United States
             Environmental Protection
Policy, Planning,
And Evaluation
                           December 1990
Policy Options For
Stabilizing Global Climate
Report To Congress
Main Report

                                           1 yf; Printed on Recycled Paper

                 REPORT TO CONGRESS
               Editors: Daniel A. Lashof and Dennis A. Tirpak
                United States Environmental Protection Agency

                 Office of Policy, Planning and Evaluation

                         December 1990

This  document  has  been  reviewed   in  accordance  with  the  U.S.
Environmental  Protection Agency's  and the Office of Management and
Budget's  peer  and  administrative  review  policies  and  approved  for
publication.  Mention  of trade names or commercial products does not
constitute endorsement or recommendation for use.
Publisher's Note:

Policy Options for Stabilizing Global Climate. Report to Congress has been
published in three parts:

21 P-2003.1   MAIN REPORT (includes Executive Summary)



Those who wish to order the Main Report or Technical Appendices should
inquire at the address below:

Publications Requests
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Washington. D.C.  20460

                          TABLE OF CONTENTS
Foreword	  xxiii
Acknowledgements 	   xxv

                              EXECUTIVE SUMMARY


     Purpose of This Study  	    2
     Scope of This Study	    2
     Current Policy Developments	    4
     Limitations 	    4

     The Greenhouse Gas Buildup	    5
     The Impact of Greenhouse Gases on Global Climate 	    8
     Natural Climate Variability 	   10

     Defining Scenarios	   10
     Scenarios with Unimpeded Emissions Growth	   12
     The Impact of Policy Choices	   14
          Accelerated Emissions Scenario 	   14
          Scenarios with Stabilizing Policies	   19

     Improve Energy Efficiency	   30
          Improved Transportation Efficiency	   30
          Other Efficiency Gains	'	   30
          Carbon Fee	   31
     Increase Use of Non-Fossil Energy Sources 	   31
          Nuclear Power	   31
          Solar Technologies	   33
          Hydro and Geothermal Energy	   33
          Commercialized Biomass	   33
     Reduce Emissions from Fossil Fuels	   33
          Greater Use of Natural Gas	   34
          Emission Controls	   34
     Reduce Emissions from Non-Energy Sources	   34
          CFC Phaseout	   34
          Reforestation	   35
          Agriculture, Landfills, and Cement  	   35

     The Tuning of Policy Responses	   38
     The Need for an International Response  	   41

NOTES	   44


                                     CHAPTER I



      Goals of this Study	  1-2
      Report Format	  1-2

      Carbon Dioxide 	  1-5
      Methane  	  1-5
      Nitrous Oxide 	  1-8
      Chlorofluorocarbons  	  1-8
      Other Gases Influencing Composition  	  1-8

      Estimates of the Climatic Effects of Greenhouse Gas Buildup	  1-8
      Studies of Future CO2 Emissions	  1-9
      Studies of the Combined Effects of Greenhouse Gas Buildup	   Ml
      Major Uncertainties	   1-12
      Conclusions From Previous Studies	   1-12

      Domestic Research and Policy Activities	   1-14
      International Activities	   1-15

 NOTES 	   1-16

 REFERENCES  	   1-16

                                    CHAPTER II

                             GREENHOUSE GAS TRENDS



     Concentration History and Geographic Distribution	   II-2
           Mauna Loa	   II-4
           Ice-core Data  	   II-4
           GMCC Network	   II-5
     Sources and Sinks	   II-8
           Fossil Carbon Dioxide 	   II-8
           Biospheric Cycle  	   II-8
           Ocean Uptake	<	  11-10
     Chemical and Radiative Properties/Interactions	  11-11

METHANE 	  11-14
     Concentration History and  Geographic Distribution	  11-14
     Sources and Sinks	  11-14
     Chemical and Radiative Properties/Interactions	  11-18

     Concentration History and Geographic Distribution	  11-18
     Sources and Sinks  	  11-20
     Chemical and Radiative Properties/Interactions 	  11-21

     Concentration History and Geographic Distribution	  11-22
     Sources and Sinks  	  11-22
     Chemical and Radiative Properties/Interactions 	  11-23

OZONE	  11-23
     Concentration History and Geographic Distribution	  11-23
           Tropospheric Ozone	  11-23
           Stratospheric Ozone	  11-25
     Sources and Sinks	  11-25
     Chemical and Radiative Properties/Interactions	  11-26

     Global Tropospheric Chemistry  	  11-27
           The Hydroxyl Radical	  H-27
           Carbon Monoxide	  11-27
           Nitrogen Oxides	  11-28
     Stratospheric Ozone and Circulation	  11-28

CONCLUSION 	'.	"	  11-28



                                   CHAPTER IH

                          CLIMATE CHANGE PROCESSES




     Solar Luminosity	   HI-6
     Orbital Parameters  	   HI-6
     Volcanoes	   IH-6
     Surface Properties	   IH-7
     The Role of Greenhouse Gases	   HI-7
     Internal Variations	   III-7

     Water Vapor 	   III-9
     Snow and Ice	   III-9
     Clouds	   III-9

      Release of Methane Hydrates	   III-ll
      Oceanic Change	   III-ll
           Ocean Chemistry	   III-ll
           Ocean Mixing  	   111-13
           Ocean Biology and Circulation	   111-13
      Changes in Terrestrial Biota 	   HI-13
           Vegetation Albedo	   111-13
           Carbon Storage	   111-14
           Other Terrestrial Biotic Emissions	   111-14
           Summary  	   111-14



 CONCLUSION  	   111-19

 NOTES 	   111-19

 REFERENCES  	   111-19

                                    CHAPTER IV

                          HUMAN ACTIVITIES AFFECTING
                            TRACE GASES AND CLIMATE



      Global Population Trends	    IV-3
      Population Trends by Region	    IV-3
           Industrialized Countries 	    IV-7
           Developing Countries	    IV-7

      History of Fossil-Fuel Use  .	    IV-8
      Current Energy-Use Patterns and Greenhouse Gas Emissions	   IV-12
           Emissions by Sector	   IV-12
           Fuel Production and Conversion	   IV-17
      Future Trends	   IV-17
           The Fossil-Fuel Supply	   IV-19
           Future Energy Demand  	   IV-19

      Chlorofluorocarbons, Halons, and Chlorocarbons	   IV-22
           Historical Development and Uses	   IV-22
           The Montreal Protocol	   IV-27
      Landfill Waste Disposal	   IV-27
      Cement Manufacture	   IV-28

      Deforestation	   IV-32
      Biomass Burning	   IV-32
     Wetland Loss	   IV-35


     Enteric Fermentation In Domestic Animals 	   IV-38
     Rice Cultivation	   IV-38
     Use of Nitrogenous Fertilizer	   IV-42


NOTES 	   IV-45


                                    CHAPTER V



     The Role of Long-Term and Short-Term Options	  V-5
     The Economics of Control Options	  V-6
     Worldwide Emissions and Control Techniques	  V-6
     Organization of this Chapter	  V-8
     Limitations  	-.	  V-10


     Near-Term Technical Potential in the Transportation Sector	  V-14
     Near-Term Technical Options: Industrialized Countries  	  V-1S
           Increase Fuel Efficiency	  V-15
           Alternative Fuels	  V-25
           Strengthen Vehicle Emissions Controls 	  V-26
           Enhance Urban Planning and Promote Mass Transit	  V-27
     Near-Term Technical Options: Developing Countries 	  V-27
           Increase Fuel Efficiency	  V-28
           Alleviate Congestion and Improve Roads	  V-29
           Promote and Develop Alternative Modes of Transportation  	  V-29
           Use Alternative Fuels	  V-30
     Near-Term Technical Options: USSR and Eastern Europe  	  V-30
     Long-Term Potential in the Transportation Sector	  V-31
           Urban Planning and Mass Transit  	  V-31
           Alternative Fuels	  V-31
           Emerging Technologies	  V-32

     Near-Term Technical Options: Industrialized Countries  	  V-35
           Improve Space Conditioning	  V-35
           Use Energy-Efficient Lighting	  V-41
           Use Energy-Efficient Appliances  	  V-41
     Near-Term Technical Options: Developing Countries 	  V-44
           More Efficient Use ofFuelwood	  V-44
           Use Alternative Fuels	  V-45
           Retrofit Existing Buildings	  V-46
           Build New Energy-Efficient Homes and Commercial Buildings	  V-46
     Near-Term Technical Options: USSR and Eastern Europe  	,  V-46
     Long-Term Potential in the Residential/Commercial Sector  	  V-47


      Near-Term Technical Options:  Industrialized Countries  	  V-50
            Accelerate Efficiency Improvements in Energy-Intensive
            Industries  	  V-50
            Aggressively Pursue Efficiency Improvements in
            Other Industries		  V 51
            Increase Cogeneration 	  V-51
      Near-Term Technical Options:  Developing Countries  	  V-52
            Practice Technological Leapfrogging	  V-52
            Develop and Use Alternative Fuels  	  V-53
            Increase Industrial Retrofit Programs  	  V-53
            Use Energy-Efficient Agricultural Practices	  V-54
      Near-Term Technical Options:  USSR and Eastern Europe 	  V-54
            Encourage Structural Change	  V-54
            Other Emission Reduction Options	  V-56
      Long-Term Potential in the Industrial Sector	  V-58
            Structural Shifts	  V-58
            Advanced Process Technologies 	  V-58
            Non-fossil Energy	  V-59


      Refurbish Existing Powerpiants	  V-62
      Pursue Clean Coal Technologies  	  V-62
      Increase Use of Cogeneration	  V-63
      Substitute Natural Gas for Coal	  V-63
            Natural Gas Use At Existing Powerpiants	  V-63
            Advanced Gas-Fired Combustion Technologies 	  V-64
            Factors Affecting Use of Natural Gas	  V-64
            Methods of Increasing Gas Resources	  V-67
      Employ Emissions Control Technologies	  V-67
            NOX Controls  	  V-68
            CO2 Controls  	  V-68
      Consider Emerging Electricity Generation Technologies	  V-70
            Fuel Cells	  V-70
            Magnetohydrodynamics  	  V-70

      Improve Efficiency of Direct Firing Methods  	  V-71
      Improve Efficiency of Charcoal Production	  V-71
      Promote Anaerobic Digestion Technology	  V-73
      Promote Use of Gasification	  V-73
      Improve Technologies to Convert Biomass to Liquid Fuels	  V-74
            Methanol from Biomass	  V-74
            Ethanolfrom Biomass	  V-74
            Biomass Oils as Fuel	  V-76

      Promote Solar Thermal Technology	  V-76
            Parabolic Troughs	  V-77
            Parabolic Dishes	  V-77
            Central Receivers	  V-77
            Solar Ponds	  V-77
      Improve Solar Photovoltaic Technology  	  V-77
            Crystalline Cells	  V-80
            Thin-Film Technologies 	  V-80
            Multi-Junction  Technologies	  V-81

      Expand Hydroelectric Generating Capacity	  V-81
           Industrialized Countries  	  V-81
           USSR and Eastern Europe	  V-82
           Developing Countries	  V-82
      Reduce Cost of Wind Energy  	  V-83
      Exploit Geothermal Energy Potential 	  V-83
      Research Potential for Ocean Energy	  V-85

      Enhance Safety and Cost Effectiveness of Nuclear Fission Technology	  V-85
      Promote Research and Development of Nuclear Fusion Technology	  V-90

      Reduce Energy Losses During Transmission and Distribution 	  V-91
      Enhance Storage Technologies	  V-92
           Pumped Storage	  V-92
           Batteries 	  V-92
           Compressed Air Storage	  V-93
           Superconducting Magnetic Energy Storage	  V-93



      Expand the Use of Chemical Substitutes  	  V-97
      Employ Engineering Controls	  V-97
      Use Substitutes for CFC-Produced Materials	  V-98

      Increase Methane Recovery 	  V-99
      Employ Recycling and Resource Recovery  	   V-100
      Reduce Demand for Cement	   V-101




      Forestry Strategy I:  Reduce Sources of Greenhouse Gases  	   V-113
           Option 1: Substitute Sustainable Agriculture for
                      Swidden Forest Practices	   V-113
           Option 2: Reduce the Frequency, Interval, and Scale
                      of Forest and Savannah Consumed by Biomass
                      Burning as a Management Practice	   V-121
           Option 3: Reduce Demand For Other Land Uses That
                      Have Deforestation as a Byproduct	   V-121
           Option 4: Increase Conversion Efficiencies of
                      Technologies That Use Fuelwood	   V-122
           Option 5: Decrease Production of Disposable Forest Products	   V-123
      Forestry Strategy II:  Maintain Existing Sinks of Greenhouse Gases  	   V-124
           Option 1: Conserve Standing Primary and Old-Growth
                      Forests as Stocks of Biomass Offering a
                      Stream of Economic Benefits	   V-124

            Option 2: Slow Deforestation by Introducing Natural
                         Forest Management of Little-Disturbed and
                         Secondary Tropical Forests	   V-124
            Option 3: Conserve Tropical Forests by Developing
                         Markets and Extractive Reserves for Non-Timber Products	   V-125
            Option 4: Improve Forest Harvesting Efficiency  	   V-126
            Option 5: Prevent Loss of Soil Carbon Stocks by Slowing Erosion
                         in Forest Systems During Harvest and from Overgrazing
                         by Livestock 	   V-126
      Forestry Strategy III: Expand Sinks of Greenhouse Gases	   V-126
            Option 1: Increase Forest Productivity: Manage Temperate
                         Natural Forests for Higher Yields	   V-126
            Option 2: Increase Forest Productivity: Plantation Forests  	   V-130
            Option 3: Expand Current Tree Planting Programs in the
                         Temperate Zone  	   V-132
            Option 4: Reforest Surplus Agricultural Lands  	   V-132
            Option 5: Reforest Urban Areas	   V-138
            Option 6: Pursue Afforestation for Highway Corridors	   V-140
            Option 7: Reforest Tropical Countries  	   V-140
            Option 8: Restore Degraded Lands	   V-142
            Option 9: Increase Soil Carbon Storage by Leaving Slash
                       After Harvest and Expanding Agroforestry  	   V-142
            Obstacles to Large-Scale Reforestation in Industrialized Countries  	   V-145
            Obstacles to Reforestation in Developing Countries  	   V-146
      Comparison of Selected Forestry Technical Control Options	   V-148


      Existing Technologies and Management Practices Affecting
      Methane Production	   V-154
            Nature of Rice Production System	   V-154
            Fertilization With Organic  Matter	   V-154
            Disposition of Crop Residues  	   V-154
            Type of Rice Variety Planted	   V-154
            Fertilizer  Use	   V-155
      Emerging Technologies	   V-155
      Research Needs and Economic Considerations	   V-157

      Existing Technologies and Management Practices Affecting
      Production of Nitrous Oxide	   V-158
            Type of Fertilizer	   V-158
            Fertilizer Application Rate 	   V-158
            Crop Type	   V-158
            Timing of Fertilizer Application	   V-158
            Placement of Fertilizer	   V-159
            Water Management	   V-159
            Tillage Practices and Herbicide Use	   V-159
            Legumes as a  Nitrogen Source	   V-159
      Technologies  that Improve Fertilization Efficiency 	   V-159
            Nitrification Inhibitors 	   V-159
            Reduced Release Rate  	   V-159
            Coatings	   V-159
      Emerging Technologies	   V-159
      Alternative Agricultural Systems  	   V-160
            Alternative Agriculture and Nitrous Oxide	   V-160
            Sustainable Agriculture and Land Conversion 	   V-160


      Research Needs and Economic Considerations	  .   V-161

      Management Practices Affecting Methane Emissions from Livestock 	   V-162
           Livestock System Productivity	   V-164
           Diet  	   V-164
           Nutritional Supplements	   V-164
           Feed Additives	   V-165
           Methane from Manure	   V-165
      Emerging Technologies	   V-166
      Research Needs and Economic Considerations	   V-166

NOTES  	   V-167


                                    CHAPTER VI

                           THINKING ABOUT THE FUTURE



      Production	    VI-3
      Consumption	    VI-5

      Scenarios with Unimpeded Emissions Growth	   VI-10
      Scenarios with Stabilizing Policies and Accelerated Emissions  	   VI-10

      Energy Module	   VI-15
      Industry Module 	   VI-18
      Agriculture Module 	   VI-18
      Land-Use and Natural Source Module	   VI-18
      Ocean Module	   VI-18
      Atmospheric Composition and Temperature Module	   VI-18
      Assumptions  	   VI-19
           Population Growth Rates	   VI-19
           Economic Growth Rates  	   VI-19
           Oil Prices  	   VI-19
      Limitations  		   VI-19

      Energy Production and Use	   VI-20
           End-Use Consumption	   VI-21
           Primary Energy Supply	   VI-23
           Greenhouse Gas Emissions From Energy Production and Use 	   VI-27
           Comparison to Previous Studies	   VI-29
      Industrial Processes	   VI-36
           Halocarbon Emissions	   VI-36
           Emissions From Landfills  and Cement	   VI-38
      Changes in Land Use	   VI-38
      Agricultural Activities	   VI-39
      Total  Emissions	   VI-41


      Atmospheric Concentrations	' . .   VI-47
      Global Temperature Increases	   VI-49
      Comparison with General Circulation Model Results	   VI-54
      Relative Effectiveness of Selected Strategies	   VI-54

      Assumptions About the Magnitude and Timing of Global Climate
      Stabilization Strategies	   VI-62
           No Participation by the Developing Countries 	   VI-62
           Delay in Adoption of Policies	   VI-63
      Assumptions Affecting Rates of Technological Change	   VI-65
           Availability of Non-Fossil Technologies	   VI-65
      Assumptions About Climate Sensitivity and Timing 	   VI-67
           Sensitivity of the Climate System	   VI-67
           Rate of Heat Diffusion	   VI-67
      Biogeochemical Feedbacks 	   VI-70
           Ocean Circulation .	   VI-70
           Methane Feedbacks	   VI-70
           Combined Feedbacks	   VI-73


 NOTES	   VI-76


                                    CHAPTER VII

                                  POLICY OPTIONS





      The Cost Issue	   VII-8



      Evidence of Market Response to Economic Incentives: Energy Pricing	   VII-13
      Financial Mechanisms to  Promote Energy Efficiency  	   VII-16
      Creating Markets for Conservation  	   VII-18
      Limits to Price-Oriented Policies 	   VII-19

      Existing Regulations that  Restrict Greenhouse Gas Emissions	   VII-22
           Regulation of Chlorofluorocarbons	   VII-22
           Energy Efficiency Standards 	   VII-23
          Air Pollution Regulations	   VII-25
           Solid Waste Management	   VII-26


          Utility Regulation	   VII-28

     Existing Regulations that Encourage Emissions Reductions	   VII-29
          Tree Planting	   VII-29
          Other Incentives/Disincentives	   VII-32

     Energy  Research and Development	   VH-33
     Global Forestry Research and Development	   VII-38
     Research to Eliminate Emissions of CFCs  	   VII-38






     Tree Planting	   VII-47
     U.S. DOE Energy Efficiency Initiatives	   VII-47
     U.S. DOE Renewable Energy Initiatives	   VII-48
     U.S. DOE Appliance Standards	   VII-48
     Clean Air Act Provisions	   VII-48
     Landfill Regulations	   VII-49
     Montreal Protocol and CFC Phaseout  	   VII-49
     How These Options May Reduce Emissions to Current Levels	   VII-49

     Tax Initiatives 	   VII-52
          Transportation Taxes	   VII-52
          Carbon Taxes 	   VII-52
     Non-Tax Initiatives 	   VII-52
          Tighter Landfill Regulations	   VII-52
          Increase in Tree Planting	   VII-52
     Implications of Additional Policy Initiatives 	   VII-52




                                  CHAPTER VIII





     Economic Development and Energy Use	  VIII-4
     Oil Imports, Capital Shortages, and Energy Efficiency 	  VIII-8
     Greenhouse Gas Emissions and Technology Transfer	  VIII-11

     International Lending and Bilateral Aid	  VIII-13
           U.S. Bilateral Assistance Programs	  VIII-13
           Policies and Programs of Multilateral Development Banks	  VIII-15
     New Directions	  VIII-20


     Restricting CFCs to Protect the Ozone Layer	  VIII-22
     International Efforts to Halt Tropical Deforestation	  VIII-23
     Ongoing Efforts Toward International Cooperation 	  VIII-24








                                  LIST OF FIGURES
       1        Concentration of CO2 at Mauna Loa Observatory and CO2 Emissions
               From Fossil-Fuel Combustion  	  3
       2        Greenhouse Gas Contributions to Global Warming .. .	  6
       3        Impact of CO2 Emissions Reductions on Atmospheric Concentrations 	  9
       4        Atmospheric Concentrations  	  16
       5        Realized Warming: No Response Scenarios  	  17
       6        Accelerated Emissions Cases: Percent Increase in Equilibrium
               Warming Commitment	  20
       7        Stabilizing Policy Strategies: Decrease in Equilibrium Warming
               Commitment	  23
       8        Rapid Reduction Strategies: Additional Decrease in Equilibrium
               Warming Commitment   	  25
       9        Realized Warming: No Response and Stabilizing Policy Scenarios  	  27
       10      Primary Energy Supply by Type 	  32
       11      Increase  in Realized Warming Due to Global Delay in Policy Options 	  40
       12      Share of Greenhouse  Gas Emissions by Region  	  42
       13      Increase  in Realized Warming When Developing Countries
               Do Not Participate  	  43


       1-1      Concentration of CO2 at Mauna Loa Observatory and CO2 Emissions
               From Fossil-Fuel Combustion  	  1-6
       1-2      Impact of CO2 Emissions Reductions on Atmospheric Concentrations 	  1-7


       2-1      Greenhouse Gas Contributions to Global Wanning 	  II-3
       2-2      Carbon Dioxide Concentration  	  II-6
       2-3      CO2 Atmospheric Concentrations by Latitude  	  II-7
       2-4      The Carbon Cycle  	  II-9
       2-5      Gas Absorption Bands  	 11-12
       2-6      Methane Concentration	 H-15
       2-7      Current Emissions of Methane by Source   	 II-16
       2-8      Nitrous Oxide Concentration 	 11-19
       2-9      Temperature Profile and Ozone Distribution in the Atmosphere  	 11-24
       2-10     Contribution to Radiative Forcing  	 11-37


       3-1      Surface Air Temperature 	  HI-4
       3-2      Oxygen Isotope Record From Ice Cores in Greenland  	  III-5
       3-3      Carbon Dioxide and Temperature Records From Antarctic Ice Core  	  IH-5
       3-4      Oxygen Isotope Record From Deep Sea Sediment Cores  	  IH-5
       3-5      Global Energy Balance   	  III-8
       3-6      Equilibrium Temperature Changes From Double CO2  	  HI-10
       3-7      Greenhouse Gas Feedback  Processes  	  IH-12


       4-1      Regional Contribution to Greenhouse Forcing, 1980s  	   IV-4
       4-2      Regional Population Growth, 1750-1985  	   IV-5
       4-3      Global Energy Demand by Type, 1950-1985  	   IV-9
       4-4      CO2 Emissions Due to Fossil-Fuel Combustion  	  IV-10
       4-5      Global Commercial Energy Demand by Region  	  IV-11
       4-6      1985 Sectoral Energy Demand by Region   	  IV-13
       4-7      Potential Future Energy Demand  	  IV-21
       4-8      Historical Production of CFC-11 and CFC-12   	  IV-24
       4-9      CFC-11 and CFC-12 Production/Use for Various Countries  	  IV-26
       4-10     CO2 Emissions From Cement Production, 1950-1985 	  IV-30
       4-11     Cement Production in Selected Countries, 1951-1985 	  IV-31
       4-12     Net Release of Carbon From Tropical Deforestation, 1980  	  IV-33
       4-13     Wetland Area and Associated Methane Emissions  	  IV-37
       4-14     Trends in Domestic Animal Populations, 1890-1985	  IV-39
       4-15     Rough Rice Production, 1984  	  IV-40
       4-16     Rice Area Harvested, 1984   	  IV-41
       4-17     Nitrogen Fertilizer Consumption, 1984/1985  	  IV-44


       5-1      Current Contribution to Global Warming  	   V-7
       5-2      Global Energy Use by End Use	   V-13
       5-3      Components of Transportation Energy Use in the OECD, 1985 	   V-16
       5-4      U.S. Residential/Commercial Energy Use	   V-34
       5-5      Average Efficiency of Powerplams Using Fossil Fuel, 1951-1987   	   V-61
       5-6      Strategies for Improving Efficiency of Biomass Use  	   V-72
       5-7      Basic Solar Thermal Technologies	   V-78
       5-8      Photovoltaic Electricity Costs  	   V-79
       5-9      Capital Costs for Nuclear Power   	   V-89
       5-10     Industrial Process Contribution to Global Warming	   V-96
       5-11     Movement of Tropical Forest Lands Among Stages of
                Deforestation and Potential Response Options   	  V-106
       5-12     Estimates of Annual Deforestation, 1981-1985 and Most Recent   	  V-109
       5-13     Cost Curves for Potential Large-Scale Afforestation in the U.S	  V-137
       5-14    Alley Cropping in Machakos, Kenya	  V-144
       5-15    Contribution of Agricultural Practices to Global Warming	  V-153


       6-1     Total U.S. Energy Consumption per GNP Dollar, 1900-1985  	   VI-4
       6-2     U.S. Consumption of Basic Materials	   VI-6
       6-3     Population by Region  	  VI-12
       6-4     Actual and Projected U.S. Coal Production  	  VI-14
       6-5     Structure of the Atmospheric Stabilization Framework  	  VI-16
       6-6     Geopolitical Region of Climate Analysis  	  VI-17
       6-7     End-Use Energy Demand by Region  	  VI-22
       6-8     Primary Energy Supply by Type  	  VI-24
       6-9     Share of Primary Energy Supply by Type  	  VI-25
       6-10    Energy Demand for Synthetic Fuel Production	  VI-26
       6-11    Emissions of Major CFCs 	  VI-37
       6-12    CO2 Emissions from Tropical Deforestation  	  VI-40
       6-13    CO2 Emissions by Type 	  VI-44
       6-14    CO2 Emissions by Regions   	  VI-45
       6-15    CH4 Emissions by Type  	  VI-46

       6-16     Atmospheric Concentrations  	  VI-48
       6-17     Realized and Equilibrium Wanning	  VI-52
       6-18     Relative Contribution to Warming, 1985 to 2100   	  VI-55
       6-19     Stabilizing Policy Strategies: Decrease in Equilibrium
               Warming Commitment   	  VI-56
       6-20    . Rapid Reduction Strategies: Additional Decrease in Equilibrium
               Wanning Commitment   	  VI-58
       6-21     Accelerated Emissions Cases: Percent Increase in Equilibrium
               Warming Commitment   	  VI-60
       6-22     Increase in Realized Warming When Developing Countries
               Do Not Participate	  VI-64
       6-23     Increase in Realized Warming Due to Global Delay in Policy Options  	  VI-66
       6-24     Availability of Non-Fossil Energy Options  	  VI-68
       6-25     Impact of Climate Sensitivity on Realized Warming  	  VI-69
       6-26     Increase in Realized Warming Due to Rate of Ocean Heat Uptake  	  VI-71
       6-27     Increase in Realized Wanning Due to Change in Ocean Circulation	  VI-72
       6-28     Increase in Realized Warming Due to Methane Feedbacks   	  VI-74
       6-29     Increase in Realized Warming Due to Change in Combined Feedbacks  	  VI-75


       7-1      U.S. Energy Consumption by Fuel Share  	   VII-11
       7-2      Atmospheric Response to Emissions Cutoff	   VII-12
       7-3      Energy Intensity Reduction, 1973-1985  		   VII-14
       7-4      U.S. Electricity Demand and Price	   VII-17
       7-5      Cost of Driving Versus Automotive Fuel Economy  	   VII-21
       7-6      U.S. Carbon Monoxide Emissions   	   VII-27
       7-7      Changes in U.S. Renewable Energy R&D Priorities Over Time  	   VII-35
       7-8      Cost of Potential Residential Conservation  in Michigan by 2000   	   VII-44


       8-1      Greenhouse Gas Emissions by Region 	  VIII-3

                                    LIST OF TABLES
        1       Approximate Reductions in Anthropogenic Emissions Required to Stabilize
               Atmospheric Concentrations at Current Levels  	  8
        2       Overview of Major Scenario Assumptions  	   13
        3       Trace Gas Emissions 	   15
        4       Scenario Results for Realized and Equilibrium Warming 	   18
        5       Examples of Policy Responses by the Year 2000  	   29


        1-1     Approximate Reductions in Anthropogenic Emissions Required to Stabilize
               Atmospheric Concentrations at Current Levels  	   1-5


       2-1     Trace Gas Data  	  11-29
       2-2     Radiative Forcing for a Uniform Increase in Trace Gases From
               Current Levels   	  11-13
       2-3     Global Warming Potential for Key Greenhouse Gases  	  11-38


       4-1     Regional Demographic Indicators   	   IV-6
       4-2     Emission Rate Differences by Sector  	  IV-14
       4-3     End-Use Energy Consumption Patterns for the Residential/Commercial
               Sectors  	  IV-16
       4-4     Carbon Dioxide Emission Rates for Conventional and Synthetic Fuels 	  IV-18
       4-5     Estimates of Global Fossil-Fuel Resources  	  IV-20
       4-6     Major Halocarbons: Statistics  and  Uses 	  IV-23
       4-7     Estimated 1985 World Use of Potential Ozone-Depleting Substances	  IV-25
       4-8     Refuse Generation Rates in Selected Cities  	  IV-29
       4-9     Land Use:  1950-1980	  IV-34
       4-10    Summary Data on Area and Biomass Burned	  IV-36
       4-11    Nitrous Oxide Emissions by Fertilizer Type  	  IV-43


       5-1      Key Technical Options by Region and Time Horizon 	    V-9
       5-2      High Fuel Economy Prototype Vehicles	  V-17
       5-3      Actual Fuel Efficiency for New Passenger Cars  	  V-19
       5-4      Summary of Energy Consumption and Conservation Potential With
               Major Residential Equipment  	  V-43
       5-5      Reduction of Energy Intensity in the U.S. Basic Materials
               Industries  	  V-49
       5-6      Energy Intensities of Selected  Economies  	  V-55
       5-7      Innovation in Steel Production Technology, Selected Countries   	  V-57
       5-8      Total U.S. Gas Reserves and Resources 	  V-66
       5-9      CO2 Scrubber Costs Compared to  SO2 Scrubber Costs   	  V-69
       5-10     Estimates of Worldwide Geothermal Electric Power Capacity Potential  	  V-84
       5-11     Capacity of Direct Use Geothermal Plants in Operation -1984   	  V-86

       5-12     Geothermal Powerplants On-Line as of 1985  	   V-87
       5-13     Estimates of Release of Carbon to Atmosphere from Top 10
               Deforestation Countries, 1980 and 1989 	  V-104
       5-14     Recent Estimate of CO2 Emissions from Biomass Burning in Amazonia  	  V-107
       5-15     Summary of Major Forestry Sector Strategies for Stabilizing
               Global Climate  	  V-110
       5-16     Potential Forestry Strategies and Technical Options  to Slow
               Climate Change 	  V-114
       5-17     Comparison of Land Required for Sustainable Versus Swidden
               Agricultural Practices   	  V-118
       5-18     Potential Carbon Fixation and  Biomass Production Benefits from
               Representative Agroforestry Systems  	  V-119
       5-19     Assessment of Potential Reductions in Greenhouse Gases from
               Large-Scale Substitution of Agroforestry for Traditional Swidden
               and Monocultural Agriculture   	  V-120
       5-20     Value of One Hectare of Standing Forest in Amazonian Peru Under
               Alternative Land Uses   	  V-127
       5-21     Effects of Adaptive Forest Management Activities on Production of
               Merchantable Volume for a Northern Hardwood Forest Under
               Two Climate Change Assumptions   	  V-129
       5-22     Productivity Increases Attributable to Intensive Plantation
               Management  	  V-133
       5-23     Summary of Major Tree Planting Programs in the U.S	  V-134
       5-24     Estimates of CRP Program Acreage Necessary to Offset CO2
               Production from New Fossil Fuel-Fired Electric Plants, 1987-%,
               by Tree Species  or Forest Type  	  V-136
       5-25     Estimates of Forest Acreage Required to Offset Various CO2
               Emissions  Goals  	  V-139
       5-26     Costs of Afforestation:  Stand Establishment and Initial Maintenance  	  V-147
       5-27     Comparison of Selected Forest Sector Control Options: Preliminary
               Estimates  	  V-149
       5-28     Overview of Three Social Forestry Projects Proposed to Offset CO2
               Emissions  of a 180-MW Electric Plant in Connecticut  	  V-151
       5-29     Water Regime and Modern Variety Adoption for Rice Production in
               Selected Asian Countries  	  V-156
       5-30     Average Meat Yield Per Animal  	  V-163


       6-1      Overview of Major Scenario Assumptions   	   VI-8
       6-2      Economic  Growth Assumptions	  VI-11
       6-3      Key Global Indicators   	  VI-28
       6-4      Comparison of No Response Scenarios and NEPP  	  VI-30
       6-5      Comparison of Stabilizing Policy Scenarios and ESW  	  VI-31
       6-6      Summary of Various Primary Energy Forecasts  for the Year 2050  	  VI-33
       6-7      Comparison of Energy-Related Trace-Gas Emissions Scenarios  	  VI-35
       6-8      Trace Gas Emissions  	  VI-42
       6-9      Comparison of Estimates of Trace-Gas Concentrations in
               2030 and 2050  	  VI-50
       6-10     Scenario Results for Realized and Equilibrium Warming  	  VI-53


       7-1      Energy Intensity of Selected National Economies, 1973-85  	  VII-15
       7-2      Payback Periods in Year for Appliances, 1972-1980  	  VII-20
       7-3      Comparison of Energy  Efficiencies of Regulated Appliances  	  VII-24

       7-4     Cogeneration Facilities  	   VII-30
       7-5     Erodible Acreage Available to Offset CO2 Emissions from
               Electricity Production  	   VII-31
       7-6     Government Efficiency Research and Development Budgets in OECD Member
               Countries, 1986  	   VII-34
       7-7     Additional Energy Technology R&D Expenditures Needed to be Prepared to
               Control CO2 Emissions 	   VII-37
       7-8     Federal Energy Expenditures and Cost Avoidance, FY 1985-FY 1987   	   VII-41
       7-9     Emissions Reductions from Current Policy Initiatives by 2000  	   VII-50
       7-10    Emission Estimates  for 1987 and 2000  	   VII-51
       7-11    Emission Reductions from Potential Tax Initiatives for the Year 2000  	   VII-53
       8-1      1985 Population and Energy Use Data from Selected Countries  	VIII-5
       8-2      Efficiency of Energy Use in Developing Countries: 1984-1985   	VIII-6
       8-3      Potential for Electricity Conservation in Brazil   	VIII-8
       8-4      Net Oil Imports and Their Relation to Export Earnings for Selected
               Developing Countries, 1973-1984	VIII-9
       8-5      Annual Investment in Energy Supply as a Percent of Annual Total
               Public Investment (Early 1980s)  	  VIII-10
       8-6      World Bank Estimate of Capital Requirements for Commercial Energy in
               Developing Countries, 1982-1992 	  VIII-10
       8-7      U.S. AID Forestry Expenditures by Region  	  VIII-14
       8-8      Gross Disbursements of Development Banks in Forestry Projects in
               1986-1988  	  VIII-16
       8-9      World Bank Energy Sector Loans in 1987   	  VIII-16
       8-10     Energy-Related Expenditures of Multilateral and Bilateral Aid Institutions  ....  VIII-18
       8-11     World Bank Energy Conservation Projects: Energy Sector Management
               Assistance Program  (ESMAP) Eerngy Efficiency  Initiatvies  	  VIII-19
       8-12     Energy Use in the Soviet Union and Eastern Europe	  VIII-21
       8-13     Countries Responsible for Largest Share of Tropical Forest Deforestation  	VIII-25

     I  am pleased  to transmit the  attached Policy  Options  for
Stabilizing Global  Climate,  the second of two  reports  on global
climate change prepared in response to a Congressional ,request in
the Fiscal Year  1987  Continuing Resolution Authority.  The first
report assessed the potential health and environmental effects of
climate  change on  the U.S.    This  report  examines  a  range  of
possible  response  options  and  estimates  their  potential  for
reducing  or  limiting emissions of  greenhouse gases  on  a global

     The magnitude  of the  effort  required to produce this report
was greater than many had anticipated.  The lead authors and many
other  contributors  have nevertheless  created an  impressive  and
scholarly  work  that  sprovides a valuable   foundation  for  the
additional  research   and  analysis   that will  be  needed  for
determining future  policy  actions.   I would  like to congratulate
all those involved.

     The report  is  one of the  first to take a comprehensive and
global approach, covering all sectors and  all greenhouse gases, in
the analysis of policy options  for reducing greenhouse"gases.  It
carefully describes the types  of gases  involved,  their physical
sources, and the level of emissions by source  as well as geographic
location.  Based  on a wide range of  policy  options,  from energy
efficiency to new methods of rice cultivation, it presents possible
future  scenarios  of  greenhouse gas emissions  to the  year 2100
depending  on  the  level  of  response as  well  as  many  other
independent factors.

     The results demonstrate that greenhouse gas emissions can be
effectively reduced.   However, the report acknowledges that the
actual  size  of these reductions  will depend upon a great many
factors, not the  least of  which are  the  accuracy of the data and
the inherent limitations of  the models employed in the analysis.
Economic  growth,  population  growth,  and  the  extent   to  which
countries  respond  to  climate  change  are among  the many  other

     Another key  limitation  of the report is that comprehensive
estimates  of  the  costs of  achieving these reductions  are  not
provided.  This was  a  conscious  decision based on  the time and
resources  available  for  preparing the  report,  as  well as  the
interest of several groups in undertaking  their own cost analyses.
Cost assessments  have  been  conducted over  the last year,  both
within  EPA and  among  other  agencies.   Additional  studies  are
underway that will improve our information on  this important topic.

     Since the final draft report was released approximately a year
ago it has undergone  a thorough and  rigorous review.   Several
additional reports on responses to global  climate change have also
been issued which have provided a further basis  for judging the


quality and thoroughness of the report.  These include reports by
the  Intergovernmental  Panel  on  Climate Change,  the Office  of
Technology Assessment, the National Research Council, and others.
Remarkably, the  final report has required  only  relatively minor
improvements to meet the standards set by our reviewers as well as
other experts studying the issue.

     I believe this is not only due to the excellent effort devoted
to the preparation of this report, but it is also a reflection of
the broad consensus that exists concerning the nature and potential
of the options we have for addressing the problem  of global climate

     Unfortunately, there is no silver bullet among them.  Choosing
among the wide range  of options  is  thus going  to be the toughest
challenge we now face.
                         Assistant Administrator
                         Office of Policy,  Planning and Evaluation

       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. Climate Change Processes                                                Daniel Lashof
                                                                                   Alan Robock

Chapter IV. Human Activities Affecting Trace Gases and Climate                       Barbara Braatz
                                                                                     Craig Ebert

Chapter V. Technical Options for Reducing Greenhouse Gas Emissions                 Paul Schwengels
                                                                                (Energy Services)
                                                       Barry Solomon (Energy Services and Supply)
                                                                      Craig Ebert (Energy Supply)
                                                                    Joel Scheraga (Energy Supply)
                                                                Michael Adler (Renewable Energy)
                                                                           Dilip Ahuja (Biomass)
                                                                       John Wells (Haolocarbons)
                                                                           Stephen Seidel (CFCs)
                                                                     Kenneth Andrasko (Forestry)
                                                                     Lauretta Burke (Agriculture)

Chapter VI. Thinking About the Future                                               Daniel Lashof
                                                                                   Leon Schipper
                                                                                  Barry Solomon

Chapter VII.  Policy Options                                                           Alan Miller

Chapter VIII.  International Cooperation to Reduce Greenhouse Gas Emissions              Alan Miller
                                                                                   Jayant Sathaye

Appendix A.  Model Descriptions                                                    William Pepper
                                                                         Parvadha Suntharalingam

Appendix B.  Implementation of the Scenarios                                           Craig Ebert

Appendix C.  Sensitivity Analyses                                                       Craig Ebert
                                                                         Parvadha Suntharalingam

        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


        Document integration was coordinated by Craig Ebert and Barbara Braatz.  Editorial assistance was

 proved by Susan  MacMillan.  Technical, graphics, and typing assistance was provided by Julie Anderson,

 Patricia Baldridge, Karen Borza, Margo Brown, Donald Devost, Courtney Dinsmore, Katie Donaldson, Michael

 Green, Amy Kim, Judy Koput, Cheryl LaBrecque, Nathaniel Watkins, Cynthia Whitfield,  Donna Whitlock,

 and Karen Zambri.

       Literally hundreds of other people have  contributed to this report,  including the organizers  and

 attendants at four workshops sponsored by the U.S. Environmental Protection Agency 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 other, Thomas Bath, Deborah Bleviss, Gary Breitenbeck, William Chandler, Jim Elkins, Robert

 Friedman, Howard Geller, James  Hansen, Ned Helm,  Tony Janetos, Stan Johnson, Julian Jones, Michael

 Kavanaugh, Andrew Lacis, Michael MacCracken, Elaine Matthews, Chris Neme, William Nordhaus, Steven

 Piccot, Steven Plotkin, Marc Ross, Stephen Schneider, Paul Steele, Pieter Tans, Thomas Wigley, Edward

 Williams, and Robert Williams.

       This  word was conducted within U.S. 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.

                             EXECUTIVE SUMMARY

      The composition of Earth's atmosphere
is  changing.   The  concentration of carbon
dioxide, the most important greenhouse gas
accumulating in the  atmosphere,  has risen
25% since pre-industrial times.   Significant
increases in the concentrations of methane,
chlorofluorocarbons, and nitrous oxide  have
also been observed.  Present emission trends
would lead to a continuing buildup of these
gases in the atmosphere.  Although there is a
good  deal  of uncertainty about the timing,
magnitude, and regional distribution of climate
change that would occur if these trends are
not reversed, significant global warming over
the next century - from 0.2 to 0.5 degrees C
per decade ~ is predicted by global climate
computer models.

      Drastic  cuts  in emissions would be
required to stabilize atmospheric composition.
Because  greenhouse   gases,  once  emitted,
remain  in the atmosphere  for decades  to
centuries,  stabilizing   emissions at  current
levels would  allow the greenhouse  effect  to
continue to intensify for more than a century.
Emissions of carbon dioxide might have to be
reduced by 50-80% to hold its concentration

      While  it is  not possible  to stabilize
greenhouse gas concentrations immediately,
world-wide implementation  of measures  to
reduce emissions would decrease the risks of
global  wanning, regardless  of uncertainties
about the  response  of the  climate system.
Scenario analyses indicate that if no policies to
limit   greenhouse   gas  emissions   were
undertaken, the equivalent of a doubling of
carbon dioxide would occur between 2030 and
2040, and the Earth might be committed to a
global wanning of 2-4C (3-7F) by 2025 and
3-6C (4-10F) by 2050. Early application of
existing and emerging technologies designed
to, among other things, increase the efficiency
of energy use,  expand the use of non-fossil
energy sources, reverse deforestation, and
phase out  chlorofluorocarbons could  reduce
the global  warming commitment in 2025 by
about one-fourth,  and the  rate  of climate
change during  the next century by at  least
60%.    A global  commitment  to rapidly
reducing greenhouse gas emissions might be
able to stabilize the concentrations of these
gases by  the  middle of  the  next century,
perhaps limiting global warming to less than
2C (3F).  The economic and  technological
analyses  needed  to determine  the  specific
actions  that  would achieve such  a  large
reduction at minimum cost have not yet been
done.    The  economic  feasibilities,  costs,
benefits, and   other  social  and  economic
implications of such actions are not known.
This study identifies a wide range of potential
options and actions which appear promising
based  on  available technical  information.
Further detailed study is required to determine
the effectiveness and economic implications of
each option.

      There is a wide range of policy choices
available that have the technical potential to
reduce greenhouse gas emissions.  Many also
appear to be consistent with other economic,
development, environmental, and social goals.
Any effective strategy will require a variety of
policies aimed at reducing emissions from
many sources and obtaining the cooperation of
many countries. Although a full assessment of
the costs and benefits of each option has not
been conducted, a number of potential actions
or policies geared toward increasing energy
efficiency,  accelerating  research   and
development,  and   reversing   deforestation
would have important benefits in addition to
reducing greenhouse gas emissions.  Decisions
on the timing of U.S. policy responses should
be based on a consideration of the multiple
benefits and costs that might result from each
policy, the additional commitment to warming
caused by delaying  action, and  the role that
U.S.  leadership  could  play in  promoting
international cooperation to limit changes in
climate variables to acceptable levels.

      Much  of  the   report's  discussion
necessarily cites information derived from U.S.
experience and data because of the limitations
of information about other regions. However,
the report's discussion of emissions, potential
response options, and their  implications is
from a world-wide  perspective.  Because of
limitations in  our  knowledge, particularly
about  economic factors  in many  regions
outside of the U.S., the report's findings  and
conclusions must be viewed as indicative  and

 Policy Options for Stabilizing Global Climate

      The  composition   of  the   Earth's
 atmosphere  is  changing  (see  Figure  1).
 Although the specific rate and magnitude of
 future climate change are hard to predict, in
 the absence of policy responses the observed
 trends  and   projected   increases  in  the
 atmospheric  concentrations  of  greenhouse
 gases are likely to significantly alter the global
 climate during the next century.  "Greenhouse"
 gases (carbon dioxide, methane, chlorofluoro-
 carbons, and nitrous oxide, among others) in
 the atmosphere absorb heat that radiates from
 the Earth's surface and emit some of this heat
 downward, wanning the climate. Without this
 "greenhouse effect," the Earth would be about
 30C (60F) colder than it is today.  Human
 activities are now increasing the atmospheric
 concentrations of greenhouse gases on a global
 basis, thus intensifying the greenhouse effect.
 The rate of greenhouse gas buildup during the
 next century will depend heavily on  future
 patterns   of   economic  and  technological
 development, which are, in turn, influenced by
 policies   of   local,  state,  national,   and
 international institutions.

 Purpose of This Study

      To better define the potential effects of
 global climate change and identify the options
 that are  available  to  limit  human-caused
 climate  change, Congress asked the  U.S.
 Environmental Protection Agency (U.S. EPA)
 to undertake two studies.  Congress directed
 that in one of these studies U.S. EPA focus on
 "the potential health and environmental effects
of climate change."  A companion report, The
Potential Effects of Global Climate Change on
the United States (Smith and Tirpak,  1989),
responds to that  request.  The second request
was that U.S. EPA undertake --

     An examination of policy options
     that  if implemented would stabilize
     current   levels  of   atmospheric
     greenhouse gas concentrations. This
     study should address the need for
     and  implications  of  significant
     changes  in  energy policy,  including
     energy efficiency and development of
     alternatives to fossil fuels; reductions
     in the use of CFCs; ways to reduce
     other  greenhouse  gases  such  as
     methane and nitrous oxide; as well
     as the potential for and  effects of
     reducing   deforestation   and
     increasing reforestation efforts.

This  study  responds  to  that  request  by
examining the impact of a wide variety of
policy  options  under a  range of  possible
economic and technologic developments. The
analysis shows that while it is not possible to
stabilize   greenhouse  gas   concentrations
immediately, a global commitment to rapidly
reduce greenhouse gas emissions might be able
to stabilize their concentrations by the middle
of  the   next   century  and   even  reduce
concentrations toward current levels by the
end of the next  century. While humans may
have already committed the earth to significant
climate change during the next century, efforts
undertaken  now  to  limit  the buildup  of
greenhouse  gases in the atmosphere  can
dramatically  reduce   the rate  and ultimate
magnitude of such change.

Scope of This Study

      The scope of  this study is necessarily
global and the time  horizon is more than a
century. To address this complex problem the
Agency enlisted the help of leading experts in
the  governmental,  non-governmental,  and
academic  research communities.  Five work-
shops,  which  were  attended  by  over 300
people, were held to  gather information and
ideas  about  factors  affecting  atmospheric
composition  and  about  response  options
related to greenhouse  gas emissions from
agricultural  and forestry practices, industrial
processes, and energy consumption and supply,
as well  as the  extent to which  developing
countries  may be contributing to  potential
global wanning.  Experts at NASA, the U.S.
Department of Energy (U.S. DOE), and the
U.S. Department of Agriculture (U.S. DOA)
contributed to this effort.

     Based   on  the   outcome  of  this
information-gathering  process,  U.S.  EPA
developed an integrated analytical framework
to organize the data and assumptions required
to calculate (1)  emissions of radiatively and
chemically active gases, (2) concentrations of
greenhouse gases, and (3) changes in  global

                                                           Executive Summary
                                  FIGURE I





   c  320

 Policy Options for Stabilizing Global Climate
 temperatures.  This  framework  is   highly
 simplified, as its primary purpose is to rapidly
 scan a broad range of policy options in order
 to test their general effectiveness in reducing
 atmospheric  concentrations  of  greenhouse
 gases.    This  analysis  represents  the first
 attempt to quantify the relationship  between
 certain  underlying forces (e.g., population
 growth, economic growth, and technological
 change) and emissions of all of the important
 greenhouse gases.  By using this framework we
 were able to estimate how assumed changes in
 these  underlying  forces  would affect  the
 composition  of the atmosphere and global
 temperatures.  It should be kept in mind that
 the  uncertainties   in deriving  temperature
 changes  from  changes  in greenhouse  gas
 concentrations are substantial. In constructing
 this framework, we used the results of more
 sophisticated models of individual components
 as a basis for our analysis (see Appendix A for
 more discussion of this framework). While we
 believe that this framework generally reflects
 the current state of scientific knowledge, there
 are important limitations.

 Current Policy Developments

      The primary objective of this report is
 to begin discussion of policies  that could  be
 adopted by the global community to respond
 to climate change  concerns.   We have not
 specifically focused on policies for the United
 States, but current  developments in U.  S.
 policy are an important part of the background
 information for readers of this report.

      Since this study was completed, many
 countries have already made commitments to
 goals  or  actions  that  help  to reduce  net
 greenhouse gas emissions.   In the United
 States the focus has been on actions that also
 have benefits for reasons  other than climate
 change.  Because of these other  benefits, such
 actions  can  be justified  despite the  very
substantial   scientific   and  economic
 uncertainties  associated  with climate change

      The  1990 Clean Air Act  Amendments
contain  provisions to  attain  and maintain
 National Ambient  Air Quality  Standards  by
regulating  emissions  of  volatile  organic
compounds,  nitrogen  oxides,  and  carbon
monoxide.  The Amendments  will not only
 produce cleaner air, but also significantly affect
 greenhouse gases or their precursors.  Major
 reductions of sulfur dioxide to 10 million tons
 below 1980 levels and of nitrogen oxides to 2
 million tons below projected year 2000 levels
 will  reduce greenhouse  gas  emissions  by
 greatly encouraging energy efficiency. Phasing
 out  CFCs,  carbon   tetrachloride,  methyl
 chloroform,  and   hydrochlorofluorocarbons
 (HCFCs) in accordance with  the  Montreal
 Protocol  and   the  Clean  Air   Act will
 substantially reduce emissions of greenhouse
 gases as well as protect the stratospheric ozone

      The President's  proposed program for
 planting a billion trees a year will produce
 substantial   benefits   for    wildlife,  soil
 conservation, and energy saving, as well  as
 directly take up CO2  from  the atmosphere.
 The  increase  in the  Federal gasoline  tax
 enacted in the  Budget Reconciliation Act of
 1990 will  reduce emissions  by encouraging
 energy  efficiency  in  road   transportation.
 Increased funding requested  in the FY 1991
 budget for research and development in solar
 and renewable energy and energy conservation
 will be important in identifying and developing
 technologies and practices that will allow us to
 meet our  energy needs in   environmentally
 efficient ways.  New energy  saving appliance
 standards promulgated by the Department of
 Energy will increase energy conservation and
 reduce demand.

      The U.  S.  has committed  to specific
 policy actions without specifying the future
 level  of aggregate emissions  that  will be
 realized.     Several  other   countries have
 committed to quantitative, aggregate, future
 emission  goals but have not  specified  the
 policy actions that will ensure achievement of
 those goals.  The  U. S. actions may have
 effects on emissions as substantial as the target
 emissions levels being promised for future
 achievement by a number of other countries.


     ' The analytical framework used in this
 report  attempts   to   incorporate   some
representation of the major processes that will
 influence   the   rate   and   magnitude   of
greenhouse warming during  the next century
within  a   structure   that   is  reasonably

                                                                        Executive Summary
transparent and easy  to  manipulate.  In so
doing  we  recognize  a  number  of  major

     Because of the scope of the analysis, it
was   not  possible   to   come   up  with
comprehensive  estimates of  the costs  or
benefits associated with  each policy option.
We   have  instead   relied  on  available
engineering cost estimates  and judgment to
select options that appear to  be the most
attractive. Subsequent studies, currently under
way, will  provide  more detailed  economic
analysis for the next few decades on a country-
by-country basis.   In particular i there are
serious limitations  in economic activity, cost,
and emission factor data for regions1 outside of
the  U.S., particularly  for the  developing
countries.  Thus,  the implications of each
policy option for such  regions are preliminary
and uncertain.  The policy options presented
herein should therefore be viewed as examples
of what could be done to reduce the buildup of
greenhouse gases, not  as recommendations of
what should be done.

     Forecasting  rates  of  economic growth
and technological  change over  decadal time
periods  is   difficult,  if   not   inherently
impossible. For this reason, the scenarios of
this report should  not be viewed as forecasts
or predictions.   While  we believe that the
scenarios presented in this report provide a
useful basis for analyzing policy options, our
alternative assumptions  may  not adequately
reflect the plausible range of possibilities. For
example, 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.  Similarly,
assumed  improvements in energy-consuming
and -producing technology in the No Response
and/or the Stabilizing Policy scenarios  (see
Table 2 for a description) may prove to be too
optimistic or pessimistic.

     The  use  of simplified  models  also
implies  that  some  potentially  important
processes   and    interactions   cannot   be
accounted   for.      These   include  the
macroeconomic implications of  the projected
changes in climate and the options designed to
limit these changes. Similarly, capital markets
are  not  explicitly considered.    This  is
particularly   significant  with   regard  to
developing countries, as it is unclear if they
will be able to obtain the capital needed  to
develop the energy supplies assumed in some
of the scenarios.  Additionally, the simplified
atmospheric  chemistry and  ocean  models
employed  may  not adequately reflect the
underlying processes, particularly as climate
changes.  Similarly, the parametric model used
to relate  global temperature  increases  to
concentrations of greenhouse gases may not  be
valid for  extrapolations beyond 6C.

     Behavioral changes  that  might  be
stimulated by climate change, by policies, or  by
individual choices to limit climate change also
have  not been  considered.    Individual
decisionmakers will take actions to adapt  to
any  changes  in  climatic conditions.   The
nature, costs, and benefits of these actions and
behavioral changes are not adequately defined
and   understood.     For  example,  future
population levels will have  an -important
impact  on greenhouse gas  emissions, but
reduced rates of population growth  have not
been analyzed as a policy response.


The  Greenhouse Gas Buildup

      Many greenhouse  gases  are  currently
accumulating in the atmosphere. The  most
important, in  terms  of  past  and  current
contribution  to radiative  forcing,  is carbon
dioxide  (COj), followed  by methane (CH4),
chlorofluorocarbons (CFCs), and nitrous oxide
(N2O) (see Figure 2 and Box  1).   Carbon
dioxide,  a fundamental product of burning
fossil fuels (coal, oil, and gas), is also released
as a result of deforestation. There are many
sources of methane, including rice cultivation,
enteric   fermentation  in   animals,  releases
during coal mining and natural gas production
and  distribution,  waste  decomposition  in
landfills,  as  well as  many natural sources.
CFCs, however,  are  produced only by the
chemical  industry.   The  sources of nitrous
oxide are not well characterized, but most are
probably  related to soil processes;  the  most
important anthropogenic sources are fertilizer
use and  various land-use changes such  as
deforestation   and   savanna   burning.
Greenhouse  gases of natural  origin include

 Policy Options for Stabilizing Global Climate
                                   FIGURE 2
        Other (8%)
Figure 2.  Based on estimates of the increase in the concentration of each gas during the specified
period.  Other includes additional CFCs, halons, changes in ozone, and changes in stratospheric water
vapor. The other category is quite uncertain. (Sources: 1880-1980: Ramanathan et al., 1985; 1980s:
Hansen et al., 1988.)

                                                                Executive Summary
             Box 1.  Concept of Global Warming Potential

     Throughout this Report, relative contributions to climate change by greenhouse gas
are calculated based on  changes  in atmospheric concentrations of each gas.   These
concentration changes alter the radiative balance of the climate system.  The scientific
community has in the past calculated contributions to radiative forcing using estimated
changes in atmospheric concentrations over some time interval (e.g., 10 years); this approach
is reflected in the left-hand figure below (and also in Figure 2) based on Hansen et al.
(1988). When discussing the various greenhouse gases in a policy context, however, there
is often a need for policymakers to have some simple means of estimating the relative
impacts of emissions of each greenhouse gas to affect radiative forcing, and hence climate,
without the complex, time-consuming task of determining the impacts on atmospheric
concentrations.  Since this Report was first prepared, several researchers have developed
indices that translate the level of emissions of the various greenhouse gases into a common
metric in order to compare the climate-forcing effects of the gases.  The index has been
called  the  Global Warming Potential (GWP), and is defined as the time  integrated
commitment to climate forcing from the instantaneous release of 1 kilogram of a trace gas
expressed relative to that from 1 kilogram of carbon dioxide. For purposes of illustrating
this concept, we  have used the GWP methodology  developed by the Intergovernmental
Panel on Climate Change for an integration period of 100 years (IPCC, 1990) to express
1985  emissions on  a  CO2-equivalent basis in order  to compare  the results  to the
methodology used by Hansen et al.  (1988); see right-hand figure below.  These two
approaches produce very different results since Hansen et al. (1988) base their approach on
the radiative forcing effects of estimated changes in atmospheric concentrations from 1980-90,
while the use of GWPs measures the radiative forcing effects of emissions for a single year
(Le., 1985) over  a  100-year time  frame (see Addendum to Chapter II for a complete
discussion of this concept).  This report uses the Hansen et al. (1988) methodology when
discussing relative current contributions of different gases and source categories.  Use of the
IPCC or other alternative integrating methodologies would change the values of these shares

        By Greenhouse Gas                   By Greenhouse Gas
            Concentrations          Emissions on a CO2-Equivalent Basis

                 1980s                                 1985
* GWP values 6om IPCC <199Q) wew wwi and apptied to jk>baiemissk>B estimates from
the RCW scenario.

 Policy Options for Stabilizing Global Climate
water  vapor and all  of those listed above
except the chlorofluorocarbons.

      Stabilizing emissions of greenhouse
gases  at  current  levels will  not  stabilize
concentrations.   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 might
reach 440-500 parts per million (ppm) by 2100,
compared with about 350  ppm today,  and
about 290 ppm 100 years ago (see Figure 3).
Nitrous oxide  concentrations would  probably
increase   by  about  20%;  methane
concentrations might remain roughly constant.

      Drastic  cuts  in emissions would be
required   to  stabilize  atmospheric
composition.  This  assertion is based on the
fact that these gases  remain in the atmosphere
for a  very long  time  and.  that  constant
emissions  at current levels  would lead to a
continuing   increase    in   concentrations.
Emissions of CO2, for  example, would have to
be reduced by 50-80% to stabilize atmospheric
concentrations (see Table  1).   Even if all
anthropogenic emissions (i.e., emissions caused
by human activities) of CO2, CFCs, and N2O
were eliminated, the concentrations  of these
gases would remain elevated for decades. It
would  take more than 50 years, and possibly
more than  a century,  following a cut-off in
CO2 emissions for the  oceans and other sinks
to absorb  enough  carbon to  reduce  the
atmospheric concentration  of CO2  halfway
toward its pre-industrial value.

The Impact of Greenhouse Gases
on Global Climate

      Uncertainties  about the  impact of the
greenhouse  gas  buildup on global  climate
abound.  These uncertainties are not about
whether the greenhouse effect is  real or
whether   increased   greenhouse   gas
concentrations will raise global temperatures.
Rather, the uncertainties concern the ultimate
magnitude  and timing of warming  and the
implications of that warming for the Earth's
climate system, environment, and economies.
                TABLE 1

        Approximate Reductions in
   Anthropogenic Emissions Required to
           Stabilize Atmospheric
     Concentrations at Current Levels
Carbon Dioxide                50-80%
Methane                      10-20%
Nitrous Oxide                 80-85%
Chlorofluorocarbons            75-100%
Carbon Monoxide (CO)         Freeze
Oxides of Nitrogen (NOX)       Freeze
      The magnitude of future global wanning
will depend, in part, on how geophysical and
biological feedbacks enhance or reduce the
warming caused by the additional infrared
radiation  absorbed by  increasing concen-
trations of greenhouse gases.  The ultimate
global average temperature increase that can
be expected from a specific increase  in the
concentrations of greenhouse gases can be
called the "climate sensitivity." This parameter
provides a convenient index for the magnitude
of climate change  that would be associated
with different scenarios of greenhouse gas
buildup.  (In this report we use a doubling of
the concentration of CO2 from pre-industrial
levels, or the equivalent from increases in the
concentrations of a number of greenhouse
gases, as the benchmark case.)

      Estimating the  impact of increasing
greenhouse  gas concentrations on  global
climate has been a focus of research within the
atmospheric science community for more than
a decade.  This research shows that:

     If nothing else changed in the Earth's
climate system except a doubling of CO2 (or
the equivalent  in  other greenhouse gases),
average global  temperature would  rise 1.2-

                                                         Executive Summary
                                FIGURE 3
      425  -

      375  -
      350 -j
         1985  2000
Figure 3.  The response of atmospheric CO2 concentrations to arbitrary emissions scenarios, based
on two one-dimensional models of ocean CO2 uptake.  The emissions scenarios are relative to
estimated 1985 levels of 5.9 billion tons of carbon per year. (Sources: Hansen et al., 1984; Lashof,
1989; Siegenthaler, 1983.)

 Policy Options for Stabilizing Global Climate
      Increased global temperatures would
 raise atmospheric levels of water vapor and
 change the vertical temperature profile, raising
 the  ultimate  global  warming caused by  a
 doubling of CO2.   Changes in snow and ice
 cover are also expected to enhance warming.
 There is strong consensus that if nothing other
 than these factors changed in the Earth's
 climate system, the global temperature would
 rise  by 2-4C.

     The  impact  of changes  in clouds on
 global warming is  highly uncertain.  General
 circulation models now generally project that
 the global warming from doubling CO2 could
 cause  changes  in  clouds  that would either
 enhance this wanning or diminish it somewhat.

     A  variety  of other  geophysical and
 biogenic  feedbacks exist  that  have  generally
 been neglected in global climate models. For
 example,  future  global   warming  has the
 potential to increase emissions of carbon from
 northern latitude  reservoirs in the form of
 both methane and carbon dioxide, and to alter
 uptake of  CO2 by the  biosphere  and the
 oceans.   Modeling analyses  attempting to
 incorporate feedbacks result in a wider range
 of possible warming, i.e., 1.5 to 5.5  C, for an
 initial doubling of CO2.

      Global warming of  just a few degrees
 would  represent  an  enormous change in
 climate.    The  difference  in  mean annual
 temperature between Boston and Washington
 is only 3.38C,  and the  difference  between
 Chicago and Atlanta is 6.7C. The total global
 wanning  since the  peak of the last ice age,
 18,000 years ago, was  only about 5C.  That
 change transformed the landscape  of North
 America, shifting the Atlantic ocean  inland by
 about one  hundred miles,  creating the Great
 Lakes, and changing the composition  of forests
 throughout the continent.

      The potential future impacts of climate
change are  difficult to  predict and are beyond
 the scope  of  this  report. Although  global
 temperature change is used as an indicator of
climate change  throughout this report, it  is
important  to  bear in  mind  that  regional
changes in  temperature, precipitation, storm
 frequency, and other variables will determine
the environmental  and economic impacts of
climate change. Predictions of such regional
 changes in climate are highly uncertain at this

      Sensitivity analyses can be undertaken to
 estimate potential impacts, as was done in the
 companion  volume,  The Potential Effects of
 Global Climate Change  on the United States.
 The collective findings of that study suggest
 that the climatic changes associated with a
 global warming of roughly 2-4C would result

      a world different from the  world
      that exists  today.   .  .  . Global
      climate   change   could   have
      significant implications for natural
      ecosystems; for where and how we
      farm; for the availability of water
      to irrigate crops, produce power,
      and support shipping; for how we
      live in our cities; for the wetlands
      that  spawn our  fish;  for  the
      beaches we use for recreation; and
      for all levels of government and
      industry (Smith and Tirpak, 1989,
      p. xxx).

Natural Climate Variability

      Because   of  long-period   couplings
between different components of the climate
system,  for example,  between  ocean  and
atmosphere, the Earth's climate would  still
vary without being perturbed by any external
influences.  This natural variability could act
to add to, or subtract from, any human-made
warming.  Natural emissions and  variations
contribute  significantly  to  climate  change.
Climate variations from glacial to interglacial
periods   have   been  caused    naturally.
Controlling  anthropogenic  greenhouse  gas
emissions will not  prevent  natural  climate


Defining Scenarios

      Defining scenarios that encompass more
than a century is a daunting task.  While this
is  an  eternity  for  most  economists  and
planners, it  is  but a  moment for geologists.
And indeed, decisions made in the next few

                                                                        Executive Summary
decades, about how buildings are constructed,
electricity is generated, and cities are laid out,
for example, will  have  an impact on the
climate in 2100 and beyond. Decisions about
what kinds of automobiles and other industrial
products to produce and how to produce them
will  also  have  a  profound impact.   These
choices, which will affect the amount and type
of fuel we use to travel, to heat and light our
homes and offices, and to  run our factories,
will influence the magnitude of greenhouse gas
emissions  for many years.

      To explore the climatic implications of
such policy and investment decisions; we have
constructed six scenarios of future patterns of
economic  development,  population growth,
and  technological change.   These  scenarios
stan with alternative  assumptions about the
rate of economic growth and policies that
influence  emissions, such as those affecting
levels of future energy demand, land-clearing
rates, CFC production, etc.  These scenarios
are  intended   to   be  internally  consistent
pictures of how the world may evolve  in the
future. They are not forecasts and they do not
bracket the full  range of possible futures.
Instead, they were chosen to provide a basis
for evaluating  strategies for  stabilizing the
atmosphere  in   the   context  of  distinctly
different, but plausible, conditions.

      Specifically,  the   policy   scenarios
discussed in  this report are meant to stimulate
further study.     They  do  not  constitute
conclusions  about what would be  the most
feasible and cost-effective strategies or plans
for responding to climate change and should
not be interpreted as  such.   What they do
show is that no single measure or limited set
of a few  measures would  be an  adequate
response to  climate change. They also show
that there are a great many potential options,
each one of which alone would have only a
modest impact.  Finally, they show that much
more work is needed to evaluate the physical,
social,  and  economic  implications of each
policy option and to identify the least socially
and economically disruptive approaches.

      Deciding on an overall climate change
response strategy will  be extremely difficult
taking  into account all of the  unknowns and
uncertainties.    The   need  for  world-wide
cooperation in  a strategy  complicates the
policy-making problem.  However, the  U.S.
has many potential options from which, if their
implications  are well  understood,  it  can
develop a response that is  likely to be both
feasible and effective.  It is already proceeding
in this manner by immediately implementing a
series of actions that can be justified for other
reasons or by their benefits even in the face of
the  uncertainties.    However,  there  are
uncertainties even about how far those actions
which the U.S.  is already  taking should be
pursued.  Not all levels of energy efficiency,
tree planting, or increased levels of R & D are
likely to  produce benefits in excess of their
costs. All countries in their specific economic
contexts need to consider the costs, benefits,
and uncertainties of taking various actions.

      It should be noted that these scenarios
have not been updated to reflect the current
status   of   the   Montreal   Protocol   as
strengthened  by the London Agreement  to
completely phase out CFCs, halons, carbon
tetrachloride, and methyl chloroform, and  to
encourage limits on HCFCs.

      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  techno-
logical change; the other,  called the  Slowly
Changing  World (SCW), represents  a more
pessimistic view of the evolution of the world's
economies. A variant of the RCW scenario,
Rapidly Changing  World  with  Accelerated
Emissions (RCWA), assumes that efficiency
improvements occur more gradually and that
policies tend to favor increased greenhouse gas
emissions.  Two additional scenarios (referred
to as the "Stabilizing  Policy" scenarios)  stan
with the same  economic  and  demographic
assumptions  as  the  RCW and  SCW, but
assume a world in which nations have adopted
policies to limit anthropogenic emissions  of
greenhouse gases.  These scenarios are called
the Slowly Changing  World with Stabilizing
Policies (SCWP) and the Rapidly Changing
World with Stabilizing Policies (RCWP).  In
addition, a variant of the  RCWP  assumes
more Rapid  Reductions in greenhouse gas
emissions (RCWR). In all of the scenarios it

 Policy Options for Stabilizing Global Climate
 is  assumed  that   the '  key  national  and
 international   political   institutions   evolve
 gradually,  with no major upheavals.   An
 overview of  the  scenario  assumptions  is
 provided in Table 2.

      The analysis for this study included a
 detailed examination of energy demand for the
 year  2025.    We  chose  this  date  because,
 although substantial change will have occurred
 by then, some currently existing infrastructure
 will  still be  in  place   and  much  of the
 technology to be deployed over this period is
 already  under   development.    Scenarios
 extending beyond this date are speculative, but
 they are included because they are necessary to
 evaluate  the  full  implications of  more
 immediate decisions and because greenhouse
 gases  affect  warming for  many  decades.
 Projections to 2100 are based on  the patterns
 and relationships  established  between 1985
 and 2025.  The six  scenarios analyzed in this
 study were developed using the Atmospheric
 Stabilization  Framework.   This analytical
 framework was constructed for the purpose of
 evaluating the impact of all anthropogenic
 activities  on  the  level  of  greenhouse gas
 emissions, and consequently, on the rate and
 magnitude of global climate change.   For a
 description of this Framework, the reader  is
 referred to Chapter VI and Appendix A.

      It  should  be  understood that  the
 discussions of climate change in Chapter 3 and
 the  discussions  of  the climate  changes
 associated  with the  various  scenarios are
 subject  to great scientific  uncertainties.  The
 general circulation models, which are the basis
 for simulating climate  changes, while among
 the most sophisticated tools  available, are
 relatively simple compared to the feedback
 mechanisms and processes that operate in the
 real atmosphere/oceans system.  The model
 physics  grossly oversimplify  the  real world.
 The models do not yet adequately describe the
 present climate and, thus, projections must be
 viewed with extreme caution.

 Scenarios with  Unimpeded
 Emissions Growth

      In "A Slowly Changing World"  (SCW)
we consider the  possibility  that the recent
experience of modest  growth  will continue
indefinitely, with no concerted policy response
 to  the  risk of climate  change.   Per capita
 income in developing regions that have very
 high population growth is stagnant for several
 decades,   and  shows   modest   increases
 elsewhere. Economic growth rates per capita
 increase slightly over time in all developing
 regions as population growth rates gradually
 decline. The population engaged in traditional
 agriculture  continues to  increase, as  does
 speculative  land  clearing  and  demand for
 fuelwood.  These factors lead to  accelerated
 deforestation until tropical forests are virtually
 eliminated toward  the  middle of  the  next
 century.  Because of slack demand, real energy
 prices increase slowly. Productivity in industry
 and agriculture improves at only a moderate
 rate.  Correspondingly, the energy efficiency of
 buildings, vehicles, and consumer  products
 improves at a slow rate.

      In "A Rapidly Changing World" (RCW)
 rapid economic  growth and  technological
 change occur with little attention given to the
 global environment.  Per capita income  rises
 rapidly in most regions and consumers demand
 more energy services,  which puts upward
 pressure on energy prices. The number of cars
 increases rapidly in developing countries, and
 air travel increases rapidly in industrialized
 countries.  Energy efficiency is not much of a
 consideration in consumer choices, as income
 increases faster than real  energy  prices, but
 efficiency increases do occur as a  result of
 technological improvements. Correspondingly,
we assume that  there  is  a  high rate  of
innovation  in  industry and   that capital
equipment  turns  over   rapidly,   thereby
accelerating reductions in energy required per
 unit of industrial output. An increasing share
of  energy is  consumed   in the  form  of
electricity, which is produced mostly from coal.
The  fraction of  global  economic output
produced in the developing countries increases
dramatically  as   services   become  more
important in industrialized countries and as
industries such as steel, aluminum, and auto-
making   grow   in  developing   countries.
Population growth rates decline more rapidly
than in the Slowly Changing World scenario as
educational   and   income  levels    rise.
Deforestation continues at about current rates,
spurred by land speculation and commercial
logging, despite reduced rates of population
growth.    Note  that  the   SCW  and  RCW
scenarios are not bounding  cases with respect

                                                                Executive Summary
                                  TABLE 2

                    Overview of Major Scenario Assumptions
      Slowly 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
      Rapidly Changing World

        Rapid GNP Growth
   Moderated Population Growth
   Modest Energy Price Increases
 Rapid Technological Improvements
  Very Carbon-Intensive Fuel Mix
      Moderate Deforestation
Montreal Protocol/High Participation
      Slowly Changing World
      with Stabilizing Policies

        Slow GNP Growth
Continued Rapid Population Growth
Minimal Energy Price Increases/Taxes
   Rapid Efficiency Improvements
Moderate Solar/Biomass Penetration
        Rapid Reforestation
          CFC Phaseout
     Rapidly Changing World
      with Stabilizing Policies

        Rapid GNP Growth
   Moderated Population Growth.
Modest Energy Price Increases/Taxes
Very Rapid Efficiency Improvements
  Rapid Solar/Biomass Penetration
        Rapid Reforestation
          CFC Phaseout
      Rapidly Changing World
     with Accelerated Emissions

       High CFC Emissions
            Cheap Coal
          Cheap Synfuets
      High Oil and Gas Prices
   Slow Efficiency Improvements
        High Deforestation
          High-Cost Solar
        High-Cost Nuclear
      Rapidly Changing World
 with Rapid Emissions Reductions

           Carbon Fee
         High MPG Cars
     High Efficiency Buildings
    High Efficiency Powerplants
     High Biomass Penetration
        Rapid Reforestation

 Policy Options for Stabilizing Global Climate
 to  emissions,  rather  the  assumptions  are
 intended to be logically related, and therefore,
 have partially offsetting implications.

      Without  stabilizing  policies,  rapid
 greenhouse gas buildup and global warming
 are  likely.  The two worlds described above
 lead to significant increases in emissions of
 carbon  dioxide  and other trace gases  (see
 Table 3) and in atmospheric concentrations of
 the  greenhouse gases (see Figure 4).  CO2
 concentrations reach twice their pre-industrial
 levels in about 2080 in the SCW scenario.  In
 the RCW this level is reached by 2055, and
 concentrations  more  than  three  times  pre-
 industrial values are reached by 2100.  When
 all the trace gases are considered, an increase
 in the greenhouse effect equivalent  to  that
 which would occur  from a doubling of CO2
 concentrations is reached by 2040 in the SCW
 and  by 2030  in the RCW. By 2100 the total
 radiative forcing is equivalent to a tripling of
 CO2 in the SCW and a factor of 5 increase in
 the  RCW.    These  results  are in  good
 agreement with those of recent  studies  that
 have  made  less  formal  estimates  based
 primarily on  current trends in concentrations
 and/or emissions.  A notable exception are the
 results for CFCs.   The June 1990 London
 Amendments will result in even lower concen-
 trations of  CFCs.   However, because  the
 London Amendments were adopted after this
 analysis, they are not included in the scenarios.

      Even a Slowly Changing World would
produce  a  2-3C  temperature increase
 during  the  next  century.    In  the SCW
 scenario,  realized  global  wanning  would
 increase by 1.0-1.5C between 2000 and 2050
 and by 2-3C from 2000 to 2100 (temperature
 ranges are based on a climate sensitivity of 2-
 4C  unless otherwise  noted; see  Box 2  and
 Figure 5).   The  maximum  realized rate  of
 change associated with this  scenario is  0.2-
 0.3C per  decade, which occurs sometime in
 the middle of the next century.  The  total
 equilibrium   warming   commitment   is
 substantially higher, reaching 3->6C by 2100
 relative to pre-industrial levels (see Table 4).1

      The "equilibrium wanning commitment"
 is the warming that would eventually result
 from  a  given  atmospheric  composition
 assuming that it were to remain fixed at that
 level.  Because the  oceans  adjust thermally
 over many years, it takes years or decades to
 reach  the equilibrium warming.   "Realized
 warming" is that portion of the equilibrium
 warming that has been reached at any point in
 time (see Box 2).

