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Page 73 9 Recommendations Despite the great uncertainties, greenhouse warming is a potential threat sufficient to justify action now. Some current actions could reduce the speed and magnitude of greenhouse warming; others could prepare people and natural systems of plants and animals for future adjustments to the conditions likely to accompany greenhouse warming. There are a number of mitigation and adaptation options available to the United States. This panel recommends implementation of the options presented below through a concerted program to start mitigating further buildup of greenhouse gases and to initiate adaptation measures that are judicious and practical. It also recommends a strong scientific program to continue to reduce the many uncertainties. International cooperation is essential in all areas. The recommendations are generally based on low-cost, currently available technologies. Topics for which new information or techniques must be developed are clearly identified. In many instances, more detailed treatments can be found in Part Two, ''The Science Base"; Part Three, "Mitigation"; and Part Four, "Adaptation." The numbers in parentheses refer to pages in this part where these topics are discussed. Reducing or Offsetting Emissions of Greenhouse Gases Three areas dominate the analysis of reducing or offsetting current emissions: (1) eliminating halocarbon emissions, (2) changing energy policy, and (3) utilizing forest offsets. Eliminating CFC emissions is the biggest single contribution in the short run. Energy policy recommendations include reducing emissions related to both consumption and production. Recommendations

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Page 74 on both global and domestic programs are included under forest offsets. The United States could reduce or offset its greenhouse gas emissions by between 10 and 40 percent of 1990 levels at low cost, or at some net savings, if proper policies are implemented. Halocarbon Emissions Continue the aggressive phaseout of CFC and other halocarbon emissions and the development of substitutes that minimize or eliminate greenhouse gas emissions. (pp. 53, 55–59) Chlorofluorocarbons not only have a role in the depletion of stratospheric ozone, they also contribute a significant portion of the radiative forcing (i.e., the ability to "trap" heat in the atmosphere) attributable to human activities. The 1987 Montreal Protocol to the Vienna Convention set goals regarding international phaseout of CFC manufacture and emissions. The United States is a party to that agreement as well as to the London Protocol, which requires total phaseout of CFCs, halons, and carbon tetrachloride by 2000 in industrialized countries and by 2010 in developing countries. Unless this agreement is forcefully implemented, the use of CFCs may continue to intensify greenhouse warming. Every effort should be made to develop economical substitutes that do not contribute to greenhouse warming. Energy Policy Study in detail the "full social cost pricing" of energy, with a goal of gradually introducing such a system. (pp. 32–33, 68, 69) On the basis of the principle that the polluter should pay, pricing of energy production and use should reflect the full costs of the associated environmental problems. The concept of full social cost pricing is a goal toward which to strive. Including all social, environmental, and other costs in energy prices would provide consumers and producers with the appropriate information to decide about fuel mix, new investments, and research and development. Such a policy would not be easy to design or implement. Unanticipated winners and losers could emerge, either through improper accounting of externalities, lack of knowledge, or lack of incorporation of other concerns (such as energy security) or through cleverness and innovation. Phasing such a policy in over time is essential to avoid shocks caused by rapid price changes. It would best be coordinated internationally. Reduce the emission of greenhouse gases during energy use and consumption by enhancing conservation efficiency (pp. 55–59, 60), including action to:

