liquid food freezing.
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   Policy Options for Stabilizing Global Climate - Review Draft
                                    Chapter IV
                                          TABLE 4-6

                                      Major Halocarbons:
                                      Statistics and Uses
Chemical
Chlorofluorocarbons
CFC-11 (CFC13)
CFC-12 (CFjClO
HCFC-22 (CHClFj)
CFC-113 (QClsFj)
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 (CBrClFj)
Halon-1301 (CBrF3)
Chlorocarbons
Carbon tetrachloride
Methylchloroform
(CHjCdj)
-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
Sources:  U.S. EPA, 1988a; Hammitt et al., 1987; Wuebbles, 1983; WMO, 1985.

NA = No data available.
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter IV








    Halons, or bromofluorocarbons, are man-made chemicals containing carbon, fluorine, and chlorine



and/or bromine (see Table 4-6 for the chemical formulae of the major halons in use today).  These



chemicals were developed in the 1970s, and are used primarily as fire  extinguishants. Halon-1211 is



used  almost exclusively for portable (i.e., wheeled  or handheld) fire  extinguishers, particularly for



situations where human exposure to the chemical is possible, such as in airplanes.  Halon-1301  is used



exclusively for total flooding fire extinguishing systems such as those used to protect computer centers,



document rooms, libraries, and military installations.  A summary of  the 1985 end-use applications



for the major CFC and halon compounds is shown  in Table 4-6.








    Chlorocarbons, man-made chemicals containing chlorine and carbon (see Table 4-6), are  used



primarily as solvents and chemical intermediates. The primary chlorocarbons are carbon tetrachloride



and methylchloroform.  In the United States, carbon tetrachloride was  once used extensively as a



solvent and grain fumigant,  but because of its toxicity,  only small amounts of  it are  used in  such



applications today.  Its primary use in the United States is in the manufacture of CFC-11  and CFC-



12, a  process which consumes or destroys almost all of the carbon tetrachloride,  resulting in very



small  emissions.  However,  carbon tetrachloride is  believed to be used as a solvent in developing



countries, resulting in  considerable emissions.  Methylchloroform is  used worldwide as a cleaning



solvent in two applications:  1) vapor degreasing (the solvent is  heated and the item to be cleaned



is  suspended in the vapor); and 2) cold cleaning (the part to be cleaned is submerged  in a tank of



solvent).   Small  amounts are also used in adhesives, aerosols, and coatings.








    Production of CFCs, halons, and chlorocarbons  has  grown  steadily as new uses have developed.



Production of the two  largest CFC compounds, CFC-11  and CFC-12, increased rapidly  in the 1960s



and early 1970s (see  Figure  4-8).  Production peaked  in 1974 at  812.5 gigagrams (Gg) and  then



declined  due to a ban  on most aerosol use in the United States, Canada, and Sweden in the late
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Policy Options for Stabilizing Global Climate - Review Draft
                                Chapter IV
                                 FIGURE 4-8
      HISTORICAL PRODUCTION OF CFC-11 AND CFC- 12

                                 (Glgagrams)
         900
         800
         700
         600
     oo
     5   500
     «t
     oc
     o
     <
     o
     3   400
         300
         200
          100
                                     Dashed line indicates estimates
                                     	I	i	
                                                                 Total
                            Non-Aerosol
                                                                 Aerosol
            1960      1965      1970      1975      1980      1985
                                     YEAR
Figure 4-8. While non-aerosol production of CFC-11 and CFC-12 has grown fairly steadily since
1960, aerosol production declined in the 1970s and then leveled off in the 1980s due to a ban on
most aerosol use of CFCs in the United States, Canada, and Sweden.  (Source: U.S. EPA, 1987.)
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter IV








1970s.12   However, non-aerosol  use  has  continued  to  grow,  with 1985 production of 703.2 Gg.



Globally, major CFC and halon consumption reached nearly one Tg in 1985 (see Table 4-7).  Global



production of carbon tetrachloride and methylchloroform in 1985 was estimated at nearly 1,029 Gg



and 545 Gg, respectively (Hammitt et al., 1987).








    Most CFC and halon consumption occurs in the United States and other industrialized nations.



Of the 7032 Gg of CFC-11 and  CFC-12 produced in 1985,  about  70% was consumed by the U.S.,



the EEC, and Japan (see Figure 4-9). Although CFC use is concentrated in the industrialized world,



consumption has also increased recently in developing countries.








The Montreal Protocol








    Concern over  the effect on  the  Earth's  atmosphere of CFCs and related anthropogenically-



produced compounds containing chlorine, bromine, and nitrogen began in the 1970s.  Because of their



stability (i.e., their long  lifetimes, see Table 4-6), CFCs are transported to the stratosphere where



they contribute  to  the destruction of ozone.  Since the early 1970s, improved understanding of this



process, accumulation of data indicating growing atmospheric concentrations of CFCs, and observed



depletion of stratospheric ozone, particularly in the Antarctic, have  fueled international concern over



this issue.







    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



in Montreal,  Canada, where a  Diplomatic  Conference  was held,  resulting in an  international



agreement (The Montreal Protocol on Substances That Deplete  the Ozone Layer," or the Montreal



Protocol) to begin reducing the use of CFCs and halons  (chlorocarbons were not included).  The
    12 1 Gg = 109 grams =  1 million kilograms.








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Policy Options for Stabilizing Global Climate - Review Draft                       Chapter IV
                                        TABLE 4-7

                           Estimated 1985 World Use of Potential
                                Ozone-Depleting Substances

                                        (gigagrams)
                                                                             Other
                                       United          Reporting             Communist
Chemical              World           States           Countries              Countries
CFC-11                 341.5            75.0            225.0                   41.5
CFC-12                 443.7           135.0            230.0                   78.7
CFC-113                163.2            73.2             85.0                    5.0
Halon 1301               10.8             5.4              5.4                    0.0
Halon 1211               10.8             2.7              8.1                    0.0
Carbon  tetrachloride    1029.0           280.0            590.0                  159.0
Methylchloroform        544.6           270.0            186.7                   87.0
Source: Hammit et al., 1986.
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Policy Options for Stabilizing Global Climate - Review Draft
     Chapter IV
                               FIGURE 4-9
            CFC-11 AND CFC-12 PRODUCTION/USE


                    FOR VARIOUS COUNTRIES

                               (Glgagrams)
     240
     210  -
     180  -
     150  -
   2
   2 120
   o
   <3
      90  -
      60  -
      30  -
                                                           Thailand
Figure 4-9. The EEC, the United States, and Japan accounted for almost 70% of the 1985 global

production of CFC-11 and CFC-12.  (Source:  U.S. EPA, 1988a.)
DRAFT - DO NOT QUOTE OR CITE      IV-39
February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter IV








Montreal  Protocol  came into force on January 1,  1989  and has  been ratified by 31  countries,




representing over 90% of current world production of these chemicals (as of January 11, 1989).  As




a result of this historic agreement,  the very high growth rates in atmospheric CFC concentrations




projected  in earlier studies (e.g., Ramanathan et al., 1985) are not likely to occur.  Nevertheless,




because of the long atmospheric lifetimes  of CFCs, their concentrations could continue to increase



for several decades (see Chapter V).








Landfill Waste Disposal








    Humans have generated  solid wastes  since they first appeared  on Earth, although disposal  of



these wastes did not become a major problem until the rise of synthetic materials (e.g., plastics) and




densely-populated urban areas. The  environment  can usually assimilate the smaller amounts of wastes




produced by rural, sparsely-settled communities.  However, because urban populations produce such



high volumes of waste, due to both  the sheer concentration of individuals contributing to the waste




stream and the high use of heavily-packaged products, urban waste disposal has become a formidable




task.








    Approximately 80% of the municipal solid wastes collected in urban areas around the world is



deposited  in landfills or open  dumps (Bingemer and Crutzen, 1987).  Sanitary landfilling (compaction



of wastes, followed by daily  capping  with a layer of clean earth),  which became common in the



United States  after World War II,  is used  primarily in urban centers in industrialized  countries.




Open pit dumping is the most common "managed" disposal method in developing countries (30-50%




of the solid wastes generated in cities of developing countries is uncollected [Cointreau, 1982]). Most




landfills and many open dumps develop anaerobic conditions, resulting in decay of organic carbon to




CH4  and  CO2.   The amount of CH4 resulting  from anaerobic decay of  organic municipal and
DRAFT - DO NOT QUOTE OR CITE        IV-40                           February 16, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter IV



industrial wastes in landfills is currently about 30-70 Tg per year (Bingemer and Crutzen, 1987),

approximately 10% of the total annual CH4 source.13



    The primary variable affecting gas generation in landfills is the composition of the refuse. Wastes

high in organic  material (e.g., food wastes, agricultural  wastes, paper products) decompose readily,

while inorganics are  relatively unaffected by the decomposition process.  While agriculture is the

largest single source of solid wastes in the U.S. (Berry and Horton, 1974), most of these wastes are

not  landfilled.   Increasing urbanization and  demand  for "convenience" items, which  encourages

marketing of single-serving and  heavily-packaged products,  has resulted in increasingly greater

proportions of  plastics, glass, metals, and  paper products,  in the waste  stream.   Other factors

influencing gas generation include inclusion of sewage sludge (which enhances gas generation), oxygen

concentration, moisture content, pH, and available nutrients.



    Disposal of  municipal solid waste in industrial nations increased by 5% per year during the 1960s,

and  by  2%  per year  in  the 1970s  (CEQ, 1982).    Currently,  per  capita waste  production in

industrialized countries is considerably larger than in  developing countries (see  Table 4-8), and the

largest contribution of landfill CH4 conies from  the  industrialized world (Bingemer and Crutzen,

1987).   Although current rates of waste  disposal in  landfills have begun  to level off in  many

industrialized countries, associated CH4 emissions are probably still growing because the total quantity

of waste in place is still increasing. In the developing world, with its high  population growth rates

and  increasing urbanization, municipal solid waste disposal is projected to double by the year 2000

(Kresse and Ringeltaube, 1982), so CH4 production from waste dumps and/or sanitary landfills  can

be expected to increase rapidly in developing countries.
    13 This estimate does not include methane from anaerobic decomposition of agricultural
wastes, which could be a significant quantity.  The total amount of carbon in agricultural wastes in
the United States alone is  already 2.5 times larger than the 113 million metric tons of waste
carbon that are generated  and dumped in landfills worldwide (Bingemer and Crutzen, 1987).
DRAFT - DO NOT QUOTE OR CITE        IV-41                            February 16, 1989

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Policy Options for Stabilizing Global Climate *- Review Draft                        Chapter IV
                                        TABLE 4-8

                          Refuse Generation Rates in Selected Cities
                                                             Per Capita
                                                               Waste
                                                            Generation Rate
    City                                                     (kg Per Day)
   Industrial Cities

        New York, United States                                 1.80
        Singapore                                                0.87
        Hong Kong                                              0.85
        Hamburg,  West Germany                                 0.85
        Rome, Italy                                              0.69

   Developing Cities

        Jakarta,  Indonesia                                        0.60
        Lahore,  Pakistan                                         0.60
        Tunis, Tunisia                                            0.56
        Bandung, Indonesia                                       0.55
        Medellin, Colombia                                       0.54
        Surabaya, Indonesia                                       0.52
        Calcutta, India                                           0.51
        Cairo, Egypt                                             0.50
        Karachi, Pakistan                                        0.50
        Manila,  Philippines                                       0.50
        Kanpur, India                                            0.50
        Kano, Nigeria                                            0.46
Source:  Cointreau, 1982.
 DRAFT - DO NOT QUOTE  OR CITE        IV-42                           February 16, 1989

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Policy Options  for Stabilizing Global Climate - Review Draft                       Chapter IV








Cement Manufacture








    Cement manufacture produces CO2, as well as numerous other exhaust gases.  As demand for



cement has grown over the last century, CO2 emissions associated with this industry have increased



from 18 to 134  Tg C between 1950 and 1985 (see Figure 4-10).  In recent years CO2 emissions from



cement production have grown at a faster rate than those from fossil  fuel combustion:  In the early



1950s CO2 emitted as a result of cement manufacture was approximately  1% of the amount emitted



from the consumption of fossil fuels; by the early 1980s this fraction had increased to 2.5%  (Rotty,



1987).








    The CO2 emissions resulting from cement manufacture occur during the production of clinker,



a material produced midway through the process.  After the raw materials  (cement rock, limestone,



clay, and  shale)  are  quarried and crushed, they  are  ground  and  blended to a  mixture  that is



approximately 80% limestone by weight.  The mixture is then fed into a kiln for firing, where it is



exposed to progressively higher temperatures that cause heating, then drying, calcining, and sintering.



Finally, the feed is heated to the point of fusion (approximately 1595°C), and clinker (round, marble-



sized particles)  is produced.  It is during the calcination process, which occurs at approximately 900



to 1000°C, that the limestone (CaCO3) is converted to lime (CaO) and CO2, and the CO2 is released.



For every million tons  of cement  produced,  approximately 0.137 Tg C as CO2 is emitted from



calcining (Rotty, 1987).14  An additional 0.165 Tg C is emitted per million  ton of cement produced



from fossil fuel used for kiln firing  and electricity.  This CO2 is 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  133 million tons in 1950 to 972 million tons in  1985 (U.S. BOM, 1949-1986).  Cement
    14 1 ton =  1 metric ton =  1000 kg.
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Policy Options for Stabilizing Global Climate - Review Draft
                              Chapter IV
                               FIGURE 4-10
          C02 EMISSIONS FROM CEMENT PRODUCTION

                             1950-1985

                             (Teragrams Carbon)
       140
       120
       100
    o
    co  80
    M
    
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Policy Options for Stabilizing Global Climate •- Review Draft                        Chapter IV



production growth rates in individual countries have varied during this period (see Figure 4-11)  due

to economic fluctuations  in cement's primary market, i.e., the construction industry, and competitive

shifts internationally among the primary cement-producing countries.  For example,  in  1951  the

United States produced approximately 28% of the  global total, while by 1985 its share had shrunk

to 7%.15   During the same time,  the production shares for the USSR grew from 8% to  13%, for

China, from less than 1% to 15%, and for Japan, from 4% to 8%. Although many national markets,

except the United  States',  experienced low levels of demand during  the 1980s, global cement

production is expected to continue to grow faster than the GNP for some time.



LAND USE CHANGE



    Over the past few centuries, man has significantly changed the surface of the Earth.  Forests have

been cleared, wetlands have been drained, and agricultural lands have been  expanded.  All of these

activities  have  resulted  in  considerable  changes  in  trace  gas  emissions  to the  atmosphere.

Deforestation results in a net release of carbon from both the biota and the soils (unless the land

is reforested) as  these organic carbon  pools burn or are decomposed.  Biomass burning, due to

shifting  agriculture,  burning  of savanna,  use of industrial wood  and fuelwood, and burning of

agricultural wastes, is a source of CO2, as well as CH4, N2O, and NOX. 16 Destruction of  wetlands,

from either filling or dredging, can alter the atmospheric CH4 budget, since anaerobic decomposition

in wetlands produces CH4.
    15 The U.S. is currently a net importer of cement; the volume of its imports has grown,
representing only a few percent of consumption in the early 1980s but as much as 18 percent hi
1986 (International Trade Administration, 1987).

    16 Shifting agriculture is the practice of clearing and planting a new area, farming it until
productivity declines, and then moving on to a new plot to start the  cycle over again.  If the land
is allowed to  reforest, there are no net CO2  emissions.
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Policy Options for Stabilizing Global Climate - Review Draft
                                                            Chapter IV
                               FIGURE 4-11
       CEMENT PRODUCTION IN SELECTED COUNTRIES


                             1951-1985


                          (Thousand Metric Tons)
       200
        150
    v>
    z
    o

    o

    B
o
    o
        100
         50
             United States
                      ^
                    s  >• •
                   /
                                                 I
                                                        J_
                                                               I
             1951  1955    1960   1965   1970   1975   1980    1985



                                     YEAR
Figure 4-11. World cement production grew at an average annual rate of about 6% between 1950

and 1985.  Growth has been particularly rapid in China, the U.S.S.R., and Japan.  (Source: U.S.

BOM, selected years.)
DRAFT - DO NOT QUOTE OR CITE
                               IV-46
February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter IV








Deforestation








    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 to 2.6 Pg  C




(Houghton et al., 1987; Detwiler and Hall, 1988), which accounts for approximately 10-30% of annual




anthropogenic CO2 emissions to the atmosphere.  Deforestation in the tropics accounted for almost




all  of  the flux; the  carbon budget  of temperate  and boreal  regions  of the world  has been




approximately hi balance in recent years.  Of the  net release of carbon from tropical deforestation,




55% was  produced by only six countries in  1980:   Brazil,  Indonesia,  Columbia, the Ivory Coast,




Thailand,  and Laos (see Figure 4-12).








    The world's forest and  woodland  areas have  been reduced  15% since  1850,  primarily  to




accommodate the expansion of cultivated lands (IIED and WRI, 1987). The largest changes 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  in  forest area over this time interval.  Forest area began  to




increase in Europe in the 1950s and in North America in the 1960s (see Table 4-9). However, recent




data from the Food and Agriculture Organization  of the United Nations  (FAO)  and the U.S. Forest




Service indicates that net deforestation may be  occurring in the United States — although there are




discrepancies between the two data sets. The FAO  data indicates that between 1980 and 1985 the



area of U.S. forest and woodlands decreased  by approximately 3.8 million hectares  (million ha) per



year, or 1.4% per year (FAO, 1986b).17 The U.S.  Forest Service (Alig, 1988) estimates that between



1977 and 1987 the area of U.S. forests decreased by approximately 0.41 million ha per year, or 0.14%



per year.
    17 1 ha  = 1 hectare  = 2.471 acres.
DRAFT - DO NOT QUOTE OR CITE        IV-47                            February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                              Chapter IV
                                 FIGURE 4-12
                  NET RELEASE OF CARBON FROM
                     TROPICAL DEFORESTATION
                                   1980

                              (Teragrams Carbon)
          Rest of World (516)
        Peru(45)

      Burma (51)

  Philippines (57)


     Nigeria (60)
          Laos(85)
           Thailand (95)
                          Brazil (336)
                                                        Indonesia (192)
               Ivory Coast (101)
                                           Colombia (123)
 Figure 4-12. Tropical deforestation accounts for approximately 10-30% of the annual anthropogenic
 CO2 emissions to the atmosphere.  Over half of the 1980 CO2 emissions from deforestation was
 produced by six countries:   Brazil, Indonesia, Columbia, the Ivory Coast, Thailand, and Laos.
 (Source: Houghton et al., 1987.)
 DRAFT • DO NOT QUOTE OR CITE
IV-48
February 16, 1989

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                                                TABLE 4-9
                                            Land Use:  1850-1980
                                                     Area (million hectares')
                                             Percentage
                                              Change
                                              1850 to

TEN REGIONS
Forests and Woodlands
Grassland and Pasture
Croplands
Tropical Africa
Forests and Woodlands
Grassland and Pasture
Croplands
North Africa and Middle East
Forests and Woodlands
Grassland and Pasture
Croplands
North America
Forests and Woodlands
Grassland and Pasture
Croplands
Latin America
Forests and Woodlands
Grassland and Pasture
Croplands
China
Forests and Woodlands
Grassland and Pasture
Croplands
South Asia
Forests and Woodlands
Grassland and Pasture
Croplands
Southeast Asia
Forests and Woodlands
Grassland and Pasture
Croplands
Europe
Forests and Woodlands
Grassland and Pasture
Croplands
USSR
Forests and Woodlands
Grassland and Pasture
Croplands
Pacific Developed Countries
Forests and Woodlands
Grassland and Pasture
Croplands
1850

5,919
6,350
538

1,336
1,061
57

34
1,119
27

971
571
50

1,420
621
18

96
799
75

317
189
71

252
123
7

169
150
132

1,067
1,078
94

267
638
6
1860

5,898
6,340
569

1,333
1,062
58

34
1,119
28

968
559
65

1,417
623
19

93
799
78

315
189
73

252
123
7

158
147
136

1,060
1,081
98

267
638
6
1870

5,869
6,329
608

1^29
1,064
61

33
1,118
30

965
547
80

1,414
625
21

91
798
81

311
189
77

251
122
8

157
145
140

1,052
1,083
103

266
638
7
1880

5,833
6,315
659

1,323
1,067
64

32
1,117
32

962
535
95

1,408
627
24

89
796
84

307
189
81

251
121
10

157
144
142

1,040
1,081
118

265
637
9
1890

5,793
6301
712

1,315
1,070
68

31
1,116
35

959
522
110

1,401
630
28

86
797
86

303
189
85

250
119
12

156
143
143

1,027
1,079
132

264
635
12
1900

5,749
6,284
773

1396
1,075
73

30
1,115
37

954
504
133

1,394
634
33

84
797
89

299
189
89

249
118
15

156
142
145

1,014
1,078
147

263
634
14
1910

5,696
6,269
842

1,293
1,081
80

28
1,113
40

949
486
156

1383
638
39

82
797
91

294
190
93

248
116
18

155
141
146

1,001
1,076
162

262
632
17
1920

5,634
6,260
913

1,275
1,091
88

27
1,112
43

944
468
179

1,369
646
45

79
796
95

289
190
98

247
114
21

155
, 139
147

987
1,074
178

261
630
19
1930

5353
6,255
999

1,251
1,101
101

24
1,108
49

941
454
1%

1,348
655
57

76
796
96

279
190
108

246
111
25

155
138
149

973
1,072
194

260
629
22
1940

5,455
6,266
1,085

1,222
1,114
118

21
1,103
57

940
450
201

1,316
673
72

73
794
103

265
190
122

244
108
30

154
137
150

961
1,070
208

259
627
24
1950

5,345
6,293
1,169

1,188
1,130
136

18
1,097
66

939
446
206

1,273
700
87

69
793
108

251
190
136

242
105
35

154
136
152

952
1,070
216

258
625
28
1960

5,219
6,310
1,278

1,146
1,147
161

17
1,085
79

939
446
205

1,225
730
104

64
789
117

235
190
153

240
102
40

156
136
151

945
1,069
225

252
617
42
1970

5,103
6,308
1396

1,106
1,157
190

15
1,073
93

941
447
204

1,186
751
123

59
784
127

210
189
178

238
97
47

161
137
145

940
1,065
233

247
609
56
1980

5,007
6,299
1401

1,074
1,158
222

14
1,060
107

942
447
203

1,151
767
142

58
778
134

180
187
210

235
92
55

167
138
137

941
1,065
233

246
608
58
1980

-15
-1
179

-20
9
288

-60
-5
294

-3
-22
309

-19
23
677

-39
-3
79

-43
-1
196

-7
-25
670

4
-8
4

-12
-1
147

-8
-5
841
Source:  IIED and WRI, 1987.
         DRAFT - DO NOT QUOTE OR CITE
IV-49
February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter IV








    Currently, it is estimated that approximately 11.3 million ha of tropical forests are lost each year,




while only 1.1 million ha are reforested per year (FAO, 1985).  Most of the tropical deforestation




is due to  transfer of forest land to agricultural use, through  shifting agriculture and conversion to




pasture.  FAO has estimated a demand for an additional  113-150 million  ha of cultivated land for




the 20-year period between 1980 and 2000 to meet food production needs (FAO, 1981).  Most of this




land will have to come from areas that were once forested, however  there is a large  potential to use




land currently under shifting cultivation by adapting low-input  agricultural techniques (Chapter VII).




Fuelwood use also contributes to  deforestation, particularly in Africa where fuelwood is a  major



source of residential  energy.  Sixty-three percent of  the  total energy consumption of developing




African countries, 17% in the Asian countries, and 16% in  the Latin  American countries, is provided




by fuelwood.  In the Sudan, Senegal, and Niger, fuelwood provides 94, 95,  and 99%, respectively, of




household energy  consumption (Anderson  and Fishwick, 1984).   Rapidly-increasing  populations,



particularly in developing nations, will result in increasing demands on forest lands to meet growing




agricultural and energy needs.








Biomass Burning








    Biomass burning, in  addition  to contributing to the atmospheric  CO2  budget,  contributes




approximately 10-20% of total annual CH4 emissions, 5-15%  of the N2O emissions, 10-35% of the



NOX emissions, and 20-40% of the CO  emissions (Crutzen et al., 1979; WMO,  1985; Logan, 1983;




Stevens and Engelkemeir, 1988; and Andreae et al., 1988).  These  estimates are for instantaneous




emissions from combustion.  Recent research has shown that biomass burning also results in longer-




term (at least up to 6 months after the burn) emissions  of NO and N2O due to enhancement of




biogenic soil emissions (Anderson et al.,  1988). Estimates of emissions of trace gases due to biomass
 DRAFT - DO NOT QUOTE OR CITE       IV-50                           February 16, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter IV



burning are very uncertain for two reasons:  1) data on amounts and types of biomass burned are

scarce, and 2) emissions per unit of biomass burned are highly variable.



    Activities  associated  with  biomass  burning  include  agriculture, colonization, wildfires  and

prescribed fires, and burning of industrial wood and fuelwood.  Currently, agricultural burning, due

to shifting agriculture and burning of agricultural wastes is estimated to account for over 50% of the

biomass burned annually (Table 4-10). Biomass burning is a particularly important  source of trace-

gas emissions  in the tropics, where forest exploitation is unsurpassed.  Continued rapid population

growth and exploitation of forests may substantially increase emissions from biomass burning hi the

future.



Wetland Loss



    Annual  global  emissions  of  CH4  from  freshwater  wetlands  are estimated  to  be 110  Tg,

approximately 25% of the total annual source of 400 to 600 Tg (Matthews and Fung, 1987).  Of the

approximately 530 million ha producing this CH4, 39% is forested bog, 17% is nonforested bog, 21%

is forested swamp,  19% nonforested swamp,  and 4%  alluvial formations.18  The bulk of the bog

acreage is  located between 40°N and 70°N, while swamps predominate between  10°N and 30°S.

Alluvial formations  are concentrated between 10°N and 40°S (see Figure 4-13).  Coastal saltwater

and brackish water environments produce minor amounts of CH4 in comparison, probably due to the

inhibitory effects of dissolved sulfate (SO4) in the interstitial water of salt-marsh sediments (DeLaune

et al., 1983; Bartlett et al., 1985).
    18 Bogs are peat- or organic-rich systems, usually associated with waterlogging and seasonal
freeze-thaw cycles; swamps are low-organic formations occurring most commonly in the tropics,
and alluvial formations are low-organic riverine formations.
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    Policy Options for Stabilizing Global Climate - Review Draft
                                      Chapter IV
                                            TABLE 4-10

                             Summary Data on Area and Biomass Burned
Activity
     Burned and/or
      Cleared Area
      (million ha)
 Burned Biomass
(100 Tg dry matter)
Burning due to shifting agriculture

Deforestation due to population
  increase and colonization

Burning of savanna and brushland

Wildfires in temperate and
 boreal forests

Prescribed  fires in temperate forests

Burning of industrial wood and fuelwood

Burning of agricultural wastes


  TOTAL
     21-62 (41)

     8.8-15.1 (12.0)


     (600)

     4.0-6.5 (5.4)


     2.0-3.0 (2.5)
     630-690 (660)
   9-25 (17)

   5.5-8.8 (7.2)


   4.8-19 (11.9)

   1.9-3.2 (2.6)


   0.1-0.2 (0.2)

   10-11 (10.5)

   17-21 (19)


   48-88 (68)
Data in parentheses represent average values.
Source:  Crutzen et al., 1979.
    DRAFT - DO NOT QUOTE OR CITE
IV-52
     February 16, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft
                                                             Chapter IV
                                    FIGURE 4-13
         WETLAND AREA AND ASSOCIATED METHANE EMISSIONS
       
       <
       o
       tc.
       (3

       K
       UJ
                 SON  70   60  50  40  30  20  10
                                        10  20  30  40  60S
    80N  70  60  SO  40   30  20   10   0
                            LATITUDE

Alluvial                  [//; Forested swamp

                       jxyj Nonf orested bog
                                                     10  20  30  40  SOS
                                                               Forested bog
         O\j Nonfcrested swamp
 Figure 4-13.   Estimated latitudinal distribution of wetland area (top) and associated methane
 emissions  (bottom).  Forested and non-forested bogs located between 40° and 70°N account  for
 approximately 50% of the current CH4 emissions from wetlands.  (Source:  Matthews  and Fung,
 1987.)
 DRAFT - DO NOT QUOTE OR CITE
                            IV-53
February 16, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter IV



     The latitudinal distribution of wetland CH4 emissions is estimated  to be very similar to the

latitudinal distribution of freshwater wetland area. About 50% of the emissions originate between

50°N and 70°N, and about 25% between 20°N and 30°S.  The source of the high-latitude emissions

is organic-rich bogs, while most of the low-latitude emissions  come from swamps (see  Figure 4-13).



    Between 25 and 50% of the world's original swamps and marshes have been eliminated by human

activities (IIED and WRI, 1987).  For centuries people have drained and filled marshes and swamps

to create dry land for agricultural and urban development. Wetland areas have been converted  to

open water by dredging and  installation of flood-control levees, and have been used as  disposal sites

for dredge materials and solid wastes.  Peat mining and pollution from agricultural and industrial

runoff have  also contributed to the destruction of wetlands. By 1970, more than half of the original

wetland acreage  in the United States had been destroyed (IIED and WRI,  1987). Between the mid-

1950s and mid-1970s, there  was a net loss of wetlands in the United States of approximately 4.6

million  ha,  97% of which occurred hi inland freshwater areas  (U.S. OTA,  1984).  Agricultural

conversions  were responsible for 80% of this freshwater wetland loss.19  Wetland loss has also been

extensive in Europe and the Asia-Pacific  region.  For example,  approximately 40% of  the coastal

wetlands of  Brittany, France, have been lost in the last 20 years, and 8100 ha of wetlands  on the east

coast of England have been converted to agricultural use since the 1950s. Large-scale wetland losses

have not been as prevalent in the developing  world, but rising populations will result  in increasing

demands for agricultural expansion. There is already pressure to develope two large wetland systems

in Africa, the  Okavango Swamps of Botswana and the Sudd  Swamps of southern  Sudan,  for

agricultural  use (IIED and WRI, 1987).
     19 For example, drainage of prairie potholes hi Iowa to provide new farmland has resulted in
the reduction of Iowa's original wetlands by over 98%, from 930,000 ha when settlement began, to
10,715 ha today.
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AGRICULTURAL ACTIVITIES








    Three agricultural activities contribute directly to atmospheric emissions of greenhouse gases:




enteric fermentation in domestic animals, rice cultivation, and use of nitrogenous fertilizer.  Global




demand for food and agricultural products  has more than doubled since  1950, fueled by rising




populations and incomes.  Agricultural advancements during the post-war years, such as the "Green




Revolution," brought improvements in soil management and disease control, new high-yielding varieties




of crops, increased application of commercial fertilizers, and increased use of machinery. Between




1950 and 1986, world grain production increased from  624 to 1,661 million tons and average yield




more than doubled, from 1.1  to 2.3 tons per ha (Wolf, 1987).  Over this same time interval, growth




of various domestic animal populations ranged from 20 to 150% (Crutzen et al., 1986) and fertilizer




consumption grew approximately 750% (Herdt and Stangel, 1984).  According to projections by the




Food and Agriculture Organization of the United Nations, by the year 2000, a world population of




about 6 billion will require an agricultural output approximately 50 to 60% greater than that required




in 1980 (FAO, 1981).








Enteric Fermentation In Domestic Animals








    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.  Both ruminant animals (e.g., cattle, dairy cows, sheep, buffalo, and goats) and some



non-ruminant animals (e.g., pigs and horses) produce CH4.  The highest CH4  losses are reported for




ruminants (approximately 4-9% of total energy intake), which are able to digest cellulose due to the




presence of specific microorganisms in their  digestive tracts.  The amount of CH4 that  is released
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from both ruminant and non-ruminant animals depends on the  type, age, and weight of the animal,




the quality and quantity of feed, and the energy expenditure of the animal.








    Of the annual global source of 400-600 Tg CH4, domestic animals contribute approximately 65-




85 Tg (Crutzen et al., 1986; Lerner et al., 1988). Domestic animals that produce the bulk of the CH4




are (in decreasing order of amount produced) cattle, dairy cows, buffalo, goats, sheep, camels, pigs,




and horses.  Currently, approximately 57% comes from  cattle, and 19% from dairy cows.  Domestic




animals in six countries, India, the USSR, Brazil, the U.S., China, and Argentina, produce over 50%




of the methane by enteric fermentation (Lerner et  al., 1988).








    The domestic animal population has increased considerably during the last century. Between the




early 1940s and 1960s, increases in global bovine and sheep populations averaged 2% per year.  Since




the 1960s, the  rates of increase have slowed somewhat, to 1.2%  and 0.6% per year, respectively (see




Figure 4-14). The annual increases in global populations of pigs, buffalo, goats, and camels since the




1960s have  been comparable:   1.4%, 1%, 1.2%,  and  0.5%, respectively.  The horse population



declined  about 0.25%  per year.  For comparison, the average  annual  increase in global human



population since the 1960s has been  about 1.8%.