      Higher  rates of economic growth are
 certainly the goal of most governments and
 could lead to higher rates of climate change as
 illustrated by the RCW scenario. The rate of
 change during the next century would be more
 than 50% greater than in  the  SCW: in the
 RCW, realized global warming increases  by
 1.3-2.0C between 2000 and 2050, and by 3-5C
 between 2000 and 2100. The total equilibrium
 wanning commitment reaches 5->6C by 2100.
 In  this case the maximum  realized rate  of
 change is 0.4-0.6C per decade,  which occurs
 sometime between 2070 and 2100.

 The Impact of Policy Choices

      Government  policies,  if   applied
 globally,  could  significantly  increase  or
 decrease  future  warming.   The  wanning
 suggested by the Slowly Changing and Rapidly
 Changing World  cases is not inevitable; it is
 the  result of the public and private choices
 implicit in these scenarios.  While some future
 warming probably is locked in,  the range of
 possible  future commitments to warming is

Accelerated Emissions Scenario

      Decisions that  will be made in the near
 future may lead to increased emissions if there
 is no clear policy goal to reduce them.  This
 potential is illustrated by a series of tests that
 were conducted  to  examine the  effect  of
 accelerated emissions on equilibrium warming
 commitment. Starting with the RCW scenario,
 eight key parameters were varied as proxies for
 recently-proposed policies  that  have  the
 potential to significantly increase greenhouse
 gas emissions (e.g., accelerated development of
 synfuels)  or  the possible  consequences  of
 government inaction  or failure (e.g., high use
 of CFCs and deforestation).

                                                                                  Executive Summary
                                              TABLE 3

                                        Trace Gas Emissions

CO, (Pg C)'
N20 (Tg N)b
CH4 (Tg CH4)
CO (Tg C)
CFC-12 (Gg)- d
HCFC-22 (Gg)d








. 5.2













* Pg C = Petagrams of carbon; 1 Petagram = 10  grams.
* Tg N = Teragrams of nitrogen; 1 Tcragram = 10" grams.
c Gg = gigagram; 1 gigagram = 10* grams.
d These scenarios were produced prior to the negotiations for the London Amendments to the Montreal Protocol.  The CFC
phaseout policy assumed in these policy scenarios  is similar overall to,  but somewhat more stringent  than,  the London

  Policy Options for Stabilizing Global Climate






 400 -
 200 -





                       FIGURE 4

         (3.0 Degree Celsius Climate Sensitivity)


                      MOW  |4000
                      tCW   3000

                      MCWM   2000
  1006 XOOO   2026   206
             1076   2106
1666 2060

                                                       Executive Summary
                               FIGURE 5
                        REALIZED WARMING
                     NO RESPONSE SCENARIOS

                   (Based on 2.0 - 4.0 Degree Sensitivity)
       1985  2000
2025       2050
2075       2100
Figure 5. Shaded areas represent the range based on an equilibrium climate sensitivity of 2-4C to
a doubling of CO2.

 Policy Options for Stabilizing Global Climate
                                         TABLE 4

                   Scenario Results For Realized And Equilibrium Wanning
Realized Warming - 2C Sensitivity
Realized Warming - 4C Sensitivity
Equilibrium Warming Commitment
Equilibrium Warming Commitment
- 2C Sensitivity 1985
- 4C Sensitivity 1985
* Estimates of equilibrium warming commitments greater than 6C represent extrapolations beyond
the range tested in most climate models, and this wanning may not be fully realized because the
strength of some positive feedback mechanisms may decline as the Earth warms. These estimates are
represented by >6C.

                                                                       Executive Summary
                   Box 2.  Equilibrium and Realized Warming
   Equilibrium Warming Commitment

   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.  This
   temperature may not be realized for several decades, and may not be realized at all if
   greenhouse gas concentrations fall.

   Realized Warming

   Because  the oceans  have a large  heat  capacity  the  temperature  change realized in the
   atmosphere  lags considerably  behind  the equilibrium level  (the  difference between the
   equilibrium warming and the realized wanning in any given  year  is called the unrealized
   warming). Realized wanning has been estimated with a simple model of ocean heat uptake.

   Climate Sensitivity

   Because the response of the climate system to changes in greenhouse gas concentrations is
   quite uncertain due to the role of clouds and other processes, we also consider a range of
   "climate sensitivities.*  Climate sensitivity is defined as the equilibrium warming commitment
   due to a doubling of the concentration of carbon dioxide from pre-industrial levels.  Given a
   particular emissions scenario and climate sensitivity,  the realized  wanning is  much more
   uncertain than the equilibrium warming commitment because the effective heat storage capacity
   of the oceans is not known.  On the other hand, because the amount of unrealized wanning
   increases with increasing climate sensitivity, fora given scenario, realized warming depends less
   on climate sensitivity than does equilibrium warming commitment.
      Figure 6 illustrates the results of these
tests as compared with the RCW scenario.
The results are  illustrated in terms of the
incremental effect of each outcome on the
equilibrium warming commitment in 2050 and
2100. As Figure 6 shows, the measures that
amplify the warming to the greatest extent are
those that reduce  the  rate of  efficiency
improvement  (historically,  energy efficiency
has improved about  l-2%#ear), reduce the
cost of synfuels, and increase the assumed rate
of  growth in  CFC  production and use.
Policies leading to accelerated deforestation
would have a large impact in the near term,
but a relatively small impact in 2100.

      The impact of all of these policies in
combination is quite dramatic.  In this case,
emissions of CO2 would be nearly five times
pre-industrial levels.   The rate  of  warming
during the next century would be over 60%
higher than in the RCW scenario.
Scenarios with Stabilizing Policies

      Three scenarios  were constructed  to
explore the impact of policy choices aimed at
reducing the risk of global  warming. The
Slowly  Changing  World  with  Stabilizing
Policies,  the Rapidly Changing World with
Stabilizing Policies, and the Rapidly Changing
World with Rapid Reductions 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 a wide
range of measures to reduce greenhouse gas
emissions are implemented beginning in the

 Policy Options for Stabilizing Global Climate
                               FIGURE 6
 1. High CFC Emissions"
        2. Cheap Coal
    3. Cheap Synfuels
4. High OH & Gas Prices
    5. Slow Efficiency
  6. High Deforestation'
    7. High-Cost Solar
  8. High-Cost Nuclear
Accelerated Emissions
 (Combination of 1-8?
                                  Percent Relative to RCW
                   -5 0     10    20    30    40    50    60    70

                                                                                 Executive Summary
                                        FIGURE 6 - NOTES

                   Impact Of Accelerated Emissions Policies On Global Warming

* Assumes a low level of participation in and compliance with the Montreal Protocol, excluding the London
Amendments, which were adopted after these scenarios were completed. The assumptions used in this case are
similar to those used in the "Low Case" analysis described in the U.S. EPA's Regulatory Impact Assessment report,
i.e., about 75% participation among developed countries and 40% among developing countries.  In the RCW case
the U.S. was assumed to participate  100%, other developed countries 94%, and developing countries 65%.

b Assumes that advances in the technology of coal extraction and transport rapidly reduce the market price of coal
at the burner tip. In the RCW scenario, the economic efficiency of coal supply is assumed to improve at a rate of
approximately 0.5% per year. In this case, it is assumed to improve at a rate of 1% per year.

c Assumes that the price of synthetic oil and gas could be reduced by 50% and commercialization rapidly accelerated
relative to the RCW case.

d Assumes that  OPEC (or some other political entity) could control production levels and thus raise the border
prices of oil and gas.  To simulate this effect, oil and gas resources were shifted to higher points on the regional
supply curves. In addition, extraction costs for oil in each resource grade were increased relative to the assumptions
in the RCW case.   In 2025 these assumptions  increased  oil prices  about  Si/barrel and  gas prices about
S0.25/thousand cubic feet.

" Assumes that technical gains in the engineering efficiency of energy use occur only half as rapidly as assumed in
the RCW case.   In the RCW case it  is assumed that efficiency improves  at rates of approximately 1-2% per year
(approximately equal to historical rates).  In the Slow Improvement case the assumed rates were reduced to only
0.5-1.0% per year.  The lower rate of improvement is similar to the assumptions in recent projections for the U.S.
DOE's National  Energy Policy Plan.

f Assumes annual deforestation increases at a rate equal to the rate of growth in population. In the RCW case the
rate of deforestation increases at a slower rate, reaching 15 million hectares/year in 2097 compared to 34 million
hectares/year by  2047  in the RCWA case.

8 Assumes that the cost of solar energy precludes the possibility of its making any significant contribution to global
energy supply. In the RCW case costs approached 8.5 cents/kwh after 2050.

b Assumes that the cost of electricity from fission electric systems becomes so high that their contribution to global
energy supply is permanently limited. In this case, an environmental tax of about 6 cents/kwh (1988S) on the price
of electricity supplied by nuclear powerplants was phased in by 2050. In the RCW case nuclear costs were assumed
to be 6.1 cents/kwh in 1985.

' All of the above assumptions were combined in one scenario. The result is not equal to the sum of the wanning
in the RCW and the eight individual cases because of interactions among the assumptions.

 Policy Options for Stabilizing Global Climate
      No  single activity is the  dominant
 source  of greenhouse  gases; therefore,  no
 single measure can stabilize global climate.
 Many individual components, each having
 a  modest  impact on  greenhouse  gas
 emissions, can have a dramatic impact on
 the rate of climate change when combined.
 The  Stabilizing  Policy  scenarios  therefore
 assume  that   many policy  initiatives  are
 undertaken simultaneously.  These scenarios
 assume  that   policies  to promote  energy
 efficiency in all sectors succeed in substantially
 reducing energy  demand  relative to the No
 Response  scenarios  (which already assume
 substantial    efficiency   improvements).
 Research and  development  investments in
 non-fossil  energy  supply  options such  as
 photovoltaics  (solar  cells), biomass-derived
 fuels  and electricity (fuels made from plant
 material), and  advanced nuclear reactors are
 assumed to make these options available and
 begin to become competitive by 2000. As a
 result,  non-fossil  energy  sources  meet  a
 substantial fraction of total demand in later
 periods. There is considerable uncertainty as
 to whether these sources could actually be
 available on a competitive basis by the year
 2000. In addition, whether these technologies
 would  be  economically  attractive in  the
 quantities projected in future scenario years is
 quite uncertain.   The  existing  protocol to
 reduce CFC and halon emissions is assumed to
 be strengthened, leading to a phaseout of fully-
 halogenated  compounds  and a freeze on
 methyl chloroform. (The London Amendments
 to the Montreal  Protocol, adopted  after  this
 analysis was completed, call for the complete
 phaseout   of   CFCs,   halons,   carbon
 tetrachloride,  methyl   chloroform,  and
encourage limits on HCFCs.)  A global effort
to  reverse  deforestation  transforms  the
biosphere from a source to a sink for carbon
by 2000, and technological innovation and
controls reduce agricultural,  industrial, and
transportation emissions.      The impact of
these measures on  wanning commitment in
2050 and 2100 is illustrated in Figures 7 and 8.
The  results  of  this analysis suggest  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 climate
change.   In the long run, advances in solar
technology  and biomass plantations also play
an essential role. These conclusions are based
upon the assumptions made in these scenarios
about these technologies and about competing
technologies, such as nuclear  fission.  How
sensitive they may be  to  variations  in  the
assumptions,  particularly  to   differences
reflecting economic differences between  the
industrialized  countries and the  developing
countries, is not fully  understood. While the
same general  emissions reduction strategies
are assumed in both  the SCWP and RCWP
cases, the degree and rate of improvement are
greater  in  the  RCWP  scenario  because
technological  innovation  and capital  stock
replacement occur at a faster pace.

      The   policies   considered  in   these
scenarios do not require fundamental changes
in  lifestyles.   For example, energy  use  in
buildings is greatly reduced in the Stabilizing
Policy scenarios  relative to the No Response
scenarios, but the floor space available per
person and the  amenity levels provided  are
assumed to be  the same.   Similarly, while
automobile fuel efficiency is assumed to be
much  higher,  restrictions  on  automobile
ownership are not considered.  The potential
impact of policies  on  personal decisions that
directly  change  lifestyles  has  not  been

      It should  be kept in  mind that these
Stabilizing   Policy  scenarios   incorporate
assessments of the technical feasibility of the
measures  included and  general  judgments
about  their  likely   economic  character.
Analyses  of  economic  feasibility,  market
penetration,  costs,   benefits,   and  other
socioeconomic implications have not been
systematically  completed.    Knowledge  is
particularly lacking about these socioeconomic
aspects under  developing country conditions
where scarcity  of capital  and  of  trained
technical people could complicate efforts to
implement these measures.

      These policy assumptions  result in a
substantial reduction in the rate of greenhouse
gas buildup, but not an immediate stabilization
of the atmosphere (see Figure 9).   In the
RCWP scenario global CO2 emissions decline
about  10% by  2025  and  remain  roughly
constant  thereafter.    This  result  implies
substantial reductions in emissions from

                                                           Executive Summary
                                  FIGURE 7
 1. Improved Transportation

 2. Other Efficiency Gains"
 3. Carbon Fee
 4. Cheaper Nuclear
   Power d

 5. Solar Technologies*
 6. Commercialized Biomass'
 7. Natural Gas Incentives9
 8. Emission Controls
 9. CFC Phaseout*
10. Reforestation'
11. Agriculture, Landfills,
   and Cementk

RCWP (Simultaneous     i
  Implementation of 1-11)
                                  Percent Reduction Relative to RCW
                                           10        15
   Figure 7. The impact of individual measures on the equilibrium warming commitment in the RCW
   scenario. The simultaneous implementation of all the measures represents the RCWP scenario.

 Policy Options for Stabilizing Global Climate
                                             FIGURE 7  -- NOTES

                            Impact Of Stabilizing Policies On Global Warming

 a The average efficiency of cars and light trucks in the U.S. reaches 30 mpg (7.8 liters/100 km) by 2000; new cars achieve 40
 mpg (5.9 liters/100 km). Global fleet-average automobile efficiency reaches 43 mpg by 2025 (5.5 liters/100 km). In the RCW
 case global vehicle efficiencies for cars and light trucks achieve 30 mpg by 2025.

 b The rates of energy efficiency improvements in the residential, commercial, and industrial sectors are increased about 0.3-0.8
 percentage points annually from 1985 to 2025 compared to the RCW and about 0.2-0.3 percentage points annually from 2025-
 2100. In the RCW case energy efficiency improvements averaged about 1-2% annually from 1985-2025, and less than 1% after

 c Emissions fees are placed on fossil fuels in proportion  to carbon content. Fees were placed only on production; maximum
 production fees (1988$) are $1.00/GJ for coal (about $25Aon), S0.80/GJ for oil (about SS/barrel), and S0.54/GJ for natural gas
 (about SO.SSAhousand cubic feet). These fees increase linearly from zero, with the maximum production fee charged by 2025.
 In the RCW case no emission fees were assumed.

 d Assumes that technological improvements in nuclear powerplam design reduce costs by about 0.6 cents/kwh (1988$) by 2050.
 In the RCW case we assumed that nuclear costs in 1985 were 6.1 cents/kwh (1988$).

 ' Assumes that low-cost solar technology is available by 2025 at costs  as low as 6.0 cents/kwh. In the RCW case these costs
 approached  8.5 cents/kwh, but these levels were not achieved until after 2050.

 f Assumes the cost of producing and converting biomass to modern fuels reaches S4.35/GJ (1988$) for gas (about $4.70Ahousand
 cubic feet) and S6.00/GJ (1988$) for liquids (about S36/barrel) by 2025, with biomass penetrating more quickly than in the RCW
 case due to more land committed to production.  The maximum amount of liquid or gaseous  fuel available from biomass (i.e.,
 after conversion losses) is 205 EJ. In the RCW case these prices were not attained until 2035, and biomass energy penetrates
 slowly because research and development is slow and because land is committed slowly to biomass energy production.

 8 Assumes that economic incentives for gas use for electricity generation increase the gas share by 5% in 2000 (thereby reducing
 prices about 1.6%) and 10% in 2025 (thereby reducing prices about 3.1%). Gas consumption for electricity generation was
 about 21 EJ in the RCW case.

 b Assumes more stringent NOX and CO controls on mobile and stationary sources, including all gasoline 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 use
 oxidation catalysts from 2000 to 2025).  In the RCW case only the U.S. adopts  three-way catalysts (by 1985); the OECD
 countries adopt oxidation catalysts by 2000, and the rest of the world does not add any  controls.  From 2000 to 2025
 conventional coal boilers used for electricity generation are retrofit with low NO, burners, with 85% retrofit in the developed
 countries and 40% in developing countries; starting in 2000  all new combustors used for electricity generation and all new
 industrial boilers require selective catalytic reduction in the developed countries and low  NO, 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 NO, burners after 2000. In the RCW case no additional controls are assumed.

 1 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 by developing countries.  In the RCW scenario we assumed compliance with the
 Montreal Protocol, which called for a 50% reduction in  the use of the major CFCs.  Note the London Amendments to the
 Montreal Protocol, calling for a phaseout of CFCs, batons, carbon tetrachtoride, methyl chloroform, and encouraging limits on
 HCFCs, are not reflected in the scenario; these Amendments were negotiated after this analysis was completed.

i 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.  In the RCW case, the
 rate of deforestation continues to increase very gradually, reaching 15  Mha/yr in 2097.

 k Assumes that research and  improved agricultural practices result in an  annual 0.5%  decline in the emissions  from rice
 production, enteric fermentation, and fertilizer use. CH4 emissions from landfills are assumed to decline at an annual rate of
2% in developed countries because of policies aimed at reducing solid waste and increasing landfill gas recovery, while emissions
in  developing countries continue to grow until 2025 and then  remain  Oat due to incorporation of the same policies.
Technological improvements reduce demand for cement  by 25%.  In the RCW case no emission rate changes were assumed
for agricultural practices.  CH4 emissions from landfills were assumed to remain constant in developed countries and increase
as  the population grew in developing countries.

1 Impact on global 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


                                                          Executive Summary

                                 FIGURE 8

                     RAPID REDUCTION STRATEGIES:

       1. Carbon Fee
     2. High MPG Cars
    3. High Efficiency
    4. High Efficiency
      5. High Biomass
6. Rapid Reforestation
     Rapid Reduction *
         of 1-6)
                                Additional Percent Relative to RCW
 Figure 8.  The impact of additional measures applied to the RCWP scenario expressed as percent
 change relative to the equilibrium wanning commitment in the RCW scenario. The simultaneous
 implementation of all the measures in combination with the measures in the RCWP scenarios
 represents the Rapid Reduction scenario.

 Policy Options for Stabilizing Global Climate
                                        FIGURE 8 -- NOTES

                      Impact Of Rapid Reduction Policies On Global Warming

a High carbon emissions fees are imposed on the production of fossil fuels in proportion to the CO2 emissions
potential. In this case, fees of about S4.00/GJ were imposed on coal (SlOO/ton), S3.20/GJ on oil (S19/barrel), and
S2.15/GJ on natural gas (S2.00/mcf).  These fee levels are specified in 1988$ and are phased in over the period
between 1985 and 2025.  No fees were assumed in the RCW case.

b Assumes that the average efficiency of new cars in the U.S. reaches 50 mpg (4.7 liters/100 km) in 2000 and that
global fleet-average auto efficiencies reach 65 mpg (3.6 liters/100 km) in 2025 and 100 mpg (2.4 liters/100 km) in
2050. Comparable assumptions for the RCWP case were 40,50, and 75 mpg for 2000,2025, and 2050, respectively.

c Assumes that  the rate of technical efficiency improvement in the  residential and commercial sectors improves
substantially beyond that assumed in the RCWP  case.  In this case, the rate of efficiency improvement in the
residential and commercial sectors is increased so that a net gain in efficiency of 50% relative to the RCWP case
is achieved in all regions. In the RCWP case rates of efficiency improvement averaged 1.5-3.0%  per year  from

d Assumes that by 2050 average powerplant conversion efficiency improves by 50% relative to 1985. In this case,
the design efficiencies of all types of generating  plants improve significantly.  For example, by 2025 new oil-fired
generating stations achieve an average conversion efficiency roughly equivalent to 5% greater than that achieved
by combined-cycle units today. In the RCW case new oil-fired units achieve an average conversion efficiency equal
to combined-cycle units today.

e The availability of commercial biomass was doubled relative to the assumptions in the RCWP case.  In this case
the rate of increase in biomass  productivity is assumed to be at the  high end of the range suggested by the U.S.
DOE Biofuels Program.  Conversion costs were assumed to fall by one-third relative to the assumptions in the
RCWP case.

f A rapid rate of global reforestation is assumed.  In this case deforestation is halted by 2000 and the biota become
a net sink for CO2 at a rate of about 1 Pg C per year by 2025, about twice the level of carbon storage assumed in
the RCWP case.

g Impact on warming when all of the above measures are implemented simultaneously. The impact is much less
than the sum of the individual components because many of the measures are not additive.

                                                        Executive Summary
                                FIGURE 9
                         REALIZED WARMING:
                    (Based on 2.0 - 4.0 Degree Sensitivity)
         Slowly Changing World
Rapidly Changing World
  1985 2000   2026   2060  2076  2100
                                      1t6  2000  2026   2060   2076   2100
Figure 9. Shaded areas represent the range based on an equilibrium climate sensitivity to doubling
CO2 of 2-4C.

 Policy Options for Stabilizing Global Climate
 industrialized countries,  however.    U.  S.
 emissions, for example, fall 40% by  2025.
 Carbon   dioxide   concentrations  increase
 gradually throughout the time  frame of the
 analysis despite roughly constant emissions (as
 discussed above).   Total radiative forcing  is
 close to being stabilized by 2100, but the level
 is equivalent to  almost a  doubling of pre-
 industrial CO2 concentrations in  the RCWP
 and to a 65% increase in the SCWP.

      The rate of climate change in the
 SCWP and RCWP scenarios is at least 60%
 less  than  in the  corresponding  worlds
 without  policy responses,  but the risk of
 substantial climate change is still significant.
 The rate of global temperature increase during
 the next century in these scenarios is 0.5-1.5C,
 while the maximum rate of change is less than
 0.2C per decade between 2000 and 2025. This
 represents much more gradual change than in
 the  No Response scenarios, but it does not
 ensure that the rate of warming will remain
 below 0.1C per decade. Some experts have
 suggested that  this rate of change represents
 the maximum to which many species of plants
 and animals  could adapt. Total equilibrium
 warming commitment could exceed 3.5C by
 2100 in the RCWP case. Given the possibility
 that the climate sensitivity could be higher and
 that   there   could   be   large   positive
 biogeochemical   feedbacks  that   are   not
 included  in  these  calculations, there  is  a
 possibility that these scenarios could lead to
 extremely rapid climate  change.  It is also
 possible  that the policies assumed in  these
 scenarios could limit climate change to about
 1C if the true climate sensitivity of the Earth
 is low.

      Only the most aggressive policy case
reverses the greenhouse gas buildup early in
 the 21st  century.  The economic feasibility,
 costs,  benefits, and other socioeconomic
implications  of such policies have not  been
determined  at  this  time.    The  Rapid
 Reduction scenario explores the  impact of
 policies  that  effect a rapid transition  away
 from fossil fuels.    In the Rapid  Reduction
scenario  net  global CO2 emissions decline
 nearly 15% by 2000 and 65% by 2025.  U.S.
 emissions decline  20% by 2000 and 50% by
 2025. The atmospheric concentration of CO2
 peaks below 400 ppm around 2025, and total
greenhouse forcing peaks at an equivalent CO2
concentration of less than 450 ppm. After this
point, equivalent CO2 concentrations decline
until  by 2100 they are about equal to current
levels  of  atmospheric  greenhouse   gas
concentrations (on a CO2-equivalent basis). It
is this level of concentration, and the policy
options necessary to achieve this level, that
Congress specifically requested U.S. EPA to
evaluate.  Despite declining concentrations,
however,  temperatures continue to rise to
about 2050, peaking at 0.9-1.5C above pre-
industrial  levels.  In this case the maximum
rate  of change  is  0.09-0.16C per decade
between 2000 and 2025, but the average rate
of change over the next century is much less
than  O.rC per decade.   The measures that
reduce the warming to the greatest extent in
the Rapid Reduction  case  relative to  the
RCWP case are those that impose stiff carbon
fees on the production of fossil fuels, improve
the energy efficiency of buildings, and increase
the assumed  level   of  renewable resource
availability.  Options for phasing in carbon
fees so as  to minimize impacts on the global
economy require additional analysis.

      To  reduce  the  amount   of global
warming to the rates projected in the RCWP
and Rapid Reduction cases, Table 5  lists
several policies that might have to be adopted
by  2000 to  begin reducing greenhouse  gas
emissions.   These examples  are meant  to
illustrate potential policy responses; a variety
of  policy  combinations might  achieve  the
reductions in global wanning estimated in each


      There is a wide variety of available, or
potentially  available,  options   to  reduce
greenhouse gas emissions that it is believed
would not unduly  interfere  with  meeting
growing demands for goods and services.  The
current status and potential of these options
are briefly reviewed below.  In most cases, the
costs  and  benefits   of  these options  for
responding to climate change cannot be fully
quantified  at  this  time,  both  because  of
scientific uncertainties about climate change
itself  and  because  of  many   economic

                                                                                 Executive Summary

                                              TABLE 5

                     Examples Of Potential Policy Responses By The Year 2000


      Research on energy efficiency and non-fossil-fuel technology is accelerated

      New automobiles in the U.S. average 40 mpg

      New automobiles in the OECD use three-way catalytic converters to reduce CO and NO^ the rest of world
       uses an oxidation catalyst

      Average space-heating requirements of new single-family homes are 50% below 1980 new home average

      Net global deforestation stops

      CFCs are phased out; production of methyl chloroform is frozen

      Fossil fuels are subject to emission fees that are set according to carbon content -- J I0/ton on coal, S2/barrel
       on oil, S0.20/thousand cubic feet on natural gas

      Accelerated research and development into solar photovoltaic technology allows solar power to compete with
       oil and natural gas (U.S. DOE long-term policy goals)

      Available municipal solid waste and agricultural wastes are convened  to useful energy

      Accelerated research on biomass energy plantations  increases current productivity by  65% (to 25 dry
       tons/hectare annually)                                                  


      Research on energy efficiency and non-fossil-fuel technology is accelerated

      New automobiles in the U.S. average 50 mpg

      Major retrofit initiatives reduce energy use in existing commercial buildings by 40%

      Average space-heating requirements of new single-family homes are 90% below 1980 new home average

      Global deforestation stops; major reforestation programs are undertaken

      CFCs are phased out; production of methyl chloroform is frozen

      Fossil fuels are subject to emission fees that are set according to carbon content - S38Aon on coal, S7/barrel
       on oil, $0.75/thousand cubic feet on natural gas

      Commercialization incentives lead to significant market penetration for solar technologies

      250 million hectares globally are committed to biomass energy plantations, i.e., 5% of forest and woodland

 Policy Options for Stabilizing Global Climate
 uncertainties  about  the  potential  options

 Improve Energy Efficiency

      The introduction of technologies and
practices that use less energy to accomplish
 a given task would have the largest impact
 on global warming in the near term.  Both
 industrialized and developing countries can
 significantly   improve   energy   efficiency.
 Although  per capita  energy  consumption is
 very low in developing countries, there is a
 large potential to  increase efficiency because
 energy use per unit of GNP is often extremely
 high.   Indeed, the  imperative  for  energy
 efficiency may be even stronger in developing
 countries to the extent that expending scarce
 capital on expanding energy supply systems can
 be avoided.   Many of the technical options
 described below may be directly applicable in
 developing as well as industrialized countries,
 but alternative approaches suited to available
 resources will also be needed. In many cases
 improved  management  of  existing facilities
 could have large payoffs.  We estimate that
 accelerated improvements in energy efficiency
 account for  about 25%  of the  difference
 between the  RCWP and the RCW cases in
 2050 (we  note that this occurs even though
 fairly rapid improvements are already assumed
 in the RCW case).

Improved  Transportation Efficiency

      A number of known technologies have
 the technical potential to increase automobile
 fuel efficiency from current levels for new cars
 (25-33  mpg  or  9.4-7.1 liters/100 km) to
significantly  higher levels.   What could be
achieved in  the foreseeable  future without
downsizing vehicles and reducing safety and
other desirable characteristics  is  uncertain.
 Given the currently available technical options
and  their  likely costs of implementation, a
 fleet average new car economy level of 40 mpg
by the  year  2000 could  require size  and
 performance reductions. The RCWP scenario
 assumes that new cars in the industrialized
countries achieve an average  of 50 mpg (4.7
 liters/100  km) in  2025 and 75  mpg  (3.1
liters/100 km) in 2050 (somewhat lower rates
of efficiency improvement are assumed in the
SCWP  scenario).   In addition, major  fuel
efficiency improvements in diesel trucks and
aircraft are possible.  The Rapid Reduction
case assumes  more aggressive measures to
improve efficiency.

Other Efficiency Gains

      More efficient building shells, lighting,
heating and cooling equipment, and appliances
are currently  commercially  available.  The
most efficient new homes currently being built
use only 30% as much heating energy per unit
of floor area as the average existing house in
the United States.  Advanced prototypes and
design  calculations   indicate   that   it  is
technically possible to build  new homes that
use only  10% of current  average  energy
requirements.  The economic feasibility, the
likely market  penetration, and  the  costs of
implementing such technological options are
uncertain.  About  20% of U.S. electricity is
consumed for lighting, mainly  in residential
and commercial buildings.  A combination of
currently available advanced technology and
careful  design has been shown  to  cost-
effectively reduce  energy  requirements for
lighting by more  than  75%.   The  RCWP
scenario assumes that the average reduction in
energy  use  per   unit  of   residential  and
commercial floor space by 2025 in the U.S. is
as much  as  75%  for  fuel and  50% for
electricity. Smaller improvements are assumed
in other regions and in the SCWP scenario.

      Advanced industrial processes currently
available can significantly reduce the energy
required to   produce  basic  materials  -
especially  if  these processes  are  used  in
combination with  recycling.   For  example,
estimates of the reductions in energy intensity
of U.S. steel  production that are technically
feasible range from 20 to 50 percent.  How
much of these savings would  be economically
feasible and at what cost is unknown. Electric
motors  are estimated  to account  for about
70% of US. industrial  electricity use.  Several
case studies show that improved motors and
motor controls now commercially  available
could reduce  energy consumption by  electric
motors  at  least  15%  relative  to  current

      While the promise of technically feasible
efficiency gains is  great,  the  uncertainties
about the rate and scale of implementation of

                                                                        Executive Summary
such measures are also great.  Many of these
gains would depend,  in the U.S. and other
developed countries, upon the rates at which
the existing capital stock is replaced by new,
more efficient capital equipment and facilities.
Such rates  depend upon a host of economic
and  other factors that are difficult to  assess:
the rates at which potential users learn about
new technologies, the age and value of existing
equipment  and facilities,  the availability and
cost of credit, the degree that existing  capital
capacity is  utilized, and so forth.   For these
reasons,  market  penetration  rates of new
technologies, and  how such rates might  be
accelerated, are very uncertain.

Carbon Fee       \

      One way to provide a market signal that
CO 2  emissions  have   environmental
consequences is to apply a "carbon1' fee to the
price of fossil fuels that is proportional to the
carbon content of the fuel.  Fees could be used
in conjunction with performance standards and
other   strategies   to  encourage   energy
conservation  and  investments  in  energy-
efficient technology. A carbon fee would also
affect the relative prices of fossil and  non-
fossil energy sources  and  the  relative prices
among the fossil fuels, reinforcing the policies
discussed  in  the  following sections.   The
revenues from such a fee could be used to
reduce other taxes, reduce the national  debt,
and/or support other national goals.  To be
least disruptive, revenues  would need to  be
offset by reductions in other  taxes. Further
analysis is required to determine these impacts
on the economy.  In particular, the full social
costs and benefits of substantial reductions in
an energy option, such as coal use, due to high
carbon  fees   or  to  command-and-control
regulations, have not been evaluated.

      Given  the  scientific  and  economic
uncertainties about the changes in climate that
are  likely  to result from given changes  in
greenhouse gas concentrations, and the net
costs to society  of  such  climate changes,
appropriate levels  for setting greenhouse gas
fees are unknown.

      If  greenhouse  gas  fees  and   other
controls on emissions are not established on a
comparable basis world-wide, the problem of
emissions-intensive activities  migrating  to
countries where fees were lower or controls
less stringent could occur, thereby reducing the
net effectiveness of the fees or controls.

Increase Use of Non-Fossil Energy

      There is a critical need for research
on  non-fossil energy  technologies.    The
development of attractive  non-fossil energy
sources is critical to the success of any climate
stabilization strategy over  the long  term.
Under  the assumptions   of  this report's
scenarios, increased penetration of solar and
advanced biomass technologies contribute little
to reduced  warming  in 2025,  but they are
responsible for 24% of the difference between
the RCWP  and the RCW case in  2050, and
over 25% of this difference in 2100.  Figure 10
shows  the relative  contribution to primary
energy supply of each fossil and non-fossil fuel
under each of our scenarios.  The exact mix of
non-fossil energy supply technologies assumed
in the  policy scenarios is rather arbitrary, but
makes  little difference to  greenhouse gas
emissions.  Some particularly promising non-
fossil technologies are described below.

Nuclear Power

      Nuclear fission produces about 5% of
global  primary energy supplies  and its  share
has been growing.  High cost  and concerns
about  safety,   nuclear  proliferation,  and
radioactive  waste disposal,  however,  have
brought new orders for nuclear powerplants to
a halt in many countries. Advanced designs, in
particular the  Modular High  Temperature
Gas-cooled  Reactor,  have  recently  been
proposed in an attempt to overcome some of
these problems.  The role  of nuclear power
could be significantly expanded in the future if
these  efforts  are   successful   and   public
confidence in  this energy source is restored.
Nuclear  power's contribution  to primary
energy supply in the SCWP  case increases to
less than 7% in 2050 and to 8% in 2100 and
in the RCWP case to 10% in 2050 and 18% in
2100.    It  is  possible that  the  nuclear
contribution could be substantially  greater, if
concerns about safety, nuclear  proliferation,
and waste disposal could be adequately dealt
with and if costs could be reduced by moving
toward the manufacture  of standardized

Policy Options for Stabilizing Global Climate
                                 FIGURE 10

    ! 2000  2026  200   2076   2100    1986 2000  2026  2060  2076  2100
                  Yr                               YMT
  Not*: FuN cl ! douM^ for MM RCWA ea.

                                                                       Executive Summary
powerplants and away from the construction of
one-of-a-kind facilities.

Solar Technologies

      There is  a range of solar technologies
currently available or under development that
could increase the use of solar energy.  Direct
use of solar thermal energy, either passively or
in active systems, is already commercial for
many water- and space-heating applications.
In some locations wind energy systems are also
currently commercial  for some applications.
In  recent years engineering advances have
resulted  in  significant cost reductions  and
performance   improvements.      Solar
photovoltaic   (PV)   cells   are   currently
competitive for many remote power generation
needs, especially  in  developing countries.
Dramatic progress has been made recently in
reducing the costs of producing PV systems,
particularly with thin-film amorphous  silicon
technology.     If  current  research  and
manufacturing development efforts reach their
objectives,  PV  could play a major role in
meeting energy needs in the next century.  The
degree to which these objectives, particularly
cost reduction,  could be achieved by specific
times and the size of the future contribution
are, of course, uncertain.   In  the  SCWP
scenario  solar   sources  of  electricity   are
equivalent to 6% of  primary energy  supply
from 2050 onward.  A larger contribution is
envisioned in the RCWP scenario:  10% in
2050, increasing to over 13% in 2100.

Hydro and Geothermal Energy

      Other  renewable resources can  also
increase  their contribution  to  total  energy
supplies.   Hydroelectric  power  is  already
contributing the equivalent of about  7% of
global  primary  energy  production,  and
geothermal power is making a small (less  than
1%) but important contribution.  There is
potential to expand the contribution of these
sources, although good hydro and geothermal
sites are limited and environmental and social
impacts  of  large-scale  projects  must  be
considered  carefully.'  Significant questions
concerning  the  economics  of  remaining
available sites,  and  the  likely environmental
constraints on  these sites, have not been
analyzed  in   detail.     Hydroelectric  and
geothermal power expands to nearly 13% of
global primary energy production in the SCWP
scenario, but increases only to about 9% in the
RCWP   case   (this   relatively   smaller
contribution  is due to  the  higher  level  of
energy production; i.e., the absolute amount is
higher, but the percentage is lower).

Commercialized Biomass

      Biomass is currently being extensively
utilized, accounting for roughly 10% of global
energy consumption, primarily in  traditional
applications (e.g.,  cooking), which  are  not
included  in  most  official  accounts   of
commercial energy use. Current and emerging
technologies   could   vastly   improve   the
efficiency of biomass use. In the near term
there is substantial potential  for  obtaining
more useful  energy  from  municipal and
agricultural    wastes.     More    advanced
technologies  for producing, collecting, and
converting biomass to gaseous and liquid fuels
and  electricity could  become economically
competitive within a decade.  The prospects
for  integrating  biomass  gasification  with
advanced combustion turbines  is  particularly
promising.  While the technical potential for
commercialized biomass is highly  promising,
important questions remain  about the scale
and  degree  of the economic potential.   In
particular, the availability of productive land
that could be devoted to growing biomass fuels
needs   further  study.      Furthermore,
environmental and societal impacts related to
large-scale biomass use, which would have to
be addressed, include competition with food
production, ecological impacts, and emissions
of volatile organic compounds.  In the SCWP
scenario biomass energy supplies  32%  of
primary energy needs in 2050 and 48% in
2100. Biomass supplies about 32% of primary
energy by 2050 and 32% by 2100 in the RCWP

Reduce Emissions from Fossil

      Inherent to the burning of fossil fuels is
the  generation of large amounts of CO2.
Although  it is technically possible  to scrub
CO2 out of central station powerplants, it is
estimated  that  this  would probably at least
double the cost of power generation, and an

 Policy Options for Stabilizing Global Climate
environmentally acceptable method of disposal
has not been demonstrated.  All fossil fuels
are not created equally, however.  Burning
coal produces about twice as much CO2 per
unit of energy released as does natural gas; the
amount of CO2 produced by oil is about 80%
of   the   amount   produced   by   coal.
Furthermore, oil and gas have the potential to
be used much  more efficiently than coal in
power generation, substantially increasing their
CO2 advantage. Thus fuel switching among
fossil  fuels  can significantly  reduce  CO2
emissions. Similarly, non-CO2 emissions from
fossil-fuel burning can be controlled, resulting
in significant  impacts  on  greenhouse gas
concentrations.  Also, when new fossil-fuel
facilities need to be built,  emissions can be
minimized by  installing the most efficient
technologies, such as the use of Integrated
Gasification/Combined Cycle (IGCC) systems
for new coal-fired generation requirements.

      The  potential  timing  and  market
penetration  of more efficient fossil-fuel-fired
technologies are uncertain, particularly in the
developing  countries,  where  most  of the
growth in emissions is  likely to take place.
The potential impact of these technologies is
significant, but their cost effectiveness is very

Greater  Use of Natural Gas

      Because of its inherent CO2 advantage
over other fossil fuels, increased use of natural
gas could significantly reduce total emissions.
Two important considerations should be kept
in mind, however. First, natural gas is a finite
resource.  Increased use of natural gas during
the next  few  decades  could   provide  an
essential bridge as non-fossil energy sources
are further developed, but unless a transition
toward reduced dependence on fossil fuels is
accomplished, reduced availability of natural
gas in later periods could offset the gains from
using  gas in earlier periods.  Second, natural
gas is  primarily methane, which is itself a
powerful greenhouse  gas.   If a substantial
amount of methane reaches the atmosphere
through leaky  transmission or  distribution
pipes, the advantage of natural gas can  be
significantly  reduced or offset.
Emission Controls

      Emissions of CO contribute to elevating
methane concentrations, and NOX emissions
contribute to tropospheric ozone formation,
both of which are important greenhouse gases.
Thus,  more  stringent  and  comprehensive
controls on CO and NOX, such as three-way
catalysts on automobiles and low-NOx burners
on boilers and kilns, would reduce greenhouse
gas concentrations as well.

Reduce Emissions from Non-
Energy Sources

CFC Phaseout

      Halocarbons (which include CFCs and
halons)  are   potent  stratospheric ozone
depleters  as  well  as  greenhouse  gases.
Concern  over their role as  a threat to the
ozone layer led in September 1987 to  "The
Montreal   Protocol   on  Substances  That
Deplete the Ozone Layer" (or the Montreal
Protocol). The Montreal Protocol came into
force on January 1,1989, and has been ratified
by 68 countries, representing just over 90% of
current world consumption of these chemicals
(as of February  1,  1991).   The London
Amendments  to the Protocol, which call for
the  phaseout  of  CFCs,   halons,  carbon
tetrachloride,  and methyl  chloroform,  and
encourages limits  of HCFCs, were adopted in
June 1990.  These amendments were adopted
after this analysis  was completed.

      Further  reductions   in  CFCs  are
needed to slow the buildup of atmospheric
concentrations. The major provisions of the
Montreal Protocol include a 50%  reduction
from  1986  levels  in the use of  CFC-11, -12,
-113,  -114, and -115 by 1998; a freeze on the
use of Halon 1211, 1301, and 2402 at  1986
levels starting in  approximately 1992; and a
delay of up to 10 years in compliance with the
Protocol  for  developing countries  with low
levels of use per  capita.  As a result of this
historic agreement, the very high growth rates
in  CFC  concentrations  assumed  in some
previous  studies   are unlikely  to occur.
However, because of the long atmospheric

                                                                        Executive Summary
lifetimes of CFCs, the probability that not all
countries will participate in the agreement,
and   the  provision for  increased  use  in
developing countries, CFC concentrations will
still rise significantly in the future unless the
Protocol is strengthened (see Figure 4).  An
international meeting to discuss strengthening
of the  Protocol  was  held in June  1990 in
London, England.  The Amendments to the
Protocol adopted in London were similar to,
but not as stringent as, the phaseout assumed
in this analysis.

      Promising   chemical    substitutes,
engineering  controls,  and  process  modifi-
cations that  could eliminate most  uses of
CFCs have now been identified.  In the policy
scenarios we assume that the use of CFCs and
halons  is phased out and that emissions of
methyl  chloroform  are frozen (no additional
growth  in  CFC substitutes  is assumed  as a
result  of the  phaseout beyond  the levels
assumed under the Protocol).   Even under
these assumptions total weighted halocarbon
concentrations increase significantly from 1985
levels, in part because the chemical substitutes
contribute significantly to greenhouse forcing,
although the final  concentrations are about
one-third of the level in the corresponding No
Response scenarios. The greenhouse forcing
potential of CFC substitutes will have to be
carefully evaluated to  improve  estimates of
their potential role in climate change. In our
analysis, phasing out CFCs was responsible for
9% of the decrease in wanning  in the RCWP
in 2050 relative to the RCW.


      Deforestation and biomass burning are
significant sources of CO2, CO, CH4, NO,p and
N2O. The world's total forest and woodland
acreage has been  reduced by about 15% since
1850, primarily to accommodate the expansion
of cultivated  lands. It is generally estimated
that approximately 11 million hectares (Mha)
of tropical forests are currently lost each year,
while only 1.1 Mha are reforested per year.
Generally, temperate and boreal forests appear
to be  in  equilibrium.   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
approximately   10-30%   of  annual
anthropogenic   CO2   emissions   to   the

      Reversing deforestation offers one of
the  most attractive policy  responses to
potential climate change.   Although a vast
area of land would  have to be involved to
make a significant contribution to reducing net
CO2 emissions, preliminary estimates suggest
that the cost of absorbed or conserved carbon
could be low in comparison to other options,
at least initially.  How rapidly reforestation
costs would increase as lands with increasingly
high  productivity   in   other  uses  were
transferred  to  forest   use  is  not  well
understood. The areas of land that would be
feasible and economic to transfer to forest use
are also not well  defined.  Furthermore, a
reforestation strategy could offer a stream of
valuable ecological and  economic benefits in
addition to reducing CO2 concentrations, such
as production of forest products, maintenance
of biodiversity, watershed protection, nonpoint
pollution reduction, and recreation. Devising
successful forestry programs presents unique
challenges to  scientists  and  policymakers
because  of  the  vast  and  heterogeneous
landscape, uncertain ownership, lack  of data,
and the need for more research and field trials.
Investments  that  would  be  small  by  the
standards of the energy industry, however,
could make an enormous impact on forestry.

      In the Stabilizing Policy scenarios it is
assumed  that  by  2000  the  biosphere  is
transformed from a source to  a sink  for
carbon. A combination  of policies succeed in
stopping deforestation by 2025, while up to
one billion hectares of  land is reforested by
2100 (some of this land is devoted to biomass
energy plantations as discussed above). This
assumed area of reforestation could exceed the
area of the United States.   Whether or  not
this much land could be made available on a
global basis for reforestation, given the needs
for  uses  for subsistence  and commercial
agriculture,  has  not   been   determined.
Reforestation accounts for almost  one-fifth of
the decrease in wanning by 2050 in the RCWP
versus the RCW scenarios.

Agriculture, Landfills, and Cement

      Domestic animals, rice cultivation, and
use of nitrogenous fertilizers  are significant

 Policy Options for Stabilizing Global Climate
 sources  of  greenhouse gases.   Methane  is
 produced  as  a  by-product  of  digestive
 processes in herbivores, particularly ruminants
 (e.g., cattle,  dairy cows, sheep, buffalo, and
 goats).      Globally,  domestic   animals
 (predominantly  cattle) are  responsible for
 about  15% of total methane emissions.  The
 gas  is also  produced by anaerobic decom-
 position in flooded rice fields and escapes to
 the  atmosphere largely by transport through
 the rice plants. The amount of CH4 released
 to the atmosphere is a complex function of
 rice  species, number and duration of harvests,
 temperature, irrigation practices, crop residue
 management, and fertilizer use. Rice fields are
 estimated to contribute approximately 10-30%
 of the  global emissions.    Nitrous  oxide  is
 released through  microbial processes in soils,
 both through denitrification and nitrification.
 The  use  of  nitrogenous  fertilizer  enhances
 N2O emissions since some of the applied N is
 converted  to  N2O  and  released  to  the
 atmosphere.   The amount  of N2O  released
 varies  a  great deal  depending on  rainfall,
 temperature, the  type  of fertilizer  applied,
 mode of application,  and  soil conditions. A
 preliminary estimate suggests that this source
 produces  1-20% of global N2O emissions.

      Future research and technological
 changes could reduce agricultural emissions,
 In the  policy scenarios we  do not assume
 changes   in  the  demand  for  agricultural
 commodities, but rather changes in production
 systems  that could  reduce   greenhouse gas
 emissions per unit of product. Although the
 impact  of specific  approaches  cannot  be
 quantified at  present, a number of techniques,
 such as feed additives for cattle, changes in
water management in rice  production,  and
 fertilizer coatings, have been identified for
 reducing methane and nitrous oxide emissions
 from agricultural sources. The extent to which
 these options are implemented depends on
 further  research  and demonstrations.    For
 simplicity we have  assumed that  methane
emissions per unit of rice,  meat, and milk
production   decrease  by  0.5% per   year
 (emissions  from   animals   not  used  in
 commercial   meat or  milk   production  are
assumed to be constant). Emissions of nitrous
oxide per unit of nitrogen fertilizer applied are
also assumed to decrease by 0.5% per year for
each fertilizer type.  In addition, we assume
that after 2000 there is a shift away from those
types of fertilizers with the highest emissions.
Under   these  assumptions  agricultural
emissions are substantially  lowered in the
policy scenarios relative to the No Response
scenarios, although absolute emissions do not

      Landfills   represent   a   potentially
controllable  source  of  methane.    Waste
disposal in landfills and open dumps generates
methane when decomposition of the organic
material becomes  anaerobic;  approximately
80% of  urban solid wastes  is  currently
disposed in one of these ways.  Most of the
decomposition in landfills and some of the
decomposition  in  open  pits  is  anaerobic.
Annual methane emissions from landfills and
open pits represent about  10%  of total
methane emissions.

      Landfilling can be expected to increase
dramatically  in  developing  countries  as
population   growth,   urbanization,   and
economic growth all  imply increased disposal
of municipal solid waste. The result is a three
and  fivefold  increase in  methane  emissions
from landfills in the SCW and RCW scenarios,
respectively.  The Stabilizing Policy scenarios
assume  that  gas recovery systems, recycling,
and  waste reduction policies will be adopted,
resulting in roughly constant global emissions
from landfills.

      Carbon dioxide is  emitted  in  the
calcining phase of the cement-making process
when calcium carbonate (CaCO3) is converted
to lime  (CaO).   For  every ton  of cement
produced 0.14 tons of carbon are  emitted as
CO2 from this reaction.   World  cement
production increased from 130 million tons in
1950 to about one billion tons  currently.
Thus, current CO2 emissions from calcining
are 0.14 billion tons of carbon (0.14 Pg C), or
more than 2% of total CO2 emissions. In the
Stabilizing Policy scenarios, advanced materials
are assumed to reduce the demand for cement
relative  to the  No Response scenarios, but
emissions still grow significantly.

      Reduced  emissions from agriculture,
landfills, and cement manufacture account for
12% of the reduced warming in the RCWP in
2050 relative to the RCW scenario.

                                                                        Executive Summary

      The prospect of global climate change
presents policymakers with a unique challenge.
The scale of the problem is unprecedented in
both  space  and  time.    Many  choices  are
available and  the consequences of  these
choices will be profound.

      A  wide range of policy  choices is
available for  reducing  greenhouse   gas
emissions.  There is an important distinction
between  short-term  and  long-term  policy
options.  In the short term, the most effective
means of  reducing  emissions   is through
strategies that rely on pricing and regulation.
There is a  wide  range of potential policy
choices that  may make  sense  despite  the
scientific and economic uncertainties.  In the
long term, policies to increase research  and
development of new technologies, to enhance
markets  through information programs  and
other means,  and  other actions making it
possible  to  achieve  world-wide  economic
growth while limiting emissions growth will be
essential  for long-term effects on the climate
change problem.

     The  most  direct  means  of allowing
markets  to  incorporate  the  risk of climate
change is to ensure that the prices of fossil
fuels  and other sources of greenhouse gases
reflect their full  social costs.   It may be
necessary to impose emission fees on these
sources according to their relative contribution
to global wanning in order to accomplish this
goal.  Unfortunately, the costs and benefits of
global wanning are  not  fully known,  and,
therefore, the  fees that would correspond to
charging  full  social costs can not now be
determined.    Better  information would be
needed as a basis for establishing levels of fees.
Fees  would also raise  revenues that  could
finance other  programs or offset other taxes.
The degree  to which such fees are accepted
will vary among  countries, but  acceptability
would be enhanced  if fees  were equitably
structured.  The impact of fees on the global
economy would depend on the size of the fees,
how  they were  phased  in,  and how  the
revenues were used, among other factors.  The
effectiveness of  fees in reducing world-wide
greenhouse gas emissions would depend on the
degree to which they are applied consistently
throughout  the world and  therefore avoid
encouraging emissions-intensive activities to
relocate to low fee areas. These issues require
additional analysis.

     Regulatory   programs  would  be  a
necessary complement if  pricing  strategies
were not effective or had undesirable impacts.
In the U.S., greenhouse gas emissions are
influenced  by  existing  federal  regulatory
programs to control  air pollution, increase
energy efficiency,  and recycle  solid  waste.
Reducing greenhouse gas emissions could be
incorporated into the goals of these programs.
New programs could focus directly on reducing
greenhouse  gas   emissions    through
requirements such as emissions offsets (e.g.,
tree  planting), performance  standards, or
marketable  permits.    Different  kinds of
regulatory  approaches would have different
degrees of efficiency and costs, differences in
treating greenhouse gases in a comprehensive
fashion, and differences in  how they permit
those  regulated   to  make   cost-optimal
decisions.   A full understanding  of  these
differences  and of the inherent advantages of
using  automatic   market  mechanisms  to
encourage environmentally sound behavior is
needed, particularly with respect to regulatory
approaches   in    countries   with   limited
experience  in market-oriented environmental
regulation.  Regulatory approaches, like other
policies, would also have to deal with the need
to  avoid  encouraging  emissions-intensive
activities to relocate to areas of less stringent

     State and local government policies in
such areas as utility regulation, building codes,
waste management, transportation planning,
and urban  forestry could make an  important
contribution  to  reducing  greenhouse gas

     Voluntary private efforts  to reduce
greenhouse gas   emissions  have  already
provided significant   precedents  for wider
action  and could  play a larger role in the

     Over the long  term, other policies will
be  needed  to reduce emissions  and can
complement pricing and regulatory strategies.

 Policy Options for Stabilizing Global Climate
 Other  policy  options  include  redirecting
 research and development priorities in favor of
 technologies that could reduce greenhouse gas
 emissions, implementing information programs
 to  enhance awareness of the problems and
 solutions,   and  making  selective  use  of
 government procurement to promote markets
 for technological alternatives.

     The United  States is implementing a
 number of actions (described above) that can
 be justified because they produce benefits that
 are not subject to the uncertainties associated
 with climate change.  Further study will most
 likely identify additional actions that fall into
 that category.    At some  point  it  may be
 desirable to consider actions that can not be
 justified  by their non-climate  benefits, but
 must depend for justification on the benefits
 from reducing  the degree of climate change.
 It will be important, at that time, to have a
 full understanding of the economic, social, and
 other implications  of such actions so  that
 decisions despite the uncertainties will be
 based on the best information that can be
 developed.  Some of the types of action that
 will need to be considered and some of the
 questions that  will  need  to be addressed are
 discussed throughout this report.

     A number of other countries have made
 public commitments to take actions to reduce
 their greenhouse gas emissions by similar or
 greater proportions.  While  such actions will
 somewhat delay the increasing concentrations
 of greenhouse gases, the problem of achieving
 economic growth and improved well-being in
 the  developing  world while  avoiding  or
 limiting  the emissions increases  from  such
 growth remains a key, unsolved problem.

      Several  studies have  been conducted
 that identify the wide range of policy choices
 that are available for reducing emissions.  For
 example, see A Compendium of Options for
 Government Policy to Encourage Private Sector
Responses to Potential Climate Change (U.S.
 DOE,  1989), the National  Energy Strategy
 (NES) which is currently under development
 by the U.S. DOE and other agencies within
 the Federal  government, and Box 3  (which is
 an illustrative analysis based on preliminary
 estimates of the impacts  of  the  policies
discussed in Box 3).
The Timing of Policy Responses

       The costs and benefits of actions taken
to  reduce  greenhouse  gas  emissions  are
difficult  to evaluate because  of the many
uncertainties associated with  estimates of the
magnitude, timing, and consequences of global
climate change, as well as the difficulty of
assessing the net social costs of strategies that
involve widespread  and long-term shifts in
technological  development.     Given   this
situation it may  be prudent  to  delay some
costly actions to  reduce  greenhouse  gas
concentrations until  the magnitude  of the
problem and the costs of responses are better
established.  The potential benefits of delay,
however,  must   be  balanced  against  the
potential increased risks.

      The models indicate that delaying the
policy  response   to the  greenhouse  gas
buildup  would substantially increase  the
global commitment to future warming.  For
this reason, the U.S. is  taking a number of
policy actions (described  earlier)  that  will
produce  a  substantial  response  to  the
greenhouse  gas buildup, particularly  actions
that can be justified for reasons not subject to
the scientific and economic uncertainties about
climate change. Analytical efforts to date have
not been able to determine  the appropriate
level of trade-off between accepting additional
costs associated with additional climate change
and incurring additional costs to avoid  that
additional climate change.   The Stabilizing
Policy cases and  the Rapid  Reduction case
both assume that immediate action is taken to
begin reducing the  rate of  greenhouse gas
buildup. The impact of delay was investigated
by assuming that industrialized countries do
not respond until 2010 and  that developing
countries wait until 2025.   Once  action is
initiated,  policies   are  assumed   to  be
implemented at roughly the same rates as in
the Stabilizing Policy cases. The result would
be a significant increase in global wanning (see
Figure  11):    the  equilibrium  warming
commitment in 2050 would increase by about
40-50% relative to the scenarios that assume
policy implementation beginning in 1990.  It is
clear that many nations are already taking or
publicly committed to taking  actions that are
not reflected in this scenario.  For example,
the U.S. has committed to a number of policy

                                                                   Executive Summary
      Box 3.  Illustrative Analysis of Current U.S. Policy Initiatives

     Several policy initiatives are currently under discussion or have been approved that could
reduce the U.S. contribution to greenhouse gas emissions. These initiatives cover a wide range
of activities that emit different types of greenhouse gases. Several examples of these initiatives
include: (1) a recently-proposed reforestation program to plant one billion trees per year that
would sequester carbon as  the trees matured; (2) a total pbaseout of the  major  CFCs and
related chemicals that deplete the stratospheric ozone layer; (3) new landfill regulations that
would restrict the amount of CH4 emissions  from decomposing wastes; and (4)  several
initiatives  that  would  reduce  the amount of energy consumed  and thereby reduce CO2
emissions, including revisions  to the Clean Air Act to control acid rain  and develop less
polluting transportation fuels and proposals by the U.S. DOE to adopt more efficient appliance
standards, improve lighting in Federal and commercial buildings, promote state least-cost utility
planning, obtain U.S. HUD adoption of U.S. DOE building standards, and expand use of
hydroelectric power and the transfer of photovoltaic technology.

     These specific  policy  initiatives are used here as examples of the types of emission
reduction policies that can  be justified for reasons other than climate change- The options
included are those for which  estimates of emissions were readily available.  Many other
potential options exist which have not been systematically evaluated. As an  illustration of the
potential for reducing emissions, however, we have combined the emission reductions from all
of the initiatives mentioned  above into a single estimate using the concept of Global Warming
Potentials (GWP) discussed in Box 1 and the Addendum to Chapter II to convert the emission
reductions estimated from each initiative to a CO2-equivalent basis (expressed as carbon). The
impact of these proposed initiatives on estimated U.S. greenhouse gas emissions is summarized
in the figure below, which indicates that this illustrative package of proposed initiatives could
reduce total U.S. greenhouse gas emissions about 13% below projected levels for the year 2000
to a level about 7% lower than estimated 1987 emissions on a CO2-equivalent basis.  If only
CO2 emissions are considered, however, the percentage reduction is substantially less - about
4% below projected 2000 emissions. Estimated redactions when only CO2 is considered are
much lower than reductions that consider all gases on a CO2-equivalent basis because the
largest source of emission reductions --  CFCs as a result of the London Amendments to the
Montreal Protocol and 1990 Clean Air Act Amendments -- is not included. For a complete
discussion of these results, see the Addendum to Chapter VII.

      ~ 2.5
0  1 n
5 xi **


                            (Carbon-Equivalent Basis)


                                                                   K3 co,
               1987 Baseline  2000 Baseline 2000 with Policy
                  Emissions      Emissions   Options Package

Policy Options for Stabilizing Global Climate
                                   FIGURE 11



                         (Based on 3.0 Degree Sensitivity)
         Slowly Changing World
        Rapidly Changing World
   s  -
  188  2000   2026    2060   2076    2100
                                                    RCWP with
                                                   Global Delay
1M6  2000   202*   2060   2076   2100
Figure 11. Assumes that industrialized countries delay action until 2010 and that developing countries
delay action until 2025. Once action is initiated, policies are assumed to be implemented at roughly
the same rate as in the Stabilizing Policy cases.

                                                                        Executive Summary
measures  that  will   mitigate  emissions.
Although this delay scenario clearly does not
correspond to currently planned actions, the
basic point illustrated is still valid.

      Policy   development   and  imple-
mentation  can   be  a  lengthy  process,
particularly at the international level  Any
decision  to  respond to the greenhouse gas
buildup cannot be fully translated immediately
into action.   Roughly a decade was required
for  the  process  that led to  international
agreement to  reduce emissions of  CFCs,
embodied in the Montreal Protocol, and it will
take another decade to implement the agreed-
upon reductions. Agreements to reduce other
greenhouse  gas emissions could take much
longer to achieve and implement.

      The development of technologies  to
reduce greenhouse gas emissions will  take
many years.  The majority of emissions are
associated with activities that are fundamental
to the global economy (transportation, heating
and cooling of buildings, industrial production,
land clearing, etc.); thus, reducing emissions by
curtailing these activities would  be highly
disruptive and undesirable.  While this report
has  identified  a  large  menu of  promising
technologies  that  can meet  our needs for
goods  and  services  while  generating much
lower emissions of greenhouse gases, many
require additional  research and development
to  become economically competitive.   The
time required to bring innovative technologies
to market is unpredictable, but the process
usually  takes  many  years.    And  once  a
technology is cost-effective, it may take years
before it achieves  a large market share and
decades more for the existing capital stock to
be replaced.  Depending on the sector, it may
take 20-50 years or more to substantially  alter
the technological base of industrial  societies,
and the cost of reducing emissions  could rise
dramatically as the time allowed for achieving
these reductions is decreased. While the rate
of change in rapidly developing countries can
be   higher   and   may  be   influenced   by
government   policies,  once   industrial
infrastructure is built, it will be many years
before it  is replaced.
The  Need  for   an  International

      If limiting U.S. and global emissions
of greenhouse gases is desired, government
action will be necessary.   Throughout  the
world, market  prices of energy from  fossil
fuels, products  made with  CFCs, forest and
agricultural products, and other commodities
responsible for greenhouse gas emissions do
not reflect the risks of climate change.  As a
result, increases in population and economic
activity will cause  emissions to grow in  the
absence of countervailing government policies.

      The risk of substantial warming is
unavoidable if developing countries do not
participate   in    stabilizing   strategies.
Increasing the availability of energy services is
a  high  priority  for developing  countries
attempting' to  meet basic human  needs.
Increased energy use in developing countries
could lead to dramatic increases in greenhouse
gas emissions unless stabilizing policies  are
adopted.   The share  of  greenhouse  gas
emissions arising from developing countries
(weighted by their estimated impact on global
wanning) increases from about 40% currently
to 50% by 2025 and almost 60% by 2100 in
the RCW scenario; the developing countries'
contribution to greenhouse gas emissions also
rises to about 50% in the  SCW (see Figure
12). We examined the implications for global
warming if industrialized countries adopted
climate  stabilizing   policies  without   the
participation   of   developing  countries.
Assuming  that   policies  adopted   in
industrialized countries have some impact even
in developing countries that do not participate
in an international  agreement, equilibrium
warming commitment in 2050 is about 40%
higher than in the Stabilizing Policy cases (see
Figure  13).   This  implies  that action by
industrialized  countries  on  their own can
significantly slow the rate and magnitude of
climate  change,   but   that  without   the
participation of the developing countries, the
risk  of  substantial  global  wanning  is
unavoidable.   Even  if developing countries
participate, the degree to  which it will be
possible, at any point  in time, to avoid

Policy Options for Stabilizing Global Climate
                                 FIGURE 12
                                       80 -
                                                                     CP A*l
                                                                    CP Europe
                                                                    United State*
                                                                    United SUte
     0 MWifmiHiit un iitiiiiiiiii.i^^BaKMHiifiiwa       0
     19852000  2025  2050  2075   2100     19852000  2028   2050  2075  2100
                   Year                                Year

    See Appendix B for further discussion of these scenarios.

                                                              Executive Summary
                                  FIGURE 13
                        (Based on 3.0 Degree Sensitivity)
           Slowly Changing World
                                      Rapidly Changing World
 o  3
 by Developing
  RCWP with
No Participation
 by Dovotopbig
   IMS  2000
   2026   2060
                                          1M0  2000
                                                      2026   2060
Figure 13.  Assumes that industrialized countries follow the Stabilizing Policies scenarios while
developing countries follow the No Response scenarios, except that there is some transfer of low-
emissions technology to developing countries despite their failure to adopt stabilizing policies.

 Policy Options for Stabilizing Global Climate
 emissions increases in developing countries
 that would  otherwise  accompany  economic
 growth is unknown.

      Although most  of the  costs  and
 benefits  of responding to climate change
 cannot  be  quantified at  this time,  some
potential actions would have other benefits.
 Benefits   could   include   reductions   in
 conventional  pollutants,  increased  energy
 security,  and  reductions in the balance of
 payments deficit, as well as reduced risk of
 warming.   Similarly, reversing deforestation
 has  a wide  range  of  benefits,  including
 maintenance of biological diversity, reduction
 in soil erosion  and  reservoir  siltation,  and
 local climatic amelioration.  The phaseout of
 production   of   CFCs,   halons,   carbon
 tetrachloride, and  methyl chloroform  under
 the Montreal Protocol will be most significant
 in reducing the risk of stratospheric ozone
 depletion and will also make  an important
 contribution to reducing the risk of climate
 change.  The U.S. is taking, or is committed to
 taking, a number of other actions  that have
benefits other than those related  to climate
change.   In total, these U.S. actions  are
estimated to have significant effects on U.S.
emissions of greenhouse gases. Some of the
options   discussed  here, such  as  reduced
agricultural  emissions,   improved  biomass
production,  and heavy  reliance  on  photo-
voltaics, would require further research  and
development to  ensure their  availability.
Relatively small investments in such research
could yield important payoffs.

1.     Estimates  of  equilibrium  wanning
commitments  greater  than  6C 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.    These  estimates  are
represented by >6C.

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

Hansen, J.,  I. Fung, A  Lacis, D. Rind, S.
Lebedeff, R. Ruedy, and  G. Russell. 1988.
Global climate changes as forecast by Goddard
Institute of Space Studies Three-Dimensional
Model.    Journal  of Geophysical Research

Hansen, J., A. Lacis, D. Rind,  G. Russell, P.
Stone, I. Fung, R. Ruedy, and J. Lerner. 1984.
Analysis of feedback mechanisms.  In Hansen,
J., and  T. Takahashi, eds. Climate Processes
and   Climate   Sensitivity.     Geophysical
Monograph  29,  Maurice Ewing Volume 5.
American Geophysical Union, Washington,
D.C. 130-163.

IPCC (Intergovernmental  Panel  on  Climate
Change).   1990.   Scientific Assessment of
Climate Change.  Draft Report of Working
Group I. April 30.

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.  March  19-23, 1982, Berkeley
Springs, West Virginia.  DOE CONF-820970,
U.S. DOE, Washington, D.C. II.3-II.62.

Komhyr, W.D., R.H. Gammon, T.B. Harris,
L.S. Waterman, T.J. 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%.

Lashof,  D.  1989.  The dynamic greenhouse:
feedback processes that may influence future
concentrations of atmospheric trace gases and
climate change. Climatic Change 14:213-242.

                                                                       Executive Summary
NOAA  (National   Oceanographic  and
Atmospheric   Administration).    1987.
Geophysical  Monitoring for Climatic Change
No. 15, Summary Report 1986.  Schnell, R.C.,
ed. U.S.  Department of Commerce, NOAA
Environmental   Research    Laboratories,
Boulder.  155 pp.

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.

Rotty, R.M. 1987.   A look at 1983 CO2
emissions from fossil fuels (with preliminary
data for 1984).  Tellus 393:203-208.
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. The
Potential Effects of Global Climate Change on
the  United  States.  U.S.   Environmental
Protection Agency, Washington,  D.C.

U.S. DOE (U.S. Department of Energy). 1989.
A  Compendium of Options for Governmental
Policy to Encourage Private Sector Responses to
Potential  Climate   Change,  Report  to  the
Congress of the  United States. U.S. DOE/EH-
0102, Washington, D.C.

                                     CHAPTER I

      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
30C colder.

      Concerns about the greenhouse effect
arise because  anthropogenic emissions of
greenhouse  gases  may further warm  the
Earth.1  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).
However, considerable uncertainty exists with
regard to the  ultimate  magnitude  of  the
wanning, its  timing, and the regional patterns
of  change.    In addition,  there  is great
uncertainty about changes in climate variability
and regional impacts.  Nonetheless,  there is a
growing political  consensus  that greenhouse
gas emissions must be reduced.  As stated by
the   major   industrial nations (the "G-7"
countries) at the  Paris summit in July 1989:
"We strongly advocate common efforts to limit
emissions of  carbon   dioxide  and  other
greenhouse  gases which threaten to induce
climate change, endangering  the environment
and  ultimately  the  economy."  (Economic
Declaration from Summit of the Arch, July 16,
1989, Paris, France).


     The   United  States  Environmental
Protection Agency (U.S. 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 U.S. EPA to
develop  two  reports on global wanning.
Congress directed U.S. EPA to include in one
of these studies:

     An examination of policy options
     that if implemented would stabilize
     current  levels   of  atmospheric
     greenhouse  gas  concentrations.
     This study should address the need
     for and implications of significant
     changes in energy policy, including
     energy efficiency and development
     of alternatives   to  fossil fuels;
     reductions  in the use of CFCs;
     ways to reduce other greenhouse
     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 Ait  series  (MacCracken and
Luther, 1985a, 198Sb; Strain and Cure, 1985;
Trabalka, 1985).

 Policy Options for Stabilizing Global Climate
       Congress  also  asked  U.S. EPA  10
 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,  forests, and
 water resources, as well as on other ecosystems
 and society.  In response to the latter request,
 U.S. EPA produced its report entitled, The
 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  U.S. 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
 affect  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).    We  do  not  attempt
 predictions with such a scope, but scenarios
 are useful to explore policy options.

      Based on these considerations U.S. EPA
 established four major goals:

      To  assemble data on global trends in
 emissions and concentrations  of all  major
 greenhouse  gases  and  activities  that affect
 these gases.

      To  develop  an  integrated analytical
 framework to study  how different assumptions
about  the  global economy and the climate
system could influence future greenhouse gas
concentrations and  global temperatures.
     To identify promising technologies and
 practices that  could  limit greenhouse  gas

     To identify  policy options that could
 influence future greenhouse gas concentrations
 and global warming.

      To achieve  these   goals  U.S. 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.  U.S. 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.  A draft of this report
 was  produced  in  February 1989  and was
 reviewed  by U.S. EPA's  Science  Advisory
 Board,  other federal agencies,  and a wide
variety of individuals and organizations from
 outside  the government. This final report has
 greatly benefitted from this review process, but
 U.S.  EPA  assumes  responsibility   for  the
 content of this document.

 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?
What technologies are available for limiting
greenhouse  gas  emissions?   How might
emissions and climate change in the future?
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

                                                                  Chapter I:  Introduction
                         CLIMATE CHANGE TERMINOLOGY
An attempt has been made throughout this report to avoid technical jargon, yet the use of
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* "farting," 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 the climate system. Examples
include:  changes in the output  of the son 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 flax 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 die 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 Ian4 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 equitibritm sensitivity)

The ultimate change in climate  that can be expected from a given radiative forcing.  Climate
sensitivity is generally measured las the change in global average surface air temperature when
equilibrium between incoming and outgoing radiation is re-established 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 from
pie-industrial levels. The National Academy of Sciences has estimated that this sensitivity is
in the range of 1-5-4.5'C, with  a recent analysts suggesting 1.5-5.5C; a reasonable central
uncertainty range is 2-4C

Policy Options for Stabilizing Global Climate
                           CLIMATE CHANGE TERMINOLOGY
   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 will be in a transient mode
   for the foreseeable future. Most general circulation models (see below), however, have so far
   examined equilibrium conditions because transient effects are much more difficult to analyze.


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


   Flow per  unit time per unit area.  The flow can be of energy /e.g., watts per square meter
   [W/m2]) or mass (e.g., grams per square meter per day [g ore**}).

   General Circulation Model (GCM)

   A computer model of the Earth's climate based on equations that describe, among other things,
   the  conservation of  energy,  momentum, and  mass,  and which explicitly calculates  the
   distribution of wind, temperature, precipitation and other climatic variables. Such models are
   applied to the atmosphere, to the oceans, or to both coupled together.

   Solar Luminosity, Solar Constant

   Solar luminosity is the total amount  of  energy emitted by the sun. The so-called  "solar
   constant" is the average amount of energy received at the top of the Earth's atmosphere at the
   mean Earth-sun distance; this amount varies with changes in solar luminosity.

   Troposphere, Tropopause, Stratosphere

   The troposphere is the lower atmosphere, from the ground to an altitude of about 8 kilometers
   (km) at the poles, 12 km in mid latitudes and 18 km in the tropics.  The tropopause marks the
   top of the troposphere; temperature decreases with altitude below the tropopause and increases
   with altitude above the tropopause to the lop of the stratosphere. The stratosphere extends
   from the tropopause to about 50 km.  The troposphere and stratosphere together contain more
   than 99.9% of the mass of the atmosphere.

                                                                    Chapter I:  Introduction
atmospheric concentrations and distributions,
and related uncertainties.  Chapter III relates
the greenhouse gases to the process of climate
change.  Once this link is made, Chapter IV
examines  those  human activities that affect
trace-gas  emissions and ultimately influence
climate change.  Chapter  V gives  a  detailed
description   of   existing  and   emerging
technologies that should be considered in the
formulation of a comprehensive strategy for
mitigating global  wanning.    Chapter  VI
discusses  the  scenarios developed  for this
report to  assist us  in thinking about  possible
future emissions and climate change, both with
current policies and  with  policies that could
decrease or increase  future greenhouse  gas
emissions.  Chapter  VII  outlines domestic
policy options, and  the concluding  chapter
(Chapter   VIII)   discusses   international
mechanisms for responding to climate change.
Three appendices provide additional detail on
the analysis for interested  readers.  Appendix
A describes the modelling  framework used to
develop the scenarios presented in Chapter VI.
Appendix B provides additional details on how
each  of  the  scenarios  was  implemented.
Appendix C  presents the results of many
sensitivity analyses that explore in detail how
alternative assumptions on  key parameters
could affect the rate and magnitude of global
climate change presented in Chapter VI.


      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 by volume (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.

Carbon Dioxide

      Carbon dioxide 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 351 ppm (see
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.2  Most  of this CO2 remains in
the atmosphere or is  absorbed by the ocean.
Even though  only  about half  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 (see Table 1-1;
Figure 1-2).
                TABLE 1-1

        Approximate Reductions in
         Anthropogenic Emissions
     Required to Stabilize Atmospheric
     Concentrations at Current Levels
Carbon Dioxide                50-80%
Methane                       10-20%
Nitrous Oxide                  80-85%
Chlorofluorocarbons            75-100%
Carbon Monoxide (CO)         Freeze
Nitrogen Oxide (NOX)           Freeze

      The concentration of methane 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).

    Policy Options for Stabilizing Global Climate
                                      FIGURE l-l

 (a) 2






(b)   c  e


          1958   1962   1966
                          1970    1974
1978   1982    1986  1989
    Figure 1-1. a) Monthly concentrations of atmospheric CO, at MaunaLoa Observatory, Hawaii. The
    yearly oscillation is explained mainly by the annual cycle or photosynthesis and respiration of plants
    in the northern hemisphere. (Sources: Keeling, 1983, personal communication; Komhyr et aL, 1985;
    NOAA, 1987; Conway et aL, 1988.) b) Annual emissions of CO2, in units of carbon, due to fossil-
    fuel combustion. (Sources: Rotty, 1987; Rotty, personal communication.)

         The steadily increasing concentration of atmospheric  CO, at Mauna Loa since the 1950s is
    caused primarily by the CO2 inputs from fossil-fuel combustion. 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.

                                                     Chapter I:  Introduction
                               FIGURE 1-2

      475  -
      450 -
   =  425  -

      400 -
      375  -
      350  -A
         1985  2000
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 of scenarios
and models. (Sources: Hansen et aL, 1984; Lashof, 1989; Siegenthaler, 1983).

 Policy Options for Stabilizing Global Climate
 Nitrous Oxide

      The concentration of nitrous oxide has
 increased by 5-10% since pre-industrial 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 were introduced
 into the atmosphere for the first time during
 this century.  The most common species are
 CFC-12 (CF2C12) and CFC-11 (CFC13), which
 had atmospheric concentrations in 1986 of 392
 and 226 parts per trillion  by volume (ppt),
 respectively.  While these concentrations are
 tiny compared  with  that of CO2, each
 additional CFC molecule  has  about  15,000
 times more impact on climate, and CFCs are
 increasing very rapidly -- about 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 20% 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.

Other Gases Influencing Composition

      Emissions of carbon monoxide (CO),
 nitrogen oxides (NOX), 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.


      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 focused principally on energy
 use and CO2 emissions (see, e.g., 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, e.g., 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.