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Page 75 • Adopt nationwide energy-efficient building codes • Improve the efficiency of the U.S. automotive fleet through the use of an appropriate combination of regulation and tax incentives • Strengthen federal and state support of mass transit • Improve appliance efficiency standards • Encourage public education and information programs for conservation and recycling • Reform state public utility regulation to encourage electrical utilities to promote efficiency and conservation • Sharply increase the emphasis on efficiency and conservation in the federal energy research and development budget • Utilize federal and state purchases of goods and services to demonstrate best-practice technologies and energy conservation programs • Utilize federal and state purchases of goods and services to demonstrate best-practice technologies and energy conservation programs The efficiency of practically every end use of energy can be improved relatively inexpensively. Major reductions could be achieved in energy use in existing buildings through improvements in lighting, water heating, refrigeration, space heating and cooling, and cooking. Gains could be achieved in transportation by improving vehicle efficiency without downsizing or altering convenience. Significant gains could also be achieved in industrial electricity use through fuel switching and improvements in process technologies. Initial calculations show that some options could be implemented at a net savings. There are informational barriers to overcome, however. For example, homeowners may not be aware of the gains to be realized from high-efficiency furnaces. There are also institutional barriers. For example, most public utility commissions disallow a rate of return to power companies on efficiency and conservation options. The panel concludes that energy efficiency and conservation is a rich field for reducing greenhouse gas emissions. Make greenhouse warming a key factor in planning for our future energy supply mix. The United States should adopt a systems approach that considers the interactions among supply, conversion, end use, and external effects in improving the economics and performance of the overall energy system. (pp. 55–59, 60) Action items include efforts to: • Develop combined cycle systems that have efficiencies approaching 60 percent for both coal- and natural-gas-fired plants • Encourage broader use of natural gas by identifying and removing obstacles in the distribution system • Develop and test operationally a new generation of nuclear reactor technology that is designed to deal with safety, waste management, and public acceptability • Increase research and development on alternative energy supply technologies (e.g., solar), and design energy systems utilizing them in conjunction with other energy supply technologies to optimize economy and performance

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Page 76 • Accelerate efforts to assess the economic and technical feasibility of CO2 sequestration from fossil-fuel-based generating plants The future energy supply mix will change as new energy technologies and greenhouse warming take on increased importance. A "systems approach" should be used to optimize the economics and performance of future energy systems. Interactions among supply options, conversion systems, end use, and external effects should receive much more attention than they have in the past. Actions for improving energy supply systems must cover all important elements in the mix. Also, it is important to prepare for the possibility that greenhouse warming may become far more serious in the future. Alternative energy technologies are unable currently or in the near future to replace fossil fuels as the major electricity source for this country. If fossil fuels had to be replaced now as the primary source of electricity, nuclear power appears to be the most technically feasible alternative. But nuclear reactor designs capable of meeting fail-safe criteria and satisfying public concerns have not been demonstrated. A new generation of reactor design is needed that adequately addresses the full range of safety, waste management, economic, and other issues confronting nuclear power. Focused research and development work on a variety of alternative energy supply sources could change the priorities for energy supply within the 50-year time span addressed in this study. Forest Offsets Reduce global deforestation (pp. 65–66), including action to: • Participate in international programs to assess the extent of deforestation, especially in tropical regions, and to develop effective action plans to slow or halt deforestation • Undertake country-by-country programs of technical assistance or other incentives • Review U.S. policies to remove subsidies and other incentives contributing to deforestation in the United States In addition to reducing the uptake of CO2 in plants and soils and being a source of atmospheric CO2, deforestation contributes to other important problems: loss of species and reduction in the diversity of biologic systems, soil erosion, decreased capacity to retain water in soil and altered runoff of rainfall, and alteration of local weather patterns. The United States now has increasing forest cover, but tropical forests worldwide are being lost at a rapid rate. Nearly every aspect of tropical deforestation, however, is difficult to measure. Even the amount of land deforested each year is subject to disagreement. Nevertheless, action should be initiated now to slow and