Rice Cultivation








    Anaerobic decomposition in flooded  rice  fields  produces  methane,  which  escapes to  the




atmosphere by ebullition (bubbling)  up through the  water column, diffusion across the water/air




interface, and transport through the rice plants. Research suggests that the amount of CH4 released




to the atmosphere is a function of rice species, number and duration of harvests, temperature,
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Policy Options for Stabilizing Global Climate •- Review Draft
                                  Chapter IV
                                    FIGURE 4-14
                TRENDS IN DOMESTIC ANIMAL POPULATIONS

                                    1890-1985
                                       (Millions)
          o
             1400
             1200
             1000
              800
              600
              400
              200
                   1890
                                 1925    1945   1960

                                       YEAR
                                                          1985
                                                                      Cattle
                                                                      Sheep
                                                                 	  Pigs
                                                                 	Goats
                                                                      Buffalos
                                                                      Horses
                                                                      Camels
Figure 4-14.  Global domestic animal populations have grown by about 0.5 to 2.0% per year during
the last century.  Currently, domestic animals account for about 15% of the annual anthropogenic
CH4  emissions. Note: The cattle population figures include dairy cows.  (Sources:  Crutzen et al.,
1986; FAO, 1971, 1982, 1986a.)
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter IV



irrigation practices, and fertilizer use (Holzapfel-Pschorn and Seiler, 1986; Seiler et al., 1984; Cicerone

et al.,  1983).



    Rice cultivation  has grown  tremendously since the mid-1900s,  due both  to  increases in crop

acreage and yields.20  Between 1950 and 1984, rough rice production grew from 163 to 470 million

tons,  nearly a 200%  increase.21   During  the  same time, harvested rice paddy area  increased

approximately 40%, from 103 to 148 million ha,  and average global yields doubled, from  1.6 to 3.2

tons per ha (IRRI, 1985).n  Average yields higher than 5 tons per ha have already been obtained

in parts of the developed world (FAO,  1986a).  The  increase  in rice production has been due both

to the "Green Revolution" of the 1960s, which resulted in the development and dissemination of high-

yield  varieties of rice and an increase in fertih'zer  use, and to a significant expansion  of  land area

under cultivation.  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.



    Over 90% of global rice acreage and production occurs in Asia.  Five Asian countries, China,

India, Indonesia, Bangladesh, and Thailand, account  for 75% of global production and 73% of the

harvested area (IRRI, 1986; see Figures 4-15 and 4-16).  Rice fields contribute 60-170 Tg of methane
     20 Rice statistics are for rice grown in flooded fields, i.e., they do not include upland rice,
since methane emissions result only from flooded rice fields.

     21 Rough rice, also called paddy rice, is rice with the hull, or husk, attached.  The hull
contributes about 20% of the weight of rough rice.  The kernel remaining after the hull is
removed is brown rice.  Milling of brown rice, which removes the bran, followed by polishing,
results in white rice.

     22 Harvested area is the area under cultivation multiplied by  the number of crops per year.
For example, 1 ha that is triple-cropped is counted as 3 ha of harvested area.
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Policy Options for Stabilizing Global Climate - Review Draft
     Chapter IV
                                   FIGURE 4-15
                         ROUGH RICE PRODUCTION
                                        1984
                                     (Million Tons)
               Rest of World
                  (75.1)
        Vietnam
         (15.4)

       Japan
       (14.8)

       Burma
       (14.5)

     Thailand
      (19.2)

    Bangladesh
      (21.5)
             Indonesia
              (37.5)
Figure 4-15.  Distribution of the total rough rice production of 470 million tons.   Five Asian
countries, China, India, Indonesia, Bangladesh, and Thailand, accounted for approximately 75% of
the 1984 global rice production.  (Source:  IRRI, 1986.)
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Policy Options for Stabilizing Global Climate -- Review Draft
                                  Chapter IV
                                    FIGURE 4-16
                            RICE AREA HARVESTED
                                         1984
                                    (Million Hectacres)
             Rest of World
                (27.9)
   Burma
    (4.7)
  Vietnam
    (5.6)
    Thailand
      (9.7)
            Indonesia
              (9.7)
                        Bangladesh
                          (10.5)
                                                                          India
                                                                          (42.8)
                                                                  China
                                                                 (34.3)
Figure 4-16.  Distribution of the total harvested rice paddy area of 148 million ha.  Five Asian
countries, India, China, Bangladesh, Indonesia and Thailand accounted for 73% of the 1984 rice
acreage harvested.  (Source:  IRRI, 1986.)
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per year to the atmosphere, or approximately, 20% of the global flux (Cicerone and Oremland, 1989).




This  estimate  is  highly uncertain because  there have  been  no comprehensive rice-paddy flux




measurements in the major rice-producing countries in Asia.








Use of Nitrogenous Fertilizer








    Nitrous oxide is released through microbial processes in soils, both through denitrification and




nitrification.  Nitrogenous  fertilizer application enhances N2O flux rates, since some of the applied




fixed  N is converted to N2O and released to the atmosphere. The amount of N2O released depends




on  rainfall, temperature, the  type of fertilizer applied, mode of application, and soil conditions.








    Nitrogen is currently the  most abundant commercial fertilizer nutrient consumed worldwide.  Its




dominance in the fertilizer markets has increased steadily over the last few decades, from  28%  of




total  nutrients (nitrogen, phosphorus, and potassium)  in 1950 to 64% in 1981 (Herdt and Stangel,




1984).  Approximately 70.5 million tons N  was consumed worldwide  in 1984/1985 in the form  of




nitrogenous fertilizers (FAO,  1987).   A preliminary  estimate  suggests  that this produced N2O




emissions of 0.14-2.4 Tg N of the global source of approximately 8-22 Tg N per year (Fung et al.,



1988) although this estimate  is  highly uncertain.  Experiments to determine the fraction of fertilizer



nitrogen lost to the atmosphere as nitrous oxide have shown a wide range of  results (see Table  4-



11,  and Chapter II). Anhydrous ammonia, which requires sophisticated equipment for application (it



is injected under pressure into the soil),  is used exclusively in the United States. It comprises about



38% of the U.S. nitrogenous fertilizer consumption.  Urea, which is usually broadcast as pellets by




hand,  comprises about 69% and 58%  of  nitrogenous  fertilizer  consumption in  Asia  and South




America, respectively.
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    Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter IV








                                            TABLE 4-11




                             Nitrous Oxide Emissions by Fertilizer Type













Fertilizer Type                                Percent of Nitrogenous Fertilizer Evolved as N2O













Anhydrous Ammonia                                         0.5 to 6.84






Ammonium  Nitrate                                           0.04 to 1.71






Ammonium  Type                                             0.025 to 0.1






Urea                                                        0.067 to 0.5






Nitrate                                                       0.001 to 0.50












Source: Eichner, 1988; GalbaUy, 1985.
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Policy Options for Stabilizing Global Climate •• Review Draft                        Chapter IV








    Asia, Western Europe, Eastern Europe, and North America consume the  major share of the




world's nitrogenous fertilizers (collectively, about 85%).  China, the  Soviet Union, and the United



States together account for approximately one-half of the world's fertilizer consumption. The twelve




largest nitrogen fertilizer consumers, all of which consume more than one million tons N annually,




are (in decreasing order):  China, the United  States, the Soviet Union, India,  France, the United




Kingdom, West Germany, Canada, Indonesia, Poland, Mexico, and Italy (see Figure 4-17). Together,




these twelve  countries  account  for  approximately  74%  of the  annual nitrogenous  fertilizer




consumption.








    Although developed nations will probably increase their consumption of commercial fertilizer over




the next  few decades, most of the increased demand will  occur in developing nations.  The World




Bank estimates that over 90 million tons N will be consumed in 1997/98, a  30% increase over




consumption in 1986/87.  Almost 50%  of the growth between  1986/87 and 1997/98 is expected to




occur in  the developing nations  (World Bank, 1988).








IMPACT OF CLIMATIC CHANGE ON ANTHROPOGENIC EMISSIONS








    Climate change will affect human activity in a myriad of ways, and thus influence anthropogenic



emissions of greenhouse gases (see Chapter III for  a discussion of the biogeochemical feedbacks of



climate change). The impact of climatic change on land-use patterns and agricultural practices could



be particularly significant in influencing the trace gas emissions  from  these sources.  The magnitude



(or even the direction) of such changes have not been examined to date.  More  information  is




available regarding the impact of climatic change on electric  utilities  (Under et  al., 1987).  A brief
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Policy Options for Stabilizing Global Climate - Review Draft
                                 Chapter IV
                                   FIGURE 4-17
                NITROGEN FERTILIZER CONSUMPTION
                                 1984/1985

                            (Million Metric Tons Nitrogen)
                            Poland (1.2)
                      Indonesia (1.3)   »    Mexico (1.2)
                    Canada (1.3)
          West Germany (1.
      United Kingdom (1.6)
                       Rest of World (18.9)
          France (2.4)
     India (5.7)
 Soviet Union (10.9)
                                                                 China (13.7)
               United States (9.5)
Figure 4-17.  Distribution of the total nitrogenous fertilizer consumption of 70.5 million tons N.
China, the United States, and the  Soviet Union together accounted for just over 50% of the
1984/1985 global fertilizer consumption.  Currently, 5-35% of the total anthropogenic N?O emissions
are attributed to nitrogenous fertilizer consumption.  (Source:  FAO, 1987.)
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter IV








discussion of this subject is presented here as an illustration of some ways in which climatic change




can, in turn, influence trace gas emissions.








    Linder and Inglis (1988) estimate that annual electricity consumption increases by 0.5 to 2.7%/°C



for utilities  in the United States, depending on the local climate and the fraction of buildings with




electrical heating and air-conditioning equipment.   If climate change leads to increases in ownership




levels, then substantially greater sensitivities are possible (Linder et al., 1987). Currently, 37% of total




CO2 emissions from fossil fuels are produced by electric utilities and  this share is expected to increase




in the future (see Chapter V). Applying the U.S. average sensitivity of 1.0%/°C obtained by Linder




and Inglis (1988) to the rest of the world implies  a feedback on CO2 emissions of 0.4%/°C.   This




feedback would be offset to an extent that has not  been estimated by lower fuel  use for heating, but




as the penetration of air conditioning rises in developing countries  this feedback could increase.








    Climate change may affect the  electricity industry from the supply side as well.  When steam is




produced to generate electricity in  a power  plant,  either water (usually from  a  nearby reservoir or




river) or air is used as a coolant to condense the steam back into water and start the process over




again. Higher atmospheric temperatures will result in warming of  these coolants, and reduction in



the efficiency of the power plants.   This effect is not likely to be as significant  as others,  however,



since seasonal temperature changes are already much greater than the warming predicted for the next



century (Linder et al., 1987).








    More immediate  and acute effects of climate change on electric utilities are likely to occur  due




to reduced availability of water.  The drought of the summer of 1988 resulted in such low river  levels




in the U.S. Midwest, that some electric plants were forced to reduce  generation due to lack of




cooling water.  More frequent and severe  droughts would also result in  reduced hydropower for
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter IV








generation of  electricity.  (This  change would also affect  barge shipping, since many rivers would



become unnavigable, and result in increased trace  gas emissions from truck and rail transport.)








    Sea-level rise and lowered stream flows resulting from climate change would  also have adverse



effects on electric utilities.  Salinities in rivers and estuaries would increase, and stream chemistry



could change,  so that the water  may become too corrosive to be used as a coolant. A few power



plants in the United States use saltwater for cooling purposes,  so the technology  exists to adapt to



more saline coolants, although the conversion process is costly.








    These feedback  mechanisms are likely to have a smaller influence on future  warming than the



biogeochemical feedbacks discussed in Chapter III.  The impact of climatic change on anthropogenic



trace gas  emissions may nevertheless prove to be important and should be investigated further.
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter IV
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Mintzer, I.M.   1988.  Projecting Future Energy Demand in Industrialized  Countries:  An End-Use
Oriented Approach.  Prepared for U.S. EPA, Washington, D,C.  40+  pp.

OECD  (Organization for Economic  Cooperation and Development).   1985.   Tlie State of the
Environment 1985.   OECD, Paris.  271+ pp.

OECD (Organization for Economic Cooperation and Development).   1987.  Energy Statistics 1970-
1985, Volume I.  International  Energy Agency, OECD, Paris. 513+ pp.

Radian  Corporation.  1988.  Emissions and Cost Estimates for Globally Significant Anthropogenic
Combustion Sources of NOa N2O, CH, CO,  and CO2,  Prepared for U.S.  EPA, Research Triangle
Park.  136+ pp.

Ramanathan, V.  1987.  Observed  increases in greenhouse  gases  and predicted climatic changes.
Testimony to the United States Senate, Committee on  Energy and Natural  Resources. Washington,
D.C.  November 9,  1987.

Ramanathan, V.,  RJ. Cicerone, H.B.  Singh, and J.T. KiehL  1985.  Trace gas trends and  their
potential role in climate change.  Journal of  Geophysical Research  90:5547-5566.

Revelle, R.   1983.  Methane  hydrates in  continental  slope sediments and increasing atmospheric
carbon  dioxide.   In National  Research Council,  Changing Climate.  National  Academy Press,
Washington, D.C. 252-261.

Rotty, R.M.  1987.  A look at 1983 CO2 emissions from fossil fuels (with preliminary data for 1984).
Tellus 39B:203-208.

Rotty, R.M., and C.D. Masters. 1985. Carbon dioxide from fossil fuel combustion: Trends, resources,
and technological implications.  In Trabalka, J.R., ed.  Atmospheric Carbon Dioxide and the Global
Carbon  Cycle. U.S. DOE, Washington, D.C. 63-80.

Sathaye, J.A., A.N. Ketoff, L.J. Schipper,  and  S.M. Lele.   1988.   An End-Use  Approach  to
Development of Long-Term Energy Demand Scenarios for Developing  Countries.  Prepared for U.S.
EPA, Washington, D.C.  35 pp.

Seiler, W. 1984. Contribution  of biological processes to the global budget of CH4 in  the atmosphere.
In Klug, M.,  and C. Reddy, eds.  Current Perspectives in Micmbial Ecology.  American Society for
Microbiology, Washington, D.C.  468-477.

Seiler,  W., A. Holzapfel-Pschorn, R. Conrad, and D. Scharffe.  1984.  Methane emission from rice
paddies.  Journal of Atmospheric Chemistry 1:241-268.
DRAFT - DO NOT QUOTE OR CITE        IV-70                           February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter IV
Stevens, C.M., and A. Engelkemeir. 1988. Stable carbon isotopic composition of methane from some
natural and anthropogenic sources. Journal of Geophysical Research  93:725-733.

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International  Economic  and  Social Affairs, United Nations, New York.

United Nations.  1987.  1985 Energy Statistics Yearbook.  United Nations, New York.

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U.S. BOM (U.S. Bureau of  Mines).  Each year (1949-1986). Minerals Yearbook,  Volume I, Metals
and Minerals. U.S. Government Printing Office, Washington, D.C.

U.S. Bureau of the Census.  1987.  World Population Profile: 1987. Department of Commerce, U.S.
Bureau of the Census, Washington, D.C. 74 pp.

U.S. DOE (U.S. Department  of Energy).   1986.   International Energy Annual:   1985.  Energy
Information Administration,  U.S. DOE, Washington, D.C.

U.S. DOE (U.S. Department of Energy).  1987.  Annual Energy  Review 1986. Energy Information
Administration, U.S. DOE, Washington, D.C. 293 pp.

U.S. EPA (U.S. Environmental  Protection Agency).  1987.  Assessing the Risks of Trace Gases That
Can Modify the Stratosphere.  Office of Air  and Radiation, EPA, Washington, D.C.

U.S. EPA (U.S. Environmental  Protection Agency).  1988a.  Regulatory Impact Analysis: Protection
of Stratospheric Ozone. Office of Air and Radiation,  EPA, Washington, D.C.

U.S. EPA (U.S. Environmental  Protection  Agency).  1988b. How Industry is Reducing Dependence
on Ozone-Depleting Chemicals.  Office of Air and Radiation, EPA, Washington, D.C. 24 pp.

U.S. OTA (U.S. Office of Technology Assessment).  1984.  Wetlands, Their Use and Regulation. U.S.
Congress, Office of Technology  Assessment, Washington, D.C. OTA-0-206.  208 pp.

Wagner,  Richard H.  1971. Environment and Man. W.W. Norton & Company, Inc., New York.  491
pp.

Wolf, E.   1987. Raising agricultural productivity.  In Starke, L., ed. State of the World 1987. W.W.
Norton & Company, New York. 139-156.

World Bank.  1987.  World Development Report 1987. Oxford University Press, New York.  285 pp.
DRAFT - DO NOT QUOTE OR CITE       IV-71                          February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter IV
World Bank.  1988.  World Bank, FAO, UNIDO Fertilizer Working Group Nitrogen Supply, Demand
and Balances for 1986/87 to 1992/93.  Washington, D.C.

World Energy Conference.  1980.  Survey of Energy Resources  1980. Prepared for the llth World
Energy Conference, Munich, 8-12 September 1980, World Energy Conference, London. 352+ pp.

WMO (World Meteorological Organization).  1985.  Atmospheric Ozone  1985:  Assessment of Our
Understanding of the Processes  Controlling its Present Distribution and Change.  Volume 1.  WMO,
Geneva, 392+  pp.

Wuebbles, Donald J.  1983. Chlorocarbon  emissions scenarios:  Potential impact on stratospheric
ozone. Journal of Geophysical Research 88:1433-1443.

Zachariah, K.C., and M.T. Vu.  1988.  World Population Projections 1987-88 Edition. Johns Hopkins
University Press, Baltimore.  439 pp.
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                                    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

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 Landfills 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
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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V








FINDINGS








•     Decisions made in the  next  few decades, about  how  electricity  is  produced,  homes are




      constructed, and cities are laid out, for example, will  have an impact on the climate in 2100




      and beyond. While it is not  possible to predict the level of greenhouse gas emissions over this




      time period, it is possible to construct scenarios of  economic and technological development,




      and a reasonable range for resulting greenhouse gas emissions, atmospheric concentrations, and




      global temperature changes.  Global temperature change estimates provide an indicator for the



      rate and magnitude of climatic change.








•     Carbon dioxide emissions are  likely to grow by a factor  of 2 to 5 during the next century if




      stabilizing policies are not adopted, primarily due to expansion of global coal consumption.




      Options  are  available,  however, that could  stabilize  or reduce carbon dioxide emissions.




      Despite the Montreal Protocol to control CFCs, global emissions of these compounds could




      remain constant or even  increase significantly unless the agreement is strengthened.  Methane




      emissions could increase  by  60-100% during the next century unless  measures to control these



      emissions are taken.








•     Although per capita  emissions of greenhouse gases  are  currently very low in developing



      countries, their share of  global emissions will rise significantly in the future.








•     The  relative contribution of  carbon  dioxide  to  greenhouse  warming is likely  to  increase




      significantly in  the future.  Carbon dioxide  accounts  for  more than  70%  of the  increased



      commitment to global warming between 2000 and 2100 in all of the scenarios analyzed in this




      report.   This represents a significantly higher estimate of the role of CO2  compared  to  its
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      roughly 50% contribution to global  warming in the last few  decades, but is similar to the



      estimated contribution of CO2 to increases in the greenhouse effect over the last century.








•     If there is no policy response to the risk of climatic change carbon dioxide concentrations are




      likely to reach twice preindustrial levels sometime in the latter half of the 21st Century, but




      total greenhouse gas concentrations equivalent to this level may occur by 2030 or even earlier,




      and are likely to occur before 2050.








•     Even with modest  economic growth  and optimistic  assumptions regarding technical progress,




      the world could be committed to an equilibrium warming of 1-2°C by 2000, 2-4°C by 2050 and




      3-6°C by 2100  (assuming the  climate sensitivity to doubling CO2 is 2.0-4.0°C).  Realized




      warming would be about 2°C by 2050 and 3-4°C by 2100.








•     With rapid, but not unprecedented rates of economic growth,  the world could be committed




      to  an equilibrium warming of 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 2.0-4.0°C).  Realized warming would be 2-3°C by




      2050 and 4-6°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.








•     The  adoption of policies to limit emissions on a global basis, such as simultaneous pursuit of



      energy efficiency, non-fossil energy sources, reforestation, the elimination of CFCs, and other



      measures, could reduce the rate of warming during the 21st century by 60% or more.  Even




      under these assumptions, the Earth could ultimately warm  by 1-3°C  or more  relative to




      preindustrial times. Extremely aggressive policies to reduce emissions would be necessary to



      ensure that total warming is less than 2°C.
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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V








INTRODUCTION








      Although technological advances in industry and agriculture have provided extraordinary wealth




to a portion of the global population of over 5 billion people, these technologies have the potential




to dramatically alter the Earth's climate by causing changes in the composition of the atmosphere as




discussed in Chapters II through IV.  Global increases in the atmospheric concentrations of carbon




dioxide (CO2), nitrous oxide (N2O), methane (CH4), and chlorofluorocarbons (CFCs) are now well




documented (Chapter II), perhaps already committing the  Earth to significant  climatic change.




Myriad human activities are contributing to this situation, and continued population and economic




growth raises the prospect of accelerated greenhouse gas buildup in the future (Chapter  IV).








      If current trends hi trace-gas concentrations continue, climatic change could be noticeable to




the "man-in-the-street" during the 1990s, and the average surface temperature of the Earth could be



warmer than  at any  time in  recorded  human history by the second decade of  the 21st century




(Hansen  et al., 1988).  If the composition of the atmosphere were stabilized by 2000, on the other




hand, detectable climatic change is still possible,  but its magnitude would be limited and the rate of




change might be similar to natural fluctuations recorded in the geologic record (Hansen et al., 1988).








      What will happen in the future cannot be  predicted.  The  future evolution of the atmosphere



will depend largely on the paths of economic development and technological change, as well as on



the physical, chemical, and biological processes of the Earth-atmosphere system.  While we have no




control over this system once gases enter the atmosphere, economic and technological change will be




influenced by  policy choices  made at local,  national, and international levels.  This chapter  explores




some of  the paths the world might follow  in the decades ahead and provides an  indication of the




relative climatic consequences under these alternatives. After a discussion of the economic and social
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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V








factors that determine emissions,  four  scenarios of economic and technological  development are



presented.  These scenarios cannot capture all the possibilities,  of course; rather, they have been




developed in order to explore the probable climatic effects under significantly different, but plausible,




economic and technological conditions.   The climatic implications of these scenarios  are  analyzed




using an integrated framework described briefly in this chapter and in greater detail in Appendix A.




The  chapter concludes with the results of this analysis and a comparison of these results with other




studies.








APPROACH TO  ANALYZING FUTURE EMISSIONS








      The  scope  of  this  analysis must be global, and because of the long lags built into  both the




economic and  climatic  systems, this study must consider a time horizon of more than a century~we




chose 2100 as the ending year for the analysis.  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 electricity is produced,  homes are constructed, 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.








      The  vast difference between the energy demand projections of the early 1970s and what has



actually occurred  illustrates the danger inherent in simple trend extrapolations and, indeed, even  in




making predictions based on results obtained from more complex models.  Our approach then is not




to attempt  to predict the  future,  but to construct what we believe are logically coherent  scenarios  of
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Policy Options for Stabilizing Global Climate -  Review Draft                         Chapter V








possible paths of economic and technological development. An analytical framework is used to keep




track  of the assumptions, data, and relationships needed to define the scenarios.   Our intent is to




define the probable climatic effects under the various economic/social/technological alternatives and,




in so  doing, increase the likelihood that these consequences will be taken into account when  policy




decisions are  made.   If we believe  that  under a  wide variety  of  assumptions about  long-term




economic growth and technological change the world will face severe climate problems in the absence




of political or economic  forces arising from concerns over the greenhouse problem, then it will be




necessary to seriously examine  the options available  for reducing greenhouse gas emissions.








      The  difficulty we  face is that  projections  of  greenhouse gas  emissions  are very  uncertain,




because of uncertainties in world economic growth, future fuel prices (which demonstrably affect both



the intensities of their use and the substitution amongst alternative energy sources), future rates of




land clearing, and rates of technological change, among other factors. For example, both the vagaries




of the world oil market  in the medium term, as  well as true  uncertainties regarding the long-term




relationship between the  cost of producing fossil fuels and the cost of using those fuels in ways that




are relatively benign to the local environment, mean that at best we can only guess at future fossil




fuel use.








      Another avenue of analysis, however, yields information that can guide policy makers faced with



these  uncertainties. If we can construct scenarios of  future energy demand, land-clearing rates, CFC



production, etc., that are driven by  reasonable  assumptions about population, economic growth,




technologies, and energy prices,  then we can develop  a plausible range  of future greenhouse gas




emissions.   To accomplish this task we  must consider  the  structural factors  that determine the




quantities and  patterns of emissions of radiatively-important gases (i.e., those gases whose presence




in the atmosphere contribute to a greenhouse warming).
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      It is conceptually useful to distinguish between production activities and consumption activities.




Production emissions arise largely from the processing of bulk materials—steel from ore, plastics from




petroleum, cement  and glass from  limestone and silicate rock—which requires large amounts  of




energy per unit of industrial value added (i.e., the difference in value between an industry's products




and its inputs) and may also be associated with direct emissions of greenhouse gases.   For  example,



during cement making, CaCO3 is reformed to CaO + CO2, which  is released to the atmosphere, and




during the making of  plastic foams, CFCs are released.  Much  lower  emissions  per  unit of value




added are generally associated with fabrication and finishing.  Food  production leads to emissions of




methane and nitrous oxide as discussed in Chapter IV, as well as to emissions of CO2 and other




gases as  a result of the energy used on and,  even more, off the farm.  The large amount of energy




required to move  freight is also attributable  to  production activities.   Consumption  leads  to



greenhouse gas emissions as individuals use energy, primarily in pursuit of comfort (heating and air




conditioning) and mobility (automobile and  air  travel).   Other major end-uses for energy include



refrigeration, lighting, water heating, and cooking.








Production








      As societies develop over time, both the quantity and the structure of activities that influence



emissions change radically. For example,  energy use per unit of Gross National  Product  (GNP) has



declined  steadily and dramatically in industrialized countries, even  in periods of declining real energy



prices (Figure 5-1).  This decline is due  to a combination of two  factors.  First, improvements  in



production processes, which often save capital and labor as well as  energy, reduce the energy intensity




per ton of physical output.  For example,  in steel production modern energy recovery and process




technology make it possible to produce a ton of steel using only  13xl09 joules (13 GJ) of final
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Policy Options for Stabilizing Global Climate -- Review Draft
                                 Chapter V
                                     FIGURE 5-1
TOTAL U.S. ENERGY CONSUMPTION PER GNP DOLLAR
1900-1985
50
45
40
35
cc
0
5 30
03
O)
T—
J2 25
0
S 20
15
10
5
0
19
(Megajoules/1982 Dollar)
~Ji
-r KM
i \ A
\J\
—

—
—
—
i i i i




Vs^-~/~\
V
\


I ! I










00 1910 1920 1930 1940 1950 1960 1970 1980
YEAR

Sources: U.S. DOE, 1987a; U.S. Bureau of the Census, 1975.
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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V








energy, less than half of the current U.S. average.1   New processes under development in Sweden



(Hired and Plasma-Smelt) that integrate a number of operations have even lower energy requirements




and reduced overall  costs (Goldemberg et al., 1988).  Second, the bulk of value added by industry




tends to shift from basic materials processing to fabrication and finishing as a country's infrastructure




matures.  Strout (1985) suggests  that consumption of steel, cement, and other raw materials  begins




to decline  after income  surpasses  about $5000 (1985$)  per  capita (Figure 5-2).   These  shifts  in




technology and the mix of products generally increase the share of energy consumed as electricity,




but do not significantly increase  absolute electricity  intensity because efficiency in  electric end-uses




improves as well (Kahane, 1986).  Rapid economic  growth over the long term can be  expected  to




accelerate  the reduction  of industrial energy intensity  in wealthier countries  by promoting the




replacement of old plant and equipment with more efficient technology, as well  as by accelerating the




shift toward a less energy-intensive product mix.








    In industrialized societies services  such  as public and private administration,  health care, and




education,  are likely to grow faster than GNP, both because much of industry is being redefined  as




services and because much of our new wealth is being created by the development and transfer  of



information.   Heating, air conditioning, and lighting, which dominate energy  and  electricity  use  in




buildings today, will become less  energy-intensive (even as indoor environmental quality continues  to



rise) as more efficient  technology is adopted. At the same time, information technology is exerting



upward pressure  on electricity use per square foot  in office  buildings and schools.   The Business



Services sector depends more on electricity than does any other sector in the  economy, although it




still uses less electricity per unit of output than industry.  If there is a large increase in electricity use



in industrialized countries, it will come from a massive expansion of the service sector.
     1 1 GJ  = 0.948 million British Thermal Units (BTU).
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Policy Options for Stabilizing Global Climate -- Review Draft
                                                         Chapter V
                                FIGURE 5-2
    a.

    U

    a-
    u
    I
              CONSUMPTION OF BASIC MATERIALS

                   Consumption Per Dollar of GNP
            3000
                    4000
                 G.N.P. Per Capita (In 1983 Dollars)

                     5000           8000
         70.
 60-



 50-



 40-



 30-


 20-



 10-
                                                   11000
                                                     I
                                                          14000
                                                         x'\
                                                              .6
      Q.

   5   §
                                                              .4
                                                              _3
                                                              _1
                                                      i     i
                      Consumption Per Capita
         TOO.
600.



500-



400.



300-



200-


100-
                                                              -60
                                                              -50
  .40
                                                               70
                T     I      I     I     i     r    i      i     i
          1890  1900   1910  1920  1930   1940   1950  1960  1970  1980
                                   Year
 Source: Williams et al., 1987
        s
      Is
       U
                                                              ,30   g"
                                                                   2

                                                              .20


                                                               10
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V








    The  greatest potential  for large increases in production-related emissions lies in developing




countries.  As these countries expand their industrial infrastructure the  demand for basic materials




could skyrocket.  But developing countries have the opportunity to take  advantage of new processes




and materials that sharply reduce the energy required to  produce a given level of amenity.  As a




result, it  is unlikely that materials and energy intensity per capita in developing countries would reach




the levels of industrialized countries today, even as similar levels of per  capita income are achieved.




The  extent to which developing countries seize these  kinds  of opportunities  will strongly influence




future greenhouse gas emissions.








Consumption








    The  factors influencing  emissions arising from consumption are quite different from those that




affect production.  In developing  countries  energy use in consumer  products can be expected to




increase  rapidly as the number of households that can afford to acquire fans, televisions, refrigerators,




and automobiles grows.  Part of the reason that developing  country energy demand has historically



increased faster than it did  in OECD countries is that  developing-country households can afford to




purchase these products at  lower income levels  than  was  the  case for  industrialized-country




households.  The declining price-to-income ratios for many of the energy-intensive consumer goods



make this possible, with the consequence  that developing country energy consumption tends to grow



more rapidly than the  experience of the industrialized countries might indicate  At the same  time,



the efficiency of many of these products is increasing, so that  per capita energy consumption in



developing countries may not reach the levels of industrialized countries  today, even if these  income



levels are surpassed.
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V








    As a society becomes wealthier,  the penetration of energy-intensive  equipment saturates (there




are, for example, 600 cars for every 1000 people in the U.S. compared to 6 in Asian countries), and




changes in the efficiency  of the stock and how the stock is used  becomes  more  important than




changes in the levels  of ownership  alone.   For  example,  as  automobile ownership shifts from




corporate  to private hands the number of vehicles increases dramatically, but the miles driven per




vehicle declines. Consumers  rarely consider energy use in making major purchases, and many key




decisions that determine energy requirements are made by developers rather than the consumers who




pay the energy bills (Ruderman et al., 1987).  Increased amenity levels can often be achieved while




simultaneously reducing energy use and emissions (better insulated houses  are more comfortable




because they are less drafty and more efficient air conditioners are usually quieter), but more affluent




consumers are likely to choose powerful cars and spacious  dwellings, paying less  attention to  the




associated operating costs.  Further, because a very wide range of efficiency can be achieved with a




small impact on total costs over the life-cycle of the product (see Chapter VIII; von Hippie and Levi,




1983; Ruderman et al., 1987), consumers who are concerned about initial cost  are unlikely to choose




a product whose level of efficiency is optimal from a social perspective.








    The level  and pattern of  mobility may be the most  significant uncertainty in future energy use.



Will we spend our free time in our air-conditioned homes  watching rented movies on the VCR/TV,



or are we more likely  to drive to  the countryside to go for  a hike?   Not surprisingly, the pattern



of automobile use at present (roughly 1/3 of all passenger-kilometers driven in the U.S. are  to/from




work, 1/3  are for family business, and 1/3  are  hi pursuit  of leisure activities; OTA, 1988) is  a




function both  of distances  among  where we live,  work,  and relax, and of how  often we  choose to




move about.  Similarly, airline travel,  already dominated  in the U.S. by personal rather than business




travel,  is  more and  more  determined by how and where people want to spend  their free time.




Meanwhile in  cities like  Hong  Kong and Sao Paulo,  but  also  in New York and  Los Angeles,
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congestion is increasingly constraining automobile use. The  level of fuel economy and emissions




achieved by a particular automobile in practice is very sensitive to average speed, which is down to




about 15-20 miles per hour in LA. and under 10 miles per hour in New York City (Walsh, personal




communication).  How and whether cities solve these congestion problems-with roads, car pools,




buses, light rail, or all of the above-will have a large impact on both urban and global environmental




quality.