 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 5C.  (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

                                                                    Chapter I:  Introduction
concentration of CO2  relative  to  the pre-
industrial atmosphere (NAS, 1979). The NAS
study  concluded that  the  planet's surface
would most likely be  1.5-4.5C wanner  under
such conditions. Subsequent re-evaluations by
NAS (1983, 1987) as well as the "State-of-the-
Art" report issued by  the U.S. Department of
Energy (U.S. DOE) (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
pre-industrial 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
5.5C. Dickinson's "best guess" was that the
actual equilibrium warming would be between
2.5 and  4.5C.

Studies of Future CO2 Emissions

      For   the   next  eighty   years  after
Arrhennius issued his  warning, little attention
was paid to the potential global  consequences
of fossil-fuel  combustion.  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 1-1), while the oil embargo of 1973 and
the nuclear power debate focused 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,  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 Qyrt

      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 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 U.S.
DOE by  varying other key parameters  in the
model (Edmonds and Reilly, 1984).  In these
new scenarios, CO, 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 (E-R) model to project
future energy use and CO2 emissions.  The
most  important  of  these  were  studies
conducted by the U.S. EPA (Seidel and Keyes,

 Policy Options for Stabilizing Global Climate
 1983) and  Rose et al. (1983).  The U.S. EPA
 study used the E-R 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 U.S.
 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 2C wanning is not very sensitive  to the
 effects of the energy policies they tested.

      Rose  and   his  colleagues  at  the
 Massachusetts Institute of Technology (MIT)
 also used the E-R 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 U.S. EPA study.  Rose et al. studied the
 effects of increased energy efficiency, increased
 fossil-fuel prices, higher nuclear energy supply
 costs,  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
 E-R  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 CO2/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
E-R model, the Nordhaus  and  Yohe (N-Y)
 model  used  a  generalized  Cobb-Douglas
 production function to estimate future energy
 demand.   In this approach global  GNP  is
 estimated us 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.

      The N-Y  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 in 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
 E-R  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

      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,

                                                                    Chapter I:  Introduction
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.
CO2 emissions  in this scenario follow a bell-
shaped trajectory, peaking at about  13.3 Pg
C/yr in 2050.

      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

      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 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  1.5C
over this period, with a little less than half 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 1C and possibly more than 5C by 2050,
when the full range of atmospheric feedback
processes was considered.

 Policy Options for Stabilizing Global Climate
       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 Warming
 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 pre-industrial
 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 pre-industrial  concentration of CO2 by
 about 2030. In Mintzer's Base Case, by 2075,
 the planet  is committed  to  an  eventual
warming of about 3-9C.  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-
 15C in 2075.  By contrast, in Mintzer's Slow
Buildup scenario, a wanning 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.
      More recently, Rotmans et al. (1988)
 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 warming.

 Major Uncertainties

      Major  uncertainties   underlie  many
 aspects  of our understanding of the climate
 change  problem, including both scientific and
 socioeconomic parameters.    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. Two
 of the largest uncertainties involve our limited
 understanding of the roles that clouds and the
 ocean 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 wanning effect of any further buildup in
the  atmospheric  concentration  of  CO2.

                                                                     Chapter I:  Introduction
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 1-2C) 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 wanning.

      The rate at which climate may change
must be of particular concern to policymakers.
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
time 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  5C;  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 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  in the
companion volume,  The Potential Effects of
Global Climate Change  on the United  States
(Smith and Tirpak,  1989).   The collective
findings of this study suggest that the climatic
changes associated with a global warming of
roughly 2-4C would result in

      a  world different from the world
      that exists today.  Global climate
      change  could  have  significant
      implications  for   natural
      ecosystems; for where and how we
      farm; for the availability of water
      to irrigate crops, produce power,
      and support shipping; for how we
      live in our cities; for the wetlands
      that  spawn  our  fish;  for   the
      beaches we use for recreation; and
      for all levels of government  and

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 in the context of risk
management or insurance-buying.

      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 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.

      Policymakers must determine how best
to minimize the costs of global wanning 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 (see CHAPTER IV).

      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 CO?  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

 Policy Options for Stabilizing Global Climate
 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 climate  change, so adaptation to
 some level of change  is essential. Adaptation
 strategies can be adopted unilaterally, and the
 costs will be  spread out into the future when
 countries may be better  able to afford them.
 Imposing climate change on our grandchildren,
 however, raises serious concerns  regarding
 intergenerational equity.   And  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.  At the
 same time, there are  policies that can reduce
 greenhouse gas emissions while promoting
 other environmental,  economic, and  social


      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 climate change.

Domestic 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 requires
 close  cooperation  between  U.S.  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
 U.S. 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.

      During  1989,  several  states  passed
 legislation  or   signed  executive   orders
 specifically addressing global warming.  The
 most common approach has been the creation
 of  procedures to  study  the  feasibility of
 reducing  greenhouse  gas  emissions  by  a
 specific amount by some target  date.   In
 Oregon, a bill passed in July requires a state
 strategy to reduce greenhouse  emissions 20%
 from  1988 levels by 2005.  In  Vermont, an
 executive  order  calls for  a similar  plan to
 reduce both greenhouse gas emissions and acid
 rain precursors by 15% below current  levels by
 the year 2000; additional restrictions on CFCs
 were adopted by the legislature.  A New York
 executive  order  accompanying release of  a
 state energy plan in September set a goal of
 reducing CO2 emissions 20% by  2008.   A
 study of how to achieve that goal will be
 conducted  jointly  by  the Energy Office,
 Department of Environmental Conservation,
 and  the  Public  Service  Commission  for
 presentation  to  the Governor by  April  30,
 1990.  A New Jersey executive order on global
warming requires state agencies to purchase
 the most energy efficient equipment available
 "where such equipment or techniques will
 result in lower costs over the  lifetime of the
equipment." In Missouri, the state legislature
created a commission to study the effects of
ozone depletion  and global wanning on  the
state and  to identify means of reducing  the

                                                                    Chapter I: Introduction
state's emissions;  findings  and recommen-
dations are due in late spring 1990.

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, is chaired
by  the  United  Kingdom;  the  second, to
assess  the  potential social and economic
effects from a warming, is  chaired by the
Soviet Union; and  the third, to examine
possible   response  strategies,   including
options for limiting emissions and adapting
to change,  is chaired by the United States.
An interim report by the IPCC summarizing
its key findings was reviewed at the Second
World Climate Conference in November

      The U.S. government has also taken a
more  active role in international discussions
on climate change.  At the Malta Summit in
December 1989, President Bush offered (1) to
convene an international meeting at the White
House in the spring of 1990 for  top level
scientific,   environmental,   and   economic
officials to  discuss  global  climate  change
issues, and (2) to  host a  conference  to
negotiate a framework treaty on global climate
      The   White  House  Conference  on
Science and Economics Research Related to
Global  Change was held  in  Washington in
April of 1990, stressing the need for enhanced
levels  of  cooperation with respect  to the
science and impacts of climate change and the
economic implications of possible response
strategies.    The  U.S.-hosted  international
meeting  to  begin  the negotiations  for  a
framework convention on climate change was
held  in the  Washington  area  in  February,

      International concern over the impacts
of climate change was also  reflected by the
major industrialized countries at the annual
Economic Summit held in Paris, France. The
G-7 countries not  only endorsed  efforts to
limit greenhouse gases,  but also stated that
"... a framework or umbrella convention on
climate change to set out general principles or
guidelines is urgently required to mobilize and
rationalize    the   efforts   made  by   the
international   community"   (Economic
Declaration,  Summit  of the  Arch, July  16,
1989).    The  call  for  an   international
framework convention on  climate has also
been endorsed by the  Ministerial Conference
on  Atmospheric  Pollution  and  Climatic
Change held in the Netherlands (November
1989), the   15th   session   of  the UNEP
Governing Council, and the XLI session of the
WMO Executive Council.

      The  Economic  Summit  of  the G-7
countries in Houston  in July  1990  reiterated
support for  the negotiation  of a framework
convention on climate change.  The Summit
also stated that the G-7 countries are ready to
begin  negotiations   on  a  global   forest
convention or agreement, which is needed to
curb   deforestation,   protect  biodiversity,
stimulate positive forestry actions, and address
threats to the world's forests.  While such a
convention is needed  for reasons other than
climate change, it would also have climate
change benefits.

      In addition, several countries  have held
or plan to hold international conferences on
global climate  change and  are  analyzing
domestic  policy  options.   These include
Canada, The Federal  Republic of  Germany,
the United  Kingdom,  Italy, Japan,  India,
Egypt, and the Netherlands.

 Policy Options for Stabilizing Global Climate
      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.

1.   Anthropogenic means  resulting  from
human  activities.   Thus, by  anthropogenic
emissions we mean those emissions caused by
man's activities, as opposed to those resulting
from natural causes.

2. One billion tons of carbon = 1015 grams of
carbon = 1 petagram of carbon (Pg C).

3. 1 terawatt = 1012 watts = 31.5xl018 joules
per year = 31.5 exajoules (EJ) per year = 29.9
Quadrillion British Thermal Units (Quads) per

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carbonic acid in the air upon the temperature
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Bolin, B., J. Jager, and B.R. Doos. 1986. The
greenhouse   effect,  climatic  change,  and
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Clark, W.C., K.H., Cook, G.,  Marland, AM.
Weinberg, R.M. Rotty, P.R., Bell, L.J. Allison,
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measurements   in   the  remote   global
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Dickinson, R. 1986.  The climate system and
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Greenhouse Effect,  Climatic  Change,  and
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Chichester. 207-270.

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

Economic  Declaration, Summit of the Arch,
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Edmonds, J.A., and J.M. Reilly. 1983a. A long-
term global energy-economic model of carbon
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Economics  5:74-88.

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

Edmonds,  J.A., and J.M. Reilly. 1984.  The
IEA/ORAU Long-Term  Global Energy CO2
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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,
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Goldemberg, J.,  T.B.  Johansson,  A.K.N.
Reddy, and R.H. Williams, 1985.  An end-use
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Goldemberg, J.,  T.B.  Johansson,  A.K.N.
Reddy, and R.H. Williams.  1987.  Energy for
a  Sustainable  World.   World  Resources
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Goldemberg,  J.,  T.B.  Johansson,  AK.N.
Reddy, and R.H. Williams.  1988.  Energy for
a Sustainable World.  Wiley Eastern Limited,
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Hansen, J., A. Lads, D. Rind, G. Russell, P.
Stone, I. Fung, R. Ruedy, and J. Lerner. 1984.
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J., and T. Takahashi, eds. Climate Processes
and   Climate   Sensitivity.      Geophysical
Monograph 29,  Maurice Ewing Volume 5.
American Geophysical Union,  Washington,
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IIASA (International Institute  for Applied
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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
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and  Consensus.    September 19-23, 1982,
Berkeley   Springs,  West  Virginia.   DOE
CONF-820970, U.S. DOE, Washington, D.C.

Keepin, W., I. Mintzer, and L. Kristoferson.
1986. Emission of CO2 into the atmosphere.
In Bolin, B., B.R. Doos, J. JSger,  and R.A.
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, T.J. Conway, W.R. Taylor, and
K.W. Thoning. 1985. Global atmospheric CO2
distribution  and variations from  1968-1982
NO AA/GMCC CO2 flask sample data. Journal
of Geophysical Research 90:5567-5596.

Lacis, A., J. Hansen, P. Lee, T. Mitchell,  and
S. Lebedeff. 1981. Greenhouse effect of trace
gases, 1970-1980. Geophysical Research Letters
Lashof, D.  1989.  The dynamic greenhouse:
Feedback processes that  may influence future
concentrations of atmospheric trace gases and
climatic change.  Climatic Change 14:213-242.

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

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.

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

Mintzer, I.M. 1987. A 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
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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
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NOAA   (National   Oceanographic   and
Atmospheric   Administration).  1987.
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Environmental   Research    Laboratories,
Boulder, Colorado. 155 pp.

Nordhaus, W.D., and G.  Yohe. 1983.  Future
paths of energy and carbon dioxide emissions.
In Changing  Climate. National Academy Press,
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Policy Options for Stabilizing Global Climate
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.   The
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                                     CHAPTER II
                         GREENHOUSE  GAS TRENDS

      The composition of the atmosphere is
changing  as  a  result  of  human  activities.
Increases  in  the concentrations  of carbon
dioxide (CO2), methane (CH4), nitrous oxide
(N2O), and  chlorofluorocarbons (CFCs)  are
wefl documented.  In addition, tropospheric
(lower  atmospheric)   chemistry   and
stratospheric (upper atmospheric)  chemistry
are being modified as a result of the addition
into the atmosphere  of these gases  as well as
emissions of carbon monoxide, nitrogen oxides,
and  other compounds.   Specifically, we find

     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.  Only  50-
60% of the fossil-fuel  CO2 remains  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 to  changes in tropospheric  chemistry.
Agricultural   sources,   particularly   rice
cultivation   and  animal   husbandry,  have
probably   been  the   most  significant
contributors  to  historical   increases   in
concentrations.    There is  the  potential,
however, for rapid growth in emissions from
landfills, coal seams, permafrost, natural  gas
exploration and pipeline leakage, and biomass
burning associated with future forest clearing.
Methane is increasing at a  rate of  ~1%  per
year and is responsible  for about 20% of  the
current increases in the greenhouse effect.  Per
molecule in the atmosphere, CH4 is about 20
times more powerful than CO2 at  current

     The concentration of nitrous oxide has
increased by 5-10% since pre-industrial times.
The cause of this increase is highly uncertain,
but it appears that  the use  of nitrogenous
fertilizer, as  well  as the  activities  of land
clearing, biomass  burning,  and  fossil-fuel
combustion have all contributed.    Nitrous
oxide, which is about 200 times more powerful
on  a per  molecule  basis  than CO2  as  a
greenhouse  gas, can  also  contribute  to
stratospheric ozone depletion.  Nitrous oxide
is currently increasing at a rate of about 0.2-
0.3%  per year, which  represents an imbalance
between sources and sinks of about 30%.
Nitrous oxide is  responsible for about 5% of
the current increases in the greenhouse effect.

     CFCs  were   introduced   into   the
atmosphere for  the  first  time during  this
century; the most abundant species are CFC-
12  and  CFC-11,  which  had  atmospheric
concentrations in 1986 of 392 and 226 parts
per trillion by volume, respectively.  While
these  concentrations  are tiny  compared with
that of CO2,  these  compounds are about
15,000 times more powerful, on a per molecule
basis, than carbon dioxide as a greenhouse gas
and are increasing very rapidly - about 5%
per year from 1978 to 1983.  Of major concern
because  of  their   potential  to   deplete
stratospheric ozone, the CFCs also represent
about 20% of the current increases in the
greenhouse effect.

     The  chemistry of the  atmosphere is
changing as a result  of emissions of carbon
monoxide, nitrogen oxides, and volatile organic
compounds, among other species, and because
of  changes in  the  greenhouse gases just
described.   This  change  in  atmospheric
chemistry alters the amount and distribution of
ozone  and the oxidizing  power   of  the
atmosphere, which changes the lifetimes of
CH4 and other greenhouse gases.  Changes in
global  ozone,  both  stratospheric  and
tropospheric, are quite uncertain and may have
contributed to an increase or decrease in the
warming commitment during the last decade.

 Policy Options for Stabilizing Global Climate

      The  composition   of   the  Earth's
 atmosphere is changing. Detailed background
 atmospheric concentration measurements  of
 trace gases 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  pre-industrial  times.
 Mounting  evidence that the atmosphere  is
 changing   has  increased  the   urgency  to
 understand   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 in Table 2-1, which appears at the
 end of this chapter.

      The  concentrations  of a  number  of
 greenhouse gases  have  already  increased
 substantially over pre-industrial 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 (see
 dioxide (CO2) 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 because of the
 more rapid growth in  other gases during the
 last   few   decades   (see  CHAPTER   IV).
 Particularly important has been  the recent
 growth  in  concentrations  of  chlorofluoro-
 carbons  (CFCs).     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 and the subsequent London
Amendments, 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 importance of CO2 is
therefore likely  to increase again in the future
 unless these emissions are also restricted (see

      The  radiative impact  of greenhouse
 gases is  characterized here in  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.


 Concentration History and Geographic

      Carbon  dioxide 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 (see Fraser, Elliott et al., 1986; 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), 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
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,

                                                Chapter II:  Greenhouse Gas Trends
                                  FIGURE 2-1
        Other (8%)

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.)

 Policy Options for Stabilizing Global Climate
 and,  as  of 1986, consisted  of ~26 stations
 (Komhyr et al., 1985;  Gammon et  al., 1986;
 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,
 Spain, West Germany,  and Switzerland.

 Mauna Loa

      The MLO CO2 record is  shown  in
 Figure  1-1 in  Chapter  I.    CO2 steadily
 increased  from 315  parts  per  million  by
 volume (ppm)  in 1958  to 351  ppm in 1988.
 This corresponds to an increase at the rate of
 0.36% per year, or a mean increase of 1.1 0.2
 ppm  per  year.  From  1958  to  1988, CO2 at
 Mauna Loa increased  by 36 ppm;  over  the
 same period,  fossil-fuel  combustion (shown
 also  in  Figure 1-1)  was a source of  123
 petagrams (Pg)1 of carbon (C) as CO2 to the
 atmosphere, which is equivalent to 59 ppm of
 CO2. The apparent fraction of the fossil-fuel
 sources  of  CO2  that  remained   in  the
 atmosphere during  this period is thus 57%.
 Because other net sources of CO2, particularly
 deforestation  (see  below),  may  have been
 important during  this  period,  the actual
 fraction of anthropogenic (induced by human
 activities) carbon emissions  remaining in  the
 atmosphere is uncertain.

      The apparent airborne fraction of CO2
 has not  remained constant.  Averaged over
 1959-1975, the fraction was 54.7%, while that
 for 1975-1988  was 61.3%  (Keeling, 1989).
 This  increase  could signal  either enhanced
 CO2  release  from deforestation or reduced
 capacity of the land-ocean system to absorb
 excess CO2.  It could  also  signal a positive
 feedback between greenhouse wanning and the
 natural carbon cycling on  land and at sea.
 Because  of the implications for accelerated
 greenhouse  warming,   understanding   the
 increase in the airborne fraction of CO2 must
 be of highest priority.

      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 photosynthesis
during the growing season, and  net return  of
CO2  to the atmosphere via respiration and
decomposition processes during the rest of the

      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 among the atmosphere, land,
and ocean reservoirs. More recently, Keeling
et al.  (1989) have also found an 11-year cycle
in CO2, which correlates with the 11-year cycle
found in the surface air temperature record
compiled  by Hansen and Lebedeff (1987).
These excursions  highlight the possibility  of
climatic feedbacks in the carbon cycle; they do
not mask  the increasing secular trend, which
mainly  reflects   the  trend in  fossil-fuel

      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 between  1976 and 1986
(Bacastow et al., 1985;  Enting,  1987).   The
causes of this amplitude trend have not been
unambiguously identified;  hypotheses involve
shifts  in the  seasonaliry 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

                                                        Chapter II:  Greenhouse Gas Trends
prior   to   the   modern   high-precision
instrumental  record (Oeschger and  Stauffer,
1986). Deep ice cores have been drilled from
many  locations  in   both  Greenland  and

      From the ice-core data, it is  deduced
that in pre-industrial times (i.e., before about
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) (see Figure 2-2).   The ice-core  data
reveal the  possible  existence  of   natural
fluctuations  on  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 time information on CO2
variations in the last 160,000 years (Barnola et
al.,  1987; see 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.

      The variation of CO2 over this  record is
approximately  in  step  with the surrogate
temperature record deduced from the same ice
core (Jouzel et al., 1987), confirming the role
of CO2 in influencing the radiation balance of
the earth.

GMCC Network

      The CO2 concentrations from  the ~25
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 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 3.0 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 supersaturated 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.,

      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
(see  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).

      The  geographical  variations  of CO2
growth rates  at the  GMCC sites show more
clearly the El Nino  perturbations, as noted
already in the Mauna Loa data. For example,
the El Nino-caused cessation of upwelling that

Policy Options for Stabilizing Global Climate
                                     FIGURE 2-2
                                    (Parts per Million)
T	1
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, probably due to 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; all cited in
Siegenthaler and Oeschger, 1987.)

                                                   Chapter II: Greenhouse Gas Trends
                                   FIGURE 2-3
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.)

 Policy Options for Stabilizing Global Climate
 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 currently under investigation.

 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
 thus  are net  sources  of carbon  to  the
 atmosphere (see Figure 2-4).

 Fossil Carbon Dioxide

      The combustion of fossil fuels, in liquid,
 solid,   and  gas   forms,  is   the   major
 anthropogenic  source   of  CO2   10  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
 U.S., 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.

Biospheric Cycle

      The terrestrial biosphere absorbs CO2
 from the atmosphere via photosynthesis on the
order of 80 Pg C/yr. Approximately the same
 amount is returned to the atmosphere annually
via autotrophic and 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, the conversion of forests to
pastures and agriculture 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.  In
temperate  and  boreal  regions  the carbon
absorbed from the atmosphere via regrowth of
forests is countered by the carbon released by
the oxidation of wood products; the result is a
net release to  the atmosphere of 0.1 Pg C/yr
(Melillo  et  al., 1988).    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).  Several recent modeling studies (see
section below) have inferred, from north-south
profiles of atmospheric CO2, that vegetation
and  soils  in   temperate  latitudes  in  the
northern hemisphere have  acted as a net sink
for excess  CO2 from  fossil-fuel  burning.
Because growth and decay cycles are intimately
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

                                                  Chapter II:  Greenhouse Gas Trends
                                   FIGURE 2-4
                           THE CARBON CYCLE
                                                  organic C: 12,000,000
                                                     limestone: 50,000,000
living plants:  800
 young soils: 1500
   old soils; 1500
            5.5 r
Figure 2-4. (a) Major reservoirs of the global carbon cycle. Reservoirs (or stocks) are in Pg C  (b)
Fluxes of carbon are in Pg C/yr. (Source: Adapted from Keeling, 1983.)

 Policy Options for Stabilizing Global Climate
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  1970s (Takahashi et al.,
1980, 1981), 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
among  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 100 Pg C/yr is exchanged between the
atmosphere  and the ocean.  This exchange
results in  a net outgassing of approximately 1
Pg Cfyr from the equatorial oceans and a net
absorption of about the same amount by the
mid to high  latitude oceans.

      Superimposed on this exchange of 100
Pg C/yr in either direction is  the penetration
of fossil-fuel  CO2  into the  oceans.   The
capacity of the ocean  to take up the excess
CO2 has  been postulated  by many authors
(e.g.,  Oeschger et al.,  1975; Broecker et al.,
1979).  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  from   direct
measurements.   A particular difficulty is the
lack of baseline or historical data of oceanic
CO2  from which to  estimate changes.  As
water  masses  in the ocean  interior move
primarily  along constant density (isopycnal)
contours,  concentration differences between
the ocean surface and interior locations along
the same isopycnal have been used to infer the
anthropogenic  CO2  signal  (Brewer,  1978;
Chen,  1982a,  1982b).     Considerable
controversy exists about this procedure,  as
mixing and biological processes also alter CO2
concentrations; correction schemes for these
other processes remain problematic  due  to
insufficient data (Broecker et al., 1982;  Shiller,
1981, 1982; Chen et al., 1982).  Takahashi et
al.  (1983) have  demonstrated  that  in  the
Atlantic, the partial  pressure of CO2 in the
ocean  (pCO2)  increased   by   8   8
microatmospheres (/tatm) from  1958  to the
mid 1970s.

      The expectation of fossil-fuel uptake by
the oceans is encouraged by 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 CFCs, recent
man-made compounds. The magnitude of the
fossil-fuel uptake is estimated using numerical
models  calibrated by these tracers.    These
models  range in complexity from simple one-
dimensional box-diffusion  models to   three-
dimensional general circulation models of the
ocean (Siegenthaler, 1983; Maier-Reimer and
Hasselman, 1987;  Peng,  1986;  JOds and
Siegenthaler, 1989;  Sarmiento et al.,  1989).
The magnitude  of the uptake varies depending
on the model architecture and the tracer used
to calibrate the model, but does not  exceed
~35%  of  the  fossil-fuel   source.     This
percentage  is  considerably  less than that
required by the CO2 budget, i.e. 45% of the
fossil-fuel  source plus 100% of the  release
from deforestation.

      It is generally assumed that the major
sink for  anthropogenic  CO2  is  the large
expanse of southern  oceans where there are
strong winds and cold waters. A recent study
(Tans  et  al.,  1990),  using  the  north-south
profile of CO2 in the atmosphere to constrain

                                                        Chapter II: Greenhouse Gas Trends

      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  250K (-23C).
   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 (nm) and
   >18   nia  (Dickinson  and  Cicerone,
   1986).    The  15 mti  band  of  CO2
   dominates absorption in  the spectral
   range  from   12  to  18  nm, 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 im> 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, CFC-11 and CFC-12 are about
   15,000 times  more  effective  than  CO2
   per   incremental   increase    in
   concentration (see Table 2-2).
the budget, argues that the CO2 sink must be
predominately in the  northern hemisphere.
Because  the  northern  oceans are  better
surveyed and are observed to be only a small
sink for CO2 (Takahashi et al., 1989), Tans et
al. hypothesize that there must be a significant
land sink to balance the CO2 budget  and
match the north-south gradient.  The need for
a land  sink for anthropogenic CO2 has long
been suggested by the  ocean models.  This
hypothesis has since been supported by several
independent studies (Enting and Mansbridge,
1989; Etcheto et al., 1989).

Chemical and Radiative Properties/

      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   1.2-1.3C.     At   current
concentrations 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 0.23C, while the same increment from 550
to 600 ppm yields a radiative forcing of only
0.16C.  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; see CHAPTER

Policy Options for Stabilizing Global Climate
                                       FIGURE 2-5

                                   Gas Absorption Bands
 wavelength 5
10       12.5   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 nm, in which there is little else to prevent radiation from the Earth escaping directly into
space.  (Source:  UNEP, 1987.)

                                        Chapter II: Greenhouse Gas Trends
                        TABLE 2-2
               Radiative Forcing for a Uniform
         Increase in Trace Gases From Current Levels
Halon 1301
Radiative Forcing
(No Feedbacks)
Radiative Forcing
Relative to CO2
Source:  Adapted from Ramanathan et al., 1985.

 Policy Options for Stabilizing Global Climate

 Concentration History and Geographic

      High-precision  atmospheric  measure-
 ments of CH4 have been  made in the past
 decade at many different locations.  The data
 show  clearly  that  the  globally  averaged
 concentration of  methane, 1670  parts  per
 billion by  volume (ppb) in  1988,  has been
 increasing at the rate of about 14-16 ppb per
 year (Blake and Rowland, 1986, 1988) (see
 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 CO2,
 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 average concentration is
approximately 100  ppb  higher than that in the
Southern Hemisphere.  The seasonal cycle in
 the Southern Hemisphere (about 35  ppb peak
 to peak) 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
 ~700 ppb and exhibited a 2.5 factor increase
to its present value in only the last 100 years
(Stauffer et al., 1985; Pearman et al., 1986)
(see 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 period  (130 kyBP).  The trend in
CH4  closely  followed  the   trend   in  air
temperature  deduced  from   deuterium
(Raynaud et al., 1988).  These measurements
show that current concentrations of CH4, like
that of CO2, 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 about 500
teragrams (Tg) CH4/yr.3  By inference, the
annual global source equals 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

      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
warming. 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 heterogeneity of natural  wetlands and
their 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 the following  factors,
among others, that affect  CH4  fluxes to the

                                                     Chapter II: Greenhouse Gas Trends
                                     FIGURE 2-6
          (Parts per Million)

        Atmospheric Data
                  i  1.6
1978  79808182838485868788

          ice-Cor* Data



Figure 2-6. Recent measurements of atmospheric CH4 show that CH4 has been increasing at the rate
of about 1%/yr in the last decade (upper panel). Ice-core data (lower panel) show that CH4 was
relatively constant in the 1800s, and began to increase rapidly at the beginning of the 20th century.
Like CO2, the recent trend in CH4 (shown as  + + + in the lower panel) is unprecedented in the
history of CH4 from ice cores. The ice-core data are from  Siple Station, Antarctica. Stars and
triangles represent results obtained from melt and dry extraction, respectively. The ellipses indicate
the uncertainties in the concentrations as well as in the mean age of the sample. (Sources: Blake and
Rowland, 1988 ~ Copyright 1988 by the AAAS; Stauffer et al., 1985 - Copyright 1985 by the AAAS.)

 Policy Options for Stabilizing Global Climate
                                  FIGURE 2-7
                 Fossil-Fuel Production
                       50-95 Tg
    Domestic Animal
       65-100 Tg
 Blomass Burning
    50-100 Tg
                               Rice Production
                                 60-170 Tg
               30-70 Tg
                             Natural Sources
                              115-345 Tg
      Rice Production
       2. China
       3. Bangladesh

  Domestic Animals      Fossil-Fuel Production
   2. USSR
   3. Brazil
1. United States
3. China
Figure 2-7. Human activities in the agricultural sector (animal husbandry, 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.)

                                                        Chapter II:  Greenhouse Gas Trends
atmosphere:  temperature,  soil  properties,
fertilizer type, and irrigation practices. These
factors  make global  extrapolation of CH4
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 humans. About
75% of the emissions are from cattle and dairy
cows.  India,  the USSR, Brazil, the U.S., 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 annual global
emissions range from close to  zero (Seiler,
Conrad  et  al.,  1984)  to  20  Tg (Fraser,
Rasmussen et al.,  1986), 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, mainly in the tropics. The amount of
CH4 produced depends on the material burned
and the  degree of combustion.   Estimates
range from 50-100 Tg CH^ (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 fuels and 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
decomposes into  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 30-70 Tg CH4/yr.  These estimates
assume  that a  large fraction  of  all organic
carbon deposited in landfills  eventually is
subject  to methanogenesis and  subsequent
emission to the atmosphere.   Cicerone  and
Oremland (1988)  also adopt a range of 30-70
Tg CH4/yr.

      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  entering the  atmosphere.
Although  natural   gas   production   and
consumption statistics are  available globally,
the nature of this fugitive CH4 source makes
it difficult to estimate how much this source
contributes to the atmospheric abundance of
CH4.  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  by  global
extrapolation (Cicerone and Oremland, 1988).
An additional 15  Tg CH4/yr is released 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).  On the other hand,
gas  distribution systems  outside  of North
America  may have much  greater leak rates.
Thus a reasonable range for these sources  may
be 20-50 Tg CH^/yr.

      Methane is also the major component of
gas trapped in coal.  The  percentage of the
CH4 component increases with the age  and

 Policy Options for Stabilizing Global Climate
 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).

      A highly uncertain but potentially large
 source of CH4 is clathrates:  stable 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 (see CHAPTER  III).

 Chemical and  Radiative Properties/

      Methane is active both radiatively and
 chemically in  the  atmosphere.   At present
 levels, an additional  molecule of CH4 will
 contribute a radiative forcing  that is equivalent
 to  that  contributed by  approximately 20
 molecules of CO2 (e.g.,  Ramanathan et al.,
 1985; Donner and Ramanathan, 1980; Lacis et
 al., 1981). These radiative transfer calculations
 suggest  that a doubling of atmospheric CH4
 (1.6-3.2  ppm)  will  contribute  a  radiative
 forcing of 0.16C (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 globally averaged lifetime
 (atmospheric abundance divided by destruction
 rate)  of  CH4 is approximately  10 years, the
 local  lifetime  being  shorter in the tropics.
 Using estimates of the average concentration
of atmospheric hydroxyl radicals derived from
measurements  of methyl chloroform, Prinn et
al.   (1987)   have   deduced  the   average
atmospheric lifetime of CH4 to be 9.6 (+2.2, -
 1.5) years. The reaction between CH4 and OH
eventually produces carbon  monoxide (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 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 [H2O2]) have
opposite  effects   on  OH  concentrations.
Changes  in   nitrogen  oxides   (NOX)  and
tropospheric ozone (O3) also strongly affect
atmospheric OH (see below).


Concentration History and Geographic

      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 about  200 times greater.  The first
high-precision measurements of  atmospheric
N2O    from   the  late   1970s   showed
unambiguously  an  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  (see Figure 2-8).  Flask
samples  of  air  from   five sites  of  the
cooperative  network of  NOAA/GMCC are
also being analyzed for N2O (Thompson et al.,
1985; Komhyr et al., 1991).

      The concentration of atmospheric N2O
was 307 ppb in 1988, and its annual growth
rate is -0.7-0.8 ppb per year, or 0.2-0.3% per
year (Prinn et al., 1990;  Elkins and Rossen,
1989).   The concentrations at the Northern
Hemisphere sites are 0.8-1.0 ppb higher than
those at  the  Southern  Hemisphere sites,
suggesting the dominance of a northern source
(Elkins  and Rossen, 1989; Butler et al., 1989;
Elkins et al., 1988).

      Ice-core  data show  that the  pre-
industrial 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

                                                    Chapter II: Greenhouse Gas Trends
                                    FIGURE 2-8
                (Parts per Billion)

             Atmospheric Data
                      3 I 0
                           N -,  O
                      508 f
C  304 r
a.      :

   302 [

                      300 L
                Ice-Core Data

                                  '   J  --'*"
                                 -t-TT   .
                  t too
Figure 2-8. Concentration of atmospheric N2O has been increasing at the rate of 0.2-0.3%/yr in the
last decade (upper panel).  The ice-core record (lower panel) shows that N2O was relatively constant
from the 1600s to the beginning of the 20th century and began increasing rapidly in the last 50 years.
(Sources:   Khalil  and Rasmussen, pers. communication;  Pearman  et al.,  1986 --  Reprinted  by
permission from Nature, vol. 320, pp. 248-250.  Copyright  1986 Macmillan Journals Limited.)

 Policy Options for Stabilizing Global Climate
 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.)   Measurements of N2O in the
 Vostok ice core show lower atmospheric N2O
 values of 244 20 ppb during the last climatic
 transition  (about 12,000 BC)  with a slight
 increase   as  the   climate  was  warming  up
 (Zardini et al., 1989).

 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  only  because  of  the scarcity  of
 measurements of N2O fluxes, but also, as  in
 the case for CH4,  because of the complexity  of
 the   biogeochemical   interactions  and
 heterogeneous  landscape where  N2O   is

      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 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.   A  source of  3.7 Tg N/yr  is
estimated from dry and  wet  tropical forests
(Matson and  Vitousek,  1989).   Seiler 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
(Elkins et al.,  1978; Seiler and Conrad, 1981;
Weiss,  1981).   Seiler  and Conrad  (1987)
estimated the oceanic contribution to be 2  1
Tg/year. Recent oceanographic measurements
of N2O suggest that there is large variability,
both temporally and spatially,  in the oceanic
flux of N2O to the atmosphere. The flux is
affected by El  Nino events and differences in
ocean circulation patterns (Butler et al., 1989;
Elkins,  pers. communication).  Because  the
oceanic reservoir of N2O is between 900 and
1100 Tg N, about one-half and two-thirds the
size  of the  atmospheric reservoir (Butler,
pers.  communication),  changes  in  ocean
circulation  as a result of climate change may
have  significant impact on  the  atmospheric
N2O concentrations.

      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 study of this N2O
source, reported by Hao et al. (1987), found
that the amount of N2O in flue  gases was
correlated with the nitrogen  content of fuels.
Using  statistics on  solid-  and  liquid-fuel
production, they estimated an emission of 3.2
Tg  N2O-N  in  1982.   Very recent  studies,
however, suggest  that  many  of  the N2O
measurements, including those of Hao et al.
(1987), may have been affected by a sampling
artifact.  A reaction  between water, sulfur
dioxide  (SO^,  and NOX 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; Muzio et al., 1989; Montgomery et al.,
1989).  Reanalysis of measurements made in

                                                         Chapter II: Greenhouse Gas Trends
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,   pen>.
communication).     Recent   measurements
conducted   by  the   U.S.   Environmental
Protection Agency (U.S. 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 combustors 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
less than 1 Tg N/yr  (see CHAPTER VI).

      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 N2O 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 70.5 million
tons  nitrogen as  nitrogenous  fertilizers  in
1984, an N2O contribution of 0.14-2.4 Tg N#r
is estimated. Although the  amount  of N2O
emissions  associated   with  the  use   of
nitrogenous fertilizers is estimated to be small
compared to emissions from natural sources,
such  emissions  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 CO, 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.  It may indeed be an over-estimate
and subject to the same sampling artifact as
that encountered in fossil-fuel combustion. A
reanalysis by Crutzen et al. (1989) yielded very
low estimates: 0.06-0.3 Tg N/yr from biomass

      Recently, Bowden and Bormann (1986)
found enhanced N2O fluxes to the atmosphere
from cleared  areas in  a temperate forest  and
elevated N2O concentrations in ground water
adjacent  to the  cut  watershed.   Similarly,
threefold increases in  N2O fluxes were  found
in pastures and forest clearings in the Amazon
(Luizao  et al.,  1989).    Extrapolating  the
Amazonian results to all deforested areas in
the globe, a  source  of 0.8-1.3  Tg  N/yr is
estimated.  In contrast, 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 if vegetation did
not return.  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/

      Relative  to  CO2,  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, reflects a
large imbalance (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.

      Nitrous oxide is an effective greenhouse
gas.  The radiative forcing of one molecule of
N2O  is  equivalent to  that   of about  200
molecules of CO2;  an  increase of 50% in N2O
and  a  doubling  of  CH4  would  yield
approximately the same radiative forcing, even
though the N2O  concentration is less, by a
factor of 5, than that of CH4.  A 50% increase
in  the  current  burden  of  N2O  in  the
atmosphere will yield a  radiative forcing of
about 0.15C (without any feedbacks).

 Policy Options for Stabilizing Global Climate
      Nitrous oxide is not chemically reactive
 in the troposphere and  is destroyed in  the
 stratosphere by photolysis and by reaction with
 atomic oxygen in  the excited  state (O(1D)].
 The latter reaction makes N2O the dominant
 precursor of odd nitrogen in the stratosphere.
 Thus, the observed increase in N2O should
 lead to increases in stratospheric NOX, which
 would significantly alter  stratospheric ozone


 Concentration History and Geographic

 (CC13F) and CFC-12 (CC12F2) began in 1970
 with the development of gas chromatograph
 techniques  using  electron capture detectors
 (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
 ALE/GAGE  stations (Cunnold et al., 1986;
 Prinn et al.,  1983; Rasmussen  and  Khalil,
 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 in  Boulder
 (Thompson et al., 1985; NOAA, 1987).

      CFC-12  is   the   most   abundant
chlorofluorocarbon in the atmosphere.   Its
average  tropospheric concentration in 1986
was  392  parts per trillion by  volume (ppt),
corresponding to a total burden of about  8.1
Tg. Its concentration rose rapidly in the 1970s
and is currently increasing at about 4%/yr.

      With a  total burden of about 5.2 Tg,
 CFC-11   is   the   second  most   abundant
chlorofluorocarbon in the atmosphere.   Its
average  concentration in 1986 was 226 ppt,
and is also increasing currently at 4%/yr.

      Other important sources of atmospheric
chlorine include methyl chloride (CH3C1, the
major natural source of stratospheric chlorine)
at a concentration of 600 ppt (no measured
trend); methyl chloroform (CH3CC13) at  125
ppt in 1986, increasing at ~5%/yr;   carbon
tetrachloride  (CC14), at  about  100  ppt,
increasing  at  1%/yr;  HCFC-22  (formerly
denoted  CFC-22; CHC1F2),  at  ~80  ppt in
1986,  increasing  at 7%/yr,  and CFC-113
(C^Cl^) at 30-70 ppt in 1986, increasing at
greater than 10%/yr (Prinn, 1988).

      Bromocarbons that are moderately long-
lived in the troposphere supply bromine to the
stratosphere where it plays an important role
in ozone destruction, especially with high
levels of active chlorine such as are associated
with  the Antarctic  ozone  hole.   Methyl
bromide  (CH3Br, 15  ppt in  1985) is  natural,
with some industrial sources, and is the major
source of stratospheric bromine. The halons
1211 (CBrClF2) and  1301 (CBrF3) currently
are small sources (2  ppt each) but  are
growing rapidly (> 10%/yr).

Sources and Sinks

      CFCs are  solely  a  product  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-11 and -12 production
by reporting companies was  1974, in which a
total of 812.5 gigagrams (Gg) of CFC-11 plus
CFC-12  was  produced.4     Annual  CFC
production decreased somewhat following a
ban on "non-essential" aerosol  uses  in  the
United States, Canada, and  Sweden.   Non-
aerosol uses have continued to increase, as has
CFC-113, and the total has  risen rapidly in
recent years, with estimated global production
of CFCs  -11, -12, and -113 in 1985 at about
950  Gg.   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 modest uncertainties (~15%) in the
magnitude of world emissions for CFC-12 and

                                                        Chapter II:  Greenhouse Gas Trends
smaller uncertainties  for  those  of CFC-11.
Cunnold et al. (1986) and Fraser et al. (1983)
have found that 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 for  CFC-113  and  HCFC-22 -
equivalent to that conducted for CFC-11 and
CFC-12 - has not been done.  A survey of
methyl chloroform has been published recently
(Midgley, 1989).

      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 llltS2 years for
CFC-12,  74 T$  years  for  CFC-11,  and
approximately  40  years   for   carbon
tetrachloride.      Compounds    containing
hydrogen  (HCFCs) react  with OH in  the
troposphere, have lifetimes on the order of 20
years or less, and pose less threat to the ozone
layer because  their concentrations do not build
up  to as large  values as would equivalent
CFCs. The ALE/GAGE lifetime for CH3CC13
is 6.3tJ; years (Prinn et al.,  1990), and  the
corresponding lifetime  for HCFC-22  is 15
years.  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.

Chemical and Radiative  Properties/

      CFCs absorb infrared radiation in  the
window region of the atmospheric spectrum
(see Figure 2-5). Although CFCs are present
in minute amounts (ppt) in the atmosphere,
together  they  are  one  of  the  dominant
greenhouse gases.  At present they have  the
highest annual fractional increase  of all  the
greenhouse gases (~4-10%/yr). Furthermore,
the radiative  forcing due to each additional
molecule of CFC is equivalent to that due to
about 15,000 molecules of CO2, and at present
levels,  this radiative  forcing would  increase
linearly   with  added   CFC   molecules
(Ramanathan et al., 1987).  A 2 ppb increase
in both CFC-11 and CFC-12 would contribute
a radiative forcing of 0.3C, equivalent to that
from a 65 ppm increase in CO2.  In the 1980s,
CFC-11  and CFC-12  together  contributed
about  15%  of   the  increase  in   global
greenhouse forcing.

      The   dissociation  products   of
halocarbons are  the  dominant sources of
chlorine  and bromine for the stratosphere
(WMO,  1985).  These elements are  major
components in the catalytic cycles that control
ozone  abundance.   Trends for  the  major
halocarbon reservoirs in the stratosphere (HC1
and HF)  have been observed from the ground
and in latitudinal surveys with aircraft. Within
the limits of observational uncertainties, the
estimated trends in these species are consistent
with trends in the source gases themselves.


Concentration History and Geographic

      Ozone is both produced and destroyed
in situ in the atmosphere.  While the other
trace gases  are relatively well-mixed vertically,
the non-uniform vertical distribution of O3 in
the atmosphere is of  prime  importance in
determining its radiative and chemical effects
(see Figure 2-9). We often  focus separately on
stratospheric   and   tropospheric   ozone.
Stratospheric O3 represents the majority of the
total  and controls the absorption  of solar
ultraviolet radiation.  Tropospheric O3 plays
an important role in air  quality and could
contribute to major greenhouse  forcing.

Tropospheric Ozone

      Ozone sondes  from  a  diverse  and
globally distributed network provide our only
record of possible trends in 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  1970s, surface O3 concentrations are
measured routinely  at the four continuous
monitoring  stations   operated  by  NOAA/
GMCC:  Pt. Barrow, Alaska;   Mauna Lao,

Policy Options for Stabilizing Global Climate
                                    FIGURE 2-9
               OZONE CONCENTRATION (cm

          10'          10"          10"
 120 -
             AND OZONE
                                                                    RADIATIVE FORCIHG
                                                                     rrariciL SIMITHITT
                                                                -0.00      0.01

                                                               DEC/DU OZONE CHANCE
                                                                                  0.02 !
                      TEMFtHATUMe 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, 1990 -- Copyright  1990 by  the American Geophysical

                                                         Chapter II: Greenhouse Gas Trends
Hawaii;  American Samoa;  and the South
Pole (see e.g., NOAA, 1987). NOAA/GMCC
also participates in international cooperative
ozone sonde profiling activities.  Because of
the reactivity of O3 near the surface and  its
short lifetime in the planetary boundary layer,
surface measurements are not representative of
the average  troposphere.

      The O3 data taken near populated and
industrial regions in the 1930s to the  1950s
generally  show   an   annually   averaged
concentration of 10-20 ppb at the surface, with
a seasonal cycle that peaked in summer.  The
data  show   a  generally   increasing  trend,
especially   in  the   summer,  in   surface
concentrations  of O3  at  sites in western
Europe,  the  U.S.,  and northern Japan.  For
example, a factor of 2 increase, from ~30 ppb
in 1933 to ~60 ppb in the  1980s, is found in
the summer 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  shows  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 trends in  the upper
troposphere  and  lower   stratosphere   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   exhibits   no
significant  trends  near  the   surface,   but
significant  positive  trends  at  700  millibars
(mb) and 500 mb.  Mid-tropospheric O3 at
Resolute, Canada  (75N), 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.

Stratospheric Ozone

      The recent record of O3 concentrations
in the upper atmosphere has been reviewed by
a NASA panel of experts (International Ozone
Trends  Panel,  see  Executive  Summary in
Watson  et  al.,  1988).   They  report  a
statistically significant  decrease  in the total
column abundance  of O3 above the  known
natural variations using ground-based Dobson
instruments from 1969 to  1986 at mid  and
high   northern   latitudes  during  winter.
Satellite data, calibrated by coincident Dobson
measurements, show a decrease of about 2-3%
from  October  1978   (solar  maximum)  to
October 1985 (solar minimum) in the column
O3 concentrations  between 53S and 53N.
The cause of this decrease over such a short
record has not been  identified but may be due
to increases in chlorine, the decline in solar
activity, or the global impact of the Antarctic
ozone hole.  The observations of stratospheric
O3 in the Northern  Hemisphere indicate that
O3 abundances have declined over the past 20
years.  The small  decreases (1-2%), if any, in
the summer months are consistent with  the
predicted change due to  increasing  CFCs.
However, the measured ozone loss poleward of
40N in winter is  greater (by a factor of 2-3)
than that predicted  by theory (Watson et al.,
1988;   Rowland,  1989).   This  unexplained
depletion of O3 in  the north is not  of the
same magnitude as  the Antarctic ozone  hole
but may  be associated with  the unusual
chemistry occurring  over Antarctica, marking
the start of a greater global decline.

Sources and Sinks

      Ozone is not emitted directly by human
activity,  but   its  concentration  in   the
troposphere   is    strongly   governed    by
anthropogenic  emissions   of   NOX   and

 Policy Options for Stabilizing Global Climate
 hydrocarbons, and in the stratosphere by 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.   Ozone's  annual concentration,
 seasonal  cycle,  and  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 (90% of the total) and
 its decreasing trend may  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/

      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 latitudinally dependent changes.

      Radiative transfer  calculations  reveal
 that  the ozone's climate forcing changes sign
 at about 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, potential
 O3  changes with  the  largest net effect  on
 surface temperatures are those occurring near
 the tropopause where the temperature contrast
 between   absorbed  and   emitted  thermal
 radiation is greatest. Ozone changes near the
surface produce little greenhouse forcing since
 the  thermal  radiation   from  the  surface
absorbed  by  ozone  is  nearly   the  same
 temperature as that which is re-emitted.
      While the radiative  effects  of  O3 are
understood  theoretically, quantifying  surface
temperature changes due to O3 perturbations
is  difficult  because  of  the  large  natural
variability in tropospheric ozone and the lack
of  global   coverage   in   the  observations.
Available ozone trend data are  limited  to
northern mid latitudes.  Some of the reported
data showed decreases in  O3  in  the upper
troposphere and lower stratosphere.   Using
these data, Lacis et al. (1990) find that during
the 1970s surface cooling resulted  from  these
changes and 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.  However,  these two-dimensional
models did not include the chlorine-catalyzed
loss associated with heterogeneous chemistry
that leads  to  substantial  ozone loss  in the
lower stratosphere (the Antarctic ozone hole).

      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.


      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 lifetimes, on the order
of 10 to 200 years; and they accumulate in the

                                                        Chapter II:  Greenhouse Gas Trends
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 CO2, 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

Global Tropospheric Chemistry

The Hydroxyl Radical

      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 CHCIF^, the
chemical lifetime  will  vary inversely with the
suitable   average  of   the   global   OH

      The OH radicals in the troposphere are
short-lived (<1 second)  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 NO^
can play an important role  in  recycling the
odd-hydrogen (HOX) from HO2 to OH,  thus
building up the concentrations  of OH;  high
levels of NOX, however,  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,  CO, CH4, NOr
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 are just developing models for OH
that  can describe these varied conditions and
accurately  integrate  the  global loss  of a
greenhouse  gas such  as CH4;  shorter-lived
gases pose a greater problem.
      In spite of these problems 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 the tropics,
particularly  in marine environments  remote
from the influence of urban areas and the
continental boundary layer,

     Increasing concentrations of CO  and
CH4 will reduce levels of OH,

     Large  scale   perturbations   to
tropospheric O3 and  H2O  (from  climate
change) may have equally  significant impacts
on OH concentrations,

     Changes in anthropogenic emissions of
NOX  are  expected  to  lead  to  significant
increases in northern hemispheric O3 and lead
to moderate increases in globally integrated

Carbon Monoxide

      Carbon monoxide  has a photochemical
lifetime of about one month in the tropics;
that lifetime becomes indefinitely long (and is
controlled by transport) in the winter at high
latitudes. The globally averaged destruction of
CO corresponds to an estimated lifetime of 2.5
months.   Carbon  monoxide  is lost  almost
exclusively through 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   (1-6%/yr),   in  the   northern
mid-latitudes over the last few decades. There
is no convincing evidence  for growth in the
Southern Hemisphere (Seiler, Giehl et al.,
1984;  Cicerone,  1988).    This  pattern  is
consistent with  a  growing  anthropogenic
source,  since  the  short  lifetime   precludes
significant interhemispheric transport.  Since

 Policy Options for Stabilizing Global Climate
CH4   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 NOX 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 NOX 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
NOX 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
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 significant 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
that  may  be  associated  with  "Antarctic"
chemistry.   In summary, if stratospheric O3
changes in the next few decades are large,  they
may lead to alterations in the lifetimes of the
long-lived greenhouse gases and also perturb
tropospheric chemistry through the supply of
O3  and  through   the increase  in   solar
ultraviolet light available to generate OH.


      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
pre-industrial  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.

                                                        Chapter II: Greenhouse Gas Trends

                                        TABLE 2-1

                                      Trace Gas Data

 CO2            CARBON DIOXIDE                                   1012 kg C

Atmospheric Burden                                                    720

    351 ppm in 1988
    Not photochemically active

Annual Trend                                                          3.0

    1.1 0.2 ppm/yr (0.4%/yr) since 1984

Annual Anthropogenic Sources                                           6-8

    1. Fossil-fuel combustion                                          S.5
       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 Anthropogenic Sinks                                             3-5

    1. Ocean                                                          <2
       Ocean's capacity to absorb CO2
       will be altered by changes in
       temperature, salinity, and
       biological activity of ocean.

    2. Biosphere                                                      0.5-4
       Enhanced photosynthetic uptake of
       CO2 due to more favorable climate
       and/or  due to CO2 fertilization

 Policy Options for Stabilizing Global Climate
                                  TABLE 2-1 (Continued)
109 kg CH4
Atmospheric Burden

     1670 ppb in 1988 (global average)
     Lifetime:  8 - 12 years
Annual Trend

     14 -  16 ppb/yr (0.8-1%/yr)

Annual Sources

     1. Fossil fuel
       Coal mining
       Natural gas drilling, venting,
       processing, and transmission loss

     2. Biomass burning

     3. Natural wetlands

     4. Rice Paddies

     5. Animals  mainly ruminants

     6. Termites
       Population unknown

     7. Oceans and freshwater lakes

     8. Landfills

     9. Methane hydrate destabilization

Annual Sinks

     1. OH destruction

     2. Dry soils
       absorption by methane -
       oxidizing bacteria in dry soils
                                                      500 100
                                                      50- 100


                                                      60- 170

                                                      65- 100

                                                      10- 100



                                                      0 -100 (future)

                                                      495 145

                                                      495 145


                                                        Chapter II:  Greenhouse Gas Trends

                                  TABLE 2-1 (Continued)

N2O           NITROUS OXIDE                                      109 kg N

Atmospheric Burden                                                     1500

    307 ppb in 1988
    Lifetime:  120 - 160 years

Annual Trend                                                           3.5 0.5

    0.7 - 0.8 ppb/yr

Annual Sources                                                         14 3 (inferred)

    1. Combustion of coal and oil                                       < 1

    2. Land-use modification
       Biomass burning                                                 <0.3
       Forest clearings                                                  0.8 - 1.3

    3. Fertilized agricultural lands                                       0.2 - 2.4

    4. Contaminated aquifers                                           0.8 - 1.7

    5. Tropical and subtropical forests and woodlands                     6 3

    6. Boreal and temperate forests                                     0.1 - 0.5

    7. Grasslands                                                     <0.1

    8. Oceans                                                         2 1

Annual Sinks                                                           10.5 3

    Stratospheric photolysis and reaction with O(1D)

 Policy Options for Stabilizing Global Climate

                                  TABLE 2-1 (Continued)

 CO    CARBON MONOXIDE                                       109 kg CO

 Atmospheric Burden                                                    525

     ~ 110 ppb
     (150 - 200 ppb Northern Hemisphere, 75 ppb Southern Hemisphere)

     Lifetime:  0.2 year

 Annual Trend                                                         4

     1 - 6%/yr Northern Hemisphere
     0 - 1%/yr Southern Hemisphere

 Annual Sources                                                       3300 1700

     1. Technological sources                                          640 200

     2. Biomass burning                                               1000 600

     3. CH4 oxidation                                                 600 300

     4. Oxidation of natural hydrocarbons (isoprenes and terpenes)          900 500

     5. Emission by plants                                             75 25

     6. Production by soils                                             17 15

     7. Ocean                                                        100 90

Annual Sinks                                                         2500  750

     1. Soil uptake                                                    390 140

     2. Photochemistry                                                2000  600

     3. Flux into stratosphere                                          110 30

                                                       Chapter II: Greenhouse Gas Trends

                                  TABLE 2-1 (Continued)

NOX           NITROGEN OXIDES                                   109 kg N
NOX  =  NO   +  NO2
        nitric     nitrogen
        oxide     dioxide

NO  = NOX + HNO2 -I- HNO3 4- HO2NO2 + NO3 + 2N2O5 + PAN + Paniculate 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  109kgN)

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                                                                  24 -  64

    1.  Wet deposition (precipitation scavenging)
        ocean                                                          4  -12
        continents                                                     8  - 30

    2.  Dry deposition                                                  12-22

Policy Options for Stabilizing Global Climate
                                  TABLE 2-1 (Continued)
Chemical Name
CCljF, CFC-12
CH,CC13 Methyl
CC14 Carbon

CHjCl Methyl
CBrCIF2 Halon 1211
226 ( 1986)
30-70 (1986)
125 (1986)
75-100 (1986)

Annual Global Prod.
Trend (10* kg)
+4% 350 (1986)
(CMA rep. co.'s
+4% 480 (1986)
(CMA reporting
co.'s plus USSR
~+7% 206 (1984)
(1986) 163 (1981)
102 (1977)
+ 11% 138-141 (1984)
91 (1979)
79 (1978)
70 (1977)
~5% ~580 (1985)
+ 1% -1000 (1985)

? (2000-5000 total,
based on OH);
500 industrial
>10% 5-10 (est. from obs.
(1985) of atm. increase)
Rigid and flexible foam;
Aerosol propellant
Rigid and flexible foam;
Aerosol propellant
Refrigerant; Production of
teflon polymers
Electronics solvent
Industrial degreasing of
metallic or metaplastic
pieces; Cold cleaning;
Solvent of adhesives,
varnishes, and paints
Chemical intermediate in
CFC-11, -12 production;
Declining use as:
Solvent in chemical &
pharmaceutical processes
and as grain fumigant
Burning Vegetation;
Release from oceans
High-tech fire
extinguisher (portable)
Removal in
Removal in
Removal by
OH in
Removal in
Removal by
OH in

Removal by
OH in
Photolysis in
and upper


                                                                 Chapter II: Greenhouse Gas Trends
                                            TABLE 2-1 (Continued)
Chemical Name
CBrF_, Halon 1301
C2C1F5 CFC-115
C2F6 CFC-116
CH3Br Methyl
CHBr3 Bromoform
C^t-j Ethylene
CHJI Methyl

Concentration Annual Global Prod.
(ppt) Trend (10* kg)
-2(1986) >10% 7-8(1984)
-3.4(1980) ~5%
(avg. of
5 sites)
5 (1985) ? 13-14 (1985)
Constant at 13
from 1979-84
4 (1985) ? ?
-4(1980)  ?
15 (1985) small ?
-2(1984) ? ?
highly variable
-1(1984) ? ?
~1(1981)  ?

High-tech fire extinguisher
(built-in systems)
Aerosol propellant;
Refrigerant; Production
of CFC-115
Leaded motor fuel;
Fumigation 50% natural
(anthropogenic sources
probably declining)
Mainly natural (oceans)
Evaporation of leaded
gasoline; Fumigation;
Anthropogenic sources
probably declining

Photolysis in
Removal in
Removal in
Removal in
Removal in
and above
Removal by
OH in
Removal by
OH in
Removal by
OH in
Removal by
OH in

Sources: Adapted from Seiler and Conrad, 1987; WMO, 1990.

 Policy Options for Stabilizing Global Climate

      Throughout  this Report the relative
 contributions of greenhouse gases to climate
 change are  measured based on changes in
 atmospheric concentrations of each gas;  these
 concentration  changes  alter  the   radiative
 balance of the climate system.  The  radiative
 forcing implied by a change in the atmospheric
 concentration of a  gas  depends on several
 factors, including the  absorptive strength of
 the gas within the infrared spectrum,  its decay
 profile, and the relative concentrations of all
 gases in the atmosphere, among other factors.
 The  scientific  community   has   typically
 measured contributions  to radiative forcing
 using  estimated  changes  in  atmospheric
 concentrations.  For example,  based on the
 work by Hansen et al.  (1988), the relative
 contributions by greenhouse gas to  radiative
 forcing during the  1980s  are summarized in
 Figure 2-10a.

      The relative contributions in Figure 2-
 lOa  are based on changes in atmospheric
 composition over the period.  These changes
 are of primary scientific  concern since they
 affect the radiative balance of the atmosphere
 and hence, the rate and magnitude of climate
 change. When discussing greenhouse gases in
 a policy context, however, it is useful to have
 some means of estimating the relative effects
 of  emissions of each greenhouse  gas on
 radiative forcing of the atmosphere over some
 future time  horizon, without performing the
 complex  and   time-consuming  task   of
 calculating    and   integrating   changes   in
 atmospheric composition over the period.  In
 short, the need is for an index that translates
 the level of  emissions of various gases into a
common metric  in  order  to  compare  the
climate   forcing   effects   without   directly
calculating   the  changes   in   atmospheric

      A number of approaches, called Global
 Warming Potential (GWP) indices, have been
developed over the past year.   These indices
account  for  direct effects  due to   growing
concentrations  of  carbon  dioxide  (CO2),
methane (CH4), chlorofluorocarbons  (CFCs),
and nitrous oxide (N2O).  They also estimate
indirect effects on  radiative forcing due to
 emissions  which  are   not   themselves
 greenhouse  gases,  but  lead  to  chemical
 reactions that create or alter greenhouse gases.
 These emissions  include  carbon  monoxide
 (CO), nitrogen oxides  (NOX), and volatile
 organic  compounds  (VOC),  all  of  which
 contribute to formation of tropospheric ozone,
 which is a greenhouse gas.

       In this study we follow the methodology
 used   by  the  Intergovernmental  Panel on
 Climate Change (IPCC, 1990). However, there
 is no universally accepted methodology for
 combining all the relevant factors into a single
 global warming potential for greenhouse gas
 emissions. In addition to the IPCC, there are
 several other noteworthy attempts to define a
 concept of global warming potential, including
 Lashof and  Ahuja  (1990), Rodhe (1990),
 Derwent (1990), WRI (1990),  and Nordhaus

       The concept of global warming potential
 developed by  the  IPCC is  based   on  a
 comparison of  the radiative forcing effect of
 the concurrent  emission into the atmosphere
 of an equal quantity of CO2 and another
 greenhouse  gas.   Each gas has a different
 instantaneous  radiative  forcing  effect.   In
 addition,   the   atmospheric  concentration
 attributable to a specific quantity of each gas
 declines   with  time.    In general,   other
 greenhouse  gases have  a much  stronger
 instantaneous radiative effect than does CO2;
 however,  CO2 has  a  longer atmospheric
 lifetime and  a  slower decay rate than most
 other  greenhouse  gases.    Atmospheric
 concentrations  of  certain  greenhouse  gases
 may  decline due  to atmospheric  chemical
 processes,  which   in   turn   create   other
 greenhouse  gases or  contribute   to  their
 creation or longevity. These indirect effects
 are included in  the GWP of each gas.

      Following this  convention, the GWP is
 defined as the time-integrated commitment to
 climate forcing from the instantaneous release
 of 1 kilogram of a trace gas expressed relative
 to that from 1  kilogram of carbon dioxide.5
 The  magnitude of the  GWP  is,  however,
sensitive  to the time horizon over which  the
analysis is conducted (i.e., the time period over
which the integral is calculated). For example,
Table  2-3 summarizes  the GWPs  of key
greenhouse gases assuming 20-year, 100-year,

                                               Chapter II: Greenhouse Gas Trends
                                FIGURE 2-10
     (a) By Greenhouse Gas
       Other (10%)

Other CFC (3%)
  O (5%)
                     (b) By Greenhouse Gas
                  Emissions on a C02-Equivalent Basis
                     Using a  100-Year Time Horizon
      Other CFC (3%)

CFC-11 *-l2(%)
                                                        Other (3%)
 Sources: Hansen et al., 1988; IPCC, 1990.

Policy Options Tor Stabilizing Global Climate
   Trace Gas
Carbon Dioxide
 Nitrous Oxide
                                       TABLE 2-3
                    Global Warming Potential for Key Greenhouse Gases
     Global Warming Potential
  (Integration Time Horizon. Years)



a Atmospheric retention of CO2 is very complex.  It is not destroyed like many other gases, but can
be transferred to other reservoirs such as the oceans or biota and then return to the atmosphere. The
IPCC used an approximate lifetime of 120 years by explicitly integrating the box diffusion model of
Siegenthaler (1983).

b Lifetime of CO was not provided, although its lifetime is generally no more than a few months.
Source:  IPCC, 1990.

                                                         Chapter II:  Greenhouse Gas Trends
and  500-year  time  horizons.  The assumed
integration period defines the time period over
which  the. radiative effects of  the  gas  are
measured. These GWPs indicate, for example,
that  1  kilogram of  methane emissions  is
estimated to have  21  times the impact  on
radiative forcing as 1  kilogram of  carbon
dioxide for a 100-year time horizon.  If a 500-
year   time   horizon is  assumed,  however,
methane is estimated to have only 9 times the
impact on  radiative forcing compared to an
equivalent  amount  of  carbon dioxide.  The
differences between the values for 100 years
and  500  years incorporate the differences in
atmospheric lifetime.   Because methane  is a
much shorter-lived gas  than  carbon dioxide -
10 years versus 120  years6  -  its  relative
contribution  to global climate  change  will
decrease (increase) over  time as the  time
horizon increases (decreases).

      For  this  discussion we will  use  the
GWPs presented in Table 2-3  for a mid-level
time horizon, i.e.,  100 years,  to convert all
greenhouse gases to a CO2-equivalent basis so
that  the relative  magnitudes  of  different
quantities of different greenhouse gases can be
readily   compared.     There  is   nothing
particularly unique  about this time horizon.
Nevertheless, it is sufficiently long that many
of the atmospheric processes currently thought
to affect concentrations  can  be considered
without  excessively weighting  longer-term
impacts on atmospheric processes that are not
well  understood.

      Using the GWPs presented in Table 2-3,
we can estimate the relative contribution of
each greenhouse gas to global warming for any
set of greenhouse gas emission estimates.  For
example, in  Figure 2-10b  we  present  the
contributions to global warming by greenhouse
gas using the global  emission estimates  for
each gas for the base year 1985 and the 100-
year GWPs.  For purposes of comparison we
also  have included the contributions to global
warming by gas for  the  1980s  based  on
estimates of  the  increase in  atmospheric
concentrations of each gas  during the 1980s
(Figure 2-10a; also presented in the Executive
Summary and Figure 2-1 based on Hansen et
al., 1988). Conceptually, the approaches used
here are quite different. Hansen et al. (1988)
base their  approach on the radiative forcing
effects  of estimated  differences  in atmospheric
concentrations between 1980 and 1990.  Since
only changes  in atmospheric  concentrations
are considered, Hansen's approach ignores any
portion  of  anthropogenic emissions  that
maintains  atmospheric   concentrations  at
previous  levels,  even  if  those levels  are
elevated above pre-industrial concentrations.
The use  of  GWPs measures the radiative
forcing effects of emissions for a single year, in
this case, 1985,  over a  100-year time frame;
this  approach   treats   all   anthropogenic
emissions as contributing to radiative forcing.
Differences occur  for several  other reasons,

           The  atmospheric concentration
changes  in Hansen et al.  (1988) include the
"decay"  of  CH4,  CO,  and  non-methane
hydrocarbons  (NMHC)  to  CO2  in  the
atmosphere.    The  contribution  of  CO2
concentrations during the 1980s will therefore
be  larger  than  the  change  due to  CO2

           Assumptions  about atmospheric
lifetimes  differ.    For  example,  the  IPCC
assumed CFC-11 had a lifetime of 60 years;
Hansen et al. (1988) assumed 75 years.  For
CFC-12 the IPCC assumed 130 years; Hansen
et  al.  assumed 150  years.7    Additionally,
atmospheric  lifetime  assumptions  are only
important to Hansen et al. to  the extent they
affect the atmospheric chemistry from 1980-90.

            The time period of the analyses
differ.   The GWPs are based  on emission
effects  over  a  100-year  time frame, while
Hansen et al. base their determination on the
estimated changes in atmospheric composition
over a 10-year period.

            The Hansen  et  al.  pie chart
(Figure  2-10a)  includes  the  impacts  for
stratospheric  water vapor and  tropospheric
ozone directly in the "Other" category; the pie
chart  using   100-year  GWPs  (Fig  2-10b)
includes these effects in the calculations of the
GWPs for the greenhouse gases, e.g., the GWP
for CH4 includes the effect that CH4 has on
the production  of  stratospheric water vapor
and tropospheric ozone.

 Policy Options for Stabilizing Global Climate

 1.     peta  = 1015, giga =  109, 1 ton =  106
 grams.  Thus, 1 petagram (Pg) = 1 gigaton

 2.     A radical is an atom or group of atoms
 with at least one unpaired electron, making it
 highly reactive.

1 Tg = 1 teragram = 10   grams.

1 Gg = 1 gigagram = 109 grams = 106
5.    The discussion here focuses on the use
of Global Wanning Potentials, where all gases
are compared relative to carbon dioxide. This
approach is used since, among  other things,
carbon  dioxide  is the largest contributor  to
radiative forcing. However, there is no reason
why another  gas could not  be used as the
common denominator, e.g., all gases could be
expressed on a methane-equivalent basis.

6.    The atmospheric lifetime of CO2  is
difficult to estimate due to the complex nature
of the carbon cycle.  Carbon dioxide is not
destroyed like many other gases, but can be
transferred to other reservoirs  such as the
oceans  or biota  and  then return  to the
atmosphere.  The IPCC used an approximate
lifetime of 120 years by explicitly integrating
results  of  the  box   diffusion  model  of
Siegenthaler (1983).

7.    Hansen et al. (1988) did not provide
atmospheric lifetime assumptions for all of the
greenhouse gases.

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gases.   In Isaksen, I.S.A.,  ed.  Tropospheric
Ozone.  D. Reidel, Hingham, Massachusetts.

Watson, R.T., M.A. Geller, R.S. Stolarski, and
R.F.  Hampson.    1986.   Present State of
Knowledge  of the  Upper Atmosphere:  An
Assessment   Report.     NASA  Reference
Publication 1162. Washington, D.C.  134 pp.

Watson, R.T. and Ozone Trends Panel, M.J.
Prather and Ad Hoc Theory Panel, and M.J.
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.

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.

WMO (World Meteorological Organization).
1990. Report of the International Ozone Trends
Panel.  Global Ozone Report No. 18. WMO,
WRI  (World  Resources
World Resources 1990-91.
Press, New York.
Institute).    1990.
Oxford University

                                                         Chapter II: Greenhouse Gas Trends
Zardini, D., D. Raynaud, D. Scharffe, and W.        Zimmerman,  P.R.,  J.P.  Greenberg,  S.O.
Seller.   1989.   N2O  measurements  of air        Wandiga, and P.J. Crutzen. 1982. Termites:  A
extracted    from   Antarctic   ice   cores:        potentially  large   source  of  atmospheric
Implications on atmospheric N2O back to the        methane,  carbon  dioxide  and   molecular
last glacial-interglacial transition. Journal of        hydrogen.  Science 218:563-565.
Atmospheric Chemistry 8:189-201.

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.

                                     CHAPTER III

                       CLIMATE CHANGE PROCESSES

     Climate exhibits natural  variability on
all  time scales,  from seasons 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 1.5-4.5C.  The
Interim Report of the Intergovernmental Panel
on Climate Change (IPCC) states:

      The evidence from the  modelling
      studies, from observations and the
      sensitivity analyses indicate that the
      sensitivity of global mean surface
      temperature to doubling CO2 is
      unlikely to lie outside the range 1.5
      to 4.5C ...  for  the  purpose  of
      illustrating the IPCC Scenarios, a
      value of 2.5C is considered to be
      the "best guess" in  light of current
      knowledge (IPCC, 1990, p. 145).

The largest factor contributing to these ranges
is uncertainty about how clouds will respond
to climate change.

     There are varieties of geochemical and
biogenic feedbacks  that  have generally not
been quantified in estimating 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 (CO2), 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 5.5C
for an  initial doubling  of CO2.   There are
biogenic and geochemical feedbacks that could
decrease greenhouse  gas  concentrations --
enhanced photosynthesis due to higher CO2,
for  example.    Although  many   of  these
feedback processes -- both those that  might
increase and  those  that  might  decrease
greenhouse  gas  concentrations - are poorly
understood, it seems likely that, overall, they
will  act to  increase, rather than  decrease,
greenhouse  gas  concentrations in a warmer

     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 is
already committed to a total warming of about
0.7-1.5C  relative  to  pre-industrial  times
(assuming  that  the  climate  sensitivity  to
doubling  CO2  is  2-4C).   The Earth has
warmed by 0.3-0.7C during the  last century,
which  is not inconsistent with  expectations
given the uncertain delay caused by ocean heat
uptake. The temperature record over the last
century,  however,  cannot  now  be used  to
confirm or refute specific model predictions.

 Policy Options for Stabilizing Global Climate

      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
 (see  CHAPTER  VI),  by  changes in  other
 climate 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  Earth's
 orbit,  changes  in 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 over the
 long  term.   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, upwelling 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
wanner global 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 (Ken, 1988).  Such variations of
the atmospheric and  oceanic circulation can
produce anomalous redistributions of energy
in  the  climate  system resulting in climate
variations with amplitudes and time scales that
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.

      To  place  in   context  the  potential
warming due to increasing greenhouse gas
concentrations, in this chapter we discuss the
magnitude and rate of past changes in climate
and the various factors that influence climate.
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 climate change. Regional climate and the
potential  impacts of climate 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).

                                                      Chapter III: Climate Change Processes

      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 in some regions,
changes  in the  number  and  location  of
stations, local temperature  changes due  to
growth of  urban  areas,  and  changes  in
instrumentation, Wigley et al. conclude that
the warming since 1900 has been in the range
of 0.3-0.7C.  The  most complete and up-to-
date  global surface air temperature record
available (Jones and Parker, 1990) is displayed
in Figure 3-la, which shows a global wanning
of about 0.3C from 1900 to 1940, a cooling of
about 0.1C from 1940 to 1975, and a warming
of about 0.2C from 1975 to 1989.   The six
warmest years in the  global record  occurred
during the 1980s: 1980,1981,1983,1987,1988,
and 1989.  The overall warming is similar in
the  land-air  temperature  record  of  the
Northern and  Southern  Hemispheres (see
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  consistent  with  the
increasing greenhouse gases during this period
(see  CHAPTER II), the  pre-1940 wanning,
which is greater than expected from increases
in greenhouse gas concentration during this
period, 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.   Data  for the
United  States, for  example,  show  that  it
warmed by about half as much as the globe as
a whole during the last century (Hansen et al.,
1989).   Because of past and potential future
emissions of greenhouse gases (see below and
CHAPTER VI), climate  changes during the
next century may be greater than the variations
shown for the past 100 years.

      Recent  climate variations are put in a
longer-term perspective in Figures 3-2 through
3-4. The amplitude of climate change over the
last millennium (see 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)  (see  Figures 3-3, 3-4)  with  globally
averaged temperatures  about 5C 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 5C, 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.  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
is predicted 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),
suggesting that  CO2  was   important  in
amplifying the relatively weak orbital forcings
during past climate variations (Genthon et al.,
1987; see Orbital Parameters below). 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.

 Policy Options for Stabilizing Global Climate
                                      FIGURE 3-1
                        SURFACE AIR TEMPERATURE
                                  (Degrees Celsius)
                            1860 1880 1900 1920 1940 1960 1980 2000
Northern Hemisphere
                    '850   1870   I8   1910   1930   1950   1970   1990
Southern Hemisphere
Figure 3-1.  (a) Global surface air temperature, 1856-1989, relative to the 1951-1980 average.  The
gradual wanning during this period is consistent 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 and Parker, 1990 -
Copyright  1990 by the AAAS.)

(b,c) Land surface air temperatures, 1851-1987 for the Northern Hemisphere and 1857-1987 for the
Southern Hemisphere.  Note the larger interannual variability before 1900, when data coverage was
much  more sparse. (Source:  Jones, 1988.)

                                                      Chapter III:  Climate Change Processes
                                       FIGURE 3-2
Figure 3-2.  Oxygen isotope (<518O) variations from ice cores in Greenland.  This is an index of
Northern Hemisphere temperature, with the maximum range equal to about 1C.  (Source:  record
of Dansgaard as given by Lamb, 1977.)
                                       FIGURE 3-3
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
temperature  swings is thought to be about 5C.  (Source:  Barnola et al., 1987.  Reprinted by
permission from Nature, Vol. 329, pp. 408-414.  Copyright  1987 Macmillan Journals Limited.)
                                       FIGURE 3-4
    0 0
    iTES  1234
                                                     11    12
                                 13  14   15  16  17    S	2C
200         300         403

Figure 3-4. Composite 518O 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 5C.

 Policy Options for Stabilizing Global Climate

      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 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 show
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; see Figure 3-3).

      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  insolation changes  have  only  been
available since 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 with
sunspot number and suggest an 11-year cycle
with an amplitude of 0.04% or 0.1 watts per
square  meter  (W/m2)  at  the  top of the
atmosphere  (Willson and Hudson, 1988).

Orbital Parameters

    Cyclic  changes  in  the  Earth's  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 latitudinal  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).


      Large  volcanic   eruptions    can
significantly  increase the stratospheric aerosol
concentration, increasing the planetary albedo
and  reducing surface temperatures by several
tenths of one 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

                                                      Chapter III:  Climate Change Processes
even be responsible for climate changes over
decades, and in fact  the warming shown in
Figure  3-1  from  1920  to   1940  may  be
attributable 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 carbon dioxide (CO2) and
methane (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
general  circulation model (GCM) studies of
climate change (Dickinson, 1984;  Sellers et al.,

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 of  the IR emitted
by the  surface  (analogous to the glass in a
greenhouse).   The energy absorbed by  the
atmosphere is then re-emitted in all directions,
and  the  downward half of this energy flux
warms the surface (see  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 climate change.  The amount of
water vapor, the dominant greenhouse gas, is
directly determined by climate and contributes
the largest positive feedback to climate 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 climate 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.