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Page 77 eventually halt tropical deforestation. Such programs need to be developed by those countries where the affected forests are located in cooperation with other countries and international organizations. Developing countries with extensive tropical forests will require substantial technological and developmental aid if this goal is to be reached. Explore a moderate domestic reforestation program and support international reforestation efforts. (pp. 55–59, 66–67) Reforestation offers the potential of offsetting a large amount of CO2 emissions, but at a cost that increases sharply as the amount of offset increases. These costs include not only those of implementation, but also the loss of other productive uses of the land planted to forests, such as land for food production. Reforesting can, at best, only remove CO2 from the atmosphere and store it during the lifetime of the trees. When a forest matures, the net uptake of CO2 stops. If the reforested areas are then harvested, the only true offset of CO2 buildup is the amount of carbon stored as lumber or other long-lived products. However, the wood might be used as a sustained-yield energy crop to replace fossil fuel use. The acreage available within the United States for reforestation, and the amount of CO2 that could be captured on these lands with appropriate kinds of trees, are controversial and may be limited. Many details remain to be resolved. Enhancing Adaptation to Greenhouse Warming The nature and magnitude of the weather conditions and events that might accompany greenhouse warming at any particular location in the future are extremely uncertain. This panel examined the sensitivity of the affected human and natural systems to the events and conditions likely to accompany greenhouse warming. The panel's adaptation recommendations are intended to help make the affected systems less vulnerable to future climate change. Most of the recommendations, by making the systems more robust, also help them deal with current climate variability. Some, such as purchasing land or easements for specific habitats or corridors for migration, would not be needed if greenhouse warming does not occur. Specific adaptation recommendations address agriculture, water systems, long-lived structures, and preservation of biodiversity. Maintain basic, applied, and experimental agricultural research to help farmers and commerce adapt to climate change and thus ensure ample food. (pp. 38–39) Farming is the preeminent activity essential to humanity that is exposed to climate. During recent decades, its successful adaptation to diverse climates and changing demand rested on vigorous research and application by

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Page 78 both government and business. As climate changes, adapted varieties, species, and husbandry must be more promptly sought and then proven in the reality of fields and commerce. Special challenges are (1) while adapting, to sustain the natural resources of land, water, and genetic diversity that underlie farming; (2) to be productive during extreme weather conditions; (3) to manage irrigation to produce more food with less water; and (4) to exploit the opportunity of increased fertilization provided by more CO2 in the air. Make water supply more robust by coping with present variability by increasing efficiency of use through water markets and by better management of present systems of supply. (pp. 40–41) Currently, weather and precipitation cause natural variability in the water supply, in soil, and in streams, and changes in climate could be expected to produce even greater variability. Fortunately, coping with the present variability makes supply more reliable or robust for future climate change when needed. In many places, supply and demand can be better matched by raising the efficiency of use through changes in rights, markets, and prices, by clever management and engineering of irrigation, and by changes in urban styles of living (e.g., water-efficient landscaping and reduced lawn maintenance). Because the joint management of supplies under the jurisdiction of several agencies can increase water yields substantially, the protracted negotiations for such cooperation should begin now. Plan margins of safety for long-lived structures to take into consideration possible climate change. (pp. 43–44) Margins of safety adequate for past climate may be insufficient for a changed climate. Most investments like bridges, levees, or dams have lives as long as the time expected for climate to change. The margins used in constructing such structures are generally computed from the historical frequency of extremes like storms or droughts. The possibility of greenhouse warming must now be considered in computing these margins of safety. A logical procedure for justifying investment in a wider margin of safety now involves two considerations: its cost in terms of its expected present value compared to that of retrofitting the structure when needed, and the probability that the alteration will in fact be needed. Move to slow present losses in biodiversity (pp. 39–40, 46), including taking action to: • Establish and manage areas encompassing full ranges of habitats • Inventory little-known organisms and sites • Collect key organisms in repositories such as seed banks • Search for new active compounds in wild plants and animals