SCENARIOS FOR POLICY ANALYSIS








    In order to explore some of the implications of the relationships discussed briefly above, we have




constructed four scenarios of future patterns of economic and technological development starting with




alternative assumptions about the rate of economic growth and the adoption of policies that influence




climatic change (Table 5-1).  These  four scenarios  cannot capture all  the  possibilities of course;



rather, they allow us to explore likely climatic outcomes and  the impact of strategies for stabilizing




the atmosphere. The sensitivity of the results to a wide range of specific assumptions has been tested




and is discussed in Chapter VT.








    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 assumes more gradual change and




is called the Slowly Changing World (SCW).  That is, we have invented a future with relatively high



and robust economic growth, and one representing a more pessimistic view  of the evolution of the




world's  economies.  The  first world would likely illustrate the upper half of the potential  range of




future greenhouse gas  emissions, because  in general higher economic activity means a  higher total
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Policy Options for Stabilizing Global Climate -- Review Draft
                                     Chapter V"
                                       TABLE 5-1
                             Overview of Scenario Assumptions
            Slowly Changing World
             Rapidly Changing 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 Poulation 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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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V








energy use and emissions; conversely, the second world could serve as a useful guide to the lower



half of the range. In either case, our scenarios are first constructed as if there were no interventions




motivated by global climate  problems.








    In constructing  these two worlds/scenarios, we have borne two important ideas in mind.  First,




evidence is clear that with more rapid economic growth, energy efficiency improves more rapidly than



with slower growth  (Schurr, 1983).   This occurs because innovation proceeds more rapidly  and




because older, less efficient systems are more rapidly replaced with new technology.  History shows,



for example, that for almost every country, energy efficiency in industry increases with increasing




incomes, as  sophistication and scale win over brute force.  At the same time, higher incomes allow




people to spend more money on two key energy-intensive uses, space conditioning (heating and air




conditioning), and automobiles. Thus not all of the technological benefits of rapid economic growth




put the brakes on overall energy use.   But more rapid economic growth does  allow society to put




resources aside to improve the efficiency of both space comfort and personal transportation. Similar




patterns  can be expected in  other emissions sectors.








    Conversely,  slower  economic growth  retards innovation, in  part  because  both consumers  and




producers do not  see  bright  economic times  that  make  innovation  and  expansion into  new



technologies useful.  Comfort and mobility still manage  to increase as important drivers  of personal



energy demand, but at a slower rate. When these  two paths are compared, the  effect of more rapid



efficiency increases hi  the  higher growth world  is to narrow  the  difference in greenhouse  gas



emissions; that is, the likely difference between emissions in the Rapidly and Slowly Changing Worlds



is  less than  the differences hi Gross National  Product.  This result makes  our  scenarios somewhat




more robust than one might otherwise think.
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Policy Options for Stabilizing Global Climate --  Review Draft                          Chapter V








    The second idea concerns energy prices.  In a world of high and robust economic growth, which




we have assumed in the Rapidly Changing scenario, energy demand will likely increase,  and in the




medium term, so will energy prices. Yet if energy efficiency increases, then energy costs can increase




more rapidly than the rate of economic growth  and still not consume an increasing share  of national




wealth and income.  In other words, energy prices can rise without putting the brakes on economic




growth, as long as the price increases are gradual (CONAES, 1979).  But in a world  of sluggish




economic growth, energy demand rises more slowly, so that energy prices would rise very  little. This




idea is an additional  reason why we believe that energy efficiency  increases  more rapidly  in the high




growth scenario (RCW) than in the low growth scenario (SCW).








    With  these ideas in mind, we can build scenarios of world energy demand by end use  and region




as well as  levels of other  activities that emit  greenhouse  gases.   The  scenarios are  not exact




predictions, but serve as guides to the level of emissions associated with each  important  purpose or




end use in the worlds  we constructed.








    One benefit of using this approach is that we can compare  the  utilization efficiencies that we



assume for the No Response scenarios with those we believe  achievable if more than just market



forces were acting.  Two additional scenarios (referred to as the  "Stabilizing Policy"  scenarios) start



with the same economic and  demographic assumptions, but examine the effect that policies could



have  on global warming. These scenarios are called the Slowly Changing World with Stabilizing



Policies (SCWP) and the Rapidly Changing World with Stabilizing Policies (RCWP).








    Using our best information about technologies that could become available, or technologies that




are already available but not  taken up by the  market because of market  failures or other reasons,




we can reconstruct activity patterns that are still consistent with our overriding economic assumptions,
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Policy Options for Stabilizing Global Climate - Review Draft                          Chapter V








but produce much lower levels of greenhouse gas emissions.  Key changes are assumed in energy




efficiency, the energy supply mix,  land-clearing rates, and other  factors that might be changed by




government policies or other means.








    In other words, we keep the basic scenarios but, for example, manipulate important energy use




patterns  within these scenarios.  These  manipulations  can only  be carried  out  if greenhouse gas




emissions in each scenario  are constructed from the bottom up, i.e., by specifying the  level of each




major-emitting activity, as well as the emissions per unit of activity (e.g., total harvested rice paddy




area and methane emissions  per square meter of paddy).








    Thus the  scenarios we constructed  are a necessary step  towards illustrating both  ranges of




greenhouse gas emissions under two quite different assumptions about economic growth, and where




there is scope for reducing emissions through a variety of strategies. In the final analysis, our work




can be  turned around:   we  can consider the levels of emissions that  under  the best and worst




assumptions about how emissions are coupled to climatic change leave the world's climate tolerable.








Scenarios with Unimpeded Emissions  Growth








    In a "Slowly Changing  World" (SCW) we consider the possibility that  the recent experience of



modest economic 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 (Table 5-2). Per capita income  is



stagnant for some time in Africa and the Middle East as rapid population growth continues. Modest




increases in per capita income  occur elsewhere, and per capita growth rates increase slightly over




time in all developing countries as population growth rates slowly decline (Figure 5-3). The  share
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Policy Options for Stabilizing Global Climate - Review Draft
                                     Chapter V
                                        TABLE 5-2




                               Economic Growth Assumptions




                                     (percent per  year)
Slowly Changing World

US & OECD
USSR&
Eastern Europe
Centrally
Planned Asia
Other Developing
Countries
WorM
1965-1975
3.9

6.2
7.0
5.6
4.4
1975-1985
2.8

NA
7.8
3.2
2.91
1985-2025
1.7

2.2
3.2
2.7
2.0
2025-2100
1.0

1.6
2.5
2.1
1.5
Rapidly Changing World
1985-2025
2.7

4.3
5.1
4.5
3.4
2025-2100
IS

2.6
4.0
3.3
2.6
a Excludes USSR and Eastern Europe.
Source:  IMF, 1988.
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 Policy Options for Stabilizing Global Climate -- Review Draft
                                        Chapter V
      14000
      12000  —
                                  FIGURE 5-3


                      POPULATION BY REGION

                                   (Millions)

                            Slowly Changing World
            1985  2000
2025        2050

        YEAR
                                                2075
                                                                   Other Developing
                                                                    S & SE Asia
                                                                   China & CP Asia

                                                                   USSR & E.Europe
                                                                   Rest of OECD
                                                                   United States
2100
                            Rapidly Changing World
      1985   2000        2025       2050

                                 YEAR

Source: U.S. Bureau of the Census, 1987
                                                    2075
                                                                   Other Developing
                                                                   S & SE Asia
                                                                   China & CP Asia
                                                                   USSR & E,Europe
                                                                   Rest of OECD
                                                                   United States
                                   2100
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Policy Options for Stabilizing Global Climate --  Review Draft                         Chapter V



of global income going to the developing world does increase with time, but not dramatically.  The

population engaged in traditional agriculture  and shifting cultivation  continues  to increase, as  do

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.



    In industrialized countries economic growth is sluggish, although per capita income reaches about

$40,000  by  2100 in  the  OECD.  Because  of slack demand, real energy prices increase  slowly.

Correspondingly, existing capital stocks turn  over  slowly and production efficiency in agriculture and

industry improve at only a moderate rate.  The energy efficiency of buildings, vehicles, and consumer

products also improve at a slow rate.



    In a "Rapidly Changing World"  (RCW) we assume  that rapid economic  growth and structural

change occurs and that  little attention is given to the global environment. Per capita income rises

rapidly in most regions and consumer demand  for energy increases, putting upward pressure  on

energy prices.  On the other hand, there is  a high rate of innovation in industry, and  capital stocks

turn over rapidly, which leads to an accelerated reduction in  energy required per unit of industrial

output.  An increasing share of energy is consumed in  the form of electricity,  produced mostly from

coal.  The fraction of global economic output produced  in the developing world increases dramatically

as post-industrial structural change continues in the industrialized world.  As educational and income

levels rise,  population  growth  declines more rapidly than  in the  SCW scenario  (Figure 5-3).2

Deforestation continues at about current rates, spurred by land speculation and commercial logging,

despite reduced rates of population growth.  Energy efficiency is not much of a factor in consumer
     2 The sole exception is China, where aggressive policies are assumed in both cases.  Slightly
higher population growth is shown in the Rapidly Changing World scenario based on  the sources
of the alternative estimates  (see Appendix B).  This could be attributed to a relaxation  of the one-
child-per-family policy hi response to greater economic growth.
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Policy Options for Stabilizing Global  Climate -- Review Draft                         Chapter V








decisions,  as incomes increase faster than real energy prices.  Private vehicle ownership  increases




rapidly hi developing countries  while  air travel increases rapidly in wealthier ones.  Nonetheless,




significant reductions  in energy intensity occur with technological innovation and structural change.








Scenarios with Stabilizing Policies








    Two variants of the above scenarios explore the impact of policy choices aimed at reducing the




risk of global warming. 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 the 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 ail sectors succeed in substantially reducing energy  demand relative  to




the No  Response scenarios and  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




into 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 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 reverse  deforestation transforms the biosphere from a source to a sink



for carbon, and technological innovation and controls reduce agricultural, industrial, and  transportation



emissions.
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V








    While these general assumptions apply to both the SCWP and  RCWP cases, the degree and




speed of improvement are higher in  the Rapidly Changing variant because technological innovation




and capital  stock replacement  are greater hi this case.   The  policies  considered do not require




changes hi basic life styles.  For example, energy use in buildings is greatly reduced hi 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.  The technological  strategies and policy




options  available to achieve  the Stabilizing Policy scenarios are  discussed in detail in Chapters VII,




VIII, and IX.








ANALYTICAL FRAMEWORK








    To  make it possible to assess the implications of the  kinds of scenarios just described, we have



developed an  integrated  analytical framework to organize the data and  assumptions required  to




calculate emissions of radiatively and  chemically active gases, concentrations of greenhouse gases, and




the rate of climatic change.  This framework is  described very briefly here, and hi more detail hi




Appendix A.








    The analytical framework consists of four emissions modules and two concentration modules as



shown in Figure 5-4.  The  four emissions modules use input data, including scenario specifications



for population growth,  GNP, energy efficiency, etc., to estimate emissions of greenhouse gases for



nine regions of the globe (Figure 5-5). Emissions are calculated every 5 years from 1985 to 2025 and




then every 25 years through 2100. Emissions of the greenhouse gases  CO2, CH4, N2O, and a number




of CFCs are explicitly calculated within the framework.  Emissions of CO and NOX, 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.
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  Policy Options for Stabilizing Global Climate -- Review Draft
                                                   Chapter V
                                         FIGURE 5-4
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Policy Options for Stabilizing Global Climate - Review Draft
                                      Chapter V
                                        FIGURE 5-5
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V-24
February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V








The concentrations of other greenhouse  gases, such  as  water vapor and ozone, are calculated



implicitly or explicitly as a function  of the other gases.  The atmospheric composition and ocean




modules together estimate global concentrations of the greenhouse gases resulting from the projected




emissions, and increases  in global  temperatures resulting from  the calculated concentrations.  The




atmospheric trace gas concentrations and temperatures affect the emissions and concentration modules




in the next time period.








Energy  Module








    The energy module consists of  a Global Energy Supply Model (SUPPLY), which is based on the




energy-CO2  model of Edmofids  and Reilly (1983a, 1984),  and was developed by ICF Inc.  for this




study; a global energy end-use analysis (DEMAND), conducted by the World Resources Institute and



Lawrence Berkeley Laboratories; and combustion emission coefficients developed by Radian (1987).








    DEMAND estimates energy consumption based on specific assumptions about the level of energy




using activities and technical efficiency by region  and sector (industry, transportation, buildings).




Although this analysis provided more detail than most previous global studies, this level of aggregation




obscures many important variations,  particularly for developing  countries.  For example, per capita



incomes vary  from  $150 for  Bangladesh  to $7000 for  Singapore within the South and East Asia



region.  The share of energy used  by the manufacturing sector, vehicle ownership levels, and types



of fuels used (particularly the importance  of  biofuels), all vary  from one economy to another.  In




conducting the analysis we capture  some of this diversity by examining energy use by regions and by



income  groups within regions.   Detailed analysis was  performed for 2025 to  anchor the demand




estimates calculated for other years using SUPPLY.
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter V








    SUPPLY includes estimates of energy resources and costs by region and can balance supply and




demand using a highly-aggregated estimate of demand as a function of price and income.  Supply-




demand equilibration takes place within SUPPLY, which  projects fuel mix and final prices.  Trace-




gas emissions are calculated by allocating the final fuel consumption among the individual combustion




technologies for which emission coefficients are available. Additional emissions associated with fuel



production are also estimated.








Industry Module








    The industry module consists of a CFC model and a model for other non-combustion trace-gas




sources.  The CFC model was developed by EPA for use in assessing stratospheric  ozone depletion




(U.S. EPA, 1987).  It projects production and emissions of the following compounds: CFC-11, CFC-




12, HCFC-22, CFC-113, CC14, CH3CCl3, CH3C1, CH3Br, CF4, Halon 1211, and Halon 1301.  Other




industrial sources of trace gases include landfilling and cement production.  Emissions from these




activities are estimated as a simple function of population and per capita income.








Agriculture Module








    The  agricultural module uses the IIASA/IOWA Basic Linked  System, or BLS, (Frohberg, 1988)



to  forecast  fertilizer use and agricultural production.   These estimates are  used with emission



coefficients derived from the literature  to calculate emissions of N2O from fertilizer use, CH4 from




rice production,  CH4 from enteric fermentation in domestic animals, and emissions of CH4, N2O,




NOX, and CO from burning agricultural wastes.
 DRAFT - DO NOT QUOTE OR CITE        V-26                           February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter V








Land Use and Natural Source Module








    This module consists of components dealing with a number of land surface processes and other




natural  sources of trace gases.  The  most important of these is carbon dioxide released from land




use  change,  particularly   deforestation,  which   is  projected  with  the  Marine  Biological




Laboratory/Terrestrial Carbon Model, or MBL/TCM, (Houghton et al., 1983) based on assumptions




about future rates of land clearing. Other anthropogenic emissions related to land clearing, such as




a portion of  CO emissions from biomass burning and N2O emissions from land disturbance, are




scaled based  on  the CO2 emissions calculated by the MBL/TCM.  Natural emissions of CO,  CH4,




N2O, and NOX from sources such as  forest fires, wetlands, soils, oceans, and fresh water are based




on  values from  the literature, and generally  are held constant  throughout the projection period




(biogeochemical  feedbacks  can be assumed to alter these emissions,  see Chapter VI).








Ocean Module








    Ocean uptake  of heat  and CO2  are modeled using the  Box-Diffusion approach introduced by




Oeschger et al. (1975) as implemented for the GISS GCM (Hansen et al., 1984).  The ocean mixing




parameter for heat uptake is chosen  to reproduce, as closely as possible, the timescales obtained in



the time-dependent calculations with  the GISS GCM (Hansen et al., 1988).  Alternative values for



this parameter can be used to approximate the timescales of other approaches to estimating ocean



heat uptake (Chapter VI).  Alternative ocean model formulations for CO2, such as  the Advective-



Diffusive  Model (Bjorkstrom, 1979)   and  the Outcrop-Diffusion  Model  (Siegenthaler, 1983), are




included in the integrating framework and can be used for alternative estimates of CO2 uptake. Total




carbon uptake is calibrated using estimates of historical emissions of CO2 from fossil fuels  (Rotty,




1987a,b) and  deforestation (Houghton, 1988).  The atmospheric CO2 concentration is  assumed to be
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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V








285 ppm in 1800 and is forced to be equal to the values obtained at Mauna Loa for the period of




record (1960-1985).  The excess flux required to meet these conditions is calculated and held constant




in the future at the average value for 1975-1985.  Alternative assumptions are considered in Chapter



VI.








Atmospheric Composition and Temperature Module








    The atmospheric composition model was developed for this study (Prather, 1988).  It estimates




changes in the concentration of key atmospheric constituents and the global radiation balance based




on the emissions/uptake projected by the  other modules.   Perturbations to atmospheric chemistry




are incorporated based on first-order (and occasionally second-order) relationships derived from more




process-based  chemical models and observations.  The model is essentially zero-dimensional, but it




does  distinguish between  the northern  hemisphere,  southern  hemisphere,  troposphere,  and




stratosphere.  Global surface temperature  change is calculated based on the radiative forcing of the




greenhouse gases derived from Lacis et al. (1981)  and Ramanathan et al. (1985) coupled to heat




uptake by the  ocean model using a specified climate sensitivity parameter. This sensitivity parameter



is set to yield a global equilibrium temperature  increase of 2 or 4°C when the CO2 concentration



is doubled, reflecting a central estimate of the range of uncertainty; a broader range of possibilities



is examined in Chapter VI (see discussion in Chapter III).
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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V








Assumptions








Population Growth Rates








    The  population  estimates  for the Rapidly Changing  World scenario  were  developed from




Zachariah and Vu (1988) of the World Bank; for the Slowly Changing World scenario estimates were




taken from U.S. Bureau of the Census (1987) of the U.S. Bureau of the Census.  These two sources




agree quite  closely on the size  of the world's population through 2000, then diverge thereafter due




to different  assumptions on the rate at which the global population will stabilize.  Zachariah and Vu




(1988) assumes that  population growth rates in  developing countries will begin to decline markedly




after 2000, achieving a net reproduction rate  of unity hi every country by 2040.  (A net reproduction




rate of unity  indicates that  people  of child-bearing age have children at a  replacement rate; it




eventually leads to a stable population level.)  U.S. Bureau of the Census  (1987)  assume that global




population stability will occur at a later date, with developing countries  experiencing rapid population




growth rates until the  middle of the next century.








Economic Growth Rates








    The primary source for the economic growth rate estimates was the World Bank (1987).  In their



report, Gross National Product (GNP) forecasts were provided for the 1986-1995 period for several



different types of country groups.  Most countries could be classified into one of these three general



categories-low income, middle income, or industrialized.  In addition, the World Bank defined several




other more  select groups for which separate growth rates were estimated, including oil exporters,




exporters of manufactures,  highly-indebted countries, and sub-Saharan  Africa.  The low growth case




was used as  a starting point for this analysis because these estimates were more consistent with recent
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V








historical  trends and other forecasts.   For the RCW (SCW)  scenario these initial  values  were



generally increased (decreased) by one percentage point for developing and East Bloc countries and



one-half percentage  point for OECD countries to reflect the greater  uncertainty regarding future



growth in  developing and centrally-planned economies. The growth rates were applied for the period



1985-2000, and were generally reduced by one-half percentage point each 25-year period, beginning



in 2000,  to  reflect  structural change  and the  decline  hi  population growth  rates over  time.



Nonetheless,  GNP per capita  continues  to increase throughout the projection period,  although the



rate of growth is substantially lower in the Slowly Changing World scenario.








Oil Prices








    The oil prices used in this analysis were taken from U.S. DOE (1988), which supplied a range



of oil price forecasts.  The Middle Price forecast from DOE was  used for  the  Rapidly Changing



World scenario (by 2000 the world oil price is about $31/barrel in 1987  dollars), while the Low  Price



forecast was used for the Slowly Changing World scenario (oil prices by 2000  were about $25/barrel



in 1987  dollars). Since the DOE price forecasts did not extend beyond  2000, oil prices were derived



from  the SUPPLY model; in each scenario prices escalated about 0.8% annually  from 2000-2100.








Limitations








    This analytical framework attempts  to incorporate some  representation of the major processes



that will influence  the  rate and  magnitude of climatic  change 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:
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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V








    •       Economic growth rates are difficult to forecast.  Our  alternative assumptions may not



            adequately reflect the plausible range of possibilities.  In particular, we have assumed that




            aggregate economic growth rates will generally decline over time from the levels assumed




            for 1985-2000; this may not be the case.








    •       Economic linkages are not fully captured.   The economic analysis  uses  a partial-




            equilibrium framework, making it impossible to 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 in




            examining developing countries as it is unclear if they  will be able to obtain the capital




            investments needed to develop the energy supplies assumed in some of the scenarios.








    •       Technological changes are difficult to forecast.  Substantial improvements in the efficiency




            of energy using and 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.  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 cost-effectiveness, but no attempt has




            been made to rank the cost-effectiveness of each strategy or to estimate the government




            expenditures  or total costs  associated with the stabilizing strategies.
DRAFT - DO NOT QUOTE OR CITE        V-31                            February 16, 1989

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Policy Options for Stabilizing Global  Climate -- Review Draft                         Chapter V
    •      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 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.
DRAFT - DO NOT QUOTE OR CITE        V-32                            February 16, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V








SCENARIO RESULTS








    We have  estimated the implications of the four scenarios described above for emissions of




radiatively-important gases arising from energy production and  use, industrial processes, changes in




land use, and agricultural activities using the integrated analytical framework developed for this study.



The resulting changes in atmospheric composition and global climate are also estimated.








Energy Sector








    The single most important determinant of greenhouse gas emissions is the level of energy demand




and  the combination of sources that are used to supply that energy.








End-use Consumption








    Government  policies that  affect  demand  for energy are likely to be  the most  important




determinant of greenhouse gas emissions  in the near term.   Figures 5-6 and 5-7 illustrate global




end-use energy consumption by region for fuel and electricity, respectively.  Total end-use energy




consumption increases from 220xl018 joules (220 EJ)  in 1985 to 320 EJ in 2025 hi the  SCW versus



420 EJ in the RCW.3  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.



Extrapolating these trends to 2100 yields 430 EJ in the SCW and 780 EJ in the RCW scenarios, while




in the Stabilizing  Policy cases there is  20% and 35%  lower demand, respectively.
       1 EJ = 0.948 quadrillion BTU (Quad).
DRAFT - DO NOT QUOTE OR CITE        V-33                           February 16, 1989

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 Policy Options for Stabilizing Global Climate - Review Draft
Chapter V
                                        FIGURE 5-6

                  END-USE FUEL DEMAND BY REGION
                                        (Exajoules)
                      SCW                                       RCW
                                                                                   Other Developing
                                                                                   China & CP Am
                                                                                   USSR * CP Europe
                                                                                   Other OECO
                                                                                   United State!
      1985 2000    202S    2060    2075    2100
                                                  1986  2000     2025    2050    2075    2100
                     SCWP
                                                                  RCWP
                                                                                    Reduction From
                                                                                    No Response Scenario
                                                                                    Other Developing
                                                                                    China » CP Asia


                                                                                    USSR » CP Europe

                                                                                    Other OECD

                                                                                    United States
                                                  1985  2000
                                                             2026     2050
                                                                 VEAR
                                                                           2075     2100
DRAFT - DO NOT QUOTE OR CITE        V-34
                                                                          February 16, 1989

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 Policy Options for Stabilizing Global Climate -- Review Draft
                                   Chapter V
                                      FIGURE 5-7
           END-USE ELECTRICITY DEMAND BY REGION
                                      (Exajoules)
                 SCW                                     RCW
            2025    2050    2075    2100

                 SCWP
                                                                          Other Developing
                                                                          Chin* & CP Asia
                                                                          USSR 9i CP Europe

                                                                          Other OECD

                                                                          United States
1985 2000    2025    20SO    2075

               RCWP
                                                                           Reduction From
                                                                           No R«spons« Scenario
  1986  2000    2025    2060     2075    2100

                 VEAR
1S85  2000    202E    2050    2075    2100
               VEAR
DRAFT - DO NOT QUOTE OR CITE        V-35
                            February 16, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V








    In each scenario the growth in end-use demand is driven almost entirely by countries outside the




OECD (USSR, Eastern Europe, China, and other developing countries) as a result of higher rates




of economic and  population growth in these regions and from more rapid efficiency improvements




and the saturation of energy-intensive technologies in the OECD (e.g., steel production, automobile




transportation, and central heating).  Fuel use, in particular, is not expected to  grow significantly  in




the U.S. and  other  OECD countries as efficiency gains compensate for increases in floor space,




mobility, and production.  Electricity use is projected to grow much more rapidly than fuel use in all




cases, and  significant increases in OECD electricity demand are reflected in the RCW.








    It is important to note that both the SCW and RCW scenarios assume substantial efficiency gains




due to technological innovation and  market forces.  For  example, fuel  use per  square meter  of




residential  and commercial floor  space is assumed to fall  by 45-55%  in the United States and



Western Europe by 2025.  Similarly, fleet average fuel efficiency of U.S. cars and light trucks reaches




7.8 and 6.9 liters per 100 kilometers  (liters/100 km), or 30 and 34 miles per gallon (mpg), in the




SCW and RCW scenarios, respectively.  In the SCW, industrial energy use per  unit of GNP falls by




1.5-2%/yr  hi the  industrialized countries, in accordance with recent trends. This rate accelerates  to



2-3.5%/yr  in the  RCW, the highest rate of improvement being for the East Bloc  countries as they



have the highest initial industrial energy intensities.  Less optimistic assumptions about efficiency gains



in the No  Response scenarios would imply higher rates of associated climatic change and greater




relative  improvement ha the Stabilizing Policy scenarios.








    In developing countries the use of biofuels for  cooking is strongly influenced by urbanization




and the efficiency with which these fuels are used.  Urban populations have better access to modern




fuels  and thus a  smaller share of urban households will use traditional fuels.  There is substantial




scope for  improvement of the  efficiency of biomass  use.   Laboratory experiments in Asia with
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Policy Options for Stabilizing Global Climate -- Review Draft                          Chapter V









improved cookstoves suggest that it is possible to achieve efficiencies of up to 33% (compared with




current averages  of  8%).   However,  experience  from the  last  decade of  improved  cookstove




dissemination projects suggests that efficiencies are unlikely to exceed 20% in  the  field.  We assume




the dissemination of efficient cookstoves to almost all users of biomass only in the Stabilizing Policy




cases.  Thus, the average efficiency of biomass use is assumed to improve to  15-17% in each region




in these scenarios.  As a result of these efficiency improvements and because an  increasingly larger




share of the population  moves to  urban areas,  where there is  better access to  modern fuels, the




amount of biofuels consumption declines hi the household sector for each scenario.









    Important structural shifts underlie  the aggregate trends in  these scenarios.  Electricity's share




of end-use consumption more than  doubles in the RCW, from 16% in 1985 to 19% in 2025 and 34%




in 2100,  while  it grows  less dramatically hi  the  SCW, reaching 24% in 2100.  These trends are




accentuated hi  the  policy scenarios as there appears to be even greater room for reductions in fuel




use than in electricity use,  partly because electricity is  substituted for fuel hi some highly-efficient




applications.  In particular, electricity accounts  for 40%  of end-use consumption by  2100 in the




RCWP scenario because of  dramatic increases  in electricity use in developing  countries.   The




distribution of energy use among the industrial, transportation, and residential and commercial sectors




also shifts  significantly, as shown hi Figure 5-8.  In the Rapidly Changing World the share of end-




use energy going  to the  residential and  commercial sectors  declines continuously, while the share




going to industry  increases until the middle  of  the 21st Century and then declines.   This pattern




reflects the increasing importance of developing countries, which generally have low heating demands




and a greater percentage of modern energy devoted to  the Industrial sector.   This  occurs despite  a




decline hi  the share of commercial energy use, particularly electricity, going to the industrial sector




within developing  country regions.  As the most intense phase of industrialization is completed the




transportation sector begins to take off, its share  rising steadily after 2025.  In the SCW  scenario the




share of end-use energy  consumed hi the industrial sector grows less dramatically  and does not peak
DRAFT - DO NOT QUOTE OR CITE        V-37                            February 16, 1989

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  Policy Options for Stabilizing Global Climate •- Review Draft
                                                                        Chapter V
                                    FIGURE 5-8

       SHARE OF END-USE ENERGY DEMAND BY SECTOR
                                    (Percent)
                  SCW
     1985 2000    202S    2050    2075   2100
                 SCWP
                                                         RCW
                                                                         Residential ft

                                                                          Commercial
                                                                       !• Industrial
                                           1985 2000   2025    2050    207S    2100
                                                         RCWP
    19S5 2000
              202E   20EO
                  YEAH
                         2075   2100
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                                                               February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V








until 2075 as industrialization in developing countries is stretched out over a longer time-span and




dramatic increases in mobility  are delayed.   In  the  Stabilizing Policy scenarios  the growth  hi




transportation energy use is suppressed by much higher fuel efficiency and the share  of end-use




energy going to the residential and commercial sectors increases  toward the end of the next century.








Primary Energy Supply








    While  policies affecting demand will  have  the largest  impact  on  near-term  greenhouse gas




emissions, changes in the supply mix will also be very important over the long term.  Global primary




energy supply is shown by source for the four scenarios in Figures 5-9 and 5-10.  Growth in primary




energy production is substantially higher than growth  in end-use energy consumption  because  of




increased  requirements for  electricity and  synthetic  fuel production.  This is most  dramatic in the



RCW, where primary energy production 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 consumption.








    The use of synthetic fuels to supplement conventional oil and gas production becomes particularly




important after 2025, influencing both total requirements and the mix of sources (Figure 5-11).  In



the RCW conventional oil and gas production increases through  2050, then begins to decline due to



resource depletion (the share of primary  energy  supplied by oil and gas declines throughout the



projection period). As a result, synthetic fuels are increasingly relied on to supply liquid and gaseous



fuel requirements.  By 2050 19% of primary energy is used in synthetic fuels production,  and this




value increases to 40% by  2100.   In the  SCW heavy dependence on synthetic  fuels begins later




because conventional oil and gas resources are depleted  more  gradually.  Coal is  the dominant



feedstock for synfuel production in both of these scenarios.
DRAFT - DO NOT QUOTE OR CITE       V-39                           February 16, 1989

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 Policy Options for Stabilizing Global Climate -- Review Draft
Chapter V
                                  FIGURE 5-9

                 PRIMARY ENERGY SUPPLY BY TYPE
                                  (Exajoules)
                     SCW                                RCW
        H8S 2000    202S    2050   207S   2100
                    SCWP
                                                                         Reduction From
                                                                         No A*spons«
                                                                         Sc«n«no
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                                                              February 16, 1989

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 Policy Options for Stabilizing Global Climate •- Review Draft
                       Chapter V
                                  FIGURE 5-10

         SHARE OF PRIMARY ENERGY SUPPLY BY TYPE
                                   (Percent)
                 SCW                                     RCW
   1985  2000    2025    2050    2075    2100
                 SCWP
                                           1985  2000     2025    2050     2075    2100
           RCWP
   1385 2000
             202S    2060
                 VCAK
                          2075    2100
2000    2025    20EO    2075    2100
DRAFT - DO NOT QUOTE OR CITE       V-41
                February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
           Chapter V
                             FIGURE 5-11

    ENERGY DEMAND FOR SYNTHETIC FUEL PRODUCTION
                              (Exajoules)
                SCW                              RCW
               2050

               SCWP
               2060
               YEAR
                                                 20SO      2100
RCWP
20SO
VEAR
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      February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V



    The mix of primary energy  resources used to generate electricity is also crucial in determining

future greenhouse gas emissions.  While non-fossil energy sources (nuclear, solar, and hydro) increase

their absolute contribution to primary energy supply in all scenarios, in the absence of policies to limit

greenhouse  gas emissions,  it is  likely that future electricity production will be dominated by coal-

based technologies over the long term  (in  the near term,  current  gas  prices  make gas-based

combustion  turbine technology very attractive in many regions).  Thus in the RCW, demand for

electricity and  synfuel  production pushes  global  coal consumption up by more than a factor of 10

between 1985 and 2100.   Correspondingly, the  share of primary  energy supplied by coal increases

from  27% in 1985 to 40% in 2025 and 63% in 2100 (Figure 5-10).  The  same  forces are at work

in the SCW, but the results are less dramatic: Coal production increases by less than a factor of 5,

and its share of primary energy reaches just over 50% by  2100.



    In the Stabilizing Policy  scenarios natural gas is relied on  more heavily in the near term while

accelerated  research and development  and other incentives are assumed to make several non-fossil

electricity supply  technologies strongly  competitive over the long term.  In particular,  photovoltaics,

biomass-based  combustion  turbines, and advanced nuclear reactors appear to  be strong candidates

to make a large contribution to  future electricity production (these and other options are  discussed

in some detail  in Chapter  VII).  In the policy scenarios these technologies begin to supply energy

after 2000 and  become strongly  competitive by 2025. By 2050 they supply 60%  and 70%  of  global

electricity in the SCWP and RCWP scenarios, respectively.4  It is also assumed that research priorities

and other policies promote the use of biomass-derived fuels rather than coal-based synfuels. In fact,

in 2025 and 2050 total synfuel production is higher in the policy scenarios because biomass production

and conversion is assumed to become  competitive with imported oil and gas in many developing




    4  This value includes all of the electricity  generated  from gas,  reflecting the assumption that
a little over half of the  synthetic gas generated from biomass is actually both produced and consumed
in integrated gasifier-combustion turbine units.