      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 the initial imposed forcing. In this
section, several of these mechanisms which are
internal  to the  physical  climate system are
discussed.  The next section describes several
recently investigated mechanisms involving the
planet's biology and chemistry.

 Policy Options for Stabilizing Global Climate
                                         FIGURE 3-5
1 / (Watts/Square Meter)
\^_ 1 Solar | Infrared 1
^ , / ' * *
340 \ 100 90 150 86
\ '
?phre 30 308
llXCO, !2XCO,
i 2 i 2 i

\ a i
\ I
\ 240 390 150 394 154
1 t f
^rr ^rr _i>~ 1X" >^
Earth's Surface ^^ ^^ ^^
'jy -'*' V" V' j/* s
RADIATION Shortwave Longwave
340 27 M 20 31 13* *
/ / / f f f
ATMOSPHERE ^\. Back:atterd / / ., , ' V^,
\\\ by A,r / / Net Ebm'"lon s+C ^V,
Absorbed by J \ \ V / / Water Vapor, Emission
Water Vapor. 66^ \ \ ., / / COj.Oj by Clouds
_ _ \ Reflected / z 3
Du"'3 \ by Clouds / Absorpt.on
\ \/ / &V Clouds i
/ \ _/*T^>-S / Water Vapor.
Absorbed by \ R.,,^ 1 "e" rlu*
Clouds \ by Surfae, Sensible
16< 390 340 24 82

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.)

                                                      Chapter III: Climate Change Processes
      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 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
(see Clouds below).

Water Vapor

      When  the   climate   warms,   the
atmosphere can hold more water vapor.  The
additional water vapor, which is a greenhouse
gas, amplifies the initial warming,  which in
turn results in 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  because of  meltwater
puddles  and debris  on  the surface.   This
reduced  albedo  causes  more energy to be
absorbed 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 it now appears that
the  thermal inertia feedback of sea ice plays a
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,
the  feedback 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 effect 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 respond directly and immediately
to changes  in climate and probably 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 determine 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 three
dimensions), the underlying  surface albedo,
and the time of day  and year of the changes.
The current net effect of clouds  is to cool the
planet, but  this does not imply that changes in
clouds will decrease the impact  of  higher
greenhouse gas concentrations (Ramanathan
et al., 1989).   Roeckner et  al. (1987) and
Somerville and Remer (1984) argue that the
liquid water content of clouds  will increase
with  warming,  substantially altering  their
optical properties.  A  comparison of recent
results with and without cloud optical property
feedbacks shows that including this mechanism
can increase or decrease total cloud feedback,
depending on related changes in other cloud
properties  (Cess  et  al.,  1989).   Overall, a
comparison of 14 GCMs found that the impact
of  cloud feedback  ranged from   a  modest
decrease in  climate sensitivity (30%) to a large
increase (150%)  (Cess et  al., 1989).


      In addition to the climatic processes
discussed above, a number of biogeochemical
feedback processes  will influence  future
concentrations  of  greenhouse gases  and
climate  change.   Increased  greenhouse gas
concentrations will alter not only the climate,
but also biogeochemical processes that affect
sources and  sinks  of  radiatively  important

 Policy Options for Stabilizing Global Climate
                                    FIGURE 3-6
                        (Based on 1.5-5.5 Degree Sensitivity)



   I  3.5
   S  3.0

   Q  2.5


      0.5  -

Figure 3-6. Equilibrium temperature changes from doubling CO2 (AT^) inferred from a review of
the strength of individual feedback processes in various climate models.   AT0 is the temperature
increase expected from doubling CO2 with no feedbacks. The subscripts w, s, and c, refer to feedbacks
due to water vapor and lapse rate, sea ice and surface albedo, and clouds, respectively. Each bar
shows the estimated two-standard deviation range of equilibrium global warming with the indicated
feedbacks included.  (Source:  adapted from Dickinson, 1986.)

                                                      Chapter III:  Climate Change Processes
gases.      Climatically   important  surface
properties,  such  as  albedo  and  evapo-
transpiration,   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
climate change, changes in marine biology, and
changes  in terrestrial  biology.    Potential
physical  effects of climate  change include
release of methane hydrates  and  changes in
ocean  chemistry,  circulation,  and  mixing.
Changes  in marine  biology  may alter  the
pumping of CO2 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 CH4  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  geothermal
temperature   gradient   (Kvenvolden   and
Barnard,   1984).   Estimates  of the total
quantity of CH4 contained  in hydrates range
from   2X103   to  5xl06   petagrams   (Pg)
(Kvenvolden, 1988). Given the climate change
associated with a doubling of CO2, Bell (1982;
as corrected by Revelle, 1983) estimated that
there could be a release of 120 teragrams
(Tg)  CH4  per  year  from  Arctic  Ocean
sediments,  and Revelle  (1983)  calculated
global  emissions of  640  Tg  CH4/yr from
continental slope hydrates.  These estimates,
however, are 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  meters)  alone
contains about as much carboji (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, e.g., 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 carbonate
chemistry, reduced mixing due to increased
stability of the thermocline, and the possibility
of  large-scale  reorganization  of  ocean
circulation and  biological activity.1

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

Policy Options for Stabilizing Global Climate
                                      FIGURE 3-7
                       TRACE GAS SOURCES
                                                                   TRACE GAS SINKS
                                          TRACE GAS CONCENTRATIONS
                  CLIMATIC CHANGE


                                                NATURAL ECOSYSTEM

Figure 3-7.   Schematic  diagram of biogeochemical feedback processes.   Changes in trace gas
concentrations produce  climate change, which may affect ocean CO2 uptake and  the  global
distribution  of  natural ecosystems.   Changes in ecosystem distribution  affect surface  albedo,
evapotranspiration, the terrestrial component of the carbon cycle (both CO2 and  CH4), and
agriculture.  Climate change can also directly affect these properties of the biosphere through the
temperature and precipitation responses of given ecosystems.  Global wanning may also lead to
methane emissions from hydrates  and changes  in  energy use.   Finally, changes in trace gas
concentrations, particularly CO2, directly affect natural and agricultural ecosystems.

                                                       Chapter HI:  Climate Change Processes
previous level, the impact of this feedback is
to increase atmospheric CO2 by about  1%/C
for a  typical scenario  (Lashof,  1989; see

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 RATE

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;  see Figure 3-2).  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  during  the next
century to  a climate  change of the  same
magnitude  as that which occurred between
glacial and interglacial periods, one must take
seriously the possibility of sudden changes in
ocean  circulation.  Should this happen, the
rate of CO2 uptake by the ocean could change
substantially. The oceans could even become
a CO2 source rather than a sink -- significantly
accelerating climate 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 time
(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 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

Changes in Terrestrial Biota

      The terrestrial  biota  interact   with
climate in a wide  variety  of important ways
(see 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 may also be globally important if
cloud properties are affected. Dickinson and
Hanson (1984)  analyzed  this problem  and
found  that the planetary  albedo was 0.0022
higher  at the  glacial  maximum   due  to
differences in mean annual vegetation albedo,

 Policy Options for Stabilizing Global Climate
an  increase of about 0.7% over the current
albedo of 0.3.  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.  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.

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 also plays an important
role in emissions of various other atmospheric
trace gases that are likely to be influenced by
climate 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, climate 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
(CO)   and    therefore   influences   the
concentration of the hydroxyl  radical (OH)
and the lifetime of CH4 (Mooney et al., 1987;
Thompson and Cicerone, 1986). As much as
0.5-1% of photosynthate 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
much greater.  Emissions, at least for isoprene
and a-pinene  are  exponentially   related  to
temperature (Lamb et al., 1987; Mooney et al.,
1987).   The  first-order impact  of climate
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).


      Of  the  feedbacks that will  come into
play during the next century, the largest will
almost  certainly   be  the  physical  climate
feedbacks  discussed earlier  (water  vapor,
clouds, ice cover, and ice and snow albedo). In
comparison, each  individual  biogeochemical
feedback discussed here is likely to be modest.
Because  feedback  systems  are non-linear,
however,  if the physical  climate  feedbacks
approach the positive end of their ranges, then
the overall sensitivity of the climate  system
would be substantially increased by  even small
additional feedbacks. If the physical feedbacks
are weak in   net,  then the  biogeochemical
feedbacks may be less significant.   Because
both   the  physical   and   biogeochemical
feedbacks are presently so poorly understood
and  because  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 biogeo-
chemical  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

                                                      Chapter III:  Climate Change Processes
vegetation  albedo  feedback,  for  example,
contributed only 0.3C out of the 3.6C 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  climate  change  on
biogeochemical  cycles  and  the  associated
feedbacks is needed.  Several aspects of the
impact  cf climate 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


      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 pre-industrial 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 ATjx (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  wanning that
will occur in  the future, even if there are  no
further increases in the forcing.  Thus, there is
certain to be some future climate response to
greenhouse  gases that were  put  into  the
atmosphere in the past, even if concentrations
were stabilized starting today. Another way of
saying this is that societal responses to the
greenhouse problem 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   AT2X.
Unfortunately,  our knowledge of both past
climate change and  the responsible forcings
are too poor to reliably determine AT2X 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 AT2x
would be approximately 2C.  If however, one
allows for other  possible forcings,  natural
variability, uncertainties in ocean heat uptake
and   the   transient  response,   and  for
uncertainties in pre-industrial greenhouse gas
concentrations (see below; Hansen et al., 1985;
Wigley and Schlesinger,  1985; Wigley et al.,
1986; Wigley, 1989), then the climate record of
the last 100 years  is consistent with any AT^
between   0  and   6C   (Wigley,   pers.

      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 Box  3-1. 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 all the
important physical interactions, especially with
atmospheric   circulation,   fully  three-
dimensional  GCMs  are necessary.   These
sophisticated  models  solve   simultaneous
equations for the  conservation of  energy,

Policy Options for Stabilizing Global Climate
                          BOX 3-1.  Simplified Modeling Framework

      The concepts discussed in this chapter can be summarized in a simple zero-dimensional
      or one-box model of climate as discussed by Dickinson (1986):
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 in CLIMATE
      tropospheric/mixed-layer temperature from the pre-industrial 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
      AT = AQ/A.
      For a doubling of CO2, AQ is about 4.3 W/m2, so the range 1.5-5.5C of AT^ discussed
      above corresponds to a range of 2.9-0.8 W m"2 C"1 in A.  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 VI and APPENDIX A).
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, 1985). Perhaps the
most important differences lie in the treatment
of oceans, ranging from prescribed sea surface
temperatures, to "swamp" oceans with mixed
layer thermal capacity but no heat transport,
to mixed layers with specified heat transport,
to full oceanic GCMs.
                    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  (AT^) is probably in the range of 1.5
               to 4.5C. 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 1.5-5.5C.  The GCM
               result of Wilson and Mitchell (1987) giving
               AT?x = 5-2c 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

                                                      Chapter HI:  Climate Change Processes
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 AT2X  is not known,
we can study the potential  impact of climate
warming caused by  greenhouse  gases  by
choosing scenarios  that  span  the range  of
theoretical calculations. Thus, we adopt 2-4C
as  a  putative  one-standard deviation  (la)
confidence interval  about the center of the
range proposed by the National Academy of
Sciences, and the range proposed by Dickinson
(1.5-5.5C)  as  2a  "bounds for  subsequent
modeling  (see  CHAPTER  VI).   When  the
biogeochemical feedbacks discussed above are
also considered, a AT2X as great  as 8-10C
cannot be ruled out (Lashof, 1989).


      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 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 one-fortieth 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 time 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  models  are
calibrated with data on the penetration  of
tracers such as tritium  and carbon-14  (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   14C  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 (Upwellmg-Diffusion

 Policy Options for Stabilizing Global Climate
or UD model), has been used by Hoffert et al.
(1980), Harvey and  Schneider (1985),  and
Wigley and Raper (1987). The addition of an
upwefling 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 time, r, of BD models is
proportional to  /c(AT2x)2, 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 /c = 1-2
cm2/s  (Hansen  et al.,  1985).   Hoffert  and
Flannery (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  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  (2-4C)
in  the equation  derived by  Wigley  and
Schlesinger  (with their recommended values
for other parameters) yields T = 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  levels,  the Earth
would still be  subject to significant  climate
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    UD   models
demonstrate the importance  of the bottom-
water formation process for the rate of ocean
heat uptake.  The  impact of  using an UD
ocean model rather than a BD 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
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

     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 climate change. Work at
the NASA Goddard Institute for Space Studies
(Hansen et al., 1988) has produced one of the
few   three-dimensional,   time-dependent
analyses  of  climate 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  wanning is  initially  most
prominent relative  to interannual variability
are  not  necessarily   those  where    the
equilibrium wanning is greatest. For example,
low-latitude ocean  regions  warm  quickly

                                                       Chapter III:  Climate Change Processes
 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.


      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,
 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.

1.    The thermocline starts at the base of the
mixed layer and extends to a depth of about
1000 m. 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.
2.    Ii is important to note that the actual
response does not correspond to exponential
decay with a single time constant, so that while
r gives the 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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                                    CHAPTER  IV

                      HUMAN ACTIVITIES AFFECTING
                        TRACE GASES AND CLIMATE

      Various  human activities  affect  the
Earth's  climate by altering the level of trace
gases in the atmosphere.   These activities
include   fossil-fuel  consumption;  industrial
processes;   land-use   change,   particularly
deforestation; and agricultural practices such
as   waste   burning,   fertilizer   use,   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 shrank 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 (CO2) and other radiatively important
gases and is  the primary cause of the buildup
of  greenhouse   gases  in  the  atmosphere.
Commercial  energy  consumption currently
accounts for more than 5  of the 6-8 billion
tons of carbon  as   CO2  emitted to  the
atmosphere  annually  from  anthropogenic
sources  (i.e., as  a result of human activities).
Between 1950 and 1986, annual global fossil-
fuel  consumption  grew 3.6-fold  and  annual
CO2 emissions grew 3.4-fold.

     Emissions of other trace gases  due to
fossil-fuel consumption are more uncertain.
Approximately 0-2 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  20-50
million tons methane  (CH4) annually to the
atmosphere,  and  coal  mining  contributes
approximately 25-45 million tons CH4.
      Three significant non-energy sources of
 greenhouse gases are associated with industrial
 activity:  production and use of chlorofluoro-
 carbons (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,  to   reduce   future
 production of certain CFCs and limit growth
 in the production of certain halons,  came into
 force on  January 1,  1989.   The London
 Amendments, negotiated  in  June  1990,
 strengthen the Protocol by completely phasing-
 out CFCs, halons, carbon tetrachloride, methyl
 chloroform, and encouraging limits on HCFCs.
 Anaerobic decay  of organic wastes in landfills
 currently  contributes  approximately  30-70
 million  tons  of CH4  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   CO2   emissions   to   the
 atmosphere, i.e.,  between 0.4 and 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 CH4 emissions  to the  atmosphere;
continued  changes   to  wetlands   could
significantly alter  the  global CH4 budget.
 Biomass burning, in addition to contributing
 to  atmospheric  concentrations   of CO2
contributes approximately 10-20% of total
annual CH4 emissions,  5-15% of the  nitrous
oxide emissions, 10-35% of the nitrogen oxide
emissions,  and  20-40% of  the  carbon
monoxide emissions.

Policy Options for Stabilizing Global Climate
     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  CH4  as a  by-product of  enteric
fermentation,   currently    contribute
approximately 65-85  million  tons  of CH4
annually.   Over  the  past  several  decades,
domestic animal populations have grown by up
to 2% annually.  Methane is also produced by
anaerobic decomposition of organic  material
in rice paddies. Currently, about one-fifth of
annual CH4 emissions, or between 60 and 170
million tons, comes from rice cultivation. Rice
production has grown rapidly since the mid-
1900s due to increases 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 climate  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.

                                                               Chapter IV:  Human Activities

      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,  animal  husbandry,   rice
cultivation,  and  nitrogenous fertilizer use).
Population growth is an important underlying
factor  affecting the level  of  growth in each

      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 regional
contributions to the increase in greenhouse
forcing that occurred in the  1980s.  Almost
50% of the forcing is attributable to activities
in the United States, the  USSR,   and  the
European Economic Community (EEC).  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 VI.

      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 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  in 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). 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.  Unfortunately, the countries that are
experiencing the  most explosive  population
growth rates are often the ones likely to suffer
the most severe environmental stresses due to
climate  change and  the  ones least able to
adapt to or accommodate these effects.

 Policy Options for Stabilizing Global Climate
                                   FIGURE 4-1

                     Regional Contribution to Greenhouse Forcing


  Rest of the World (36%)
 United States (21%)
   Japan (4%)
                                                                  USSR (12%)
         India (4%)
                Brazil (5%)
EEC (11%)
                                China (7%)
Figure 4-1. Estimated regional contribution to greenhouse forcing for the 1980s, based upon regional
shares of current levels of human activities that contribute to greenhouse gas emissions.  (Sources:
U.S. EPA, 1988; 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.)

                                                     Chapter IV:  Human Activities
                                  FIGURE 4-2

      4  -
      3  -

      2  \-
                                            North America
                                              & Oceania

                                            Latin America


                                            Europe & USSR
1800      1850      1900
1950   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.)

Policy Options for Stabilizing Global Climate
                                        TABLE 4-1

                              Regional Demographic Indicators
North America
East Asia
Southeastern Asia
Latin America
Southern Asia
Western Asia
Total Fertility3
Infant Mortality6
Annual Population
Growth Rate
 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.

b The infant mortality rate is the average number of infant deaths (deaths before the first birthday)
per 1000 live births.

Source: Adapted from IIED and WRI, 1987.

                                                               Chapter IV: Human Activities
Industrialized Countries

      Population   growth   rates   in   the
industrialized countries are substantially lower
than 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 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
population  (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 in  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;  for  example,  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
in 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 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;  Zachariah  and
Vu,  1988; see CHAPTER VI) project that by

 Policy Options for Stabilizing Global Climate
 2025,   Latin   America's   share  of  world
 population  will  grow  to  9.1% and  8.7%,


      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   (CO2)   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,
 i.e., nitric oxide [NO] and nitrogen dioxide
 [NO2]), and nitrous oxide (N2O)/

      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.

 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, 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.   Since  1950,  global
primary  energy  consumption  has increased
nearly fourfold (see 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 in 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 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 (Rotty,
1987).  Currently fossil-fuel  combustion  also
contributes  approximately 0-2 teragrams  of
nitrogen (Tg N) as N2O, 20 Tg N as NOX and
180 Tg C as  CO to the atmosphere each year.

      In recent decades there has also been a
significant shift in 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

                                                  Chapter IV: Human Activities
                                FIGURE 4-3
                              1950- 1985
       250  -
                                                            Natural Gas
                                                            Liquid Fuels
                                                            Solid Fuels
          1950  1955  1960  1965   1970   1975  1980  1985
     * Data Is for commercial energy only; blomaes Is not Included
Figure 4-3. Global demand for fossil fuels has more than tripled since 1950. Ibday, about 85% of
the world's energy needs are met by fossil fuels. (Sources: United Nations, 1976,1982,1983,1987.)

Policy Options for Stabilizing Global Climate
                                  FIGURE 4-4

                             (Petagrams Carbon/Year)

         5 -
         4 -
3  -
                                                                  Natural Gas
Figure 4-4. Carbon dioxide emissions from fossil-fuel consumption have grown from less than 0.1 Pg
C in the mid-1850s to approximately 5.4 Pg C in 1986. This is the major reason why the atmospheric
concentration of CO2 increased from approximately 290 ppm in 1860 to approximately 348 ppm in
1987.  (Sources:  Rotty and Masters, 1985; Rotty, 1987, pers. communication.)

                                                 Chapter IV: Human Activities
                               FIGURE 4-5

      300  -
      250  -
   S  200
   5  150
       100  -
         1950  1955  1960  1965   1970  1975  1980  1985

Figure 4-5. Primary energy use by region. Between 1950 and 1985, the share of global energy demand
for the OECD declined, while that for the centrally-planned and developing economies increased.
(Sources: United Nations, 1982, 1987.)

Policy Options for Stabilizing Global Climate
proportion of energy consumed by the OECD
is expected to decline further as the developing
world  continues  to experience  more rapid
population growth and economic development
and,  thus, significantly  expands its  energy
requirements (see CHAPTER VI).

Current Energy-Use Patterns and Greenhouse
Gas Emissions

      The allocation of energy consumption
among  end-use  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-thirdresidential/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
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

      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  powerplants  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 example, when natural gas is
used as the fuel, combined cycle units produce
about 40% lower CO2 emissions than  simple
cycle units (see CHAPTER V) because of the
greater generating efficiency obtained through
the use of these technologies. 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.

                                                     Chapter IV: Human Activities
                                  FIGURE 4-6


19.0 ^rVV^^^ 27.0


Figure 4-6.  End-use energy demand by sector for three global regions. While energy demand in the
OECD countries is split almost equally among the three sectors, over 50% of the energy in 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.)

 Policy Options for Stabilizing Global Climate
                                             TABLE 4-2

                                Emission Rate Differences by Sector

                                       (grams per gigajoule)*
Electric Utility (g/GJ delivered electricity)
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
Industrial (g/GJ delivered steam for boilers; energy output
Residual Oil-Fired
Natural Gas-Fired
Kilns - Coal
Dryer - Natural Gas
Dryer - Oil
Dryer - Coal
Residential/Commercial (g/GJ energy
Wood Stoves
Coal Stoves
Distillate Oil Furnaces
Gas Heaters
Wood Boilers
Gas Boilers
Residual Oil Boilers
Coal Boilers
Transportation (g/GJ energy input)
Jet Aircraft
Light Duty Gasoline Vehicle
Light Duty Diesel Vehicle
Light Duty Compressed
N. Gas Vehicle



for others)




















*  All emission rates are based on total molecular weight.

NA = Not Available
[ ] = No Net CO2 if based on sustainable yield

Source:  Radian Corporation, 1990; except N2O data, which is based on unpublished EPA data.  N2O emission
        coefficients are highly uncertain and currently undergoing further testing and review.

                                                               Chapter IV:  Human Activities
      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  machine
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

     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.

     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

     Other - This category consists primarily
of industrial activities requiring electricity, e.g.,
motors  and  lighting.    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

      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.

      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

Policy Options for Stabilizing Global Climate
                                        TABLE 4-3

                          End-Use Energy Consumption Patterns for
                             the Residential/Commercial Sectors

                                    (% of total energy)
South/Southeast Asia
United States



Type of Energy
Fossil Fuels







Sources:  Sathaye et al., 1989; Mintzer, 1988; EIA, 1987; Leon Schipper, pers. communication.

                                                               Chapter IV: Human Activities
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

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.

      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.  The amount of
natural gas  flared  and vented  is   highly
uncertain.  On  average, it is estimated to  be
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   (EIA,  1986).9      Currently,
approximately 50 Tg of CO2 are released to
the atmosphere from flaring of natural gas
(Rotty, 1987)/"
      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 is released
to the atmosphere each year from leaking and
venting  of  natural  gas   (Crutzen,  1987;
Cicerone and Oremland, 1988).

      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
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,  1988).    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 Irends

      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

 Policy Options for Stabilizing Global Climate
                                        TABLE 4-4

                       Carbon Dioxide Emission Rates for Conventional
                                    and Synthetic Fuels
CO2 Emission Rate
    (kg C/109J)
  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
                     Differences are partly attributable to
                     product mix, i.e., gasoline versus fuel
                     oil and gasoline
 Synthetic Fuels (rates for production and consumption)

   Shale Oil                             104.3
   Liquids from Coal
   High Btu Gas from Coal


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
Generic 75% thermal efficiency
SRC-II, liquid and gas products

Generic 66% thermal efficiency
Via synthesis gas with by-product
Source:  Marland, 1982.

                                                               Chapter IV:  Human Activities
main factor  that has led to an  increase in
atmospheric CO2 concentrations -- from about
280 parts per million by volume (ppm) in pre-
industrial periods to about 350 ppm today. As
discussed   in   Chapter  II,   future   CO2
concentrations will depend on  many factors,
but most important will be the rate of growth
in energy demand and the type of energy that
is consumed in 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 mineral supply;  a  reserve is a
mineral supply that is known with a  high
amount of geologic certainty. A reserve may
or may not be presently economical to extract;
if not, it is likely to become economical in the
future. The estimates of the lifetimes of fossil-
fuel reserves  are  based  on 1985  rates  of
production.  The lifetime estimates of fossil-
fuel resources  are  based  on  linear  and
exponential  extrapolations of recent  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 long time. As will
be  discussed  in Chapter VI,  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 available  (see
CHAPTER VI). 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  (see Tkble 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 terawatts
(TW) (or equivalently about 8000 exajoules
[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.


      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  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.

Policy Options for Stabilizing Global Climate
                                         TABLE 4-5

                          Estimates of Global Fossil-Fuel Resources9

Resource Lifetime (Years)

a Resources estimates, as of 1985, are from the World Energy Conference (1980), adjusted for global
production from 1979-85. Reserve estimates are from EIA (1986); oil and gas estimates as of January
1, 1986; and coal estimates as of 1981.

b Based on 1985 rates of production.

c Includes estimates for the Middle East and USSR.

Sources: World Energy  Conference, 1980; United Nations, 1983, 1987; EIA,  1986.

                                                     Chapter IV:  Human Activities
                                  FIGURE 4-7

     6000  -
     5000  -

     3000  -
     2000  -
     1000  -
                	Exponential Growth
1970       1990       2010
Figure 4-7.  Two hypothetical cases of future energy demand.  The upper case is based on an
exponential extrapolation of the average annual growth rate in energy demand between 1950 and 1973,
a period of rapid growth in demand. The lower case is based on a linear extrapolation of the average
annual growth rate in energy demand between 1973 and 1985, when the growth rate was much lower.
These two cases illustrate potential upper and lower bounds on future energy demand. (Sources for
historical data: United Nations, 1976,1982, 1983, 1987.)

 Policy Options for Stabilizing Global Climate
 Chlorofluorocarbons, Halons, and

 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 in 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  time  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.

      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  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
 methyl  chloroform.   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.  Methyl
 chloroform  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
 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 methyl chloroform  in  1985
 was estimated at nearly 1029 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 703.2 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,

                                                                Chapter IV:  Human Activities
                                          TABLE 4-6

                             Major Halocarbons:  Statistics and Uses

CFC-11 (CC13F)
CFC-12 (CC12F2)
HCFC-22 (CHC1F2)
CFC-113 (C^CljF^
(parts per Atmospheric
trillion by Lifetime
volume) (Years)

226 75 +l]
392 lll^2
80 (1985) 15
30-70 90

Current Annual
Growth Rates Major
(%/yr) Uses

4 Aerosols,
4 Aerosols, Foams,
7 Refrigeration,
11 Solvents
Halons (Bromofluorocarbons)
Halon 1211 (CBrClF2)
Halon 1301 (CBrF3)
Carbon tetrachloride
Methyl chloroform
-2 25
-2 110

75-100 -40

125 61
>10 Fire
>10 Fire

1 Production of
CFC-11 and
5 Solvents
Sources:  U.S. EPA, 1988; Hammitt et aL, 1987; Wuebbles, 1983; WMO, 1985.

   Policy Options for Stabilizing Global Climate
                                    FIGURE 4-8



           800 -
           700 -
           500 -
              1960      1965
                                        * Dashed line* Indicate estimates

                                   I      	I	I	
1970     1975     1980     1985

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.)

                                                                  Chapter IV:  Human Activities
                                           TABLE 4-7
                               Estimated 1985 World Use of Potential
                                    Ozone-Depleting Substances

                                           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
Methyl chloroform          544.6            270.0            186.7                  87.0
Source: Hammitt et al., 1986.

 Policy Options for Stabilizing Global Climate
                                FIGURE 4-9
              1985 CFC-11  AND CFC-12 PRODUCTION/USE
                        FOR VARIOUS COUNTRIES
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, 1988.)

                                                               Chapter IV:  Human Activities
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 action on 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  Montreal Protocol came  into force on
January 1, 1989, and has been ratified by 68
countries, representing just  over 90%  of
current  world  production of these chemicals
(as of February 1, 1991).  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
VI).     In June  1990  the  Protocol  was
strengthened by the  London Amendments
calling for a complete  phase-out of CFCs,
halons,   carbon  tetrachloride  and methyl
chloroform and a non-binding resolution to
phase out HCFCs.

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

      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
not  collected  [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  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, have 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.

 Policy Options for Stabilizing Global Climate
      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 comes 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

 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 also increased.  Between 1950
 and   1985,   CO2  emissions  from  cement
 manufacture grew from 18 to 134 Tg C/yr (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 (round, marble-sized
particles),  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 1595C), and clinker is
produced. It is during the calcination process,
 which occurs at approximately 900 to 1000C,
 that the limestone (CaCO3) is  converted  to
 lime (CaO) and CO2, and the CO2 is released.
 For  every  million'  tons  (Tg)  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
 tons of cement produced from fossil fuel used
 for kiln firing and electricity generation. 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 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
 shirts  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 GNP for some

      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  NOr 16  Destruction of
wetlands, from either filling or dredging, can
alter the atmospheric CH4 budget, since

                                                            Chapter IV:  Human Activities
                                      TABLE 4-8

                        Refuse Generation Rates in Selected Cities
                                                              Per Capita
                                                          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, Tbnisia                                             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.

 Policy Options for Stabilizing Global Climate
                                       FIGURE 4-10

+ A f\
! 100
o 80
2 60


(Teragrams Carbon/Year)
! I I I I I
50 1955 1960 1965 1970 1975 1980 19


Figure 4-10. Carbon dioxide emissions from cement production grew from 18 to 134 Tg between 1950
and 1985, an average annual rate of growth of about 6%.  (Sources:  Rotty, 1987;  U.S. BOM, 1949-
1986, selected years.)

                                                 Chapter IV:  Human Activities
                               FIGURE 4-11


                           (Thousand Metric Tons)




       100  -
           1951  1955    1960   1965   1970   1975   1980   1985


i	|

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,

1949-1986, selected years.)

 Policy Options for Stabilizing Global Climate
 anaerobic decomposition in wetlands produces


      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  in 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 (Mha) per
year, or 1.4% per year  (FAO, 1986b).17  The
 U.S. Forest Service (Alig, 1989) estimates that
 between 1977 and 1987 the area of U.S. forests
 decreased by approximately 0.41 Mha per year,
or 0.14% per year.

      Currently,   it   is   estimated   that
approximately 11.3 Mha of tropical forests are
lost  each  year,  while  only  1.1  Mha  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  Mha 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 (see CHAPTER V). 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 through fuelwood burning.  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

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
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, savanna burning, and burning  of
agricultural wastes, is estimated to account for
over 70% of the biomass burned annually (see

                                                    Chapter IV:  Human Activities
                                FIGURE 4-12
                    NET RELEASE OF CARBON FROM

                       TROPICAL DEFORESTATION

                             (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, Colombia, the Ivory Coast, Thailand, and Laos. (Source:
Houghton et al., 1987.)

 1'olicy Options for Stabilizing Global Climate
                                                              TABLE 4-9

                                                        Land Use:  1850-19803
                                                             	   1850 to
                                1850   1860  1870   1880  1890   1900  1910   1920  1930   1940   1950  1960   1970  1980    1980
                                   Area (million hectares)
 Forests and Woodlands
 Grassland and Pasture
5,919  5.898  5.869 5,833  5.793  5,749  5,696  5,634  5,553  5,455  5,345  5.219  5,103  5,007     -15
0.350  0.340  6.329 6,315  6,301  6,284  6,269  6.260  6,255  6,266  6,293  6.310  6,308  6.299      -1
  538   569   608   659   712   773   842   913   999  1,085  1,169  1.278  1.396  1,501    179
 Tropical Africa
 Forests and Woodlands
 Grassland and Pasture
1,336   1,333  1,329  1,323  1,315   1,396  1,293  1,275  1.251  1,222  1,188  1,146  1,106  1,074     -20
1.061   1,062  1.064  1,067  1.070   1,075  1,081  1,091  1,101  1,114  1,130  1,147  1.157  1.158      9
   57     58     61     64     68     73    80     88   101    118   136    161   190    222    288
 North Africa and Middle East
 Forests and Woodlands
 Grassland and Pasture
  34     34    33     32    31     30    28     27    24     21     18     17    15     14     -60
1,119  1,119  1,118  1,117  1,116   1,115  1,113  1,112  1,108  1,103  1,097  1,085  1,073  1,060      -5
  27     28    30     32    35     37    40     43    49     57     66     79    93    107    294
North America
Forests and Woodlands
Grassland and Pasture
Latin America
Forests and Woodlands
Grassland and Pasture
Forests and Woodlands
Grassland and Pasture
South Asia
Forests and Woodlands
Grassland and Pasture
Southeast Asia
Forests and Woodlands
Grassland and Pasture
Forests and Woodlands
Grassland and Pasture
Forests and Woodlands
Grassland and Pasture
Pacific Developed Countries
Forests and Woodlands
Grassland and Pasture
























































































































a These three categories refer to aggregate data from eleven categories of natural land cover.  Land areas covered by snow, ice, rock, or desert are the only
categories not included here.
Source:  IIED and WRI, 1987.

                                                              Chapter IV: Human Activities
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 in  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  Mha
producing this CH4, 39% is  forested bog, 17%
is  nonforested  bog, 21% is forested  swamp,
19% is nonforested swamp,  and 4% is alluvial
formations.18  The bulk of the bog acreage is
located between 40N and 70N, while swamps
predominate between 10N and 30S. Alluvial
formations are concentrated between 10N and
40S (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).

      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 50N and 70N, and about
25% between 20N  and 30S. 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 Mha, 97%  of which
occurred in inland  freshwater areas  (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 develop 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).


     Three agricultural activities contribute
directly   to    atmospheric   emissions   of
greenhouse gases:   enteric  fermentation in
domestic animals, rice cultivation, and use of
nitrogenous fertilizer.20  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 1661 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

    Policy Options for Stabilizing Global Climate
                                             TABLE 4-10

                             Summary Data on Area and Biomass Burned
 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

21-62 (41)*

8.8-15.1 (12.0)


4.0-6.5 (5.4)

2.0-3.0 (2.5)
630-690 (660)
     9-25 (17)

     5.5-8.8 (7.2)


     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.

                                                       Chapter IV: Human Activities
                                   FIGURE 4-13
       1200  i
        400  '
        200  I
               BON  70   60   60   40   30   20  10
                                                       10   20   30  40   SOS
               80N   70   60   60   40  30   20   10   0   10  20   30  40   608
     \/l Alluvial

     s -V'
     \\i Nonf or*td wmp
Forested swamp

Nonf orat*d bos
Forottod bog
Figure 4-13.  Estimated latitudinal distribution of wetland area (top)  and  associated methane
emissions (bottom).  Forested and non-forested bogs located between 40 and 70N account for
approximately 50% of the current CH4 emissions from wetlands. (Source:  Matthews  and Fung,

 Policy Options for Stabilizing Global Climate
 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 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 of  organic
material  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, 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.21  Between 1950 and
1984, rough rice production grew from 163 to
470  million tons, nearly a  200% increase.22
During  the  same time, harvested rice paddy
area increased approximately 40%, from 103 to
148 Mha,  and average  global yields doubled,
from  1.6 to 3.2  tons per ha (IRRI,  1986).25
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 fertilizer 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, in order  to increase yield, more
organic matter is incorporated into the paddy

      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 per
year to the atmosphere, or approximately 20%
of the global flux (Cicerone and  Oremland,
1988).  This  estimate is  highly  uncertain
because there have been no comprehensive
rice-paddy  flux measurements  in the major
rice-producing countries in Asia.

                                                    Chapter IV:  Humnn Activities
                                FIGURE 4-14

                                                              x	Goats
                                                             x    !
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.)

 Policy Options for Stabilizing Global Climate
                                   FIGURE 4-15
                         ROUGH RICE PRODUCTION
                                   (Million Tons)
             Rest of World

                                               India (91.0)
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.)

                                                       Chapter IV:  Human Activities
                                   FIGURE 4-16
                            RICE AREA HARVESTED
                                  (Million Hectares)
           Rest of World
Figure 4-16.  Distribution of the total harvested rice paddy area of 148 Mha. Five Asian countries,
India, China, Bangladesh,  Indonesia, and Thailand, accounted for 73% of the 1984 rice acreage
harvested. (Source: IRRI, 1986.)

 Policy Options for Stabilizing Global Climate
 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.  Fjcperiments  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.

      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).


      Climate  change  will   affect   human
 activity in a myriad of ways, and thus influence
 anthropogenic emissions of greenhouse gases
 of climate change on land-use patterns and
 agricultural practices could  be particularly
 significant  in  influencing  the  trace gas
 emissions  from these sources.   For example,
 increases  in  the frequency and  severity  of
 droughts in farm  belt  regions will increase
 irrigation   needs   and  associated   energy
 requirements,  resulting in  increased  energy
 emissions.  However, the magnitude (or even
 the direction) of such changes  have not been
 examined   to  date.   More  information  is
 available  regarding  the  impact  of  climate
 change  on electric  utilities (Linder  et al.,
 1987).   A  brief  discussion  of  this subject  is
 presented here as an illustration of some ways
 in which climate change can, in turn, influence
 trace gas emissions.

      Linder  and Inglis (1989)  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 of this
equipment,  then   substantially  greater
sensitivities are possible (Linder et al., 1987).
Currently,  37% of total CO2 emissions from

                                                              Chapter IV: Human Activities
                                        TABLE 4-L1

                          Nitrous Oxide Emissions by Fertilizer Type
Fertilizer Type
Percent of Nitrogenous Fertilizer Evolved as N-,0
Anhydrous Ammonia

Ammonium Nitrate

Ammonium Type


              0.5 to 6.84

              0.04 to 1.71

              0.025 to 0.1

              0.067 to 0.5

              0.001 to 0.50
Source: Eichner, 1988; Galbally, 1985.

 Policy Options for Stabilizing Global Climate
                                  FIGURE 4-17

                           (Million Metric Tons Nitrogen)
                         Poland (1.2)
                 Indonesia (1.3)  \   Mexico (1.2)
              Canada (1.:
    West Germany (1.!
United Kingdom (1.6)

     France (2.4)
    India (5.7)
                                                           Rest of World (18.9)
  Soviet Union
                                                             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 N2O emissions is
attributed to nitrogenous fertilizer consumption.  (Source: FAO, 1987.)

                                                               Chapter IV:  Human Activities
fossil fuels are produced by electric utilities,
and  this share  is expected to increase in the
future (see CHAPTER VI).  Applying the U.S.
average  sensitivity  of  1.0%/C  obtained  by
Linder  and Inglis (1989)  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
powerplant, 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 powerplants. 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,

      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  generation  of
electricity.   (This change would also  affect
barge snipping,  since many  rivers would
become  unnavigable, and result in increased
trace gas  emissions   from   truck  and  rail

      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,  possibly
causing  the water to become too  corrosive to
be used as a coolant.   A few powerplants in
the United States  use  salt water for cooling
purposes, so the technology to adapt to more
saline  coolants  does  exist,  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 climate change on
anthropogenic   trace  gas  emissions  may
nevertheless prove to be important and should
be investigated further.

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.

2.    Throughout the report these gases are
often referred to as greenhouse gases, although
strictly  speaking,  CO  and  NOX are  not
greenhouse gases since they do not  directly
affect radiative forcing (see CHAPTER II).
However, these two gases indirectly affect
greenhouse forcing  due  to their chemical
interactions  with   other  gases   in   the
troposphere.  As a result, for simplicity,  we
shall refer to them as greenhouse gases.

3.    In  some  developing countries,  the
dependence on biomass can approach 95% of
total energy requirements.

4.    Non-commercial biomass estimates are
not included in these figures.
      In 1986 CO2 emissions from fossil fuels
were approximately 5370 million metric tons
C, or 5.37 Pg C.  1 billion  metric tons = 1
                   " grains.
gigaton = 1 pg = 1015
6.    The OECD countries include Australia,
Austria, Belgium, Canada, Denmark, Finland,
France, the German Federal Republic, Greece,
Iceland, Ireland, Italy, Japan, Luxembourg, the
Netherlands, New Zealand, Norway, Portugal,
Spain,  Sweden,  Switzerland,  Turkey,  the
United Kingdom, and the United States.

 Policy Options for Stabilizing Global Climate
 7.     1 GJ = 1 gigajoule = 109 joules. 1055
 joules = 1 Btu.

 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

 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

 10.    1 TR =  1  teragram =  million  metric
 tons = 10   grams.

 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.

 12.   1 Gg = 109 grams = 106 kg.

 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).

 14.   1 ton = 1 metric ton =  1000 kg.

 15.   The U.S. is currently a net importer of
cement; the volume of its imports has grown,
 representing  only  a  small   percentage  of
consumption in the early 1980s but as much as
 18% in 1986  (ITA, 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  for  a long
 enough period of time, there are no net CO2

 17.    1 ha = 1 hectare = 2.471 acres.

 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.

 19.    For  example,  drainage  of  prairie
 potholes in 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.

 20.    Emissions due to energy requirements in
 agriculture, such  as energy use for irrigation
 equipment  and  other  farm  machinery, are
 accounted for as  part of industrial energy use

 21.    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.

 22.    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.

 23.    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.

Alig, R.J. 1989.  Projecting land cover and use
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Assessment. Forest Service, \\fcshington, D.C.

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                                     CHAPTER  V

                       GREENHOUSE GAS EMISSIONS

     A number of technical changes which
could reduce sources of greenhouse emissions
are believed likely to be feasible at reasonable
economic  costs.   No  single  technology or
small  set  of  technical  options  offers "a
solution" to greenhouse gas emissions.  Only
by aggregating  the effects of many technical
opportunities over a long time can significant
reductions  in  greenhouse gas emissions be
achieved. This chapter highlights options that
appear  to   be  "relatively   cost-effective."
Detailed analysis necessary to quantify total
costs  of   the   measures   has  not  been

     Improvements   in   end-use  energy
efficiency provide the best option for reducing
carbon dioxide (CO2) emissions over the next
few decades. Reductions in energy use would
also reduce emissions of  methane  (CH4),
nitrous oxide (N2O), nitrogen oxides (NOX),
and  carbon monoxide  (CO).   Examples of
potential efficiency improvements  are:

           Transportation    50 mile per
gallon automobiles are  technically  feasible
with currently-available technology.  Further
improvements could increase fuel efficiency to
more than 80 miles per gallon.  What effects
these changes  would have  on size,  safety,
performance, cost, and other desirable  product
characteristics need to be carefully  considered.
In addition, major improvements  in the fuel
efficiency of diesel trucks, rail transport, and
aircraft are possible.

           Residential and Commercial - By
2025  accelerated improvements in building
shells,  lighting,  space  conditioning,  and
appliances could reduce energy consumption
per square  foot by 75% below current levels
for residences,  and by 50%  for commercial
buildings.     The   rate  at   which  such
improvements would find market  acceptance
both in increases in the building stock and in
retrofitting or replacing the existing building
stock is dependent on  a number of complex
economic factors, including the costs  of such
improvements,   and   therefore   is   quite

            Industrial  Energy    Advanced
industrial processes for energy-intensive basic
materials, recycling of used  basic materials
(i.e.,    steel,    aluminum,    and    glass),
cogeneration, and  improved  electric motors
could    reduce    industrial   energy    use
significantly.  This  is  especially important for
most   developing  countries  and   Eastern
Europe,  where  industrial energy is currently
the largest share of total energy use and rapid
growth is expected.

     Reforestation may offer one of the most
cost-effective technical options  for reducing
CO2 and other gases.  At some point, the costs
of reforestation are likely to rise rapidly, as the
costs of reforesting poorer lands rise or as the
costs of bringing lands into forestry from other
uses with high economic yields increases. The
world-wide  cost  curve  for  reforestation
opportunities   is   not   well   understood.
Preliminary  estimates  of the feasibility  of
large-scale  reforestation  suggest that with
aggressive reforestation programs the current
deforestation trend might be reversed and that
a significant net increase in forest biomass is
possible. An effective program could include
programs to increase  forest biomass  - by
replanting   marginal   agricultural   lands,
improving  management  of  existing  forests,
building tree plantations, and increasing urban
planting  ~ as well  as programs to  reduce
demand  for wood  where  resources  are
currently stressed.  This, according to some
estimates,   could   convert  world   forest
management practices from a net source to a
net sink for 0.7 petagrams of carbon/year, or
more, by the year 2025.

     Elimination   of   chlorofluorocarbons
(CFCs) and related compounds over the next
decade appears  technically feasible and cost-
effective. Substitutes or process changes now
available or under development have been
identified to reduce  or eliminate almost all
applications of  CFCs  and  halons.    Key
examples are:

 Policy Options for Stabilizing Global Climate
             Worldwide replacement of CFCs
 as  an  aerosol  propellent  with  substitutes
 already  in  use  in  the  U.S.,  Canada,  and

             Replacement of  CFC-12  with
 substitutes  (such  as  HFC-134a  or  other
 hydrochlorofluorocarbons)   in   mobile  air

             Replacement of CFC solvent use
 with  aqueous cleaning  in  the  electronics

             Replacement of CFC-blown foam
 insulation with  other materials  or use of
 alternative blowing agents.

     Several  actions  may  be  possible to
 reduce greenhouse gas emissions from agri-
 culture.   The magnitudes of the agricultural
 sources,  as well  as  the  potential  effects of
 control measures, are difficult to quantify.
 Further detailed  research and data collection
 will be required in order  to produce credible
 estimates.    Major agricultural activities of
 interest are:

            Methane emissions from livestock
 might be reduced through increases  in pro-
 ductivity  of  livestock  systems  and  use  of
 methanogenesis inhibitors for beef cattle.

            Methane  emissions  from  rice
 production may be reduced somewhat through
 productivity  increases  and removal of crop
 residues.  In  the  long term, improvements in
varieties  of rice, soil amendments, and water
 management  practices  could  decrease  CH4

            Biomass burning associated with
agricultural practices produces N2O, CO, and
CH4.  Changing those  practices, for example,
practicing sustainable agriculture or utilizing
crop residues, is technically feasible and could
substantially  reduce emissions.

            N2O  emissions from fertilizer  use
could probably be reduced  through better
placement  of  the   fertilizer,  nitrification
inhibitors,  and  fertilizer coatings, which may
also reduce  farming  costs  and agricultural
runoff problems.
      Near-term  reductions  in  greenhouse
 gas emissions from electricity generation are
 possible through:

             Efficiency    improvements
 Improved    fossil    electricity   generation
 technology,  such  as  advanced  combustion
 turbines and cogeneration, can  increase the
 efficiency of using  these fuels by up  to 25%.
 More efficient transmission and distribution,
 availability   or  capacity  improvements  at
 existing non-fossil  powerplants  (i.e.,  nuclear,
 hydro), and changes in electric  utility system
 operation (i.e., dispatching,  wheeling across
 regions or even internationally)  can reduce
 CO2 emissions by  a few percent per kwh of
 electricity delivered.  The rate at which such
 efficiency  improvements are  likely to  be
 implemented is uncertain. Electric generation
 facilities are long-lived,  and  the economic
 factors entering into  decisions  to  replace
 existing facilities are complex.

            Fuel switching - Use  of more
 natural gas  to displace coal as a   fuel for
 generating  electricity  could   reduce   CO2
 emissions by a substantial amount in the near
 term.  The potential of this option is largely
 dependent on availability and cost of natural
 gas  in  the future.   Wood,  municipal waste,
 wind, etc., could play a somewhat larger role
 than they currently play in the near term.

      Alternative  fuels  that do not   emit
 significant amounts of greenhouse gases could
 make an important contribution to  reducing
 these  emissions  in the medium term and
 could virtually eliminate many  categories  of
 emissions over the long term.  For widespread
 use of alternative fuels, important engineering,
 economic, environmental,  and  social issues
 must be resolved.

            Hydroelectric  power is  already
 making a significant contribution to global
 energy  production.  There appears  to be a
 significant    potential    to   expand   this
contribution,  although  environmental  and
social impacts of large-scale projects must be
considered carefully. How great the potential
for expansion,  after taking into  account the
economic costs  and  benefits  of available
hydropower  sites and the limitations due to
environmental and social impacts, is unknown.

                                                                Chapter V:  Technical Options
            Biomass energy is currently being
extensively utilized, particularly in developing
countries. Current and emerging technologies
could vastly improve the efficiency of that use.
More  advanced  technologies,  especially  for
conversion of biomass to gaseous and liquid
fuels    and    electricity   could   become
economically  competitive  within a decade.
Measures to increase biological  productivity
are also  under study. These advances  would
allow biomass to provide a much  larger share
of global energy services over the long term,
particularly  in developing countries.  There
are certain  environmental and social  issues
associated with large-scale biomass use; these
involve,  for example, land  use, competition
with  food  production,  and  paniculate  and
organic emissions.

            Solar energy offers a large range
of  options.   Direct use  of solar thermal
energy, either passively or in active systems, is
already commercially available for water and
space heating applications in many regions.
These  applications  could  be   expanded
considerably in the near to  medium term.
Solar thermal concentrating  technologies are
widely being  tested for power generation or
industrial  process   heat and are already
competitive  in  some  locations.    Solar
photovoltaic   cells   are   economically
competitive   for   some   remote   power
generation   needs,  especially  in  developing
countries.   If current research  and testing
succeeds  in lowering the cost in  the next
decade,  solar  electricity generation and/or
photolysis could play a major role in meeting
energy needs in the next century.

            Geothermal  energy resources are
extensive and widely distributed. Systems are
commercially    available   for   electricity
generation, and over 7 gigawatts  of capacity
are   currently   in   operation  worldwide.
Technologies   are   improving   and  being
demonstrated  rapidly.  It may be possible to
expand this  energy source significantly  in the

            Wind   energy   systems    are
currently commercial in some applications and
locations.    In  recent   years  engineering
advances have resulted in reductions in cost
and improvements in performance. Assuming
this  trend continues, wind energy can play a
larger role in  future energy production.

      --  Nuclear fission is a technology that
is currently widely used and  increasing its
contribution to  global energy supply due to
the completion of powerplants ordered during
the  1970s.  High cost and  concerns about
safety, nuclear  weapons proliferation,  and
radioactive waste disposal have brought  new
orders to a halt  in  most countries.   It  is
technically feasible to expand the contribution
of this energy  source beyond what is currently
projected in the future, if these problems are

     Emission   controls   --    Control
technologies are currently available and in use
in some  countries that reduce CO and NOX
emitted  from  automotive  and  industrial
sources  and   NOX   produced  by   power
generation at relatively  low  cost.    Other
technologies, which remove larger fractions of
these pollutants but at higher cost,  are  also
available. Emerging control technologies and
combustion technologies with inherently lower
NOX  emissions  are  being tested  and could
reduce NOX emissions drastically at a lower
cost.  In  a few very  limited situations (i.e.,
combined with enhanced oil recovery), CO2
recovery  from powerplant flue gases  may be

     Methane  emissions  from coal seams,
natural gas production, and landfills can be
reduced.   The current emissions  from coal
production and landfills are projected to grow
in  the   future.    Natural  gas  (primarily
methane) is   sometimes  vented  and often
flared  in conjunction with  oil production.
Technologies exist for economically recovering
this   methane  and  using  it  for  energy
production,  thereby   partially  augmenting
natural gas supply.

     Aggressive research programs may be
the most important policy option for the long
run.    Resolution  of  several  key  technical
issues could vastly expand the economically
attractive options for reducing greenhouse gas
emissions  in   the  next  century.    Some
important examples are:

 Policy Options for Stabilizing Global Climate
             Improved   characterization  of
 sources and control options in several areas
 would  allow  better  policy  and  research
 planning decisions to be made.  Since sources
 of N2O and CH4 are  poorly  understood at
 present, field measurement and data collection
 work  are  needed  to  increase our  under-
 standing of the potential role that reductions
 in  these emissions  could play  in an overall
 climate stabilization strategy.   Detailed cost
 analysis is also  needed  for   most of  the
 technical  reduction options   identified  to
 support policy decisions in the  future.

            Solar photovoltaic technology has
 been improving rapidly over the last decade.
 Continuing or accelerating this progress could
 bring   this   technology  into  widespread
 commercial viability early in the next century.

            Biomass conversion technologies
 that   could   make   substantially   greater
 contributions  currently exist.   Commercial
 demonstrations of some existing technologies,
 additional  research  on  advanced  biomass
 conversion technologies, and improvements in
 biomass productivity could greatly expand the
 role of biomass energy.

            Nuclear fission does not currently
 appear viable in many countries because of
 concerns   about  safety,  waste   disposal,
 proliferation, and cost.  Research is underway
 in   several  countries   to   develop   and
 demonstrate   "second   generation"  fission
 technologies, which  reduce cost and safety
 concerns. The establishment of waste disposal
 plans acceptable to society is also an area of
 intense study  in  several  countries  already
 committed to  nuclear  fission.   Satisfactory
 resolution of these problems could expand the
 role of nuclear fission in future decades.

            Energy  storage technology could
 play a crucial role in integrating intermittent
 technologies  such as  solar  and wind  into
energy  supply  systems.    A  number  of
 promising concepts are  currently under study.
Accelerating  research and testing to reduce
cost and to improve performance of storage
technologies for electrical energy could greatly
 expand the potential roles of some alternative
 energy sources.

             Hydrogen energy systems offer a
 long-term potential for reducing or eliminating
 CO2 emissions, if the hydrogen is produced
 from non-fossil energy inputs.   Hydrogen is
 not a primary energy source  but rather  an
 "energy  carrier,"  an intermediate  form like
 electricity.  As an energy carrier, it can help
 resolve some of the energy storage issues with
 renewables and  substitute  in  some  existing
 fossil-fuel applications.    Research  needs
 include improved conversion processes using
 solar, hydroelectric, nuclear, wind, or other
 renewable energy inputs. Additional concerns
 include  transmission and storage and also
 applications  to transportation, space  heating,
 industrial processes, and other end uses.

             Research in  energy  efficiency
 could be helpful  in accelerating the  rate  of
 improvement   and  ensuring   continued
 improvements over the longer term. Industrial
 technology, for example, could be developed to
 the extent  that  developing  countries and
 Eastern  Europe  could substantially increase
 their standards of living without producing the
 enormous increases in CO2  emissions that
 accompanied this development  in the OECD.
 Further  research  to improve efficiency  of
 automobiles  and other vehicles could make a
 significant long-term  contribution.    Also
 potentially   effective  would   be  a  major
 cooperative research effort to adapt advanced
 technologies  that are being developed in the
 OECD to the particular constraints and needs
 of the rapidly industrializing areas.

            Agricultural research to  identify
 and  develop  alternative  rice  production
 systems,  which  reduce  the production  of
 methane, could play a significant role in a
 long-term solution to the greenhouse problem.
 Similarly, improvements  in productivity and
 other  technological  options  for  reducing
 methane  emissions  from domestic  animals
 (cattle, sheep, etc.) are possible.  Concentrated
 research in these  areas could make a major
long-term  contribution   toward  reducing
greenhouse emissions.

                                                               Chapter V:  Technical Options

      This chapter describes a wide variety of
 alternative technologies and other means by
 which greenhouse gas emissions  from  man-
 made sources could be reduced.  It builds on
 the   discussion  in   the   previous  chapter
 describing major sources of greenhouse gas
 emissions in some detail.  The catalogue of
 technical  options  presented here provides a
 background for the development of scenarios
 that are presented in  Chapter VI to illustrate
 the  effects  of  possible  combinations  of
 emission  reduction options over time.  A
 range of policy actions that might be taken to
 implement  various  technical  measures  for
 reducing emissions are described in Chapters
 VII  and  VIII, which address  domestic and
 international policy, respectively.

      The  preceding  chapters  discuss the
 diverse  sources   and  economic  activities
 responsible for greenhouse gas emissions. It
 should not be surprising,  therefore, to find
 that  there  is  an equally  diverse array of
 methods   for   reducing   greenhouse   gas
 emissions.     The   primary   means  of
 accomplishing  this goal is  the development
 and use of technologies that reduce energy
 requirements (i.e., improve energy efficiency),
 use less carbon-intensive fuels, or replace or
 reduce emissions of other greenhouse gases.
 In addition to this  technological approach,
 there  are  also   several  areas  in which
 management  strategies  are the means of
 reducing    greenhouse   gas    emissions,
 particularly with  respect  to the  buildup of
 gases  resulting   from   some   agricultural
 practices and the use of forest resources.

      In general, technical options presented
 in  this chapter  assume  that  the  level of
 consumer  services remains  constant.   For
 example,  technical options are presented that
 could   dramatically   reduce   the   energy
 consumed per square  meter of residential
 buildings.  It is assumed, however,  that the
 number of square meters of residential  space
per capita would  not change as a result of
 implementation of any  technical measures.
 Obviously, policies could be implemented that
 encouraged smaller homes, smaller or  fewer
 cars,  less  consumption of greenhouse gas-
 intensive  goods, etc.  Such policies could be
 effective in reducing emissions,  but involve
potentially difficult tradeoffs with standards of
living or lifestyles. It is not the intent of this
report to argue for or against such tradeoffs.
Rather,  the  focus  of  this  report  is on
identifying those emissions reduction measures
that could  be implemented with minimal
impact  on lifestyles.   This appears to  be  a
logical  first  step  in  the  policy  evaluation

The Role  of Long-Term and  Short-Term

      In the time frames considered  in this
report, long-term options become critical. In
order to stabilize or reduce the concentrations
of greenhouse gases, new sources of energy
supply   and  dramatic   improvements  in
efficiency will be necessary. However, there is
also much  that  could be done  to  reduce
greenhouse   gas  emissions  over   the  next
decade by improving  energy efficiency, making
greater  use  of natural gas, reducing  use of
chlorofluorocarbons    (CFCs),    promoting
reforestation  and   other  applications  of
available technologies and techniques.

      While  the  current  generation  of
technical measures will not  be sufficient to
stabilize global  greenhouse  gas  emissions
several  decades hence, efforts to  adopt such
technologies  are  exceedingly  valuable for
several  reasons.  First, reducing the rate of
growth  in global emissions now would make
it  easier to  stabilize  concentrations  in the
future  because  of  the  long atmospheric
lifetimes of greenhouse gases. Second, short-
term strategies are often intermediate  steps
toward  long-term strategies;  for  example,
implementation   of   currently-available
efficiency improvements will encourage the
development   of   future  efficiency
improvements.    Finally,   the   incentives
necessary for longer-term strategies, such as
emission fees on  carbon-intensive fuels, will
generally  be  consistent  with  short-term

      Over the long term, the most important
options  are  advanced,  non-fossil  energy
technologies,   combined   with   major
breakthroughs  in end-use  technology  that
would drastically reduce energy requirements.
Also,  changes in   agricultural and   forest
management  technologies   could become

 Policy Options for Stabilizing Global Climate
 important.  In addition to the incentives that
 may  flow  out of short-term strategies, it is
 important in  the short  term to  promote
 research  and development by  governments,
 and  the  identification and advancement  of
 promising long-term  technologies  by  the
 private sector.

 The Economics of Control Options

       For several reasons, this report does
 not attempt  either a detailed comparison of
 the  economic  cost  of  specific   emission
 reduction  options or  an assessment  of  the
 aggregate cost of entire emission  reduction
 scenarios.    For  one  thing,   the  analysis
 presented in  this report is, of necessity, global
 and very long-term.  It is very difficult, if not
 impossible, to produce credible estimates  of
global costs of policy scenarios. Similarly, it
 is of questionable value to project costs  of
 alternative   policy  actions  or   particular
 technologies  more than a hundred years into
 the future. A primary focus of this chapter is
 to  identify techniques  that appear promising
 today but are not  yet  widely accepted  in
 today's markets. As discussed above, the need
 to  foster  new technological developments is
 necessary because of the long-term  nature  of
 the problem.  The future costs of currently
 emerging   technologies   are   inherently
 unknowable now.

      It is more appropriate to begin serious
cost analyses on a  country-by-country basis
and over a time horizon  of a few decades.  A
number of such  cost  studies are  underway
now  in  the  United  States Environmental
Protection Agency (U.S. EPA) and other U.S.
agencies as well as in other countries.  Even
when  limited  to  individual countries  and
shorter  time  horizons,   however,   many
difficulties remain  in  evaluating  costs   of
alternatives.  For example, the cost of some
options is difficult to evaluate partly because
the absence of a market for reducing the risks
of climate change has meant relatively little
effort toward research and development.

      The  recent   rapid  development  of
substitutes  for  CFCs   demonstrates  the
importance of creating a market incentive to
improve technology and  reduce costs.  Until
it   became   apparent   that environmental
regulation  would create  a market  for CFC
 substitutes, industry reported that there were
 few feasible options at any price.  Now, an
 intensely competitive  race to commercialize
 substitutes  is underway around  the world  at
 costs orders  of  magnitude below estimates
 from just a few years ago.

      Similarly,  current  prices   may  not
 accurately reflect costs since climate change is
 a potential  major cost not currently reflected
 in  the  cost  of goods  and  services.    As
 discussed in Chapter VII, it may be desirable
 to incorporate the risk of climate change into
 markets through the imposition of carbon fees
 or  other policies,  in which  case currently
 more expensive  options  may become  more

      A detailed  economic analysis of options
 discussed  in  this  report   has  not  been
 attempted for all  of  the reasons discussed
 above.   It  is worth  noting,  however, -that
 anecdotal  information  and partial analyses
 cited in this chapter  indicate many of the
 near-term reduction options are  economically
 justified, or nearly so today, even based on
 current prices.  This is particularly true for
 measures to improve energy efficiency, where
 substantial  opportunities  for  cost saving
 investments  exist  despite  recent  progress.
 Chapter VII discusses  these opportunities as
 well as some of the current constraints to
 their implementation.

 Worldwide Emissions and Control Techniques

      Figure 5-1 shows the contribution to
 global warming, by trace  gas  and by sector.
 Figure S-la identifies the "greenhouse gases"
 and  illustrates  their  estimated percentage
 contributions to the greenhouse effect in the
 1980s.   All  of  these  gases  are  produced
 through a diverse range of human activities,
 which  we have  classified  into  five broad
 categories. Energy-related activities have been
 broken   down   into   two    categories:
 "applications"  of energy,  that  is,  energy
services, or "end uses," and the production of
 energy,  or energy supply.  Other  emissions-
 producing activities are related to industry,
which  include the  use  of  CFCs, forestry
 (particularly deforestation),  and agriculture.
Often a single broad category of activity -
 fossil energy consumption, deforestation, for
example - contributes  to several of the gases

                                         Chapter V: Technical Options
                         FIGURE 5-1
        By Trace Gas

Other (13%)
       CFC-11 &-12
                                           C02 (49%)
         By Sector

              Other Industrial (3%)
              Forestry (8%)

     Agriculture (15%)

    Other CFCs (3%)

        CFC-11 (4%)

                              Energy (57%)

 Policy Options for Stabilizing Global Climate
 of  concern.     Figure 5-lb   shows   the
 proportions  that the  major  categories  of
 human activity contribute to global warming.

       As the modeling results  in  the  next
 chapter  make clear,  the  U.S.  is likely  to
 account    for  a declining  share of future
 greenhouse  gas   emissions.     Stabilizing
 concentrations will  require  control  options
 applicable to the needs of  other countries,
 particularly developing  countries with  very
 different resources. The special conditions in
 the  Soviet Union and Eastern Europe  may
 also  require  somewhat  different technical
 approaches.  Some technologies, such as more
 efficient lighting, are relevant to virtually all
 parts  of  the world, but other needs  vary
 considerably. This chapter therefore discusses
 improved cookstoves, strategies for  arresting
 tropical deforestation, and other options  of
 particular relevance to developing countries.
 It also identifies special needs in the USSR
 and  Eastern Europe such as improvements in
 existing  district  heating systems and  the
 industrial infrastructure. Table 5-1 illustrates
 some  of the promising options for various
 regions under near-term and long-term time

 Organization of this Chapter

       Because  of the enormous amount  of
 information  presented in this  chapter  (in
 truth,  a separate chapter could be devoted  to
 each major source category discussed here),
 we have departed somewhat from the format
 used throughout the rest of this Report  to
 Congress and divided  the remainder of this
 chapter into five parts.

      The  first two  parts  discuss  energy-
 related activities. The single most important
 determinant of greenhouse gas emissions  is
 the  level   of  energy  demand and  the
 combination  of sources used  to supply  that
 energy.   Energy  use  causes,  in different
 proportions, emissions of five important gases:
 carbon dioxide (CO2), carbon monoxide (CO),
 methane (CH4),  nitrous oxides  (N2O),  and
 nitrogen   oxides  (NOX).    Energy  use  is
 integrally  linked  with virtually  all forms of
economic  and recreational  activity within
 industrialized  countries.     In  developing
 countries,  current  biomass  energy  use
 contributes to greenhouse gas emissions, and
 potential increases in commercial energy use
 could  be  the  largest source  of  increasing
 greenhouse gas emissions in the future.

      Thus,  evaluation  of  the options for
 reducing  greenhouse  gas  emissions  from
 energy  use  must  begin  with a  systematic
 analysis   of all  aspects  of energy   use.
 Although  there   are  "end-of-pipe"  control
 options  for removing  some  of the relevant
 emissions from energy use, while leaving the
 basic process intact, the potential impact of
 such approaches  is very small relative to the
 magnitude of the overall problem.  Given the
 dominance  of fossil fuels  as a  source of
 greenhouse gas  emissions,  technologies  to
 reduce use of fossil fuels must play a central
 role in any effort to stabilize concentrations.
 Accordingly, a major  focus  for policies to
 reduce emissions, discussed in Chapters VII
 and VIII, must  be to  promote demand-side
 measures that reduce total energy demand and
 supply-side   measures   that   promote   less
 carbon-intensive   fuels.    Technologies  to
 achieve these goals are a major focus of this

 reviews  the basic  applications  for which
 energy   is  ultimately   used   and   the
 opportunities  for   reducing  greenhouse
 emissions at the point of end use.  PART
 TWO:    ENERGY  SUPPLY  reviews  energy
 supply,   conversion  activities,  and  related
 opportunities for  reducing emissions.  This
 includes  improvements in efficiency in energy
 conversion and distribution and the potential
 for increasing supplies of non-fossil  energy
 sources.   Also discussed are reductions  in
 emissions  of CH4  from coal  mining and
 natural gas production and distribution.

      PART THREE:  INDUSTRY discusses
 technical  options  for  controlling  emissions
 from  industrial   activities.     Non-energy
 industrial activities contribute to greenhouse
wanning in three significant ways.   First and
foremost, industrial activities are the source of
all   CFC  emissions.    As  discussed  in
Chapters IV  and  VIII,  an  international
process is already underway to reduce global
emissions of CFCs because  of their role in
depleting the stratospheric ozone layer.  This

                                                           Chapter V:  Technical Options
                                     TABLE 5-1
                   Key Technical Options By Region and Time Horizon
                    Near Term (by 2010)
Energy Efficiency - autos, lighting, space heating
CFC Controls
Technology Development	
Developing Countries
Energy Efficiency -- industrial processes, transport
Low-Carbon Energy -- hydroelectricity, biomass, natural gas
Reversing Deforestation
Eastern Europe
Energy Efficiency - industrial processes, space heating,
Natural Gas
Non-fossil electricity
       All Regions
                        Long Term

Alternative Fuels -- biomass, solar, nuclear, hydrogen
Agriculture - rice production, animals
Forest Plantations

 Policy Options for Stabilizing Global Climate
 chapter  discusses  the  technical potential for
 reducing CFCs  beyond  the  level  required
 under the current protocol.

       A  second  source  of industry-related
 emissions  are   landfills,  which   produce
 emissions of  CH4.   This source  category
 represents a small portion of  total  methane
 emissions, but emissions from  this  source
 could increase rapidly in  the future.  Finally,
 production  of cement produces CO2 as a
 process   emission  (in   addition  to  CO2
 produced by energy consumption). This again
 is a small component of total CO2 emissions
 currently, but the  percentage contribution
 from cement production  has  been growing
 rapidly in recent years.

       PART FOUR:  FORESTRY examines
 current forest management practices (resulting
 in  a  net annual  loss of biomass),  which
 account  for a significant share of emissions of
 CO2 and CO  as  well as some  portions of
 other  gases.   It  should  be noted  that  the
 importance  of forestry  is greater  than  its
 percentage contribution to global warming as
 implied  in Figure 5-1.  Forests are  the only
 category that, over time, can be shifted from
 a  source to a  major sink for  carbon.  It is
 technically  possible, though  by no  means
 simple,  to  reverse  the  long-term  trend of
 global deforestation and  to begin increasing
 the  amount of forested  lands.  There  are
 several components to reforestation strategies
 that need to  be considered.   For  example,
 reductions in demand for forest products (e.g.,
 fuelwood) in some areas may be necessary to
 relieve   the  pressures  that   have  caused
 deforestation in recent years.

examines the technical options for reducing
emissions resulting from agricultural activities,
which are an important source of CH4, N2O,
NO,p and CO.  The  principal activities of
interest   are   rice  production,    enteric
fermentation in domestic animals (primarily
cattle, sheep, etc.), fertilizer use, and biomass
burning.   It is apparent that  considerable
flexibility exists,  particularly over  the long
term, to  alter  agricultural practices in the
specific categories that constitute the  large
emitters, but the technical  potential is difficult
to quantify.
       In  general, most of the research and
 analysis of agriculture to date has focused on
 opportunities  for  improving  productivity.
 Productivity   improvements   should
 automatically lead  to some reductions  in
 greenhouse gas emissions per unit of output;
 however,   this   relationship  is  not   well
 quantified.  Additional options  for  reducing
 emissions, beyond productivity changes, can be
 envisioned  for  each    of  the    specific
 categories  mentioned,  though,  again,  very
 little work has been done as  yet to quantify
 the potential effects and costs of such options.


       In   this   review   the   information
 presented, although somewhat detailed, can
 only  begin  to illustrate  potential   technical
 options that currently appear most promising.
 The analysis also highlights the uncertainties
 and need for further study of many options.
 In  some  cases,  the  impact   of   specific
 technologies cannot be estimated at present,
 for  example,  technologies  for   reducing
 emissions  from  agricultural  sources.    In
 general, however, there are fewer uncertainties
 about  how  to achieve emission reductions
 than  there are about the rate  of  warming,
 change in climate, and the ultimate effects of
 an increase in greenhouse gas  concentrations.
 While some currently  emerging  technologies
 may  not fulfill  current expectations,  the
 options are sufficiently diverse that we can
 encourage the  development  and  use  of
 technologies  that are relatively less intensive
 sources of greenhouse gas emissions if we so

       The   source   of   most   of   the
 uncertainties discussed in this chapter is the
 difficulty  of  predicting future technological
 developments. Many of the options that may
 have the  greatest  impact  on the buildup of
 greenhouse gases, such as the development of
 new engine  technology for cars,  new designs
 for nuclear plants, and the use of hydrogen as
 a substitute  for liquid fuels,  are long-term
 possibilities  that  require  substantial further
 research.  It is important to recognize several
 key limitations:

           The   discussion  cannot  deal
exhaustively with  the  tremendous  range of

                                                                Chapter V: Technical Options
technical options that have been identified in
the areas  of energy efficiency improvements,
fuel   substitution,    industrial    emissions
reductions,   forest    management,   and

           Because   of    the   limited
information  available,  but  even  more  so
because of the extensive scope of  this study
(in terms  of emissions-producing activities as
well as  the global diversity of emissions), it
was  not   possible    to  provide  detailed
quantification   of    expected   emissions
reductions and costs for many of the technical
options discussed.

           Much  data  development  and
detailed analytical work remains  to be done.
A more detailed technical assessment of U.S.
emission  reduction options  and costs,  also
mandated by Congress, is now underway and
will be  completed  in  1990  by  the   U.S.
Department of Energy and U.S. EPA.

           Estimates of the potential perfor-
mance of technical options, as discussed la
this chapter, are often  based on  engineering
design calculations,  prototype performance,
laboratory results,  etc.   Actual  achievable
performance may be less, in  practice, since
mass   production   often  requires  some
engineering   compromises   relative   to
laboratory or prototype specifications.  Also,
performance of technology under  conditions
of day-to-day use often deteriorates somewhat
from design or new product performance.  On
the   other  hand,   currently   unforeseen
developments  may   improve   performance
beyond levels estimated today.
           This  chapter   identifies   and
attempts where possible to quantify technical
potentials for reductions  in  greenhouse gas
emissions.   Even where  technical options
appear economically attractive on a life-cycle
basis,  there  are   generally  institutional,
behavioral,  and  policy   constraints   that
currently  operate  to  limit  their  market
penetration.    The   portion of   identified
technical potential  that can be achieved in
practice is largely a function of the availability
and   effectiveness  of  policy options,  as
discussed in Chapters VII and VIII.

 Policy Options for Stabilizing Global Climate
                              PART ONE: ENERGY SERVICES
      The services that energy provides (also
often referred to as end uses), such as lighting
and fuel-driven locomotion,  are  an integral
part of human society and, at the same time,
constitute the largest category of greenhouse
gas  emissions.   While  the production and
conversion of primary energy (e.g.,  coal, oil,
gas)  is  the immediate  source  of  a  large
portion  of  energy-related  greenhouse  gas
emissions, it is the application of this energy
to provide specific services that justifies this
production and conversion. Thus, minimizing
the  energy  required  to  provide  various
services  or using  non-fossil fuels in specific
end-use  applications can reduce production-
and conversion-related emissions as  well.

      For convenience,  energy services are
classified as belonging to one of three major
sectors:       transportation,   residential/
commercial,    and   industrial   (including
agriculture).    Each of  these  sectors uses
energy in distinctly different ways and offers
different opportunities for reducing energy use
and/or shifting to alternative fuels. Figure 5-2
shows  the relative contributions of the three
sectors  to  global  energy  use  as  of 1985.
Figure  5-2a shows  the  secondary  energy
actually consumed at end-use points.  Figure
5-2b  shows  the  energy  use  by sector  in
primary  energy production equivalent terms;
that  is,   the  production,  conversion, and
transmission losses are ascribed to  the end-
use sectors based on the  characteristics of the
energy  they use.    Figure 5-2c  shows  the
proportions  that  the   equivalent   primary
energy   use  for  these   three  categories
contributes to global greenhouse emissions in
the  1980s.  The differences are due  to the
variations in greenhouse  gas emissions from
the different primary energy sources.

      There are two time horizons  that are
useful  in  discussing technical options  for
energy services.   Near-term options refer  to
technologies currently available or expected to
be commercially  available by the year 2010.
These   are   the   options  about  which
information  is  available;  such  information
could  provide a basis  for near-term policy
action. Long-term options are those that are
not expected to be available until after 2010
and, in some cases, well after.

      An  attempt is made to  hypothesize
about  potential technological  developments
over the longer term and  to discuss the role
research  could  play  in  accelerating   the
availability  of advanced options.   Some of
these technologies are speculative and require
additional research.  They are included in the
analysis because they have the  potential to
play major roles in the long run.

      In discussing global energy-use patterns,
it is important to distinguish between modern
and  traditional  energy  forms, particularly in
order to understand energy use in developing
countries.   For this  discussion, the terms
modern or commercial energy are used  to
describe all fuels and energy forms that  are
priced and sold  in energy markets (or, in  the
case    of    centrally-planned    economies,
accounted   for   and   valued   in  national
economic planning).   In  this category  are
virtually all of the fossil fuels, which are  the
major  source of greenhouse gases, as well as
electricity from all sources.  Readily available
energy  statistics,   which  pertain  almost
exclusively  to  modern  energy, accurately
represent energy-use patterns in industrialized

      For   developing  countries,  however,
traditional energy  accounts for a substantial
fraction of the total energy used.  This type of
energy  includes  fuels  such  as  firewood,
agricultural waste, and animal waste that  are
gathered and used  informally, usually without
being priced and sold in commercial energy

      Technical options, especially in the near
term, vary substantially from region to region
and often among  individual countries.   For
each of the sectors discussed in  this part
(transportation,  residential/commercial,  and
industrial), we look first at  near-term options,

                                             Chapter V: Technical Options
                            FIGURE 5-2

(a)   Secondary Energy Use    (b)   Primary Energy Equivalent
              industrial  Transportation
       (c)    Contribution to Warming
     Other CFCs (3%
                                           Transportation Energy Use
              Other Industrial
                                      Industrial Energy
                                         Use 25%
                                Energy Use  14%

 Policy Options for Stabilizing Global Climate
 for   industrialized   countries,   developing
 countries, and the USSR and Eastern Europe,
 then briefly discuss the long-term options.