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Page 79 • Control and manage wild species to avoid over-exploitation • Pursue captive breeding and propagation of valuable species that have had their habitats usurped or populations drastically reduced • Review policies, laws, and administrative procedures that have the effect of promoting species destruction • Consider purchasing land or easements suitable for helping vulnerable species to migrate to new habitats Even without greenhouse warming, a series of steps to slow present losses in biodiversity are warranted. Any future climate change is likely to increase the rate of loss of biodiversity while it increases the value of genetic resources. Greenhouse warming therefore adds urgency to programs to preserve our biological heritage. Much remains to be done to ensure that key habitats are protected, that major crop cultivars are collected, and that extensive options are retained for future use. Serious initiatives have only recently been started. In most countries, the driving forces behind the degradation of biodiversity relate to the development context within which people farm; harvest forest products; utilize fresh water, wildlife, and fish; and otherwise invest in land or water. Moreover, there are policies that actually promote destruction by fostering open tillage crops, short-term timber-harvesting concessions, excessive use of water, and inappropriate fishing technology. If climate changes, existing reserves and parks may become unsuitable for species currently living there, and landscape fragmentation may make migration more difficult. Conservation efforts should give more attention to corridors for movement, to assisting species to surmount barriers, and to maintaining species when their natural habitats are threatened. Improving Knowledge for Future Decisions Data collection and applied research can make exceptional contributions in reducing uncertainties of greenhouse warming. The return on investment in research is likely to be great. The panel identifies the following areas for emphasis: collection and interpretation of data on climate change, improvement in weather forecasting, key physical mechanisms in climate change, and research on the interactions between the biosphere, human activities, and the climate system. Continue and expand the collection and dissemination of data that provide an uninterrupted record of the evolving climate and of data that are (or will become) needed for the improvement and testing of climate models. (pp. 19–22, 22–25, 26–27) Current data collection programs should be maintained and should be continued after the new (and different) collection systems (e.g., EOS, the Earth Observing System) have become operational. Earlier modes of collection

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Page 80 should be phased out only when the interpretation of new and old data streams has proceeded for an appropriate time. Uncertainties in the climate record and its interpretation should not be exacerbated by change in instrumentation. Continuous monitoring of key indices that can reveal climate change is needed for identifying adaptations that will be needed in the future. These include the supply of water in the streams and soil of a region, sea level, ocean currents, and dates of seasonal events like blooms and migrations. Improve weather forecasts, especially of extremes, for weeks and seasons to ease adaptation to climate change. (p. 36) If storms could be accurately forecast several days in advance, people could prepare for or escape them and hence could live in climates with greater variation and extremes. If extremely cold or dry seasons could be foreseen confidently, appropriate crops could be planted and harvested, and floods and droughts managed more effectively. Continued improvement of several-day forecasts, provision and dissemination of forecasts for additional parts of the world, and increasing knowledge of atmosphere-ocean interactions may help enhance adaptation to greenhouse warming. Continue to identify those mechanisms that play a significant role in the climatic response to changing concentrations of greenhouse gases. Develop and/or improve quantification of all such mechanisms at a scale appropriate for climate models. (pp. 19–21, 27–28) Some of the mechanisms already known to need such attention include those involving the role of clouds, the role of the oceans in heat transfer, the possible release of CO2 in the oceans (i.e., into the atmosphere) with change in ocean temperature, the role of the biosphere in the storage and release of CO2 and CH4, and the effect of particle concentrations on cloud cover and radiative balance. It is also necessary to improve the quantification (at a scale suitable for climate models) of processes such as precipitation, soil moisture, and run-off. Some current mathematical characterizations are unable to provide credible regional projections of these factors even when used for scenarios in which the greenhouse gas concentrations are not changing. Conduct field research on entire systems of species over many years to learn how CO2 enrichment alters the mix of species and changes the total production or quality of biomas. Research should be accelerated to determine how greenhouse warming might affect biodiversity. (pp. 39–40, 71) Communities of plants and animals are complex and intricate. Simplified and controlled experiments in laboratories can help understand them better. Greenhouse warming is likely to increase the rate of loss biodiversity, and so it adds urgency to experimental programs to preserve our biological