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Policy Options for Stabilizing Global Climate •- Review Draft                         Chapter V








regions  starting around  2010 (Walter,  1988).   The  particular  mix among the  non-fossil  supply




technologies shown in Figure 5-10 is rather arbitrary, but the type of non-fossil technologies is of little




consequence to total greenhouse gas emissions.








Greenhouse Gas Emissions From Energy Production and Use








    The heavy reliance on coal in both the SCW and RCW scenarios leads to large increases in both




CO2 and CH4 emissions (see Figures 5-14 and 5-16 later in the chapter).  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 11.1




Pg C in 2100.5  Emissions reach more than twice this level in the RCW scenario: 10.3 and 24.4 Pg




C in 2025 and 2100, respectively.  This growth in emissions of 0.5 Pg C per decade in the SCW and




1.3 Pg C per decade in the RCW between 1985 and 2025 compares with average growth of 1.1 Pg




C per decade between 1950 and 1980. 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 CH4  total, respectively.








    The  combination of higher efficiency and greater reliance  on non-fossil fuels assumed in the



Stabilizing Policy scenarios serves to substantially curtail 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.
     5  1 petagram = 1015 grams.




     6 1 teragram =  1012 grams.
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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V
    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



NOX 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




NO., 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 technology in utility and industrial applications




after 2000, with developing countries following after 2025.








Comparison to Previous Studies








    Despite the  large range of outcomes illustrated by the four scenarios developed here, none  of




the global rates  of  change are unprecedented (Table 5-3).  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 0.0-1.3% per year with



significant declines only apparent hi 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 over coal.








    While we know of no previous attempts to develop  long-term scenarios for emissions of the full




set of gases discussed above based on explicit economic and technological assumptions, there have




been a number of previous studies that relate to many of the components examined here. Over the
DRAFT - DO NOT QUOTE OR CITE        V-45                           February 16, 1989

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Policy Options for Stabilizing Global Climate ~ Review Draft
                                     Chapter V
                                       TABLE 5-3

                                  Key Global Indicators
Parameter
*
GNP/capita
(1000 1988 $)
Primary Energy
(EJ)b

Fossil Fuel CO2

GNP/capita
(%/y)
Energy/GNP
(%/yr)

Fossil Fuel
COj/Energy
(%/yr)
Scenario"
SCW, SCWP
RCW, RCWP
SCW
RCW
SCWP
RCWP
SCW
RCW
SCWP
RCWP
SCW, SCWP
RCW, RCWP
SCW
RCW
SCWP
RCWP
SCW
RCW
SCWP
RCWP

1985
3.0
290

5.1


1985-2025
0.5
2.0
-1.1
-1.6
-1.3
-1.9
-0.1
0.0
-0.5
-1.3
Year
2025
3.7
6.7
430
580
380
520
7.2
10.3
5.5
5.5














2025-2100
0.9
2.3
-0.8
-1.4
-1.0
-1.8
-0.0
-0.0
-1.2
-1.1

2100
7.1
35.6
680
1410
550
940
11.1
24.4
3.2
4.3






    SCW  = Slowly Changing World; SCWP  = Slowly Changing World with Stabilizing Policies;
    RCW = Rapidly Changing World; RCWP = Rapidly Changing World with Stabilizing Policies.

    EJ =  exajoule  = 0.948 quadrillion BTUs

    Pg C  = petagrams of carbon; 1 petagram = 1015 grams.
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February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V


last decade there have been many studies of U.S. energy futures that can be compared to our U.S.
results.  In addition there have been several  recent studies of long-term global energy use and CO2
emissions  (Chapter I).  One recent study has developed "conventional wisdom reference scenarios"
for CH4, CO, NOX, and N2O  emissions related to major energy sources (Darmstadter et al, 1987).
This section compares the scenarios presented here to those developed in previous work.

                                                                                    •
    Since  the OPEC oil embargo focused the  world's  attention on energy in 1973  a  number  of
studies have examined the future of energy supply and demand in the United States.  Those analyses
contain  much more detail, particularly in the short term, than is possible in this study, as our focus
is necessarily global and long  term. Nonetheless, it is useful to compare the results of this study for
the U.S. with selected previous work.  The  National Energy Policy Plan (NEPP) prepared by the
Department of Energy (U.S.  DOE,  1987b)  and Energy for A  Sustainable World (ESW), an
international study supported by the World Resources Institute (Goldemberg et al., 1985,  1987, 1988)
are examples of two important recent studies.


    The results of these studies for the United States are summarized and compared  with our
scenarios in Tables 5-4 and 5-5.  A key point is that both of the No Response scenarios developed
here incorporate much lower growth in  energy use and CO2 emissions than is projected in the NEPP
reference and NEPP high-efficiency cases.  The largest discrepancies are in demand for electricity and
consumption  of  coal, although  all  energy sources other than gas  and all sectors  show higher
consumption in the NEPP projections.  The NEPP Reference  Case projects an increase of almost
40% in  U.S. CO2 emissions between 1985 and 2010, while  the High  Efficiency case produces about
a 20% increase.  By contrast,  the RCW scenario, which has GNP assumptions similar to those used
in NEPP,  estimates  about  a  10% increase  in  CO2  emissions, while the  SCW  scenario predicts
essentially flat emissions.  Had the NEPP reference case been adopted as one of our No Response
DRAFT - DO NOT QUOTE OR CITE        V-47                           February 16, 1989

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Policy Options for Stabilizing Global  Climate - Review Draft
                                         Chapter V
                                           TABLE 5-4

                        Comparison  of No Response Scenarios and NEPP
End-Use Energy Demand
(exaioules)
Sector
Residential/Commercial
Transport
Industry
Total



Fuel
Elec
Fuel
Elec
Fuel
Elec
Fuel
Elec

1985
11
6
21
0
18
3
50
9


SCW"
10
6
21
0
20
3
51
9
Primary
Estimated
RCW"
11
7
19
0
21
4
51
10
for 2010
NEPP-RC0
13
9
23
0
26
7
58
15

NEPP-HEd
19'
22
0
28e
51
13
Energy Consumption
(exaioules)
Estimated for 2010
Primary Energy
Coal
Oil
Gas
Other*
Total






1985
19
33
19
7
77
sew
18
32
19
8
77
RCW
22
29
22
8
82
NEPP-RC
38
35
19
18
110
NEPP-HE
31
33
17
16
97
Carbon Dioxide Emissions
(oetaarams of carbon)

CO2


1985
1.3

sew
1.3
Estimated
RCW
1.4
for 2010
NEPP-RC
1.8

NEPP-HE
1.6
1 Slowly Changing World scenario.
b Rapidly Changing World scenario.
c National Energy Policy Plan (NEPP) Reference Case (DOE, 1987b)
d National Energy Policy Plan (NEPP) High Efficiency Case (DOE,  1987b)
* Fuel + Electricity.  Separate values not given.
' Excludes dispersed wood.
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February 16,  1989

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Policy Options  for  Stabilizing Global Climate - Review Draft
                                           Chapter V
                                              TABLE 5-5

                        Comparison  of Stabilizing Policy Scenarios and ESW
End-Use Energy Demand
(exaioulesl
Sector
Residential/
Commercial
Transportation
Industry
Total
Primary Energy
Coal
Oil
Gas
Other
Total

Fuel
Elec
Fuel
Elec
Fuel
Elec
Fuel
Elect



1985
11
6
21
0
18
3
50
9

1985
19
33
19
7
77

SCWP"
8
'5
15
0
18
3
41
8
Primary

SCWP
11
24
18
12
65
Estimated
RCWP"
5
5
12
0
21
4
38
9
Energy Consumption
fexaioulesl
Estimated
RCWP
9
18
22
18
64
for 2020
ESW-S0
5
4
12
0
14
5
31
9

for 2020
ESW-S
11
13'
13e
14
52

ESW-Rd
5
4
14
0
15
5
34
9


ESW-R
13 •
14e
14e
14
56
Carbon Dioxide Emissions
Cpetaerams of carbon")

CO2


1985
1.3

SCWP
1.0
Estimated
RCWP
0.8
for 2020
ESW-S
0.7

ESW-R
0.8
* Slowly Changing World with Stabilizing Policies.
b Rapidly Changing World with Stabilizing Policies.
c Energy for a Sustainable World, Goldemberg et al., 1987, 1988. Assumes a 50% increase in per capita GNP from 1980 to
  2020.  Note that the SCWP case assumes a 50% increase from 1985 to 2020.
d Energy for a Sustainable World, Goldemberg et al., 1987, 1988. Assumes a 100% increase in per capita GNP from 1980 to
  2020.  Note that the RCWP case assumes  a 120% increase from 1985  to 2020.
* Given as Oil + Gas.  A 50% split is assumed  following the global supply scenario given by Goldemberg et al., 1987, 1988.
DRAFT -  DO NOT QUOTE OR CITE
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February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter V








scenarios, the  U.S. contribution to global emissions would have been substantially higher than what




we have  estimated in the SCW and RCW cases, and the difference between the No Response and




Stabilizing Policy cases would have been significantly greater.








      Comparing low emissions scenarios, U.S. energy use  is considerably higher in the Stabilizing




Policy cases than  in  those given in Energy for a Sustainable World.  The largest differences  in




consumption  are in  the  industrial sector, with  significant  differences  also in the residential and




commercial sectors in the slow-growth cases.  We assume that slower turnover  of the housing stock




leads to higher residential and commercial demand in the slow growth variant, whereas Goldemberg




et al. assume that income does not effect demand in this sector.  Despite higher energy consumption




in our scenario,  the  two  rapid-growth cases  have similar CO2 emissions due to lower consumption




of coal and heavier reliance on gas and non-fossil energy sources in the RCWP scenario compared




with the  ESW cases.








      The global energy  use and  CO2 emissions calculated for 2050 in the four scenarios developed




here are  compared to the bounding extrapolations discussed in Chapter IV and the results of selected



previous  studies  in Table 5-6.  The total energy use derived in our scenarios falls within the  lower



end  of the range given by trend extrapolation and previous  analyses. In those  studies  that included



a "Base  Case" that did not assume the  implementation of policies to reduce CO2 emissions,  the



estimated primary energy demand for the year  2050 ranges from 21 to 52 terawatts  (TW)7.  This



level of energy demand is approximately 2.2 to 5.5 times 1985 consumption levels of 9.4 TW.  The




Rapidly  Changing World scenario has total energy demand that  is quite similar to the Base Case




given by  a number of previous studies, including Edmonds and Reilly (1984), Seidel and  Keyes (1983),




and  World Energy Conference (1983). The Slowly Changing World scenario, with  almost  50% less
     7 1 terawatt  = 1012 watts = 31.54 EJ per year.
 DRAFT - DO NOT QUOTE OR CITE        V-50                           February 16, 1989

-------
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Policy Options for Stabilizing Global Climate ~ Review Draft                         Chapter V








total energy use in 2050, lies between the median and 25th percentile non-zero correlation scenario




of Edmonds et al. (1986) and Reilly et al. (1987). The estimated uncertainty bounds in the systematic




uncertainty analysis conducted by Edmonds  et  al.  are  not symmetric; their  median scenario has



significantly lower energy use and CO2 emissions than both the mean of their results and the result




of using the median values for all model parameters. The implication is that  very high energy use




scenarios may be much less probable  than is suggested by simply considering the range given by many




studies.








      Compared with the energy use estimates there is substantially less, though still considerable,




variation in the CO2 emissions estimates for 2050.  None of the studies cited in Table 5-6 approach




within a factor of four the result of exponentially extrapolating the pre-1973 rates of energy demand




growth,  assuming no change in the mix of sources. This reflects the constraint due to the finite size




of the fossil  fuel resource base  (Chapter  IV), which implies that very high growth in  energy




consumption would have to be accompanied by a significant  shift away from fossil fuels (but not




before atmospheric CO2 concentrations reached extraordinarily high levels).  Considering the full




range of values  for both energy use  and CO2 emissions represented in Tables 5-4 and  5-5,  it does



appear that, as intended, the Slowly Changing and Rapidly Changing  World scenarios represent very



different but not extreme possibilities.








      While  the general agreement found between this study and previous studies at the aggregate



level may be comforting, substantial disagreements are possible when the results are examined  more




closely.  For  example, the global increase in energy demand obtained  in the Rapidly Changing World




scenario is the result of almost level demand in OECD countries coupled with very vigorous demand




growth in developing countries. Other scenarios with nearly identical  global demand in 2050 may not




distinguish among regions  (e.g., Nordhaus and Yohe,  1983) or may have a more  even pattern of
DRAFT - DO NOT QUOTE OR CITE        V-52                           February 16, 1989

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Policy Options for Stabilizing Global  Climate -- Review Draft                         Chapter V








energy demand growth (e.g., Edmonds and Reilly, 1984).  Similarly, the GNP growth rate assumed




in the RCW scenario is higher than what was assumed by Seidel and Keyes (1983), but because




higher rates of technical efficiency improvements were assumed in the RCW case, energy demand




and CO2 emissions are almost identical in 2050.








      The results obtained in the policy scenarios developed here  are  most appropriately compared




with the results of Lovins et al. (1981), Rose et al. (1983), and Goldemberg et al. (1985, 1987, 1988).




These studies all emphasize the possibility that increased efficiency of energy use could limit energy




demand and CO2 emissions while allowing for sustainable economic  growth.  They conclude that




energy demand in 2050 could be held to between 5 and 16 TW by supplying energy services with




advanced cost-effective technology that is either available or nearly  commercial today.   In  these




scenarios efficiency improvements combined with shifts in energy supply allow CO2 emissions  to be




held at or below today's level, and Lovins et al. (1981) argue that it is technically feasible to reduce




fossil fuel CO2 emissions by about 80% over 50 years. The SCWP and RCWP scenarios have energy




consumption of 15 and 24 TW  respectively—similar to, but somewhat higher than, what previous




studies suggested was feasible. Part of this difference may be explained by the high rate of economic




growth assumed in the RCWP case and, particularly in comparison to Lovins et al., our assumption




that efficiency measures are not  adopted up to their technical potential. The CO2 emissions in the



policy scenarios are 10-20% below current  levels, again consistent with  some previous analyses.  This



result is obtained in different ways, however.  For example, the lowest CO2 scenario given by Rose



et al. assumes  substantially more contribution from non-fossil energy sources than do the policy




scenarios developed here, while the Goldemberg et al. high demand scenario has somewhat more oil



and gas and less coal  than does  the RCWP case in  2020.
DRAFT - DO NOT QUOTE OR CITE        V-53                            February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V








      The estimates of energy-related (fossil fuel and wood use) emissions of CH4, N2O, NOX, and



CO developed here are compared in Table 5-7 with results of a study by Darmstadter et al. (1987).



While the main purpose  of their study was to develop an historical database, reference values  for



future emissions are presented assuming either constant emission coefficients or coefficients declining



by 1% per year.  The emissions calculated with constant coefficients by Darmstadter et al. increase



much more  rapidly than those obtained in any of our scenarios.  These differences are not too



surprising given  our  explicit  assumptions regarding technological  change,  including  increasing



penetration of emission control technologies.  The largest discrepancy is for N2O, reflecting not only



our assumptions regarding  technical  change,  but also the much higher initial emission coefficient



adopted by Darmstadter  et al. based on Hao et al., 1987  (see Chapter II).  The initial estimate of



CO emissions given by Darmstadter et al.  is a factor of two lower than ours, probably due primarily



to their extrapolation of the U.S. emission coefficient  for gasoline to the rest of the world; we have



attempted to account for variations hi automobile emission control technology by region, with most



regions  having higher  average CO emissions than the U.S.  The closest agreement is  for  CH4,



probably because these emissions are directly proportional to the total  quantity  of coal and gas



produced, and are not  assumed to depend on production technology in our No Response scenarios.








      When  Darmstadter et  al. assume that all  emission  coefficients  decline by 1% per year, they



obtain estimates of NOX emissions that are similar to those occurring  in the RCW case and CH4



emissions estimates closer to those obtained in the RCWP  case;  their CO emissions estimate falls



between these two cases.  Overall, the RCWP case has significantly lower emissions than are obtained



by Darmstadter et al. even when they decrease their emission coefficients by 1%/y for a full century.



This is a result not  only of the assumptions regarding emission control technology,  but also because



our policy scenarios have substantially lower total energy demand and  a very different fuel mix.
DRAFT - DO NOT QUOTE OR CITE       V-54                           February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                     Chapter V
                                       TABLE 5-7



                Comparison of Energy-Related Trace-Gas Emissions Scenarios
Trace Gas
CH4
(Tg CH4)


N2O
(TgN)


NOX
(TgN)


CO
(TgC)


Scenario
RCW
RCWP
* Darmstadter et al.
** Darmstadter et al.
RCW
RCWP
* Darmstadter et al.
** Darmstadter et al.
RCW
RCWP
* Darmstadter et al.
** Darmstadter et al.
RCW
RCWP
* Darmstadter et al.
** Darmstadter et al.

1985/1980
68

63

1.1

4.3

25

20

202

108

Emissions of Trace
(teragrams')
2025/2030
141
73
192
117
2.1
1.2
16
9.5
43
27
62
37
318
122
292
177
Gases
2075/2080
301
74
432
131
3.8
1.4
57
21
77
21
184
68
651
82
614
226
 * Constant Emission Coefficients.



** Emission Coefficients Decline 1% Per Year.
DRAFT - DO NOT QUOTE OR CITE
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February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V








Industrial Processes








Halocarbon Emissions








      The most important industrial source of greenhouse gases not directly associated with energy




use is the production and release of CFCs and halons. In  both  the Slowly Changing World and




Rapidly Changing World scenarios, the Montreal Protocol as currently formulated is assumed to come




into force and apply throughout the projection period.  This agreement (described in Chapter IV,




VIII, and IX) calls on developed countries to reduce their emissions of certain CFCs 50% from 1986




levels by  1998,  and to freeze  the use  of halons.   Developing  countries with  low per capita




consumption, however, are allowed to increase the use of these compounds for up to 10 years~as a




result, emissions  of the controlled compounds could actually increase substantially, depending on the




number of countries that participate in the Protocol and the rate at which use increases in developing




and non-participating nations (Hoffman and Gibbs, 1988).  For the Slowly Changing World scenario




we adopt the assumptions of the Protocol scenario developed for the Regulatory Impact Assessment




of rules to implement the Montreal Protocol in the United States  (U.S. EPA, 1988).  Namely that,



in addition to the U.S., 94% (in  terms of current CFC consumption) of developed countries and 65%



of developing countries  participate in the agreement.  In this scenario the global  average annual



growth rate  in demand  for products and services that  would use CFCs, if they were available, is



approximately 4.0% from 1986 to 2000 and 2.5% from 2000 to 2050 (constant production is assumed



after 2050).  Growth in demand  is much higher in certain developing countries, particularly India and




China.  These growth rates are  not applied directly to CFC use in non-participating and developing




countries, however, because it is assumed that shifts in technology  development away from CFCs in
DRAFT - DO NOT QUOTE OR CITE        V-56                           February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V



the United States  and other participating countries "rechannels" demand in other countries as well.8

The Stabilizing Policy scenarios assume that the Montreal Protocol  is strengthened to produce a

complete phase-out of CFCs in participating countries by 2003.9



      Figure 5-12 shows the estimates for  emissions of CFC-11, -12,  and -13, and HCFC-22 under

the four scenarios. Emissions change more slowly than production because a significant portion of

each year's production is "banked" in air conditioners, refrigeration systems, and closed-cell foams.

The model keeps  track of the size of this bank and estimates the gradual release of these  CFCs.

In  the  Slowly  Changing World scenario emissions  are relatively constant  despite the Protocol's

requirement  of a  50% reduction in participating  industrialized countries.  After declining to 12%

below 1985 levels  between 1990 and 2020, emissions of CFC-11 begin to rise again, reaching 1985

levels by the  end of the projection period.  CFC-113 emissions also fall significantly for a few decades

but rise again toward 1985 levels.  CFC-12 emissions  never decline to 1985 levels: they decline by

11% between 1990 and 2015, reaching a few percent  above  1985 values, then they rise slowly, almost

reaching the  1990 peak levels towards the end  of the 21st Century.  Emissions of HCFC-22 grow

rapidly as a substitute for the fully-halogenated species that have the highest ozone-depletion potential.

Although HCFC-22 has  a shorter lifetime and  weaker radiative forcing  than the fully-halogenated

compounds,  it  could  make  a significant contribution  to global warming  during  the next century

because it is  not controlled by the Montreal Protocol.
    8 In the Slowly Changing World scenario this rechanneling effect is assumed to decrease growth
in CFC demand by 63% hi developed countries and by 50% in developing countries.  In the Rapidly
Changing  World scenario the baseline growth rates are  increased by a factor of 1.7 to reflect the
higher rate of economic growth, but participation is assumed to be 100% in developed countries and
75%  in developing countries, and  rechanneling  reduces  the baseline  growth  rates  by  63% in
developing countries (rechanneling does not affect  developed countries in this scenario as 100%
participation in the Protocol is assumed).

    '   Participation is assumed to be  100%  in  industrialized  countries  and 85%  in  developing
countries;  rechanneling reduces the baseline growth rates of non-participants by 75%.
DRAFT - DO NOT QUOTE OR CITE        V-57                           February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
           Chapter V
                               FIGURE 5-12

                   EMISSIONS OF MAJOR CFCs
                               (Gigagrams)
              CFC-11
CFC-113
400
300
O
200
100
0
19
500
400

300
i
o
0
200

100
0
19
-
RCW
•^"^'•-. .•'•'
•"V"0^ "
- \\
\\
\\
\\
J RCWP
SCWP
96 2000 2025 2050 2076 21
CFC-12
....
// ""-"'
•°x/'«""^"""''"«— — ^*"'***""~^ scw
''~\\
- \\
\\
\\
\\
\\
\\
\\ RCWP
1
SCWP
tC 2000 2025 2060 2075 2
400
300
200
100
0
00 19
3000
2500
2000


1500
1000
500
0
00 "
-
-
RCW

*••''-.
y ,_\> SCW
' \ \
" V
*" s RCWP
SCWP \ \
— — ^™"

85 2000 2025 2050 207E 21
HCFC-22
RCW
,' RCWP
1
•
.
1
1
SCW
/ „ - .. -T
* s*' — "" scwp
1 1 1 1
96 2000 2025 2050 2076 21
YEAR VEAR
 DRAFT - DO NOT QUOTE OR CITE      V-58
       February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V
      In the RCW, higher growth rates in developing countries more  than compensate for higher




participation and rechanneling rates.  CFC-11 emissions  decline by no more than 6% below 1985




levels, while CFC-12  and -113 each increase by more than 25%.   Emissions' of HCFC-22 grow




dramatically in this scenario.  In the SCWP case emissions of the fully-halogenated compounds  fall




by more than 80% from 1985 levels by 2025, which is sufficient to reverse the trend in concentrations




(see Figure 5-18). Emission reductions in  the RCWP case are not quite as large, but still lead to




declining concentrations after 2025.  HCFC-22 emissions are assumed to be the same in the  No




Response and Stabilizing  Policy cases; however, these emissions could  rise  as  a result of a CFC



phase-out if chemical substitution is the primary approach to eliminating CFCs, or fall, if product




substitution and process redesign are the major approaches (see Chapter VI).








Emissions From Landfills  and Cement








      Other important activities bcluded in the industrial category are CO2 emissions  from cement




making and CH4 emissions from landfills.  The growth of these activities 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- to four-



fold increase in  CO2 emissions from cement in the SCW and RCW scenarios, respectively, though



emissions remain less  than 0.5 Pg C/yr hi all cases. Landfill  CH4 emissions increase by more than



five-fold hi the RCW,  reaching 15%  of the total by 2100. In the  policy scenarios, advanced materials



are assumed to reduce the demand for cement (relative to the  No Response scenarios), while gas



recovery systems and  waste  reduction policies are assumed to limit emissions from landfills. The




result is that emissions from cement making  still  increase by  a factor of two to three, but CH4



emissions from landfills are held essentially constant.
DRAFT - DO NOT QUOTE OR CITE        V-59                           February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V
Changes in Land Use








      Deforestation  has been  a significant source  of CO2 to the atmosphere over the last  two




centuries, as clearly shown by the measurements of CO2 concentrations in Greenland and Antarctic




ice  (Chapter II).  If current trends continue, tropical forests could be completely eliminated during




the next century, adding significantly to the CO2 emissions from fossil fuels.   On the other hand,




efforts are underway to reverse deforestation;  if these efforts succeed, reforestation could become a




net sink for atmospheric CO2.  The total amount of carbon that can move in either direction between




the atmosphere and terrestrial ecosystems is ultimately constrained by the  area of forests available




for  deforestation or by the area of land  available to support new forests. The timing and magnitudes




of these fluxes  of  carbon are  determined by  the  timing  and  extent of  changes in  land  use as




influenced by local, national, and international policies.








      The causes of deforestation are  complex and  vary from country to  country.  This makes 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



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 and tropical deforestation increases from  11  million



hectares per year (Mha/yr) in 1980 to  34 Mha/yr in 2047, when ah1 the unprotected forests in Asia




are exhausted.  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
DRAFT - DO NOT QUOTE OR CITE        V-60                            February 16, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V




increase very gradually, reaching 15 Mha/yr in  2097, before the unprotected forest areas of Latin

America are exhausted.



      In the Stabilizing Policy scenarios it is assumed that a combination of policies succeed in

stopping deforestation by 2025, while more than 1000 Mha is reforested by 2100.  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 (Sanchez and Benites,

1987). In addition, 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 (sufficient  to  produce  the

biomass  energy  requirements  of  the RCWP  case with productivity  increases  expected  by  the

Department of Energy; Walter,  1988), the rest absorbs carbon at a much lower rate but reaches  a

higher level of average  biomass.



      The  carbon fluxes  associated  with  these  deforestation/reforestation  scenarios based  on

Houghton's  (1988) low  estimates of average biomass are shown  in Figure 5-13.  In the SCW 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.  Total deforestation emissions are almost the same in the RCW  but

they are spread out over a longer period. Emissions are close to 1 Pg C/yr from 2000 to 2100.  In

the Stabilizing Policy scenarios the biosphere becomes a sink for carbon by 2000 and reaches its peak
        Plantation products decay at various rates at the end of each rotation; no attempt to protect
this carbon from oxidation is assumed.
DRAFT - DO NOT QUOTE OR CITE        V-61                            February 16, 1989

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  Policy Options for Stabilizing Global Climate - Review Draft
                                                               Chapter V
                               FIGURE 5-13


             C02 EMISSIONS FROM DEFORESTATION



                      C02 From Deforestation

                            (Petagrams Carbon)
o
CD
CC.
<
O

-------
Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V








absorption of 0.7 Pg C/yr before 2025. The size of this sink declines gradually, after 2025 as forests



reach their maximum  size and extent.








Agricultural Activities








      The demand  for agricultural products is a direct function of population, but is not strongly




dependent on income levels.  Thus, there are only small  differences between the  scenarios  as  the




much higher incomes  largely offset the somewhat lower populations in the RCW compared with  the




SCW.  The land area used  for rice  production,  and thus  the methane emissions from this source,




bcreases by only about 50% by 2100 in both the SCW and RCW scenarios (production per hectare




increases by 80-100%). Meat production increases more, about 125%, as demand rises with income



to some extent.  Satisfying  the  demands of increasing populations  with a finite  amount of land




requires more intensive cultivation, and fertilizer use increases by 160% as  a result.








      In the  Stabilizing Policy scenarios we do not assume changes in the  demand for agricultural



commodities, but rather changes in technology and production methods that could reduce greenhouse




gas emissions per unit of product.  Although the  impact of specific  technologies cannot be estimated




at present, a  number  of techniques have been identified for reducing methane emissions associated



with rice and meat  production and nitrous  oxide emissions related to the use of fertilizer (Chapter



VII).  For simplicity, we have assumed that CH4 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 N2O per  unit of nitrogenous  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.   Based on these




assumptions, CH4 emissions from rice production  remain roughly constant until 2075, after which time
DRAFT - DO  NOT QUOTE OR CITE        V-63                           February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                          Chapter V








they fall by about 20%  as the global population stabilizes.    Methane emissions from enteric




fermentation increase by 40-50% by the middle of the 21st Century, before falling to within  about




30% of 1985 levels.  Similarly, N2O emissions from fertilizer increase from  0.3  to 0.5  Tg N/yr



between 1985 and 2025  and then remain roughly constant.








Total Emissions








      Total emissions of the key  radiatively-important  gases, the  aggregate  of  estimates of  the




emissions  from each  activity discussed above and of natural emissions,  are  shown in Table 5-8.




Overall, emissions increase gradually in the Slowly Changing World scenario and more  dramatically




in the Rapidly Changing  World, while in the policy scenarios emissions are reasonably stable  or



declining.








      In the No  Response  scenarios CO2 emissions are projected  to increase to a much greater




extent than emissions of the other gases.  This is because all net CO2 emissions are assumed  to be




anthropogenic in  origin  and because CO2 is a fundamental  product of all fossil-fuel combustion.  In



the SCW increased deforestation contributes significantly to near-term growth in CO2 emissions, and



total emissions are relatively constant between 2025 and 2075 as forests are exhausted (see Figure



5-14).  In the RCW CO2 emissions are dominated by the growth  in fossil-fuel combustion and total



emissions  increase by a factor of three by 2050.  In the Stabilizing Policy scenarios increased end-



use efficiency and reforestation contribute significantly to producing decreasing emissions in the near-




term, while decreased reliance on fossil fuels in conjunction with continued improvements in efficiency




allow for further  decreases later on.
DRAFT - DO NOT QUOTE OR CITE        V-64                            February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                    Chapter V
                                      TABLE 5-8




                                  Trace Gas Emissions

C02 (Pg C)
sew
RCW
SCWP
RCWP
N20 (Tg N)
sew
RCW
SCWP
RCWP
CH4 (Tg CH4)
sew
RCW
SCWP
RCWP
NOX (Tg N)
sew
RCW
SCWP
RCWP
CO (Tg C)
sew
RCW
SCWP
RCWP
CFC-11 (Gg)
sew
RCW
SCWP
RCWP
CFC-12 (Gg)
sew
RCW
SCWP
RCWP
CFC-22 (Gg)
sew
RCW
SCWP
RCWP
CFC-113 (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

278.3
278.3
278.3
278.3

363.8
363.8
363.8
363.8

73.8
73.8
73.8
73.8

150.5
150.5
150.5
150.5
2000
7.2
7.6
5.3
5.5

12.3
12.0
11.0
11.0

569.4
576.7
519.0
527.3
59.3
60.0
50.9
51.5

616.1
571.1
3823
382.3

292.0
314.2
261.8
293.1

401.1
471.8
354.2
433.3

192.1
247.4
192.1
247.4

119.3
171.8
93.2
148.7
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

248.1
267.3
47.3
60.2

379.7
4373
54.9
85.9

385.0
829.1
385.0
829.1

124.2
167.4
9.0
19.7
2050
9.8
16.6
4.2
5.1

13.7
14.0
10.6
10.8

739.9
879.6
534.0
567.2
70.8
91.7
40.9
46.1

858.7
894.6
2453
241.7

275.6
300.3
47.8
52.4

404.8
483.6
62.3
83.6

6863
2,194.2
6863
2,194.2

140.4
190.3
13.8
25.4
2075
9.7
22.2
3.7
4.8

12.2
15.0
10.6
10.8

773.3
1,025.4
522.2
542.6
65.2
108.2
41.0
44.8

594.7
1,049.9
250.6
242.0

280.4
306.3
50.3
54.2

410.3
492.3
65.7
86.4

785.7
2,744.9
785.7
2,744.9

140.4
190.3
13.8
25.4
2100
11.4
253
3.1
43

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

6033
1,207.1
250.9
244.9

280.8
306.8
50.6
54.3

410.8
493.1
66.0
86.6

794.8
2,795.6
794.8
2,795.6

140.4
190.3
13.8
25.4
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Policy Options for Stabilizing Global Climate -- Review Draft
                Chapter V
                                    FIGURE 5-14
                          C02 EMISSIONS BY  TYPE
                                  (Petagrams Carbon)
                  SCW
    RCW
     19*6 2000   2025   2060    2076    2100
                                                198S  2000    2026    2050    2075    2100
                  SCWP
  I
  5 10
     1MB 2000    202S    20CO    2071    2100

                   VEAR
   RCWP
                                                                               Commercial
                                                                                En.rgy
2026    2060    2076    2100
    YEAR
DRAFT - DO NOT QUOTE OR CITE       V-66
          February 16, 1989

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Policy Options for Stabilizing Global Climate — Review Draft                         Chapter V








      The  regional allocation of CO2 emissions shows a  rapid increase in the share attributed to




developing  countries in all scenarios (Figure 5-15).  This share increases from about 34% currently




to 57% by 2025 and levels  off at about 60% after 2050  in  the RCW.  The developing countries




account for a  little  over 50% of  CO2  emissions in the  SCW after 2025,  with the share  from




developing  countries  other  than  China decreasing after  2050  as  deforestation emissions decline.




China's share of emissions grows most dramatically in the Stabilizing Policy scenarios as deforestation




is  eliminated  in other developing  countries  and  China  becomes  by far the world's largest coal




consumer.  About  70% of global CO2 emissions are from China and other developing countries by



2100 in the RCWP scenario, but  only 42% in the SCWP.