      The industrial  market economies, the
 members of the  Organization  for Economic
 Cooperation and  Development (OECD), have
 many similarities  in  terms  of economic
 activities and resources,  and  hence  are
 discussed as a group.  Energy  use in these
 countries is  relatively high but not expected to
 grow rapidly; rising incomes are being devoted
 increasingly to products that do not  require
 significant energy inputs.

      The  developing  countries  are vastly
 different from industrialized countries both in
 current levels and types of economic activities
 and available resources.  Energy use in the
 developing countries will grow significantly in
 the  future,  but  there  is  great uncertainty
 about the rate of growth.

      The USSR and Eastern  Europe share
 with  most  developing  countries  a  much
 greater emphasis  on government intervention
 in economic planning and industrial activities
 than  occurs in OECD  countries.   On  the
 other hand,  these countries have massive and,
 in many ways, technologically sophisticated
 industrial infrastructures that  are in some
 ways  more  similar to  those of the  OECD
 countries than they  are  to  the industrial
 infrastructures of most  developing countries.
 Energy  use  in Eastern  European countries
 (and associated greenhouse gas emissions) has
 been  growing rapidly and is expected to grow
 in the future.  While less is known about the
 technical potential to  reduce  emissions in
 these countries, it is  generally believed that
very substantial improvements can be made in
energy efficiency.


      Transportation   currently  consumes
approximately 27% of global modem energy
use.   Virtually all of  the energy used in
transportation is derived from oil.  In 1985 in
OECD   countries,   energy    used   for
transportation accounted for about 23% of all
energy consumed (27% in the U.S.), expressed
as primary energy equivalents. As a share of
secondary energy consumption, transportation
accounted for about 34% in  the  OECD,
 approximately  97%  of which was  oil (U.S.
 DOE, 1987b).

       In  industrialized countries it is likely
 that the private automobile will continue to
 be the primary means of transportation in the
 near future.  Fortunately, there are near-term
 opportunities for improving the efficiency of
 this mode  of  transportation.   Near-term
 improvements in efficiency of freight transport
 and aircraft will also be cost-effective over the
 next  few  decades.    A  few industrialized
 countries (e.g.,  Canada, New Zealand)  are
 also pushing  ahead with  major alternative
 fuels programs in the near term.

      Over  the  longer   term,   additional
 reductions in energy consumption may come
 from  shifting  to  more efficient  modes  of
 transportation   and   substitutes   for
 transportation (e.g., advanced communication
 technologies).  Also,  increasing the  use of
 non-fossil-based fuels  in  the transportation
 sector is essential  in order to greatly reduce
 or eliminate greenhouse gas emissions (see

      In developing countries and the USSR
 and Eastern Europe, transportation currently
 accounts  for a smaller percentage of total
 energy  use.   (In some  African  countries,
 however,  the  percentage  is much higher.)
 However, in the future, as economies expand
 and  incomes  rise  in these  regions,  the
 potential  exists  for  explosive  growth   in
 transportation energy use.

 Near-Term Technical Potential in the
 Transportation Sector

      With aggressive programs to improve
 transportation  energy  efficiency across  the
 board in industrialized  countries, it appears
 that  significant overall reductions could be
 made over time.  By 2010  in the OECD,
 improvements in the  efficiency of light-duty
vehicles and  freight  transport could reduce
energy use in  the transportation  sector by
about 7 exajoules (EJ) from expected levels.
 If the  same  efficient  technologies  were
transferred to developing  countries and  the
USSR  and Eastern  Europe,  even  larger
reductions below expected  levels  could  be
achieved because of  the rapid expansion of
vehicle stock in those areas.  This suggests

                                                               Chapter V:  Technical Options
that  the  technical  potential  may  exist to
reduce energy use 25 EJ worldwide by 2010.
Furthermore,  it  appears  that  there  are
alternative   fuel  options  that  could   be
implemented during this time period, which
could reduce the greenhouse  gases emitted
per   unit    of   energy   consumed   in
transportation. The overall potential of these
options has not been quantified.  Near-term
options in the various regions are discussed

Near-Term Technical Options:  Industrialized

      Within  the  transportation  sector,
technical options to reduce greenhouse gas
emissions  include  improvements  in  fuel
efficiency, alternative fuel use, stricter  and
more   universal   emissions   control,
improvements in urban planning, and greater
use of mass transit.

Increase Fuel Efficiency

      Light-duty vehicles,  mainly passenger
cars, account for the bulk (about 63%) of
current transportation energy use (see Figure
5-3).  Other major contributors are freight
transport vehicles (diesel trucks,  ships,  and
railroads),  accounting  for about  25%,  and
aircraft, primarily  those used in passenger
travel, accounting for 12% of transportation

      Light-Duty Vehicles.  In the past decade,
a great deal of attention has been devoted to
options for improving the efficiency of light-
duty vehicles.   Consequently,  a number of
very  promising  approaches   have  been
identified and well-documented (see Bleviss,
1988; Goldemberg et  aL,  1988,  for more
extensive discussions of the technical options
for improving the fuel efficiency of light-duty
vehicles).    These  efficiency  improvements
must be considered in the context of several
societal and consumer concerns  related to
light vehicles, such as urban air quality, safety,
comfort, and performance.  These other goals
also affect the patterns of vehicle technology

      Although average fuel  efficiency for
new cars  in the industrialized countries is
between 25 and 33 miles per gallon (mpg), or
7.7-10 liters  ()/100  kilometers (km) (IEA,
1987), several vehicles that are roughly twice
as efficient are  commercially available: the
Honda  Civic and  the Chevrolet Geo Metro
both average greater than 50 mpg (5  
 Policy Options for Stabilizing Global Climate
                                FIGURE 5-3
                        INTHEOECD:  1985
        Dltl (Primarily

         Trucks, 20%)
        Gaaolin* (Primarily Paaang*r
         Car* and Light Truck*. 83%)
Source: OECO, 18T.

                                                                                                                                                      Chapter V:  Technical Options
                                                                                   TABLE 5-2

                                                                       High Fuel Economy Prototype Vehicles
Number of
namic Drag
Curb Weight


61 City
74 Hwy


41 City
AUTO 2000


63 City
71 Hwy


74 City
99 Hwy


63 City
81 Hwy


63 City
81 Hwy


78 City
107 Hwy


55 City
87 Hwy
ECO 2000


70 City
77 Hwy



57 Cily
92 Hwy


89 City
1 10 Hwy
Source:  Bleviss, 1988.

Policy Options for Stabilizing Global Climate
to assume that fuel economy levels achieved
by prototypes could be  readily achieved by
production vehicles in the near  term.  On the
other hand,  the  prototypes do  illustrate that
a wide range of technologies exist to improve
on today's fuel economy  levels.

      Box 5-1 outlines several examples of
the   many   automobile   fuel-efficiency
improvements already  possible with current
technology.   Research is proceeding rapidly
and    will   undoubtedly    yield   further
opportunities for improved fuel efficiency in
the next decade. It is clear that opportunities
exist for major reductions in  light-duty fuel
use by the  end  of this century.  This  is
particularly true for the United States, which
is  still behind  most other  industrialized
countries in the average fuel efficiency of new
cars sold (see   Table  5-3), partly  because  of
                    BOX 5-1. Technologies for Automotive Fuel Efficiency

                 Weight Reductions - Many of toe most efficient cars substitute
                 non-traditional materials for steel to achieve weight reductions,
                 which contributes to their superior operating efficiency. Much
                 greater weight reduction appears possible by substitution of
                 high-strength  steels,  aluminum,  plastics,  ceramics,   and
                 composite materials (Bleviss, 1988).

                 Aerodynamic and Drag Improvements - In 1979 the average
                 "coefficient of drag" (CD) for the US. was 0.48, and for Europe,
                 0.44.   Currently, some production models such as  the Ford
                 Sable and Taurus, Subaru XT Coupe GL-10, and Peugeot 405
                 achieve a CD of 0.3 or less. AD experimental prototype, the
                 Ford Probe V, has achieved a CD of 0.13?  (Bleviss, 1988).
                 Incorporating some of  the prototype  design features could
                 reduce drag for production vehicles significantly over the next
                 decade.  Rolling resistance is being reduced with  advanced
                 radial tires. General Motors has recently introduced a "fourth
                 generation'1 radial tire that reduces rolling resistance by 10-12%
                 from the previous generation.   An Austrian  company  has
                 developed a more advanced tire concept, a licjuid-injection-
                 tnolded (LIM) poiyurethaae tire.  Preliminary  tests indicate
                 improvements in  roiling resistance as well as tread mileage
                 (Bleviss, 1988).

                 Engine  and Drive Train Improvements -  Several researchers
                 have identified a number of improvements to conventional
                 light-vehicle propulsion  systems and transmissions that couW
                 dramatically increase efficiency (see Bleviss, 1988; von Hippel
                 and Levi, 198$ Gray, 1983; OTA 1982).   One interesting
                 example is the use  of continuously  variable  transmissions
                 (CVT), which eliminate some  of the energy losses during
                 shifting and allow the engine to be operated closer to Ml load
                 at varying speeds. Another possible innovation is an engine-off
                 feature with energy storage capability during Idle and coast. In
                 addition, advanced engine designs currently in prototype could
                 be much more fuel efficient than current technology.  One
                 example is the adiabatic diesei engine shown to Box 5-2.

                                                                                                 Chapter V: Technical Options
                                                         TABLE 5-3

                                         Actual Fuel Efficiency for New-Passenger Cars
                                       (Gasoline consumption in liters per 100 kilometers)

United Kingdom
United States
a 1987 target.
b 1995.
c 1975.
** nrtitf fimir^c fr\r

Ttalv r^nm

*c**nt ot/4*ra A*

 tfffiri*>n/n/ e

if tho trttal ,

r>ar flii>t



1990 2000
7.4 6.8-b

8.6 7.8

8.8 8.2

Source:  IEA, 1987a.

 Policy Options Tor Stabilizing Global Climate
 the preference for larger cars in the U.S.  If
 light  trucks were included in  these averages,
 the U.S. would be even further behind most
 other OECD countries.

      Despite  the  fact that  improvements
 have  been identified, it is not clear whether,
 and  at what  rate, new technology will be
 incorporated   into    automobile   designs.
 Clearly, opportunities for dramatic efficiency
 improvements exist, but costs associated with
 these  opportunities   must  be  considered.
 Several  years   ago,   the   U.S.  Office  of
 Technology Assessment (OTA) conducted a
 detailed analysis of the potential for and cost
 of future improvements in the fuel efficiency
 of new automobiles.   The study,  which was
 based on extensive interviews with automobile
 manufacturers and other fuel-efficiency experts
 found  that it   was   technically  feasible to
 achieve average new-car fuel efficiency  in the
 range of 50-70 mpg (3.4-4.7  2/100  km) by
 2000.  It also found that "the consumer costs
 of fuel efficiency range from values that are
 easily competitive with today's gasoline prices
 to values that are considerably higher" (OTA,

      OTA found that the projected cost of
 efficiency  improvements varied considerably,
 depending  on   the  actual  performance of
 potential design changes, whether production
 techniques  to   hold  down  variable  cost
 increases are successfully developed, and the
value consumers place on future fuel savings.
 Under optimistic assumptions, OTA estimated
the cost of fuel efficiency measures to be as
low as $60-5130 per car during the 1985-2000
time period.  Under  alternative assumptions,
the cost of efficiency  improvements could be
as high as $800-52,300 per car.

      Von Hippel and Levi (1983) conducted
a computer analysis of the cost of introducing
a number of  specific measures that would
improve fuel efficiency, beginning with the
 1981 Volkswagen Rabbit diesel. A package of
specific improvements that would improve the
fuel economy from 5.2 to 3.3 /100 km (45 to
71 mpg) was estimated to cost about $500 per

      Goldemberg et al. (1988) and Bleviss
(1988), however, suggest that  cost estimates
 toward the lower end of the OTA range are
 more  likely for several  reasons.  First, the
 efficiency improvements would yield a number
 of   other  benefits    to   the   consumer.
 Alternative materials, for example, could also
 reduce maintenance costs. There is also some
 anecdotal evidence  that, contrary to  popular
 expectations, use of more plastics and plastic
 composites  may  in  some  cases increase
 passenger safety (Bleviss,  1988).  In  other
 cases, alternative materials may reduce safety.
 The inclusion of the  engine-off feature may
 prolong  engine  life.  If the value of these
 other  benefits is deducted from the cost of
 fuel-efficiency  improvements,   more  rapid
 improvements may be cost-effective.

      A  second  reason  for  lower  cost
 estimates is  that  the  cost  of  individual
 improvements may not be  additive.  Some
 costs  may be  offset by the  savings  from
 combining measures and integrating a number
 of related changes  into ongoing production
 process  changes.    Vehicle  manufacturers
 periodically make major investments in design
 changes, incorporating style concerns as well
 as  engineering  improvements.    Chrysler
 recently  conducted a study  comparing  the
 costs of producing a conventional steel vehicle
 and  an alternative made   principally    of
 composite plastics. Although the composite
 material  is  more  costly, its  use allows a
 dramatic reduction  in the number of parts
 and  hence,  assembly  costs.    The study
 concluded that the number of parts might be
 reduced  by  as much  as  75%,  and that  the
 overall production costs for the composite
vehicle would  be only 40% of those for the
corresponding steel vehicle (Automotive News,

      On  the  other   hand,  automobile
manufacturers have expressed the  view  that
further fuel  efficiency improvements may be
more  difficult and costly  to achieve  than
estimates from  the  early  1980s  suggest
 (Plotkin,  1989).   Concerns  raised  by  the
manufacturers  include the following:

          Most   of   the   cost-effective
efficiency measures that are  acceptable to
consumers have been implemented in the last

                                                                Chapter V: Technical Options
            Performance of actual production
 models  incorporating  design  changes  for
 efficiency have fallen  short  of engineering

            There . are   major  technical
 uncertainties   and  marketability  problems
 associated with many  of  the fuel-efficiency
 technologies (e.g., advanced diesels, two-stroke

            Real  trade-offs do exist between
 further  fuel-efficiency   improvements  and
 environmental   standards  (particularly  for
 nitrogen oxide  [NOX]  emissions) and safety

       Other recent research on potential fuel
 economy improvements has also emphasized
 the  difficulties of achieving  cost-effective
 improvements in the near term.  For example,
 in diFiglio et al. (1989), several constraints on
 vehicle efficiency  improvements  were noted,
 including  that  auto  manufacturers  require
 several years  to  retool existing production
 lines, decisions on production are essentially
 locked in already  for the next several years,
 and   the  technical acceptability  of  many
 efficiency    improvements  has  not  been
 demonstrated  on many  models.     Also,
 consumer purchasing decisions are affected by
 many   factors,   including   vehicle  size,
 acceleration,    braking,   maneuverability,
 comfort,  etc.   Nevertheless,  diFiglio et al.
 pointed    out    that   some    efficiency
 improvements  are  cost-effective,  even  if
vehicle size, performance, and  ride quality are
 held constant to current (1987)  levels.  They
 noted  that  new-car fuel efficiency could be
 increased  17% (to 31.6 mpg) by  1995 at a net
savings to the  consumer (i.e., including fuel
savings using a  10% discount rate over four
years). Additional improvements to  surpass
36 mpg would  be  cost-effective  over  the life
of the vehicle by 2000 (also see Plotkin 1989).

      Fuel   Efficiency   Tradeoffs.      The
governments of many industrialized countries
regulate   light-duty  vehicles   to   reduce
emissions  of a  number  of air  pollutants.  In
addition,   consumers   value   performance
attributes other than fuel efficiency, as well as
comfort, safety, and cost in  their choice of
automobiles.   To the  extent that  proposed
fuel-efficiency  improvements or  alternative
fuels involve tradeoffs  against these other
goals,  or  are  perceived  to  require  such
sacrifices,  they  may  be more difficult to

      Safety  is  a  major   concern  long
associated  with light-duty vehicles.   Some
industrialized   countries    regulate   the
manufacture,  sale,  and  maintenance  of
vehicles to improve safety. In the 1970s and
1980s,  U.S.  safety  standards  significantly
improved vehicle safety.  Some evidence exists
of  a correlation  between size and weight
reductions and increases in injury and fatality
for currently available vehicles (OTA, 1982).
Clearly, effects on safety must be  considered
in the evaluation of technical alternatives for
improving  fuel efficiency.

      Weight reductions to improve efficiency
may in fact reduce the structural strength of
vehicles, thus making them less safe. It is not
true, however,   that  the   use   of  lighter
materials necessarily reduces safety.  Early
attempts  in  the   1970s  to improve  fuel
efficiency  often  involved  simple  weight
reductions   throughout   a   vehicle  with
corresponding declines in crashworthiness. In
recent years manufacturers  have  employed
other methods to  achieve weight reductions,
including  the   use  of lighter,  composite
materials  and changes  in body designs  that
maintain  or  enhance  structural  integrity.
These types of improvements are reflected in
U.S.  government  crash tests where some
smaller   vehicles  have  consistently  shown
superior  crash performance to other vehicles
weighing as  much as  50%   more  (Bleviss,
1988).  In contrast, some comparatively heavy
vehicles  have   the  lowest  crashworthiness
ratings among available models.  These crash
tests, however, do not accurately reflect safety
concerns  in crashes  between  vehicles  of
different weights.

      Weight reductions, aerodynamic design
and engine improvements could also stimulate
increased use of composites, plastic, and other
new materials.   Ultimately,  these materials
might  present  new   solid  waste  disposal
problems as the cars are eventually scrapped.
This area should be evaluated in more detail
in the future.

 Policy Options for Stabilizing Global Climate
       Emissions are another major  concern
 associated with automobiles.  Vehicles emit
 several  pollutants  --  particulates,  volatile
 organic compounds (VOCs), carbon monoxide
 (CO), and nitrogen oxides (NOX)  --  which
 contribute  directly  to  urban  air   quality
 problems  and indirectly  to climate  change.
 Some options for increasing fuel efficiency
 (and thus reducing greenhouse gas emissions)
 have  the   potential  to   worsen  local  air
 pollution  problems.   For  example,  diesel
 engines are more fuel efficient than gasoline-
 powered automobiles, but diesel engines tend
 to  produce greater  emissions of particulates
 (many   of   which   are   cancer-causing
 compounds) per mile travelled.

      The   design   of   vehicle  emission
 standards can be another complicating factor.
 In  most  industrialized countries  pollutant
 emission requirements for vehicles are applied
 on a  grams-per-mile  (or  kilometer)  basis.
 One  concern about this approach is  that it
 may   not    encourage   development   of
 technologies   that   would   simultaneously
 improve fuel  efficiency  and reduce emissions
 of  urban air pollutants,  even  though such
 technological options exist (Bleviss, 1988).  In
 addition,  as  fuel  efficiency  improves,  the
 marginal  cost  of  driving  would  decline,
 assuming fuel prices remain constant, which
 might induce  vehicle operators to drive more
 than  they otherwise would.  If  this effect is
 significant,  it would  offset  some  of  the
 expected   reductions   in   greenhouse   gas
 emissions  and could  also result  in  a  net
 increase  in  emissions of conventional urban
 air pollutants.

      Conversely,  some of the options  for
 reducing emissions of pollutants can  lead to
 increases in emissions  of  greenhouse gases.
 As  noted above, switching to methanol fuels
 could increase greenhouse gas emissions if the
 methanol is derived from coal.  Similarly,  use
 of electric cars might result in net increases in
 greenhouse gas emissions  if the electricity
were  generated from fossil fuels,  although
 recent evidence indicates  that  electric  cars
would likely  achieve  a  net  reduction in

      There are potential solutions to all of
 the problems  illustrated.  For example, new
diesel  cars  are much  cleaner  than  earlier
 models.  Mercedes Benz and Volkswagen have
 now developed emission control devices  that
 make it  possible  for their diesel cars to meet
 the strict California paniculate standard of 0.2
 grams/mile  (Bleviss,  1988).    In  addition,
 emission standards could be modified (e.g., to
 grams per gallon in conjunction with  higher
 efficiency standards, or  direct regulation of
 carbon dioxide [CO2] emissions) to encourage
 fuel-efficiency improvements that would  also
 benefit local air quality.  Over the long term,
 it is important that options like  methanol-
 fueled and electric vehicles are promoted in
 conjunction with non-fossil (or at  least  low
 carbon)  energy inputs.

      Many consumers are concerned about
 sacrificing    size,   comfort,    or    driving
 performance to achieve major improvements
 in fuel economy.  On the other hand, many
 consumers may also be concerned about the
 environmental impacts of their consumption
 patterns, and willing to alter those patterns, if
 informed of the  environmental implications.
 Nonetheless,  analysts  have   demonstrated
 possible  design  changes that would  reduce
 fuel consumption while retaining the size and
 performance  of  a  large  automobile (e.g.,
 Forster,  1983).

      Some of the prototype high-efficiency
 vehicles  have  already demonstrated that  size
 and acceleration do not necessarily have to be
 sacrificed.   The  Volvo LCP 2000, with  an
 average fuel efficiency of 65 mpg (3.9 {/100
 km), accelerates from 0 to 60 miles per hour
 in 11 seconds  - compared with 13.1 seconds
 for the average acceleration of the U.S. new-
 car fleet (1986 models, which averaged only
 28 mpg [8.4 1/100 km]).  Likewise, a recently
 developed  lightweight  prototype  car,   by
 Toyota,  is  designed  to  seat  five  to  six
 passengers while achieving 80 mpg (2.9 2/100
 km) under urban driving conditions (Bleviss,

      In summary, it appears technologically
 feasible  to  achieve  average new-car fuel
 efficiency of at least 40 mpg (3.8 2/100 km) in
 the U.S.  by 2000. A new fleet average of 50
 mpg (4.7 2/100  km)  would be technically
 feasible with continuing technical innovation,
size reductions, and vehicle turnover.  This
would  require a  strong  commitment   by
government and industry,  but the reductions

                                                               Chapter V: Technical Options
in energy use, and greenhouse gas emissions,
from this improvement would be significant.
However, a new car fleet average of 40 mpg
by   the   year   2000  could  require  size,
performance,  and  safety reductions.   The
length  of  the  development   period and
the  degree  of technical  change  required-
to  achieve a  new fleet  50 mpg  average
without   compromising  safety  and  other
desired  product  characteristics  are   highly

      The U.S. Department of Energy (U.S.
DOE, 1987c) has projected that automobile
vehicle miles travelled (VMT) in the U.S. will
increase  over 50% by the year 2010 (from
1,315 to 2,032  billion miles).  In calculating
future transportation energy use, the  report
also projects that  automobiles  will average
about 27 mpg (8.7 J/100 km) in 2010 (overall
average of all operating vehicles, not new-car
average).   If automobiles averaged  50 mpg
(4.7 0/100 km), the energy consumed  would
be  reduced by over 45%, or  more than  30
billion   gallons  of  gasoline (3.8  EJ1)  in
2010 -- more than a 40% decline from the
1985 consumption  level  (as opposed to the
7%  increase projected by  U.S.  DOE).  To
achieve these results, it  would be necessary
for automobiles to perform at the specified
on-road  fuel efficiency  over the life  of the
vehicle.  Currently, there is a widening gap
between  nominal  test  values  and on-road
performance   as   well   as    considerable
degradation in fuel efficiency over the  life of
an automobile.  These factors require further
study and could limit  the  expected  energy
savings from fuel economy programs.

      In addition,  the current trend in the
U.S. toward the use of light-duty trucks for
personal transportation  could offset some of
the  efficiency gains if  it continues  in the
future. Efficiency improvements in light-duty
trucks and/or programs to discourage personal
use of these vehicles could produce significant
energy savings in the U.S.  The recent trend
toward slower turnover of older vehicles could
also  offset  efficiency  improvements  if  it
continues. Conversely, programs to stimulate
more road turnover and scrappage of older
vehicles   could  improve  efficiency   gains.
Decreasing fuel use in  the U.S. could also
support many important national goals such
as reducing international trade  deficits and
improving energy security.  Improvements of
this magnitude could be made for the OECD
as a whole and would undoubtedly also spill
over to the non-OECD countries that  produce
vehicles for sale  in the OECD and/or import
vehicles or technology from the OECD.  Most
light-duty vehicles currently in production are
derived from designs that  originated in  the
OECD (Bleviss,  1988).

      Freight Transport Vehicles. Diesel trucks
use about 14%  of the oil consumed  for
transportation  in  OECD  countries  (von
Hippel and Levi,  1983).   Improvements  in
efficiency in this sector could, therefore, have
a  noticeable  effect on total  energy  use.
Current  prototype  vehicles  could  reduce
energy use per  ton-mile in  the  U.S.  by  as
much as 40% for truck transport (Automotive
News,  1983).  Goldemberg et al. (1988) have
estimated that further improvements on  the
order  of 50% or  better could be achieved
with existing technology and at  reasonable
cost.   Box 5-2  describes one  of the  most
promising  advanced  diesel   technologies.
OECD truck fuel use for 1985 totaled about
5.3 EJ.    A 50%  improvement   in  fuel
efficiency over the next several decades seems
feasible if aggressively  pursued.   As  truck
freight ton-miles are projected to grow in the
future, this level of improvement could save
at least 2.6 EJ by 2010.

      Both rail and water transport are  much
more efficient than truck transport on a ton-
mile basis. In 1984, the U.S. average energy
intensity of freight movements was estimated
at 1,610 British thermal units (Btu)Aon-mile
for trucks, while waterborne shipping averaged
350 Btu/ton-mile and rail freight was 510
Btu/ton-mile  (Holcomb et al., 1987).  To the
extent  that  shippers  could be encouraged,
either through price incentives or other policy
mechanisms, to shift from truck transport to
these modes in the future, net energy use for
freight  transport could be reduced.  One
interesting approach  is  being  tested   by
General Motors Corporation (GM).  GM has
developed a new truck trailer that  can also be
easily converted to a rail car and connected to
a freight engine.  This would allow loading of
truck  trailers at  source points, truck  hauling
to the nearest rail terminal, and conversion to
rail without unloading/reloading.   Likewise,
near the destination, the transition back to

Policy Options for Stabilizing Global Climate
                         BOX 5-2.  Adiabatic Diesel Engine Technology
      The diesel engine is currently the most efficient powerplant used in heavy-duty, and some
      light-duty, vehicles.  Little has changed in its basic design over the years.  However,
      motivated by the energy crises of the 1970s, engine designers began trying to improve the
      fuel efficiency of diesels even further. One of the most promising results of this research
      is  the adiabatic engine,  which  combines  new  structural ceramic materials and
      turbocharging to increase the effective use of the heat generated during combustion.

            Adiabatic design, which means "without heat loss," increases efficiency by
             retaining heat  in the combustion chamber instead of losing it to exhaust
             gases and the engine coolant, harnesses the high pressure exhaust gases, and
             reduces weight and parasitic power losses by eliminating the normal cooling

            As shown in the figure below, turbocompounding increases the pressure of
             gases in the combustion chamber using a turbocharger and then harnesses
             the extra pressure  of the exhaust gases with a turbine connected to the
             engine  crankshaft.   Structural ceramics, which are being developed to
             withstand temperatures and pressures reaching 1000C and 2000 pounds per
             square inch, respectively, will be used to insulate the combustion chamber,
             allowing greater thermal efficiency.

            Cummins  Engines and Adiabatics  in  the U.S., as well  as  Japanese
             automakers, are at the forefront of introducing the adiabatic engine both for
             heavy-duty trucks and passenger vehicles. A Ford Tempo with an adiabatic
             engine is projected to achieve a fuel economy of 80  mpg.  Along with the
             consequent reduction  in  CO^  additional reductions are expected in
             hydrocarbon, CO, and NOX emissions, and paniculate emissions are expected
             to be reduced by as much as 60-80% over current diesel technology (Kamo,
                                                        Exh*i*t Sy*twn
                                                 Htgh Soccd
                                               Reduction Gearing
                                           V*relton ttoMfwn
                                             FK*> Couotng)
                                   Power Transfer
                                    To Cr*n*n*
                                                               Chapter V:  Technical Options
 truck is  simple.  GM has estimated that for
 hauls of over 200 miles, this approach could
 reduce energy use to 20% of current energy
 use  for  an all-truck  haul or  50% of a
 conventional rail shipment (Sobey, 1988).

      Improvements in ship fuel efficiency are
 also possible. Using some of the same diesel
 engine   technologies  identified   for  truck
 engines,  30-40% improvements in efficiency
 may be possible over the next several decades.
 Wind-aided  cargo  ships  may  also  improve
 efficiency somewhat in the future.

      Aircraft.   Dramatic improvements in
 fuel efficiency  have  been  achieved in   the
 airline industry over the past decades.  From
 1970 to 1980 fuel use per passenger mile in
 the  U.S. declined by over 40% (Holcomb et
 al., 1987).  Nevertheless, by 1980 energy still
 accounted  for about 30% of total operating
 costs for  commercial airlines in the  U.S.
 (Goldemberg et al., 1988). Since 1980, energy
 intensity has continued to decline due to
 some additions of more efficient aircraft  and
 continued   improvements  in  load  factors
 (revenue passenger miles divided by available
 seat miles ~ U.S. DOT, 1988), but  at a slower
 rate (from  1980 to  1984  the improvement
 was  about 4% - Holcomb et al., 1987).  The
 decline in the rate of efficiency improvement
 is  highly correlated  with declining energy
 costs. For example, between 1980 and 1987,
 nominal  fuel prices declined by nearly 40%
 (U.S. DOE, 1988b), reflecting a drop of more
 than 50% in real terms. Combined with some
 efficiency improvements, this has  resulted in
 energy costs being reduced to a much smaller
 percentage, 10-15%, of total operating costs.
 Thus, the economic incentive to reduce energy
 intensity  has been greatly reduced.

      Because of the historical importance of
 fuel  costs,  however, a great deal  of research
 has  been conducted  within the  industry to
 identify    opportunities   for   efficiency
 improvements.     Currently,   commercially
available new planes are more than 25% more
efficient  than the 1980 fleet average (Smith,
1981, for  1980 average; Ropelowski, 1982,  for
test  results of  new 757 and  767 models).
Already  improvements have been identified
 that, if incorporated into aircraft design, could
reduce fuel use per passenger mile to  less
than  one-third  of  the  current  average
 (Maglieri and Dollyhigh, 1982; Smith, 1988).
 It may be technically possible to reduce fuel
 use per passenger mile to 50% of the current
 average by the year 2010.

       The rate at which  airline passenger
 miles will increase in the future is, however,
 a  matter  of considerable uncertainty.  Some
 industry sources are projecting very high rates
 of growth in  the next  few decades, which
 could more than offset the projected gain due
 to improvements in energy  per passenger
 mile.    Kavanaugh  (1988),  for  example,
 projects increases in global jet fuel use of 60-
 120%  by  the  year  2025 - despite assuming
 significant substitution of more  fuel-efficient
 aircraft during  the same period.

Alternative Fuels

      A   number of  alternative  fuels for
vehicles have been proposed in  the past few
years.  In the U.S. these proposals have been
driven primarily by concerns about the effects
of emissions on urban air quality and the
impact of petroleum-based fuels on energy
security.   Only recently have analysts  focused
attention  on the greenhouse contributions of
alternative fuels.   Near-term  options  of
interest include the use of alcohols  ~ both
ethanol   and   methanol,  as  blends  with
traditional fuels or as complete substitutes -
and  direct use of  compressed  natural  gas.
The discussion below  refers  to dedicated
alternative-fueled  vehicles  designed   and
optimized for the alternative fuel. In the near
term, however,  "flexible fuel" vehicles  may be
produced; these would be capable of burning
one or more of the alternative fuels as well as
gasoline.  In this case, because vehicles are
not optimized, energy efficiency may  be less
than optimal (and greenhouse gas emissions
would  be  higher).

     Methanol.  Although methanol  can be
produced  from biomass, in  the  U.S.  and
globally, natural gas would be the most likely
feedstock  for methanol in the near term. The
estimated   net  contribution  to greenhouse
gases when natural gas is used as a feedstock
will  be  roughly equivalent  to  that  from
burning gasoline from petroleum.   On the
other hand, greenhouse gas emissions  from
the use of coal-based methanol, measured
over the  entire  fuel  cycle, are about  double

 Policy Options for Stabilizing Global Climate
 those    from   crude-oil-derived    gasoline
 (DeLuchi et al., 1987).  A shift from natural
 gas to coal in the long run could lead to large
 increases in greenhouse gas emissions.

      Compressed natural gas (CNG) as a
 transport fuel produces fewer CO2 emissions
 per  unit of  energy released than  any other
 fossil fuel and also seems to be  among the
 cleanest  fuels available when considering its
 emissions of other gases that affect urban air
 quality (e.g., NOX, CO, and VOCs, although
 some questions remain about the level of NOX
 emissions from CNG vehicles).   However,
 leaks of natural gas, primarily methane (CH4),
 from the production, distribution, and refuel-
 ing processes, could add to the concentrations
 of this  greenhouse gas.  Some researchers
 estimate that this increase in CH4 could offset
 the advantage of lower  CO2 emissions. The
 degree to which CH4  releases would  increase
 or could be controlled is highly uncertain.

      CNG is currently used as a transport
 fuel in Canada and  New  Zealand,  among
 other  industrialized  countries.    In  New
 Zealand,  CNG,  liquified   petroleum  gas
 (LPG), and synthetic gasoline  (from natural
 gas) meet half of the total gasoline demand.
 Other  industrialized  countries have  small
 alternative  fuels programs, mainly based  on
 CNG, LPG, and methanol (Sathaye, Atkinson,
 and Meyers,  1988).

      Ethanol.    Ethanol  is  likely  to  be
 produced from biomass but is also likely to
 have difficulty competing economically unless
 its production is subsidized  by government.
Additionally, ethanol production by means of
current   technologies   relies, on  biomass
feedstocks such as corn and sugarcane, which
are also  food crops.   This competition with
 food production raises concerns  about the
 long-term viability of  this  approach.   As
discussed later, new technology for producing
ethanol from woody  biomass  may  become
commercial and alleviate this concern in the
 long term.   If fossil  fuels are used  in the
 production   process    (e.g.,   in    fanning
 operations  to  produce biomass  or  during
distillation), this could offset the greenhouse
gas benefits of biomass as a feedstock.

      In  summary, it appears that in the near
 term there is limited  technical potential for
 industrialized countries to achieve reductions
 in greenhouse gas emissions from the use of
 alternative fuels.   The CO2 reductions from
 alternative fuels  in  industrialized countries
 would not  be enough to  offset  projected
 growth  in  VMT.    However,  the  use  of
 alternative  fuels   in  combination  with  fuel
 efficiency  improvements may  help  alleviate
 other concerns related to  urban air quality
 and energy security without  increasing  the
 global warming commitment.   As discussed
 later, in  the  longer  term,  alternative fuels
 derived from renewable sources may play a
 key role in reducing greenhouse gas emissions
 in the transportation sector.

 Strengthen Vehicle Emissions Controls

      The United States  and  most other
 OECD  countries  currently  regulate   the
 emission  of hydrocarbons (HCs), CO, NOr
 and  paniculate  matter  on  a  gram   per
 kilometer (g/km)  basis.   Many  developing
 countries   have   recently  adopted  some
 emission  control  standards as  well.   The
 standards  vary for the weight class of  the
 vehicle as well as by the type of engine.

      International comparisons of emissions
 standards  are difficult because test procedures
 vary, but  it is  generally recognized that U.S.
 standards  are among the most stringent in the
 world. For light-duty gasoline vehicles (which
 constitute a majority  of the U.S. fleet),  the
 U.S. standards are 2.1, 0.25, and 0.62 g/km for
 CO, HCs, and NOr respectively.  Emission
 standards  in most European  countries  are
 significantly less stringent than in the U.S.
 (OECD,  1988).  Many developing countries
 have much less stringent standards, or none at

      Vehicles  sold in the United  States
 control emissions in two steps.  The first step 
 is to control the amount of pollutants formed
 during the  combustion  process.    During
combustion, the primary determinant of  the
amount of CO formed is the air/fuel mixture.
As  the air/fuel ratio increases,  CO  emissions
fall.  On the  other  hand, NOX  emissions
increase as the air/fuel ratio rises, a result of
the  concurrent  increase   in  combustion
temperatures, the primary determinant of NOX
formation. Higher combustion temperatures
are often associated with  increased power.

                                                              Chapter V: Technical Options
An engine designed for greater  power will
generally  produce higher "engine-out" NOX
emissions than an engine designed for fuel
economy.   Electronic  engine  management
systems, however, have been able to minimize
these tradeoffs, since  many  of the critical
engine parameters (like the air/fuel ratio) can
be controlled much more precisely (NAPAP,
1987; OECD,  1988).

      The second step is to treat the "engine-
out" exhaust after combustion to reduce emis-
sions to the acceptable standard.  To control
the "engine out" emissions, both catalysts and
exhaust gas recirculation (EGR) are used on
virtually all new U.S. and Japanese passenger
cars,  usually  in conjunction  with electronic
engine management systems.   Since 1981, the
primary catalyst system  used  on U.S.-bound
cars  has  been the  three-way  converter  
named for its  ability to reduce emissions of
HC, NOr and CO, as opposed to just one or
two  of the  gases.   Some cars also  use a
second oxidation  catalyst to catch additional
HC  and  CO.   Catalysts use  a variety of
precious metals, including platinum, rhodium,
and palladium, to break down or reduce the
unwanted emissions  without  causing the
metals themselves to  react (Automotive News,
1988; OECD,  1988;  White,  1982).    EGR
reduces  NOX   emissions  by  reinjecting  a
portion of the inert exhaust into the engine's
incoming  air.  The inert exhaust  gas cannot
react  in the  combustion process and reduces
peak  temperatures during combustion.  As a
result, less NOX is formed.  Today, all U.S.
light-duty  vehicles   have   EGR  systems
(Husselbee, 1984).

      Some   tightening  of  existing  U.S.
standards has been considered  and determined
to be technically  feasible, although probably
expensive on a dollar-per-ton removed basis
(NAPAP,   1987).       More   significant
improvements in global emissions of NOX and
CO could result from the extension of U.S.
standards  to the  rest  of the OECD and
ultimately, to the rest of the world.

      Current   technologies  for compliance
with  U.S. emissions standards have  added
substantially to the  cost of new vehicles,
although  improving  technology may reduce
the incremental cost in the future (U.S.  EPA,
1985; NAPAP, 1987).   Also,  with existing
technologies,  a  modest  tradeoff has  been
documented between  emissions control, and
fuel efficiency and performance, at the current
level  of U.S. emissions standards   (White,
1982; OECD,  1988).  Tradeoffs and cost for
tighter standards, however, would depend on
the stringency of the standards and the level
of  technology, as  well  as  the demand  for
other characteristics like performance.

Enhance Urban Planning and Promote  Mass

      In   addition   to    fuel   economy
improvements,  some  near-term  technical
opportunities undoubtedly exist for reducing
VMT in  personal  vehicles.   Programs to
encourage car pooling and use of mass transit
by urban communities may be justified on the
basis  of traffic congestion  and/or  local  air
quality benefits, but would also reduce energy
consumption and greenhouse gas emissions.
Similarly,  programs to improve maintenance
practices and to modify traffic problems (i.e.,
sequenced  traffic lights, one-way streets) to
encourage  driving  at  more efficient  speeds,
also have multiple benefits.

Near-Term Technical Options: Developing

      Transportation energy use  is a  serious
concern in developing countries for  several
reasons.     Worldwide,  energy  used  for
transportation  is almost exclusively from oil.
From 1973 to 1986 oil  use by developing
countries increased by 60%.  During this same
period, oil use by OECD countries declined
by  13%.   Recent projections by the U.S.
Department of Energy (U.S. DOE)  indicate
that the overwhelming majority (86%) of
growth in oil consumption in the "free world"
(defined  by U.S.  DOE  to  exclude  the
centrally-planned   economies  of   Eastern
Europe,  the Soviet  Union, China,  Cuba,
Kampuchea, North  Korea,  Laos, Mongolia,
and Vietnam)  through the  year  2010 could
come  from developing countries (U.S. DOE,
1987c).    The  largest  component   of  the
dramatic increases in oil use in developing
countries  during the  last decade is  in the
transportation  sector.  For  IS of the largest
developing  countries,  about  50%   of  the
growth in oil consumption in the 1970-1984
period has been in transportation applications

 Policy Options for Stabilizing Global Climate
 (Meyers,  1988).   Thus, indications are that
 energy  use  for  transportation   has   been
 growing at a very rapid rate in recent years in
 developing  countries, and this  high rate of
 growth is projected to continue  in the future.

      Although some  developing countries
 have   been  successful   in   implementing
 programs to reduce fossil fuel use (or at least
 oil use) in other sectors, very little attention
 has been paid to the  transportation  sector,
 either by these countries themselves  or  by
 international development assistance agencies
 (with a few notable  exceptions, e.g.,   Brazil
 and,  more  recently,  the  Philippines).   It is
 difficult   for   developing   countries   to
 implement  the  technical  options  that  have
 been   relatively  effective to date  in  the
 industrialized countries.

      First, information about transportation
 energy  use   is limited in many  developing
 countries.  It is very difficult  to estimate, for
 example, what portion  of the fuel  is used in
 new  versus  old  vehicles, light-duty  trucks
 versus heavy-duty  trucks, two- and  three-
 wheeled vehicles, etc. The information that is
 available,  however, suggests other problems.

      The average age of road vehicles tends
 to be higher in developing countries for two
 reasons.  Vehicles tend to be kept in service
 longer, and  used vehicles from industrialized
 countries  are  often  resold  to  developing
 countries. In addition, vehicles are often used
 for purposes other  than what  they  were
originally  designed   for.    There is  some
evidence that aging vehicles are often poorly
maintained  in developing countries.   Poor
roads also contribute to increased energy use
per vehicle kilometer of travel (VKT). Urban
congestion can also have this  effect, although
in some cases it may also act as a deterrent to
increases in  VKT.  Although heavily utilized,
 mass-transit systems in developing countries
 are generally poorly developed  and are also
 affected by poor or congested road systems.

      Thus,  the approaches  that  have been
successful   in  slowing   the  growth  of
 transportation energy use in the industrialized
countries over the past 15 years may not be
as effective  in  many developing  countries.
 Industrialized countries have been able to
significantly reduce the average  consumption
 of fuel per highway mile by replacing existing
 vehicles with more efficient newer models and
 developing or expanding mass transit in urban
 areas. The effectiveness of both strategies in
 most  developing countries  is  much  more
 limited because  of the slower  turnover  of
 vehicles  and  lack of  capital  to invest  in
 infrastructure improvements.

       On the other hand, it is expected that
 as developing countries reach a  certain per
 capita income, there will be a rapid explosion
 in the demand  for  personal  vehicles,  which
 will    dramatically  increase   transportation
 energy use  (Sathaye et al., 1988). The fuel
 efficiency of new vehicles available during that
 period can have a significant effect on future
 transportation energy use.

       Those developing countries that do not
 have domestic oil resources are concerned
 that  increasing  their  imports  of oil will
 diminish the already-limited foreign exchange
 available to finance development and hence,
 will  limit long-term growth.  Thus, there is
 great interest emerging in limiting oil use for
 transportation.    Efficiency  improvements,
 though often more difficult to achieve than in
 industrialized countries, clearly are pan of the
 solution.  Biomass-based alternative fuels are
 very important for some developing countries
 (Brazil, for example) in the near term.  Other
 developing countries (like some industrialized
 countries) may have natural gas that can be
 used for  transportation  or other types  of
 biomass-based  options.     Generally,  the
 transportation energy solutions that would be
 attractive to  developing countries for the
 purpose of  reducing oil  imports ~ efficiency
 improvements and alternative fuels -- are also
 beneficial   in   reducing   greenhouse  gas
 emissions.   One exception is the  use of coal
 as a  rail fuel, which occurs in China and India
 and  results in both lower energy efficiency in
 rail  transport  and in more CO2 per unit  of
 fuel  consumed.    This option  may  appear
 attractive to countries concerned primarily
with minimizing oil imports.

Increase Fuel Efficiency

      As   individual  developing  countries
reach a certain level of economic activity and
per  capita income,  it is expected that the
demand for personal vehicles will "take off,"

                                                                Chapter V: Technical Options
 as  occurred  historically  in  several  more
 industrialized countries.  Currently, gasoline
 prices  are   higher   in   many   developing
 countries, and oil imports frequently make up
 a large fraction of total imports.  Therefore,
 improvements  in  the  efficiency  of  new
 vehicles, both light- and heavy-duty, should be
 very  attractive  in developing  countries  to
 reduce fuel costs.

       Because of capital scarcity, all types of
 vehicles are kept in  service far longer  than
 they are in industrialized countries. Certainly
 for some developing countries, programs to
 improve  the  quality  of  maintenance or
 accelerate retirement  of older vehicles may be
 very useful  in reducing oil consumption and
 greenhouse gas emissions.

       For the same reason that aging vehicles
 are   kept  in   service,   new  classes  of
 intermediate vehicles, often used as low-cost
 transport   vehicles,    have   emerged    in
 developing  countries.  These  are generally
 produced locally, often by small companies or
 even  a single individual.  Some  alternative
 vehicles,   notably   the   Chinese   tractor
 converted   for   passenger  transport,   are
 adaptations of  vehicles designed for other
 purposes. In  India also, a  significant amount
 of   road   transport   in   rural   areas   is
 accomplished  with tractors.  As a means of
 passenger or freight transport,  many of these
 vehicles are  very energy-inefficient.    The
 Chinese tractors, for  example,  are estimated
 to use 75% more fuel than would a 4-ton
 truck while  carrying only 1 ton; these tractors
 account for  27% of the total diesel fuel use in
 China  (World Bank, 1985).  Programs to
 improve the efficiency of these vehicles or to
 replace them with more efficient alternatives
 may be very  effective in  the  near term in
 some developing countries.

Alleviate Congestion and Improve Roads

       In  rural  areas of  many  developing
 countries, roads are so poor  that traffic must
 move much  more slowly than is customary for
 intercity travel  in industrialized  countries.
 Frequent stops and starts are also a problem
 in these areas.   These conditions inevitably
 lead to reduced energy efficiency regardless of
 the quality  of the vehicles  themselves.   A
 recent  study  has concluded, however,  that
poor road conditions do not appear to act as
a deterrent to increased vehicle ownership in
rural areas of developing countries  (Meyers,
1988).    Thus,  carefully  planned  highway
improvements could result in net  reductions
in fuel use in some countries.  In addition to
reducing  fuel  use  in  the  existing  mix  of
vehicles, better roads may allow "upsizing" of
some of the existing traffic  to larger trucks
and buses  that are much more efficient on a
passenger- or ton-km basis.  Encouraging the
use of more efficient modes of transportation,
such as rail transport, may also be possible in
some cases.

      In urban  areas,  congestion  is clearly
already a major  problem in  many developing
countries   (as it  is   in  many  industrialized
countries)  and  is likely to  become more
severe as  rapid  urbanization  continues  in
many  developing  countries.     Although
congestion, as  already  mentioned,  reduces
efficiency  in fuel  use,  it may  also act as a
deterrent to increased vehicle use, promoting
the   widespread  use   of   more   efficient
alternatives to personal automobiles, such as
motorcycles and mass transit.  The degree to
which congestion  functions as a deterrent to
increased   transportation   energy   use   is
uncertain  and needs further investigation.

      Thus,  it  is  important to  carefully
evaluate   local    conditions  in   designing
improvements   to   urban   road   systems,
including   more extensive   roads,  but  also
better road maintenance and road planning.
It  may  also  be  important  to combine road
improvements with  other measures such  as
mass transit to achieve overall improvements
in energy efficiency.

Promote  and Develop Alternative Modes  of

      In addition to encouraging expansion of
urban mass transit, developing countries  may
wish  to promote alternatives  to  highway
transport  in  both  rural and intercity travel.
Because major investments  may be required
to develop or  improve highways for these
types of travel, it  may be more economically
attractive   to direct this   investment   into
improved  rail systems, for example, which
move passengers and freight more efficiently.
If highway  improvement programs are carried

 Policy Options for Stabilizing Global Climate
 out, however, they may be combined with the
 introduction of efficient  bus  systems, which
 would offer an attractive alternative to owning
 and using a personal vehicle.

 Use Alternative Fuels

       Alternative   fuels   based  on  locally
 available resources may be economically viable
 and important options in developing countries
 much  sooner  than is the case  for indus-
 trialized countries.   In countries that  have
 abundant  agricultural  land,   like  Brazil,
 commercial technologies to convert crops such
 as sugarcane or corn for  ethanol production
 may make sense (see PART TWO for more
 detailed discussion of the Brazilian ethanol
 program).     A  fuels  program  based  on
 sustainable   biomass  production   can   be
 extremely  beneficial  in   reducing  net  CO2
 emissions.      However,   most  developing
 countries  would have difficulty in diverting
 significant  amounts  of   biomass,  which  is
 currently used for food, to energy purposes.
 Converting  agricultural   residues  or  forest
 products to fuel may make more sense if the
 conversion    processes   can   be   made
 economically attractive.

      In  other countries  locally  available
 natural gas may be readily converted to CNG,
 which would reduce emissions of CO2 as well
 as many other air pollutants and also reduce
 oil imports. A recent review of international
 programs noted that most Asian countries and
 many  Latin  American countries  that  have
 domestic   gas  resources  are  conducting
 feasibility studies of CNG  use and many have
 pilot programs in place (Sathaye et al., 1988).
 Where  natural  gas is currently vented  or
 flared as a by-product of oil production, (e.g.,
 in the  Middle East), the availability of cheap
 local oil discourages investments in natural
 gas distribution and utilization systems.

      A final fuel-switching option that could
 be helpful in the near term is replacing coal
with  diesel   fuel   or electricity   in   rail
 transportation systems.  Coal is seldom  used
 anymore as   a  rail  fuel  in  industrialized
 countries - primarily because coal-fired  rail
systems are markedly less efficient than the
alternatives.   In energy consumed  per  mile
travelled, diesel trains are more than 3.5 times
as efficient, and electrified rail transport is 13
 times more efficient (compared on the basis
 of secondary energy consumed). If electricity
 is  generated  from  coal,  primary  energy
 consumed is three times greater than the end-
 use  energy  consumed. Electric rail transport
 in this worst case would be about  four times
 more efficient than coal-fired rail transport in
 primary  energy consumption and  net  CO2
 emissions.  However,  a   few  developing
 countries with abundant coal resources and
 extensive rail systems - notably  India and
 China -- still use coal in rail transport. India
 has  a   program   of  gradual  replacement
 underway, which is expected to eliminate coal
 use in rail systems by the year 2000.  A shift
 to   diesel  fuel  should  reduce  the  CO2
 emissions from this source by a factor of five.
 Research  is   also  underway  to  develop
 advanced,  more  efficient  technologies  for
 using coal as fuel in rail transport (Watkins,
 1989). This could also reduce CO2 emissions
 per mile travelled.
Near-Term  Technical  Options:
Eastern Europe
USSR  and
      In  the  USSR and  Eastern Europe,
transportation  makes  up  a  much  smaller
proportion  of  total energy  use  than  in
industrialized  countries  - primarily because
there are many fewer automobiles and trucks.
However, that number  is growing  rapidly:
from 1970 to 1980 the number of automobiles
in the Soviet Union increased from 1.6 to 6.9
million  (a rate of 15%/year), and the number
of  trucks  rose  from  3.2  to  5.1  million

      On the other hand, fairly significant
improvements  have  been  made  in  recent
decades in the efficiency of freight transport,
primarily  transport by rail.   From 1960  to
1975, ton-kilometers of  freight hauled by all
forms of transport  in  the  Soviet  Union
increased  by 276%, while fuel use increased
by 2.4% and electricity use increased by 418%
(from a  very  small base).   Overall,  this
represents a significant  increase  in  energy
efficiency  that  is   primarily  due  to  the
replacement of coal locomotives by much
more efficient diesel and electric engines
(Hewett, 1984).

      Given the rapid growth in the numbers
of automobiles and trucks in the recent past,

                                                                Chapter V: Technical Options
and in the number projected in the scenarios
developed for this report, it appears that an
important option for these countries will be
to  increase  the efficiency of new highway
vehicles.   In addition,  because of the large
natural gas resources available in the Soviet
Union  (discussed  in   PART  TWO),  the
feasibility of using compressed natural gas as
a   vehicle  fuel   may   deserve   further

Long-Term Potential in  the  Transportation

      The number of  technical possibilities
for  reducing  greenhouse emissions in  the
transportation  sector increases considerably
over the  long  term.  The range  of options
runs from making further improvements in
highway vehicles  and  expanding the use of
alternative   fuels,  to   using   alternative
transportation modes, to developing measures
that would reduce the need for transportation.
All options for the long  term are  somewhat
speculative and very sensitive  to assumptions
about the nature of society in the long term.
The discussion here is  intended to illustrate
possible  options  rather  than  to  suggest

Urban Planning and Mass Transit

      A major concern in many urban areas
throughout the industrialized countries (and
in  many  developing countries as well) is
increasing traffic congestion.  When vehicles
spend an increasingly  greater  proportion of
their time idling in stop-and-go traffic, they
use more fuel  and emit more air pollutants
per  mile  travelled.    In  the  near  term,
solutions  to  urban congestion problems  are
extremely  difficult   For the  long  term,
however, alternative approaches to alleviating
this problem will tend to incidentally benefit
the climate wanning problem.  Mass-transit
systems not only reduce highway commuter
traffic, but also use much less energy  per
passenger mile.  Average intensities (over all
time periods)  for bus  and rail transit  are
reported to range  from about 2.0-2.5 mega-
joules  (MJ)/passenger-km (Holcomb et  al.,
1987).   At normal commuting times, transit
systems tend to  be  much closer to  fully-
loaded, however, so that the energy intensities
per  passenger-mile would be  even  lower.
 Similarly, carpooling can  relieve  congestion
 and reduce  fuel use at the same time.

      Another  possibility  is  shifting  to
 smaller, commuter vehicles.  General Motors
 Corporation is testing a three-wheeled, one-or
 two-passenger, narrow, commuter car, which
 is essentially more like a covered motorcycle
 than a  traditional automobile.  Because the
 vehicle  is  much  narrower  than  a  normal
 passenger car, a standard traffic lane could be
 split in  half to double the carrying capacity of
 existing roads.  Because the vehicle is small
 and aerodynamically designed, it would also
 be much more fuel efficient than today's cars,
 achieving  over  100  mpg  (Sobey,   1988).
 Clearly,  some   safety  issues   and  other
 complexities in integrating such vehicles into
 current  urban   traffic  patterns   must  be

      The technical potential exists to design
 and construct  urban areas that are much more
 energy   efficient   in   terms   of   their
 transportation requirements (as  well as in
 their energy requirements for other end uses).
 By  comparing  cities  whose transportation
 energy  use  is very low,  relative to global
 averages, with cities whose energy use in this
 sector  is high,  it  is  possible  to  identify
 differences  in location patterns, mass-transit
 systems, and other factors that can partially
 explain  the differences in energy demands.  In
 theory,  it should be  possible to introduce
 incentives that  would encourage the more
 energy-demanding cities to develop along the
 lines of the  less energy-demanding cities over
 time.   This may be especially important in
 developing  countries  where  populations,
 especially urban  populations, are  growing

Alternative Fuels

      Use of alcohol fuels as an alternative to
 gasoline in highway vehicles is an option that
 is already receiving considerable interest for a
 number of  reasons.   Technologies currently
 exist for  producing ethanol  and methanol
 from various  types of  biomass.   Further
 research,   testing,   and   commercial
 demonstrations could be helpful in improving
 performance and lowering  cost  In the long
 run  it  appears  that production  of ethanol
 using current grain- or sugar-based technology

 Policy Options for Stabilizing Global Climate
 could play only a limited role.  Methanol may
 be  the  preferred  alternative  because  its
 biomass feedstock does not necessarily have a
 food value and  therefore is  not in  direct
 competition with food production. Research
 is underway to develop  and  commercialize
 technologies for ethanol production from non-
 food biomass  such as wood,  grass, and waste
 paper (Lynd,   1989).  If  these technologies
 become cost  effective, ethanol  may  play a
 much   larger   role   as    a    long-term
 transportation  fuel.   (See PART TWO for
 more discussion of alternative  fuels.)

      Technologies   currently   exist   for
 operating highway vehicles  with hydrogen fuel.
 Such vehicles  are not currently viewed  as
 commercial, primarily because of the high cost
 of hydrogen fuel  and the difficulty of storing
 enough  hydrogen  on board  for highway
 driving.    A  hydrogen-powered   automobile
 built by Daimler-Benz of West Germany and
 a  hydrogen-powered bus built by the Billings
 Energy  Corporation  of   Provo,  Utah,  are
 examples of current test vehicles.  These two
 vehicles use metal hydride  storage tanks, one
 promising approach to the storage problem
 (Ogden and Williams, 1988).  In  addition, if
 the  fuel-efficiency improvements described
 above are incorporated, future vehicles may
 be able to achieve driving  ranges comparable
 to today's vehicles while carrying much less
 fuel  on board.  The possibilities for producing
 hydrogen  at   competitive  costs  are  also
 improving  with  the development of solar
 photovoltaic technology (see  PART TWO).
 Another  attractive  feature  of  hydrogen
 vehicles is  that  the  engines  and internal
 structure required  are very  similar to what
 CNG-powered  vehicles would require.   CNG
 is  already being used in fleet applications in
some countries and will be more widely used
 in the future.  This could provide a market
 for the initial  transition to  hydrogen  when
 and if cost and storage problems are resolved.

      Electric-powered  vehicles  have  been
discussed for  many years  as an  option  for
 reducing oil use and/or urban pollution.  As
with hydrogen, the problem of storing enough
energy  on  board to  provide  a  reasonable
driving  range  is an unresolved obstacle.   In
addition, vehicle cost and performance ability
comparable to the cost and  performance  of
today's  vehicles have not  yet .been realized.
 Concerns about higher future electricity costs
 could also retard penetration of electric cars,
 even if other problems are resolved.

      The source of primary energy for both
 electric and hydrogen-powered vehicles will
 determine whether a  switch to these fuels
 increases   or   decreases   greenhouse   gas
 emissions.   Use of  non-fossil  sources  of
 electricity, such as solar or nuclear energy,
 would decrease emissions of CO2 and other
 greenhouse gases.  Conversely, use of coal-
 fired generating  capacity  as  the  primary
 source  of  electricity or  hydrogen  would
 increase greenhouse gas  emissions.

 Emerging  Technologies

      Telecommunications may substitute for
 many transportation  services in the  future.
 Teleconferencing is already replacing some
 types  of   business   travel,  although   the
 magnitude of this substitution has not been
 quantified in  energy   terms  as yet.    In  the
 future,  as  video  conferencing  equipment
 improves  and is more widely  available, this
 option  could  become  more   important,
 particularly if higher transportation costs and
 congestion  act as  incentives.    Catalogue
 shopping,  electronic   mail,   electronic
 advertising, and electronic banking are other
 applications of  telecommunications  that  are
 used to accomplish tasks and conduct business
 that formerly  required  travel.   A  recent
 analysis projects that  transportation  energy
 use may decline in  OECD countries because
 of these substitutions.   As  is  the case with
 many energy  efficiency  improvements,   the
 motivation for this substitution has very little
 to do with  energy  use.  These substitutions
 are  taking  place  because   consumers  and
 businesses perceive advantages in convenience,
 time saving, access to wider selections,  and
 cost savings (Schipper  et al., 1989).

      Fuel cell technology has many potential
 applications  (described   briefly   in   PART
 TWO).  Two appealing characteristics of fuel
cells  are   that  cost-effectiveness  is  not
 fundamentally a function  of size, as with many
energy technologies and that  the cells are
virtually pollution-free at the point of use
 (Jessup, 1988).  Because of these character-
 istics, one possibility is to use small fuel cells
to power highway vehicles. Input fuel can be

                                                               Chapter V: Technical Options
derived from natural gas, coal, or, ultimately,
renewables-based hydrogen. Several different
fuel-cell approaches are being researched and
tested currently.  If they prove economic, the
fuel cell could provide very efficient and clean
power for mobile sources at some point in
the future.

      High-speed rail systems are currently in
commercial use in  Japan  and France. They
compete well with aircraft or automobiles on
a performance basis for some intercity travel.
Energy  consumed  per   passenger-km  is
significantly lower than with automobile or air
travel alternatives.  As technologies develop
in the  future (e.g., superconductors), these
systems could become more  efficient  and
economically   attractive.     The  primary
constraints  appear  to  be  the  cost  of
constructing the systems and concerns about
safety and rights of way.


      In  the  United States  residential  and
commercial energy  services consumed 17 EJ
in 1985,  or about 29% of  total secondary
energy  (36% of equivalent primary energy).
For the OECD as a  whole, the picture is
quite  similar, with residential and commercial
energy use amounting to  about 30% of the
total secondary energy.  Figure 5-4 shows the
distribution of energy  use within the U.S.
residential/commercial  sector.   The  largest
component   (more  than  one-third)   of
residential/commercial energy use is for space
heating; combined with air conditioning  and
ventilation, the overall use of energy for space
conditioning  accounts  for more than half
(54%)  of all residential and  commercial
energy  use.  Lighting accounts for another
15%,  hot  water heating, 11%,  refrigeration,
7%,  and  the  remaining   energy  (13%) is
divided among  all   other  appliances  and
equipment used in residences and commercial
establishments (U.S. DOE, 1987b).

      Global energy use in the residential and
commercial sectors is  expected  to grow
significantly in the future.  In addition, a shift
toward  electricity for a higher percentage of
energy use in these sectors is likely, resulting
in increases in end-use efficiency, but implying
that primary energy required (accounting for
losses  in electricity  generation)  will grow
more rapidly.

      It  is  expected  that residential and
commercial energy use will grow most rapidly
in developing  countries as economic growth
rapidly translates into increasing demands for
energy-related  amenities  in   homes  and
commercial  buildings.   In the USSR and
Eastern Europe large increases are expected
for similar reasons.

      Due to  major technical improvements
demonstrated   in   recent  years,   future
residential  and  commercial buildings could
require substantially less energy for heating
and cooling.  Because the stock of buildings
turns over so  slowly,  it is also important to
focus on retrofitting, which could  reduce air
conditioning and heating  needs in  existing
buildings.     Dramatic   improvements   in
efficiency are   also  possible   in   lighting,
particularly in  commercial buildings, where
lighting may account for a  large share of the
electrical  energy used.    Improvements  in
lighting efficiency  also frequently have  the
added  benefit  of  reducing the amount  of
waste heat produced  by the  lighting system
and thus  reducing  the  air  conditioning
requirements as well.

      Options for reducing energy use in the
residential and commercial sectors are fairly
well characterized, at least in the OECD.  As
discussed below, potentials are very great, but
due to the long turnover tune of building
stock, improvements may have  to  be phased
in over a  long time  period.   In addition,
alternative   fuels    may   be   introduced,
particularly in  developing countries, which
would further  reduce  the greenhouse impact
of energy use.

      With aggressive programs to improve
the energy efficiency of buildings,  it  appears
technically feasible to reduce projected U.S.
energy use in the  residential/commercial
sector at least  50% by the year 2010.  The
technical potential in the OECD as  a whole
is   probably  close  to that  of  the U.S.
Although more detailed analysis is required,
preliminary indications are that the technical
potential to reduce projected residential and
commercial energy in the much more rapidly

Policy Options for Stabilizing Global Climate
                                   FIGURE 5-4
            Spac* Heating
                                    Hot Water Heating
                                         3.2 EJ
                                                                 Air Conditioning
                                                                 nd Ventilation
                                                                       6.3 EJ
 Source: U.I. DOE, ig*7e.

                                                               Chapter V: Technical Options
growing  developing  countries  and  in  the
USSR and  Eastern Europe is  even  greater
than   that   estimated   for   industrialized

      It  appears  technically  feasible  with
today's    technology   to   reduce   space
conditioning energy requirements  in  new
homes by 50% relative to the current average
for new homes.   Retrofits of existing homes
could reduce space conditioning energy use by
an  average  of 25% with the "house-doctor"
approach.   It may  be technically feasible to
reduce  energy use  in  existing commercial
buildings   by  at   least  50%,  and  new
commercial buildings  could easily be  75%
more  efficient   than   the  average  U.S.
commercial  building.    In  1985   the  U.S.
consumed about  15.3 EJ of energy (primary
energy   equivalent)   for   residential  and
commercial space conditioning  (U.S. DOE,
1987a).  Retrofits to existing stock could save
at least 4 EJ.

      Current   estimates   indicate   that
residential and commercial energy  use in the
U.S. and in the  OECD  as a whole  may
remain roughly constant through 2025 under
"business as usual" assumptions. With rapid
widespread  penetration of the most efficient
new   buildings,    instead   of    gradual
improvement,   the   growth   in   energy
consumption from  new buildings  could  be
greatly reduced.

      Based on  potential  energy savings  of
more than  60%  for almost  all  types  of
appliances,  a  50%  overall  reduction  in
appliance energy use by  the  year  2010 is
technically   feasible.     To  achieve    this
reduction would require  aggressive policy
actions  that  would  (1)  ensure  that   all
appliances produced in the next  decade be as
energy efficient as the best current technology
can produce and (2) encourage rapid turnover
of existing appliances.   Current energy use
from such appliances is in the range of 7.4-8.4
EJ  (expressed as primary energy equivalent).

      Near-term  technical  options in the
residential/commercial sector for industrialized
countries,  developing  countries,   and  the
USSR  and Eastern  Europe are  discussed

Near-Term Technical Options: Industrialized

Improve Space Conditioning

      Improved    efficiency   in   space
conditioning (heating  and cooling) can  be
obtained in several ways. First, the design of
new buildings can be altered to improve their
insulating qualities, thus reducing  losses in
heating  or  cooling.    Second,   improved
technologies can be applied  to make existing
buildings  more  weathertight, requiring  less
energy  for  heating  and  cooling.   Finally,
advanced technologies for heating and cooling
equipment can be dramatically more efficient
than devices currently in wide use.  A number
of very thorough and high-quality  reviews of
the   potential    for  energy   efficiency
improvements   in   buildings   have  been
produced  in recent years  (see, for example,
Hirst et al., 1986; Schipper et al., 1985).  The
discussion  below  draws  on  the  extensive
published literature to illustrate the technical
potential for improvement.

      New  Residences.   The potential  for
improving energy efficiency in new homes is
very significant.   Simply  by  modifying  the
building shell   to  improve   its   insulating
capabilities,    space   heating   energy
requirements can  be  reduced dramatically.
Current new homes in the U.S. require, on
average, almost  40%  less energy to achieve
the same level  of heating  as the average
existing house in the U.S. (See Box 5-3, which
illustrates the range of energy requirements
for space heating on a per unit of floor space
basis.)  What is even more interesting is that
the most efficient new houses are 50% more
efficient  than   the  average  new  home.
(However, relatively few of these very energy-
efficient homes  are currently being built.)
Very   advanced   prototypes   and  design
calculations indicate  that  it  is  technically
possible to build homes whose heating energy
requirements would range  from  15 to 20
kilojoules per square meter  per degree  day
(kJ/m2/DD),  or  10-12%  of  the  average
requirements for today's homes.2

Policy Options for Stabilizing Global Climate
                BOX 5-3.  Improving Energy Efficiency in Single-Family Homes

                    Space Heat Requirements in Single-Family Dwellings
     United States

         Average, housing stock                                           160
         New (1980) construction in U.S.                                   100
         Mean measured value for 97 houses in Minnesota's
             Energy Efficient Housing Demonstration Program                51
         Mean measured value for 9 houses built in Eugene, Oregon           48
         Calculated value for a Northern Energy Home, New York area        15


         Average, housing stock                                           135
         Homes built to conform to the 1975 Swedish Building Code           65
         Mean measured value for 39 houses built in Skane, Sweden           36
         House of Mats Wolgast, in Sweden                                 18
         Calculated value for alternative versions of the prefabricated
             house sold by Faluhus
             Version #1                                                   83
             Version #2                                                   17
     Source: Goldemberg, 1988.
         The striking energy savings (compared with the average home), up to 90%, that is
     possible with new "low-energy" homes, as illustrated by the figures above, are achieved
     through the use of state-of-the-art construction and design techniques and technologies;
     a few of the areas where significant changes have occurred include the following:

           Building Envelope - Larger wall and ceiling cavities, allowing for significantly
            more insulation, have been obtained with new construction materials and
            designs, such as "I-beam" framing members, raising R-values to as high as R-
            38 in some  low-energy homes.  Polyethylene vapor/air barriers in external
            walls reduce infiltration of outside air, one  of the major sources of heat loss
            in most homes. Windows are being triple  and even quadruple glazed, and,
            in  some cases, incorporate  low-emissivity films  and inert gases, such as
            argon, between the panes to improve their insulating quality.

                                                               Chapter V: Technical Options
                 BOX 5-3.  Improving Energy Efficiency in Single-Family Homes
            Mechanical -- These include heating, cooling, and ventilating systems.  In
             addition to high-efficiency furnaces, heat pumps, and air conditioners, many
             low-energy homes incorporate air-to-air heat exchangers. These are needed
             to bring fresh air into the house,  since natural infiltration is significantly
             reduced, but they improve energy efficiency by extracting approximately half
             the heat from the  exhaust  air and transferring it to incoming air.  The
             newest development in mechanical ventilation is the heat-pump exhaust
             system, which uses warm exhaust air to provide water heating.

            Active/Passive Solar Design, Thermal Storage - Many different designs have
             been  developed to make better use of solar gain to provide heat. These
             include use of south-facing windows, greenhouses,  atriums, etc., and are
             often combined with thermal storage systems that store heat collected during
             peak  daylight hours for redistribution when it is needed at other times.
             Storage systems can also work in the reverse way, collecting cool air during
             the night and circulating it during  warmer hours.
      In  addition  to  the  potential  for
improving the thermal properties of building
shells, equally important advances have been
made in developing high-efficiency equipment
for both space heating and cooling.  Already
being marketed in the U.S. and in Europe are
high-efficiency gas and oil furnaces  that are
about  95%  efficient,  compared with  the
average of 75%  for new furnaces in  the U.S.
(Geller, 1988).

      Substantial energy savings are possible
in electrically heated (and cooled) homes with
recently designed efficient heat pumps. The
most  efficient pumps on today's market are
about one-third  more  efficient than  average.
Advanced ground-coupled heat  pumps have
recently been commercialized and will provide
even more efficient  options over  the  next
decade.  These commercial systems have been
shown to achieve  a "seasonal  performance
factor" (SPF) of 2.5-3.0, which compares with
an SPF of 1.5-1.9 for electric air-source heat
pumps (Strnisa,  1988).  In addition,  gas heat
pumps are currently being demonstrated and
may be commercial soon.  These systems may
be even more efficient than advanced electric
heat pumps.
      With super-insulated shells it may not
be  necessary  to install  a  central  heating
system at all.  Some of the advanced designs
require so little heat input that small electric
resistance heaters may be  cost-effective in
moderate climate areas. The greatly-reduced
capital cost for this option  may offset the
increased cost for the superinsulating features.
In very cold regions, the  added cost of very
efficient gas or oil furnaces would be justified.
In regions where cooling is also required, the
advanced heat pumps would probably be the
most economic choice.

      If all options were used in combination,
it  appears  technically quite   feasible  for
advanced   building shells    and  efficient
heating  and  cooling  equipment to  reduce
space  conditioning  energy requirements in
new  homes to  less than 10%  of current
average use.

      Existing Residences.  It is expected that
the net growth in housing stock will be slow
in the  future  in  industrialized  countries
because  of the extensive  existing stock  and
low population growth.  In addition, existing
housing  stocks have  very  long lifetimes.

 Policy Options for Stabilizing Global Climate
 Therefore, existing stocks  will dominate the
 residential sector for many decades.  Thus, it
 is   extremely   important   to   focus   on
 opportunities   for   reducing   energy
 requirements in existing buildings.  Many of
 the  advances that have made  possible the
 enormous potential energy savings  for  new
 homes  are  to  some extent applicable to
 existing homes.

      In  general,  retrofit  improvements are
 somewhat less effective and more  costly than
 those incorporated in the  initial design of a
 new  home.    Nonetheless,  cost-effective
 technical   options  exist  for  substantially
 reducing  energy  requirements  of  existing
 homes.    Storm windows,  added  insulation,
 clock thermostats, and  retrofit  of heating
 systems have been  considered conventional
 conservation measures for  several years.  In
 addition, improved maintenance of equipment
 and  building shells and more  attention to
 operation  of  equipment   (i.e.,  automatic
 setback thermostats, automatic light switching)
 could reduce energy consumption in existing
 buildings  at relatively low cost.  Programs to
 encourage consumers to  implement these
 conservation options have been carried out in
 a  number  of  areas  and   have   shown
 considerable success.  One study of  40,000
 retrofits monitored by U.S. utility companies
 in  the  early  1980s  showed  that  energy
 consumption fell  by 25% on average,  and
 homeowners received a 23% return  on their
 investments (Goldman, 1984).

      Despite  the favorable  economics  of
 some retrofit conservation  measures, only a
 small portion of the potential energy savings
 from conservation retrofits  has been realized
 to date.   This  is  especially  true in  rental
 housing where the landlords do not  perceive
 a financial interest in investing in retrofits.
 Also, low-income  families,  even if they own
 their homes, often lack  the information or
 upfront  capital  to  carry  out cost-effective
 conservation measures.     If  conventional
 retrofit programs could be extended to larger
 percentages of existing housing stock, energy
savings could be substantial.

      Beyond   conventional   conservation
programs, there are now more sophisticated
options  for improving the retrofit  savings.
Detailed  measurements since  the  late 1970s
 have shown that existing homes have obscure
 defects in their thermal envelopes, leading to
 very large heat losses.  Conventional walk-
 through energy audits are unlikely to identify
 these   defects,   nor   would   subsequent
 conservation  retrofits  correct  them.   New
 instrumented  analysis  procedures developed
 over  the last few  years  can locate these
 defects quickly, but these instrumented audits
 are  expensive  compared  with the standard
 energy audits  now provided by many utilities.

       On  the other  hand,  many of  the
 "hidden" defects, once detected, can be easily
 corrected at small cost.  This has led  to the
 development of the "house-doctor" concept as
 an alternative to traditional audits. For this
 type of audit a team of technicians conducts
 an instrumented audit and repairs many of
 the defects  on the  spot.  One test of  this
 concept  showed average immediate  energy
 savings of 19% from one-day "house-doctor"
 visits.   Subsequent  conservation  retrofitting
 done at the recommendation of  the  house
 doctors   increased   the  average   energy
 reduction to 30%.   The average cost  of all
 retrofit measures was $1300 and the average
 real internal rate of return in fuel savings was
 20% (See Goldemberg et al., 1988).

      Another  approach   to    improving
 residential and commercial energy efficiency
 has been proposed recently by researchers at
 Lawrence Berkeley Laboratory.      Their
 approach  is  a  reworking  of the  age-old
 concept of  using  shade  trees to assist in
 cooling residential buildings.  In their analysis
 the authors point out that in addition to the
 direct  benefit in  terms  of reducing  air
 conditioning loads at each house, the indirect
 effect of planting trees throughout an  urban
 or suburban area, as well as  other measures
 to increase  the reflectivity of surfaces,  can
 reduce  the  "heat  island" effect,  lowering
 ambient temperatures and further reducing air
 conditioning loads. In addition, of course, the
 trees   directly  remove  CO2   from   the
 atmosphere, although the CO2 reductions due
 to reduced  cooling  loads  from well-placed
trees  are  probably  much  greater than  the
CO2 absorption by the trees  (see Rosenfeld,
 1988; Akbari et al.,  1988).  The city of  Los
Angeles has announced their intent to start
such a program (Washington Post,  1989).

                                                               Chapter V:  Technical Options
      The advanced furnaces and heat pumps
available for new homes could  also provide
significant  benefits in  the retrofit  market.
Economics   of  efficient   equipment   are
generally more favorable as retrofits.  Even
after  a  retrofit shell  improvement program,
including the house-doctor approach, energy
use in existing  homes will remain well above
the best levels  achievable for  new super-
insulated homes.  Thus, the added expense of
advanced heating and cooling equipment will
be paid back much faster in energy savings.

      In one  example, existing  homes that
had already been  visited by house doctors and
had received associated shell  improvements
were evaluated for improved furnaces.  Shell
improvements were shown  to have  reduced
gas use for space  heating to about 70% of the
previous requirement.  Researchers estimated
that  retrofit  of  advanced  condensing  gas
furnaces would further reduce space heating
energy  use  to   44%  of  the   original
requirement.   The  estimated  incremental
investment   (to replace a  worn-out  furnace
with the 95% advanced furnace rather than a
conventional 69% model)  was estimated to
average $1000 and result in fuel savings that
correspond  to a  real  rate of return of 15%
(Goldemberg et al., 1988).