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Page 81 heritage. But scientists also must learn how disparate, entire systems of species live and react to changes in their habitats and especially to changes in the concentration of CO2. The effect of combined CO2 enrichment and greenhouse warming on the mix of species and other attributes of natural communities cannot be determined without field research conducted over many years. Strengthen research on social and economic aspects of global change and greenhouse warming. (pp. 70–71) The U.S. research program has emphasized issues of atmospheric chemistry, climate modeling, and monitoring, while relatively little attention has been given to issues of impacts, mitigation, and adaptation. Major priorities should be (1) improved understanding of the costs for mitigating greenhouse gas emissions, particularly in the energy sector, (2) more detailed studies of the impacts of and adaptations to climate change, (3) a better understanding of the social and economic processes generating greenhouse gas emissions, (4) policy analysis of options and strategies relating to climate change, and (5) improvements in the data base for understanding economic and environmental trends relating to global change. Greenhouse warming is a global problem; therefore it will be important to encourage interdisciplinary and international programs. Thorough analytical studies of the impacts of greenhouse warming currently are limited to a few relatively high income countries. Yet it is the poor countries, with a large fraction of their population and output in the farm sector, who are the most vulnerable to climate change. In the research areas listed above, it will be important to examine behavior in developing countries as well as in hihg-income countries like the United States. Evaluating Geoengineering Options Undertake research and development projects to improve our understanding of both the potential of geoengineering options to offset global warming and their possible side effects. This is not a recommendation that geoengineering options be undertaken at this time, but rather that we learn more about their likely advantages and disadvantages. (pp. 54–61 Several geoengineering options appear to have considerable potential for offsetting global warming and are much less expensive than other options being considered. Because these options have the potential to affect the radiative forcing of the planet, because some of them cause or alter a variety of chemical reactions in the atmosphere, and because the climate system is poorly understood, such options must be considered extremely carefully. These options might be needed if greenhouse warming occurs, climate sensitivity

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Page 82 is at the high end of the range considered in this report, and other efforts to restrain greenhouse gas emissions fail. The first set of geoengineering options screens incoming solar radiation with dust or soot in orbit about the earth or in the atmosphere. The second set changes cloud abundance by increasing cloud condensation nuclei through carefully controlled emissions of particulate matter. Despite their theoretical potential, there is convincing evidence that the stratospheric particle options contribute to depletion of the ozone layer. The stratospheric particle options should be pursued only under extreme conditions or if additional research and development removes the concern about these problems. The cloud stimulation option should be examined further and could be pursued if concerns about acid rain could be managed through the choice of materials for cloud condensation nuclei or by careful management of the system. The third class increases ocean absorption of CO2 through stimulating growth of biological organisms. The panel recommends that research projects be undertaken to improve understanding of both the potential of these options to offset global warming and their possible side effects. Such assessments should involve international cooperation. This is not a recommendation for implementing these options at this time. Exercising International Leadership As the largest source of current greenhouse gas emissions, the United States should exercise leadership in addressing responses to greenhouse warming. Control of population growth has the potential to make a major contribution to raising living standards and to easing environmental problems like greenhouse warming. The United States should resume full participation in international programs to slow population growth and should contribute its share to their financial and other support. (p. 65) Population size and economic activity both affect greenhouse gas emissions. Even with rapid technological advances, slowing global population growth is a necessary component of a long-term effort to control worldwide emissions of greenhouse gases. Reducing population growth alone, however, may not reduce emissions of greenhouse gases because it may also stimulate growth in per capita income. If the nature of economic activity (especially energy use) changes, some growth will be possible with far less greenhouse gas emissions. Encouraging voluntary population control programs is of considerable benefit for slowing future emissions of greenhouse gases. In addition, countries vulnerable to the possible impacts of climate change would be better able to adapt to those changes if their populations were smaller and they had higher per capita income.

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Page 83 The United States should participate fully with officials at an appropriate level in international agreements and in programs to address greenhouse warming, including diplomatic conventions and research and development efforts. (p. 67) There is a growing momentum in the international community for completion of an international agreement on climate change in time for signing at the 1992 United Nations World Conference on Environment and Development. The United States should participate fully in this activity and continue its active scientific role in related topics. The global character of greenhouse warming provides a special opportunity in the area of research and development. International cooperation in research and development should be encouraged through governmental and private sector agreements. International organizations providing funds for development should be encouraged to evaluate projects meeting demand for energy growth by conservation methods on an equal footing with projects entailing construction of new production capacity.