      The  projected increases in CH4 emissions in the No Response scenarios are  a result of growth




in a variety of sources (see Figure 5-16).  In the SCW almost 60% of the increase  between 1985 and




2050 is due to enteric fermentation  and rice cultivation, whereas in the RCW these sources account




for less than 40% of the increase and the growth in emissions from fuel production  accounts for




another 40%.  In both of these scenarios emissions from landfills increase steadily, becoming  quite




significant by the end of the  period.   Reduced growth in each component is responsible for relatively



stable CH4 emissions in the policy scenarios.  The total increases gradually until  2025  and declines



after 2050,  falling below 1985 levels by the end of the period in both the SCWP and RCWP cases.








      The  regional contributions  to CH4 emissions do not shift as dramatically as for  CO2 (Figure



5-17). The  share of CH4 emissions from industrialized countries increases in the RCW scenario due



to rapid growth in coal production,  but this share declines  somewhat in the other  three scenarios.








      Total N2O emissions do not increase dramatically in any of the scenarios,  although we note



again that current,  and therefore future, emissions of N2O are highly uncertain. These uncertainties,
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Policy Options for Stabilizing Global Climate - Review Draft
                              Chapter V
                                     FIGURE 5-15


                   SHARE OF C02 EMISSIONS BY REGION
                                       (Percent)
                    SCW
    1?li 2000    2025     20(0    2075    2100
                  SCWP
                                                              RCW
                                                                               Other Developing
                                             20 p
                                                                               Chin* a> CP An.
                                                                               USSR & CP Europe
                                                                               Reit of OECD
                                                                               United St«t«<
                                              1*11 2000    2021     20CO    2075    2100
                                                             RCWP
                                                                               Other Developing
    U«5 2000
               202S     20SO
                    YEAR
                             2075    2100
                                                                               Chin* k CP Afl.
                                                                               USSR k CP Europe
1MS  2000
          2025    20CO
               VEAB
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                         February 16, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft
                  Chapter V
                  sew
                                       FIGURE 5-16

                          CH4  EMISSIONS BY TYPE
                                       (Teragrams)
RCW
                                                                                D*tor«jt*tion
                                                                                   iiom*« Burning
   1986  2000    2025    2060    2075    2100
                                               1986 2000    2026    2060    2076    2100
                  SCWP
                                                              RCWP
1000 -
                                                                                 Blomass Burning
                                                                                Fuel Production

                                                                                Ric« Production
                           2075     2100
                                                          2025    2050
                                                              VEAR
                                                                       2075    2100
DRAFT - DO NOT QUOTE OR CITE       V-69
           February 16, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
      Chapter V
                                    FIGURE 5-17

                SHARE OF CH4 EMISSIONS BY REGION
                                    (Petagrams)
                SCW                                     RCW
  1111  tooo    ioai    toio    aori    a 100
                                         100
                                          mi tooo    ion    ioio

                                                         RCWP
                                                                 1071
                                                                          Other Developing
                                                                          China * CP Alia
                                                                          USSR k CP Europe
                                                                          Other Developing
                                                                          China k CP Ana




                                                                          USSR k CP Europe



                                                                          Rest of OECD


                                                                          United States

                                                                          Oceans
                                                     2026     2050
                                                          YEAR
                                                                  2076    2100
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V








however, do not appear to have a large impact on the overall rate or magnitude of climatic change




in these  scenarios (see Chapter  VI).   In the  SCW, emissions related  to deforestation  and land-




clearing, as well as fertilizer-induced emissions, increase significantly through 2025, and total emissions




decline after 2050.  In the RCW, emissions growth is driven mainly by a four-fold increase in fossil-




fuel combustion emissions between 1985 and 2100. In the policy cases, total emissions decline slightly




due to the assumed decreases in  emissions per unit  of fertilizer use and fossil-fuel  combustion, and




because deforestation is halted.








      In the  No Response scenarios, emissions  of both NOX and  CO  increase significantly through




2050.  After 2050 declining emissions related to deforestation in the SCW compensate for continued




increases in energy-related emissions. The deforestation assumptions have a particularly large impact



on CO emissions as deforestation accounts for 40-50% of the total between 2000  and 2050  in this




case.  In the RCW, deforestation emissions are relatively uniform, and both CO and NOX emissions




continue  to increase through 2100. In the Stabilizing  Policy cases emission controls produce relatively




stable  NOX emissions and declining  CO  emissions from  fossil-fuel combustion sources,  while



deforestation emissions are eliminated.  The  result is moderate  decline in NO, emissions and more




than a 50% cut in CO emissions by 2050.








Atmospheric  Concentrations








      Figure 5-18 shows concentrations of greenhouse gases that result from the pattern of emissions



discussed above. Because  CO2, N2O, and CFCs are long-lived in the atmosphere,  their concentrations




respond gradually to changes in emissions.  CH4 has an intermediate lifetime (about 10 years), which




is itself affected by changes in  emissions of CO, NOX, CH4, and other trace gases, so its atmospheric



concentration responds rapidly to changes hi emissions.
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 Policy Options for Stabilizing Global Climate - Review Draft
                             Chapter V
                                     FIGURE 5-18
800
                     ATMOSPHERIC CONCENTRATIONS
                           (3.0 Degree Celsius Climate Sensitivity)
             CARBON DIOXIDE               .                   METHANE
               (Parti Par Million)
   1985  2000     2025     2060     2075     2100
                  YEAR
                                             5
                                             £ 3000
                                                             (Parti Par Billion)
 1185  2000     2025     2050     2075    2100
                YEAR
            NITROUS OXIDE
             (Partf Par Sllllon)
              2025     20*0
                 VIAR
                            2075    2100
      CHLOROFLUOROCARBONS
      (Parti Par Trillion of CFC-12 Equivalent)
                                             u 2000
                                             
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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V








      CO2 concentrations reach twice their preindustrial levels (570 ppm) in about 2080 in the Slowly



Changing World scenario;  this level is  reached  by  2055  in  the Rapidly  Changing World  and




concentrations more than three times preindustrial values are reached by 2100 (Figure 5-18).  Despite




declining CO2 emissions  in the policy scenarios, CO2 concentrations continue to increase throughout




the projection period, reaching almost 440 ppm in  the  SCWP case and 470 ppm in the RCWP case




by 2100.  It is interesting to note  that the fraction of  total CO2 emissions during the 21st  Century




that remain in the atmosphere in 2100 is 46% in the RCW case  and 39% in the RCWP case, so that




emission reductions have a more than linear impact on concentrations.








      CH4 concentrations increase by almost a factor  of 2 in the SCW and a factor of 2.6 in the




RCW, with the most rapid growth  occurring between 1985 and 2050 (Figure 5-18). Interestingly, the




2050 concentration obtained in the SCW is similar to the result of linearly extrapolating the currently




observed growth rate of 1% per year, whereas the RCW value is  close to an exponential extrapolation




of current growth; the 2100 values lie substantially below a continuation of such extrapolations for




another 50 years. In the  policy cases CH4  concentrations increase by 13-18% between 1985 and 2025,




after which they level off and decline to roughly 1985 levels by 2100.  CH4 concentrations are  affected




by temperature feedbacks on atmospheric chemistry: Increasing the climate sensitivity of the model




from 2.0°C to 4.0°C reduces concentrations by 100 ppb in the SCWP  and 210 ppb in the RCW.








      By contrast with methane, N2O concentrations increase gradually in all the scenarios as a result



of the current imbalance between sources and sinks (Figure 5-18).  The  concentration increase is



about 80 ppb in the SCW and 100 ppb  in the RCW compared with 50 ppb in the Stabilizing Policy



cases.  Thus, the policy assumptions reduce the .concentration growth  by 40-50%.
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V








      CFC concentrations increase dramatically in the No Response scenarios despite the assumption




that  at least  65% of developing countries and 95%  of industrialized countries  participate in the




Montreal Protocol (Figure 5-18).  The total concentration of CFCs weighted by their contribution  to




the greenhouse  effect increases  by a factor of 4.2  and  6.5  in the SCW  and RCW scenarios,



respectively.  On the other hand, the phase-out assumed in the policy cases does stabilize  CFC




concentrations (other than HCFC-22) by 2025, but their total greenhouse forcing still increases by




1.5-2.4 times  over current levels.








      It is interesting to compare the concentration changes calculated here, on the basis of explicit




assumptions linking emissions with activities, to recent studies that have made less formal estimates




based primarily on current trends in concentrations and/or emissions (Table 5-9).  Our No Response




estimates of future concentrations are in good agreement with those of Ramanathan et al. (1985) for




2030 and Dickinson and Cicerone (1986) for 2050. 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.  In addition, our 2030 estimates of N2O concentrations are somewhat below the




lower end of the  range  given  by Ramanathan et  al., although they fall within  the  lower end  of



Dickinson and Cicerone's range for 2050. The differences between the SCW and RCW scenarios are



significantly less than the ranges suggested by these authors for all the compounds listed in Table  5-



9~at  least partially because  the only differences between  the SCW and  RCW scenarios are



assumptions about activity levels and technology, whereas the estimated ranges from the literature also



consider  uncertainties in current sources,  atmospheric  chemistry,  and  ocean carbon uptake




(uncertainties in these factors are considered in Chapter VI). Also,  the Slowly Changing World and



Rapidly  Changing  World scenarios  are  not intended to  completely bound future possibilities;




significant reductions in emissions per unit of GNP are built into the No Response scenarios-if this
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    Policy Options for Stabilizing Global Climate -- Review Draft
                                      Chapter V
                                           TABLE 5-9

               Comparison of Estimates of Trace-Gas Concentrations in 2030 and 2050
Concentrations in
Trace-Gas
C02 (ppm)
CH4 (ppm)
Trop-O3 (%)
N20 (ppb)
CFC-11 (ppb)
CFC-12 (ppb)
HCFC-22 (ppb)
Ramanathan
et al. (1985)
450
2.3(1.8-3.3)
12.5
375(350-450)
1.1(0.5-2.0)
1.8(0.9-3.5)
0.9(0.4-1.9)

GISS
A B
443 427
3.5 2.5
* 0
381 352
2.3 0.8
3.9 1.4



C
368
1.9
0
314
0.2
0.5

sew
440
2.5
19
340
0.5
1.0
0.4
Concentrations in
Trace-Gas
C02 (ppm)
CH4 (ppm)
Trop-C-3 (%)
N20 (ppb)
CFC-11 (ppb)
CFC-12 (ppb)
HCFC-22 (ppb)
Dickinson &
Cicerone (1985)
400-600
2.1-4.0
15-50
350-450
0.7-3.0
2.0-4.8


GISS
A B
513 465
4.7 2.7
* 0
480 376
4.2 1.0
7.3 1.8



C
368
1.9
0
314
0.2
0.4

sew
490
2.8
23
360
1.2
1.2
0.6
2030
RCW
450
2.6
18
340
0.5
1.1
0.7
2050
RCW
540
3.1
26
360
1.4
1.4
1.7

SCWP
400
1.8
-1
330
0.3
0.7
0.3

SCWP
410
1.8
-2
330
0.3
0.6
0.5

RCWP
400
1.9
-1
330
0.4
0.8
0.6

RCWP
420
1.9
0
340
0.3
0.7
1.6
* In this scenario the effect of O3 and other trace gas changes is approximated by doubling the radiative forcing
contributed by CFC-11 and CFC-12.
    DRAFT - DO NOT QUOTE OR CITE
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V








fails to materialize, and/or if economic growth is more rapid than assumed here, concentrations of




a number of greenhouse gases could be significantly higher than is estimated in these scenarios.








Global Temperature  Increases








      Evaluating the  consequences of alternative climate change scenarios is beyond the scope of this




report (a variety of potential effects are examined in the companion report Potential Effects of Global




Climate Change on the United States; Smith  and Tirpak,  1988), but an  indicator of the relative




magnitude of change is needed as  a basis for comparing the scenarios considered here. Analysts of




trace-gas emissions have often emphasized the date at which carbon dioxide concentrations (or the




equivalent combination of trace  gases) can be expected to reach twice  their  pre-industrial level of




2xCO2.  In the absence of policies  to reduce emissions, however, climate change is potentially open-



ended.  Atmospheric composition and climate would continue to change after the 2xCO2 level were




reached and the ecological and social consequences may depend as much on what happens after CO2




doubles (if it  does)  as  on when this benchmark  occurs.   More relevant to ecological and social




systems are the average and maximum rate  of climatic change.  In order to compare scenarios, we



therefore focus on the average rate at which global temperature may increase during the next century



as well as the  maximum rate of change. We emphasize that these parameters are only indicators of



global change;  changes at the regional level  will  vary  in  both magnitude and tuning and changes in



precipitation may be as  important as changes in  temperature.  Nonetheless, the global quantities



calculated here can be used to compare the scenarios presented here among themselves  and with




results of more detailed climate  models.








      The changes in concentrations  shown in Figure 5-18 produce the estimated global temperature




changes shown in Figure 5-19 for  a range of climate  sensitivity (2.0-4.0°C  equilibrium increase in
DRAFT - DO NOT QUOTE OR CITE        V-76                           February 16, 1989

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 Policy Options for Stabilizing Global Climate - Review Draft
                                   Chapter V
                                    FIGURE 5-19

                 REALIZED AND EQUILIBRIUM  WARMING
                     (Degrees Celsius; 2.0 - 4.0 Degree Climate Sensitivity)
           REALIZED WARMING                           EQUILIBRIUM WARMING
        Slowly Changing Scenarios
                       SCWP
  19BS  2000     2026     2060     2075     2100

           REALIZED WARMING
        Rapidly Changing Scenarios
              Slowly Changing Scenarios
        1385  2000    202E    2050    2075     2100

               EQUILIBRIUM WARMING
  1385  2000
                           2075    2100
              Rapidly Changing Scenarios
                                              1385  2000
                                                         2025    2050
                                                              YEAR
                                                                       2075    2100
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter V








global temperature from doubling the atmospheric concentration of CO2; see Chapter III).  Both the



"equilibrium wanning commitment" and the "realized warming" are presented as a function of time.



The  equilibrium warming commitment for any  given year is the temperature  increase that  would



occur in equilibrium if the atmospheric composition was fixed in that year. Because the oceans have



a large heat capacity the temperature change realized hi the atmosphere lags considerably behind the



equilibrium level. Realized warming has been estimated with a simple model of ocean heat uptake



as discussed hi Chapter III.  Because the response of the climate system to changes in greenhouse



gas concentrations is quite uncertain we also consider a range of "climate  sensitivities".   Climate



sensitivity is defined as the equilibrium warming commitment due to doubling the concentration of



carbon dioxide from preindustrial levels. Given a particular emissions scenario and climate sensitivity,



the realized warming is much more uncertain than the equilibrium wanning commitment because the



effective  heat storage capacity  of the ocean is not known.  On the other hand, because the amount



of unrealized  warming increases  with increasing climate sensitivity, for a given scenario realized



warming depends less on climate  sensitivity than does warming commitment.








      Both the SCW and RCW scenarios lead to substantial global warming.  In the SCW, estimated



realized warming increases  1.0-1.5°C  between  2000 and 2050, and 2-3°C between 2000  and 2100



(Figure 5-19).   The maximum decadal rate of change associated with this scenario is  0.2-0.3°C



sometime in the middle  of the next century.   The  total  equilibrium warming  commitment is



substantially higher, reaching 3-6°C by 2100 relative to preindustrial levels. The equilibrium warming



commitment equivalent to doubling the concentration of CO2 from preindustrial levels is reached by



about 2040 in the SCW scenario.








      The rate of change during the next century would be more than 50% greater in the RCW



scenario, which shows a global temperature increase from 2000 of 1.2-1.9°C by 2050 and 3-5°C by
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V



2100 (Figure 5-19).  In this case the maximum rate of change is 0.4-0.6°C per decade, which occurs

sometime between 2070 and 2100. The equilibrium warming commitment is 5-10°C by 2100 in this

scenario  and the 2xCO2 equivalent level is reached by about 2030.11



      By contrast, the rate of climatic change in the  Stabilizing Policy scenarios would be less than

1.6°C per century. 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.

The maximum rate of change in these  scenarios is less than 03°C per decade and occurs before 2010,

largely as a result of warming to which the world may already be committed.  (Indeed, the 0.3°C per

decade figure, obtained assuming a climate  sensitivity of 4°C, occurs at the very beginning of the

simulation and may be  an artifact of how the model is initialized.)   In these cases the additional

commitment to warming is greater between  2000  and 2050 than it is between 2050  and 2100:  0.3-

0.9°C versus 0.1-0.4°C.  Total equilibrium warming commitment reaches 1.4-2.8°C in the SCWP and

1.7-3.3°C in the RCWP.   While not without some risk, the rate of change represented  by the

Stabilizing Policy scenarios would give societies and ecosystems much more time to adapt to climatic

change than would be the case in the No  Response scenarios.



      Carbon  dioxide accounts for  more  than 65%  of increased commitments to global warming

between  2000 and 2100 in all of the scenarios analyzed in this report (Figure 5-20).  This represents

a significantly higher estimate of the role of  CO2 compared to roughly 50% in the last few decades

and in  Ramanathan et  al.'s scenario for 2030.  Much of this difference is due to  smaller increases

in CFCs  in our scenarios due to our  assumption  that the Montreal Protocol comes into force.  In

addition,  growth in emissions of CH4 and N2O is projected to be slower than that of CO2, particularly
    11  Estimates  of  equilibrium warming commitments greater than 6°C represent  extrapolations
beyond the range  tested in most climate models, and this warming may not be fully realized because
the strength of some positive feedback mechanisms may decline as the Earth warms.
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 Policy Options for Stabilizing Global Climate -- Review Draft
                                                                 Chapter V
                                FIGURE 5-20
                   RELATIVE CONTRIBUTION TO
                         WARMING BY 2100
                                (Percent)
       SLOWLY CHANGING WORLD

      66'-
                               4%
                           12%
            13%
       SLOWLY CHANGING WORLD
            WITH POLICY
     73%
                             10%
                         6%
                   11%
           RAPIDLY CHANGING WORLD

         68%,,
                                                                     4%
                                12%
                     12%

            RAPIDLY CHANGING WORLD
                 WITH POLICY
                                           71%
                                                                     0.3V.I
                                                                    13%
                                                       11%
               Carbon Dioxide

               Methane
   Nitrous Oxide
                                     CFCs
                                                              5%
                          Ozone
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February 16, 1989

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Policy Options for Stabilizing Global Climate -  Review Draft                        Chapter V



after 2030.  The role of CO2 is greatest in  the  policy scenarios because our  assumptions lead  to

relatively stable concentrations of CH4 and tropospheric ozone, while  CO2 concentrations  continue

to increase gradually.



Comparison with General Circulation Model Results



      Hansen et al.  (1988) analyzed three transient trace-gas scenarios using the GISS GCM.  The

GISS A scenario, based on exponentially extrapolating current greenhouse gas trends, most closely

resembles our RCW with 4.0°C climate sensitivity (the climate sensitivity of the GISS GCM is 4.2°C).

Indeed, both the equilibrium and realized global  warming in these cases are within 0.1°C in 2025.12

By 2050 the continuation of exponential  growth in trace-gas concentrations in the GISS A scenario

leads to an equilibrium warming commitment  that is  about 40% higher than  in the RCW, with a

corresponding realized warming of 3.4 versus 2.8°C (all references to realized warming -in the  GISS

scenarios are based on 5-year running means, Figure 3b in Hansen et al., 1988a).  By 2060, the end

of the GISS simulation, the realized warming in the GISS A scenario is 4.2°C compared with  3.3°C

in the RCW.  The  GISS B scenario, which is based on linearly increasing trace-gas concentrations

at current rates, is most similar to the RCWP case (with 4.0°C climate  sensitivity). These two cases

have very similar equilibrium  warming commitment and realized warming in 2030 (the end of the

GISS simulation  for this scenario).   The final scenario examined by  GISS (case C) assumes that

atmospheric composition is stable after 2000, which leads to realized warming of about 0.9°C by 2040.

The policy cases examined here do not achieve this result; realized warming reaches 1.3-1.4°C by 2025

if the climate  sensitivity is  4.0°C.   Thus,  the  GISS scenarios bracket the  range of the scenarios
    12  The  path  to  2025, however,  is not identical.   The GISS scenarios  are  referenced to the
atmospheric composition of 1960, whereas our scenarios are referenced to the  estimated preindustrial
atmospheric composition. Thus, the  warming  commitment in 2000 is already 2.1°C in the RCW,
whereas it is only  1.9°C in the GISS A scenario.
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V








developed here, and may provide some indication of the regional differences in the  rates and



magnitude of change that might be associated with our cases.








Relative Effectiveness of Selected Strategies








      The major assumptions that distinguish the  Worlds where governments provide leadership in



pursuing stabilizing policies from the Worlds with no  such policies have been grouped into eleven



categories in order to examine the relative importance of different policy strategies.  Each set of



options was applied  individually to the RCW case; the combination of all the strategies  represents



the RCWP case. Figure 5-21 presents the results in terms of the effect  of  each policy strategy in



reducing the  equilibrium warming commitment in 2050  and 2100.   This  analysis  suggests that



accelerated energy efficiency improvements, reforestation, modernization of biomass use, and carbon



emissions fees could have the largest near-term impact on the rate of climatic change. In the long



run, advances in solar technology and biomass plantations also play an essential role.








CONCLUSIONS








      While the future  will never  be  anticipated with certainty,  it is  useful  to explore  the



consequences of alternative plausible scenarios.  The results  of this exercise suggest that even with



sluggish rates of economic growth and  optimistic assumptions regarding  technical innovation, the



world  could  experience significant  rates  of climatic change during the next  century.  Temperature



increases reach 3-4°C by 2100 under our assumptions;  and  the  world would be committed  to an



additional wanning of up to 2°C at this  date.  With higher rates of economic growth, certainly the



goal of most governments, significantly more rapid rates of climatic change are possible. With our



assumptions, which involve lower global  energy use than considered in many previous studies, a
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      Policy Options for Stabilizing Global Climate - Review Draft
                                       Chapter V
                                     FIGURE 5-21
                          STABILIZING POLICY STRATEGIES:
               DECREASE IN EQUILIBRIUM WARMING COMMITMENT
                            Percent Reduction Relative to RCW Scenario
  1. CFC Phaseout
  2. Reforestation
  3. Improved Transportation
     Efficiency0
  4. Other Efficiency Gains
  5. Energy Emissions Fee8
                    f
  6. Promote Natural Gas
  7. Emission Controls*
  8. Solar Technologies
  9. Commercialized Blomass
 10. Agriculture, Landfills,
     and Cement
 11. Promote Nuclear
     Power
RCWP (Simultaneous
 Implementation of 1-11)
                        L
j_
i
                        0        5

      DRAFT - DO NOT QUOTE OR CITE
         10       15
            Percent
         V-83
                                                               2050
                              2100
                                                                         45V.
                                               65%
         20       25

                February 16, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V



                                   FIGURE 5-21 -- NOTES

                      Impact Of Stabilizing Policies On Global Warming


a 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.

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  points  by  2025  compared  to  the RCW, and about 0.3-0.4
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 S0.36/GJ for  oil,  and  S0.23/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 fee changed  by 2025  and maximum production fee
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.

* Assume 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 NOX
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 hi 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 at costs as low 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.
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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter V



                            FIGURE 5-21 -- NOTES (continued)

                      Impact Of Stabilizing Policies On Global Warming


J 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 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%.

k Assumes that technological improvements in nuclear design  reduce cost  by  about $4/gigajoule
(1985$) by 2050 (about 0.5% per year efficiency improvement).

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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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter V








wanning of 4-6°C could be expected by 2100, with an additional commitment of 1-4°C by that date.



On the  other hand, by vigorously pursuing a variety of technical and policy options simultaneously,



it would be possible to  reduce the average rate of warming during the next century by more than



60%.  Chapters VII-IX  of this report explore these options in more detail.
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter V
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Darmstadter, J., L. Ayres, R. Ayres, W. Clark, P.  Crosson, P. Crutzen, T. Graedel, R. McGill, J.
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Edmonds, J., and J. Reilly.  1983b. Global energy and CO2 to the year 2050. Energy Journal 4:21-47.

Edmonds, JA.,  J. Reilly, J.R. Trabalka,  and  D.E. Reichle.  1984. An Analysis of Possible Future
Atmospheric Retention of Fossil Fuel CO2. Report No. DOE/OR/21400-1, U.S. Department of Energy,
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Edmonds, J., J. Reilly, R. Gardner, and A. Brenkert. 1986.  Uncertainty in Future Global Energy Use
and Fossil Fuel  CO2 Emission 1975 to 2075. Report DOE/NBB-0081.  U.S. Department of Energy,
Washington, D.C. 95 pp.

Frisch, J.R., ed. 1983. Energy 2000-2020:  World  prospects  and regional stresses.  World  Energy
Conference, Conservation Commission. Graham and Trotman, London.

Frohberg, Klaus. 1988. Tlie  Basic Linked System: A Tool for National and International Food Policy
Analysis.  Unpublished summary paper.

Goldemberg, J., T.B. Johansson, A.K.N.  Reddy,  and R.H. Williams. 1985. An End-Use Oriented
Global Energy Strategy. TJie Annual Review of Energy 10:613-688.

Goldemberg, J., T.B.  Johansson, A.K.N. Reddy, and R.H. Williams.  1987. Energy for a Sustainable
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Goldemberg, J., T.B. Johannson, A.K.N. Reddy, and R.H. Williams.  1988. Energy for a Sustainable
World. Wiley Eastern Limited, New Delhi, India.   517 pp.

Hansen,  J., I. Fung, A. Lacis, S. Lebedeff, D. Rind, R. Ruedy, G. Russell, P. Stone. 1988.  Global
climate changes as forecast by the Goddard Institute for Space Studies Three-Dimensional  Model.
Journal of Geophysical Research 93:9341-9364.
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter V
Hansen, J., A. Lacis, D. Rind, G. Russel, P. Stone, I. Fung, R. Ruedy, and J. Lerner.  1984. Climate
sensitivity: Analysis of feedback mechanisms. In: Hansen, J. and T.Takahashi, eds. Climate Processes
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Union, Washington, DC. 130-163.

Hansen,  J., and S.  Lebedeff. 1988.  Global  surface air  temperatures:   Update  through  1987.
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Hao,  W.M., S.C. Wofsy, and M.B. McElroy.  1987. Sources of atmospheric nitrous  oxide  from
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Hoffman, J.S.,  and M.J. Gibbs. 1988. Future Concentrations of Stratospheric Chlorine and Bromine. U.S.
EPA, Office of Air and Radiation, Washington, D.C.

Houghton, R.  1988. Reply to S. Idso, Comment on "Biotic changes consistent with increased seasonal
amplitude of atmospheric CO2 concentrations." Journal of Geophysical Research 93:1747-1748.

Houghton,  R., J. Hobbie, J.  Melillo, B. Moore, B. Peterson, G. Shaver,  and G.  Woodwell.  1983.
Changes  in the carbon content of terrestrial  biota and soils between 1860 and 1980:   A net release
of CO2 to the  atmosphere. Ecological Monographs 53:235-262.

IMF  (International Monetary Fund).   1988.   International Financial  Statistics  XLI(IO).   IMF,
Washington, D.C.

Kahane, A.  1986. Industrial Electrification:  Case Studies of Four Industries.  Berkeley: LBL 22098.

Keepin, W., I. Mintzer,  and L. Kristoferson. 1986. Emission of CO2 into the atmosphere.  In Bolin
B., B.R.  Doos,  J. Jager, and RA. Warrick,  eds.  The  Greenhouse  Effect,  Climate Change,  and
Ecosystems. Scope 29.  John Wiley and Sons,  Chichester.  35-91.

Lacis, A., J. Hansen, P. Lee, T. Mitchell,  and  S. Lebedeff. 1981. Greenhouse effect  of  trace gases,
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Lovins, A., L.  Lovins, F. Krause, and W. Bach. 1981. Least-Cost  Energy: Solving the  CO2 Problems.
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Mintzer,  I. 1987. A Matter of Degrees:   The Potential for Controlling  the Greenhouse Effect. World
Resources Institute, Washington, D.C. 60 pp.

Mintzer,  I.  1988. Projecting Future Energy Demand in Industrialized Countries: An  End-Use Approach.
Prepared for U.S. EPA, Washington, D.C. 40+ pp.

Nordhaus, W.D. & G. Yohe. 1983. Future  paths of energy and carbon dioxide emissions. In National
Research Council, Changing Climate. National Academy Press, Washington, D.C. 87-153.

Oeschger, H.,  U. Siegenthaler, U.  Schotterer,  and A. Gugelmann.  1975. A box diffusion model to
study the carbon dioxide exchange  in nature. Tellus 27:168-192.

OTA (Office  of Technology Assessment, U.S. Congress). 1988. Technology  and  the American
Economic Transition: Choices for  the Future.  OTA-TET-283 Washington, DC: U.S. Government
Printing Office, May 1988.
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V
Prather, Michael  J. 1988. An Assessment Model for Atmospheric Composition. NASA Conference
Publication XXXX.

Radian  Corporation. 1987. Emissions and Cost Estimates for  Globally Significant Anthropogenic
Combustion  Sources of NOX  N2O, CH, CO,  and CO2. Report  prepared for U.S. EPA, Research
Triangle Park.

Ramanathan, V., R J. Cicerone, H.B. Singh, and J.T. Kiehl. 1985. Trace gas trends and their potential
role in climate change. Journal of Geophysical Research 90:5547-5566.

Reilly, J., J.  Edmonds, R. Gardner, and A. Brenkeri.  1987. Uncertainty analysis of the IEA/ORAU
CO2 emissions model. The Energy Journal 8:1-29.

Rose, DJ.,  M.M. Miller, and C. Agnew. 1983. Global Energy  Futures  and CO2-Induced Climate
Change. MITEL  83-015. Prepared  for  National  Science  Foundation.  Massachusetts  Institute of
Technology,  Cambridge.

Rotty, R. 1987a. Annual Carbon Dioxide Production From Fuels (Updates). Unpublished Memorandum.

Rotty, R. 1987b. Estimates of seasonal variation in fossil fuel CO2 emissions. Tellus 39B:184-202.

Rotty, R. 1987c. A look at 1983 CO2 emissions from fossil fuel (with preliminary data for  1984).
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Ruderman, H., M. Levine, and J. McMahon. 1987. The behavior  of the market for energy efficiency
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Schurr, S. 1983.  Energy Policy.

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Strout, Alan. 1988. Structural change in industry over the long run. Presented at: the Lawrence
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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter V
U.S. Bureau of the Census. 1975. Historical Statistics of the United States:  Colonial Times to 1970.
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Stratospheric Ozone.  Office of Air and Radiation, U.S. EPA, Washington, D.C.

von Hippie, F., and B.G. Levi.  1983. Automotive fuel efficiency: The opportunity and weakness of
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Walter, Donald K. 1988. Personal  communication to Daniel Lashof. Donald K. Walter, Director.
Biofuels and Municipal Waste Technology Division, Department of Energy.

Williams, R.H., E.D. Larson, and  M.H. Ross.  1987. Materials, affluence, and industrial use. The
Annual Review of Energy 12:99-144.

World Bank. 1987. World Development Report 1987.  Oxford University Press, New York. 285 pp.

World Energy Conference. 1983. Energy 2000-2020:  World Prospects and Regional Stresses; and Oil
Substitution:  World Outlook to 2020.  London, Grahm and Trotman and Oxford University Press.

Zachariah,  K.C., and M.T. Vu. 1988.  World Population Projections,  1987-1988 Edition.  World Bank,
Johns Hopkins University Press, Baltimore. 440 pp.
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                                   CHAPTER VI

                              SENSITIVITY ANALYSES

FINDINGS  	   VI-3

INTRODUCTION	  VT-12

ASSUMPTIONS  ABOUT THE MAGNITUDE AND TIMING  OF GLOBAL CLIMATE
       STABILIZATION STRATEGIES 	  VT-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
             Anhydrous Ammonia	  VI-38
             N2O Leaching From Fertilizer	  VI-39
       N2O Emissions From Combustion  	  VI-39

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 NO,	  VI-71
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Policy Options for Stabilizing Global Climate -- Review Draft                      Chapter VI
BIOGEOCHEMICAL FEEDBACKS	  VI-72
       Ocean Circulation  	  VI-72
       Methane Feedbacks	  VI-73
       Combined Feedbacks 	  VI-75

REFERENCES	  VI-78
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter VI









FINDINGS








    •       The degree  of  participation by  developing countries in policies to limit




            warming  is  one  of the  most  important factors affecting  equilibrium




            temperatures in the year 2100.  If only industrialized countries adopt policy




            measures, equilibrium temperatures could increase by 40% or more relative




            to scenarios with global cooperation. This suggests that, despite uncertainties




            about future economic growth rates, developing countries will be a significant




            determinant in the ultimate level of global warming.









    •       Delaying any response to global warming by OECD and East Bloc  Countries




            until the year 2010 and by developing countries until 2025 might increase the




            equilibrium warming commitment in 2050 by 30-40%.