      Commercial Buildings. Like residences,
commercial   and  institutional  buildings
currently use significant amounts of energy,
particularly   for   space  conditioning  and
lighting.      Opportunities  for  efficiency
improvements   also    appear   significant
Commercial buildings in the U.S.  use about
3.6 EJ of fossil fuels annually  (mostly gas in
the U.S. - other OECD countries continue to
heat a significant percentage  of  buildings
with oil)   and about  2.6 EJ of  electricity
(equivalent to about 8 EJ of primary energy)
(Rosenfeld  and Hafemeister, 1985).

      Some progress is already being made in
improving  energy efficiency in  commercial
buildings.  While surveyed  commercial space
in the U.S.  increased by almost 10% between
1979  and  1983,  total  energy  consumption
actually declined  by about  4%.   Electricity
consumption, however,  increased in absolute
terms as well as in share of total commercial
energy  use.    Thus,   the  primary  energy
equivalent  of  commercial  end-use  energy
consumption  has  increased  (U.S.  DOE,

      While  progress has  been  made,  it is
evident that  commercial energy use  in the
U.S. could still be reduced significantly with
cost-effective efficiency measures. Estimated
commercial energy use in the U.S. was about
3.0 gigajoules (GJ)3  per  square meter per
year in 1980 (expressed as equivalent primary
energy production). This figure is down  from
5.7 GJ in 1973, but could still be  greatly
improved (Flavin and Durning, 1988).  One
recent analysis estimated that energy  use in
new commercial buildings could be reduced by
more than 50% below the current averages
(Rosenfeld and Hafemeister, 1985).

      As in the residential  sector, traditional
building shell conservation  measures, such as
added  insulation  and   window  glazing,
reductions in infiltration rates of outside air,
passive  solar energy  concepts, and  heat
exchange  between  exhaust  and  incoming
ventilation air are effective  although  less
important. The traditional approach  of tree
shading combined with reflective surfaces to
achieve direct cooling can, as discussed above,
also be applied to commercial buildings.

      In addition, some  more sophisticated
techniques are   cost  effective  for  larger
commercial buildings.    New  commercial
buildings  are  being designed with  "smart"
energy   management   systems.      These
computerized  systems monitor outdoor and
indoor temperatures,  levels of sunlight and
location  of people in the building.    The
system can then allocate heating, cooling and
ventilation efficiently (Brody, 1987).

      Another advanced   technique  being
applied for commercial energy efficiency is
thermal storage.  In this case, some storage
medium, such as a body of water, is used to
store  heat or cooling when  it is readily-
available and  then the warm or cool air is
released  later when  it  is needed.    This
concept has been used in new  commercial
buildings in Sweden, storing heat energy from
people and equipment, and in Nevada to chill
water with cool night air and use the  chilled
water to offset the need for air conditioning
during the day (Rosenfeld  and Hafemeister,

 Policy Options for Stabilizing Global Climate
      Window technology is also improving
rapidly.  A special "heat  mirror" film, which
doubles  the  insulation value of windows, is
now  commercially available.    The  film  is
designed to let light in without allowing heat
to escape.  Another available technology is to
create a vacuum  in the  space  between  two
panes, creating a thermos effect.  These and
other  advanced  technologies   may  allow
commercially-available windows  in the 1990s
to have the same insulating value as ordinary
walls (Brody, 1987; Selkowitz, 1985).

      As was the  case with residences, many
of the advances in energy efficiency for new
commercial  buildings  are  transferable  to
retrofit applications to a lesser degree.  A
study conducted some years ago  attempted to
estimate the potential energy savings available
from  retrofits   of   existing   commercial
buildings.   The conclusion  drawn  from a
survey of several  experienced engineers  and
architects  was  that   a   target   of  a  50%
reduction in energy use in U.S. commercial
buildings by the year 2000  was reasonable
(SERI, 1981).

      More  recently,  Amory   Lovins  and
others at  the  Rocky Mountain  Institute
conducted  a detailed analysis of the retrofit
potential of  commercial  buildings in  the
Austin, Texas, area.   This study identified
potential savings  in electrical  energy  that
totaled   73%  of  the   buildings'  current
electrical energy use (for lighting and other
equipment as  well  as space  conditioning).
The cost of these  measures was  estimated to
be lower than the operating costs of existing
powerplants   (Rocky  Mountain  Institute,
1986).  There  is some question as to what
proportion of these calculated savings could
be achieved in practice.

      District   Heating   and  Cooling/
Cogeneration.   Use  of district  heating and
cooling (DHC) can be an extremely efficient
approach to space conditioning, particularly in
dense urban areas and when the heat source
is   also    a  cogenerator   of  electricity.
Technologies for cogeneration -- simultaneous
production of electricity and heat or steam for
other useful purposes -  are  described  in
PART TWO. Cogeneration with DHC could
serve a very large  potential market for these
efficient  technologies, with the possibility of
 offsetting  significant  amounts  of  oil  and
 natural gas that would otherwise be used  in
 dispersed  space  heating  applications.    In
 addition, heat from a central cogenerator can
 be used to generate air conditioning in high
 efficiency,  heat-activated chillers that do not
 use chlorofluorocarbon  (CFC)  refrigerants,
 possibly offsetting  significant  amounts   of
 electricity  use and  contributing to needed
 reductions in CFC production. This approach
 is already  widely  used in  the Soviet Union
 and in many European countries and may be
 expanded  in the  future.   In Denmark, for
 example,  46%  of  current space  heating
 requirements  are  met with district heat  -
 27% based on cogeneration and the other
 19%,  single  district  heating.    A recent
 projection  estimates that  by  2000 district
 heating  based  on  cogeneration  will satisfy
 almost   37%   of   total   space   heating
 requirements   (Mortensen,  1989).     The
 efficiency improvements in this type of system
 are substantial and contribute to reduced CO2
 emissions even if  fossil fuels are used,  as  is
 normally the case.  The International Energy
 Agency  (IEA)  is  coordinating a significant
 amount of research  by member  countries to
 develop  more cost-effective technologies for
 DHC.   A  recent  report  documents  47
 advanced  technologies  that  can  improve
 efficiency or lower costs (IEA, 1989).

      Interest in DHC has grown in the U.S.
 as well in  recent  years.   In New York, for
 example, three  demonstration  systems  are
 currently in operation in Buffalo, Rochester,
 and Jamestown.   Studies  are  underway  to
 design  systems  in five  other  communities
 (Strnisa, 1988).  At a recent conference on
 DHC technology,  one participant estimated
 that   widespread  application   of
 cogeneration/DHC systems could reduce U.S.
 carbon  dioxide emissions by 10-15%.   This
 would also be expected to produce significant
 local and  regional  economic  benefits   -
 reducing and stabilizing energy costs to local
 government  and   business  communities,
 creating  jobs  for  skilled  and  unskilled
workers, and retaining a greater proportion of
 total  energy  expenditures in  local  areas
 (Clarke,  1989).

      Indoor Air  Quality.    One  of  the
concerns   about  increasing  the  energy
efficiency of buildings is  the  increase  in

                                                               Chapter V: Technical Options
 indoor air pollution that can result, primarily
 from efforts  to reduce air infiltration.  Most
 homes in the U.S. have air exchange rates, on
 average, of more than one change  per  hour,
 meaning all the air in the house is replaced
 by outside air once each hour. As new homes
 are constructed more tightly and some  older
 homes are retrofitted with vapor barriers and
 better seals around doors and windows, the
 air exchange rate drops.  Without additional
 ventilation measures, concentrations of several
 harmful  pollutants,  including  radon   gas,
 formaldehyde,  combustion   products  from
 tobacco smoke and wood stoves, and asbestos
 particles, can reach harmful levels.

      Control  strategies  for these  forms of
 indoor air pollution include air cleaning, local
 ventilation, mechanical ventilation with heat
 recovery, and exhaust ventilation  with  heat
 pump heat recovery. Heat recovery or air-to-
 air exchange  systems have  become  more
 popular  as  homes  have   become  better
 insulated and more tightly sealed. These can
 ensure   the   generally-accepted   minimum
 standard of about 0.5 air changes per hour,
 while reducing heat loss  by  using the heated
 exhaust air to  warm the incoming  fresh air.
 Unfortunately,  the costs of these systems are
 high and studies in Canada suggest that  their
 efficiencies may be lower than manufacturers
 have  claimed (Hirst et al., 1986).  This may
 be due  in part to improper  maintenance by
 homeowners.   Heat recovery systems, which
 usually  draw air  continuously and  can  have
 problems with  condensation forming in the
 heat  exchanger,   require   more   routine
 maintenance  than the average homeowner is
 accustomed to devoting to a major appliance.
The  use of  exhaust  ventilation  systems
connected to an air or water heat pump is a
 new technological  approach that  may  hold
some promise for improving cost-effectiveness
and  improving some of  the maintenance
issues.  These  systems are  being developed
primarily in  Sweden.   It  appears  that
currently-available commercial technology can
be applied  to  maintain indoor  air  quality
standards while significantly reducing energy
 requirements.   Current technology develop-
ment efforts  directed at reducing costs and
 maintenance  requirements should be  a  high
priority research area.
 Use Energy-Efficient Lighting

      Lighting consumes about 20% of U.S.
 electricity,  most  of  it  in  residential  and
 commercial buildings.  This end  use  offers
 some of the most  cost-effective opportunities
 for saving energy.  One study has estimated
 that  40  large  U.S.  powerplants  could  be
 replaced  by simply implementing currently-
 available,  cost-effective  lighting  efficiency
 improvements  (Rosenfeld  and Hafemeister,
 1985).  Cutting electricity use for lighting in
 industrialized countries  by three quarters has
 been  proposed as a reasonable goal (Flavin
 and Durning, 1988). Box 5-4 describes several
 key advanced lighting technologies.

      A  number  of currently  commercial
 measures,  implemented in combination,  can
 achieve dramatic  energy reductions ~ over
 75%  in   commercial/institutional  settings.
 These measures include improved controls,
 reflectors,  spacing of  lighting,  and  more
 efficient bulbs and ballasts.  The University of
 Rhode  Island  reported reductions of 78% in
 lighting  energy after implementing such  a
 program.    The cost of saved  energy  was
 calculated to be less than 1 cent per kilowatt-
 hour  (kwh) (New England Energy  Policy
 Council, 1987).  An added benefit of lighting
 improvements in warm climates is  that more
 efficient lighting  reduces  waste heat  and,
 therefore,  air  conditioning  loads.    The
 California  Energy  Commission has estimated
 that in  Fresno, every  100-watt  savings  in
 lighting  reduces  air  conditioning energy
 requirements by 38 watts (Rocky  Mountain
 Institute, 1986).

 Use Energy-Efficient Appliances

      After space  conditioning and lighting,
 remaining  energy uses  in  residential and
 commercial buildings are largely associated
with  large  appliances.    Opportunities  for
significant energy efficiency improvements in
 this category  have been well  documented.
 Table   5-4   illustrates   some   of   these
 opportunities.   U.S.-made refrigerators,  for
 example, currently  average 1450 kwh per year.
 The best currently commercial model in  the
 U.S. uses about half  that much energy.   A
 recent study calculated that efficient new

Policy Options for Stabilizing Global Climate
                           BOX 5-4. Increasing Lighting Efficiency

      Research and development into energy efficient lighting and design features has produced
      a constant stream of new products and advances. Below are brief descriptions of several
      of the areas where major advances have taken place.

            Compact Fluorescent Lamps:  Compact fluorescent lamps are designed to be
             screwed into a standard light socket and thus have begun to compete directly
             with incandescent bulbs.  Because they are 60-70% more energy-efficient
             than incandescent  (Hirst et al.,  1986) and are beginning to gain wider
             acceptance, they represent potentially significant energy savings.  If compact
             fluorescent replaced all incandescent lighting, it has been  calculated that this
             could displace 7.5% of total electrical consumption in the U.S. (Lovins and
             Sardinsky,  1988).

            High Intensity Discharge (HID) Lamps: These  are  designed primarily for
             warehouses, factories, street  lighting, etc.  Three types  of HID lamps are
             currently in use:  high-pressure sodium, low-pressure sodium, and metal
             halide. High- pressure sodium and metal halide give approximately 45-60%
             savings over mercury vapor or fluorescent lighting. Low-pressure sodium is
             somewhat more efficient, but its intense yellow light can be undesirable for
             many applications (Hirst et al., 1986).

            Electronic Ballasts:  In conventional fluorescent lights the voltage required
             for operation is provided by  an electromechanical ballast which itself
             consumes a portion of the energy used.  New electronic ballasts reduce this
             additional power consumption by 20-35% (Hirst et at, 1986) and, became
             of  their smaller size, are a key factor  in the emergence of compact
             fluorescent lamps.

            Daylighting:  Daylighting is a design approach that enhances the use of
             natural light  either from windows, sidelighting, clerestories, monitors and
             skylights, or from the use of light pipes or optical fibers to transmit light to
             the location needed. The use of light colored paints and light shelves helps
             to distribute the light into the building interior.

            Additional  Advances:  Several other advances in lighting technology and
             design deserve mention.  One advance is specular ("mirrorHke11) reflectors
             that increase  total reflectivity, direct the light in a more  optically favorabk
             direction, and maintain their  high reflectivity significantly longer. Lighting
             controls, which include time clocks, scheduling controls,  personnel or
             occupancy  sensors, and daylighting sensors, reduce power consumption by
             turning off lights when they are not  needed.  Task  lighting improves
             efficiency by directing light onto the specific task area where it is needed
             most, rather than lighting entire areas.

                                                              Chapter V:  Technical Options
                                        TABLE 5-4
                 Summary of Energy Consumption and Conservation Potential
                             with Major Residential Equipment

                                   (kwh/yr or therms/yr)
Central AC
Room AC
Elec. water heating
Elec. range
Elec. clothes dryer
Gas space heating
Gas water heating
Gas range
for 1990s3
a Unit energy consumption per typical installation in the 1986 housing stock.

b Unit energy consumption for the typical model produced in 1986.

c Unit energy consumption for the best model mass-produced in 1986.

d  Unit energy consumption  possible in  new  models by  the mid-1990s if further cost-effective
advances in energy efficiency are made.

Source:  Geller, 1988.

 Policy Options for Stabilizing Global Climate
refrigerator freezers that would use about 200
kwh per year, or less than 15% of the current
average use, could be cost-effectively produced
(Goldstein and  Miller, 1986).  Water heaters
also  account   for  a  large  percentage  of
appliance  energy  use.    The potential  for
energy savings is  significant through the use
of the most efficient technologies and also by
switching  from electricity to  gas.    Other
energy-intensive  appliances   also  provide
opportunities for energy savings.  As shown in
Table 5-4, the  potential  exists  for  advanced
technologies that  could be produced in the
1990s that are at  least   50%  more energy
efficient than the  1986 average for  all  major
energy-using  residential  appliances  (Geller,
1988).  As discussed in Chapter VII, recently
enacted  national  appliance energy  efficiency
standards are expected to produce substantial
improvements in the United States.

Near-Term Technical Options:   Developing

      In   developing  countries   markedly
different  strategies  may be necessary  to
address  residential  and  commercial energy
services. In many developing countries there
are distinct modern and  traditional sectors.
In the modern sector, energy-use patterns are
very similar to those in industrial economies
(adjusted    for    climate   differences).
Commercially-marketed    fossil   fuels   and
electricity  provide  the energy  input  for  a
similar   mix  of  energy  services:     space
conditioning,  water heating,  lighting, and
appliances     for    cooking,   refrigeration,
entertainment,  etc.   This  modern sector,
however, is often smaller  than the traditional
sector,  which exhibits completely  different
energy-use patterns.

      The  energy  sources in  the traditional
sector are  largely "noncommercial" biomass,
used  primarily  for  cooking  and,  in  some
colder or high-altitude regions of developing
countries, for space heating. Also, fossil fuels
(e.g.,  kerosene)  are frequently  used  for
lighting.  (In  China and the coal districts of
India, unlike most  other developing countries,
coal is also used for residential cooking and
space heating in the traditional sector.)  The
task of development projects in these poorer
sectors is to vastly  increase the level of energy
services   available    for    residential   and
commercial  applications.     Altruism  and
development objectives aside,  this approach
can   contribute   significantly   to  solving
the climate warming problem  because many
developing countries have used fuelwood  to
such  an extent that they  have become net
consumers of forests, and global deforestation
is one of the significant causes of increasing
greenhouse  gas    concentrations.      The
important issue from a climate perspective is
to increase energy services without increasing
greenhouse gas emissions.

      As the developing countries continue to
increase their  per  capita  energy use, the
implications  in terms of  energy use and
greenhouse gas emissions are enormous. It is
technically possible, however, for developing
countries to  substantially increase per capita
energy services without substantially increasing
fossil-fuel use.  Emissions-reducing strategies
similar  to  those proposed for industrialized
countries can be  promoted in the modern
sectors of the developing countries.  However,
strategies suitable  for  the traditional, poorer
sectors  must be  integrated  into  ongoing
economic development programs if they are
to  be  accepted by the  local  population.
Technical options for reducing greenhouse gas
emissions must not only be efficient, but also
be  designed  to increase energy  services to
these poorer sectors.

More Efficient Use of Fuelwood

      The primary use of biomass energy in
developing countries is in residential cooking,
traditionally  done in  inefficient  and  smoky
conditions.   The inefficiency of combustion
can  exacerbate  deforestation  and lead  to
increased time and effort devoted to gathering
fuelwood  (and  fodder),  and  the   smoky
combustion results in exposures to significant
emissions of  health-damaging air pollutants.

      Recognition  of  these  problems has
focused   a   great  deal  of  attention on
improving  the  cookstove   as  a  low-cost
solution. Existing cookstoves have efficiencies
only on the order of 10%.  Relatively simple
improvements in stove design can in theory
reduce   wood   requirements  by  35-70%
(Goldemberg et al.,  1987).  However,  getting
people in developing countries  to accept and
use better-designed stoves has proved difficult

                                                                Chapter V: Technical Options
for a number of reasons (Miller et al., 1986).
In spite of spirited efforts by a  number  of
dedicated   groups,  generous    grants   by
international  aid  agencies,  and  substantial
expenditures  by  many governments,  it has
proved  surprisingly difficult to coax people
away from traditional cooking  stoves and
practices.   Traditional stoves come  in   a
bewildering variety of designs and materials
and  have evolved to suit local fuels and diets.
They perform a multitude  of functions that
were  not  considered  by   designers  and
promoters of early "improved" stoves.  Failure
of the newer  designs to incorporate features
that could perform some of  these functions
often hampered their acceptance.  Current
improved designs represent a third generation
in   this  technology  development  process
(Smith, 1989).

      West Africa, Kenya  and   Karnataka,
India,  and  a  few  others,  are  successfully
promoting improved-design stoves (Baldwin et
al.,  1985;  Reid et al., 1988).   Successful
designs are based on sound principles of heat
transfer  (Baldwin,  1987), are targeted  to  a
particular  region  (generally  where cooking
fuel   is   traded),   require  no   substantial
behavioral modification from users, and are
provided with follow-up support.

      Predicted fuel savings  with improved
stoves, which  are based on  laboratory water-
boiling efficiency tests, have invariably proved
to be overestimates under field conditions.  If
fuel  savings observed in the laboratory were
directly transferable to the field, an improved
stove with 40% efficiency  would  result in  a
75% fuel saving when it replaced a traditional
stove with 10% efficiency.   Yet  only a few
programs have reported fuel savings (at best
on the order of 20%), though greater savings
could be possible  as programs improve with
experience (Ahuja, 1990).

      Despite  the   limited    efficiency
improvement with  new fuelwood applications,
the payback period is on the order of a few
months and therefore economically attractive
(Manibog, 1984).  As Williams (1985) points
out,  the adoption of improved stoves is a far
more cost-effective method  of dealing  with
the fuelwood crisis than any "supply-oriented"
solution to  the  problem  that  emphasizes
growing trees for fuel.
      Widespread introduction of the current
designs of improved stoves, while  reducing
total  emissions  of oxides  of  carbon  per
cooking task, will change the ratio of CO2 to
CO emitted.  This ratio on a mass  basis for
traditional stoves is close to 10:1, whereas for
more efficient stoves it could be reduced to
5:1, reflecting the more complete combustion
in traditional  stoves  (Joshi  et al.,  1989).
Although CO is not a  radiatively interactive
gas, it does interact with  hydroxyl ions;  as a
result, its presence increases the concentration
of methane and ozone in the troposphere (see

Use Alternative Fuels

      In  the traditional  sectors  of many
developing countries,  substitution  of fossil-
based  end-use  technology  for  traditional
biomass  use may  be desirable as part of a
larger  strategy even though it  may directly
increase greenhouse gas emissions to a small
degree.  Gaseous  fuels (natural gas, LPG,
etc.) are very attractive relative to fuelwood
for several reasons, including  their vastly
superior convenience and controllability. In
addition, a well-designed gas-fueled stove can
be five to eight times more  efficient than
traditional firewood stoves (Goldemberg et
al., 1988).  Thus, the shift to gaseous cooking
fuel can  decrease  the  demand for fuelwood,
which may slow the rate  of deforestation in
some areas, or  free  up  vast  amounts of
fuelwood for use as a feedstock for advanced
biomass energy systems, or both.  In a few
developing countries, such as China, coal  is
used  for  cooking  and space heating;  the
advantages discussed above for gaseous fuels
also  apply as a replacement  for coal (with
associated  reductions  in  greenhouse  gas

      In  the  traditional  sectors  of many
developing countries,  lighting frequently  is
achieved  with very  inefficient  combustion
technologies.   In  India,  for  example, it  is
estimated that 80% of the rural households
illuminate   with   kerosene  lamps.     The
efficiency of illumination of these  lamps  is
very  low.    Providing the  same  level of
illumination with incandescent electric bulbs
would be 200  times more efficient at the end
use (Goldemberg et al., 1988).  (In  fact, the
availability of electricity will actually allow a

Policy Options for Stabilizing Global Climate
much  greater  level    of   illumination  in
homes).     Thus,  even  if  the  electricity
production is only 30% efficient, and is coal-
fired (worst-case assumptions), the equivalent
electric lighting would  still produce less net
CO2.  If  the most efficient current compact
fluorescent  lighting were used, the benefit
would be  even  greater.  Of course,  the major
constraint to substituting electricity for fossil
fuels is the limited availability of electricity in
developing   countries.     Small-scale  local
generation based on renewable technologies
could  make  major  contributions in  this
situation.    These and  other options  for
increasing electricity in developing countries
are discussed in PART TWO.

Retrofit Existing Buildings

      For those  residential  and commercial
segments  of developing countries  that have
similar   characteristics   to   industrialized
countries, many of the same retrofit efficiency
measures  are appropriate. In fact, it is likely
that many retrofit  measures would be more
effective in developing countries. As pointed
out in a recent U.S. AID study (I988b), while
"industrialized  countries  have  made  major
strides in using  electricity more efficiently
over the last decade, few achievements have
been  made  in  developing countries in using
electricity more efficiently. The opportunities
for improvements are  tremendous, and  the
cost is only a fraction  of the generation
expansion   option."      In   addition,   air
conditioning  requirements   are  generally
heavier in   tropical  developing  countries.
Thus, improvements in building shells and air
conditioning  equipment  could   be   very
effective in reducing electricity use.  Similarly,
the  air  conditioning  benefit  of  improved
lighting (due to less waste heat) would also
be greater in developing countries.

      A recent study of Pakistan  identified
cost-effective efficiency  improvements  that
could reduce electricity use in the commercial
sector  by  over 30%.  Based on commercially
available  improvements   in  lighting,   air
conditioning and fans, and thermal insulation,
the study  projected national savings of 1800
megawatts (MW) of generating capacity and
18,200 gigawatt-hours (GWh) of electricity
generation (U.S. AID, 1988b). An analysis in
Brazil  indicated   the  potential to  reduce
 electricity use  for lighting by 60%  in  many
 commercial buildings (Geller, 1984).

 Build  New   Energy-Efficient  Homes   and
 Commercial Buildings

      Rapid expansion of the residential and
 commercial building stock  is  expected to
 occur   in   conjunction  with   economic
 development in the developing countries over
 the coming decades.  Use of the efficiency
 options discussed for industrialized countries,
 adapted  to  local conditions  and objectives,
 could minimize the  increases in energy use
 associated with this growth.  Obviously, since
 the rate of construction of new building space
 (and distribution of appliances, etc.) will be
 much  higher  in developing  countries, the
 importance and potential impact of efficiency
 measures will be proportionately greater as

      Several  recent studies  have identified
 significant potential  for reductions in energy
 use   in   new  commercial   buildings  in
 developing countries (see, e.g., Turiel et al.,
 1984; Deringer et al., 1987).  In Singapore,
 careful  use of daylighting  alone   has the
 potential to  reduce energy use by  roughly
 20% relative  to  the current  building  stock
 (Turiel  et  al.,  1984).   Other  important
 improvements   include   efficient   lighting
 systems,  external shading,  and  size  and
 placement of windows.

 Near-Term Technical Options:  USSR and
 Eastern Europe

      Energy use in buildings in the Soviet
 Union is dominated by space  heating:  25%
 of the  population  lives in  a climate that
 requires the use of heating between  210 and
 over 300 days per year.  An additional 40%
 live in a climate characterized by  a  180- to
 280-day heating season (Tarnizhevsky, 1987).
 Since the early 1970s, the Soviets have made
 dramatic  progress   in  improving   energy
 efficiency in  specific applications, "in  large
energy uses easily identified and controlled by
 the planning apparatus" (Hewitt, 1984).  The
dominant approach  advocated  by  Soviet
 researchers   for  space  conditioning  is
consistent with this experience.  Centralized,
or "district"  heating  systems,  have been the
preferred approach to space heating for some

                                                               Chapter V:  Technical Options
time. By 1980, about 70% of residential and
commercial heat demand in cities and towns
was  provided by central systems.  Sources of
heat   for   these   systems  are   primarily
cogeneration  from  both  fossil-fueled  and
nuclear  powerplants  and  some  waste heat
recovery from  large industrial  process heat
uses  (e.g.,  ferrous  metal,  chemicals,  and
petrochemicals) (Vavarsky et al., 1987). Most
of the  residences in the  USSR are  multi-
family  rather  than  single-family structures
which should, in principle,  require less space
heat because of the lower  surface-to-volume
ratio.  Living space per capita  is also much
lower than in  OECD countries.   A  recent
estimate for the  USSR is about 15 square
meters per capita as compared  to roughly 50
square   meters  per  capita  in   the  U.S.
(Schipper and Cooper, 1989).

      Despite the predominance of district
heating and multi-family structures, the energy
intensity  of space  heating  in  the  USSR
appears  high  relative  to  OECD countries.
Schipper and Cooper (1989) have estimated
that  space  heating  in  the USSR  requires
about 230 kJ/m2/DD,  which is about 50%
higher  than the  U.S.  average  and  about
double  the value  for  Sweden.    There is
obviously room for considerable  efficiency
improvement in space heating.  This may be
very  important if heating  space  per  capita
increases with  incomes  in the  future.   A
Soviet research institute has projected that
energy  use in  industrial  and  commercial
buildings may rise by over 40%  between 1985
and 2000 (Bashmakov, 1989).

      There is already considerable interest in
improving  efficiencies in  buildings  in  the
USSR.  Plans for improving energy efficiency
include:  1) further replacement of local heat
sources  with district heat from  cogeneration;
2)  weatherization   of  buildings;   and  3)
reductions  in  heat losses  in distribution
networks  (Tarnizhevsky, 1987).   As many
western  visitors to the Soviet Union have
noted,  a common  method  for  regulating
temperature in over-heated  buildings is simply
to   open  windows.     Improvements   in
temperature  control  systems  could  save
considerable space heating  energy.

      Electricity consumption in buildings is
also  growing in the Soviet Union, principally
for  lighting   and  household  appliances
(including some electric  ranges).   The most
significant sources of growth from 1975-1985
were attributed to increasing proliferation of
household   applications   associated   with
improving  living  standards.   One  Soviet
researcher estimated that significant electricity
savings are achievable through manufacture of
more energy-efficient appliances and lighting,
optimized  use of  lighting,  elimination  of
known losses  or  "wastes" of electricity,  etc.
(Tarnizhevsky, 1987).

Long-Term Potential in the Residential/
Commercial Sector

      In the  long term, the  potential  for
reducing  energy  use   in    buildings   is
considerable.  The majority of current  per
capita energy consumption in buildings could
be eliminated over the long run by simply
incorporating  the best  currently  available
building  and  equipment technologies  into
housing and commercial building stock as it is
expanded and replaced over the next 50-100
years. Further efficiency improvements could
come from emerging technologies and broader
application of existing technologies. In space
conditioning,   examples   include   "smart
windows," which sense light and adjust opacity
to utilize solar heat and light most effectively,
and  new  building  materials,  which  may
provide  better   insulating  qualities  at a
reduced cost.  Existing  technologies for large
buildings, such as use of thermal storage  and
computer controls, could be applied to small
buildings and residences as well.

      As improved building and  equipment
technologies are incorporated over time, space
conditioning will probably become a  much
smaller  component of total building energy
use.  Appliances and information technologies
(computers, telecommunications) may become
more important determinants of residential
and   commercial   energy    consumption.
Advanced   technologies   may    provide
comparable  or improved services with  less
energy.   For  example,  some  experimental
concepts have been developed for storing food
that  might  greatly  reduce  the  need  for
refrigeration.   As information  technology
continues to  evolve,  it  may  well  provide
improved energy efficiency as a  byproduct, as
has  been the case in  the evolution from

Policy Options for Stabilizing Global Climate
vacuum tubes to semiconductors to integrated

      Alternative fuels could also play a more
important  role  in  buildings  over  the long
term.   Advances in  solar photovoltaic  and
other    small-scale    renewable    energy
technologies may  make  it  economical  to
generate most or all of the needed electricity
locally.   Hydrogen may become an energy
option for building energy needs by utilizing
or  adapting the existing  infrastructure for
distribution of natural gas (see PART TWO).


      Industrial end  uses account  for  the
largest single component of energy use in the
industrialized countries ~ almost 43% of the
energy consumed in the OECD  in 1985 (in
primary energy equivalent terms  [U.S. DOE,
1987b]).      Actual   secondary    energy
consumption was about 36%.   In developing
countries, if agriculture is included as part of
industry (as it  is in  this  chapter),  then the
industrial sector generally consumes an even
higher  percentage  of  total  commercially
traded energy.  In developing countries as a
whole, industrial energy makes up almost 60%
of total  modern energy use.   In the USSR
and Eastern Europe, the percentage is slightly
under 50%  (see CHAPTER IV).

      Industrial use is also an  area in which
impressive efficiency gains have been observed
in recent years.  In  the  United States, for
example, "end-use  energy  consumption  per
constant dollar of industrial output declined
by 28% between 1974 and 1984  ~ reflecting
substantial improvements in energy efficiency
as well as the relative decline in output from
energy-intensive industries in  this  country"
(U.S. DOE, 1987b).

      Several researchers have documented
the components of changing industrial energy
use in developed countries (see  Ross, 1984,
1986; Goldemberg et  al., 1987; and  Williams
et al., 1987).  One significant component of
declining industrial energy use is a structural
shift to  products  that are  inherently less
energy-intensive to produce. It is now a well-
documented   phenomenon   that   as
industrialized countries  proceed beyond  a
certain  level of economic  development and
affluence, their  per capita  consumption  of
some of the most energy-intensive industrial
products  (e.g.,  cement,  steel,  and  durable
goods)  declines.   Thus,  having approached
"saturation"   in   many   energy-intensive
products, industrialized countries will likely
continue to consume less energy per dollar of
GDP in the future as incomes continue  to
rise.    Major  programs  to rebuild  aging
infrastructure (roads, bridges, water and sewer
systems, etc.)  in the U.S. and  other  OECD
countries are being discussed and could offset
the saturation effect somewhat.

      The other major component of declines
in energy intensity over the  past decade and
a half has been actual improvements in the
efficiency of production  processes.  Energy
price shocks  of  the  1970s often affected
industrial energy  users  more  than  other
sectors.   As  stated by  Goldemberg et al.
(1988):   "Because the cost of providing them
energy involves much less unit transport and
marketing  cost, industrial users are  more
sensitive than other energy consumers  to cost
increases  at  or near  the  point of  energy
production."   In  addition,  industrial  users,
particularly  where  energy  costs  are  a
significant component of product cost, tend to
be  more aware of  and responsive to the
return on  investments in energy efficiency
than are customers in other sectors.   Ross
(1986)  has  noted many  cases  in  which
industrial managers have pursued aggressive
efficiency improvement policies in response to
the price signals of the 1970s.

      Efficiency improvements  to date have
largely been in a few industries that are the
most energy-intensive:  petroleum  refining,
chemicals, cement, metals, pulp and  paper,
glass, clay, etc.  (see Table 5-5).  There  is
reason to believe that efficiency improvements
will  continue  rapidly in the future  in the
energy-intensive  sectors of  industry in the
developed countries, particularly if real energy
prices begin to rise again.  It is also expected
that the  structural  shifts  to  less energy-
intensive products  will also continue in these
countries (Williams et al., 1987).  Technical
options may exist for accelerating these trends
and  also taking  advantage of  additional
efficiency improvements  possible  in  other
industries.  Evidence exists that  economically
attractive energy  conservation investment

                                                               Chapter V: Technical Options
                                        TABLE 5-5
                               Reduction of Energy Intensity"
                      in the U.S. Basic Materials Industries (1972-1983)




            Petroleum refining*1

            Energy Weighted Reduction





a  Generally  energy per pound of product, unadjusted for environmental and other changes.
   Purchased electricity accounted for at 10,000 Btu/kwh (2.5 Mcal/kwh).

b  Not including fuels used as feedstock.

c  Not including wood-based fuels.

d  Changes in inputs and outputs and environmental regulations have had a  particularly strong
   impact on petroleum-refining energy. Adjusted for such changes, energy intensity was reduced

Source:  Ross, 1985.
opportunities exist in industries outside  of
those few that  are energy-intensive.  For a
number   of   reasons   these   investment
opportunities  are  often  being  overlooked
(Ross, 1984, 1986).

      In contrast to industrialized countries,
the developing  countries generally are in the
midst of, or beginning, a period  of  rapid
expansion of energy-  and  materials-intensive
industries to raise per capita income levels.
In  addition, industries in  these countries
currently use energy far less efficiently  than
do   similar  industries  in   industrialized
countries.  In many cases, this is related  to
the  government's  subsidization  of energy
prices, lack of access to  the  most modern
technologies, and lack of management skills
for identifying and implementing efficient
options  (Flavin  and  Durning, 1988).   If
developing  countries  industrialize without
dramatically improving energy efficiency, the
result  would  be  enormous  increases  in
industrial energy use.    As these countries
develop industrial infrastructure and as their
standards of living rise  in the future,  the
energy requirements for  the  production of
basic industrial materials  could be enormous.

      There  is  a  widening  recognition,
however, that this type of growth may not be
sustainable  and  may  indeed become  self-
defeating.  Continuing along current energy-
intensive industrial development  paths may

Policy Options for Stabilizing Global Climate
result  in  increases  in  energy  impoits, which
absorb  foreign exchange credits  that  are
needed  for  further  development.   Local
environmental  concerns and  capital  scarcity
may also constrain the conventional industrial
development option.   Developing countries
and development assistance organizations are
now beginning to focus much  more attention
on  the  energy consequences of  industrial
development decisions.

      Technical  options  may   exist   for
"leapfrogging" from  current obsolete  energy-
inefficient technologies   directly  to  very
advanced  efficient  technologies  in  some
developing countries  (although  new policy
actions will be required; see CHAPTER VIII).
In addition, opportunities exist for designing
industrial  development  based  on   locally
available  alternative fuels,  which  has been
initiated in some developing countries.

      In  the  USSR  and Eastern  Europe
countries, significant heavy industrial capacity
is already installed, with energy often used
very  inefficiently.     For  these  countries
reducing  industrial  energy  demand  may
require structural  shifts away  from heavy
industry as well as  the use of more efficient
industrial technology.

      With the technical options  identified
below, industrial energy consumption could be
reduced by 25% below levels projected for the
2000-2010 time frame.  One  recent analysis
indicates that cost-effective conservation could
result in an absolute decline of about  19% in
industrial  energy  consumption   (fuel  and
purchased electricity) in the U.S. by the year
2010 (Ross, 1988).

      Some available  projections based  on
trends   in structural  change and  process
technology improvement alone suggest  that
industrial energy use in the OECD countries
may not rise significantly over the next 25-40
years (Williams et  aL, 1987).  Very  recent
data for  1987  and  1988 in  the U.S. show
sharp increases in  durable goods and basic
materials  production (U.S. DOC, 1988).   If
these very recent trends continue,  industrial
energy use in  OECD countries  could grow
significantly in the  future. Industrial energy
consumption in the USSR, Eastern Europe,
and developing  countries  is expected  to
 increase substantially under "business-as-usual"

      Near-term technical  options  in  the
 industrial sector in  the  three regions  are
 described below.

 Near-Term Technical  Options:  Industrialized

Accelerate Efficiency Improvements in Energy-
Intensive Industries

      As   discussed   above,   significant
 improvements in energy efficiency were made
 in the basic materials industries during the
 late 1970s and early 1980s (see Table 5-5 for
 improvements in key industries).   Despite
 these improvements,  in most industries the
opportunities for further  reductions are still
quite large.   This is  true for  two basic
reasons.   Industrial process technology  has
improved significantly in recent years, and the
pace of energy-related technology investment
has  been relatively  slow,  particularly  in
industries that are not growing  overall (Ross,

      The  steel   industry  provides  one
interesting example.  For the integrated, or
ore-based industry (excluding scrap-based steel
making), the average  energy intensity in the
U.S.  in  1983 was  about 31.2 GJ per  ton
(Ross,   1987).     The   reference   plant
documented by  the International  Iron and
Steel Institute (1982) would consume about
 19.2 GJ per ton producing roughly the same
mix  of  products.   Thus,  if  existing  U.S.
capacity  were replaced with plants equal in
efficiency to this reference plant,  it would
produce a 39% savings.  The costs and other
implications of  such  replacement  have not
been assessed.   Other estimates find a 20%
savings possible, if necessary  investments were
made (Barker, 1990).

      More energy-efficient technologies, once
proven commercially, will  likely be extremely
attractive on the basis of cost-effectiveness,
including improvement in overall process cost
and  environmental  impact as well as energy
efficiency.   Thus,  the marketplace can be
expected to encourage all producers to adopt
advanced technologies in the long run. From
the  perspective  of climate wanning,  the

                                                                Chapter V:  Technical Options
important  concern  is  whether  there  are
opportunities for  accelerating  this turnover,
either through research initiatives or through
programs  to promote  more  rapid  capital
replacement  in selected industries.

      Other  major energy-consuming  indus-
tries  - petroleum refining,  chemicals, pulp
and  paper,  etc.   -  are  also  undergoing
transformations that will result in continuing
declines  in energy  intensity  in  the  future.
Quantifying  the potential energy  efficiency
improvements in each major industry and in
various OECD  countries will  require  more
detailed analysis than has been carried out to
date.  Technically-feasible improvements (e.g.,
assuming that each industry average improves
to  match the energy efficiency of the best
currently-available  or emerging  technology)
could be much greater. With the exception of
primary  aluminum,  other energy-intensive
industries  have   even   greater   technical
opportunities for energy conservation than  the
steel industry (Ross, 1988).

      One  important  component  of   the
technical potential for reducing energy use in
basic   industries   is   materials   recycling.
Recycling of  inorganic wastes, such as bottles
and aluminum cans, saves energy and reduces
waste  streams.     Substituting  recovered
materials for virgin materials to produce steel,
aluminum,  and  glass  conserves  energy.
Depending  upon  the  types  of  materials
recycled, estimates of energy savings can range
from an average of 5 GJ per ton of material
recycled  (Gordon,  1979) to  25 GJ per ton
(Stauffer, 1988). Recycling 24 million tons of
paper, cardboard, glass, and aluminum (about
16% of our current waste stream) could result
in savings of  up to 0.6 EJ (Stauffer, 1988).

      Unfortunately,    economic   policies
discourage recycling and the use of recycled
materials. Differentials in transportation rates
favor  virgin loads over secondary loads, and
favorable  tax treatment toward  production
from  virgin  materials  continues  to  make
recycled materials  more expensive to use.   If
these  policies were eliminated or reversed
(e.g., creating incentives to boost demand  for
recycled products), the technical potential  for
energy savings  is  quite  large.   Increased
recycling would also have the added benefit of
reducing waste.
Aggressively Pursue Efficiency Improvements in
Other Industries

      While  there   is  clearly  measurable
progress in the energy-intensive, and therefore
energy-price-sensitive, industries, less progress
has been made in energy efficiency in other
industries.  Industries for which energy is not
a major component of product cost frequently
pass up opportunities for investing in energy
efficiency with high estimated rates of return
(Ross, 1984).

      The  technical  potential  for  energy
savings  could be  important for widespread
penetration  of just  a  few  energy-saving
measures.   The  Electric  Power  Research
Institute  estimates  that  95% of  industrial
electricity use is represented by three major
applications:   electromechanical drives  or
motors, 70%, electrolysis,  15%, and process
heat,  10%  (Kahane  and  Squitieri,  1987).
Recent   studies have estimated  that  cost-
effective  replacement of motors  and  the
addition of variable-speed drives could reduce
total electricity use in motors by as much as
17% in  some regions (Geller et al., 1987;
Alliance to  Save Energy, 1987).

      Comparable  efficiency  improvement
measures have also  been  identified for the
other   major   components  of  industrial
electricity use (Kahane and Squitieri, 1987).
In addition, many of the efficiency measures
identified  earlier  for  lighting  and  space
conditioning in large commercial buildings are
also applicable to industrial users.  A recent
study  examined  current  electricity-saving
projects  in automobile manufacturing plants
in the U.S. and Europe.  The results showed
roughly 30% savings from the current cost of
purchased electricity (Price and Ross, 1988).

Increase Cogeneration

      Technologies   for   cogeneration  -
production of electricity and heat or steam for
other   useful   purposes   from   a  single
combustion source - are described in PART
TWO.  The primary market for cogeneration
is in large industrial  facilities (although large
commercial/institutional and district heating
applications are important in the USSR and
Eastern Europe and  are also beginning to be
seen  in   the  U.S.).     From  industry's

 Policy Options for Stabilizing Global Climate
perspective, cogeneration is one method for
improving energy efficiency.  The industrial
facility  benefits,  either  in the  form  of
electricity used on-site or revenues from sales
of electricity to the local utility,  from the fuel
it would otherwise have consumed solely for
industrial production purposes.

       Industrial   cogeneration   has   grown
rapidly in the U.S. since the 1978 passage of
the Public Utilities Regulatory Policies Act
(PURPA), which ensures that  cogenerators
(among others) can sell electricity to utilities
at the utility's avoided cost  (the cost  that the
utility  would  otherwise  have  to  pay  to
produce or obtain the electricity).    As  of
1985,13 GW of cogeneration capacity were in
operation  (Edison Electric  Institute, 1985).
Projects that would  yield  an additional 47
GW have  been registered  with  the  Federal
Energy  Regulatory   Commission  (FERC)
through October  1987 (FERC,  1988).  One
company specializing in  cogeneration has
estimated  that cogeneration capacity  could
reach  100  GW   (equal  to about  15%  of
current  capacity)  by  the  year  2000 (Naill,

      All of these projects tend to  reduce
potential greenhouse  gas emissions  as  they
result in more efficient use of energy.  To the
extent that industrial cogeneration  projects
are based on natural gas or oil -- or industrial
waste products such as black liquor or bark in
pulp and paper --  and displace new coal-fired
electric generating capacity, the net impact on
greenhouse gas  emissions (as well as local
environmental  loadings)  could  be much

Near-Term  Technical Options:   Developing

      As noted  above, developing countries
generally are in the  early stages of  a rapid
expansion   in   producing   energy-intensive
materials  associated  with  infrastructure
development and widespread access to basic
consumer durables.  If this  process proceeds
along the path experienced historically by the
industrialized  countries,  the  increases in
energy consumption and CO2 emissions will
be enormous.  In fact, the need to import
fossil  fuels  to support  rapid expansion of
heavy  industry could  become self-defeating,
 operating as a  brake on  the  rate at which
 some developing countries can industrialize.

      Understandably,  developing countries
 and development assistance organizations are
 concerned about  alternative  approaches  to
 industrial  development  that  would allow
 developing  countries  to  increase  economic
 activity  without  having  to  devote  ever-
 increasing shares  of their  foreign exchange
 earnings  to  financing  fossil-fuel  imports.
 Several possible strategies for achieving this
 goal are very compatible with concerns about
 long-term greenhouse warming.

 Practice Technological Leapfrogging

      This   phrase  has   been   used   by
 Goldemberg  et   al.  (1987)   in  discussing
 industrial  development  options   for  both
 industrialized  and  developing  countries.
 Theoretically, at least, developing countries
 could   adopt  the  most  efficient   process
 technologies currently available, or even push
 ahead with experimental technologies as  they
 invest in major expansions of heavy industry
 necessary to foster economic development.  If
 this strategy were implemented, the projected
 massive increases  in industrial energy use  in
 the   developing    countries   would    be
 significantly reduced.

      There are a number of reasons why this
 may not occur in practice.  Because capital
 (and entrepreneurial experience) is scarce  in
 developing countries, there is  a tendency  to
 avoid risky investments.  Conventional wisdom
 suggests that these countries  should adopt
 technologies  that are already "mature" in the
 industrialized countries.   This "conventional
 wisdom"  has  affected  decisions  both  by
 developing  countries  themselves  and  by
 relatively  conservative  lending  institutions
 (banks  or assistance organizations) called
 upon to provide capital. Often, though by no
 means  always,   advanced  energy-efficient
 technologies require larger capital investments
 than older technologies.  It is also extremely
 important   to   recognize   the  differences
between   developing    countries    and
 industrialized countries (and among individual
developing  countries)   in  terms  of  the
availability and cost of certain components of
production  ~  labor, capital, and  natural

                                                               Chapter V:  Technical Options
      Thus,  developing  countries will have
difficulty   achieving   rapid    industrial
development with currently mature,  but also
relatively   energy-intensive,    technologies
available  from the  industrialized countries.
On the other hand, "leapfrogging" to the most
advanced technologies now being developed in
industrialized countries may be inappropriate
in terms of the  local availability of labor,
capital, and natural resources. What appears
to  be needed is to  identify and  develop
advanced industrial process technologies that
are appropriate to each developing country's
individual endowment of resources.   To the
extent that developing countries  move in this
direction,  energy  efficiency,  or  at  least
efficiency in fossil-fuel use, should be a major
characteristic  of  the desirable  options for
most developing  countries.    Since many
developing countries have difficulty raising the
capital required for  many investments, some
special   form  of  international  financial
arrangements may  be   necessary to assist
developing  countries  in adopting   energy-
efficient technologies as they industrialize (see
CHAPTER VIII for further discussion).

Develop and Use Alternative Fuels

      As discussed  above, most developing
countries are interested in  limiting increases
in   fossil-fuel   imports   associated   with
industrialization.   For this reason, they will
undoubtedly  provide a proving  ground for
development of  heavy  industry  based  on
alternative fuels.

      One  option  for  some   developing
countries  may  be   to  develop potential
hydroelectric generation  resources and base
industrial   development    on   advanced
electricity-intensive processes.  (Opportunities
and  difficulties in developing hydroelectric
generation are discussed in  more detail  in
PART TWO.)    In  general,   developing
countries are  relatively rich  in  biomass
resources and,  in some  cases, undeveloped
hydropower, while they are net importers of
fossil fuels.  Thus, the tailoring of industrial
development strategies to local resources will
likely reduce greenhouse gas emissions  in
addition  to achieving other benefits.

      For  those  developing countries with
abundant coal resources, most notably China,
there may be a tradeoff between energy self-
sufficiency  goals  and  climate  warming
concerns. Even in these situations, promoting
the most energy-efficient technologies should
be  a  common  goal.    When developing
countries have  both natural gas  and coal
resources, local environmental and economic
concerns, and consideration of the greenhouse
phenomenon,  should all  encourage a near-
term emphasis on natural gas.

Increase Industrial Retrofit Programs

      A  recent report by the U.S. Agency for
International Development (U.S. AID, 1988b)
reviewed  the  electricity supply-and-demand
situation in a number of developing countries.
The report  documented serious concerns in
many developing countries about  current or
projected shortages in electricity. However, it
also found that "few achievements have been
made  in  developing  countries   in  using
electricity more efficiently.  The opportunities
are  tremendous,  and  the  cost  is only a
fraction of the generation expansion option."
According to  the report, over  40% of the
electricity use in developing countries is by
electric motors  in the  industrial (including
agriculture) sector (U.S. AID,  1988b).  One
detailed energy analysis  in Pakistan identified
specific  industrial  efficiency improvements,
including improved controls and  lighting,
which   could   reduce   industrial  energy
consumption by  more  than 20%  in  2005
(Miller et al., undated).

      Other  recent studies  in Kenya  and
South Korea indicate that efficiency programs
have been successful in reducing  energy use in
heavy  industry (Geller,  1986).   A detailed
analysis   of   the  electricity   conservation
potential   in   Brazil   indicates   that
improvements in electric  motors and motor
controls  could reduce  industrial electricity
consumption by an amount equivalent  to 8.7
CW of  new  generating  capacity  (Geller,
1984).    Many of the  potential  industrial
energy savings  in developing countries  are
undoubtedly not yet identified because of the
relatively little attention that has been given
to these  options  in the past.  However, the
fragmentary  evidence  currently  available
suggests  that these opportunities are  much
greater in percentage terms than those in
industrialized countries and are much cheaper

 Policy Options for Stabilizing Global Climate
 than the incremental cost of increasing energy

 Use Energy-Efficient Agricultural Practices

      On a global scale, agriculture accounts
 for a small  part of "commercial" (excluding
 traditional biomass) energy use -- about 3.5%
 in 1972-73.  However, the percentage in some
 developing countries is higher.  In addition,
 the   projected   transition   in   developing
 countries  from  traditional  labor-intensive
 agricultural practices to modern  mechanized
 practices is expected  to increase the use of
 commercial energy in agriculture significantly
 in developing  countries  by the year  2000
 (FAO, 1981).

      A major  goal  of  most  developing
 countries  is  to  increase  productivity  in
 agricultural production either for  domestic
 consumption or for  export  purposes.  If
 energy conservation is viewed as a constraint
 to such improvements, it generally will not be
 viewed   as   a   more  important  objective.
 However,  productivity  increases  may  be
 possible   through    several    alternative
 approaches,    with    markedly    different
 implications  for energy and  employment.

      Many   developing   countries   are
 interested in holding down  imports of  fossil
 fuels. They may also suffer from widespread
 unemployment   or  underemployment  and,
 therefore, may seek modernization  without
 displacement of employment. It is important
 that   agricultural    modernization    be
 incorporated into an  overall  development
strategy  appropriate  to   each   individual
country.  In this context, energy savings may
be  achieved  in  conjunction  with  other
objectives.  Goldemberg et al.  (1988) point
out that some agricultural modernization can
occur  without  such   large  increases  in
commercial   energy    consumption    (and
associated reductions in labor requirements).
 Using  one  type  of  rice  production as  an
example, they illustrate that many benefits of
 the "green revolution" in increasing yields per
 hectare  can  be achieved  with intermediate
approaches   that  do  not  go   as  far  in
substituting mechanical energy for labor.

      Expanded agricultural energy needs can
also  present an  attractive  opportunity for
 biomass energy development.  FAO (1981)
 projected that an increase  of  17 petajoules
 (PJ) of oil-equivalent agricultural energy use
 would be required to double food production
 in   developing   countries   by   2000.4
 Goldemberg et al.  (1988) calculate that this
 amount  of  energy in the form of methanol
 could   be   produced   by   thermochemical
 processes from  40% of the present organic
 wastes  (crop residues,  animal  manure,  and
 food-processing   wastes)   in   developing
 countries.    Alternatively, feedstocks  could
 come from tree plantations representing land
 equivalent to 3% of current forest land in
 developing  countries.   Other possible areas
 for   efficiency  improvements   include
 electromechanical pumping of  water  for
 irrigation, more efficient use of existing water
 resources, and the use  of alternative energy
 supplies such as wind for  pumping.

 Near-Term  Technical Options:  USSR  and
 Eastern  Europe

      In  the  Soviet  Union  and  Eastern
 Europe,  industrial energy use  accounts for
 nearly 50% of secondary energy  use.  As a
 share  of primary energy equivalent  (with
 electricity conversion losses  allocated to  end
 uses of electricity) it is even larger (Mintzer,
 1988).  These countries have very high energy
 consumption per unit of GNP.  One recent
 analysis  indicates that  the  current  energy
 intensity of the Soviet economy is "akin to the
 IEA energy economies of the early 1970s," as
 shown in Table  5-6 (IEA,  1988).   In  fact,
while energy intensity in OECD  countries was
declining by over 20%  from 1973  to 1986,
 energy use  per  unit of GDP in  the USSR
 actually increased slightly.

Encourage Structural  Change

      One major reason  for the very  high
energy/GDP  ratio in the  Soviet Union  and
many Eastern European countries  is the large
share of industrial activity devoted to heavy
industry (production of basic materials such as
metals,  cement,  etc.)  which  is  inherently
energy intensive.  Over the past  several years,
a widespread belief  has been  expressed in
these countries that their economies need to
move rapidly toward producing a  different
(and less energy intensive) mix  of goods and
services (see, e.g., Gorbachev, 1987; Makarov

                                                               Chapter V:  Technical Options
                                        TABLE 5-6

                          Energy Intensities of Selected Economies

                                    (energy/unit of GDP)

            United States

            IEA Pacific

            IEA Europe

            IEA Total

            Soviet Union










            Source:  IEA, 1988.
and Bashmakov,  1990; Sitnicki et al., 1990;
Jaszay, 1990).  The interest in "restructuring"
or structural change  is driven primarily  by
economic necessity.  The economic concerns
have both supply and demand components.
On the supply side, Makarov and Bashmakov
(1990), as well as  Sitnicki et al. (1990), report
rapidly  rising marginal costs of  increasing
energy supplies  in  the  Soviet  Union and
Poland.   Thus,  they argue that  economic
growth on the current energy intensive path
will be constrained by  the ever-increasing
investment cost of producing more and more

      On the demand side, it is believed that
a shift toward production of consumer goods
and services  is necessary to increase living
standards and revitalize these economies. The
mix of goods and  services currently demanded
in the more affluent market economies of the
OECD countries  requires less basic materials
and   considerably  more  fabrication  and
finishing as well as service-oriented economic
activity  per unit  of GDP.   Most of  the
countries of Eastern Europe, as well as the
USSR, have indicated their intention to move
toward market economic systems and away
from  central  planning  as  the  means  of
allocating economic resources  and  activity.
This  is  viewed primarily as  a  means  of
improving the efficiency of economic activity,
stimulating economic growth and ultimately
raising living standards.  To the extent that
these economic  reforms  are successful, they
will  have  significant  ancillary  benefits  in
reducing the rate of growth in greenhouse gas

      Makarov and Bashmakov (1990) provide
several  alternative  scenarios  of economic
activity and energy consumption in the Soviet
Union. In the base case or "business-as-usual"
scenarios aggregate energy efficiency improves
very little through the year 2030. The authors
conclude that continuation  of  this  type of
economic development would require invest-
ments of capital and other resources in energy
production "so large as to preclude possibility
of realizing any but the pessimistic economic

 Policy Options for Stabilizing Global Climate
 growth  case."   The pessimistic  economic
 scenario assumes growth of GDP at 2%/year.
 In  contrast, a  "structural  change" scenario
 results in a 25% decrease in energy per unit of
 GDP  by the year  2030.   This allows more
 rapid economic growth (3%/year) while using
 about 15% less energy and reducing  carbon
 emissions by 14% (below the base case).

       Sitnicki et al. (1990) report even more
 significant reductions in energy consumption
 under a structural change scenario for Poland.
 Relative to a "business-as-usual" base case, the
 structural  change   case   reduces   energy
 consumption by 47% and carbon emissions by
 43% in  the year 2030.  Jascay (1990) shows
 for  Hungary  that  structural change  in  the
 economy could result in  significantly  lower
 energy requirements and carbon emissions in
 the  future   relative  to   the most recently
 published  official   economic   projections.
 These analyses suggest  that policies  being
 considered in the USSR and Eastern Europe
 to encourage economic growth would also
 have  significant   benefits   in   reducing
 greenhouse gas emissions.

 Other Emission Reduction Options

      A  closer  look  at   some   specific
 industries verifies the general impression of
 energy inefficiency.  The USSR is by far the
 world's largest producer of steel  (WRI and
 IIED,  1988).    Unfortunately,  it is  also
 apparently  close  to  last  in the  world  in
 efficiency.  Estimates for  1983 indicate that
 the USSR used 31 GJ to produce a  ton of
 steel as compared to the Japanese standard of
 about  19 GJ (Chandler, 1986).  As shown in
 Table  5-7,  the  Soviet   Union  and   many
 Eastern   European  countries continue  to
 produce  a large percentage of their steel in
very  inefficient "open hearth" furnaces, which
 have been virtually eliminated in the OECD.
 They also do very little recycling, as indicated
 by the small percentage of steel produced in
 electric arc furnaces.

      One analyst has suggested that  Soviet
 industry has shown some success in improving
 efficiency in their heavy industry with existing
 technology  (e.g.,  "housekeeping"  measures,
 refinements of existing technologies), but has
 failed  to assimilate distinctly  different and
 inherently less energy-intensive technologies.
An example  is the cement industry, a heavy
energy-using  sector for which energy use can
be greatly reduced by switching from the wet
process to a newer dry calcining  process.
Although  the dry  process is available in the
Soviet Union, it has not been widely utilized
(Hewitt, 1984).

      There  are  several  reasons  for  the
extraordinarily  high  energy   intensity  of
Eastern  European  industry.    The  Soviet
Union  (and  to  a  lesser  extent  Eastern
Europe) has  enormous  energy resources and
has  historically  invested heavily  in  energy
development  due to national economic policy
rather than  demand.   Hence,  scarcity  of
energy  resources   has  not  provided   an
incentive to conserve. In addition, the "mark-
up" pricing systems  used in these countries
do   not  provide  a  strong  incentive  for
efficiency improvements. In fact, it has  been
argued that the reward system  has actually
provided  managers  with  an  incentive  to
consume more energy (Chandler, 1986).

      More  recently,  the  value  of  energy
efficiency  has  been  recognized by  Soviet
leadership.  As  described by  Soviet  energy
analysts, "the energy economy of the Soviet
Union is entering  a new period of develop-
ment.  The most  economical  and favorable
located oil and gas  resources   ...   are
gradually running out" (Makarov et al., 1987).
The  result is that development of new energy
resources   is  much  more  expensive  and
difficult than  in the past. One result of rising
costs of energy development  has been the
explicit inclusion of energy efficiency measures
in central  economic and  energy planning.
Targets have been set  that would  result in
more than a  20% reduction in  the  energy
intensity of the Soviet economy (Makarov et
al., 1987).

      The Soviet Union has historically done
very  well in the utilization of industrial waste
heat  for electricity generation (cogeneration)
and  for other heat needs, such as district
heating.  This trend  is continuing.   In the
Leningrad region, for example, the 1981-1990
energy  plan  calls  for  reducing  projected
industrial energy use by about 2 EJ through
a  combination    of   improved   industrial
technology and  expanded use of waste heat

                                                              Chapter V:  Technical Options
                                        TABLE 5-7
                          Innovation in Steel Production Technology
                                  Selected Countries, 1985
Economy Type
"Inefficient"            "Recycling"
Open Hearth          Electric Arc
           (% of production)
South Korea
United Kingdom
West Germany
United States
China a
India a
East Germany
Hungary a
Soviet Union
M = Market-oriented; C = Centrally-planned.

a Though this country's agricultural economy is market-oriented, its indi^try is not.

Source:  Chandler, 1986.

 Policy Options for Stabilizing Global Climate
 for  both  electricity and  other  heat  needs
 (Glebov and Kovlenko, 1987).

       In addition to efficiency improvements,
 other  options for reducing  greenhouse gas
 emissions  from  industry in  the  USSR  and
 Eastern Europe  are  possible through  fuel
 switching.  Although the major resources are
 generally located far from  current  industrial
 centers, the Soviet Union  has  the world's
 largest proven recoverable natural gas reserves
 in the world, amounting to  about 39%  of the
 World  total (IEA,  1988).    In addition, its
 undeveloped  geothermal  and hydroelectric
 resources  are significant  (as discussed in
 PART  TWO).    It  would   be  technically
 possible, therefore, for the USSR to substitute
 various  alternative  fuels  for current  and
 projected  coal use  in the  industrial sector,
 although the costs of such substitution have
 not been well analyzed.

 Long-Term Potential in the Industrial Sector

      Over  the  long  term,  technological
 options for improving efficiency in  industrial
 energy  use are  very  speculative.   Several
 concepts advanced  by various analysts  may
 warrant further  study to identify  potential
 options  for reducing long-term  industrial
 demand for fossil fuels.

 Structural Shifts

      Over the   long  term,  shifts in  the
 structural  composition of industrial activity
 will  undoubtedly continue,  with significant
 energy consequences. As discussed by Ross et
 al. (1987),  production of basic (and inherently
energy-intensive)  materials  has  tended to
decline over time as a share of GNP after an
economy achieves a certain level of affluence.
There are  three components of this shift:

           substitution of new  (and  often
 less energy-intensive) materials;

           product and production design
changes that result in more efficient  materials
 use; and

           saturation  of major markets for
 material-intensive   products,    including
 infrastructure and material-intensive consumer
      These  effects   can  be  expected  to
 continue in the future and to some degree are
 incorporated  in  all the scenarios  of future
 energy  use  presented in  this  report  (see
 CHAPTER VI).    With  combinations  of
 policies, such as  economic  incentives  and
 aggressive  research and development, these
 effects  can  be   accelerated   considerably,
 especially in the developing countries where
 major increases in industrial energy  use are
 expected.    It is currently  very difficult  to
 identify, much less quantify, the  effects  of
 actions to  achieve the technical  potential.
 Further study of  long-term trends  in  the
 structure  of industrial activity and  specific
 policy options for influencing these trends is

Advanced Process Technologies

      As  pointed out by  Ross (1985), major
 reductions  in energy intensity  in  industrial
 processes can come  about  through "revolu-
 tionary"  change   in  process  technology.
 Typically,  such  change  is  not  motivated
 primarily  by  energy  conservation; however,
 large reductions in  energy intensity often
 result from technological advances.  As an
 example, advanced steel-production technology
 now under  development could result in  very
 large energy  savings per  unit of  output.
 About 40% of the energy  used in iron and
 steel  production is related to  shaping  and
 treating.      Advanced   processes  utilize
 controlled solidification, often very rapidly, of
 thin castings that approximate the final shape.
 When fully developed, this technology should
 eliminate   almost  all  of  the   energy  use
 currently associated with rolling and shaping
 (Ross, 1985).

      In the petrochemical  industry, research
is currently underway to identify  advanced
separation techniques that   could  eliminate
many of the losses inherent in the  current
distillation   process.       Gas  separation
membranes, gas adsorption, and liquid mass
separating agents are all currently commercial
for very specialized petrochemical applications
and  use considerably less  energy  than the
distillation processes they have replaced (Mix,
1987). Over the long term, wider applications
of these or similar technologies may further
reduce process energy requirements.

                                                                Chapter V:  Technical Options
      In general, advanced technologies are
attractive because of the lower total  cost,
better   quality    control,   reduction   in
inventories, greater flexibility, etc., as well as
the improved energy  efficiency.  It is difficult
to   identify   possible   process   technology
improvements  that could become  available
through  research and development over the
long  term, although  it is likely that energy
efficiency improvements will be part of these

      Another  long-term area  of process
technology   advancement  is  the   use  of
biological phenomena in production processes.
Although  it  is  difficult to  even  identify
specific applications of biological processes at
this   time,   they  appear  to  offer  possible
improvements  in  the  speed, control, and
precision of process technologies (Berg, 1988).
As   such  technologies   emerge,  they  will
undoubtedly offer additional opportunities for
reductions  in  fossil  energy  use.  Industrial
policies designed to  stimulate technological
advances and capital  turnover will ultimately
also lead to reduced energy requirements.

Non-fossil Energy

      Although  it  is  likely  that energy
intensity of industrial activity will continue to
decline over  the  long term, significant levels
of energy consumption will no doubt still be
required.   Opportunities exist for  meeting
these demands with non-fossil energy sources.
Many industrial technology experts (see, e.g.,
Berg, 1988;  Schmidt,  1987) have  suggested
that increased  use of electricity in industrial
processes over  the long run is  likely because
of its superior characteristics of controllability
and minimal loss or error.

      Even though  production of electricity
involves large  losses,  this  is  often  offset
because the  more sophisticated and precise
production processes it allows are generally
less  energy-intensive  at   the  end   use.
Increasing    electrification   of   industrial
processes at  the  end-use point allows  for a
wide variety of alternative generation options
(as  discussed  in PART  TWO), which can
reduce greenhouse gas emissions.

      In addition, one analyst  has suggested
that economic competition will cause energy-
intensive industries  over  the  long run to
locate  in areas where isolated resources of
cheap   and  hard-to-transport  energy  are
available. Examples cited include natural gas
and hydro  locations  in  Canada,  Brazilian
hydropower sites, and natural gas locations in
the  Middle East (Ross,  1985).   The  same
logic could  also  apply  to locations  with
geothermal  and  solar resources  as  those
technologies  become competitive.   Policies
could be implemented to discourage fossil-fuel
use (see CHAPTERS VH and VHI), as well as
to encourage movement of heavy industry to
locations where  renewable resources  are
economically attractive.

Policy Options for Stabilizing Global Climate
                               PART TWO:  ENERGY SUPPLY
      This section discusses technical options
for reducing greenhouse gas emissions by (1)
making more efficient use of fuels for power
generation  and  (2)  altering  the  types of
energy supplies we use. These two goals have
one common objective:   to supply a similar
amount of useful energy services compared to
current energy  consumption practices, but in
such a way that greenhouse gas emissions are
minimized.  Options for reducing greenhouse
gas   emissions   in   end-use   applications,
particularly by improving energy efficiency and
switching fuels, were discussed in PART ONE:
ENERGY SERVICES.  This section focuses
on possible options for improving the delivery
of  energy  services  by reducing the  losses
during  energy   production  and conversion
processes.  Additionally, the types of energy
supplies can be altered by developing sources
of energy that do not emit greenhouse gases.

      The first part of this  section discusses
possible options for altering current patterns
of fossil fuel use.  This is clearly one of the
highest near-term priorities, since as discussed
in Chapter IV, current commercial energy use
globally is dominated by fossil fuels.  In many
cases,  however, options  exist for  reducing
emissions from these  applications.   This is
followed by a  discussion of possible supply
alternatives to fossil fuels, including increased
use of  biomass,  solar resources,  additional
renewable energy resources, nuclear power,
and options for enhancing energy storage and
delivery to  final consumers.


      As discussed in  Chapter IV, fossil-fuel
consumption is  responsible  for  the  vast
majority of CO2 emissions.  On an energy-
equivalent basis, coal produces the most CO2
(about 25 kg C/gigajoule); oil, about 80% that
amount (about 20 kg C/gigajoule); and natural
gas, about 55-60% that amount (about 14 kg
C/gigajoule).    Given  these  rates   of  CO2
emissions, fossil-fuel consumption would have
to be drastically reduced or eliminated over
the  long run  to  control  greenhouse  gas
emissions.  With the current global reliance
on fossil fuels,  however, the shift away from
fossil fuels  cannot be  accomplished easily,
even with international agreement to pursue
this  objective.  Steps can be  taken now to
begin or accelerate the transition to non-fossil
energy by minimizing the greenhouse impact
of the fossil fuels  that are used.   Possible
actions include  improving the efficiency with
which fossil fuels are produced and convened
to electricity, switching from  more carbon-
intensive fuels  to less carbon-intensive fuels
(e.g., from coal to natural gas), and applying
various   engineering  controls  to   reduce
emissions of greenhouse gases during  the
production and consumption of fossil fuels
(e.g., NOX control, CH4 recovery).

      Since one of the primary uses of fossil
fuels currently is the production of electricity,
one potential option is to produce  electrical
power more efficiently, using less energy input
to produce electricity.  For example, in the
U.S. during the 1950s and  early 1960s,  the
efficiency of powerplants  consuming fossil
fuels increased  from 25% to about 32% (see
Figure 5-5).  This  improvement has stalled
since  the  early   1960s  because  of  fewer
technical   improvements    in   combustion
techniques,  higher  energy consumption  by
auxiliary equipment used for pollution control
(e.g., electrostatic precipitators for paniculate
removal and scrubbers for SO2 removal), and
increased use of less efficient  fuels, such as
subbituminous coal and lignite.

      Although   electricity  production  is
currently one of the primary uses for fossil
fuels, other applications have been proposed
in  order to  meet  future  energy  needs.
Specifically,   as   conventional   petroleum
resources  are  depleted, it is  possible  that
much of  the  demand  for  liquid  (oil  and
natural gas liquids)  and gaseous (natural gas)
fuels will ultimately be met by synthetic fuel
production from solid fossil fuels.  Although
there   is  currently  little  synthetic  fuel

                                              Chapter V: Technical Options
                            FIGURE 5-5

                           1951- 1987
 - 30

                     I	I
                                                  I	I
      1900     1988    19*0    19H    1970    1978


Avrag f ftcUncy at aH xtothHI coal, 0, and natural gat powcrplanU.
                                                 19*0     1968     199O

 Policy Options for Stabilizing Global Climate
 production 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 more conventional resources.

       The  production  of  synthetic  fuels,
 however, typically requires the consumption of
 significant amounts of energy to produce the
 liquid  or  gaseous  fuels.   These conversion
 processes produce greenhouse gas emissions,
 particularly CO2, so that the total  emissions
 per  unit of energy  are  higher for synthetic
 fuels than for conventional fossil fuels.  For
 example, the CO2 emissions  from production
 and  consumption of liquid fuels from coal is
 about  1.8 times the amount from conventional
 liquid  fuels from crude oil (see CHAPTER IV
 for further discussion).

       The following sections explore possible
 options for reducing the greenhouse impact of
 fossil fuels. Using fossil fuels more efficiently
 is  discussed,  including   refurbishment  of
 existing powerplants, repowering opportunities
 (including   application  of     "clean   coal
 technologies"),  and cogeneration.   Greater
 use of natural gas is then discussed since it
 produces less CO2 than oil or coal.  Methods
 for controlling greenhouse gas  emissions are
 also  presented.

 Refurbish Existing Powerplants

      Energy use at existing  powerplants can
 be reduced by refurbishing the plant to keep
 it operating at optimal efficiency.  Over time,
 these efficiencies decline due  to  wear  and
various aging processes.  For many economic
reasons  it  has become clear over  the past
decade that utilities in the U.S. are planning
to keep existing powerplants in service longer
than initially planned (Democker et al.,  1986).
 It is  likely that this trend will occur globally
as well to minimize the need  to invest in new
powerplants.   As  these  powerplants age,
 however, declining  efficiency  will  become
 more widespread than in the past.

      In response,  the U.S. electric power
industry  has developed new techniques  for
extending the life of powerplants.  The extent
of efficiency improvement depends on how
badly the specific plant had degraded and the
 extensiveness of the upgrades.  Increases in
 efficiency in the range of 3-4% appear to be
 possible at many existing units,  with  even
 greater improvements possible in some cases
 (PEI, 1988).

      In   developing   countries,   the
 opportunities for improving the efficiency of
 electricity  generation may be much greater.
 According to  a recent  study by  U.S.  AID
 (1988b), "The majority of thermal powerplants
 in developing countries operate at lower-than-
 design capacity and efficiency." Many of these
 powerplants use more than 13 MJ5 of fuel to
 generate a kWh of  electricity, compared to
 typical design heat rates  of 9-11  MJ/kWh. It
 is estimated that  a rigorous  program  of
 powerplant rehabilitation  could  improve
 overall  fuel use efficiency for  thermal power
 generation  by  10%  or more  in  most
 developing countries (U.S. AID, 1988b).

 Pursue Clean Coal Technologies

      As new powerplants are constructed to
 meet increasing electricity needs,  many of
 these plants are likely to  be fossil fueled.  To
 the  extent that  new powerplants  use fossil
 fuels, greenhouse gas emissions can still  be
 reduced by using the most efficient conversion
 technologies.    The  U.S.  Department  of
 Energy, the Electric Power Research Institute,
 and  many other  organizations have been
 investing  significant  funding  in  research,
 development, and demonstration  of "clean
 coal technologies"  designed to allow burning
 of coal  to generate electricity with maximum
 efficiency and minimum environmental impact
 (U.S. DOE, 1987d). These technologies offer
 the  potential  to  significantly  reduce   the
 amount of traditional air pollutants  such as
 sulfur dioxide and nitrogen oxides.  However;
 they  may  also   affect  the   amount   of
 greenhouse gas  emissions,  particularly  for
 those technologies that improve the overall
efficiency  of convening  coal  to electricity.
 For example, some of these technologies such
as the Kalina Cycle could improve efficiency
by at least  10% relative to conventional  coal
combustion technologies.

      Three of these advanced technologies
currently  in the  demonstration  phase  are
atmospheric   fluidized    bed   combustion
 (AFBC), pressurized fluidized bed combustion

                                                               Chapter V:  Technical Options
(PFBC),   and   Integrated    Gasification/
Combined Cycle (IGCC).   AFBC relies on
CO2-emitting limestone or dolomite and is
likely  to be  very similar in efficiency to
conventional technology, and therefore, not
beneficial   in   reducing   CO2   emissions.
Moreover, it is  believed research has indicated
that this technology may significantly increase
N2O emissions  as compared with conventional
coal-fired powerplants.  The PFBC and IGCC
systems, however, can be combined and are
projected to increase conversion efficiencies as
much   as   10-20%,   with  corresponding
reductions in  CO2 emissions per  unit of
electricity produced (U.S. DOE, 1987d).

      Clean coal technologies can be used for
newly  constructed powerplants, but also to
"repower"   existing    powerplants.       In
repowering, the basic combustion components
of existing powerplants are replaced with one
of the new  technologies.  Additionally, new
components, such as a gas  turbine cycle, may
also be installed in combination with  some
refurbished   components  of  the  existing
powerplant. The result is a hybrid plant with
performance very  much  like  that  of  an
efficient new unit.

Increase Use of Cogeneration

      Cogeneration refers  to the production
of both steam  and electricity from the  same
source; the steam is used to meet heating and
process requirements at the facility,  and the
electricity is used on-site or sold to electricity
customers. Because it is more energy-efficient
than conventional generating options, it has
been encouraged in the U.S. recently by many
regulatory and legislative   initiatives.    For
example,  the  Public  Utilities  Regulatory
Policy Act (PURPA) encouraged Cogeneration
by  establishing  a  process  ensuring  that
cogenerators with low production costs could
sell  this  cogenerated  electrical  power  to
electric utilities.

