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panel reflect additional analysis, deliberation, and judgment beyond those of the other panels contributing to this study.

Policy Considerations

The phenomenon of greenhouse warming is complex, and so are the possible responses to it. First, the extent, timing, and variation of future warming and its likely impacts need to be assessed. Second, both the cost and the effectiveness of options to slow greenhouse warming must be estimated and compared to the costs of postponing action. Third, the possible advantages and disadvantages of these actions need to be evaluated in light of the extent to which people, plants, and animals are likely to adjust by themselves or with assistance to changes in the climate. Fourth, the policymaker needs to evaluate these actions in comparison to other ways resources might be used. Before acting, we need to be confident that expenditures to slow climate change make sense. Fifth, decision makers will judge all these factors in a broader context. Responses to greenhouse warming will be determined by people worried about economic growth, food supply, energy availability, national security, and a host of other problems. Many responses appear to produce sizable benefits with regard to other goals, such as reducing air pollution. This study makes no attempt to assess these additional dividends. Instead, it focuses on response to greenhouse warming as such.

Capacities of Industrialized and Developing Countries

Different countries have quite different capacities to respond to change. Poverty, in particular, makes people vulnerable to change and substantially reduces their flexibility in responding to change. Countries with low percapita income face difficult trade-offs between stimulating economic development and alleviating environmental problems. These countries, which already have difficulty coping with environmental stresses today, will be even more sorely pressed when confronted by climate change.

This report examines response to greenhouse warming in the United States, a country richly endowed with natural and human resources, and one benefiting from a geography that encompasses many climate zones. Compared to many other countries, the United States is well situated to respond to greenhouse warming.

This panel does not attempt to view greenhouse warming from the perspective of a country less well endowed. Of course, greenhouse warming is a global phenomenon, and many global aspects must be included in any analysis. Nevertheless, most of the data utilized in this study to evaluate