    •       The sensitivity of the climate system to a given increase in greenhouse gases




            is among the most important causes for uncertainty about  the ultimate




            magnitude of global warming.  For most  of the analysis in  this report, we




            have assumed that the  climate sensitivity to doubling CO2 is  2.0 to  4.0°C;




            broadening the  range of climate  sensitivity to between 1.5 and 5.5°C for a




            CO2 doubling causes the estimated range for equilibrium warming in 2050




            to become 2.0-7.4°C in  the Rapidly Changing World scenario.  The impact




            on realized warming is less: the estimated range for 2050  increases from




            1.9-2.8°C to  1.5-3.2°C.  This  uncertainty has important implications for the




            timing and stringency of policy responses.  Even the lower values, when




            considered with information on the impacts of global warming, suggests a




            need for caution about future emissions.
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Policy Options for Stabilizing Global Climate ~ Review Draft                         Chapter VI








    •       Uncertainties in biogeochemical feedbacks appear to be the potentially most



            important  reason to suspect that global warming may ultimately be greater



            than predicted by current general circulation models.  Changes in the  ocean



            circulation, methane releases  from hydrates, bogs,  and rice cultivation and



            other positive feedbacks could amplify realized warming in 2100 by 20-40%



            for a climate sensitivity of 2.0-4.0°C.  These estimates are speculative, they



            are based on the fragmentary evidence currently available, and these positive



            feedbacks  may not occur or may be delayed until the later part of the next



            century, but  the potentially large impact  on the  magnitude of warming



            suggests that even more drastic policy measures than those considered in the



            Rapidly Changing World with Stabilizing Policies scenario might be needed.








    •       Sensitivity analyses with  four ocean models  for CO2 uptake suggest that the



            path of atmospheric  concentrations  could  follow  somewhat  different



            trajectories, but very little difference is observed in  equilibrium warming for



            the year 2100.  These  equilibrium temperatures  differ  by at  most 10%



            depending on the type of ocean model.  More complex ocean circulation



            models currently in the research stage could broaden or decrease this range



            in the future.








    •       Assumptions  about the  total supply of oil and gas are among  the least



            significant factors affecting global warming in the year 2100. While gas may



            be desirable as a transition fuel, sensitivity tests that assume very optimistic



            estimates of oil and gas availability at each price  level suggest only small



            changes in global warming. A larger impact could  occur  if policy  measures



            were adopted to take advantage of the assumed increases in gas resources.
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter VI








    •      The sources of methane  are subject to considerable uncertainty. Estimates



           of some individual emission  sources  vary by  a factor of  two to three.




           Sensitivity  tests that  consider  extreme assumptions about  anthropogenic




           methane emission sources suggest that uncertainties in this budget could




           cause  equilibrium warming commitments in 2100 to vary by  about  5%.




           These results  should  not be interpreted to  mean  that methane is not an




           important greenhouse gas, but simply that uncertainties in the current budget




           do not greatly affect the ultimate temperatures  derived in  this  report.








    •      A comparison between current atmospheric concentrations and growth rates




           for  the  greenhouse  gases and  those calculated with  the atmospheric




           composition model, based on estimates of preindustrial concentrations and




           past emissions, show good agreement.  The largest discrepancies are for



           relatively short-lived gases that have been increasing rapidly in recent years,




           such as HCFC-22 and carbon tetrachloride.








    •      Non-greenhouse gases such as NOD CO, and Non-methane hydrocarbons



           (NMHC)  affect the lifetimes and concentrations of tropospheric ozone and




           methane.   A  comparison  of different chemistry models  suggests  that



           increases in methane  concentrations  may vary by approximately a  factor of



           two  for similar assumptions about NOj/CO/NMHC.  This  range may be



           attributed to differences in initial budgets and modeling approaches and may



           ultimately increase or decrease as other models become available.








    •      The most important determinant of future atmospheric concentrations of




           methane appears to be the growth rate of methane sources. While  NOX and
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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter VI








           CO affect the lifetime of methane, model studies suggest that assumptions




           about the  emissions  of these gases are less important than assumptions




           about the direct emissions of methane. However, considerable  research is



           needed to further our understanding of the chemistry of the atmosphere.








    •      There is considerable uncertainty about future concentrations of tropospheric




           ozone and about changes in composition at different altitudes. While model




           comparisons all suggest that increases in ozone are likely, the effect of these




           changes in global  temperatures is difficult to predict.








    •      For the major sensitivity analyses  presented in this  chapter,  Table  6-1




           summarizes  the impact  on realized warming  and equilibrium warming by




           2050 and 2100 (assuming  a 3.0°C  climate sensitivity).  Throughout  this




           chapter results are discussed for 2.0-4.0°C climate sensitivities for the Rapidly




           Changing World Scenario, with any figures using the midpoint of this range,




           i.e., a 3.00C climate sensitivity, unless stated otherwise.  Other assumptions




           would not change the basic findings, only the absolute  size of the impacts;



           these are presented in Appendix C.
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Policy Options for Stabilizing Global Climate  -- Review Draft
                                      Chapter VI
                                         TABLE 6-1

                      Impact of Sensitivity Analyses on Realized Warming
                                  and Equilibrium Warming
                           (degrees Celsius--3.0°C climate sensitivity)
                                                      2050
                                 2100
                                               Realized   Equilibrium    Realized  Equilibrium
Rapidly Changing World - No Response (RCW)       2.4°

Rapid Changing World - Stabilizing Policies  (RCWP)   1.5
                     4.0°

                     2.2
  4.T

  1.9
IT*

 2.5
Sensitivity Case Assumptions

No Participation by Developing Countries3

Global Delay in Adopting Policies'1

Non-Fossil Technology'

Fossil Resources

    High Coal Prices'*

    High Oil Supply6

    High Gas Supply*

Methane Budget8

    High CO  Emissions

N2O From Fertilizer

    Anhydrous Ammoniah

    N2O Leaching'

N2O From Combustion1
         2.1

         2.4

         2.4

      2.3-2.5
         2.4

         2.4

         2.4
3.1-3.3
3.1
3.4-3.7
3.5
4.0
4.0
3.9-4.2
To
4.0
4.0
4.0
3.2-3.7
2.6
3.6-4.0
3.6
4.7
4.7
4.6-5.0
be added
4.7
4.7
4.7
              ,53

              71*

              72*

          7.0-7.6*
              72*

              72*

              72*
* Estimates of equilibrium warming commitment greater than 6°C represent extrapolations beyond
the range tested in most climate models; this warming may not be fully realized because the strength
of some positive feedback mechanisms may decline as the Earth warms.
DRAFT - DO NOT QUOTE OR CITE
VI-7
February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter VI
                                  TABLE 6-1  (continued)

                     Impact of Sensitivity Analyses on Realized Warming
                                 and Equilibrium Warming
                          (degrees Celsius~3.0°C climate sensitivity)
                                                      2050	          2100	
                                               Realized   Equilibrium    Realized  Equilibrium
CO2 From Biomass*
CO2 Models'
Oeschger et al.m
Bolin et al."
Bjorkstrom"
Siegenthalerp
Unknown Sinkq
1.5-5.5°C Sensitivity
Heat Diffusion5
Prather Model
CFC-11 Lifetime'
Chlorine/Col O3U
Trop 03/CH4V
OH/NO,"
Feedbacks
Ocean Circulation*
Methane5'
CO2/CH4/Uptakez
2.4

-
-
-
-
2.2-2.5
1.5-3.2
1.9-2.7

2.4
2.3
2.4
2.4

3.1
2.7
3.0
4.1

3.9
3.9
3.9
3.9
3.7-4.2
2.0-7.4
4.0

4.0
3.8
4.1
4.0-4.1

4.1
4.6
4.9
4.8

-
-
-
-
4.1-4.9
2.9-6.6
3.9-5.3

4.7
4.4
4.8
4.7-4.8

7.1*
5.5
6.3
73*

69
69
69
63
6.2-7.4*
3.6-13.2*
7.2*

7.2*
6.6
7.3*
7.1-7.3*

7.6*
8.4*
8.9*
* Estimates of equilibrium warming commitments greater than 6°C represent extrapolations beyond
the range tested in most climate models, and this warming may not be fully realized because the
strength of some positive feedback mechanisms may decline as the Earth warms.
 DRAFT - DO NOT QUOTE OR CITE        VI-8                           February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter VI
                                    TABLE 6-1  -- NOTES


a    Developing countries were assumed to not participate in climate stabilization policies.  The range
    represents uncertainty in the rate of technological diffusion, i.e., even if developing countries do
    not  participate, they will indirectly benefit from technological improvements  as  a result of
    stabilization policies among the developed countries.

b    Impact if developed countries do not respond to global warming until 2010; developing countries
    delay to  2025.

c    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 0.5%
    annually with the optimistic assumptions and  remain  relatively flat  in the modest assumptions.
    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 EJ.

d    The impact of an escalation in  coal prices  above the RCW case  by about 1% annually from
    1985 to 2100.

e    The impact of an increase  in global oil resources to 25,000 EJ, more than  double the  estimate
    in the RCW case, assuming proportionate increases in resource availability at each cost level.

f    The impact of an increase in global natural gas resources to 27,000 EJ, more than 2.5 times the
    estimate in the RCW case,  assuming proportionate increases in resource availability at each cost
    level.

g    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).

h    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%.

    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.

J    The  impact  of higher  emission coefficients  for  N2O from  combustion;  assumes that  N2O
    emissions are about 25% of NO^ emissions and the N2O emissions from combustion sources in
    1985 equaled 2.3 Tg N, over 2 tunes the level assumed in the RCW case.

k    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 in emissions of carbon of 281 Pg from 1980 and 2100 compared to 188 Pg C in the
    RCW scenario.
DRAFT -  DO NOT QUOTE OR CITE        VI-9                            February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter VI
                              TABLE 6-1 -- NOTES  (continued)


    Realized warming was not  calculated in these tests.

    This box-diffusion model represents carbon turnover  below 75 meters  as  a purely diffusive
    process.

    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 which divides the ocean into cold and warm compartments;
    water downwells directly from the  cold surface compartment into intermediate and deep layers.

    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.

    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 si2e decreases  to
    zero exponentially at 2% per year.

    Atmospheric response  to a doubling of CO2 was varied from 1.5-5.5°C.

    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"4
    m2/sec was increased to 2X1CT4 and decreased to 2xlO"5 m2/sec.

    The atmospheric lifetime of CFC-11, 65 years in 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 chlorine contained in CFCs was increased
    from a 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  was increased.   In
    the RCW case, this variable for the Northern Hemisphere is a 0.2% change in tropospheric
    ozone for each percentage change in CH4 concentration; it was changed to 0.4% hi the sensitivity
    analysis.

    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.

    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.
DRAFT - DO NOT QUOTE OR CITE        VI-10                           February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter VI
                              TABLE 6-1 -- NOTES (continued)
    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.

    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 thermocline, 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.
DRAFT - DO NOT QUOTE OR CITE       Vl-11                           February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter VI



INTRODUCTION



        The Rapidly Changing World and Slowly Changing World scenarios presented in Chapter V

describe two significantly different futures for the global community.  Although these two potential

paths capture a wide range of uncertainty, they do not represent all possible outcomes.  Alternative

assumptions are clearly possible for many of the parameters specified in these  scenarios;  these

alternative specifications could alter the timing and magnitude of global climate change described in

the Rapidly Changing World and Slowly Changing World scenarios.  To understand the importance

of these alternative assumptions, this chapter examines how changes in key parameters  affect our

portrayal of the rate and magnitude of global  climate change.  These sensitivity  analyses include

alternative assumptions about:  the magnitude and timing of global policies to combat climate change,

rates of technological change, trace-gas  source strengths and emission coefficients, the carbon  cycle,

sensitivity of the climate system, atmospheric chemistry, and feedbacks.



        The sensitivity analyses discussed in this chapter are generally run relative to  the Rapidly

Changing World scenario, unless specified otherwise.  Overviews of each case are provided to describe

the basic results for  the reader; more detailed  discussion of the sensitivity analyses are provided in

Appendix C.
ASSUMPTIONS   ABOUT  THE   MAGNITUDE   AND  TIMING   OF  GLOBAL  CLIMATE
STABILIZATION  STRATEGIES
        The analyses of the Stabilizing Policy scenarios presented in this Report are based on the

assumption  that the global community takes immediate, concerted action to contend  with  the

consequences of climate change.  Potential actions, which are discussed in Chapters VII - IX, include

reducing the amount of energy required to meet the world's increasing needs, developing alternative
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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter VI








technologies that do not require the consumption of fossil  fuels, halting  deforestation, and making



changes in agricultural practices, among  others.  For many reasons, however, the world may not




respond to the threat of climate change in a timely fashion.  This section  explores the consequences




of other  possibilities, particularly the unwillingness or inability of some  countries to  participate hi




climate stabilization  programs and the implications of delaying global action until a later date.








No Participation by the Developing Countries








        Most  of the greenhouse gas emissions currently committing the world to climate change can



be traced to activities by the industrialized countries.  Although the quantity of emissions generated




by  developing countries has been increasing,  the argument  is  sometimes made that since the




greenhouse problem has been largely caused by the industrialized countries, these countries should




be responsible for solving the problem.  Also, despite the potential environmental consequences of



global climate change, other problems facing the developing countries, such as poverty, inadequate




health care, and  other apparently more pressing environmental problems may make it difficult for




developing countries to commit  any resources to climate stabilization policies.








        Regardless of the merits of these arguments, for this  sensitivity  analysis  we have assumed




that developing countries do not  participate in any climate  stabilization  activities; that  is, only



developed countries  adopt policies to limit global climate change.  For this  analysis the developing



countries  include  China and Centrally-planned  Asian economies,  the Middle East,  Africa, Latin



America, and  South/Southeast Asia.  We have assumed that industrialized countries (i.e., the U.S.,




the rest of the OECD countries, and the USSR and Eastern Europe)  follow the path assumed in the



Rapidly Changing World with Stabilizing Policies (RCWP) scenario, while developing countries  follow




the path assumed in the Rapidly Changing World  No Response (RCW) case, in which the  entire




global community does not respond to climate change.
DRAFT - DO NOT QUOTE OR CITE       VMS                            February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter VI








        Even  if developing countries do not participate in global  stabilization  policies, however,




policies adopted by  the  industrialized countries are likely to lead to technological advancements,




altered market conditions, etc., that indirectly reduce emissions in the developing countries  as well.




For example, advancements by the developed countries in automobile fuel efficiency or fuel supply




technologies may be partly adopted  by the developing countries, tangentially allowing  for some




climate stabilization benefits. If the developing countries do not participate, however, they may tend




to adopt technological advances more slowly and at a higher cost  than if they had participated from




the start.  This slower rate of technological diffusion could occur for many reasons  ~ for example,




if the industrialized countries take actions that prevent  easy access to improved technologies or they




are unwilling  or unable  to make the necessary capital available  for  investment, or if developing




countries decide to invest their limited resources in other areas.








        Since we cannot be certain of the direction that non-participation by the developing countries




might  take, we analyzed  two cases to capture the potential range of likely possibilities.  In the first




case, little technological diffusion  was  assumed, resulting in a future path of energy consumption and




investment trends for developing  countries similar to those assumed in the RCW scenario.  In the




second case, developing countries  were assumed to have greater access to the efficiency improvements



and technological advances assumed for the RCWP case as a result of policies by the industrialized



countries to make these  improvements available and extend the credit  necessary for investment by




the developing countries  in these  improvements.








        In this analysis key assumptions  for the developing countries included the following:  (1)




rates of energy efficiency improvements for all sectors are the same as in the RCW  case or midway



between the RCW and  RCWP case; for example,  automobile efficiency levels, which by  2050 in




developing countries were 5.9 liters/100  km  (40 mpg)  in the RCW case  and  3.1 liters/100 km (75




mpg) in the RCWP case, were varied from 5.9-4.1 liters/100 km (40-58 mpg);  (2) CFCs  are  not
DRAFT - DO NOT QUOTE OR CITE       VI-14                            February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter VI








phased out (although compliance  with the Montreal  Protocol  would still occur); (3) agricultural



practices that cause methane  emissions from rice and enteric fermentation and nitrous oxides from




fertilizers do not change or would show modest improvements; (4) deforestation continues as in the




RCW  case with an exponential decline in forest area; (5) non-fossil energy supply  technologies




developed  by the industrialized countries are available to developing countries at a later date and a




higher cost  than  assumed in the RCWP case;  for example,  technological diffusion of biomass




gasification technology would occur 10 years later than it would in the RCWP  case, but feedstock




costs would remain high due to a lack of investment by the developing countries in highly productive




energy plantations; and (6) no additional incentives are provided for increased use of natural gas.








        Without the participation of the developing countries to stabilize the atmosphere, the amount




of greenhouse gas  emissions will increase substantially:   In the analysis  considered here,  CO2




emissions  are 3-4 Pg C higher  than  in  the  RCWP case by 2050 and 6-13 Pg  C higher by 2100




(emissions by 2100 are  8.1 to 14.7 Pg C  lower than  in the RCW case since industrialized countries




adopt climate stabilization policies);l other greenhouse gas emissions are also higher. These emission




increases are sufficient to increase realized warming  by 0.4-0.6°C in 2050 compared with the RCWP



case and 1.0-2.1°C by 2100 (see Figure 6-1), with equilibrium warming by 2100 up to 1.4-4.1°C higher.




Figure 6-1 also shows the results for the Slowly Changing World scenarios. In this scenario, emission




increases are sufficient to increase realized warming  by 0.3-0.5°C in 2050 compared with the SCWP



case and 0.6-1.10C by 2100, with equilibrium warming by 2100 up to 0.8-2.0°C higher.








        The implications of these results are clear:  even if the industrialized countries adopt very




stringent policies to counteract  the effects of climate change,  the atmosphere continues to warm at




a rapid rate. As a result,  unilateral action by the industrialized countries can significantly slow the
     1 Pg = petagram; 1 petagram =  1015 grams.
DRAFT - DO NOT QUOTE OR CITE        VI-15                           February 21, 1989

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 Policy Options for Stabilizing Global Climate - Review Draft
                                                      Chapter VI
                               FIGURE 6-1
               INCREASE IN REALIZED WARMING

    WHEN DEVELOPING COUNTRIES DO NOT PARTICIPATE

               (Degrees Celsius; Based on 3.0 Degree Sensitivity)
I  3
UJ
o
v>
UJ
UJ
CC  2
o  *
UJ
a
         SLOWLY CHANGING WORLD
No Participation

by Developing

 Countries
                        SCW  ,'
                         SCWP
                                    RAPIDLY CHANGING WORLD
                                                          RCW .'
                                           No Participation

                                           by Developing

                                            Countries
                                                          RCWP
  1985 2000  2025  2050  2075  2100    1985 2000  2025  2050   2075  2100

                YEAR                               YEAR
 DRAFT - DO NOT QUOTE OR CITE     VI-16
                                                 February 21, 1989

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Policy Options for Stabilizing Global Climate « Review Draft                         Chapter VI








rate and magnitude of climate change, but because of the growing impact that developing countries




have on the global climate, without the participation of the developing countries, substantial global




warming is unavoidable.  Because most of the world's population resides in these countries, their role




in climate  stabilization becomes  increasingly important as the demand  for resources to feed and



clothe their growing population and improve their standard of living expands.








Delay in Adoption of Policies








        For the  Stabilizing Policy cases presented in  Chapter  V  it is assumed  that  the  global




community takes immediate action to respond to the dangers  posed by climate change.  For this




sensitivity analysis we have assumed that the global community  delays any response to the threat of




climate change, with developed countries (i.e, the United States, the rest of the OECD countries, the




USSR  and centrally-planned European economies) delaying action  until 2010, and the  developing




countries delaying action until 2025.   Additionally, once regions do  initiate action to combat global




warming,  they do so at a slower rate than assumed in  the RCWP case.  This  slower approach




assumes a minimum 25-year delay in  attaining the policy goals  of the RCWP case;  that is, levels of




technological improvement, availability of alternative energy supply technologies, etc., will be achieved




at least 25 years later.  For example, in the RCWP case, automobile  efficiency reaches 3.1 liters/100



km (75  mpg)  by  2050; in the  Delay case industrialized  countries  reach 3.9 liters/100 km (60 mpg)



by 2050, while developing countries reach 4.7 liters/100 km (50 mpg); the rate of energy efficiency



improvement  for the residential, commercial, and industrial sectors is  unchanged from the rates




assumed in the  RCW case,  through 2010  for industrialized  countries and  2025  for  developing



countries. After these years, energy efficiency improvements occur at the same  rate assumed in the




RCWP case; and the implementation of production and consumption taxes on fossil fuels from the




RCWP case was  delayed until 2010 for developed  countries and 2025 for developing countries.
DRAFT - DO NOT QUOTE OR CITE       VI-17                           February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter VI








        Delaying the adoption of policies to stabilize the atmosphere significantly  increases the




Earth's commitment to global warming.  With delay by the industrialized countries until 2010 and by




the developing countries until  2025, the increase in realized warming compared to that assumed in




the RCWP case is 0.4-0.6°C by 2050 and 0.5-0.9°C by 2100; equilibrium warming is 0.6-1.2°C higher




by 2050 and 0.7-1.4°C higher by 2100 (based on climate sensitivities of 2.0-4.0°C; see Figure 6-2).




Figures  6-2 also shows  the  results for the Slowly Changing World  scenarios.  If global delays do




occur, the  increase in realized warming compared to that  assumed  in the SCWP case is 0.3-0.5°C




by 2050 and 0.3-0.6°C by 2100; equilibrium warming is 0.5-0.9°C higher by 2050  and 0.4-0.8°C higher




by 2100 (based on climate sensitivities of 2.0-4.0°C).








ASSUMPTIONS AFFECTING RATES OF TECHNOLOGICAL CHANGE








        The  extent  of  global warming  will depend  on the  availability  of  energy supplies  and




technologies that minimize dependence on carbon-based fuels,  nitrogen-based fertilizers, and other




sources  of greenhouse  gas emissions.   The  availability of non-fossil fuel technologies  and the




development  of new production methods that  significantly  increase the supply  of natural gas could



have an impact on the rate of change in greenhouse gas emissions. Alternative assumptions regarding



these factors are presented below.








Availability of Non-Fossil Technologies








        Most  technologies in use currently rely on fossil fuels to' supply their energy needs.  In the




Rapidly Changing World, fossil-fuel-based technologies  continue to dominate  throughout  the  next




century:  by 2100 fossil  fuels still supply over 70% of primary energy needs.  However, if non-fossil




technologies can be  commercialized earlier, the magnitude  of global climate change can be reduced




because these technologies do  not emit the greenhouse gases that cause global warming. To evaluate
DRAFT - DO NOT QUOTE OR CITE       VMS                           February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                                   Chapter VI
V)

I  3
_!
IU
o
00
LLI
UJ

§  2
uu
o
                               FIGURE 6-2



                INCREASE IN REALIZED WARMING

          DUE TO GLOBAL DELAY IN POLICY ADOPTION

                 (Degrees Celsius; Based on 3.0 Degree Sensitivity)
         Slowly Changing World
                          SCW
Global Delay

                        SCWP
                                  Rapidly Changing World
                                                             RCW  '-
                                                Global Delay  /
                                                             RCWP
  1985  2000  2025  2050  2075  2100   1985 2000  2025  2050  2075  2100

                YEAR                               YEAR
DRAFT - DO NOT QUOTE OR CITE     VI-19
                                              February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter VI








the implications of the availability of non-fossil technologies, two different scenarios  were analyzed:




(1) an  Early Non-Fossil case, in which non-fossil technologies,  specifically  solar  photovoltaics,




advanced nuclear power designs, and production of synthetic fuels from biomass, are commercially




available by 2000  at a rate  faster than that assumed in the RCWP case; and  (2) an Intermediate




Non-Fossil case,  in  which non-fossil technologies  are  widely  available  by the  middle  of  the  next



century (i.e., greater  use of non-fossil technologies than in the RCW case, but less than in the RCWP




case).   The  intent  of these two cases is to capture  a  range of possible  roles for non-fossil




technologies,  with the  first case reflecting very optimistic assumptions on non-fossil availability and




the second case reflecting more modest assumptions.








        In the Early Non-Fossil case, non-fossil energy sources increase  their share of total primary




energy supply from 12% in  1985 to about 50% by 2025 and 65% by 2100, while in the Intermediate




Non-Fossil case the  share for non-fossil technologies increases to 21% by 2025 and about 60% by




2100  (see Figure 6-3a).  As shown in  Figure 6-3a, in the near term the non-fossil share of total




energy could be greater than reflected in the RCWP case if commercial availability is achieved at an



earlier  date.   In  this  sensitivity analysis, however, the non-fossil share is  lower in the  long run



compared with the share in  the RCWP  case because other policies that were included in the RCWP



case to  discourage the use of fossil fuels were not included in  this case.  In both cases,  however, an



increased role for non-fossil technologies can affect  the  amount  of global warming.  As shown in



Figure 6-3b,  for the two cases presented here the  amount of realized warming compared  with the



RCW case could  be reduced about 0.1-0.3°C by 2050  and 0.6-1.3°C by 2100; equilibrium  warming




could be reduced about 0.2-0.9°C by  2050 and  0.9-2.50C by 2100 (based on 2.0-4.0°C climate




sensitivities).
DRAFT - DO NOT QUOTE OR CITE        VI-20                           February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                                   Chapter VI
                             FIGURE 6-3
       AVAILABILITY OF NON-FOSSIL ENERGY OPTIONS


  (a) Non-Fossil Share Of Total Primary Energy Supply
                             (Percent)
   UJ
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   cc
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   a.
  (b)
    v>
    UJ
    o
    v>
    ui
    UJ
    cc
    O
    UJ
    o
       100
        80
60
        40
        20
            RCWP


            Non-Fossil

             Energy Options
                                                     RCW
         1985  2000
                2025      2050

                      YEAR
2075
2100
         Increase In Realized Warming

       (Degrees Celsius; Based on 3.0 Degree Sensitivity)
                                                     RCW
                                             Non-Fossil
                                               Energy Options
                                             RCWP
         1985  2000
                                                   2100
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                        VI-21
             February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter VI








Cost and Availability of Fossil Fuels








        As discussed in Chapters IV and VII, there is significant  uncertainty over the amount  of




fossil-fuel resources available globally and the cost at which these resources could be produced.  The



development of the fossil energy  resource estimates and the associated extraction costs used in this




analysis are documented in ICF (1988).  Given the  uncertainties about the cost  and availability  of



fossil  energy supplies, several sensitivity cases were analyzed. These are discussed below.








High  Coal  Prices








        In  the RCW case from 1985 to 2050 there was  no real escalation in coal prices. Given the




vast quantity of coal  resources available worldwide, and the rate of productivity improvements in coal




extraction that have helped to contain cost increases,  coal prices may not escalate in real terms (e.g.,




from  1949 to 1987, U.S. coal prices declined an average of 0.2% annually [U.S. DOE, 1988]).  Since




the longer-term price path for coal is highly uncertain, however, we analyzed  the impacts of a high




price  coal case where coal prices escalated about 1  percent annually from  1985 to 2100.








        As illustrated in Figure 6-4a, increasing coal prices have a significant impact on the amount



of primary  energy consumed; for example, by 2100 total primary energy demand  is more than 20%



lower compared with this demand in the RCW case.  Most of this reduction in energy demand is



due to  the decline  in coal use as consumers respond to the escalating  prices.  Because coal is  a




major energy resource for electricity production and synthetic fuel production, the impact on the level




of greenhouse gas emissions is fairly substantial.  For example, CO2 emissions are reduced nearly




50%  by 2100.  The reductions in greenhouse gas emissions have a significant impact on global




warming, as shown in Figure 6-4b, which indicates a decline in realized warming from the RCW case
DRAFT - DO NOT QUOTE OR CITE       VI-22                            February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                             Chapter VI
                             FIGURE 6-4
IMPACT OF  1% PER YEAR REAL ESCALATION IN COAL PRICES
 (a)
 Total Primary Energy Demand

             (Exajoules)
     1500
     1250
    LU 1000

    O

      75°
      500



      250
                                        RCW




                                        High Coal Prices


                                        RCWP
         1985  2000
         2025
   2050

YEAR
2075
2100
 (b)
  Increase In Realized Warming

(Degrees Celsius; Based on 3.0 Degree Sensitivity)
   v>
   CO
   co
   111
   LU
   CC.
   a
   LU
   O
                                                      RCW
                                                      High Coal Prices
                                       RCWP
        1985  2000
        2025      2050

               YEAR
            2075
         2100
DRAFT - DO NOT QUOTE OR CITE
                 VI-23
                         February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                         Chapter VI








of 0.2-0.3°C  by  2050 and 0.9-1.3°C  by  2100 (assuming  2.0-4.0°C  climate  sensitivities).   The



corresponding decrease in equilibrium warming by 2100 is 1.3-2.5°C.








Alternative Oil and Natural Gas Supply Assumptions








        There are many uncertainties concerning the amount of oil and natural gas supplies available




worldwide. As discussed in Chapter VII, for example,  the viability of increased  use of natural gas




as a near-term option for  reducing  greenhouse gas emissions critically depends  on the amount of




natural gas available, its price, the length of time over which adequate supplies can be secured, etc.




To explore how sensitive the level of greenhouse gas emissions  may be  to the amount of oil and



natural gas supplies, two sensitivity cases assuming higher global supplies have been analyzed:  (1)




a high oil resource case and (2) a high natural gas resource case.  The higher oil  resource estimates




were  derived from Grossling and  Nielsen  (1985),  who indicated that resources may be more than




double the estimates used in the base case  analyses (which were about 12,000 EJ  of conventional oil




resources).2  For this analysis we assumed conventional  oil  resources of about 25,000 EJ.  Natural




gas estimates were derived from Hay et al. (1988), which assumed in-place resources of about 150,000




EJ.   For purposes of this sensitivity case, we assumed that technological improvements in gas



extraction would permit an additional 10%  of in-place resources to be economically recovered.  This



amount was  added  to the baseline estimates of proved reserves and  economically recoverable



resources, for a total resource base  of about 27,000 EJ. We must emphasize  that  these sensitivity



cases do not  examine policy options  that encourage greater oil and natural gas use; rather,  they only




attempt to examine  how current uncertainties concerning  the  size of the resource base for  these




energy supplies can directly affect the rate and magnitude of global climate change.  Policy options
      EJ = exajoule; 1 exajoule  = 10  joules.
 DRAFT - DO NOT QUOTE OR CITE        VI-24                            February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter VI








encouraging greater use of these fuels in conjunction with higher resource estimates would have a




substantially different  impact.








        High Oil Resources. An increase in global oil  resources to 25,000 EJ is more than double




the resource estimates assumed  in the RCW case.  These additional resources were assumed to be




available at the same economic  costs, such that the amount of oil available at any given price was




twice the amount assumed in the RCW case. This increase in oil resources had  two major impacts:




(1) the amount  of synthetic production  of liquid  fuels from coal declined  substantially  since




conventional oil supplies were available  at a competitive price to meet this demand; and  (2) total




demand for energy, mainly oil, increased as consumers responded to the increased availability of oil




supplies at the  same price (since twice the amount of oil was available at a price  equal to that in the




RCW case).  The net effect of these impacts is a small increase in total primary energy demand (a




4% increase by 2050), a major shift from coal (primarily for synthetic fuel production)  to oil, and a




decrease in the portion of total primary energy supplied by non-fossil resources since oil is more




plentiful  and competitive; for example,  non-fossil fuels supply  about 22% of  all  energy by 2050




compared with 24% in the RCW case (see Figure 6-5).  The net effect of these factors is an increase




in CO2 emissions of  0.4  Pg C  by  2050 and 2.2 Pg  C by 2100.  The decline  in coal production,




however, lowered methane  (CH4) emissions  since the amount of CH4 emitted  during coal mining




decreased substantially (e.g., by  2100  CH4 emissions from fuel production declined from about 360



Tg in the RCW case to 210  Tg), resulting in a modest decline of less than 0.1°C in realized warming



by 2100 compared with the  RCW case warming (assuming 2.0-4.0°C climate sensitivities).3








        High Natural Gas Resources.  For the high natural gas resource case, natural gas  resources




were increased from about 10,000 EJ  to  27,000  EJ.  As in the high oil resource case, higher natural
     3 Tg  = teragram; 1 teragram =  1012 grams.
DRAFT - DO NOT QUOTE OR CITE       VI-25                           February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                                    Chapter VI
                             FIGURE 6-5
              IMPACT OF HIGHER OIL RESOURCES

             ON TOTAL PRIMARY ENERGY SUPPLY

                               (Exajoules)

                                 RCW
   Crt
   UJ
   _l

   o
   -J
   4
   X
     1500
     1250
     1000
750
      500
      250
  _

  O

  
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Policy Options  for Stabilizing Global Climate -- Review Draft                        Chapter VI









gas resource estimates  result in two major impacts:   (1) an increase  in  demand for energy,




particularly for  gas, since natural gas is more plentiful compared with the amount available in the




RCW case; and (2) a decline in the conversion of coal to synthetic gas, since natural gas supplies are




available to meet the demand.








        Overall, by the end of the 21st century the amount of primary energy consumed changes very




little from the RCW case.  In the near term energy demand increases slightly compared with the




RCW case, since natural gas is more plentiful (e.g., by  2025 energy demand is about 2.5% higher




compared with the RCW case; see Figure 6-6).  However, the total amount of energy required in the




long run is less because  a greater portion of end-use energy demand is met with natural  gas rather




than with synthetic gas from  coal.  This increase in conventional natural gas consumption reduces




the total primary energy required to satisfy  demand because the decline in synthetic fuel  demand




from the RCW case reduces  the amount of  energy required for synthetic fuel conversion, although




this impact is small: by 2100 primary energy demand is lower by less than 1%.