      As discussed earlier in PART  ONE,
Cogeneration has been very  popular with large
industrial energy users as  one approach for
reducing their overall energy costs. Most of
the  approximately  18  GW of  currently-
operating Cogeneration projects in the U.S.
and  an additional  29 GW  under active
development fall into this category (Williams,
 1988). Similarly, as electric utilities face more
 competition from industrial cogenerators and
 independent power producers (i.e., companies
 that produce and market power but are not
 regulated as utilities),  they may  choose to
 retrofit some existing generating facilities with
 Cogeneration,  using  the waste  heat  from
 electricity production for district  heating or
 industrial    process   heat   applications.
 Engineering  assessments have shown  this
 potential retrofit option to be economically
 attractive for powerplants that burn coal and
 are located close to steam load centers (Hu et
 al., 1984), though other fuel sources can be

 Substitute Natural  Gas for Coal

      Natural   gas  (which   is  primarily
 methane) has 55-60% of the carbon  per unit
 of energy as coal.   In applications  such as
 electricity production where coal is frequently
 used,  switching  to   natural  gas  would
 substantially  decrease  CO2 emissions.    As
 discussed previously in PART ONE, natural
 gas is currently used in several key end-use
 applications,  particularly in a wide variety of
 industrial  energy   applications   and  in
 residential and  commercial space heating.  In
 addition  to its  end-use  potential, natural gas
 can   be  used   as   a  fuel  for  electricity
 generation.  The discussion below  focuses on
 the technical options and advantages of using
 natural gas as a fuel for electricity generation.
 The role of natural gas as an end-use fuel and
 a  fuel for  electricity generation,  however,
 depends on the  natural gas resources available
 and the cost at which these resources can be

Natural Gas Use At Existing Powerplants

      There are several near-term alternatives
 for increasing  the  use  of  natural  gas for
electricity  generation.     One  relatively
 inexpensive option  would be to increase the
 utilization of existing natural gas- and oil-fired
 (most of which  can also consume natural gas)
 powerplants.  For example, in 1987 average
capacity utilization rates for U.S. oil- and gas-
 fired  powerplants were  40%, compared with
 58% for  coal-fired powerplants.  Thus, there
is some technical potential to increase gas use
by increasing the utilization of natural-gas-
 fired powerplants.  However, these plants are

 Policy Options for Stabilizing Global Climate
 utilized  less because the variable (operating
 and maintenance) cost of power is  higher at
 most oil and gas plants than at coal, nuclear,
 and hydro powerplants.  In addition, oil- and
 gas-fired  powerplants can be easily operated
 intermittently  and  with  less  wear on  the
 systems  (i.e., to meet peak load conditions).
 Since  electric  utilities  (usually)   produce
 electricity  with    their   least   expensive
 powerplants, policies would first have to be
 adopted  to increase utilization of natural gas

Advanced Gas-Fired Combustion Technologies

      An  additional  option for increasing
 natural gas use is to construct  new gas-fired
 combined  cycle   or  combustion   turbine
 powerplants. Although the variable cost may
 be higher, these powerplants cost significantly
 less to build than coal-fired powerplants and
 are  typically more  energy  efficient.  They
 could also be  part of a near-term  solution
 since the lead times for gas-fired plant siting
 and construction average  about 2-4 years
versus 6-10 years  for coal-fired powerplants.
 These advanced combustion technologies are
 not  in  greater  use  primarily because  of
 investors'  expectations  that  the   costs  of
 natural gas over  the operating life of the
 facility would  be substantially higher  than
other fuel alternatives such as coal.  As  a
 result, despite the lower capital  costs of these
technologies,  electric  utilities  have  often
invested  in other alternatives because total
generating  costs   of  combined  cycle   or
combustion turbine technologies have been
perceived to be greater than those  of coal-
fired powerplants.

      Combustion Turbines: Simple/Combined
Cycles. Combustion turbines are similar to jet
aircraft  engines in  that  fuel  is burned  in
compressed air, with  the combustion gases
then  used to turn a  turbine  for electricity
generation.  This process  is  known as a
simple-cycle turbine.  After the  hot gases are
used to produce electricity,  the exhaust gases
can be used to  convert water to steam in a
steam turbine.  Together these two processes
generate  power in  a  process known  as
combined cycling.  Most combustion turbines
in  use  are simple  cycles,  which  are used
primarily for peak power requirements due to
their   favorable    intermittent  operating
 characteristics   (primarily  their  ability  to
 increase power production quickly) and low
 capital costs, although  operating  costs are
 high.  Combined cycle capital costs are higher
 but  the technology uses  fuel more efficiently,
 and hence, is  currently  preferred  for units
 expected to be utilized more frequently.

      Aeroderivative  Combustion  Turbines.
 Recent advances in jet engine (aeroderivative)
 technology,  including   new  materials  and
 designs that enable combustion  to occur  at
 higher temperatures, have made turbines more
 efficient.  Many of these advances are being,
 or could be, applied to turbines for generating
 electric power.  Existing simple and combined
 cycle systems have efficiencies of about 32%
 and 42%,  respectively,  compared  to  new
 conventional coal-fired  powerplants,  which
 have efficiencies of about 33-35%.   Recent
 advances in aeroderivative technology could
 significantly  improve  these   cycle  system
 efficiencies.  One technology that  has been
 recently commercialized in California is the
 steam-injected  gas turbine (STIG).   STIG
 units take  any steam not needed for process
 heat requirements and inject it back into the
 combustor for added power and efficiency.  In
 a simple-cycle  application, the  efficiency  of
 the turbine might be 33% with an output  of
 33 MW, while  with full steam injection the
 efficiency  would increase to  40% with an
 output of 51  MW (Williams,  1988).   An
 improvement in steam injection that has been
 proposed is the intercooled steam-injected gas
 turbine (ISTIG). ISTIG cools  the compressor
 bleed  air  used for  turbine  blade  cooling,
 allowing  a  much   higher  turbine   inlet
 temperature.    With  this technology,  the
 single-cycle efficiency  cited  above   would
 increase from 33% to 47% and output from
 33 MW to 110 MW; the estimated capital
 cost of ISTIG  is about  $400/kW (Williams,
Factors Affecting Use of Natural Gas

      Resource Base.   There is a significant
amount  of  research  and  debate  over the
quantity  of natural gas  that is  available. As
discussed in Chapter IV, global gas resources
are estimated to be significantly smaller than
global coal resources (resource estimates by
the World Energy Conference indicate that
coal resources are about 30 times greater than

                                                                Chapter V:  Technical Options
gas  resources).   Within  the U.S., there is
disagreement over the size of this difference.
One source has indicated that in the U.S., the
natural gas resource base  is as large  as  the
coal resource base when one compares  the
economically   recoverable   and   usable
resources; the supply should be adequate for
hundreds of years (Hay et al., 1988).  On  the
other hand, based on 1985 consumption levels
of about 18.6  EJ,  the U.S. Department of
Energy  (U.S.  DOE)  has  estimated  that
technically recoverable U.S. gas  resources
would last only  about 70  years  at current
usage rates, and only about 45 years if limited
to supplies that could be marketed for about
a  maximum  of S5/GJ  (see  Table 5-8).  In
contrast, U.S. coal  reserves are estimated to
be about 350 times greater than  1985 U.S.
consumption levels (U.S. DOE, 1988d).

      Significant gas reserves are  available
outside of the U.S., though they are not well
matched  with  potential  demand centers.
More than half of the world's proved reserves
are located in just  two countries, the  USSR
and Iran. Soviet gas reserves alone are eight
times those available in the U.S., and Iran has
over two and one-half times the quantity of
U.S. gas reserves. While roughly 30% of the
world's proved reserves of natural gas exist in
the Middle East, only 5%  are  in Western
Europe, and less than 1% are in China and
Japan combined (British Petroleum Company,

      Cost.  In addition to  the potential limit
on  gas  supplies, there are  also  questions
about the cost of additional gas supplies, the
location of supplies vis-a-vis  the areas of
demand, the cost and availability of improved
transmission and distribution systems, and in
the case of international  trade  in liquified
natural gas (LNG), the costs of liquefaction,
transportation, and regasification facilities.

      Concerns over the cost and availability
of natural gas may appear unwarranted given
the existence  of  excess capacity and  falling
prices in the U.S. gas industry in recent years.
However, these  market conditions may  be
temporary.  Current excess capacity followed
a period in the 1970s when natural gas  was in
short  supply.    The  recent  changes  are
primarily  because   of  natural   gas   price
deregulation, which allowed prices to increase
from previously controlled levels.  The price
increases  had  two  effects:    (1) demand
decreased  and  (2) supply  increased.   The
duration   of   the   current  slack   market
conditions is a matter of much debate, but as
the demand and supply for  natural gas come
into balance,  natural gas may no longer  be
available at current prices.

      The relevance of these concerns is not
that natural gas cannot play a role in reducing
CO2   emissions;  unquestionably,   it  can.
However, the ability of natural gas to replace
fuels with higher carbon content is a  function
of the quantity of natural gas available and
the cost at which natural gas can be supplied
to consumers.  That is, even if natural gas is
available, the extent to which it replaces other
fuels will depend on its available supply and
cost relative  to alternative fuels and  the
available  pipeline  delivery system.   Any
policies promoting  increased use  of natural
gas must recognize these factors.

      Electric  Utility Gas Consumption.    In
1985,  gas  consumption by U.S.  electric
utilities was about one-fifth of total U.S. gas
use, or about 3 EJ. Even though U.S. electric
utilities consume only  a minor fraction  of
natural gas, they can have a large  impact on
prices  because  they  are   frequently   the
marginal buyer. That is, utilities often have
alternative generation options such as oil  or
coal  and  can easily  switch, unlike  many
residential or  commercial gas users  who do
not have such  flexibility.  Increases in electric
utility  demand for  natural  gas would affect
residential,   commercial,   and   industrial
customers, who would be charged higher gas
prices.   For  example,  assuming  13 EJ  of
consumption,  a Sl/gigajoule price  increase
would increase natural gas costs by $13 billion
per year  among all consumers.

      To replace  a  significant  amount  of
electric utility coal consumption would require
a   very   large  increase  in  natural  gas
consumption.    For  example,  utility  gas
consumption in 1985 was 3  EJ, whereas coal
consumption by utilities  was about 15 EJ.
Thus, to  replace 40% of coal consumption (6
EJ),  a   200%  increase  in   utility  gas
consumption would  be necessary  (assuming
current  efficiencies),  raising U.S.  electric
utility gas  use  to unprecedented levels. As a

Policy Options for Stabilizing Global Climate
                                                          TABLE 5-8

                                             Total U.S. Gas Reserves And Resources
                                                                         Recoverable Gasa
                   Recoverable Gas by Priceb
                     <$3/Mcf    $3-5/Mcf
Lower 48 States (Conventional)
Proved Reserves, 12/31/86, Onshore and Offshore
Inferred Reserves/Probable Resources, 12/31/86, Onshore
Inferred Reserves, 12/31/86, Offshore
Extended Reserve Growth in Nonassociated Fields, Onshore
Gas Resources Associated with Oil Reserve Growth0
Undiscovered Onshore Resources
Undiscovered Offshore Resources'1
Lower 48 States (Unconventional)
Gas in Low-Permeability Reservoirs
Coalbed  Methane
Shale Gas
Inferred Reserves (Cook Inlet Area)
Undiscovered, Onshore and Offshore



8 Volumes of gas judged recoverable with existing technology.
b Volumes of gas judged recoverable with existing technology at wellhead prices shown (1987$).  Mcf represents one thousand
cubic feet (about 1.1 GJ), which is a common measure of gas quantity.
c Judged at oil prices of <$24/bbl and $24-40/bbl.
d Outer Continental Shelf.
Source:  U.S. DOE 1988c.

                                                                Chapter V: Technical Options
 result, any policy to increase natural gas use
 needs to  recognize  possible impacts on gas
 supply and the market price of gas.

 Methods of Increasing Gas Resources

      Two  ways to  increase  the available
 supply of gas to consumers  are to (1) reduce
 or  capture methane  emissions  during  the
 production and distribution of natural gas and
 (2) extract methane from coal seams.  In each
 of  these  cases,  increasing the  amount  of
 methane available to consumers would often
 have other positive environmental benefits by
 reducing the amount of CH4 and CO2 emitted
 to the atmosphere.

      Reduce  or  Capture  Emissions  from
 Natural Gas Flaring, Venting, and Leaking. As
 discussed   in   Chapter  IV,   during   the
 production of oil and natural gas, natural gas
 may be vented  to the atmosphere as  CH4 or
 flared (producing COj).6   Additional  CH4
 emissions   are   also  produced during  the
 refining,  transmission,  and distribution  of
 natural gas. These emissions can be reduced
 through   more  careful   production   and
 maintenance procedures  or by capturing the
 gas for on-site use or sale to gas customers.

      Gas vented  or  flared  in  the   U.S.
 represents around 0.5% of annual domestic
 production,  while   gas   losses   during
 transmission and  distribution  have  been
 estimated  to represent less than 0.5% of gas
 consumption (A.G.A., 1989).   These values
 are presumed to  be much lower than  the
 global average  because of several  factors,
 including  regulations prohibiting the flaring
and  venting of gas  in  the U.S., and  the
existence  of markets  and infrastructure  to
 transport  and  sell the gas.  In areas in the
U.S. where no market for the gas exists (e.g.,
Alaska), gas produced during oil production
activities is reinjected into  the reservoirs in
order to  maintain  pressure.   Opportunities
exist in the U.S. for reducing gas (methane)
 losses  during transmission  and distribution,
 such as through maintenance and replacement
 of old, outdated distribution lines.  Globally,
 a larger percentage of natural gas is vented or
flared because of fewer regulations governing
 these   releases   and    a    less-developed
 infrastructure  for  utilizing the  gas.   The
quantities  of gas vented or flared could be
 reduced    through   development   of   an
 infrastructure to market the gas or through
 regulations governing these releases.

      Extract Coalbed Methane.  As discussed
 in   Chapter   IV,  during   coal  mining,
 particularly  underground  mining, methane
 trapped   in  the  coal  seam   is  released.
 Historically,  trapped coalbed  methane  has
 been viewed  as  a  safety  problem  since
 methane can accumulate in the coal mine to
 the point where it can explode.  U.S. mining
 regulations require  that  underground coal
 mines be adequately ventilated to prevent this
 problem.   Recently, however, there has been
 a  growing  interest   in   utilizing  coalbed
 methane as a natural gas resource.

      Methane  extraction  from  coalbeds,
 which is being done  commercially in  a  few
 areas in  the U.S., differs  from  traditional
 natural  gas production in  several respects.
 Perhaps most importantly, the gas production
 profile differs from conventional gas wells in
 that maximum output generally occurs two to
 three years  after the  wells  are  in  place,
 compared  to  immediately  afterwards  for
 conventional wells.  For a given production
 site,  more wells  are drilled  to  maximize
 methane flow.  Also, because these wells are
 drilled into  available  coal  seams, they  are
 generally  quite shallow (i.e., not more than
 3000-4000 feet deep).   While the relatively
 shallow access helps to reduce drilling costs,
 more ground water is encountered, requiring
 additional efforts to extract clean gas.

      Because coalbed methane recovery is a
 relatively   new industry,  it  is  difficult  to
quantify  the  potential size of this resource.
 In addition to offering another gas source,
 coalbed methane recovery could occur before
 the coal seam is mined.  Such recovery would
 help to ease the problem of methane buildup
 in coal mines (possibly reducing coal mining
costs) and reduce the emissions of CH4 to the
 atmosphere that result from current coal-
 mining operations.

Employ Emissions Control Technologies

      One technological option for reducing
the amount of greenhouse  gas emissions is
the use of emission  control techniques on
combustion technologies that generate these

 Policy Options for Stabilizing Global Climate
 emissions.  NOX and  CO2 emission  control
 options  for  stationary combustion  sources,
 such   as  electric  utility  powerplants,  are
 discussed below.
      Nitrogen  oxides  (NOX)  are  formed
during   combustion   primarily   by   the
combination at high temperatures of nitrogen
(N2) and oxygen (O^ naturally found in the
air, and secondarily by the nitrogen that  is
found in fuels such as coal and oil. Of these
two factors, the combustion temperature  is
usually  the most critical factor affecting the
NOX emission rate.  Fluidized bed combustion
is one  possible way to significantly reduce
NOX emissions.  There are several additional
available   methods   for   controlling  NOX
emissions (based on NAPAP, 1987):

           Low Excess Air (LEA)fOverfire
Air.  These two combustion techniques alter
the flow of air during the combustion process.
With low  excess air the amount of excess
combustion air  is reduced, thereby lowering
emissions by as  much as 15%. With overfire
air, some combustion air is  redirected to a
region above the burners, which can reduce
emissions by as much as 30%.   Potential
drawbacks are incomplete combustion of the
fuel, increased smoke, and the extensive plant
modifications that may be required.

           Low NOX burners.  This  control
technique operates within the furnace to limit
the mixing  of coal  and combustion air  to
create a low-temperature combustion zone.
This technique can be applied to existing and
new units,  although  experience on  existing
units is quite limited.  Removal efficiencies in
new units approach 50%.

            Air  and  Fuel  Staging.   When
combined with low NOX burners,  these two
controls  can  achieve  up to 75% removal
efficiencies.   With air staging alone, up  to
50% of  the combustion air is directed above
low-NOx burners.  With fuel staging (also
known as reburning) additional fuel is  burned
in a region above the burners to create a fuel-
rich combustion  zone.  Within this zone NOX
is  destroyed  by reducing  conditions  that
convert  NOX  to molecular  nitrogen.  This
technique   has   been  used  in  full-scale
 applications  abroad,  but  only in  pilot-scale
 facilities in the U.S.

            Selective    Catalytic   Reduction
 (SCR).  SCR  is a post-combustion  control
 technology that uses a catalyst to reduce NOX;
 reductions of 50-80%  are  possible.    Its
 advantages   include   relatively   simple
 equipment,  no  byproduct,  and  minimal
 efficiency  loss.    Its  cost-effectiveness   is
 unproven,  however, and depends on  catalyst
 lifetime, which  depends  primarily  on fuel
 characteristics. SCR has been used abroad on
 low-sulfur  coal,  particularly  in  Japan and
 West Germany. Testing of this technology's
 performance on U.S. high-sulfur coal began in
 late 1989.

 CO2 Controls

      Technologies have been developed  to
 remove carbon dioxide from powerplant flue
 gases and  dispose  of it  in a manner that
 prevents it from reaching  the  atmosphere.
 These technologies,  however, are unproven
 and very costly at this time.  In one process,
 carbon dioxide in the flue gas is mixed with
 water in a solvent solution at temperatures
 slightly above ambient  conditions.    The
 carbon  dioxide  binds to the reagent and
 passes  to  a  regenerator  chamber  where
 temperatures  are  elevated.   The   reverse
 reaction  then occurs and CO2 is released,
 removed,  pressurized, and  liquified.   The
 reagent is regenerated and reused.  The liquid
 carbon  dioxide  could  then  be  used  for
 commercial applications, or  pumped to deep
 ocean locations, deep  wells, or salt  domes for
 permanent disposal.   The  volume of CO2
 currently produced dwarfs existing markets for
 reuse,  however,  so  any control  program  of
 significant  scope would involve  very large
 disposal costs.

      In order to  understand the  relative
costs of this CO2 removal process, the costs
of this system are compared to a conventional
sulfur dioxide scrubber in Table 5-9.  The
carbon dioxide scrubber is  250-350% more
costly than the sulfur dioxide scrubber and
would  increase electricity costs  by 60-80%.
The cost of transporting and disposing of the
large volume  of removed CO2 has not been
adequately   assessed,   but   is   likely   to
substantially increase this estimate.  Although

                                                         Chapter V: Technical Options
                                    TABLE 5-9

               CO2 Scrubber Costs Compared To SO2 Scrubber Costs'

Capital Cost ($/kW)d
Variable Operation and Maintenance
Costs (mills/kWh)
Energy Penalty (%)
Capacity Penalty (%)
Fixed Operation and Maintenance
Costs (S/kW-yr)
Total Cost (mills/kWh)e
CO2 Scrubberb
SO2 Scrubber0
a Ninety percent removal of both CO2 and SO2.

b Source:  Steinberg, Cheng, Horn, 1984.

c Source:  U.S. EPA Interim Acid Rain  Base Case Estimates, 1987.

d Greenfield Site.

e Sixty-five percent capacity factor; 9% capital charge rate; incremental power costs 65 mills
per kilowatt-hour; new plant costs of $l,200/kW; fixed O&M for CO2 scrubber is assumed
to be $10 per kilowatt-year for comparison purposes only, actual costs could well be higher,
1988 dollars assumed to be worth 42% less than 1980 dollars.

 Policy Options for Stabilizing Global Climate
some CO2  could  be used for enhanced oil
recovery or stored in  exhausted  oil and gas
wells, large-scale disposal would most  likely
have to be  in the  ocean.  This raises serious
environmental  concerns that  have not been

Consider Emerging Electricity Generation

      There are several technological options
that could be available in the longer term that
would substantially alter the way fossil fuels
are utilized.   Two  of the   most-discussed
options  -  fuel  cells and   magnetohydro-
dynamics -- are discussed below.

Fuel Cells

      Fuel  cell technology is  now in use in
the U.S. space program and  is  expected  to
eventually  be commercially available to  the
electric power industry.   The   technology
converts fuel  energy to electricity using an
electrochemical  process  similar   to   that
employed in chemical batteries.

      Total  fuel  cell  plants may achieve
efficiencies  of up to 85%.  There are several
drawbacks  to  the  technology at this  time,
especially:   (1)  special  fuel requirements, and
(2) relatively low reliability.

      The  fuel cell closest to commerciali-
zation  is   the  Phosphoric Acid  Fuel  Cell
(PAFC).   This fuel cell converts hydrogen
into electricity and water. The hydrogen must
be produced, however; considering the conver-
sion losses, overall powerplant efficiencies for
large  fuel   cell plants (e.g.,  several  MW)
approach 45%.  Second-generation technolo-
gies, such   as  molten  carbonate and  solid
polymer electrolyte fuel cells, could offer 60%
efficiencies. In theory,  the chemical reaction
could continue  as long as fuel is supplied, but
in practice the  materials fail after prolonged
operation.    The   current  goal  is  40,000
generation hours which, even if  achieved, is
still  well   below  that  of  conventional
powerplants.  Another drawback is  that the
production  of   hydrogen from  fossil  fuels
creates CO2.

      The   use of  hydrogen  in fuel  cells
suggests the possibility  of coupling fuel cells
with renewable energy sources.  For example,
solar powerplants could use any power not
delivered  to customers to create hydrogen,
which  could   then  be  used   when   solar
powerplants  are  not  operating  or  when
demand exceeds  solar capacity  (Ogden  and
Williams,  1989).  Molten carbonate fuel  cells,
under research and development at the U.S.
DOE   at  this   time,  could   expand   the
capabilities of fuel cells to include natural gas
and gasified coals.


      Magnetohydrodynamics (MHD)  is  an
advanced, efficient generation technology that
could use coal as a fuel.  In a MHD system,
coal is burned at very high temperatures and
the  hot  combustion gases  are chemically
treated.   The gases then  pass through  a
magnetic  field created with superconductors,
thereby generating power. The gases can also
be  used  in  a  steam  cycle   to  produce
additional power.   The  MHD system is
expected to  eventually achieve efficiencies of
60%.   In comparison, existing conventional
coal powerplants operate at about  31-32%
efficiencies and advanced pressurized fluidized
bed  combustion  (PFBC)  and  Integrated
Gasification/Combined  Cycle  (IGCC)  coal
units, now being demonstrated, are expected
to achieve 35-37% efficiency.

      There are several  drawbacks to  the
MHD technology. It is very capital-intensive,
requires  superconductors  that   have   only
reached the  laboratory stage of development,
and the high temperature combustion could
result in high  nitrogen oxide emission rates.
Nonetheless, many observers believe MHD
systems will eventually be available as  these
obstacles are overcome, creating an option for
very efficient coal combustion.


      Biomass  in  one  form   or  another
continues  to be the predominant source of
energy  for  at  least half  of   the  world's
population.    In many  countries,  such  as
Nepal, Ethiopia, and Guatemala,  over 90% of
total  energy  used  comes  from  biomass
(Goldemberg et al., 1988).  Although on a
global basis  it  accounts  for only  one-seventh
of all  energy  consumed, for over 2 billion

                                                               Chapter V: Technical Options
people it is close to being the only source of

      A number of studies have reported on
the alarming rate  of  global deforestation as
the current demand for biomass resources far
exceeds the natural rate of regeneration (e.g.,
IUCN, 1980; WRI and IIED,  1988). It is  this
difference  between  growth  and  use that
contributes to net greenhouse gas  emissions.
Despite this current situation, biomass energy
over the long term offers some of the most
promising opportunities  for displacing large
amounts of fossil fuel use.

      Although  biomass fuels  account  for
about 14% of global primary energy use, they
deliver  a  much smaller fraction  of  useful
energy because  of the inefficient  nature of
their current use. However, technologies exist
or are under development to provide many
times the current level of energy services from
the amount of biomass currently  consumed
globally.  In addition, it is also technically
possible  to  greatly  increase  the   annual
increment of biomass available for energy use.
Methods  for  increasing  supply  through
agroforestry,  biotechnology,  etc,  and  for
reducing extractive use of forest products for
non-energy purposes are discussed in PART
FOUR:  FORESTRY.  In this section various
approaches are  discussed to reduce biofuel
demand through fuel switching, by  improving
end-use  efficiencies,  and  by   increasing
conversion  efficiencies using upgraded fuels
(see Figure 5-6).

Improve Efficiency of Direct Firing Methods

      The primary uses of biomass in direct
combustion   applications  include use   in
cookstoves,  space  heaters, bakeries,  brick
kilns, and boilers  of  various sizes.  Typical
conversion  efficiencies  range from  5-15%.
There is tremendous potential for  improving
the end-use efficiency in each of these energy
conversion processes.  In fact, this may be the
most  cost-effective,  immediate option  for
decreasing the demand for biomass resources
(e.g., see discussion on technical options for
improving efficiency of biomass use in PART

      Wood or wood products (bark, sawdust,
chips, bagasse) are already  used directly as a
boiler fuel  (especially in agroforestry-based
industries  with readily-available  access  to
wood supplies). But there are a number of
modern  technologies that can  be used  to
extract much more useful output.  Due to the
physical variability of biomass (and the lower
density of crop residues), some improvements
in combustion properties can very often be
achieved just  by  properly sizing the solid
biofuels. The energy requirements for sizing
and  densification  must be weighed against
improved combustion, convenience, and ease
of transport.   While this  is not  absolutely
essential when the application is for heating,
some amount  of sizing and/or briquetting is
critical  in  more efficient boiler or gasifier

      Another area  in  which  combustion
efficiency can  be significantly increased is in
the use of advanced burner systems, such as
fluidized bed combustors. These use a stream
of hot  air  to suspend  the  fuel and  thus
achieve more complete combustion. Some of
these technologies can also use certain fuels
with high ash  or silica content, such as rice
husks, that would  be harmful  to standard
combustion systems.

      In a few areas, central power stations
have been constructed specifically to use wood
as a  fuel.   The facilities that are burning
wood for electrical power range in size from
5 to 50 megawatts. Depending on the cost of
fuel, conventional wood burning is generally
not competitive with conventional fuels due
to lower combustion efficiency  and greater
fuel  bulk, which  necessitates  larger fuel-
handling facilities.   The  localities served by
these plants gain various benefits that  may
offset these inefficiencies. For example, local
timber  industries   may  be   assisted,  and
environmental benefits may be obtained from
reduced CO2 emissions.

Improve  Efficiency of Charcoal Production

      Charcoal is produced by heating wood
in the   absence  of air (also  known  as
pyrolysis).     The   traditional   method  of
producing charcoal in kilns made of earth, as
used for centuries in many regions such as
Africa, is very inefficient  Only 15-30% of the
energy content of the wood is retained in the
charcoal  as all of the gases produced during

                         Strategies for Improving Efficiency of Biomass Use

                                            Improve conversion
                                              After processing
                                                    vegetable oil,
       electricity, steam

                                 Direct use as solid fuel
                             (improve efficiencies of stoves
                              boilers, brick kilns, bakeries)
                                                                         L    J

                                                                Chapter V:  Technical Options
pyrolysis are allowed to escape.  Substantial
efficiency  improvements are  possible,  for
example, Brazilian kilns built of brick, which
produce charcoal for steel manufacture, have
achieved overall efficiencies of up  to  50%,
twice that of traditional methods, by utilizing
the gaseous by-products (Miller et al, 1986).
Even  further  improvements  are   expected
(Goldemberg et al.,  1987).

Promote Anaerobic Digestion Technology

      Anaerobic digestion   is a  biological
process  whereby  a   combustible   gas   is
produced in the absence of oxygen; this gas is
a  mixture  of methane and carbon dioxide
similar to the marsh gas produced in swamps
and   landfills.    This  technology   has  the
attractive feature of separating  the energy
content of biomass  from its value as a soil
conditioner and fertilizer.  The energy content
is  released in  a gaseous form (i.e., biogas)
that can be utilized at a higher efficiency than
the original solid biomass. Biogas is primarily
used  for cooking and lighting, but  can also
partially substitute for diesel in engines used
for irrigation pumping.

      China  and India have had  extensive
biogas  programs for  more than  15 years
(Moulik,   1985).    Both  programs  have
concentrated on  household  systems,  with
manure and other farm wastes being the most
common feedstocks; over 7 million systems
have  been  installed,  most of these in China.
Programs in both countries have had to deal
with  design,  construction, and maintenance
problems so that many of the digesters are no
longer  functioning  (Miller et  al., 1986),
demonstrating  the  difficulty of introducing
even relatively "simple" low-cost technologies
in  remote, rural areas of developing countries.
Some larger  institutional plants have had a
higher   probability   of  succeeding   than
household-size  facilities.

      Financially,  the  feasibility  of biogas
plants depends  largely on whether the biogas
and  biomass  residues substitute for fuels or
fertilizers  that  have  traditionally   been
purchased or obtained at zero financial cost
In cases where  the biogas or residues do not
generate incomes or reduce cash  outflows,
they are less likely to be economically viable.
However, the nonfinancial benefits  of these
programs,  such as improvements in  public
health due to lower emissions during cooking
or  increased mortality  of pathogens in the
digester, reduced deforestation,  less  reliance
on  imported fuels, etc.,  motivate countries
such as China and India to continue subsidies
for biogas  projects (Gunnerson and Stuckey,

      There   are  a   number  of   other
approaches  being  tried  to  make   this
technology more appealing.  Ideally, what  is
required   is   a   low  capital-investment
technology that permits the use of a wide
variety of feedstocks and  results in high gas
yields over a range of ambient temperatures.
In Taiwan, a durable and cheap above-ground
bag digester  made  from  bauxite  refining
wastes has been used with success (Miller et
al.,  1986).    Other  promising  anaerobic
digester designs being  explored include the
upflow  sludge  blanket  and baffled reactor
(Gunnerson and Stuckey,  1986).

Promote Use of Gasification

      Many  cellulosic   materials  can  be
gasified and then either  used directly or
liquified into methanol.  There are two routes
for gasifying biomass  - one  resulting  in
producer  (or wood) gas  and the other in
synthesis  gas   with  higher  calorific  value.
Producer gas is made by heating wood in an
almost oxygen-free environment so that the
unburned fuel  breaks down  into gases, ash,
and tar.   Producer gas was used  to  propel
trucks in World War II when oil was scarce.
Synthesis gas is made at higher temperatures
with a purer oxygen source than producer gas,
thus eliminating nitrogen, and lends itself to
conversion  into  methanol  (see  Improve
Technologies to Convert Biomass  to  Liquid
Fuels below).

      Producer  gas  can  be made using  a
number of raw materials: wood, charcoal, crop
residues, and urban refuse.  There are more
than   20  companies   world-wide   selling
gasifiers, with  Brazil  and  the  Philippines
leading in the  use  of  this  technology.
Gasifiers have  been used  to power tractors,
motor boats, and irrigation pumps  and to
provide electricity for  food processing and
other rural needs. They can also replace oil
as a boiler fuel.

 Policy Options for Stabilizing Global Climate
      Kjellstrom (1985) has shown that for
conventional power generation applications,
biomass gasifiers  compete favorably  if the
operating times are long, load factors  high,
and power outputs large.  The  economics are
most favorable for wood-based  systems rather
than charcoal  systems,  and  could become
substantially more attractive if oil prices  were
to  increase or biomass input  costs were to
decline.   One  drawback  to gasifiers at  this
time is  that current designs do not accept all
types of crop  residues.   Kjellstrom  also
demonstrated  that at 1985  diesel  prices it
would be uneconomic to run diesel tractors or
trucks  on  producer gas  or  to  use  it  in
industrial applications except  for  industries
with surplus  biomass  residues.    Another
technical problem is the need  to understand
the  pollution  impacts due to  CO  emissions
and  tar condensates  from  the  biomass

      While there are a number of problems
to be resolved before biomass gasifiers can be
easily   used  to  replace natural  gas  in
conventional   applications,    research    at
Princeton   University   has   shown   that
integrated gasifier-combustion turbine systems
could provide, at small scales (e.g., 5-50 MW),
power that is less expensive than power from
new hydroelectric, coal,  or  nuclear plants.
(See Box 5-5;  Larson et al., 1987).

Improve Technologies to Convert Biomass to
Liquid Fuels

      Biomass-produced    ethanol    and
methanol can  be  used as liquid  fuels.  In
addition, other biomass-derived oils have been
combined with diesel and used as fuel.

Methanol from Biomass

      Methanol from biomass is  attractive
because   current   technologies   use   raw
materials grown on lands not required for
food production, unlike ethanol from corn or
sugarcane.   The state of Hawaii, which must
import  all  of its oil, has  enacted  legislation
supporting the construction of a  methanol-
from-biomass  facility towards the  goal of
replacing gasoline  and  diesel  fuel   with
methanol (Phillips et al., 1990).
      Methanol is  produced by first  making
synthetic  gas  (a mixture of CO and  H2) by
gasifying  (partially oxidizing)  biomass,  and
then catalytically reacting the product gases.
Though the process for converting synthesis
gas  to  methanol  is  fairly  well established,
promising research is underway to improve
the conversion efficiency by using  novel low-
temperature, low-pressure catalysts (Boutacoff,
1989).    However,  converting  biomass  to
clean, usable  synthesis  gas provides a major
technical  and economic challenge.  Various
gasification processes are under development,
for example,  coal  gasification  technologies
such as the German Winkler gasifier could be
modified  to  accept  wood as  a feedstock
(Williams,  1985).     In  the  U.S.,  most
evaluations have been based on bench-scale
testing of gasifiers.   The next milestone in
commercializing this process calls  for scaling
up the gasification and gas-cleaning plants
and operating the facility for extended  periods
to confirm gas yields, quality, and operational
integrity (Phillips et al., 1988).

      As with most renewable energy projects,
the   economics   of   biomass-to-methanol
processes  are less  favorable now  than they
were in the early 1980s due to lower world oil
prices.  Moreover, it  is significantly cheaper
currently to derive methanol from natural gas,
and  even  coal, than  from  biomass.   With
wood costing $34 per dry ton (Phillips et al.,
1988)  methanol  could  be produced at  a
wholesale  price  of S15/GJ.   Taking into
account  that   methanol  has   a   20% fuel
economy  advantage over  gasoline,   this  is
equivalent to  a gasoline price of S12/GJ (or
about  $1.60/gallon).     As  a  result,  the
production of methanol from biomass should
be regarded  as a long-term opportunity  as
conventional  fuel  prices  rise   and/or  if
technical    improvements    reduce   costs
(Williams, 1985).

Ethanol from Biomass

      Biomass can  also be  used to produce
ethanol.    Ethanol  is  useful  both  as an
automotive fuel and as a feedstock for the
production of ethylene  and other  chemicals.
Because of certain inherent requirements, as
discussed  below, its applicability is limited to

                                                               Chapter V:  Technical Options
                         Box 5-5.  Biomass-Fired Combustion Turbines

              Adaptation of the integrated-gasifier-combustion-turbine technology discussed
       above (combined cycle or aeroderivative turbines -- see FOSSIL-FUEL OPTIONS) to
       use biomass presents an attractive option for generating electricity in developing
       countries (Larson  et al., 1987), and could also become important in industrialized
       countries with advances in  biomass plantation productivity (see PART FOUR).
       Indeed, the use of this technology with biomass should be simpler than with coal
       because biomass is easier to gasify and sulfur removal is unnecessary.  The use of
       aeroderivative turbines (STIG and ISTIG, see Substitute Natural Gas for Coal) may
       be particularly attractive because this technology remains quite economic at small
       scales.  While the individual components of such a system have been tested, a
       commercial demonstration of the integrated package could be very important in
       increasing investor confidence in this technology.

              Biomass-based electricity generation Is most economical where the fuel has
       already been collected for other reasons (e.g., the forest products industry, the cane
       sugar industry). A prime example is the use of bagasse (i.e., sugarcane residues) at
       sugar mills and ethanol distilleries. Although these waste products are currently used
       to provide on-site needs for process steam and often electricity, there has been little
       interest in increasing efficiency once on-site requirements are satisfied. Indeed, steam
       and electricity production is often intentionally inefficient because of the desire to
       consume the wastes.  Substituting an ISTIG-based cogeneration system for current
       steam turbines could increase electrical output by a factor of 20, while still meeting
       process steam requirements; total system efficiency could exceed 50% (Larson et a!.,
       1987).  This could make the cane sugar industry a  major electricity producer in
       developing countries:  if this technology were adopted in the  70 sugar-producing
       countries, total capacity could exceed 50 GW, increasing electricity supplies by 25%
       in these countries.

              Design  calculations suggest that the costs would be very  competitive with
       alternatives.  Capital costs could be less  than $l,OOQ/kW, and  electricity could be
       generated for 3-4 cents/kWh where biomass is available for S2/GJ or less (Larson et
       al., 1987).  (Bagasse in the sugar cane industry is essentially free, implying that the
       additional costs for producing electricity could be less than 2 cents/kWh.) The barriers
       to adoption of this technology appear to be primarily institutional  collaboration
       between the cane sugar or other biomass producers and  the utility industry is required.
       Furthermore, an integrated biomass-based advanced  turbine system needs to be
       commercially demonstrated,  but  it is difficult  to attract investors in developing
       countries  where this technology is most attractive for projects considered to entail
       technological risk (see CHAPTER VET).
a few countries.  However, to the extent  it
can replace petroleum products, net emissions
of  CO2 will  be zero since ethanol  from
biomass is produced on a renewable basis.

      Today, Brazil has the most extensive
ethanol development program in  the world.
The purpose is to  provide alternative trans-
portation  fuels, based largely on  sugarcane-
derived  ethanol  (Sathaye   et  al.,  1988).
Although Brazil has succeeded in reducing its
oil imports, its program has received mixed
reviews,  largely because  the program  has
depended on substantial subsidies to ensure
its success. Similar efforts in other countries,
such as  Kenya, have  been  less successful,
usually due to a lack of low-cost biomass or
industrial expertise such as  that available in

 Policy Options for Stabilizing Global Climate
Brazil (Miller et  al.,  1986).   Despite these
problems, alcohol production may offer future
benefits, as  a number  of  other  feedstocks
(e.g.,  grain,  sorghum,  corn)  may  provide
cheaper  ethanol  and  as  technologies  to
produce  ethanol from wood are developed
(Brown,  1980).

       Currently, the simultaneous saccharifi-
cation and  fermentation  process  (SSF)  is
believed  to  have the greatest promise  to
achieve low costs and high yields (Wyman and
Hinman, 1989). The large volume market for
ethanol   demands   that    feedstock  and
conversion costs be low.  Only the low costs
of lignocellulosic feedstocks provide sufficient
margin to cover conversion  costs for efficient
processes.  Although the cost of ethanol from
SSF  has  dropped   from  S3.60/gallon  to
$1.35/gallon   over   the  last  eight  years,
improvements   are    still   needed    in
pretreatment, enzyme  production, hydrolysis,
xylose fermentation and recovery steps before
ethanol can compete with conventional fuels
at today's prices ($0.75/gallon at the refinery
gate) (Wyman and Hinman, 1989). This price
reduction can reasonably be expected  by the
year 2000 even if research continues at today's
levels  (Lynd, 1989).

Biomass  Oils as Fuel

      One  technically-feasible option  with
biomass-derived liquid  fuels  is to use coconut,
palm, and other vegetable oils in combination
with diesel fuel. These oils can be grown on
plantations with high yields,  but their worth is
usually greater as food than as fuel.   The
Philippines   briefly  experimented   with  a
mixture  of  coconut  oil  and  diesel  until
changes in relative prices made the  approach
uneconomical (Miller et al., 1986).


      Solar energy technologies, as described
in  this  section,  are  those  that  collect,
concentrate, and convert solar radiation  into
useful energy.  Technologies  for converting
solar energy into useable energy offer some of
the  greatest  long-term  opportunities  for
replacing fossil fuels.  Within  this  category,
however,   there  are   several   types   of
technologies.  Some solar energy applications
for the residential and commercial  sectors
were discussed in  PART ONE.  This section
will  focus  on  solar  thermal  and  solar
photovoltaic options.

      Solar thermal systems  that are  more
sophisticated   than  the   residential   and
commercial systems described earlier and that
can concentrate solar radiation  to  prodace
higher  temperatures are  being developed.
These higher temperatures could be used to
make steam, electricity, or power for other
industrial process  heat  applications.    The
most   sophisticated   solar   conversion
approaches are photovoltaic technologies that
convert solar radiation directly into electricity.
These techniques have received considerable
research attention over the last  10-15  years
and have progressed considerably as  a result.
The potential of both photovoltaic and  solar
thermal technologies, which produce power
directly only during daylight  hours, will be
even greater   as  more   efficient  storage
technologies increase the cost-effectiveness of
storing  excess  power generated  during the
daytime for use at other times, as discussed
further in Enhance Storage Technologies.

Promote Solar  Thermal Technology

      Solar thermal technology is a promising
area of solar  research since it can provide
thermal energy at temperatures from  150-
1700C for heat or electricity applications, at
almost  any scale,  and   with  conversion
efficiencies as   high  as 31.6% for electricity
and 80% for heat (IEA, 1987).  Solar thermal
concentrating systems have been extensively
demonstrated   in   recent  years for  both
industrial heat and electricity generation.  670
MW  of electricity generating capacity are
already  in  place or under construction in
seven countries (Shea, 1988).  In the  U.S.,
solar thermal capacity is projected to increase
to 550  MW in the next  5 years based on
announced industry plans (U.S. DOE, 1987a).
The U.S. Department of Energy has estimated
recently that a further cost  reduction  by  a
factor  of  1.5   to  2  would  make  these
technologies competitive with conventional
electricity generating technologies. U.S. DOE
has  also  identified several  key technical
improvements currently being researched that
could achieve the needed cost improvements,
leading  to economic competitiveness by the
mid-1990s (U.S.  DOE, 1987a).  In recent

                                                                Chapter V: Technical Options
years  most  research  and  development  has
focused  on  three  thermal technologies   --
parabolic  troughs,  parabolic  dishes,   and
central receivers.

Parabolic Troughs

       Parabolic troughs are often referred to
as line focus systems because they use  one
axis only to track the sun; each concentrator
(collector) has its own receiver, with parabolic
troughs  often connected to form a series of
collectors (see Figure 5-7). Troughs operate
at  lower  temperatures  than  most  other
technologies,  for  example,  up  to  400C,
making  them  most  suitable  for industrial
process  heat  applications.    The  thermal
efficiencies of  these units have improved
significantly in recent years, reaching 65-70%,
with availabilities exceeding 95% (IEA, 1987).

Parabolic Dishes

       Parabolic dishes differ from troughs in
that they are point focus systems, in  other
words, a two-axis tracking system is employed
to follow  the sun  (see  Figure  5-7).   The
higher concentration ratios  allowed by  this
design (from one hundred to several thousand
suns)  produces temperatures  approaching
1700C, making electricity conversion possible.
This   technology  currently  holds   many
efficiency  records,   including  the  highest
conversion efficiency (31.6%).  Several of the
most ambitious development projects are in
the  U.S.,  with installed  capacity at  some
projects  approaching  5 MW. DOE estimates
total system cost at $3,400/kW, although cost
reductions of 40% are considered  feasible
(IEA,  1987).

Central Receivers

      Central receivers represent the largest-
scale  thermal technology.   The  receiver is
typically  mounted on a tower surrounded by
a large field of nearly flat tracking  mirrors
called  heliostats  (see Figure  5-7).    The
heliostats  focus the  solar  energy on  the
receiver,  achieving working fluid temperatures
of 1500C or higher  (IEA, 1987).   Several
countries are studying central receivers.   The
largest plant,  located in southern California
(10 MW), has exceeded peak design output by
20%,  operated  at  night  from storage, and
achieved an overall plant efficiency of 13%
(IEA,  1987).  Heliostats account for 40-50%
of total costs, and consequently are the focus
of   most  cost  reduction  efforts;   recent
developments indicate that cost reductions of
50% could  be achieved in one or two years
(IEA,  1987).

Solar Ponds

      Solar ponds  collect and store heat in
large bodies of water and operate at much
lower temperatures than other solar thermal
technologies (85-100C).  In a typical design,
a salt  gradient below  the surface acts as an
insulating barrier by trapping incoming solar
radiation. Large heat exchangers are used to
extract the thermal energy, which can be used
for many purposes, including seasonal heat
storage for  space heating, low temperature
process heat applications, or even electricity
production.    Research into  this technology
has achieved thermal efficiencies of 15%, with
electrical conversion efficiencies  of about 1-
2%  (IEA,   1987).    Despite  these  low
efficiencies, solar ponds can be attractive since
capital costs are very low.

Improve Solar Photovoltaic Technology

      Solar  photovoltaic  (PV)  technologies
convert solar  radiation to electricity (DC, or
direct  current) without  moving  parts  or
thermal  energy  sources.     Photovoltaic
technology  was  initially  developed  in  the
1950s;  these  first  systems were about  100
times  more  expensive  than  conventional
generation    technologies,   but   major
improvements have reduced this differential to
3-4  times  current  energy  costs.    This
differential is  even lower  when compared to
current replacement costs. Figure 5-8 shows
the  dramatic  progress that  has been  made
since 1975 in reducing the costs of electricity
from photovoltaic systems.

     The    principal   drawback   with
photovoltaic technology  is the  high  capital
costs.  The current goal is to reduce costs to
about 6 cents/kwh  (which is comparable to
the best conventional  powerplant costs), at
least  for  conditions  in  the  southwestern
United States where insolation is high.  The
U.S. DOE  is projecting  that its cost goal
($0.06/kwh) may be achieved in the 1990s and

Policy Options for Stabilizing Global Climate
                                 FIGURE 5-7
      Parabolic Trough
Parabolic Dish
Central Receiver
                              Receiver   \ Coneeninlof
  Source: IEA, 1987.

                                        Chapter V: Technical Options
                         FIGURE 5-8
          Small Stand-Alone
            1st Large (60kW)
                   Intermediate (20-200KW)
                          Present Status   Research Goal:
          Austin Electric m-	6C/kWh
Source: U.S. DOE, 1tS7

Policy Options for Stabilizing Global Climate
that photovoltaic systems could provide up to
1.5 GW of generation capacity by 2005 (U.S.
DOE,  1987a).    Researchers at  Princeton
University   are   also   projecting   major
technological breakthroughs  in amorphous
silicon  solar cell  technology.   They  have
projected that capital costs (almost the entire
cost for PV) for  these cells  may decline  by
over  80%  by  the  year  2000,  while  the
conversion efficiency of photovoltaic arrays
roughly doubles (Ogden and Williams, 1988).
This could greatly expand the contribution of
photovoltaic  electricity generation over the
next several decades.

      The  basic  principle  behind  solar
photovoltaic  power is that as  light enters the
PV cell, electrons are freed from  the semi-
conductor materials,  thereby generating an
electric  current.    To  generate  substantial
amounts of power with PV,  individual  cells
(which produce about 1 watt of direct current
electric   power)   are   combined  into  a
weatherproof-unit called a module. Modules
can then be connected together into an array,
with the  power output  limited only by the
amount  of  area  available.   The  modular
nature of PV arrays allows  them to be built
in increments  to conform  more closely  to
power requirements as demand for electricity

      The principal photovoltaic technologies
for current commercial power applications use
silicon  for   the   semi-conductor  materials.
Several   efforts  are  underway  to  improve
silicon-based   photovoltaic  cells,  including
optical  tracking that  orients the cell toward
the sun, concentrating devices that increase
the amount of solar energy  hitting the plate,
layering  materials  to absorb  more  of the
energy,  and amorphous thin film techniques
that can lower production costs.

Crystalline Cells

      Crystalline  silicon cells are the  earliest
and most-established  PV technologies.  The
most popular material has been single-crystal
silicon, which had 90% of the global market
in 1980  but  only 44% (10.8  MW) by 1985
(DBA, 1987).   Single-crystal silicon PV cells
are relatively  efficient (production efficiencies
are  12-14%;  laboratory efficiencies  up to
21%), but have lost market share primarily
due to the high cost of manufacturing.  This
involves  several energy-intensive stages  to
produce  the  large silicon crystal  ingots from
which wafers are  cut (which destroys about
half the  crystal ingot), then final  preparation
and assembly.

      In response to some of the problems
encountered  with single-crystal  technology,
other  crystalline  technologies  have  been
developed.  Polycrystalline silicon cells use a
casting process that is less expensive but only
slightly less efficient than single-crystal silicon,
for example, commercially-produced cells have
a  conversion  efficiency of  11-12%,  with
laboratory efficiencies of 18% (IEA,  1987).
Polycrystalline silicon cells captured  about
20% of the global market in 1985. Another
alternative is polycrystalline silicon  ribbon,
which avoids the need to produce slices (or
wafers) by producing  sheets  or  ribbons  of
polycrystalline silicon. The advantages of this
technology are the potential for high-speed
production and less material waste, although
its efficiency is somewhat lower, for example,
production    efficiencies are  10-13% and
laboratory efficiencies are 17% (IEA,  1987).
This technology has been commercialized only

Thin-Film Technologies

      As  an   alternative   to   crystalline
technologies, researchers have focused on thin
films.  Thin-film solar cells can be produced
less  expensively  using  less  material and
automated production techniques.  There are
many  semi-conductor   thin-film  materials
under  investigation,  including  amorphous
silicon,  copper  indium  diselenide,  gallium
arsenide, and cadmium telluride.

      Amorphous Silicon. Amorphous silicon
cells have received the most attention of the
thin-film technologies, supplying 35% of the
global market in 1985 (EA, 1987).  The vast
majority  of this was for use in the consumer
market, especially calculators.  Because this
material   does  not  possess  the  natural
photovoltaic properties of crystalline silicon,
efficiency levels  have been a  problem  -
laboratory  efficiencies   are  about   13%.
Additionally,  amorphous silicon suffers from
a light-induced power degradation problem
that can cause a 22-30% loss of power output

                                                               Chapter V: Technical Options
over  time.   Thus,  large-scale projects can
currently   expect   to  achieve   about  5%
efficiency  over  the  life  of the  project.
Research into  this problem continues, with
amorphous  silicon  thin-film cells considered
one of the best potential  technologies for
power applications as efficiencies improve and
production costs are lowered.

      Other Semiconductor Materials.  Other
materials  are being investigated that do not
utilize  silicon,  including  copper   indium
diselenide, gallium  arsenide,  and cadmium
telluride.    Copper  indium  diselenide  is
attractive due  to its high efficiency (up to
12% currently) and stability when exposed to
sunlight over  extended  periods.    Gallium
arsenide  technologies  have  achieved  the
highest efficiency of any  PV material, 29%
(Poole, 1988), but are also some of the most
costly.  Research  continues  on  production
processes, such  as electroplating, that would
significantly reduce current production costs.

Multi-Junction Technologies

      Multi-junction, or tandem, technologies
combine the characteristics of two or more
different PV technologies to take advantage of
different  light   absorption   characteristics,
thereby increasing  total cell efficiency (e.g.,
two-junction devices  can  achieve efficiencies
of  18-35%;  U.S.   DOE,  1987b).     This
technique has been  used to produce the most
efficient solar cell to date - a 31%  efficient
cell  that  combined a single-crystal  gallium
arsenide cell and a single-crystal silicon cell
(Poole, 1988).  Multi-junction devices can also
be  used in solar concentrators, which are
optical  systems designed to  improve  PV
output by increasing  the amount of  sunlight
striking  a  cell by  10-1000 times.    In
combination these technologies may help to
achieve in  practice  the  25-30% efficiency
range   considered   critical   for    utility
applications (U.S.  DOE, 1987b).    Multi-
junction  thin  film  technologies are also
expected to become more important as multi-
layering increases efficiency more quickly than
system costs.

      There are  opportunities for increased
use of additional renewable energy  sources,
such as hydroelectric, wind, geothermal, and
ocean energy.  Many of these resources are
utilized today (often to supply electricity) and,
with continued research and development,
have  the   potential  to  make  important
contributions to meeting future energy needs
without increasing emissions of greenhouse
Expand Hydroelectric Generating Capacity

      Hydropower  currently  provides  the
largest   share   of  renewable   electricity
generation in the U.S. and globally.  In the
U.S., hydroelectric capacity accounted for 10-
14% of total electricity generation for the
years   1983-1987   (US.   DOE,    1988a).
Globally, hydroelectric generation accounts for
about  20% of total  electricity  and  7% of
primary  energy production (United Nations,
1988).    The technical  potential exists  to
expand the contribution of hydro at least by
a factor of two by the year 2025.

Industrialized Countries

      Traditional   large-scale   hydropower
projects are no longer a significant option for
most industrialized countries.  Many of the
most  attractive  sites  have  already been
exploited in  these  countries and remaining
potential sites are often highly valued in their
natural state for  recreational, wilderness, or
ecological purposes. The U.S. has more large
hydroelectric capacity in operation than does
any other country  in the world.   However,
new sites are no longer being developed, and
the U.S. Bureau of Reclamation,  the federal
agency historically responsible for large dam-
building projects  in the West, announced in
1987 that its mandate to develop new water
supplies  has  virtually expired and that it
would  be contracting in size and  shifting its
focus to  other activities over the next decade
(Shabecoff, 1987).

Policy Options for Stabilizing Global Climate
      Among industrialized countries, Canada
has  the  potential  to  greatly  expand  its
hydroelectric generating capacity.  The U.S.
Department  of  Energy  recently  identified
potential  hydro  sites  in Canada  which,  if
developed,  could more  than  double  peak
hydro-generating capacity in  Canada  (from
about 55 GW to over 127 GW).  This level of
expansion  would  not  be required  to  meet
projected Canadian  demand for  many years.
However, excess capacity developed in Canada
could  be   used  to  generate   power  for
transmission to  the  U.S.  where  it  could
compete  favorably  with other generation
options in  many regions.  The DOE analysis
estimates  that  U.S.  imports  of power  from
Canada could more  than  doubled by 2010  if
the potential hydro sites discussed above were
developed (U.S. DOE, 1987c). In lieu of this
hydro  development,  additional generating
capacity in the  U.S. during this period would
predominantly   be  fossil-fueled.     Thus,
displacing   U.S.   capacity  additions   with
Canadian hydro development would reduce
CO2  emissions.    However,   any  hydro
development raises  potential bilateral and
environmental issues with Canada that would
need to be resolved.

      Expansion  of small-scale  hydropower
(e.g., less than 30 MW) could be an  option in
many industrialized countries.  In the U.S. up
to 10 GW of potential capacity additions in
this category have been identified (U.S. DOE,
1987a).   Other  OECD  countries,  such  as
Canada and West Germany, are evaluating the
potential   for   expanding   small-scale
hydroelectric generation (Shea,  1988).

USSR and Eastern Europe

      In the USSR and Eastern  Europe,
there  appears  to  be  significant  technical
potential for expanding both large- and small-
scale  hydro  use.    In  1981,  hydroelectric
generation   provided about  13%  of  total
electricity in the USSR.  Soviet researchers
estimated that this was only about 19% of the
country's  potential  large  hydro  capacity.
Much of the  untapped potential  is in Siberia,
requiring  potentially  costly long   distance
transmission  to  reach major  load centers
(Hewitt, 1984). In Eastern Europe  there are
indications that opportunities for large hydro
projects still exist as well. Between 1980 and
1985  Romania  increased  its  hydroelectric
capacity by 2.5 GW, which was more than a
70% increase  in total capacity (World Bank,

      Opportunities also exist for expanding
small-scale hydro in the USSR and Eastern
Europe.   Poland,  for example, has recently
initiated a program to rehabilitate 640 small
dams that had fallen into disrepair and return
them to electric generation (Shea, 1988).

Developing Countries

      In  developing countries the  potential
for   large-scale   and   small-scale   hydro
development is very large.  For  example,  by
1980 it is  estimated that North America and
Europe had developed 59% and 36% of their
large hydropower potential, while  in contrast,
Asia,   Africa,  and  Latin   America   were
estimated  to have developed only 5-9%  of
potential resources. In  fact, most large-scale
hydro development in  the 1980s has taken
place in the developing  countries.

      Between 1980 and 1985, hydro capacity
additions  in 12 developing countries  totaled
over 38 GW  (over 8% of total generating
capacity in  developing  countries).   Several
developing countries,  notably Brazil, China,
and   India,  have   ambitious large   hydro
development programs planned for the future.
Total  capacity  additions   in   developing
countries  could  exceed  200 GW  by 1995 if
these plans  are  implemented (World  Bank,

      There is some question,  however,  if
these plans  will be fully implemented.  A
recent study  by   the  U.S.  Agency . for
International Development (U.S. AID, 1988b)
points out that many developing countries are
finding  it increasingly  difficult   to finance
capital-intensive  power  projects, especially
hydro, which have construction periods of  10
years  or  more.  In addition, the AID and
others have pointed out that  concerns about
ecological  and  land-use  impacts  such  as
submergence  of forested areas   as  well  as
resettlement impacts of large hydroelectric
projects may slow  such development in the

                                                               Chapter V:  Technical Options
      As in industrialized countries, there is
also significant potential for small-scale hydro
potential in developing countries. At least 28
developing  countries  already  have  active
programs   for   developing   small-scale
hydropower (World Bank, 1984). Equipment
for  small-scale  hydro generation  is   now
manufactured  in  a  number  of developing
countries, resulting in designs that are both
less  costly  and  more  suitable  to  local
conditions (U.S. AID, 1988a).

Reduce Cost of Wind Energy

      Wind-powered   turbines  were   first
connected to electric  power systems in 1941.
Currently,  there  are  several  technologies
available,  primarily  horizontal axis wind
turbines and  vertical  axis  wind  turbines.
Under optimal conditions, these systems can
produce power at 10 to 15 cents per kilowatt-
hour, or about  two  to  three times more
expensively  than  conventional fossil-fueled
powerplants.   The goal  is  to reduce these
costs such that in areas with wind resources,
these systems can be  used economically.  In
particular, wind energy systems may be very
suitable  for remote sites  where the cost of
conventional generation technologies may also
be quite high.

      Considerable   improvement   in   the
performance and economics of wind electric
generation was achieved  in the early 1980s.
In California, electricity generated from "wind
farms" increased  from 10 terajoule-hours to
16    petajoule-hours    (primary    energy
equivalent), while  capital  costs  fell from
$3,100 to $l,250/kW between  1981 and 1987
(Shea, 1988).   The Department of  Energy
reports  that the cost of electricity from wind
turbines has fallen from about 30 cents/kWh
to  10-15 cents/kWh  in  the  1980s.   DOE
projects that this improvement will continue
and that wind energy  could  provide as much
as 0.7 EJ of electricity in the U.S.  by 2005
(U.S. DOE, 1987a).

      Considerable international attention is
now being paid to wind energy. Wind farms
are   being   installed  in  Denmark,   the
Netherlands, Great Britain, Greece, and Spain
(IEA,  1987).     Other nations that  have
announced plans for  expanded wind energy
development   include    China,   Australia,
Belgium,  Israel, Italy, the Soviet  Union, and
West Germany (Shea, 1988).

Exploit Geothennal Energy Potential

      Geothermal energy  is thermal  energy
stored in rocks and fluids within the earth.  It
has been estimated that approximately  10% of
the  world's  land mass  contains accessible
geothermal resources that could theoretically
provide hundreds  of thousands of megawatts
of energy for many decades (IEA, 1987). As
indicated in Table 5-10, geothermal resources
suitable for generating electricity are extensive
and geographically widespread. From a global
wanning context,  several  countries  with the
most  extensive  geothermal  potential,  for
example, the U.S., China,  and the USSR, are
also  currently heavily  dependent  on  coal
consumption.   Geothermal  energy may, in
these  countries,   provide one   option  for
displacing  coal as  a source of  baseload
electricity  generation  and  industrial heat.
Significant geothermal resources also exist,
and  are  being developed, in several  Pacific
Rim countries, where economic growth rates,
and  thus  demand for additional energy,  is
expected to be high.

      While  certain  types  of  geothermal
resources,   specifically   hydrothermal   and
geopressured  reservoirs,   are not   strictly
renewable on a human time scale, resources
are so extensive that with careful phasing and
reservoir management, geothermal energy can
make a significant long-term contribution to
global energy needs. Unlike renewable energy
sources such  as  solar radiation and wind,
geothermal  resources  are  available  on  a
constant basis,  making  them suitable  for
baseload electricity generation and industrial
applications without  the  storage problems
associated with intermittent energy sources.

      There are several types of  geothermal
resources  that require somewhat  different
approaches  for exploitation.  Hydrothermal
resources  contain hot water and/or  steam
trapped  in fractured  or porous  rock  at
accessible  depths  (e.g.,   100-4500  meters).
These are the most commonly used resources
currently,  and  the only  resources currently
commercially  exploited.     Technology  for
exploiting  these  resources  involves sinking
wells, extracting the hot fluids, and using the

Policy Options for Stabilizing Global Climate
                                       TABLE 5-10

                            Estimates of Worldwide Geothermal
                             Electric Power Capacity Potential

                                      (in Megawatts)
Costa Rica
El Salvador
Korea (N. & S.)
New Guinea
New Zealand
Saudi Arabia
Soviet Union


        Source:  U.S. DOE, 1985c.

                                                               Chapter V: Technical Options
steam or hot water for electricity generation
or  direct  heat applications.   Steam  can be
used  directly in  steam electric generating
turbines.   Hot  water  resources are  either
"flashed"  to  produce  steam, or  used  to
vaporize another working fluid which  in turn
drives a turbine.

      Another type of geothermal resource of
long-term  interest is hot  dry rock.   These
potential  resources  are widely  distributed
around the world, but more difficult  to exploit
than hydrothermal resources.  To extract heat
from  hot  dry rock, it is necessary to inject
liquid into one well and withdraw it through
another  well after it  has  absorbed heat.
Considerable research is underway to improve
technologies for extraction of energy from hot
dry rock.  A geothermal resource still at the
conceptual  stage   of     development   is
magma,    which   is liquefied or  partially-
liquefied rock.  Potential  resources may be
greater  than any other geothermal resource
and the very  high temperatures  available
suggest  that power could be economically
produced;  however,  development  of  the
necessary  technologies  is  seen  as  a  major

      Geothermal energy is currently used in
several countries for direct heat and electricity
generation.  Table 5-11 shows the  extent of
direct heat use in  1984. Table 5-12 indicates
the   installed   capacity  for   geothermal
electricity  generation  by  country  in  1985.
Although they represent only a small fraction
of total energy use,  these  facilities  have
demonstrated   the commercial  viability of
geothermal  technologies.     In   the  U.S.
geothermal   systems   currently   produce
electricity at a cost that is competitive with
coal and  nuclear plants,  and the average
geothermal  unit  today is  available on-line
more  than  95%  of  the  time (U.S.   DOE,
1987a).  The Department of Energy projects
that U.S. geothermal electric capacity  will
more than  double  by 1995  to about 4.7 GW.

      Geothermal energy may also play an
even more important role in some developing
countries.      Eight  developing   countries
currently have  installed  geothermal electric
capacity, and about  50  more  have been
identified as having potential for  geothermal
development (U.S. AID,  1988a).   In  the
 1980s, the  costs of  geothermal technology
 have come down considerably, and small-scale,
 ready-to-install generators  (1-1.5 MW) have
 also  been  developed and  proven  reliable.
 These and other developments should make
 geothermal electricity more attractive to many
 developing countries (U.S.  AID, 1988a).

 Research Potential for Ocean Energy

      There are several types  of  potential
 ocean energy   sources,  including  thermal
 gradients and waves.  Research is underway in
 many countries, including the U.S., to develop
 technologies that can exploit these resources.
 In one technology, cold water located deep in
 the ocean is used to condense a working gas
 such as freon or ammonia.  The liquid then is
 reconverted to gas  by warm  surface waters
 and  used to drive  a turbine  and generate
 electricity.   Current  costs for such a system
 are   roughly   three  times   higher   than
 commercial  alternatives, and  there  remain
 significant   technological    uncertainties
 regarding system components and operation
 in an ocean environment.


      This section discusses the potential role
 for nuclear power  to  meet  future  energy
 needs.   From  the  perspective of global
wanning, nuclear power  technologies  are
attractive in that they emit only negligible
amounts   of carbon  dioxide  and  methane
 (Wahlen  et  al, 1989). As  will be discussed,
 however,  there  are   serious problems that
beset the nuclear power  industry.   Fission
 technologies are currently used  to operate
 nuclear  powerplants.    One  of  the  key
attributes of this technology is its  need for
 fissionable,  radioactive material in  order to
 operate.  Fusion technology is a longer-term
 nuclear option currently in the research and
development   stage.      Unlike    fission
 technologies, fusion  technologies would  not
 require  large   inventories  of  radioactive
materials such as uranium and plutonium.

Enhance  Safety and Cost  Effectiveness  of
Nuclear Fission  Technology

      Nuclear   fission  technology  is  an
important  source of electricity   in  many
regions of the  world. For example, nuclear

Policy Options for Stabilizing Global Climate
                                      TABLE 5-11

                         Capacity of Direct Use Geothermal Plants
                                   In Operation  1984

                       (For countries having capacity above 100 MW)
                          Power                   Energy                Load
   Country                MW                   GWh                  %
   China                  393                     1945                  56
   France                  300                      788                  30
   Hungary                1001                     2615                  30
   Iceland                 889                     5517                  71
   Italy                    288                     1365                  54
   Japan                  2686                     6805                  29
   New Zealand            215                     1484                  79
   Romania                251                      987                  45
   Soviet Union            402                     1056                  30
   Turkey                  166                      423                  29
   United States            339                      390                  13
   Other                  142                      582                  47
   Total                  7072                    23957                 39*

   *  Based on total thermal power and energy.

   Source:  IEA, 1987.

                                                         Chapter V: Technical Options
                                   TABLE 5-12

                    Geothermal Powerplants On-Line as of 1985
No. Units
United States
New Zealand
El Salvador
Soviet Union
France (Guadeloupe)
Portugal (Azores)
Greece (Milos)
a DS = dry steam; 1F.2F = 1- and 2-flash steam; B = binary.

b Includes plants under construction and scheduled for completion in 1985.

Source:  IEA, 1987.

 Policy Options for Stabilizing Global Climate
plants provided almost 20% of total electricity
generated in the U.S. in  1988.  This total is
projected   to   increase  throughout   the
remainder of this century as about  16 GW of
new nuclear powerplants, which are currently
under  construction,  are  completed.    The
prospects  for   further  capacity   additions,
however, are clouded. According to the U.S.
Department of Energy,  "No additional orders
for  nuclear  powerplants  are  likely  in this
country until the conditions  of the past few
years  are  changed"  (U.S.  DOE,  1987a).
Moreover, between 2000 and 2015, about 40%
of existing  nuclear powerplant capacity will
have to be  retired unless current  operating
licenses are extended beyond their expiration

      The situation  is  somewhat similar  in
many  other industrialized countries.    The
International Energy Agency (IEA)  reports
that nuclear energy was the fastest growing
fuel for electricity generation in the OECD
countries  between 1985 and  1987,  although,
"It  should be kept  in  mind, however,  that
present additions  to nuclear capacity come
from  stations   authorized in  the  second
relatively  intense  "cycle"  of nuclear  plant
construction activity in the 1970s. Compared
with  some  239 GW  of nuclear  capacity
operating in the OECD countries at the end
of   1987,   around   52   GW  are   under
construction"  (IEA,  1988).     In  addition,
planned nuclear electricity production  in the
1980s  in  the USSR has  been consistently
behind  schedule due to construction delays.
By  1988,  nuclear  generation was  providing
only 13% of electricity in the USSR.   In the
wake of the  Chernobyl disaster of April 1986,
the Armenian earthquake of December 1988,
and  unprecedented public  protest of nuclear
power, the nuclear program in the USSR has
experienced  numerous reactor  cancellations.
Further delays in the nuclear power program
are likely and future contributions are thus
difficult to project (Sagers, 1989).

      Nuclear power has  been beset  by a
series of problems.  Plant  capital costs have
increased  so dramatically  that  new nuclear
powerplants  are   no   longer  considered
economical  (see Figure 5-9).   The  real non-
fuel  operating costs of nuclear powerplants
have  also  escalated  rapidly  (U.S.  DOE,
 1988b).  Powerplant lead times (i.e., the time
 from project initiation  to  completion) are
 greater than  ten years, increasing project risk.
 Additionally, in many countries such as the
 U.S., the regulatory environment is generally
 unfavorable  toward large, long-term capital
 investments  and   nuclear  powerplants  in
 particular (U.S. DOE, 1987a).

      Public  opposition  to   new  nuclear
 powerplants is strong, in part due to concerns
 about safety in the aftermath of the accidents
 at  Three Mile Island and Chernobyl.   In
 addition to  plant  safety,  radioactive  waste
 disposal is  an  issue of  major   concern.
 Although several countries utilizing nuclear
 power are working on the problem, none have
 identified  an  acceptable  solution  to  the
 problems of long-term nuclear waste  disposal.

      Finally,    the   nuclear   weapons
 proliferation issue must be resolved if nuclear
 power is to become publicly acceptable.  A
 present-day 1000 MW nuclear plant produces
 some 141 kg of fissionable plutonium annually
 in its spent fuel.   For comparison, it takes
 less than 10 kg of fissionable  plutonium to
 make a nuclear weapon.   Currently, this
 spent, intensely-radioactive fuel is stored at
 plant sites.   If nuclear  power  were to be
 greatly  expanded  in  the  future,  limited
 supplies of uranium worldwide  would rapidly
 force a  shift from today's "once  through"
 nuclear cycles (i.e., the nuclear fuel is only
 used  once) in the  U.S. and Canada to fuel
 cycles involving the reprocessing of spent fuel
 and the recycling of recovered plutonium for
 use as  fuel in  present reactor types, as is
 commonly practiced in Europe and Japan, and
 a  new  generation  of  plutonium  breeder
 reactors. The amount  of fissionable  material
 required would pose a formidable institutional
 challenge  to  the  world  community   to
 safeguard  relatively   large  quantities   of
 plutonium that would circulate in worldwide
 commerce  (Albright  and Feiveson,  1987;
 Ogden and Williams, 1989).

      In the U.S., the Department of Energy
 has  recognized many of  these potential
obstacles. In  its 1987 Energy Security report
 (U.S. DOE, 1987a), the U.S. DOE identified
three basic obstacles that must be overcome
before new orders will  be forthcoming:

                                                     Chapter V: Technical Options
                                FIGURE 5-9
a    12


at    10
               (Avcrag* $/kw


              t-pnt dollart)





              1971-74     1976-76      1977-80     1981-84

                                Yar of Commercial Operation
 Source: U.8. DOE, 187a.

 Policy Options for Stabilizing Global Climate
           Given current reactor designs and
 regulatory processes,  nuclear  power  is not
 economically  competitive  with  alternative
 generation options.

           Public  concerns  about  reactor
 safety make licensing of new plants difficult.

           Currently  unresolved  questions
 about  the viability of  long-term radioactive
 waste  disposal  options  have  become   a
 significant barrier  to expansion of  nuclear

      The U.S.  DOE has initiated efforts  to
 deal with all of these problems.  First, it has
 underway a research program  aimed at the
 development  of improved  reactor designs.
 Program  goals  include new  designs  for
 "enhanced safety, increased simplicity,  and
 improved reliability."  To meet these goals,
 the  new  designs  incorporate  innovative
 concepts of passive safety that hopefully would
 ensure that any equipment or operator failure
 would   cause  the  plant  to  shut  down
 automatically.  A second important attribute
 of the advanced designs is standardization  of
designs, which could reduce cost, shorten the
 permitting process, and improve reliability and
 safety.  Third, the new designs are for smaller,
modular units, which should make them more
compatible with the utility industry's needs for
 smaller capacity addition.  Another design
concept is that the portion  of the plant  that
 is  actually within the  nuclear  containment
vessel  can be minimized and modularized,
 thereby allowing the balance of the plant  to
be built  according to standard construction
specifications.  An example of  this approach
is  Sweden's  ASEA-ATOM's PIUS reactor,
which places the steam generator and primary
pumps outside the containment vessel (U.S.
DOE,  1988a).     More   stringent   safety
standards for nuclear    powerplants  could
then focus on the smaller nuclear component.
Ultimately,  the  nuclear portion  may  be
designed  to be fabricated at the manufacturing
plant and transported in its entirety to the
powerplant   site  for  insertion  into  the
remainder of the plant (Griffith, 1988).
      These principles  are  being  applied to
 several basic reactor types, such as:

          Advanced Light  Water Reactor
 (ALWR).  Light water  reactor technology is
 currently the type most widely in  use in the
 U.S.  The hope is to develop a standardized
 design  incorporating the lessons  of recent

          Modular High Temperature Gas
 Reactor (HTGR).    This  is  an  advanced
 concept that has not been demonstrated yet
 but  is  being  designed to  provide  a next-
 generation nuclear capability that goes further
 toward  meeting  the design criteria  mentioned
 above than the ALWR.

          Advanced Liquid Metal Reactor
 (LMR).   For the longer term, designs  are
 being developed that would  incorporate the
 design  goals stated  above  into a potential
 breeder reactor  option.

      Finally,  on   the   radioactive  waste
 disposal  issue,   DOE   is   evaluating   the
 suitability of Yucca  Mountain, Nevada, as a
 site for long-term deep geologic disposal of
 high-level  wastes, while  also  favoring  the
 construction  of a  Monitored Retrievable
 Storage (MRS)  facility for spent reactor fuel
 (Blowers  et al.,  1990).    Thus,  DOE  is
 attempting to address many of the constraints
 affecting the nuclear power  industry.  It is
 difficult to predict at this point how effective
 these programs  will be.   In  addition,  the
 DOE's  Energy  Security  report  does  not
 mention the weapons proliferation problem
 that   is  also  perceived  as  a  long-term
constraint by many observers.

 Promote  Research   and  Development,  of
Nuclear Fusion Technology

      Nuclear fusion, like nuclear fission, is
an attractive power  generation  technology
from a global wanning perspective  because it
does not generate significant greenhouse gas
emissions.  Fusion power has two key advan-
tages  over fission power: (1)  It uses secure

                                                                Chapter V:  Technical Options
and inexhaustible fuels, in that lithium and
deuterium are obtainable from seawater, and
(2)  it does not  create  large inventories  of
radioactive wastes.

      Fusion reactor technology, however, is
only  in  the early  stages  of  research  and
development; it is not expected to be a viable
technology  before  2025.   The  costs   of
development for this technology are expected
to  be high.  To hasten fusion  development
and to defray the costs that need to be borne
by any single country, additional international
cooperative agreements  concerning research
and development of this technology are likely
to be signed in the next few years.


      One possible option for  reducing the
amount  of greenhouse  gas emissions  from
electricity  is to  improve the  efficiency  of
transmission,  distribution,  and  storage   of
electrical power.

Reduce Energy Losses During Transmission
and Distribution

      Electrical   energy  losses   from
transmission and distribution are normally  in
the 5-10% range in industrialized  countries.
When generation is primarily from fossil fuels,
as in the U.S., programs to reduce efficiency
losses associated with electricity transmission
and distribution may provide one option for
modest   reductions   in   greenhouse  gas
emissions.  In developing countries, however,
it is very likely that significant improvements
are  technically possible.   Many developing
countries experience losses of over 20%, even
30%.       Relatively    inexpensive   and
straightforward technological solutions exist
for   upgrading   utility   transmission   and
distribution systems to  recover  a  major
portion  of these losses.  On the other hand,
in many  countries it is estimated that half  of
the "controllable" losses are due to theft (U.S.
AID, 1988b);  despite  many  reasons  for
reducing these thefts, it is not clear whether
a straightforward solution to these  electricity
thefts exists nor would this mean a significant
reduction in greenhouse gas emissions, except
to the extent demand is reduced as consumers
are charged for the power they use.
      Electric  utility companies  normally
operate  their systems and  interconnections
with  other systems  in  such a  way  as to
minimize  generation  costs,  subject  to  a
number   of  other   constraints.     Thus,
powerplants with the lowest variable operating
(including fuel) costs would be operated more
of the time, and power available from other
utility systems would be purchased when its
cost is lower than the incremental cost of
generating additional power within the system.

      Within this  framework, there may be
some flexibility to shift more of the overall
load to non-fossil or natural-gas-fired capacity
without greatly increasing overall generating
costs.     Although   difficult   to  achieve
institutionally,  such   alternative  dispatching
options may be technically feasible and cost-
effective in the near term. This could include
"wheeling"  power  from region to region to
take  maximum   advantage   of  non-fossil
generating  capacity.   On  its   largest  scale,
this   type    of  strategy  could  result  in
international   electricity  transfers  from
countries with less carbon-intensive generating
capacity  to  countries  with   more  carbon-
intensive available options.   For  example,
expanded Canadian power imports to the U.S.
based on hydroelectric generation would be
one such possibility.

      Superconductors offer no resistance to
electrical flow.   Recently, breakthroughs in
superconductivity research have increased the
prospects   that  this  technology  could   be
applied to power production.  Until recently,
superconductivity could only be achieved in
extremely cold environments (e.g., more than
200C below zero).   The superconductivity
effect can now be achieved at much higher
temperatures,  although they  are still well
below ambient conditions.  In the long term,
superconductivity could significantly improve
the transmission  of  power.   Conventional
transmission systems  lose about  8% of  the
power they conduct;  superconductors  could
greatly reduce, if not eliminate, these losses.
Superconductivity could also be beneficial for
power production.   For  example, several
technologies use electromagnets, including the
MHD  system discussed above.  During  the
power production process, electromagnets are
typically   the  source of  some  lost power.

 Policy Options for Stabilizing Global Climate
 Superconductors could reduce the energy lost
 in generating power by reducing the losses
 associated with  electromagnets.   Also,  as
 discussed below, superconductivity could  be
 useful for energy storage.

 Enhance Storage Technologies

      There are  a variety  of technologies
 currently available or under development for
 energy storage.  Storage systems can perform
 several tasks, including the following:

           Load Leveling, which would allow
 inexpensive baseload electricity to be stored
 during periods of low demand and released
 during periods in which the marginal cost of
 electricity is high (e.g., powerplants could  be
 run during the night and the power stored to
 meet peak  requirements in  the afternoon).
 One  drawback  is  that storage  may allow
 baseload  coal to substitute for natural  gas,
 increasing greenhouse gas emissions, unless
 renewable energy sources are used.

           Spinning Reserve,  in  which the
 energy would be used as backup  in  case  of
 failed generating systems.

           System Regulation, in other words,
 to  balance  a   utility's  constantly-shifting
 generation and load requirements.

      The development of adequate energy
 storage systems could be particularly crucial
 for the competitiveness of many renewable
 energy technologies that can  only  produce
 power when the  resource  is  available,  for
 example,  during daylight hours for solar  or
when the wind is  blowing for wind energy
 systems.   To enhance their competitiveness,
 renewable technologies  could  be used  in
 tandem with storage systems that would allow
 power to be generated whenever available and
 then stored until needed.

      There  are  many different  types  of
 energy storage  systems,  including pumped
 storage,  batteries, thermal, compressed  air,
 and superconducting magnetic energy storage.
 Several  major energy  storage  systems  are
 discussed below.
Pumped Storage

      Pumped  storage  is  a  hydroelectric
power  storage  option  that  has  been  used
recently by the electric utility industry to meet
electricity  requirements during  periods  of
peak demand.   With  this  system water  is
pumped from a lower storage reservoir to an
upper storage reservoir during off-peak hours,
using electricity from a baseload  powerplant
(which  is  frequently coal-fired or nuclear).
During peak demand  hours,  the water  is
released to the  lower reservoir much like it
would be at a typical hydroelectric dam.  This
system  essentially  stores  power from  the
baseload powerplant when it is not needed for
use  during  peak demand periods when the
baseload plant is already committed 100% to
meeting the peak power requirements.

      While  there  are numerous pumped
storage plants in the U.S., their efficiency  is
low  and  additional  siting  is  likely  to  be
difficult if they involve large, above-ground
reservoirs.  When underground reservoirs are
used, the systems are only economical in very
large facilities (e.g., 1000 MW).


      Batteries  are  attractive primarily for
their flexibility; because they are  modular,
plants can be constructed quickly on an as-
needed   basis.     Recent   research  and
development has focused on advanced lead-
acid  batteries and  zinc-chloride batteries.
Lead-acid battery technology has been  used
for decades (e.g., in automobiles), although its
use in utility applications may be limited by
its capital costs.  Due primarily to the lower
cost of the construction materials, the zinc-
chloride battery is  expected to  be  less
expensive than the lead-acid battery  in the
longer  term;  possibly  less  than  S500/kW
compared to $600/kW or higher for lead-acid
batteries (OTA,  1985).   Plans to test both
types of batteries on  a  commercial scale are
currently  being  planned.    Other  battery
technologies  that could be available  in  the
longer  term  include  zinc-bromide, sodium-
sulfur,  iron-chromium,  and  lithium-iron
sulfide batteries.

                                                               Chapter V:  Technical Options
 Compressed Air Storage

      Compressed air energy storage (CAES)
 uses off-peak electricity to store energy in the
 form of compressed air in an underground
 cavern  such as  salt  reservoirs,  hard  rock
 reservoirs, or aquifers.  The compressed air is
 used  in tandem with natural gas or oil in a
 modified  gas turbine where  the  compressed
 air  is  used   in  lieu  of  a  conventional
 compressor in  the turbine  cycle, thereby
 allowing the turbine efficiency to increase up
 to  three  times its  normal efficiency (OTA,
 1985).   CAES  is dependent on geological
 characteristics that can be found in about 3/4
 of the U.S.  and uses technology that is well-
 advanced. However, no CAES facility has yet
 been  built in the U.S.; there  is a facility  that
 has  been operating  since  1978  in  West
 Germany.   There are two sizes proposed for
 CAES plants;   a mini-CAES  (about 50 MW)
 costing about  $392/kW and a   maxi-CAES
 (about  220 MW)  costing about  $515/kW;
 construction lead times are estimated to be 4
 to 8 years (OTA, 1985).

 Superconducting Magnetic Energy Storage

      Superconducting   magnetic   energy
 storage (SMES)  would  function  like more
 conventional storage technologies, but would
 be able to store energy with  an  efficiency of
 approximately  95%  compared to  75%  for
 pumped  storage or 65% for battery storage
 (Schlabach,  1988).   At  this  time  SMES is
 clearly a long-term technology pending further
 improvements  in  basic  superconductivity


      One  concept   for    reducing  CO2
 emissions is the long-term  phaseout of  a
carbon-based economy and the  adoption of
 one utilizing   hydrogen and electricity  as
 complementary energy  currencies.  Hydrogen
would serve as  an "energy carrier"  since
 electricity or some other source of power is
 required to produce it.  Hydrogen is attractive
 for this  role  because  it  is nonpolluting,
 portable, and relatively safe. Hydrogen could
be produced in a number of ways, including
 chemical  processes  beginning with coal  or
 natural gas, and electrolysis using electricity
 from  the full  range of  potential electricity
 production  options.  Of course, production
 chemically  from fossil  fuels or  the use of
 fossil-based  electricity  would  not  provide
 significant long-term reductions in greenhouse
 gas emissions.   However, these technologies
 are currently available and could play a  role
 in a transition  to greater use of hydrogen as
 an energy source (Harvey, 1988).

      One  technology   under  development
 holds some  promise for allowing hydrogen to
 be generated from fossil fuels  without CO2
 emissions. The process, known as hydrocarb,
 produces  hydrogen and carbon black through
 a  process  of  gasification  and  distillation.
 When  coal  is   used   as   the   feedstock,
 approximately  20% of the energy  value  is
 converted into  hydrogen. The carbon black
 produced could be disposed of in mines or
 other disposal facilities.  Biomass can be used
 as the feedstock, although it is a less efficient
 source of hydrogen (Grohse and Steinberg,

      While large-scale hydrogen use would
 have to be considered a long-term option, this
 fuel could begin to make contributions in the
 near term.  Researchers at Princeton Univer-
 sity have suggested that use  of hydrogen  as a
 transportation fuel in urban areas may be its
 first   significant   role   toward  replacing
 traditional fuels (Ogden and Williams, 1988).
 Existing   transport  fuels  are   high-priced
 (allowing  hydrogen to compete more easily),
 and urban air  quality problems are already
 forcing many cities to look for alternatives to
 gasoline and diesel fuel in the transportation
 sector. Ogden and Williams also suggest  that
 recent and  projected improvements in  the
 economics of amorphous silicon photovoltaic
 cells  may make hydrogen  fuel  production
 from solar PV  electricity cost competitive in
 some  areas of the U.S. before the end of this

      Another  attractive feature of hydrogen
 that   would be   helpful  in  a  long-term
 transition away from fossil fuels is that it can
 substitute relatively easily for natural gas in
 many applications.  For example,  natural gas
space heating could be replaced by hydrogen
over  the  long  term; natural gas pipelines
could be  used  to  transport hydrogen  and
 hydrogen  is the basic  fuel for fuel cells.
Storage of hydrogen could occur in salt mines,

Policy Options for Stabilizing Global Climate
aquifers, and depleted oil and gas fields for       hydrogen accomplished by the electrolysis of
large needs and as liquid hydrogen and metal       water.
hydrides for small applications.
                                                        Conversion  efficiencies in  producing
      In a  long-term hydrogen economy, non-       hydrogen from renewable energy exceed 80%
fossil energy could be provided by a variety of       and efficiencies for conversion back to energy
renewable  sources,   with   conversion   to       in fuel cells range from 58-70%.

                                                             Chapter V:  Technical Options
                                PART THREE:  INDUSTRY
      Figure  5-10  illustrates  the  overall
current  contribution of industrial  processes
(excluding energy) to the greenhouse wanning
problem. By far the largest component is the
production  and  ultimate  release to  the
atmosphere  of chlorofluorocarbons (CFCs),
batons, and  chlorocarbons.  Other  industrial
processes are  relatively minor, but growing,
contributors: carbon dioxide (COj)  is emitted
from cement manufacture and methane (CH4)
is  produced by solid  waste landfills.   In
addition,  industrial  process  emissions  of
carbon   monoxide   (CO)  contribute   to
atmospheric chemistry, which indirectly affects
the concentration of tropospheric ozone (O3)
and CH4.


      As a result of the Montreal Protocol
and  the June 1990 London  Amendments
(discussed in CHAPTER vni), emissions of
the most important CFCs will be capped in
1989, reduced  to half of 1986 levels by 1995,
and  phased  out by 2000.   Halons will  be
frozen at 1986 levels beginning in  1992 and
phased out in 2000.   In addition to the CFC
and halon phaseouts, phaseout schedules for
carbon tetrachloride and methyl chloroform
were set, and a non-binding declaration was
made   regarding    the   phaseout    of
hydrochlorofluorocarbon (HCFC) production.

      A  series  of  recent  detailed  reports
prepared under Article 6 of the  Protocol by
international experts examined the available
and emerging options for reducing CFCs, as
well as halons,  methyl chloroform, and carbon
tetrachloride, which are of potential concern
for  both  stratospheric O3 depletion and
greenhouse warming (UNEP, 1989).  These
reports  asserted that  technical options are
currently available for virtually eliminating all
CFCs, methyl  chloroform (reductions of 90-
95%), carbon  tetrachloride,   and  halons
(minority  view stated  only  50%  reduction
      As  a  reflection of  this technological
progress, many industrial groups (e.g., rigid
foam electronics, auto manufacturers) have
announced goals of eliminating their use of
CFCs in the mid-1990s  or sometime before
the end of the century.

      Some  of  the substitute  compounds
affect greenhouse warming but  to  a much
smaller   degree  than   do  the   controlled
substances.    Most  of  the  unregulated
compounds  have much  shorter atmospheric
lifetimes, which decreases their impact on the
greenhouse problem.

      Use and emissions of CFCs could be
reduced by three possible mechanisms:

           Chemical substitution - switching
from production processes in which CFCs are
used to those in which  other chemicals are
used; for example, using FC-134a or blends of
other non-fully halogenated HCFCs instead of
CFC-12 in mobile air conditioning.

           Engineering controls - in the near
term, switching  to  production  technologies
that use fewer CFCs (or substitutes)  per unit
of output, such as recycling equipment that
collects  and  recycles CFC  emissions during
the production of electronics.

           Product substitution - switching
from CFC-using products to other products;
for example, replacing CFC-based foam egg
cartons with paper-based egg cartons.

      This chapter surveys existing and future
product substitutes, engineering controls, and
chemical substitutes that can reduce use and
emissions  of CFCs and  halons.    The
information presented is based on a detailed
series of industry studies  performed by the
U.S. Environmental Protection Agency (U.S.
EPA) for use in its Regulatory Impact Analysis
for stratospheric ozone protection and from a
technical assessment performed by the Parties

Policy Options for Stabilizing Global Climate
                            FIGURE 5-10
                     TO GLOBAL WARMING
        Energy Use
      and Production
CFC-11 (4%)
                                                     Other CFCs (3%;
                                                 Land Use

                                                              Chapter V:  Technical Options
to the Protocol (U.S.  EPA,  1987).  Unless
otherwise noted, information in this section is
drawn from U.S. EPA (1988b).

Expand the Use of Chemical Substitutes

      Several chemical substitutes that have
physical properties (e.g., boiling point) similar
to those  of CFCs  either do  not contain
chlorine or have short atmospheric lifetimes
that   reduce  their  potential   to  deplete
stratospheric O3.

      FC-134a,   HFC-152a   and   blends
including   non-fully  halogenated  HCFCs
(HCFC-22, HCFC-124, HFC-152a) appear to
be the most promising chemical substitutes
for   refrigeration   and   air   conditioning
applications, including commercial chillers and
mobile  air conditioning,  and  along  with
HCFC-141b and HCFC-142b appear  to be
likely alternatives to CFC-11 and CFC-12 in
production   of  polystyrene   sheet   and
polystyrene  boardstock.    Several  major
chemical producers have announced plans to
build commercial-scale  production  facilities
for  FC-134a   and  HCFC-141b.       An
international   consortium   of   chemical
producers  has  been  formed to undertake
toxicity testing of FC-134a and other chemical

      HCFC-141b    and   HCFC-123    are
expected to become commercially available in
the early  1990s and could replace CFC-11
currently   being  used  in  manufacturing
slabstock flexible polyurethane foam and rigid
polyurethane foam.  In blends with HCFC-22,
HCFC-142b appears to  be an option  for
replacing the remaining "essential" CFC use in

      HCFC-22 is currently used in residential
air  conditioners  and  might  be used  in
commercial  chillers.  It could substitute  for
CFC-11 and CFC-12 as a leak-testing agent in
several refrigeration applications. Mixtures of
HCFC-22 and other compounds could be used
in mobile air conditioners.

      HCFC-22 has already been adopted as
a substitute for CFC-blown polystyrene sheet
products.   It was recently approved by the
Food  and  Drug  Administration  as   an
alternative  blowing  agent for  use  in  food
packaging.  The Foodservice and Packaging
Institute,   in   concert   with   several
environmental  groups,  recently  completed
implementation of an industry-wide program
to eliminate within one year the use of CFC-
11 and CFC-12 in food service packaging by
substituting HCFC-22.

      A   major  manufacturer  of extruded
polystyrene  boardstock  recently announced
that it will substitute  HCFC-22  and other
partially   halogenated    CFCs   in    its
manufacturing processes beginning in  1989.

      Blends of HCFC-22 with dimethyl ether
and HCFC-142b can be used to replace the
remaining  "essential"  CFC use in aerosols.
Hydrocarbons have largely replaced CFCs as
aerosol  propellants  in  the United  States.
Other nations can reduce their use of CFCs
in  aerosol  propellants   by  reformulating
aerosol products.

      Ethytene  oxide   (EO)  is  currently
blended   with  CFC-12  for  use  in  the
sterilization  of  medical   equipment   and
instruments. Reductions in CFC-12 use could
be achieved by using pure  EO, a blend of
CO^/EO,  radiation, or the  use of HCFC or
HFC  substitutes.

      Aqueous cleanings and terpene-based
solvents can be used instead of CFC-113 to
clean  electronic components.   One major
manufacturer expects to replace one-third of
all its CFC use in electronics manufacturing
with  terpene-based   solvents.     Aqueous
cleaning  can also reduce  CFC-113  use in
many  applications for  cleaning  electronic

Employ Engineering Controls

      Recovery and recycling can reduce CFC
emissions from several applications. Recovery
and   recycling  during  servicing  of  air
conditioning  and  refrigeration  equipment,
such  as commercial chillers and mobile air
conditioning   units,   can   achieve    large
reductions in CFC emissions.  An industry-
wide voluntary purity standard for recycling
CFC-12 from car air conditioners was recently
adopted.    U.S.  EPA  has  recently  been
petitioned  by an  industry  trade group  to
establish  a national recycling program.

 Policy Options for Stabilizing Global Climate
      Carbon  adsorption  units  could  be
installed  to  capture CFC  emissions  during
manufacture of slabstock flexible polyurethane
foam.   Simple  housekeeping  improvements
and process  modifications such as automatic
hoists   and  covers,  carbon   adsorption,
reclamation, and  recycling can  substantially
reduce  CFC-113  emissions during solvent
cleaning.  Furthermore, many electronics firms
are   finding   that   cleaning    during  the
manufacturing process can  be  substantially
reduced and in some cases eliminated without
sacrificing product quality or reliability.

      Alternative  leak-testing  agents  can
reduce  halon emissions  during discharge
testing  of  total  flooding  fire-extinguishing

      Improved system design  can  reduce
CFC emissions.   Attractive  techniques  in
mobile   air   conditioning   include  design
improvements, such as  the  use of  more
refrigerant-tight hose materials, shorter hoses,
and improved compressor seals and fittings.

      Alternative  processes  can be used to
produce final products without using  CFCs.
For example, the CFC-blown  flexible foam
process can be modified to eliminate  use of
CFC-11, but the foam will be  slightly denser
as a result.  Nearly all uses of molded flexible
foam could be  converted  to water-blown

      Training  could  reduce  unnecessary
discharges of CFCs during air conditioning
servicing.      Adoption   of   new  training
procedures, such as  use of simulators,  could
reduce  halon  emissions  during  military
training exercises.

Use Substitutes for CFC-Produced Materials

      Research efforts are exploring ways to
replace  the use of CFC-blown insulation in
refrigerator walls by insulating vacuum panels.
A prototype vacuum panel refrigerator, which
could achieve sizeable  gains  in  insulating
properties, is currently being built.

      CFC-blown   slabstock   flexible
polyurethane foams can be replaced by other
products.   Fiberfill materials, cotton batting,
latex foams,  and  built-up cushioning  that
contains springs may be suitable substitutes,
but  they are more expensive and  lack  the
durability of flexible polyurethane.

      Some product substitutes are  available
for rigid polyurethane foam products.  Many
alternative products are currently available for
use as sheathing or roof insulating materials.
Expanded   polystyrene   foam  headboard,
fiberglass,   fiberboard,  and   gypsum,   for
example,  could   be   used   instead   of
polyurethane foam, as they were 30 years ago
when  polyurethane  foams  were  not   yet
manufactured.    In  some  cases, wall  and
roofing  insulation  can be made  thicker to
achieve  the  same  insulating  capacity as at
present,  but the  use of foam blown with
chemical substances  is  likely  to  continue
where it offers the  advantages of  reduced
labor costs and  smaller bulk and  meets a
building's energy efficiency requirements.

      Some product substitutes are  available
for poured or sprayed foam, depending on the
specific  use.    In  applications   such  as
packaging  and  flotation, product  substitutes
are numerous.  Combinations of plastic and
non-plastic materials  can provide  equivalent
degrees of cushioning, shock resistance,  and
water resistance.   At present,  however,  no
other insulation materials have the equivalent
ability to be poured or sprayed, nor can other
materials of the  same thickness insulate as
well as rigid polyurethane foams.

      Polystyrene sheet competes with many
other disposable packaging and single service
products, including paper, cardboard, solid
plastic, metal foils, and laminar composites of
foil,  plastic film  and paper.   Any  of these
substitutes could eliminate CFC use in food
packaging applications.

      Current and possible future alternatives
to foam  boardstock as insulation include a
host  of  product   substitutes,  including
fiberglass board, perlite, expanded polystyrene,
fiberboard, cellular  glass, insulating concrete,
rock wool, vermiculite, gypsum, plywood, foil-
faced laminated board, and insulating brick.
Greater thicknesses of these alternatives may
be required to provide equal energy efficiency.

      Pre-sterilized, disposable products are
one  possible  alternative that  will enable

                                                              Chapter V:  Technical Options
 hospitals to reduce their dependence on CFC-
 12 for sterilization.

      Pump sprays and roll-ons are product
 substitutes that can replace CFC-propelled
 personal care aerosols.


      Over 1.6 million tons of municipal solid
 waste is generated on the  planet each day
 (adapted from Bingemer and Crutzen, 1987).
 Approximately 80% of this volume is disposed
 of  on  land  in  landfills  or  open  dumps.
 Anaerobic decomposition of municipal  and
 industrial solid wastes  in  landfills results in
 the generation of 30-70 Tg of CH4 each year
 (Bingemer and Crutzen, 1987).

      The amount of gas produced by a given
 site is   a function of  the  amount  and
 composition of landfilled wastes.  The rate of
 gas production is a function of the age of
 material in the landfill, oxygen and moisture
 concentrations, pH, and  the  presence  of
 nutrients.  Methane production is  highest
 when the organic content of the refuse is
 high, the wastes are relatively new, and there
 is  adequate   moisture   available.    The
 decomposition  process only occurs  in an
 environment  that  is oxygen-free  and  has  a
 moderate pH.  There is a one- to two-year lag
 period between landfilling of wastes and the
 beginning  of  gas  generation.    Methane
 production occurs once all available oxygen
 has been consumed and the  environment
becomes anaerobic. Food and garden wastes
generally decompose over a 1- to 5-year time
frame, while paper wastes  could require 5 to
20  years  to   decompose  (Bingemer and
Crutzen, 1987). These  factors and the active
life of a landfill affect  the duration of CH4
production.  It can take anywhere  from  10
years  to  over  100 years  for a  landfill  to
produce significant amounts  of CH4 (Wilkey
et al., 1982).

     Estimates  place  the  rate  of  CH4
production between 1000 and 7000 cubic feet
per ton  (31-218  m3/mt) of  municipal solid
waste deposited (Wilkey et  al., 1982).  The
United  States generated approximately  148
million tons of municipal solid waste in 1988
(U.S.  EPA, 1988c), which,  using the rates
above, would produce between 2.9 and 20.7
 teragrams  (Tg) of  CH4.    Using a  CH4
 production rate suggested by Bingemer and
 Crutzen  (1987), the same  amount of solid
 waste would  produce an estimated 7  Tg of

 Increase Methane Recovery

      Landfill   gas,   which   is   typically
 comprised  of approximately  50%  methane,
 50%  carbon  dioxide,  and   some   trace
 constituents of volatile organic compounds,
 can be recovered and used as fuel. The gas is
 a  medium-British  thermal unit (Btu)  fuel
 (approximately 500 Btu/standard cubic foot),
 which can be used directly in boilers or for
 space heating, in gas  turbines to generate
 electricity, or can be processed to high-Btu
 pipeline quality gas (Zimmerman et al., 1983).
 The gas is purified prior to use:  for medium
 Btu-gas,  processing  requires  removal  of
 particulates and water, for high-Btu gas, CO2
 and  most trace components must also be

      Landfill   gas   can   present    an
 environmental  hazard  because  of its  high
 combustibility and ability to migrate through
 soil Methane is flammable in concentrations
 between  5 and 15% by volume in air at
 ordinary  temperatures.   Methane can  rise
 vertically or can migrate horizontally out of a
 landfill.   Methane  migrates  easily through
 porous soils,  drainage corridors and  other
 open   areas,   often  travelling  significant
 distances.   Migrating CH4  gas  has  caused
 explosions  and flash  fires,  resulting  in
 property  damage and death.  Malodors and
vegetative damage have also been attributed
 to migrating landfill gas.

      Methane  control  systems,  required
 under certain circumstances by the  Resource
 Conservation and Recovery Act (RCRA), can
 help to mitigate malodors, gas  hazards, and
vegetative  stress.    RCRA  requires   that
 concentrations not exceed a lower  explosive
 limit of 5% methane (10% landfill gas) at the
 landfill   boundary.       Controls   include
impermeable    barriers,  induced   exhaust
systems, evacuating  and  venting or  flaring
 (burning) of the gas, and recovery for use as
an energy source.   Of these controls, only
flaring and recovery of the  gas reduce the
amount of CH4 emitted into the atmosphere.

 Policy Options for Stabilizing Global Climate
      Of the  6,584 municipal  solid  waste
landfills  in  operation  in  the  U.S.,  1,539
(16.6%) employ some methane recovery  or
mitigation system such as venting or flaring.
Only  123 of  these sites  (1.9%  of  total)
recover methane for energy use (U.S.  EPA,
1988c).   New  regulations proposed by U.S.
EPA under the Clean Air Act would require
collection and  control of landfill gas at both
new and existing landfills. These regulations
have the  potential to significantly reduce the
emission  of  CH4 from landfills in  the U.S.
(U.S. EPA, 1988a).

      Estimates  place  the quantity of gas
generated by sanitary landfills  in the U.S.  at
1%  of the nation's  annual  energy  needs,  or
approximately  5%  of current  natural gas
utilization (Escor,  1982).     The   recovery
efficiency of  methane from landfills can  range
between 60  and 90% of the  gas produced,
depending upon the quality and design of the
gas recovery  system,  spacing of recovery  wells,
and  landfill covering.

      The economic viability of CH4 recovery
at a landfill  depends upon the landfill's size,
location, proximity to potential users, current
competing  energy  costs,  and  regulations
governing the  site.   The  capital  costs  of
recovery  projects   are  about  $1000/kW.
Suggested minimum requirements for recovery
include  an  in-place  refuse  tonnage  of  2
million tons, a disposal rate of 150  tons per
day, an average refuse depth of 40 feet (ft), a
surface area  of 40  acres, and two  years  of
remaining active fill  life (EMCON Associates
and   Gas  Recovery Systems,  Inc., 1981).
Probably fewer  than  1,000 landfills in the U.S.
are of sufficient  size to meet  these criteria.
Sanitary landfills in developed countries hold
the best potential for economical recovery  of
methane.  Currently, there is  little potential
for CH4  recovery from  open dumps in the
developing world; if the practice of sanitary
landfilling is adopted, the prospect of CH4
recovery will  improve.

      Over 408 (about 5%) of the municipal
solid waste landfills in the U.S. receive  more
than 500  tons  of municipal solid waste per
day  (U.S. EPA,  1988c).  Collectively,  these
landfills  receive  over  75 million  tons  of
municipal solid waste each year (over 50%  of
the  total  generated in the U.S.).   If  CH4
 recovery  were  implemented  only  on  the
 largest  5%  of  landfills  in  the  U.S.,  an
 estimated  2.2-3.3  Tg   of CH4  could  be

      Constraints on the economic feasibility
 of recovery projects  have  hampered further
 adoption  of this technology.  Under current
 market   conditions,   projects   are   not
 economically viable unless  there is a suitable
 gas user within two to three miles of the site,
 or the electricity generation can be tied into
 an electricity  grid.    Current  regulations
 governing  many sites  also  discourage  the
 recovery of methane.  Some state regulations
 subject   resource   recovery   projects   to
 unlimited   liability   for    any   potential
 contamination  problems at  a landfill -  a
 significant disincentive to recovery.

      Various  techniques  can  be  used  to
 enhance gas production and yield  from  a
 landfill,  including  controlled  addition  of
 moisture and nutrients (usually in the form of
 landfill leachate or landfill gas  condensate),
 bacterial  seeding, and  pH  control.   The
 addition of leachate and condensate is only
 permitted at landfills where there is a liner.
 Further research in these areas could increase
 the economic viability of CH4 recovery.

 Employ Recycling and Resource Recovery

      Recycling and resource recovery hold
 the   potential   to   affect   emissions   of
 greenhouse   gases    through   both   waste
 reduction   and  reducing  energy  demand.
 Source separation and waste-stream reduction
 have many benefits for  the municipality and
 the environment.  A reduced waste stream
 means less refuse going to the  landfill, an
 increasingly limited resource.  In addition, the
 energy  savings  from   recycling  can  be
 significant as discussed in PART ONE.

      Separating organics  from  the  waste
stream, such as paper and food,  lawn, and
 garden  wastes, can  achieve  many benefits,
 including   reduced   production   of  CH4.
 Reducing  organics in the  landfill results in
less  CH4  production  from   that  source.
 Organics that are separated  and composted do
not produce CH4 if the composting includes
aeration to keep the process aerobic

                                                              Chapter V:  Technical Options
      Within the industrialized countries of
the OECD, garden and park wastes make up
about  12-18% of the municipal solid waste
stream and account for about 10-14% of its
organic content, while food wastes make up
between  20  and 50%  of the stream  and
account for over 20% of the organic content.
Within developing countries, garden and park
wastes are insignificant, while food wastes
account for between 40 and 80% of the waste
stream and over 70% of the organic content
(adapted from Bingemer and Crutzen, 1987).
Given these high proportions of food, garden,
and  park wastes, the potential for reducing
CH4 production through aerobic composting
could be significant.

Reduce Demand for Cement

      Carbon dioxide emissions from cement
production originate from two sources:  1) as
a chemical by-product of the manufacturing
process, and 2) as a by-product of fossil-fuel
combustion used for kiln  firing  and plant
electricity.  Energy consumption emissions are
discussed  in the  end-use section of  this
chapter.  The CO2 emissions that result as a
chemical by-product  occur  during the firing
process, when the raw materials (cement rock,
limestone,  clay,  and  shale) are exposed to
progressively higher  temperatures in a kiln.
It  is during calcination,   which  occurs at
approximately  900  to  1000C,   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
as a result of this chemical process  (Rotty,
1987).  For comparison, approximately 0.165
Tg C per million tons of  cement produced
result from energy consumption.

      Although cement manufacture currently
accounts   for  only   a  small  percentage
(approximately 2%, not including  the energy
consumption   emissions)   of  the  global
anthropogenic  source  of  CO2,  emissions
associated with this industry  have increased
rapidly  over the last few decades and can be
expected to continue to grow in the future as
demand for cement grows. Between 1950 and
1985, cement production and associated CO2
emissions grew at an average annual rate of
6%.  Regional production growth rates have
varied during this period due  to economic
fluctuation  in  the   construction   industry
(cement's primary  market)  and shifts  in
international   competition   between   the
cement-producing  countries.    Today,  the
USSR, China, Japan, and the U.S. account for
43% of the world's cement production.
      Since CO2 is an  inherent product of
cement manufacture, the only way to slow the
rate of growth in emissions is to  limit the
amount of cement required, that is, reduce
demand through more efficient use of cement
and/or  through  substitution  with  other
materials (e.g., steel and glass). Increases in
efficiency  can  be  achieved  through  both
material  and fabrication improvements, for
example, through the use of pre-stressed and
steel-reinforced   concrete   products.
Substitution of cement with other  materials
such as steel, glass, or wood also would slow
the  growth  in  cement  demand,  although
substitution  with  such  energy-intensive
materials as steel may result in greater net
CO2 emissions.  In fact, in some applications
cement products have been used in lieu of
other  materials, such as  steel  Improved
efficiency has already occurred in much of the
developed world due to improved engineering
design in construction.    Also, most basic
infrastructure has been built in the developed
world, so demand may slow somewhat in the
future.  This is not likely to be the case in
the developing world, however, where demand
will probably continue to grow more rapidly
than GNP,  particularly  since  cement  is an
inexpensive building material.

Policy Options for Stabilizing Global Climate
                                 PART FOUR: FORESTRY
      Forests, which store 20-100 times more
carbon per unit area than croplands, play a
critical role  in  the  terrestrial carbon cycle
(Houghton  et al.,  1988b).   Active  forest
management to maintain  high  amounts of
standing   biomass,   to   reduce   tropical
deforestation, and to  aggressively  reforest
surplus agricultural or degraded  lands, offers
significant potential  for slowing  atmospheric
buildup  of  carbon  dioxide  (CO2),  carbon
monoxide (CO), nitrous  oxide  (N2O),  and
methane  (CH4).    Forestry-related  policy
responses to climate  change  are particularly
important because they (1)  are capable of
partially  offsetting current fluxes of CO2, (2)
require modest costs relative  to non-forestry-
related   options,  (3)  do  not  require  the
development  and   dissemination  of  new
technologies, and  (4) offer a wide range of
ancillary   social  benefits   (e.g.,  increase
fuelwood supply, reduce soil erosion, improve
preserve  wildlife habitat) significant enough to
justify forestry  options even without  the
specter  of global warming  (Andrasko  and
Tirpak,   1989;  USDA/EPA,  1989).   For  a
general overview of climate change and forest
ecosystems  and  management  (effects   of
climate   change,  adaptation  options,   and
mitigation   opportunities),   see  Andrasko
(1990a, 1990b).

      Most   research   on  greenhouse  gas
emissions from natural and disturbed forest
ecosystems,   and  on  the implications   of
accelerating  rates of tropical deforestation for
global change, has focused on emissions of
CO2 and CO and large-magnitude fluxes in
the carbon  cycle from  burning  and gradual
decay of biomass associated with clearing of
tropical  forests.  Since less  work has been
done  on other  gases,  this  section   will
concentrate  on the carbon cycle.


      The ecological diversity and geographic
range of vegetation  communities  determine
the degree of carbon sequestering by  forests
and  the rate of carbon  emissions  due  to
disturbances of forests.  Forests cover about
one-third  of the Earth's  land, or 4 billion
hectares (ha),8  of which  about  42%  is  in
developed countries  (mostly temperate) and
58%  is  in  developing  countries  (mostly
tropical)  (FAO/WRI/World   Bank/UNEP,
1987).  The  carbon content of tropical moist
forests (with closed canopies, like Amazonian
rain  forest)  averages 155-160 tons of carbon
per hectare  (t C/ha) of standing  biomass  in
Latin America and Asia and ranges up to 187
t C/ha in Africa.9 The carbon content of dry
tropical forests  (closed or open  forests on
relatively  dry soils  with  grassy  or herbal
ground cover) averages 27 t C/ha in Latin
America and Asia and 63 t  C/ha in Africa
(Houghton et al., 1988).

      Recent estimates of boreal (northern,
largely coniferous) forest in North America,
however,  suggest  that all  of our  carbon
content and biomass  estimates  commonly
utilized in calculations  of global carbon cycle
fluxes may be seriously flawed.  Botkin and
Simpson  (1990)    recently    used   more
statistically  reliable  methods  to estimate
North American boreal forest biomass carbon
content at about 9.7 billion  metric  tons  -
only one-quarter of previous estimates of 13.8
to 40 billion tons of carbon used routinely  to
balance the global  carbon  budget.

      Anthropogenic  alterations   of  forest
ecosystems  now account  for  emissions  of
atmospheric CO2 equal to about  10-50%  of
total  emissions  from  combustion of fossil
fuels, as carbon stored in vegetation and soils
is released   by  clearing, fire,   or  decay
(Houghton,   1988a).    Releases   of gases
continue for a  long time following  forest
clearing; emissions of CO2, N2O, and CH4  in
Amazonia decline to one-third or  one-half  of
their  initial  rate  after 10  days,  but  then
appear to continue for a year at  a constant
rate   (Goreau  and de Mello,  1988).  One
estimate of total CO2 emissions  from burning
the entire Amazonia forest ecosystem suggests
that  only  15%  of the  total carbon emitted

                                                               Chapter V:  Technical Options
would be  contained  in the initial  biomass
burning; fully 85% would be  released over
years or decades from soils (Fearnside, 1985).

      Recent estimates of annual net carbon
flux from deforestation range from 0.4 to 2.6
petagrams  (Pg)  C/yr  for 1980,10  primarily
due  to  land-use  change  in  the  tropics
(Detwiler and Hall,  1988b; Houghton et al.,
1987). Brazil, Indonesia, and Colombia were
the largest of the top  ten producers of net
carbon release from  tropical deforestation in
1980 (see Table 5-13), although new estimates
of forest loss rates for the 1980s move Burma
into  the  top  three  (WRI  et al.,  1990;
Houghton, 1989,  in Myers, 1989).  These ten
combined account for about 70% of the CO2
emitted  due   to  changes   in   land  use
(Houghton et al., 1987; WRI et al., 1990).

      Very  recent  estimates  of forest loss
rates, some not  yet fully reviewed  by the
forestry community and controversial, suggest
far higher rates of deforestation and, hence,
carbon emissions. Myers (1989) has estimated
that the rate of conversion of tropical closed
forests has risen 82%  since the 1981 FAO
estimate of 7.2 million ha/yr of closed forests,
to 13.9 million hatyr for 1989.  This produces
an  estimate (by Houghton, in Myers, 1989)
for  current   emissions  of  carbon   from
deforestation of 2.0-2.8 Pg, with a mean of 2.4
Pg,  although   this  has  not  been  widely
reviewed by experts.  Similarly, a tally of new
country-level estimates for forest loss by WRI
et al.  (1990; see below) suggests  that the
standard FAO  1980 deforestation figure  of
11.4 million ha may be  revised upward  by
other new studies to about 20.4 million ha for

      Uncertainties still exist in determining
carbon storage in and emissions from changes
in forest cover associated with various land
uses.  For example, emissions of greenhouse
gases from cropping practices in swidden (i.e.,
shifting, or slash-and-burn cycle) agriculture
versus  sedentary (permanent) agriculture,
including agroforestry systems, have not been
quantified.   Neither  do we  have  reliable
estimates  of biomass,  carbon  content, and
trace gas emissions in a truly representative
sample  of natural  and  disturbed  tropical
forests and carbon fluxes in disturbed tropical
soils  (which may account for one-third  of
carbon flux from deforestation) (Houghton et
al., 1988).  Permanent conversion of natural
forest to pasture or cropland results in net
loss  of  carbon  stored  both  in standing
biomass  and  soils;  the  amount  lost  is
dependent  on the biomass productivity  and
soil carbon storage rates of the former versus
the new land use.  Cyclical harvest of forest
for timber  or fuelwood  similarly  releases
carbon from  slash (nonmarketable tree parts:
branches,  leaves) that  is burned  or left to
decay on-site, and  from timber milled into
non-durable  wood and  paper products (and
wastes like sawdust and scrap) that are soon
burned or discarded.

      Forests  in  temperate  regions  are
essentially now in balance in terms of carbon
cycling, with  annual incremental growth rates
roughly equal to  rates of timber harvest  and
deforestation for urban growth and other land
uses.  Consequently, temperate forests do not
currently  contribute  significantly  to  the
increase in atmospheric CO2 (Houghton et
al., 1987).  However, they now cover much
smaller areas than  in  the  past, and  have
historically  contributed heavily  to  global
carbon emissions, as forests  were cleared in
Europe,  North  America,  and Russia  for
agricultural production.

      Widespread reforestation programs that
could expand temperate forests into former
forest ranges  and reduce net carbon emissions
are discussed below. Trees newly  planted in
urban areas  would  alleviate  the greenhouse
problem in two ways:  (1) by reducing the
need   for   air   conditioning  and   hence
electricity, and (2) by increasing the uptake of
carbon in  biomass  growth  (Akbari  et  al.,


      Each   year,  at  least  11.4  million
hectares, and perhaps as much as 20.4 million
hectares (see below), of forest are cleared in
the tropics, an area larger than Austria or
Tennessee  (Lanry,  1982;  TIED  and  WRI,
1987).  The rate of deforestation - combined
with the escalating  growth  in  demand for
forest  products  -  is  such  that while  33
tropical countries are currently net exporters
of wood products, this number may decline to
fewer than  10 by the  end  of the  century

Policy Options for Stabilizing Global Climate
                                       TABLE 5-13

                     Estimates of Release of Carbon to Atmosphere from
                              Top 10 Deforestation Countries,
                                       1980 and 1989

                                  (million tons of carbon)
                       1980                                        1989
Ivory Coast
          Note:  Estimates based on area deforested and biomass estimates, and
          reflect limits in data available.

          Sources: For 1980:  Houghton et al., 1987; for 1989:  Houghton, 1989,
          in Myers, 1989.

                                                                Chapter V:  Technical Options
(Repetto, 1988).  If this trend could be halted
and reversed, tropical forests could serve as a
vast carbon sink, reducing global CO2 levels.

      Figure 5-11 illustrates the movement of
tropical forest lands among different stages of
the deforestation cycle (an approach used by
several  researchers, e.g.,  Houghton  et  al.,
1985;  Lugo,  1988).      The  figure  also
summarizes the  reductions  or increases  in
forestland conversions that could shift tropical
forests from net sources of greenhouse gases
to net sinks using the range  of technologies
(i.e.,   forest   management   and   land-use
practices)  and policies  identified  below  as
potentially   available   response   options.
Deforestation   pressures   and    their
socioeconomic and ecological consequences
are complex, however, and greatly complicate
the  task   of  devising   technical   control

      The  underlying causes of deforestation
vary widely by ecosystem and region, and are
often  complex, involving the  interplay  of
historical, biological, economic, and political
factors at  both macro  (national and trans-
national) and micro (household and village)
levels.  A recent  international conference on
the state  of  the  world's  tropical  forests
concluded that

      the causes of  deforestation are
      well    known.    They    include
     population pressure for agricultural
      land,  the demand for  industrial
      timber production  and export, and
      inappropriate government policies
      regarding land  tenure,   economic
      incentives, forest  settlement, and
      other population issues (Bellagio,

      The   predominant    causes    of
deforestation  vary  by  region.   In   tropical
Africa and  in South and Southeast Asia, rapid
population growth appears to be the critical
factor affecting deforestation.  The majority of
the population practices agriculture, and most
of the increases  in agricultural production
necessary to sustain  high birth rates have
come  from  increases  in  the area  under
cultivation  through  deforestation.    Seventy
percent of Africa's deforestation stems from
swidden  (shifting)  agriculture.    Logging
activities, both commercial and individual, in
Malaysia,  Indonesia,  and  the  Philippines
provide access to partially cleared forest lands
that facilitates further clearing of forest for
agriculture (Houghton, 1988a).

      Rural populations rely on wood as the
major  source of energy, another important
cause of deforestation.   More than a billion
people  are  currently affected   globally by
fuelwood shortages. The fuelwood  deficit in
arid and  semi-arid regions of the  world in
1980 affected 29.3 million people, and totaled
13.1 million cubic meters (m3) of wood.  This
fuelwood  gap  between  consumption  and
supply is anticipated to grow to 130% for the
Sahelian  countries  overall  by  2000,   with
single-country forecasts as high as 620% for
Niger (Anderson and Fishwick, 1984).

      One  of  the critical first  steps  in
devising ways to slow tropical deforestation is
for national  and international development
assistance agencies to support local people in
introducing sustainable  forest management
and reforestation techniques that provide for
basic  needs  -  fuelwood,  food, fiber, and
fodder  --  for growing  populations without
mining  primary forest.

      The  Amazon  region  in  Brazil  is
experiencing one  of the  highest  rates of
tropical deforestation in the world (Setzer and
Pereira,   1988;   IIED   and   WRI,   1987;
Fearnside,  1987).     As  a  consequence,
Amazonia is  emitting greenhouse  gases  at
rates  and  quantities  high enough  to affect
global  CO2 and climate  cycles.  Salati  et al.
(1989) estimate that the Amazon region has
already emitted from 3.5 to 12 Pg  C to the
atmosphere - totalling  2-7% of the  total
release  of  CO2 to  the  atmosphere  from
deforestation and biomass burning up to 1980
(see Table 5-14).  Current  annual emissions
from Amazonia alone are estimated at 0.24 to
1.6 Pg C, or 4-25% of global CO2 emissions
from all sources, assuming 7 Pg C per year
from all sources.

      Centralized  government  policies  that
undervalue standing forest and  provide tax
and other fiscal incentives for conversion to
crop  and  pasture  lands  contribute  to
increasing  deforestation  rates  in   Brazil
(Binswanger, 1987; Repetto and Gillis, 1988).

 Policy Options for Stabilizing Global Climate

                                      FIGURE 5-11


                                      (Millions of Hectares)

    * Decrease forost loss

    to development

    * Substitute sustainable

     Improve efficiency

    of blomass fuels

    * Decrease production

    of disposable wood


* Plant plantations

* Reforest degraded

forest lands

* Increase harvest


* Increase forest


* Reforest degraded


* Substitute sustainable

                                                                    * Plant plantations

                                                                    * Support agroforestry

                                                                    * Substitute sustainable


                                                                    * Reforest degraded

Figure 5-11.  Pathways of conversion of tropical closed and open forest lands, and where technical
response options discussed here would intervene to slow conversion.  Data were derived from FAO
(1981) and from Lanly (1982) and are expressed in millions of hectares. Numbers inside boxes
represent total area in category in 1980. Numbers on lines tipped with arrowheads represent annual
rates  of conversion.   Data include both closed forests  (complete canopy) and open  forests
(incomplete canopy and grass herbaceous layer). Source: Pathway data modified from Lugo, 1988.
Houghton et al. (1985) offer similar conversion data.

                                                 Chapter V:  Technical Options
                           TABLE 5-14

Recent Estimate of CO2 Emissions from Biomass Burning in Amazonia
                                 Range of CO2 Emissions
   Estimate of Carbon       	(x 1015 g carbon')
Biomass Available3
(tons/ha = 108 g/km2)
Lower (140)
Upper (200)
Cumulative Totalb
3.5 to 8.4
5.0 to 12.0
Total in 1988C
0.24 to 1.1
0.34 to 1.6
   NOTE: Estimate based on the assumption that 100% of the
   burned biomass is transformed into CO2.

   a Based on data from Martinelli et al. (1988).

   b The  total range of emissions is calculated as the product
   of the  lower and upper estimates of the carbon biomass
   available and the lower (250,000 km2 in INPE, 1989) and
   upper  (600,000 km2 in Mahar, 1988) estimates of the total
   area deforested.

   c The range of emissions for 1988 is calculated as the
   product of the lower and upper estimates of the carbon
   biomass available and the lower  (17,000 km2 in INPE, 1989)
   and upper (80,000 km2 in Setzer and Pereira, 1991)
   estimates of the area deforested in 1988.

   Source: Salati et al., 1989.

Policy Options for Stabilizing Global Climate
With the vast scale of its forest resources and
international   pressures,  Brazil  has   the
potential to slow deforestation  if proactive
adjustments in government, commercial, and
colonizing  forest   use  and   development
practices are adopted (e.g., see discussion of
options  to reduce biomass burning, below).

      Brazil  has  357  million   hectares  of
closed tropical  forest -- 30% of the global
total, and three times as much as Indonesia,
which is second to  Brazil in its  extent  of
forest area.  The area deforested per year in
the  Amazonian  state  of  Rondonia tripled
from 7,600  square kilometers (km2) in 1980
to 26,000 km5 in 1985, while the population
increased roughly 15%  per year  during  1976-
81 (Malingreau  and Tucker,  1988; Woodwell
et al, 1986).  The major factors driving the
loss   of  forests  include  land   speculation,
inflation, negative-interest and   special-crop
loans, government  tax  and  fiscal incentives
undervaluing standing  forest (land is worth
more cleared than forested), production  of
beef for export, and population redistribution
in response  to  high growth rates  and the
mechanization of  agriculture   in  southern
Brazil (Repetto  and Gillis, 1988).

      The situation  in Brazil  is  changing
rapidly.  Analysis conducted  at the Brazilian
Space Research Center  found that forest fires
during 1987 covered 20 million ha  (77,000
square miles,  or 1.5  times the area of New
York state), of which 8 million ha were virgin
forest (Setzer and  Pereira, 1988).   This
observation  has   forced   reevaluation   of
standard  mid-1980s  estimates  (e.g., Lanty,
1982) of 11.4 million ha deforested  for the
entire globe's closed and open tropical forests
and could raise estimates, to perhaps as high
as 20.4 million ha/yr for the 1980s.  The wide
disparity between FAO's interim estimates for
selected  countries and  newer studies, often
relying on remote sensing, is shown  in Figure
5-12 (WRI et al., 1990). The emissions from
these fires contribute roughly 10% of total
global emissions of CO2 (Fearnside, 1985).  If
the   Brazilian  Amazon   were  completely
cleared,   11  Pg   C   would  be   released
immediately,  augmented  by a  continuing
gradual release that would elevate the total  to
62 Pg (Fearnside, 1985). Thus, deforestation
in Brazil poses  serious global consequences
 for  climate  change  as well as  the much
 discussed loss of species diversity.


      Technical  control options  involving
 forestry  can sequester  carbon  through the
 growth of woody plants, reduce anthropogenic
 production  of CO2,  and complement other
 strategies  for  reducing  the  buildup  of
 greenhouse gases.  Forestry-sector strategies
 for  responding  to  the threat  of  global
 warming fall into two major categories from
 an economic standpoint: those technical and
 policy options that reduce  the demand for
 forest land and forest products, and those that
 increase the supply of forested land and forest
 products. From a greenhouse gas  accounting
 perspective,  these   can  be  divided more
 profitably into  three classes:

      1.     Reduce Sources of Greenhouse

      2.     Maintain Sinks  of Greenhouse
            Gases;  and

      3.     Expand  Sinks  of  Greenhouse

 Table 5-15 lists the components of these three
 classes of forestry-related strategies.

      The set of potential response options in
 the  forest sector fall into three  categories.
 First, adaptive measures in forest management
 practices (e.g.,  planting drought-tolerant tree
 species in areas likely to undergo  reduced
 precipitation  during  climate  change,   or
 shortening  tree-crop  rotations  to  allow
 planting   of  different   species  as  growth
 conditions change), which are not reviewed
 here, offer one  set of options (see Larson and
 Binkley, 1989; Binkley, 1990; and AFA, 1990).
 Secondly, technologies and land-use practices
 are currently available that, if widely utilized
 by forest  managers, could reduce emissions
 from forestry.    These  are  reviewed here.
 Lastly, government and corporate policies and
 fiscal incentives could  be  generated  that
would encourage market forces  to  reward
 forest managers for greenhouse-positive forest
 management (see CHAPTER Vffl).

                                                 Chapter V: Technical Options
                               FIGURE 5-12
                    1981-1985 AND MOST RECENT

Policy Options for Stabilizing Global Climate
                                        TABLE 5-15

                        Summary of Major Forestry Sector Strategies
                                for Stabilizing Global  Climate
Reduce Sources of Greenhouse Gases

           Substitute sustainable, sedentary agricultural technologies for swidden (slash-and-
            burn) agriculture resulting in deforestation

           Reduce  the frequency,  interval,  scale,  and amount  of forest and  savannah
            consumed by biomass burning to create pasture and maintain grassland

           Decrease consumption of forest for cash crops and development projects through
            environmental planning and management

           Improve  the efficiency of biomass  (fuelwood)  combustion in cookstoves and
            industrial uses

           Decrease the production of disposable forest products (e.g., paper, disposable
            chopsticks)  by substituting durable wood or other goods and by recycling wood

Maintain Existing Sinks of Greenhouse Gases

           Conserve standing primary and old-growth forests as stocks of biomass offering
            a stream of economic benefits

           Introduce natural forest  management systems  utilizing sustainable harvesting
            methods to replace inefficient and destructive logging

           Substitute extractive  reserves producing timber and non-timber products with
            sustainable  practices through integrated resource management and development

           Increase harvest efficiency in forests by harvesting more species with methods
            that damage fewer standing trees and use more  of total biomass

           Prevent loss of soil carbon stocks by slowing erosion  in forest systems during
            harvest and from overgrazing by livestock

                                                               Chapter V:  Technical Options
                                  TABLE 5-15 (Continued)
                        Summary of Major Forestry Sector Strategies
                                for Stabilizing Global Climate
Expand Sinks of Greenhouse Gases
            Improve  forest  productivity  on  existing forests  through  management and
            biotechnology on managed and plantation forests

            Establish plantations on surplus cropland and urban lands in industrialized
            temperate zones to produce high biomass and/or fast-growth species to fix

            Restore degraded forest and savannah ecosystems through natural regeneration
            and reforestation

            Establish plantations and agroforestry projects in the tropics using both fast-growth and
            high-biomass species on short rotations for biofuels and timber

            Increase  soil carbon  storage by leaving slash  after  harvest  and  expanding

 Policy Options for Stabilizing Global Climate
       In addition to the obvious benefit, from
 the climate change  perspective, of  increasing
 the supply of forested land (i.e.,  trees absorb
 CO2), afforestation has a number of valuable
 ecological  and economic  benefits worthwhile
 on their  own merits.   For  example, more
 forests may  mean  more jobs in  the  forest
 products industry, enhanced maintenance of
 biodiversity,   better  watershed  protection,
 greater non-point  pollution  reduction,  and
 more areas for recreation.

       Compared with the annual crop cycles
 of agriculture, rotation time in forestry (the
 time necessary for one cycle of a forest crop
 to be planted, grown, and harvested) is slow,
 typically on   the  order  of 25-80  years  in
 temperate  zones  and  8-50  years    in  the
 tropics where growth is  faster.  Essentially,
 therefore,  forestry   climate  strategies  can
 create a net  CO2  sink  for a fixed period,
 albeit  long, since trees  eventually die or are
 cut and release carbon   through  decay  or
 burning. Harvesting on short rotations, at the
 point  where  the   rate   of  mean   annual
 increment  (MAI) of  biomass  added per year
 begins  to  level off, in  conjunction  with
 aggressive replanting, must be combined with
 greatly expanded storage of carbon in durable
 products like construction beams,  crates, or
 fences until they decay,  and regeneration of
 new biomass at high rates of  growth and
 carbon fixation.

      The  set of strategies  in  Table  5-15
 could be evaluated by resource managers for
 the optimal   mix  of land use  and  forest
 management  practices and policies best suited
 for any given forest management unit (e.g., a
 farm,  watershed, national forest, integrated
development   project, or  nation).    Some
options,  however,   are   better  suited   to
industrialized countries and some  are more
appropriate   for    developing    countries.
Strategies  for maintaining  the  volume  of
standing stock,  maximizing biomass growth
rates,  and expanding the  area in sustainably
 managed,   rapidly  growing  forest  are  all
 needed. Species and ecosystems that produce
 high volumes of biomass (e.g., Douglas fir old
growth in the Northwest, mixed hardwoods in
 the East,  and mahogany and  teak in  the
tropics) usually grow slowly (e.g., 70-200 years
 to mature)  and may  be most  useful  as
response options in  industrialized  countries
and well-managed  protected  areas in  the
tropics, where socioeconomic conditions favor
long-term  forest  protection  and  intensive
management.  Developing countries especially
need to maximize biomass growth  rates, to
restore degraded and desertifying lands,  and
to produce fuelwood and timber. Developing
countries face rapid forest depletion and high
population  growth  rates,  and  have limited
institutional  capability  to  guarantee   long
forest  rotation  times  in the face  of  these
realities.    However,  developing  countries
should  also  plant high-value,  long-rotation
hardwood  stands  and  protect  existing  old-
growth forests from cutting and burning.

      Because of  the long rotation times for
forest  growth, technical options will need to
integrate short-term educational, harvesting,
and   research   work   with   longer-term
adaptations in  forest planting,  management,
and product use.

      All strategies should be, to the extent

            sustainable  over time,  without
deteriorating the  natural  resource base  or
introducing ecological  changes  (i.e., pests),
especially relying on improved management of
both  undisturbed  (virgin)  and secondary
(disturbed or fallow) forests;

           capable of addressing the direct
and indirect causes of forest loss by providing
viable   alternatives  to   current   land-use

           economically attractive (low-cost
and offering income commensurate to present
land uses);

           capable   of    providing   an
equivalent spectrum of forest products (e.g.,
fuelwood, fodder)  and jobs, at rates of return
to labor (or time) and capital comparable to
current forest-use  patterns;

           socially integrative  or adaptive,
building on local needs and tradition;

           technologically   simple   and
durable, to overcome low reforestation success
rates on lands  degraded by human  resource
use  patterns  (e.g.,  upland  forests  cut  for

                                                                Chapter V: Technical Options
timber and fuelwood and then overgrazed by
goat and sheep); and

           readily  adaptable  to changing
economic,  political,  social,  ecological,  and
climate  change  realities  (e.g.,  civil  war,
drought, resource-driven population  shifts,
and climate change impacts on forest growth).

      Table  5-16 presents  a  summary  of
potential technical options for implementing
forestry strategies to reduce  demand and to
increase supply.

Forestry Strategy  I:    Reduce  Sources  of
Greenhouse Gases

      Both  tropical  and  temperate  forest
lands are in high demand to  provide a range
of alternative land uses  and  forest products.
Forests are  consumed  in  areas of rapid
population growth worldwide as villages and
cities expand,  transportation  corridors  are
built to connect them, and additional arable
land is  sought for food production.   Other
major forces contributing to  deforestation in
the   tropics,   include   swidden   (shifting)
agriculture, large-scale economic development
projects  (often  financed   by  multilateral
banks),  cattle ranches and palm  oil, timber
and rubber plantations, and fuelwood demand.

      Based on population growth, projected
demand for fuelwood by the year 2000 will
require  the creation of 20-25 million ha (or
perhaps as high as  50  million ha) of  new
closed forest plantations for fuelwood,  at a
cost of $50 billion, a rate 10-20 times current
planting tallies (Nambiar, 1984; FAO, 1981;
Lundgren and  van  Gelder,  1984).     An
additional 200 million ha of croplands will be
needed  (Postel and Heise,  1988) just  to
maintain the already inadequate 1980 levels of
per capita food supply.

      Currently, more than  10 hectares  are
lost to each one that is planted, based on the
ratio of global deforestation to tree planting
(Lanly,  1982).   Models of forest product
demand from 1980-2020 project tropical forest
removals  (harvest  for  timber)   to  double
between 1980 and 2000, and then plummet to
72% of their 1980 level by  2020  (WRI and
IIED, 1988;  Grainger, 1987).
Option 1: Substitute Sustainable Agriculture for
Swidden Forest Practices

      Sustainable agricultural  systems are
those  that  rely  on  biological  recycling  of
chemical nutrients in soils and energy, and on
naturally occurring mechanisms for protecting
crops from pests, to produce annual harvests
that can be  sustained in perpetuity (Dover
and Talbot,  1987).  Generally, such systems
use low levels of agricultural technology (i.e.,
minimal agricultural  pesticides or fertilizers  or
improved  seeds,   and   few  conservation

      Sustainable   agriculture,    especially
agroforestry,  offers all three major types  of
greenhouse gas cycle benefits:

           Reductions   of  emissions   of
greenhouse gases:

                  reduced demand for natural
forest wood  products, since fuelwood, poles,
and fodder  are grown  in many sustainable
agricultural systems

                  reduced demand for new
land cut from primary or secondary forest for
swidden agriculture  (by  substituting higher-
nutrient  sedentary  systems  on  permanent

                  lower soil erosion, thereby
less volatilization of soil carbon and methane,

                  diminished  reliance  on
fertilizers, reducing N2O emissions.

           Conservation and enhancement of
gas sinks:

                  increased supply of woody
biomass fixing carbon in trees  and soils  in
forest-crop systems,

                  maintenance of soil carbon
stocks, due to reduced erosion.

      Swidden agricultural  methods  involve
cutting and, usually, burning forest patches  to
plant crops that are harvested for  1-7 years,
and then abandoning and leaving the patches
fallow for about 7-14 years as new patches are

Policy Options for Stabilizing Global Climate
                                                                            TABLE 5-16

                                                             Potential Forestry Strategies and Technical
                                                                  Options to Slow Climate Change
                                                                      Technical Options
          Regions Potentially Most
                Effective In
   Reduce Sources of Greenhouse Cases

   Substitute sustainable agriculture
                                                         Small-scale agroforestry
                                                         Financial incentives for swidden colonists to shift
                                                         to sustainable practices
                                                         Technical aid in soil and crop selection
                                                         Plan into development projects by banks, state
Tropical moist and dry forests with strong central
governments (Brazil, Colombia, Malaysia,
   Decrease forest consumption for development and
   sustainable agricultural systems
                                                         Assistance from multilateral banks and state
                                                         agencies contingent on planning.  Loans
                                                         contingent on minimal forest loss
                                                         Mitigation of loss by 2:1 protection of forest
                                                         Government tax and  fiscal policies to prevent
Strong central governments and banks with ability
to plan and manage (Brazil,  Costa Rica, India,
China, Mexico)
   Improve efficiency of biomass combustion
                                                         Widely distribute efficient cookstoves
                                                         Incentives for industrial cogeneration
Areas with inefficient current stoves, good
extension, and difficult-access or expensive
fuelwood (Nepal, India, Sahel, Haiti)
   Decrease production of disposable forest products
                                                         Substitute durable wood products for disposables
                                                         Establish recycling programs for wood
Areas with cheap substitutes for wood and
developed markets (industrialized areas of
developing countries, Japan, U.S.)	
   Reduce biomass burning in forests and savannah
                                                         Manage savannah more actively to prevent
                                                         overgrazing of forage
                                                         Establish fire prevention plans and brigades in
                                                         forestry development projects
                                                         Provide government surveillance and enforcement
Savannah and dry forest areas already under
active management and readily accessible
Countries with remote sensing real-time detection
of fires and will to enforce
                     Sinks of Greenhouse Ga
   Conserve standing primary and old growth forests
                                                         Establish protected areas and prevent forest loss
                                                         Biosphere reserves
Old-growth forests in Pacific Northwest (U.S.),
and developed countries
Inaccessible and/or actively managed tropical
moist forest

                                                                   TABLE 5-16 (Continued)

                                                          Potential Forestry Strategies and Technical
                                                               Options to Slow Climate Change
                                                                                                                                  Chapter V:  Technical Options
             Technical Options
          Regions Potentially Most
                Effective In
Maintain IMUH Sinks of Greenhouse Gases

Introduce natural forest management (NFM) systems
Introduce widely several NFM techniques
Development or forest management projects in
Substitute extractive reserves for unsustainable
logging and agriculture
Extractive reserves for rubber, fruits, and nuts
Expand markets for non-timber forest products
Brazil, Indonesia, Malaysia
Tropical forests with indigenes and colonists near
markets and transport
Increase forest harvest efficiency
Increase number of species harvested
Decrease damage to standing trees
Use harvest slash and mill scraps
Any area, if marketed, and countries with large or
multinational logging concessions (Brazil,
Prevent loss of soil carbon
Soil erosion via soil management, cover crops,
windbreak plants
Prevent overgrazing of pasture, forest via livestock
management and fodder tree planting
                                                                                                               Dry forest and savannah in tropics
                                                                                                               Hilly agricultural areas with active extension
Expand Sink* of Greenhouse Ga

Increase forest productivity
Manage temperate forests
Apply natural forest management in tropics
Increase plantation productivity
Intensify timber stand improvement all forests
Apply fertilizers and biotechnology to plantations
Extend natural  forest management practices
Developed countries and industrialized developing
countries, with extension capability
Plant trees on crop and urban lands in temperate
Expand tree planting programs
Reforest croplands
Reforest urban areas
Reforest highway corridors
Reforest surplus cropland
Plant fast-growth plantations
Plant trees near buildings, highways, rivers
Developed countries
U.S.:  Southeast, North Central states, West

Policy Options for Stabilizing Global Climate
                                                                  TABLE 5-16 (Continued)

                                                          Potential Forestry Strategies and Technical
                                                               Options to Slow Climate Change

Reforest degraded forest lands
Plant fuelwood and timber plantations in tropics
Increase soil carbon storage
Technical Options
 Incentives for agroforestry
 Establish extension farms and workers for
 Require commercial and village loggers to replant
 Plant strip-mined, overgrazed, and abandoned
lands in U.S.
 Organize village tree planting
 Mobilize youth and religious groups to plant trees
 Include plantations in all development projects
 Leave slash after harvest
 Prevent soil erosion with management practices
Regions Potentially Most
Effective In
 Tropics, where rainfall and soils are adequate
 Degraded lands in U.S., with adequate soil
nutrient and rainfall
 Throughout tropics, especially in moist soils and
in desertifying areas
 All managed temperate and tropical forests

                                                                Chapter V: Technical Options
cut and farmed.   About  41 million ha of
tropical  primary  and secondary  forest are
burned  annually  (see   CHAPTER  VIII).
Tropical forests store up to 90%  of a plot's
nutrients  (some of  which are released by
burning)  in  woody  plants, compared with
temperate forests, where only 3% are stored
in plants and 97%  in  soils (Keay, 1978).
Swidden systems persist throughout the world,
especially in  remote and  hill districts,  and
during  times  of individual  or  regional
economic stress.   For  example, on Negros
Island in the Philippines,  the  number of
swidden fanners rose by  80%  in only  two
years in the mid-1980s because of declines in
the  sugarcane industry  that forced under-
employed workers into swidden agriculture to
grow food.   Ecologists  predict that a major
rain  forest there could be  destroyed by the
year 2000 (Dover and Talbot, 1987).

      Sustainable  agriculture    and   soil
management systems  can be introduced as a
substitute for swidden systems  that destroy
virgin or secondary forest.  For every hectare
farmers put  into such methods, 5-10 hectares
of tropical  rainforest may  be saved  from
destruction    to   store   carbon,    conserve
hydrologic   cycles,  and   retain  biological
diversity, according to Sanchez (1988). Table
5-17  shows   the  equivalent  area  of forests
needed for traditional swidden  practices for
every one hectare of forest land needed for
more resource-intensive sustainable uses.

      Agroforestry is the combination  of
agricultural    and  forestry  techniques  to
produce woody plants on the same parcels as
food or commodity crops or animals, with a
mutually beneficial synergism. It offers one of
the most promising approaches for providing
both fuelwood and food needs, while reducing
greenhouse  gas releases and environmental
externalities   (e.g.,  pesticide   use,  pest
population    surges,    high   irrigation
requirements) associated with monoculture!
row  cropping.  Interest in agroforestry has
surged since the late  1970s, and  development
assistance for agroforestry  during the mid-
1970s to mid-1980s reached $750 million in
approximately 100 developing nations (Spears,

      Agroforestry   systems  derive from
traditional forest farming practices  of many
indigenous peoples and are sustainable over
long  rotations,  large  acreages,   and  low
population densities.    The Lacandon Maya
Indians, who live in the rainforest in Chiapas,
Mexico,  practice  a  multiple-layer cropping
system  utilizing  up to 75 species in one-
hectare plots that produce crops for 5-7 years.
As soil fertility wanes, the Lacandon plant
tree crops (cacao, citrus, rubber, avocado) that
provide  valuable  products   as   the  plots
regenerate with secondary forest.  This forest
is cut again when the  trees  overgrow the
managed species.  It is estimated that  only 10
hectares of  rain  forest are  consumed per
farmer throughout his career with this  method
of  sustained  agroforestry.    In  contrast,
immigrant  colonists consume  two or three
times  as  much  forest area  (Nations  and
Komer, 1983).

      Newer systems  build on these local
methods by incorporating trees and bushes in
erosion-control strips, hedges,  nitrogen-fixing
trees  in fields, and cash  and fodder crops
(e.g.,  see,  Wimerbottom  and Hazelwood,
1987;  Dover and Talbot, 1987;  Kidd  and
Pimentel, forthcoming 1991; and OTA, 1984).
For example, a typical agroforestry system in
steep uplands with poor soils in  Himachal
Pradesh, India, is stocked with 20.5 trees/ha,
which  produce a yield  of 2.0 m3/ha/yr of
wood,  or  0.8 t C/ha/yr, plus  the potential
savings of  roughly a 5:1 ratio of  hectare of
virgin  forest  retained intact per  hectare
convened to  permanent cultivation.  A more
intensive stocking  rate of 322 trees/ha in
home gardens in  Surakarta, Indonesia, yields
7.3 nr/ha/yr  wood, or  1.9 t C/foa/yr.   Data
from  Indonesia and Tanzania indicate  that
200-300 trees are sufficient to provide wood
production  needs  of  a  typical   household
(Lundgren  and  van   Gelder,  1984).   An
overview of  potential  carbon cycle benefits
from  a range  of agroforestry   systems is
presented in Table 5-18, and  a summary of
potential   greenhouse   gas    reduction
implications of agroforestry is  given in Table

      Obstacles to substituting agroforestry
for traditional agriculture include the need for
suitable environmental conditions  (soils and
rainfall), and human population densities and
institutions adequate to encourage multi-year
resource management  Either overcrowding

Policy Options for Stabilizing Global Climate
                                        TABLE 5-17

                        Comparison of Land Required for Sustainable
                            Versus Swidden Agricultural Practices
Sustainable Agricultural Practices
Number of Swidden Hectares Required
 for Every One Hectare of Sustainable
Flooded rice

Low-input cropping (transitional)

High-input cropping

Legume-based pastures

Agroforestry systems




           not determined
Sources:  Derived from 17-year ongoing research by North Carolina State team at Yurimaguas,
Peru, in tropical moist lowland forest (Sanchez, 1988; Sanchez and Benites, 1987).

                                                              Chapter V: Technical Options
                                        TABLE 5-18
                      Potential Carbon Fixation and Biomass Production
                      Benefits from Representative Agroforestry Systems

Type of System
Natural forest
management and

Steep uplands,
poor soils
Alley cropping
Location Hectare

Himachal 20.5

(t C/ha/yr) Species Used
0.8 native shrubs
0.9-3 nitrogen-fixing
shrubs (Glicidia,

Products Produced
wood, mulch, crops,
gums, fodder,

fuelwood, fodder,
maize in alleys
between hedgerows
                                                         Leucaena, Calli-
                                                         andra, Sesbania)
                                                        cut for mulch and
Home gardens
Surakarta,     322
fruit, fodder, mulch
CARE Agrofor-
estry and Re-
source Conser-
vation Project
Guatemala    400
4.7       conifers (high-
         lands), hard-
         woods (lowlands).
         20 species in total
fuelwood, fodder,
Note:  Soil carbon storage benefits are not available, and may be significant.

Sources:  Winterbottom and Hazelwood, 1987, and WRI and IIED, 1988 (Niger, Nigeria); Lungren
and van Gelder, 1984 (India, Indonesia); Trexler et al., 1989, and WRI,  1988 (Guatemala).

Policy Options for Stabilizing Global Climate
                                        TABLE 5-19

          Assessment of Potential Reductions in Greenhouse Gases from Large-Scale
       Substitution of Agroforestry for Traditional Swidden and Monoculture! Agriculture
Source of Gas
Potential Effect of Agroforestry
Clearing of forest
Biomass burning
C02, CH4
C02, CH4,
N20, CO, NOX
Sustainable  agroforestry would provide fuelwood and
fodder,  reducing  forest  clearing  for  unsustainable
cropping and biofuels

Displacement of shifting cultivation would free forest
fallow for reforestation and carbon fixation in biomass
and soils
Cultivation and
degradation of

Denitrification by

Denitrification of
nitrogen fertilizer

Denitrification by
Reduced disturbance of soils during plowing, reduced
introduction  of  mulch to soils, and reduced erosion
should increase carbon storage in soils

Agroforestry could reduce denitrification by improving
soil chemical and physical properties

Agroforestry  could substitute symbiotic fixation  for
fertilizer use, reducing N2O emissions

Use of nitrogen-fixing tree species with associated soil
and by root Rhizobial symbionts could facilitate
Source: Adapted from Franz, 1989.

                                                               Chapter V:  Technical Options
or  pervasive poverty will shift  the  focus to
short-term  survival.   Social  and economic
factors likely to promote success include clear
and  relatively  equitable  land  tenure  for
farmers,  local   decision-making,   political
systems that at least  tolerate medium-term
investment  by villagers of various  classes,
developed and accessible markets for crop and
forest products, and adequate protection of
agroforestry systems from grazing livestock,
villagers,  civil  strife,  and  rapid economic
changes (Winterbottom and Hazelwood, 1987;
IIED and WRI, 1987).

      Constraints   to  wide   diffusion  of
agroforestry  include  the   difficulty  of
technology  transfer to remote populations
with traditional values that do not encourage
innovation,  the need for systems tailored to
site-specific conditions, capital requirements
to purchase and maintain seedling nurseries
and to  fund extension efforts and research,
and  the   vast   scale  of  implementation
necessary    to   slow   forest   degradation
(Lundgren and van Gelder, 1984).  The long-
term sustainability of new agroforestry systems
has not been fully demonstrated in many first-
generation  projects,  which often still  rely
upon high levels of fertilizer and labor.

Option 2:  Reduce  the Frequency, Interval, and
Scale of Forest and Savannah Consumed by
Biomass Burning as a Management Practice

      Techniques  to reduce  the  frequency,
interval,  and scale  of forest  and  savanna
burned  during  management  for  livestock
grazing  and for  forest land  conversion to
agriculture and grazing may offer  significant
benefits in decreasing emissions from biomass
burning.  Little analysis of this potential has
been  performed.  Another option may be to
expand  fire  risk  management  on  selected
pasture  and  forest   lands  already  under
intensive  management in the  dry  tropics
through technology transfer. This option may
be feasible as a new best management practice
that alters burning frequency or extent enough
to  reduce  greenhouse  gas  emissions.   No
detailed discussion of how such an expansion
for  climate  change  purposes could  be
achieved,  and  its  benefits,  is  currently
      Relevant  examples  of potential  fire
management  practices  include  fire  (and
grazing) protection of abandoned pasture land
around Guanacaste  National  Park,  Costa
Rica, to  allow  natural regeneration of dry
forest (Jansen, 1988a, 1988b; see below), and
fire  protection  as   a  component  of  the
CARE/AES   Guatemala    forestry  project
designed  to  offset  CO2  emissions of  an
electric plant in  Connecticut  (Trexler et al.,
1989;  see below).   In  Brazil, the  federal
environmental agency IBAMA launched  a
vigorous burning management program in the
dry season of 1989 in which the  space agency
INPE identified areas being burned through
remote   sensing;   a   helicopter   with
environmental police was then dispatched to
the site within 6 hours to ascertain if a burn
permit had been obtained and to  levy fines.
IBAMA has indicated that this  enforcement
program,  along  with  the unusually long wet
season, contributed to a major  reduction in
number of fires and area  burned in 1989,
although  the program is being challenged in
court at present and no fire fines  have been
collected  as  yet  (Setzer and Pereira, 1991;
U.S. EPA, 1989; Prado, 1990). Results of the
1990 dry  season  burning  rates are  eagerly
awaited by analysts and IBAMA.

      The constraints in limiting burning are
many, including the low level of management
often associated with grazing lands, highly
decentralized  land use  and  ownership, and
ecological reliance on burning  to stimulate
nutrient  flow and primary  productivity  of
grasslands.  Exploratory  analysis of biomass
burning response options is needed.

Option 3:  Reduce Demand For Other Land
Uses That Have Deforestation as  a Byproduct

      Large development  projects, especially
those planned in the tropics by transnational
corporations  and multilateral development
banks, consume  huge  tracts of forest  for
roads,  hydroelectric  project reservoirs, and
new  communities.     For   example,   the
Mahaweli project in  Sri Lanka  will destroy
260,000 ha of tropical moist forest in order to
generate  466 MW  of  electric power and
provide flood control and irrigation benefits.
The  Narmada   Valley Project in  Madhya

Policy Options for Stabilizing Global Climate
Pradesh, India, may inundate 350,000 ha of
teak and bamboo forest (Kalpavriksh, 1985).

      Pressure on banks and governments to
reduce adverse impacts on tropical forests has
mounted   since  1980  and  spawned  new
development planning methods that include
protection of forest tracts  in order to offset
consumptive  use  of  other forested  lands
(Rich, 1989; Gradwohl and Greenberg,  1988).
In 1986, the World Bank  issued  a new six-
element policy on wildlands to guide planning
of Bank development projects.   This  policy
states   preference   for   choosing  already
degraded (e.g., logged over) and least valuable
lands for development purposes.  It requires
compensation for wildlands converted by Bank
projects in the form of an added wildlands
management  and  preservation  component
(Goodland, 1988; World Bank,  1986).  India
is   experimenting    with   compensatory
reforestation at a 2:1 replacement ratio for
forest cut for hydro  projects.  Compensatory
mitigation  planning for  forest  areas during
development project design can be expanded
as a  response option, although problems still
remain  with  such  approaches,   including
management responsibility over  long  time
frames and potential productivity rates of new
compensatory forests.

      The  probability of  forest  loss  along
transportation  corridors and in  settlement
projects in Indonesia has been quantified by
Soemarwoto  (1990)  based  on  data  on
population  pressures, carrying capacity  of
given land  tracts, and targeted standard  of
living.   Several policies and  practices with
potential to reduce forest loss in new planned
settlements,  like  the huge  transmigration
projects   in  Indonesia,   were   noted   by
Soemarwoto,  including:     increasing  the
agricultural  production  per  unit area  by
improving  technological  inputs, introducing
crops with  high market values, increasing off-
farm income, reducing the number of farmers
by   providing   alternative    employment
opportunities through  economic  diversifi-
cation, and reducing the population growth

      Forest loss for creation of new pasture
in Amazonia has  been estimated for 1970 to
1990 at 17.5 million ha, emitting about 2.6
billion tons CO2, resulting in a net loss (after
accounting for  growth of  new  biomass  in
pastures of about 10 tons/ha/yr)  of about 2.4
billion tons CO2 (Serrao,  1990).  Response
options identified by Serrao (1990)  to slow
this conversion  include  intensifying  cattle
production on pasture already degraded, using
appropriate  technology  like   second-cycle
pastures   and   silvo-pastoral   systems;
regenerating degraded pasture with economic
tree species offering additional  income; and
increasing use of existing  natural grassland
ecosystems,  now  undergrazed,   to   reduce