        The amount of natural gas consumed does increase significantly; for example, in 2050 natural




gas consumption increases  to 215 EJ compared with  100 EJ in the RCW case.  However,  the




increased availability of natural gas  also reduces the portion of energy supplied by non-fossil fuels;




for example, by 2050 non-fossil energy sources  supply about 20% of total demand compared with




24% in  the RCW case.  The net  impact on  CO2 emissions due  to these factors is quite  small:  no




change  in emissions by 2050 and a decline of 0.7 Pg  C by 2100.   The  impact  on realized  and




equilibrium warming is negligible  (less than 0.1°C).
DRAFT - DO NOT QUOTE OR CITE       Vl-27                           February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                               Chapter VI
                           FIGURE 6-6
      IMPACT OF HIGHER NATURAL GAS RESOURCES ON
              TOTAL PRIMARY ENERGY SUPPLY
                             (Exajoules)
                               RCW
     1500
     1250  -
                                                       Biomass
                                                       Solar
        1985   2000
2025       2050
       YEAR
          2075
          2100
     1500
                   High Natural Gas Resources
        1985   2000
2025
2050
2075
2100
                              YEAR
DRAFT - DO NOT QUOTE OR CITE
      VI-28
                  February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter VI








Availability of Methanol-Fueled Vehicles








        The transportation sector  throughout the  world is heavily dependent on petroleum-based




fuels. This dependence, particularly on gasoline and diesel fuel, produces substantial quantities of




greenhouse gases  (see  Chapter IV).   A  variety  of non-petroleum-based  alternatives  are  under




development, including the use of methanol. There are many potential advantages to using methanol




as a transportation fuel rather than gasoline; according to recent research, advanced methanol-fueled




vehicles could be 20-40% more energy efficient, emit much  lower levels of CO, and  reduce non-




methane hydrocarbon (NMHC) reactivity up to 95%  (Gray, 1987).  Methanol's potential to reduce




NMHC reactivity could reduce levels of urban ozone, which would improve ambient air quality in




urban areas.  These reductions could be on the order of about 5-20% of peak ozone levels (DeLuchi




et al.,  1988).   However, it is  not clear how reductions in  urban ozone levels may translate to




reductions in  average  tropospheric  ozone  and,  therefore, changes in  radiative  forcing.   Current




understanding of these atmospheric  processes attributes urban  ozone changes primarily to NMHC




and  NOX flux, while tropospheric  ozone  changes  depend primarily on  (in  descending order of




importance) CH4, CO, NOX flux, and NMHC flux  (Prather, 1988).  Interactions between urban air




quality and the rest of the troposphere cannot be evaluated with the aggregate model used here.








        Since the ability of methanol to affect tropospheric ozone levels cannot be reliably estimated,



we cannot reflect all of the potential advantages of using methanol as  a  transportation fuel.  It is



useful to note, however, that in addition to  reducing emissions of CO and other gases, methanol can



be produced from different types of feedstocks, such as natural gas, coal, or biomass.  When biomass



is the feedstock, the carbon emitted during  the combustion process is recycled from the environment




as the  biomass  is grown.  As a result, the net CO2 emissions are zero when biomass  is used.



Greenhouse gas emissions from methanol, however, can be greater than those from gasoline if coal




is used as the  feedstock because  additional emissions  will be  generated during the  methanol
DRAFT - DO NOT QUOTE  OR CITE        VI-29                           February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                       Chapter VI



production process.  According to one analysis, methanol production from coal would generate about

twice the amount of CO2-equivalent emissions (based on their radiative effect) compared to gasoline

from crude  oil, while methanol from natural gas would only be slightly better (about 3%) than

petroleum-based fuels (DeLuchi et al. 1988).  From a global warming perspective, DeLuchi et al.

concluded that only biomass-derived  methanol would substantially reduce the amount of radiative

forcing from transportation fuels, although as mentioned above, this argument does not incorporate

any potential benefits from reductions in urban ozone levels.
ATMOSPHERIC COMPOSITION: COMPARISON OF MODEL  RESULTS TO ESTIMATES OF
HISTORICAL CONCENTRATIONS
        The atmospheric composition model was applied to estimates of historical emissions of trace

gases and the results compared to historical data on atmospheric composition.  This exercise provides

insight on how the model performed under conditions much different from the reference year, 1985,

and  provided one mechanism to validate the model.  The exercise included  the development of a

single scenario of historical emissions of trace gases and application of the  model using different

assumptions on climate sensitivity and chemistry parameters in the model.



        The scenario of historical emissions of trace gases is based on estimates of natural sources

from the Atmospheric Stabilization Framework described in Chapter V, estimates  from a study by

Darmstadter et al. (1987) on historical emissions from various anthropogenic sources, and estimates

of historical CO2 emissions from Rotty (1987)  and Houghton (1988).  For natural emission sources,

historical emissions were assumed to be constant from  1870  to 1985 at the  levels  assumed in the

scenarios described in Chapter V.  The exception is emissions of CH4 from wetlands, which were

assumed to be larger in 1870 by 50%  and to decline to current levels due to destruction of wetlands.
DRAFT - DO NOT QUOTE OR CITE       VI-30                          February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter VI








The estimates of historical emissions of CFCs and Halons were taken from EPA's Regulatory Impact




Analysis on Stratospheric Ozone Protection (U.S. EPA,  1988).








       The alternative scenarios of historical atmospheric composition and global warming reflect




a range of assumptions concerning the climate sensitivity  and the first and second order relationships




assumed in the model. Figure 6-7 illustrates the increase in realized warming projected from 1840




to 1985, which  ranges from 0.4°C to 0.8°C based on  a range  of climate sensitivities (from  1.5  to




5.5°C  for doubled  CO2).   These results  compare well with results from Wigley et  al.  (1986), who




estimated  a global temperature increase of 0.3-0.7°C in  the last century, and Hansen et al. (1988),




who  estimated  a global temperature  increase of 0.4-0.8°C during the same  period.  The model




produced estimates of atmospheric concentrations of CO,, CH4, N2O, CO, and CFC-12 within 1.5%




and estimates of concentrations of CFC-11 within 3.5% of observed values in 1985.  In addition, the




pattern  of  estimated  atmospheric  concentrations  over  tune  conformed well  with  historical




measurements for CO2, N2O, and CH4.  Estimates of concentrations of some gases such as  CFC-22




varied  from the  historical measurements to a  greater extent,  which reflects  their more recent




introduction and rapid growth in atmospheric concentrations.  Table 6-2 summarizes the results for



the long-lived gases.








       For CO2, the atmospheric concentration over  time matched the Mauna Loa and Ice Core



measurements by design through the use of the unknown sink in the model (see Unknown  Sink in



Carbon Cycle).  The unknown sink is zero through 1940 and then slowly rises  to 1.9 Pg C per year



by 1985, which represents  about  one-third of the estimated anthropogenic emissions.








       The estimates of CH4 concentrations match atmospheric and ice core  measurements well,




especially given the uncertainties in the  emissions estimates and the historical measurements.  The




model shows somewhat higher than expected growth in the late 19th century, which may reflect the
DRAFT - DO NOT QUOTE OR CITE       VI-31                           February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                                          Chapter VI
                               FIGURE 6-7
                 REALIZED WARMING THROUGH 1985

               (Degrees Celsius; Based on 1.5-5.5 Degree Climate Sensitivity)
   co

   M

   U


   »
   UJ
   ui
   a:
   o
   UJ
      0.9  -
      0.8  -
      0.7  -
      0.6  -
0.5  -
      0.4  -
      0.3  -
      0.2  -
       0.1  -
         1840      1865      1890
                                1915


                               YEAR
1940      1965    1985
 DRAFT - DO NOT QUOTE OR CITE      VI-32
                                                     February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft
                                               Chapter VI
                                      TABLE 6-2
                  Comparison of Model Results to Concentrations in 1986
       Trace Gas (units^

       C02 (ppm)
       N20 (ppb)
       CH, (ppb)'
       CFC-11 (ppt)
       CFC-12 (ppt)
       HCFC-22 (ppt)
       CC1< (ppt)b
       CH3CC13 (ppt)
       Halon 1211 (ppt)
                 Model     Atmospheric     Observed
Model Results  Growth Rates  Measurements   Growth Rates
346
314
1650-1750
212-222
391
37
70
186
0.4
0.4%
0.27%
1%
4%
4%
14%
0.6%
12%
100%
346
310
1675
226
392
100
121
125
2
0.4%
0.2-0.3%
1%
4%
4%
7%
1.3%
6%
>10%
1 1987 value.
b 1982 value.
DRAFT - DO NOT QUOTE OR CITE
            VI-33
February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter VI








uncertainties surrounding the scenario of historical emissions. Using the reference assumptions, the




model achieves  an atmospheric concentration of 1671 ppb in 1985 compared to the observed value




of 1675  ppb.  The CH4  concentrations vary considerably in  the sensitivity analyses and range from



1650 ppb to 1750 ppb for alternative chemistry parameters.








        Of the three dominant greenhouse gases, the estimates of N2O concentrations vary the most




from historical measurements.  The model predicts concentrations of 314 ppb in 1985 compared to




308 to 310 ppb  cited in the literature.  From 1979 to 1986, the model estimates growth  in N2O




concentrations of 310 to  314 ppb compared to measurement  data that suggests growth of 303 to 310




ppb.  One of the  possible  explanations  of these results is  that  the relative share of emissions of




N2O from anthropogenic sources  is larger than estimated in the model.  A larger anthropogenic



source combined with lower natural emissions or a shorter atmospheric  life would be needed to




reduce the overall  concentrations and obtain the growth in concentrations seen from 1979 to 1986.




These results suggest that the model may underestimate future atmospheric concentrations of N2O.








        The model "predicts" very little deviation from  current  levels for the short-lived gases,




including OH, O3,  and CO.  The results for levels in 1870 include higher  levels of OH by 14-26%,



lower levels of tropospheric O3 by 19-29%, lower concentrations  of CO by approximately 50%, and



increased levels of upper stratospheric ozone by 4.5%.
ASSUMPTIONS ABOUT TRACE-GAS SOURCES AND STRENGTHS








        Among the various greenhouse gases there is some uncertainty over the quantity of emissions



that can be attributed to specific sources and the ability of these gases to modify the atmosphere.



The most critical of these uncertainties are examined below.
DRAFT - DO NOT QUOTE pR CITE       VI-34                           February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter VI








Methane Sources








        The available evidence on CH4 indicates that annual production ranges from 400-640 Tg of




methane (based on  known  sources  and sinks, its atmospheric  lifetime, and current atmospheric




concentrations).  Within this  budget, however, there is  much dispute over the size of individual




sources.  For example, research indicates that current CH4 emissions from rice paddies could be 60-




170 Tg; similarly, estimated emissions from biomass burning range from 50-100 Tg  (Cicerone and




Oremland, 1989).








        To account for these uncertainties,  the initial CH4 budget was varied to construct two cases:




(1) a high  anthropogenic  impact case,  where  the  starting methane  budget was biased toward




anthropogenic sources by assuming that anthropogenic activities such as fuel production and landfilling




caused higher emission levels than assumed in the RCW case, while lower emission estimates were




assumed from natural processes such as  oceans, wetlands, wildfires, and wild ruminants; and  (2) a




low anthropogenic impact case, by assuming lower emissions from anthropogenic activities such as




fuel production, enteric fermentation, and rice cultivation, with corresponding emission increases from




natural processes such as oceans and wetlands.  The specific emission  assumptions for the starting



budget are summarized in Table 6-3.








        The alternative starting budgets  in Table 6-3 result in different  growth paths  for CH4, since



emissions from anthropogenic sources increase by different amounts over  time.  These  differences



alter the atmospheric concentration of CH4: by 2100 the  atmospheric concentration is about 3500-




3700 ppb in the Low Impact case and 5200-5500 ppb  in the High Impact case (compared with 4100-




4400 ppb in the RCW case).  The  increase (decrease) in CH4 also increases (decreases) the amount




of tropospheric ozone.  The impact on realized  warming is summarized in Figure 6-8, which indicates




a decline of 0.1-0.2°C by 2100 in the Low Impact case compared with the RCW case and an increase
DRAFT -  DO NOT QUOTE OR CITE        VI-35                           February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                   Chapter VI
                                      TABLE 6-3

                 Low and High Anthropogenic Impact Budgets For Methane
                               (teragrams/year as of 1985)
Source of Methane
Fuel Production
Enteric Fermentation
Rice Cultivation
Landfills
Oceans
Wetlands
Biomass Burning— Anthropogenic
Biomass Burning— Natural
Wild Ruminants
Other Sources
TOTAL
Low Impact
50
70
60
30
40
150
35
20
44
11
510
RCW
60
75
110
30
15
115
35
20
44
__6
510
High Impact
95
75
110
58
6
100
35
15
10
_6
510
 DRAFT - DO NOT QUOTE OR CITE
VI-36
February 21, 1989

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 Policy Options for Stabilizing Global Climate -- Review Draft
                                    Chapter VI
                              FIGURE 6-8
   oo
   2
   oo
   _J
   LU
   O
   W
   UJ
   UJ
   tc.
   O
   UJ
   0
                INCREASE IN REALIZED WARMING

          DUE TO CHANGES IN THE METHANE BUDGET

                (Degrees Celsius; Based on 3.0 Degree Sensitivity)
                                   j_
                                                        High Methane
                                                        Low Methane
                                                        RCWP
        1985  2000
2025
   2050


YEAR
2075
2100
DRAFT - DO NOT QUOTE OR CITE
        VI-37
                        February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter VI








of 0.2-0.3°C by 2100 in  the High Impact case.  The corresponding effects on equilibrium warming




by 2100 are a decline of 0.2-0.3°C in the Low Impact case and an increase of 0.3-0.5°C in the High




Impact case.








Nitrous Oxide Emissions From  Fertilizer








        N2O is naturally produced  in soils  by  microbial  processes  during  denitrification and




nitrification.  When nitrogen-based fertilizers are applied, N2O emissions from the soil can increase



as a result of the additional nitrogen source.   The  amount of fertilizer nitrogen evolved  as N2O is




highly variable and  uncertain.  We have used  the emission estimates developed by Galbally (1985)




in our base cases:  0.5% for anhydrous ammonia, 0.1% for ammonium nitrate, 0.1% for ammonium




salts, 0.5% for urea, and 0.05%  for nitrates.  Alternative assumptions are explored below.








Anhydrous Ammonia








        One of the key uncertainties concerns the emission coefficient for anhydrous ammonia.  A




review of the scientific literature on measurements of N2O emissions by fertilizer type indicates that



the percentage of anhydrous ammonia evolved as N ranges from 0.05-6.84%, with  most measurements



ranging from 0.5-2.0% (Eichner, 1988). The impact of this uncertainty was evaluated by changing



the anhydrous ammonia coefficient from 0.5% to 2.0%. This change Increased  the amount of N2O



from fertilizer applications by 0.1 Tg of N annually, an increase in 2025 from 0.7 to 0.8  Tg,  which




was too small to affect  the amount of global warming.
DRAFT - DO NOT QUOTE OR CITE       VI-38                           February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter VI









H,O Leaching From Fertilizer








        As discussed above, in the RCW case N2O emissions from fertilizer were based on estimates




by Galbally  (1985).   One N2O emission pathway not included in this estimate is leaching from the




fields into the ground water or surface water due to the application of the fertilizer.  The rate of




emissions related to leaching is highly uncertain; Conrad et al. (1983) and Kaplan et al. (1978) have




suggested that the  amount of N2O evolved due  to  leaching may  be  as large  as  N2O  from the




denitrification/nitrification processes in the soil. The impact of leaching on total N2O emissions and




the resulting global warming was analyzed by increasing all of Galbally's  emission coefficients by one




percentage point. The higher  rate of N2O from fertilizer due to leaching resulted in an increase in




emissions of about 1.0-1.5 Tg annually.








        Atmospheric N2O concentrations  increase about 20 ppb by  2100  compared  with the RCW




case (from 403 to 424 ppb; see Figure 6-9).  While N2O concentrations  increase when leaching is




assumed, the impact on global warming is not as certain. In this case,  global warming was slightly




reduced  (less  than 0.1°C) due  to the  chemical interactions that occur with increased N2O  levels.




Specifically,  higher N2O levels  in  the stratosphere reduce the amount of stratospheric ozone, which




in turn allows more ultraviolet (UV) radiation to penetrate to lower elevations.  The increased UV




radiation increases the amount of CFC destruction, which reduces the contribution of CFCs to global




warming. None of these reactions are very strong, since the change in N2O emissions due to leaching




does not have a major effect on atmospheric concentrations, but they are sufficient to counteract the




warming effect of higher N2O  concentrations alone.








N2O Emissions From Combustion









        During the combustion process, chemical interactions downstream from the  combustion
DRAFT - DO NOT QUOTE OR CITE        VI-39                           February 21, 1989

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 Policy Options for Stabilizing Global Climate « Review Draft
             Chapter VI
                             FIGURE 6-9
     CHANGE IN ATMOSPHERIC CONCENTRATION OF N20


                         DUE TO LEACHING

                  (Parts Per Billion; 3.0 Degree Celsius Sensitivity)
      500
      400  -
   tr
   iu
   a.
   cc
   <.
   a.
       300
       200
                           I
                                      I
                                                           Leaching



                                                           RCW
         1985  2000
2025      2050



       YEAR
2075
2100
DRAFT - DO NOT QUOTE OR CITE     VI-40
                                                      February 21, 1989

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Policy Options  for Stabilizing Global Climate - Review Draft                        Chapter VI









chamber can lead to N2O formation from nitrogen oxides.  The rate of this  formation  is highly




uncertain, although recent evidence indicates  that it is likely to be fairly small.  In the RCW case




these low emission coefficients were assumed  (see Chapter II).  To ascertain the impact of higher




emission coefficients, N2O coefficients from combustion  were increased  such that emissions from




energy in 1985 were 2.3 Tg N rather than 1.1 Tg N as obtained in the RCW case.  The higher N2O




emission levels  increased atmospheric concentrations about 50 ppb by 2100 (as shown  in Figure 6-




10);  the resulting impact on global warming was  negligible (less than 0.1°C)  for the same reasons




discussed above under leaching from fertilizer.









UNCERTAINTIES IN THE GLOBAL CARBON CYCLE









        The  global  carbon  cycle,  which  regulates  the flow  of carbon through the environment,




including  the atmosphere, biosphere,  and hydrosphere,  was  discussed in Chapters  II  and  III.




Uncertainties in the size of the various sources and sinks for carbon and the interactions that govern




the flow of carbon increase  the difficulty of estimating the impact of anthropogenic  activities on




global climate.  In this section the major uncertainties in the global carbon cycle are evaluated.  The




first  part focuses  on the impact of deforestation on  CO2 emissions.  The second part discusses the




ability  of the oceans to absorb CO2 and heat.   Currently, the oceans are the dominant sink for




anthropogenic CO2 emissions, with the mixed  layer  alone  containing about as much carbon as the




atmosphere.  The oceans' ability  to operate as a net sink for carbon and  heat  is an important




component of the global climate system;  any changes in this absorption ability could have profound




effects  on global  climate (see  Chapter III).
DRAFT - DO NOT QUOTE OR CITE        VI-41                           February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft
                                    Chapter VI
                              FIGURE 6-10
    CHANGE IN ATMOSPHERIC CONCENTRATION OF N20

                       DUE TO COMBUSTION

              (Parts Per Billion; Based on 3.0 Celsius Degree Sensitivity)
      500
      450
      400
   CO
   OL
   01
   O.

   w  350

   cc.
   <
   a.
      300
      250
      200
                                                             Combustion
                                                             RCW
         1985  2000
2025
   2050


YEAR
2075
2100
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       VI-42
                       February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter VI








Unknown Sink In Carbon Cycle








        Atmospheric CO2 concentrations have changed historically due to an imbalance between the




sources  and sinks for carbon.  If the production of carbon exceeds the ability of the various carbon




sinks to  absorb it, then the  atmospheric CO2 concentrations will increase (and vice versa).  When




analyzing the  amount of carbon produced from various sources in the  past, atmospheric scientists




have been unable to balance the  carbon cycle. That  is, given current estimates of carbon sources,




it  would  appear  that  atmospheric CO2 concentrations would  have to be higher than  currently




measured, since all known sinks do not appear to be able to absorb all of the carbon produced.  To




account for this imbalance,  we have assumed the existence  of an  "unknown sink"  that absorbs the



unaccounted-for' carbon.  The size of this unknown  sink depends on  the  assumed magnitude  of




known sources and sinks-by definition,  the  unknown sink is simply:   sources minus sinks minus




atmospheric accumulation.








        For our base cases,  the size of the unknown sink was kept constant at 1.6 Pg annually based




on  its  calculated value (from the model) for 1975-1985.   However,  alternative  assumptions  are




plausible.  To  capture these  uncertainties, 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 (this increase  might occur, e.g., because the size of the unknown sink is related



to the fertilization of terrestrial ecosystems by increasing CO2);  and (2) a low case, where the size



decreases to zero exponentially at 2% per year (e.g., because the process responsible for the unknown



sink has a limited capacity).








        When the unknown sink is assumed to increase in proportion to CO2 concentrations in the




RCW case, the amount of carbon absorbed by the unknown sink  increases to  11.6 Pg annually by




2100.  This rate  of carbon  absorption results in a decline in CO2 concentrations relative to  the
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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter VI








Rapidly Changing World, which reduces realized warming by 0.1-0.2°C in 2050 and 0.5-0.7°C in 2100;




equilibrium warming is reduced in 2050 by 0.2-0.5°C and in 2100 by 0.7-1.4°C (based on 2.0-4.0°C




climate  sensitivities).








        In the low case, that is, when the unknown sink decreases to zero, the estimated impact on




warming is significantly lower, since the  unknown sink was only 1.6 Pg annually to start.  As a result,




CO2 concentrations do increase, but the increase in realized warming is less than 0.1°C  in 2050 and




0.1-0.2°C in 2100 (based on 2.0-4.0°C climate sensitivities; see Figure 6-11).








Amount of CO2 From  Deforestation








        Estimates of the amount of CO2 emitted from  deforestation activities vary due to different



assumptions on the rate of deforestation, the fate of the deforested lands, and the amount of carbon




contained in the forest vegetation  and soils.  In the base cases we used the lower  carbon estimates




(i.e., lower biomass estimates) given by Houghton (1988); for 1980 the resulting net flux of carbon




to the atmosphere was about 0.4  Pg of  carbon.  Higher estimates of initial biomass have also been




analyzed by Houghton  (1988); with these estimates the net flux of carbon to the atmosphere in 1980



would have been about 2.2 Pg.   These higher biomass estimates are evaluated here for the three



deforestation scenarios discussed in Chapter V.  The net flux of carbon for each of these scenarios



is presented in Figure  6-12.








        In the RCW case the rate of CO2 emissions from deforestation was based on an exponential




decline  in forest area using the lower biomass assumptions.  If the higher biomass estimates are used,




the total carbon flux from deforestation  from 1980 to 2100 is 281 Pg compared with  118 Pg using the



low estimates of carbon stocks (Houghton 1988).  Similarly, in the population-based deforestation




scenario the total carbon flux to the atmosphere from 1980 to 2100 is about 138 Pg using the lower
 DRAFT - DO NOT QUOTE OR CITE       VI-44                            February 21, 1989

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 Policy Options for Stabilizing Global Climate •- Review Draft
                                       Chapter VI
                               FIGURE 6-11
             IMPACT ON REALIZED WARMING DUE TO

                      SIZE OF UNKNOWN SINK

                (Degrees Celsius; Based on 3.0 Degree Sensitivity)
   v>
   UJ
   Ul
   cc.
   a
   UJ
   a
       1985   2000
2025
2050
                                YEAR
2075
                                                            2% Decline

                                                            RCW
                                                            Proportional
                                                              Increase
2100
DRAFT - DO NOT QUOTE OR CITE     VI-45
                                                          February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft
                                 Chapter VI
                              FIGURE 6-12
     C02 FROM DEFORESTATION ASSUMING HIGH BIOMASS

                         (Petagrams of Carbon/Year)
         3 -
      O
      CO
      cc.
      «t
      O
      u.
      O
      <£
      a
      «t
      t-
      UJ
      CL
        -1
                                SCW /
                                        //I
                                       /   I
        RCW
                             Stabilizing

                             Policy Scenarios
                               I
         1950       1980
2010      2040



     YEAR
2070      2100
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                            February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter VI









biomass estimates and 324 Pg using the higher biomass estimates.  In the reforestation scenario, the




total accumulation of carbon from the atmosphere was 38 Pg using the lower biomass estimates and




59 Pg using the higher biomass estimates.








        Despite the substantial increase in the amount of carbon from deforestation when the higher




biomass estimates are used  (e.g., by 2050 CO2 emissions  from deforestation are 2.3 Pg compared




with 1.0 Pg in the RCW with the lower estimates), the resulting atmospheric concentration of CO2




is only slightly higher (see Figure 6-13 for the differences in the RCW case, i.e., forest area declines




exponentially). This result is due to the larger size of the "unknown carbon sink" in our model  when




higher deforestation emissions are assumed (see Unknown  Sink above).   In our analysis the increase




in the  size of the unknown  sink was sufficient  to absorb  some of the  additional carbon when the




higher biomass estimates are used, assuming that the size  of the unknown sink remains constant at




its average 1975-1985 value (i.e., 2.6  Pg C with high biomass vs. 1.6 Pg  C  with low biomass).  The




additional increase in  CO2 increased realized warming and equilibrium warming less  than  0.1°C by




2100 compared with the RCW case warming (assuming 2.0-4.0°C climate sensitivities).









Alternative CO2 Models of Ocean Chemistry and Circulation








        In the RCW case ocean chemistry was represented using a diffusion model of the ocean (the




Modified  GISS model)  based on  the model  described by Hansen  et  al. (1988).   Several  other




approaches have  also been developed and adopted for the EPA framework  by W. Emmanuel and B.




Moore. These include:









        •      Box-Diffusion Model introduced by  Oeschger et al. (1975), which represents the




               turnover of  carbon below 75  meters as a  purely diffusive process.
DRAFT - DO NOT QUOTE OR CITE       VI-47                           February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft
     Chapter VI
                             FIGURE 6-13
         IMPACT OF HIGH BIOMASS ASSUMPTIONS ON
           ATMOSPHERIC CONCENTRATION OF C02
             (Parts Per Million; Based on 3.0 Degree Celsius Sensitivity)
     1000
      800  -
    UJ
    a.
    v>
    
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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter VI








        •       12-Compartment Regional Model by Bolin et al. (1983), 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.








        •       Advective-Diffusive Model by Bjorkstrom (1979), which divides the surface ocean into




                cold and warm  compartments; water  downwells  directly from the cold  surface




                compartment into intermediate and deep layers.








        •       Outcrop-Diffusion Model by  Siegenthaler (1983), which allows direct ventilation of




                the  intermediate  and deep  oceans at  high latitudes by incorporating outcrops




                connecting all sublayers to the atmosphere.








        Because each of these models uses a different  approach  to  evaluate ocean chemistry, the




resulting impact on atmospheric CO2 concentrations could vary from one approach to the next. To




determine how comparable these models were, the RCW case was evaluated using each model in



turn.








        The estimates of future  CO2 concentrations from each model are summarized in Figure 6-



14a. These results indicate that  the Modified GISS model tends to project higher atmospheric CO2



concentrations  than the other models; for example, by 2100 CO2 concentrations are about 6-7%



higher than concentrations estimated by Oeschger et al.,  Bolin et al., or Bjorkstrom, and about 19%




higher than those estimated by Siegenthaler.  There are two basic reasons  for these differences: (1)




The Modified GISS model, unlike the  other models, incorporates  temperature  feedback that alters




ocean carbonate chemistry; that is, as the mixed  layer  of the oceans  warms  due  to atmospheric




warming, the  amount of carbon that can be absorbed by the oceans decreases; and (2) The Modified
DRAFT - DO NOT QUOTE OR CITE       VI-49                           February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter VI








GISS model does not incorporate any heat or CO2 transfer between the thermocline and the deep




ocean (below 1,000 meters); to the extent heat or CO2 is  transported to the ocean depths in the long




run,  the Modified GISS model understates the oceans' absorption capacity.








       Siegenthaler's Outcrop-Diffusion Model estimates lower CO2 concentrations than any of the




other models. This  result  is anticipated because the Outcrop-Diffusion  Model allows CO2 to  be




absorbed from the atmosphere to the deep layers rather  than diffuse through the intervening layers,




so that, in this model, carbon is absorbed more  quickly in the oceans than in the other models.  By




2100 equilibrium warming using Siegenthaler's  model is 0.6-1.2°C  lower  than the RCW  case (see



Figure 6-14b  for warming estimates from all five models).








ASSUMPTIONS ABOUT CLIMATE SENSITIVITY AND TIMING








Sensitivity of the Climate System








       A general  benchmark for comparing atmospheric models is their  response to a doubling of




CO2 concentrations (2xCO2; see Chapter  III).   Put  simply, this benchmark describes how much



warming  would be expected once  the atmosphere stabilizes following a  two-fold increase  in CO2



concentrations.  In our analyses we have used the range from 2.0-4.0°C.  As discussed in Chapter



III, there is a great deal of uncertainty about the strength of internal climate feedbacks, and, in some



cases, whether a feedback will be positive or negative.  If cloud and surface albedo changes produce




large positive feedbacks, as  suggested by some analyses, the  climate sensitivity  could be 5.5°C or




greater.  On  the other hand, these  feedbacks could be weak and  cloud feedbacks could be negative,




resulting  in a climate sensitivity as low as 1.5°C.  For  the sensitivity analysis,  therefore, we have




evaluated the extent of global warming using 1.5 and 5.5°C as lower and upper bounds, respectively.




The impact of these  assumptions on realized warming is summarized in Figure 6-15 for the RCW
DRAFT - DO NOT QUOTE OR CITE        VI-50                           February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft
                                                            Chapter VI
                             FIGURE 6-14
         COMPARISON OF DIFFERENT OCEAN MODELS


                     CO2 CONCENTRATIONS

                           (Parts Per Million)
  z
  o
     900
     800
  d  700


  a.
  LU
  o-  600
     500
     400
     300
                                              Siegenthaler



                                              Oeschger
                                              Bolin
                                              Bjorkstrom
       1985  2000
                        2025
   2050


 YEAR
2075
2100
              IMPACT ON EQUILIBRIUM WARMING

                   (Based on 3.0 Degree Celsius Sensitivity)
    2
    v>

    ui
    o
    w  .
    u  4
    UJ
    cc.
    o
    ui
    a
                                              Siegenthaler
                                               Oeschger
                                               Bolin

                                               Bjorkstrom
       1985  2000
                        2025
   2050


YEAR
2075
2100
DRAFT - DO NOT QUOTE OR CITE     VI-51
                                                       February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                     Chapter VI
                               FIGURE 6-15
              IMPACT OF CLIMATE SENSITIVITY ON
                         REALIZED WARMING
                (Degrees Celsius; 1.5-5.5 Degree Climate Sensitivity)
       Slowly Changing World Scenario
Rapidly Changing World Scenario
  1985 2000  2025  2050  2075  2100   1985 2000  2026  2050  2075  2100
                   YEAR                                 YEAR
 DRAFT - DO NOT QUOTE OR CITE     VI-52
                 February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                         Chapter VI








and SCW cases.  In the RCW case, the range of realized warming for a 1.5-5.5°C climate sensitivity



would be 1.5-3.2°C by 2050 and 2.9-6.6°C by 2100, compared with a range of 1.9-2.8°C by 2050 and



3.6-5.6°C by 2100 when the climate sensitivity is bounded by 2.0-4.0°C.  The corresponding values



for equilibrium warming for a  1.5-5.5'C climate sensitivity are 2.0-7.4°C by  2050 and 3.6-13.2°C by



2100,  compared with 2.7-5.4°C by 2050  and 4.8-9.6°C by 2100 for a 2.0-4.0°C climate sensitivity. In



the SCW case, the range  of realized warming for a 1.5-5.5°C climate sensitivity would be 1.3-2.9°C



by 2050  and 2.0-4.7°C by  2100,  compared with  a range of 1.6-2.5°C  by 2050 and 2.5-4.0°C by 2100



when the range of climate sensitivity is 2.0-4.0°C. The corresponding values for equilibrium warming



for a 1.5-5.5°C climate sensitivity are 1.7-6.1°C  by 2050 and 2.4-8.6°C by 2100, compared with 2.2-



4.5°C by 2050 and 3.1-6.3°C for  a 2.0-4.0°C climate sensitivity.








Rate  of Heat Diffusion








        CO2  and heat are currently transferred from the atmosphere to the oceans and within the



ocean itself as a result of many complex chemical and physical interactions.  One of these interactions



is  the transfer of heat from the mixed layer to the  thermocline, thereby  delaying global warming.



Additionally,  changes in ocean  mixing and  circulation patterns as a result of climate  change could



alter the capacity of the oceans  to absorb heat (see BIOGEOCHEMICAL  FEEDBACKS for further



discussion). The rate at which  heat is  absorbed only affects the rate of realized warming,  not the



rate of equilibrium warming, because the oceans cannot absorb heat indefinitely.








        In our model the  rate at which mixing occurs between the mixed layer and the  thermocline



is parameterized with an eddy-diffusion coefficient (see Chapter III). The value of the eddy-diffusion



coefficient  in the base cases was assumed to be 0.55 x 10"4 m2/sec.  For purposes of this sensitivity



analysis alternative values  of 2 x 10'5 and 2 x 10"4 have been evaluated.
DRAFT - DO NOT QUOTE OR CITE       VI-53                            February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                       Chapter VI








       As shown in Figure 6-16 the rate at which the oceans absorb heat can noticeably affect the



amount of realized warming by 2100.  If the rate of heat absorption is greater than that assumed in



the base  cases (i.e., if the eddy-diffusion coefficient is 2 x 10"4 m2/sec), realized warming by 2100



would be 0.5-1.2°C less than in the RCW case (assuming 2.0-4.0°C climate sensitivities).   For the



smaller eddy-diffusion coefficient of 2 x 10"5 m2/sec, realized warming by 2100 would be  0.3-0.9°C



higher.








ASSUMPTIONS ABOUT ATMOSPHERIC CHEMISTRY:  A COMPARISON OF MODELS








       As discussed in Chapters II and III, the chemistry of the future  troposphere is one of the



uncertainties in the prediction of atmospheric composition.   The principal factors contributing to this



uncertainty are:    (1)  the complexity and  tremendous  natural  variability  of  chemistry  in the



troposphere, especially regarding oxidant formation; (2) the range of interactions between tropospheric



chemistry and radiation perturbed by  climate change and changes in stratospheric composition; and



(3) the range of uncertainties in future emissions of CH4> CO, NOn and non-methane hydrocarbons



(NMHC).  This section focuses on the first two aspects of uncertainty in  atmospheric composition.








       Recognizing the  uncertainty  in tropospheric  chemistry, EPA sponsored a  workshop on



atmospheric composition  to  discuss recent modelling  efforts among members of the atmospheric



sciences  community  and  to  construct a  parameterized atmospheric  chemistry model that would



incorporate the latest scientific  findings.  The end result was the Assessment Model for Atmospheric



Composition (AMAC), the model used to obtain the findings discussed in this report.  AMAC was



developed by Prather of NASA/GISS as a result  of the workshop, which was held in January 1988



(see Prather, 1988). To obtain insight into the uncertainties introduced by the physical simplifications



made by the AMAC and to  ensure results that are comparable to  current, more-detailed  modeling
DRAFT - DO NOT QUOTE OR CITE       VI-54                          February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft
                                   Chapter VI
                             FIGURE 6-16
      4  -
       3  -
    v>

    55
    _i
    UJ
    o
    v>
    UJ
    O  2
    UJ  '
       1  -
                   CHANGE IN REALIZED WARMING


               DUE TO RATE OF OCEAN HEAT UPTAKE
                  (Degrees Celsius; Based on 3.0 Degree Sensitivity)
       1985   2000
2025
2050
2075
                                YEAR
                                                            2x 10



                                                            RCW
                                                                 -5
                                                            2x 10
                                                                -4
2100
DRAFT - DO NOT QUOTE OR CITE      VI-55
                               February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter VI








efforts, a set of common scenarios of CH4, CO, and NOX emissions were analyzed in the AMAC,



as well as in two current research models:  a 2-D tropospheric chemistry model developed by Isaksen



(Isaksen and Hov, 1987); and a multi-box photochemical model of the global troposphere developed



by Thompson and co-workers at NASA/Goddard (Thompson et al.,  1988).








Model  Descriptions








       Each of these models is briefly  described below.








Assessment  Model for Atmospheric Composition








       The focus of interest in tropospheric  composition is on O3, CH<, and OH, because the two



former gases are key greenhouse absorbers and OH (together with ozone) determines the oxidizing



capacity of the atmosphere and the abundance of many gases such as methane, carbon monoxide,



methyl chloroform, and HCFC-22  (CHF2C1).








       For the simulation of the troposphere  in this model, the Northern and Southern Hemispheres



(NH & SH) are treated separately because  significant asymmetries are observed in many of the



important shorter-lived gases, such as  CO and NO,.  These species play a major role in the budgets



for CH4,  O3, and OH in each hemisphere.








       In  the AMAC,  tropospheric  OH  can be treated as a steady-state variable as it responds



immediately to the annual average  values of the trace gases. To derive perturbations to OH, a non-



linear system is solved equating a "production" term to a "loss" term.  OH losses are partitioned



among the predicted gases (CH4, CO), the specified fluxes (NMHC), and self-reactions  (OH). The



production  side of the equation includes a positive response to increases in UV radiation (i.e., loss
DRAFT - DO NOT QUOTE OR CITE        VI-56                           February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter VI








in column ozone) and in tropospheric H2O, O3 and NOX fluxes.  Coefficients for variations in either



the production or loss  terms with respect to column O3) tropospheric water vapor, trop-O3, CO,




CH4, and fluxes of both NMHCs  and NOX are based on results from 1-D and 2-D models  (Liu et




al., 1987; Thompson and Cicerone, 1986; Is'aksen and Hov, 1987; Isaksen et al., 1988).  Major  sources




of uncertainty in calculating OH are the spatial averaging for this highly variable constituent  and the




nonlinearity in perturbation coefficients, especially with respect  to NOX distribution.








        Perturbations to tropospheric ozone affect both tropospheric temperatures and the long-lived




source gases  controlled by OH.   A significant fraction of  tropospheric ozone originates in the




stratosphere and is  destroyed by surface deposition; it is sufficiently short-lived (a few months) that




the AMAC calculates ozone perturbations separately  for each hemisphere. Changes in tropospheric




ozone are associated with perturbations  to the total ozone  column, and to  tropospheric chemical




reactions, which are  evaluated with sensitivity coefficients, dln(O3)/dln(X), ascribed to the precursor




gases (Column -O3, 0.8; CH4, O.2; CO, O.I; NO., flux, O.I; NMHC flux,  O.I).  The coefficients are




based on detailed  photochemical models  for typical  tropospheric  air  parcels (Liu et al.,  1987;



Thompson  et  al., 1988), but their uncertainties are  large, approximately a factor of 2.  Also, the




efficiency of O3 production varies widely with the NO, levels (Liu et al., 1987), which in turn cannot




be adequately characterized throughout the entire troposphere due to their large dynamic range.  A




similar concern applies  to the simplified treatment of non-methane hydrocarbons.








Isaksen  Model








        The Isaksen model is a 2-D transport model that calculates absolute concentrations for  O3




and OH (and  several dozen other trace  chemical  constituents  in  the troposphere) as functions of




altitude and latitude, as emissions  are varied over time (Isaksen  and Hov, 1987; Isaksen et al., 1988).




Unlike the AMAC, this model  resolves latitudinal and altitude distributions,  and emission changes
DRAFT - DO NOT QUOTE OR CITE        VI-57                           February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter VI








are introduced with latitudinal discrimination.  The transport of longer-lived constituents can locate




key areas of tropospheric ozone and OH change that  the AMAC will miss; because a 2-D  model



resolves  altitude, the  effects of  high-altitude aircraft emissions  on NOX  and  ozone  or cloud




perturbations to radiation fields, for example, can be explored. The Isaksen model differs from the




AMAC  in that the  troposphere  is not  coupled to  the stratosphere, so that the impact of changing




climate or perturbations on stratospheric ozone are not included.  Methane flux changes are included




in annual updates of the model.








Thompson et al. Model








        The Thompson model couples the result  of 1-D model calculations of the time history for




eight  chemically coherent global regions, which are then averaged  to estimate net global changes.




A steady-state method is  used: emissions are specified in simulations to represent conditions at 5-



year  intervals.  This  is  somewhat inadequate  for lifetime changes,  tending  to  underestimate




tropospheric ozone  increases (up to 30% in one  test  case) and  to overestimate increases  in CH4




concentrations.








        The description of chemically coherent  regions offers  insight into  regional variability, a



feature lacking in the version of the Isaksen model used here, which does not have the longitudinal



variation needed to  treat emissions that are restricted to the source area but that can have extensive



effects on ozone and OH.  Like the Isaksen model, the Thompson model includes  a more complete




set of chemical constituents than does  the AMAC and can identify other effects and interactions of




climate  perturbation.  For example, the oxidants that contribute to sulfuric acid formation in clouds




and rain (HO2 and H2O2)  are very sensitive to  changes in stratospheric ozone  and  tropospheric




water vapor.  At the 2035 year point, stratospheric  ozone depletion and climate change (temperature




and water vapor) effects are added to  calculations with perturbed CH4, CO, and NO,, emissions.
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Policy Options for Stabilizing Global Climate -- Review Draft                       Chapter VI








Results  from the Common Scenarios








        It is  not easy to compare  the models because the structure, input,  and derived quantities




from the three models are not treated comparably. Nevertheless, insights into uncertainties can be



obtained by comparing selected results from each model. EPA supplied eight scenarios of alternative




estimates of CH4, CO, and NO, for evaluation in each model. In this section one of these scenarios



is discussed (EPA Scenario #2), which assumes low CH4, low CO, and high NO^ growth in sources,




a rapid growth scenario for CO2 and N2O from combustion, and a CFC and halon scenario consistent




with the Montreal Protocol.  Table 6-4 summarizes  the emission estimates  for this scenario  and




compares them to estimates from the Rapidly Changing World (RCW) and Slowly Changing World




(SCW) scenarios (Appendix C provides more detail for all eight scenarios).  The RCW and SCW




cases could not be explicitly included for this model comparison because the  development of these




cases occurred simultaneously with  the model comparison. Table 6-5 summarizes the results for all




eight scenarios.








        The EPA  #2 emission estimates are in  the  same range as those  of the other two cases




except for CO emissions. These estimates are much lower than both the RCW and SCW cases  and




are similar to the Stabilizing Policy cases due to stringent control assumptions on transport vehicle




emissions.  For the other emissions, the CO2 emission estimates in EPA #2 fall between the RCW



and SCW cases for most of the time periods, approaching the RCW estimates by 2100.   The CH4



and NO, estimates are similar to those for the SCW case, except that NO,, estimates after 2050 fall



between the RCW  and SCW  estimates.








        The  AMAC's  troposphere  is basically a parameterized  2-box model:  it reports  mean




tropospheric values (ppb) for  CH4, and separate perturbations (% change)  to OH and O3 in each




hemisphere.  For the global average perturbation to OH and O3, Northern and Southern Hemisphere
DRAFT - DO NOT QUOTE OR CITE       VI-59                          February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                   Chapter VI
                                      TABLE 6-4

                      Comparison of Emission Estimates For EPA #2,
                                 RCW, and SCW cases
                         (in teragrams, unless indicated otherwise)
Emissions Estimates bv Year
Trace Gas
C02 (Pg C)
EPA #2
RCW
SCW
CO (as C)
EPA #2
RCW
SCW
CH,
EPA #2
RCW
SCW
NOX (as N)
EPA #2
RCW
SCW
1985

6.3
5.9
5.9

316
502
502

500
510
510

59
53
53
2000

7.3
7.6
7.2

226
571
616

548
577
569

59
60
59
2025

10.4
11.5
9.2

194
699
842

640
712
676

64
73
69
2050

13.7
16.6
9.8

192
895
859

721
880
740

72
92
71
2075

17.9
22.2
9.7

178
1050
595

779
1025
773

82
108
65
2100

25.2
25.5
11.4

192
1207
604

809
1089
816

104
118
70
 DRAFT - DO NOT QUOTE OR CITE
VI-60
February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                    Chapter VI
                                      TABLE 6-5

        Comparison of Results From Atmospheric Chemistry Models for the Year 2050
                                   Compared to 1985
Model

Increases in Methane (ppb)
Low NO,,
Prather
Isaksen
Thompson et al.
High NO,
Prather
Isaksen
Thompson et al.
Percent Change in CO
Low NOX
Prather
Isaksen
Thompson et al.
High NOX
Prather
Isaksen
Thompson et al.

LOW
Low CO

EPA#1
806
400
750
EPA#2
801
350
870

EPA#1
16
-13
-10
EPA#2
17
-9
-2.4
Test Case
CH4
High CO

EPA#3
1031
720
1000
EPA#4
1048
550
1240

EPA#3
43
8
25
EPA#4
44
8
58
Results
HIGH C
Low CO

EPA#5
1750
950
1710
EPA#6
2082
1010
2210

EPA#5
55
0
16
EPA#6
70
8
35


High CO

EPA#7
2022
1220
1890
EPA#8
2242
1200
2560

EPA#7
82
17
52
EPA#8
99
19
97
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February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                  Chapter VI
                                TABLE 6-5 (continued)

        Comparison of Results From Atmospheric Chemistry Models for the Year 2050
                                  Compared to 1985
Model

Percent Change in OH
Low NOX
Prather
Isaksen
Thompson et al.
High NOX
Prather
Isaksen
Thompson et al.
Percent Change in O3
Low NO,
Prather
Isaksen
Thompson et al.
High NOX
Prather
Isaksen
Thompson et al.

LOW
Low CO

EPA#1
-9
5
-9.4
EPA#2
- 2
8
-8.9

EPA#1
1
-1
3.7
EPA#2
5
5
10.0
Test Case
CH4
High CO

EPA#3
-14
- 1
-15.5
EPA#4
- 9
4
-17.4

EPA#3
8
2
9.9
EPA#4
13
8
17.5
Results
HIGH
Low CO

EPA#5
-23
1
-20.1
EPA#6
-22
5
-22.1

EPA#5
21
3
13.2
EPA#6
33
10
23.1

CH.
High CO

EPA#7
-26
- 2
-27.6
EPA#8
-25
3
-23.9

EPA#7
27
5
18.3
EPA#8
39
13
29.0
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VI-62
February 21, 1989

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Policy Options for Stabilizing Global Climate -- Review Draft                       Chapter VI








results are averaged with equal weight.  In addition to the perturbed species discussed here with the



tropospheric chemical models, the AMAC calculated other significant perturbations, such  as a 12%



decrease in column ozone, a 2°K rise in mean tropospheric temperature, along with a 10% increase



in tropospheric water vapor.   These perturbations have an impact on tropospheric OH, O3, CO, and



CH4. Additionally, unlike the other two models, which provide point estimates, the AMAC produces



a range of trace-gas scenarios in response to specified uncertainties in the model coefficients  (only



the mean of each range is provided in Table 6-5).








    The Thompson model averages over  eight "chemically coherent regions"  (Appendix  C gives a



description of how the EPA scenarios were assigned to the  regions).   This  approach is probably



adequate for  short-lived species such as OH, and possibly for tropospheric O3.  However, it makes



it difficult to interpret CH4 calculations, which predict different CH4 concentrations among the boxes,



when in fact the long lifetime of CH4 ensures that it is well mixed throughout the troposphere. The



methane results  in Table 6-5 have been averaged over  the eight regions and  scaled to account for



the CH4 lifetime changes  occurring in the perturbed atmosphere.  Also summarized are percent



changes in CO (surface mixing ratios) and OH and  O3 (column-integrated from 0-15 km).  The CH4



and  CO changes obtained by the Thompson model are very similar  to those  obtained with the



AMAC.  Although not shown in the  global averages in Table  6-5, the most useful  results of the



regional calculations are localized estimates of OH and O3 changes in each chemically defined region



where CO and  NOj growth rates may differ  considerably.   The differences between areas with



controlled emissions (Urban  1) and without controlled emissions (Urban 2) are very striking (Figure



6-17).








    The  Isaksen model calculates  perturbations  as  a function of latitude, altitude  (0-16  km), and



time of  year.  The increase in CH4 is distributed uniformly throughout the troposphere as expected.



There is a problem with the  implementation  of the EPA #2 scenario in that the CH4 concentrations
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Policy Options for Stabilizing Global Climate - Review Draft
                                                             Chapter VI
                              FIGURE 6-17
            REGIONAL DIFFERENCES FOR URBAN AREAS


            WITH DIFFERENT EMISSIONS OF CO AND NO
            Fraction Change: 1965-2050
                                               Fraction Change: 1985-2050
     -I









     9.1




     3




     t.S




     2




     1.6
  W




  I  '



  i  •!.»




     0




    -OA




     -I
I
          Fraction Chance: 1965-2060
Fraction Ch»nj«. 1085- 3050
         UrUn-l
       1 2 3 4 S « 7 6
                         Urban-2
Source: Thompson, 1988.
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                                VI-64
            February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter VI








decline at the beginning of the model integration.  This may be due to the low estimate of global



CO flux.  Initial fluxes were scaled in the AMAC and Thompson models to obtain a steady-state of



current concentrations.  CH4 does not recover to its initial concentration for at least 20 years into




the scenario,  and  this is probably the reason for  the Isaksen model predicting such a small increase




in CH4. The patterns for OH and O3 perturbations are distinct (Figure 6-18). The greatest changes



in O3 are below 2 km altitude:  there is  a large increase between 0° and 35°N and a small decrease




centered at 50°N.   The spatial pattern of changes in OH are interesting:  in the upper  troposphere




between 12 and 16 km the OH increases by 10-30% in the Northern Hemisphere, whereas throughout




most of the Southern Hemisphere OH decreases.  Both of these changes may be driven  by increases



in CH4. In the dry upper troposphere in the presence of NOB CH4 increases the OH concentration




during its  atmospheric oxidation, but in  the lower troposphere the CH4 provides merely a sink for



OH.








    Overall, all three models predict similar increases in tropospheric O3.  The Thompson et al.




and AMAC models predict  decreases in tropospheric OH, while the Isaksen model reports a globally



averaged increase. This discrepancy may be explained by the large increases  in OH above 12 km as




noted above, something that is  also calculated by the Thompson model.   However, most  of the




difference in  OH levels seems attributable to  the lower CO and CH4  concentrations calculated by



Isaksen compared with the  other two models.  As shown in Table 6-5  for all eight scenarios, none



of the increases in CO  by  2050 are more than  15-20% in Isaksen, whereas Thompson et  al. and



AMAC show CO increases  up to 100%  (see scenario #8).  Some of the CO and OH differences



between Isaksen et al. and the other  two models are due to the difference in initialization described




above, but most of the OH difference may be due to how CO behaves in each model.  This  may be



one of the more  prominent uncertainties in predicting future tropospheric composition. CO has a




moderate lifetime (typically about a few  months) with considerable spatial variability that is not well
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Policy Options for Stabilizing Global Climate -- Review Draft
                                  Chapter VI
                                    FIGURE 6-18
                       OH AND OZONE PERTURBATIONS

                       IN THE ISAKSEN AND HOV MODEL
                                    (Percent Change)
                                        Ozone
                is.oo-;
                2.00-!
                    S3  80  10 50 SO
                                     50 JO
                                          OH
                                              0 -<0 -20 -SO -*0 -SO -SO -10 -90 -SO
                                                                 LATITUCE
                    30  SO  10 SO SO *0  SO  20  '0
                                              3 -'0 -20 -SO ~*0 -50 -€0 -10 -90 -90

                                                                 LATITUCE
Figure 6-18.   Perturbation in O3 and OH from the Isaksen model using the EPA #2  emission
estimates.  Solid line indicates an increase in the parameter; dashed line indicates a decrease. O3
shows large increase between 0° and 35°N; OH shows increases up to 30% in Northern Hemisphere,
and decreases in Southern Hemisphere.  Source: Isaksen and Hov, 1987.
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February 21, 1989

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Policy Options for Stabilizing Global  Climate - Review Draft                        Chapter VI








resolved  in any  of the models.   Perhaps the Isaksen model gives a  lower  limit  to  CO and OH




changes,  and  the other two models estimate the largest expected changes.








EVALUATION OF UNCERTAINTIES USING AMAC








    Comparing the results of AMAC to other models given identical scenarios  provides  one approach




to evaluating uncertainties related to atmospheric chemistry.   Valuable information can  also be




obtained by testing  the robustness of the AMAC results to changes  in  critical model parameters.




This section examines these impacts by varying  key parameters  within AMAC and then comparing




the results to the RCW scenario.








Atmospheric  Lifetime of  CFC-11








    The  assumed atmospheric lifetime for CFC-11 in the AMAC for the RCW case was 65 years.




Its atmospheric lifetime,  however, may range from 55 to 75 years (Prather  1988); these estimates




were evaluated to determine the impact on atmospheric chemistry.  The changes in atmospheric




concentration for CFC-11 are  summarized in Figure 6-19, which indicates that concentration levels




may vary from about 650  to 810 ppt by 2100. Increases (decreases) in the atmospheric  concentration



of CFC-11,  however, tend  to be offset  by corresponding decreases (increases) in atmospheric



concentrations of other trace gases, such  as other CFCs  and CH4. That  is, the increase (decrease)



in the lifetime of CFC-11 increases (decreases)  the amount of stratospheric ozone  depletion, which



increases (decreases) the amount of UV radiation; these higher (lower) UV levels increase (decrease)



the rate  of  destruction of these other  gases.  As  a result, the impacts  on global  warming are




negligible (less than 0.1°C).
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Policy Options for Stabilizing Global Climate -- Review Draft
                                     Chapter VI
                              FIGURE 6-19
        SENSITIVITY OF ATMOSPHERIC CONCENTRATION

                    OF CFC-11 TO ITS LIFETIME
              (Parts Per Trillion; Based on 3.0 Degree Celsius Sensitivity)
      800  -
      700  -
      600  -
   O
   -J  500  -
   
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Policy Options  for Stabilizing Global Climate - Review Draft                        Chapter VI








Interaction of Chlorine with Column Ozone








    Chlorine in the  stratosphere has a negative, non-linear impact on total column  ozone.   This




chemical interaction is one of the primary causes of stratospheric ozone depletion due to the chlorine




contained in CFCs; this interaction has been included in the AMAC, however, primarily for its ability




to affect the rate of  tropospheric ozone formation.  In the RCW case this relationship was defined




as a 0.03% decline in total column ozone/(ppb)2 of stratospheric chlorine.  A higher value, 0.20%,




was evaluated, which would increase the rate of  column ozone destruction.








    With the 0.20%  assumption, total column ozone depletion was 45-47% by 2050 (assuming 2.0-




4.0°C climate sensitivities) compared with a  total column  ozone depletion of 16.8% with the  lower



value (i.e., the -0.03% value used in the RCW case).  The increase in total column ozone depletion




has a positive feedback on the tropospheric OH  levels due  to the increase  in UV radiation.  The




resulting OH interactions with other trace gases substantially reduces the atmospheric concentration




of CH4,  HCFC-22, methyl chloroform, and  methyl chloride, and reduces the rate of tropospheric




ozone formation. (The role of O3 is problematic, O3 at 10-12 km probably would increase.  At this




altitude,  O3 probably has the largest greenhouse effect.  See  Chapter II)  These impacts reduce the



amount of global warming; as shown in Figure  6-20, the decline in realized warming is 0.1°C by



2050, compared with the RCW case, and  0.3-0.4°C by 2100;  the decline in equilibrium warming by



2100 is 0.4-0.8°C (assuming 2.0-4.0°C climate  sensitivities).








Sensitivity of Tropospheric Ozone to CH4 Abundance








    Tropospheric ozone formation is affected by the  amount of CH4 present, although  the rate at




which tropospheric ozone forms as a result  of CH4  abundance is subject to some uncertainty. In



the RCW case, this variable for the Northern Hemisphere was assumed to be a 0.2% change  in
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Policy Options for Stabilizing Global Climate - Review Draft
                                    Chapter VI
                            FIGURE 6-20
                  CHANGE IN REALIZED WARMING


       DUE TO RATE OF INTERACTION OF CLx WITH OZONE

                 (Degrees Celsius; Based on 3.0 Degree Sensitivity)
   w
   UJ

   i
   g
      1986  2000
2025
2050
                              YEAR
2075
                                                        RCW
                                                        CLx/Ozone

                                                         Interaction
2100
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                               February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter VI








tropospheric ozone for each percentage change  in CH4 concentration; other evidence suggests  that




a higher value, 0.4%, is possible  (Prather,  1988).








    Using this higher value increases the change in tropospheric ozone in 2100 by about 50% over




the RCW case (tropospheric ozone increases by  about 63% compared with about 43% when a value




of 0.2% is  assumed).   The increase in tropospheric ozone  indirectly results in a decrease in CH4




concentrations since the tropospheric ozone increase also increases  OH formation, which  destroys




CH4.  Due to this partially offsetting effect, the  increase in global  warming is less than 0.1°C.








Sensitivity of OH to NOX








    Tropospheric OH formation  is affected by the level of NO, emissions, although the rate of  OH




formation  is uncertain. In the RCW case, we assumed a 0.1% OH change for every 1.0% change



in NO, emissions for the Northern Hemisphere. We evaluated a  range of uncertainty from 0.05%




to 0.2%.








    An increase (decrease) in the amount of OH due to a higher (lower) sensitivity to NOX emissions



results in less (more) tropospheric ozone formation as well as lower (higher) levels of CO and CH<.



The higher sensitivity value of 0.2% reduces realized warming about 0.1"C by 2100 compared with



the RCW case (assuming 2.0-4.0°C climate  sensitivities; equilibrium warming is about 0.2°C lower by



2100), while the lower sensitivity value of 0.05% increases realized warming less than 0.1°C by 2100



(equilibrium warming increases a maximum of 0.1°C by 2100).
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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter VI








BIOGEOCHEMICAL FEEDBACKS








    The  sensitivity  of the  climate  system  to anthropogenic perturbations  is  determined  by a



combination  of feedbacks  that  amplify  or dampen  the direct  radiative effects  of increasing



concentrations of greenhouse gases.   Several important internal climate feedbacks, such as  those



resulting from changes in water vapor, clouds, and sea ice albedo,  are included in the estimates of



climate  sensitivity discussed  throughout  this Report.   There are a number  of  feedbacks  of a



biogeochemical origin, however, that may  also play an  important role in climatic change that were



not included in the analyses on which this  range is based.  Biogeochemical sources of feedback



include  releases of methane hydrates; changes in ocean  chemistry, biology, and  circulation; and



changes in the albedo of the global vegetation.








    Any attempt to quantify the impact of biogeochemical  feedbacks is necessarily quite speculative



at this time;  however, it  does appear that they could have an important impact on global climate.



For example, Lashof (1989) has estimated  that the gain from biogeochemical feedbacks ranges from



0.05-0.29 compared with  a 0.17-0.77 gain from internal climate feedbacks.   (The gain is defined as



the portion of global equilibrium temperature change attributable to  the feedback divided by the total



global equilibrium temperature when the feedback is included).  Some of these key feedbacks were



incorporated into the  AMAC for  these sensitivity  cases to  determine the magnitude of their impact



on global warming.








Ocean Circulation








    As mentioned above, the oceans are currently a major sink for heat and CO2.  Concerns have



been raised, however, that the basic circulation patterns that allow these processes to continue  could



be significantly altered as the global climate  changes. This possibility is suggested by the rapid rate
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Policy Options for Stabilizing Global Climate -- Review Draft                        Chapter VI








of atmospheric CO2 change during past  periods  of climate  change (e.g.,  see Chapter  III).   If



circulation patterns did change, it is plausible that the oceans would no longer be a net sink for heat




and CO2.








    It is not known at what  point ocean circulation would be altered.  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.  This  would increase atmospheric CO2 concentrations




from 10-25% by 2100,  and would reduce the difference between realized and  equilibrium  warming




as the atmosphere warmed  more quickly due  to the oceans'  inability to  continue to act as a heat



sink.  As shown in Figure 6-21, this feedback is sufficient to increase realized warming up to 1.4°C




by 2050 and 1.3-3.5°C by 2100 compared with the warming  estimated for  the RCW case.








Methane Feedbacks








    Increases  in global temperature could increase the amount of CH4  emissions  due to several



feedback processes:  (1) release of methane from hydrates, which are methane compounds contained




in continental  slope sediments, as increasing temperatures destabilize the  formations; (2) additional




methane  from high-latitude  bogs due to longer growing seasons and higher temperatures; and  (3)



increased rate of methanogenesis from rice cultivation.  The amount of CH4 that could be released



from each of these feedback processes,  and the rate at which any releases might  occur, are highly



speculative.  For each process we have  assumed that the rate of CH4 release  is linearly related to



the increase in temperature, with each 1°C increase leading to an additional 110 Tg from  methane




hydrates, 12 Tg from bogs, and 7 Tg from rice cultivation (Lashof, 1989).  These methane feedbacks




could have a  major impact  on  atmospheric CH4  concentrations:   by 2100 concentrations would



increase to about 7000-8350  ppb, compared with 4150-4400  ppb in the RCW case.  As shown in
DRAFT - DO NOT QUOTE OR CITE       VI-73                           February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                    Chapter VI
                             FIGURE 6-21
   CO
   3
   55

   UJ
   o
   v>
   ui
   iu
   o
                 INCREASE IN REALIZED WARMING

              DUE TO CHANGE IN OCEAN CIRCULATION
                  (Degrees Celsius; Based on 3.0 Degree Sensitivity)
       1985   2000
2025
2050
                               YEAR
                                                         Ocean
                                                          Circulation
                                  RCW
2075
2100
DRAFT • DO NOT QUOTE OR CITE     VI-74
                               February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft                        Chapter VI








Figure 6-22, this increase in CH4 would be sufficient to increase realized  warming relative to the



RCW case about 0.2-0.4°C by 2050 and 0.4-1.0°C by 2100 (assuming 2.0-4.0°C climate sensitivities).








Combined Feedbacks








    In addition  to the two  separate feedbacks discussed above,  we analyzed the combined impact




of several types of biogeochemical feedbacks.  The following specific feedbacks were included:  (1)




methane from hydrates, bogs, and rice cultivation, as previously discussed; (2) increased stability of




the thermocline, thereby slowing the rate of heat and CO2 uptake by 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 at  the rate of 0.3 Pg C per ppm.   See




Lashof (1989) for further discussion.








    The  combined  impact of these  feedbacks on realized  warming  is an increase of 0.4-0.9°C by




2050 and 0.8-2.5°C  by 2100 relative  to the RCW case (assuming 2.0-4.0°C  climate sensitivities; see




Figure 6-23); the increase in equilibrium warming is 0.4-1.7°C by 2050 and 0.7-3.2°C by 2100. These



preliminary analyses strongly suggest that biogeochemical feedbacks could have a major impact on



the rate  of climatic change  during the next century.
DRAFT - DO NOT QUOTE OR CITE       VI-75                            February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                   Chapter VI
                             FIGURE 6-22
       5  -
       4  -
    M  3  _
    LLJ
    U
    W
    \u
    1U
    oc
    o
    IU
    o
       2  -
                  INCREASE IN REALIZED WARMING

                    DUE TO METHANE FEEDBACKS
                  (Degrees Celsius; Based on 3.0 Degree Sensitivity)
        1985  2000
2025
2050
2075
                                YEAR
                                                           Methane
                                                            Feedbacks
                                                           RCW
2100
 DRAFT - DO NOT QUOTE OR CITE      VI-76
                               February 21, 1989

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Policy Options for Stabilizing Global Climate - Review Draft
                                   Chapter VI
                            FIGURE 6-23
                 INCREASE IN REALIZED WARMING

            DUE TO CHANGE IN COMBINED FEEDBACKS
                 (Degrees Celsius; Based on 3.0 Degree Sensitivity)
   v>
   tu
   o
   (A
   IU
   O
   £
       1965   2000
2026
2050
                               YEAR
2075
                                                        Combined
                                                         Feedbacks
                                                         RCW
2100
DRAFT - DO NOT QUOTE OR CITE      VI-77
                              February 21, 1989

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 Policy Options for Stabilizing Global Climate - Review Draft                        Chapter VI
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Bolin, B., A. Bjorkstrom, K. Holmen, and  B.  Moore.  1983.  The simultaneous use of tracers for
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Cicerone, RJ. and R.S. Oremland.  1989.  Biogeochemical aspects of atmospheric methane.  Global
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Conrad, R., W. Seiler,  and G. Bunse. 1983. Factors influencing the loss of fertilizer nitrogen into
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Darmstadter, J., L. Ayres, R. Ayres, W.  Clark, P. Crossan, P. Crutzen, T. Graedel, R. McGill, J.
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DeLuchi,  MA.., RA.  Johnston  and D.  Sperling  1988.   Methanol  vs. natural gas vehicles:   A
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Eichner, M. 1988.  Current  knowledge of fertilizer-derived nitrous oxide emissions.  Paper prepared
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Galbally, I. 1985. The  emission of nitrogen to  the remote atmosphere: Background paper.  In J.N.
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Gray, C.   1987.   Tlie  Research  Behind the Regulations.  Paper presented  at The Alcohol Week
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Grossling,  B.,  and  D.  Nielsen.   1985.  In  Search of Oil.   Financial Times Business Information,
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 Policy Options for Stabilizing Global Climate -- Review Draft                       Chapter VI
 Houghton, R. 1988. The Flux of COn Between Atmosphere and Land as a Result of Deforestation and
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 Isaksen I., T. Berntsen, and S. Solberg. 1988. Calculated  Change in Tropospheric Distributions of
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 Kaplan, W., J. Elkins, C. Kolb,  M. McElroy, S. Wofsy, and A. Duran. 1978.  Nitrous oxide in fresh
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 Lashof, D. 1989.  The  Dynamic Greenhouse: Feedback Processes That May  Influence Future
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 Liu, S.C., M. Trainer,  F.C. Fehsenfeld, D.D. Fairish, EJ. Williams, D.W. Fahley, G. Hubler, and
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