dramatic shifts in climate have occurred when factors controlling the climate system were changing. This has important implications for future climate in that it suggests that increasing human perturbation of the earth system may make abrupt change more likely.

Some sectors of the economy and ecosystems might be highly sensitive to abrupt climate change. Because the economy is more “managed” than are ecosystems, particularly in the industrial sectors of developed societies such as the United States, the major vulnerability to the effects of abrupt climate change is likely to lie at the intersection of human societies and ecosystems, such as for agriculture, forests, and water systems.

It is important not to be fatalistic about the threats posed by abrupt climate change. Societies have faced both gradual and abrupt climate changes for millennia and have learned to adapt through various mechanisms, such as moving indoors, developing irrigation for crops, and migrating away from inhospitable regions. Nevertheless, because climate change is likely to continue and may even accelerate in the coming decades, denying the likelihood or downplaying the relevance of past abrupt changes could be costly. Societies can take steps to face the potential for abrupt climate change. The committee believes that increased knowledge is the best way to improve the effectiveness of response, and thus that research into the causes, patterns, and likelihood of abrupt climate change can help reduce vulnerabilities and increase our adaptive capabilities. The committee’s research recommendations fall into two broad categories: (1) implementation of targeted research to expand instrumental and paleoclimatic observations, and (2) implementation of modeling and associated analysis of abrupt climate change and its potential ecological, economic, and social impacts. What follows is a discussion of recommended research activities to support these two themes.

IMPROVE THE FUNDAMENTAL KNOWLEDGE BASE RELATED TO ABRUPT CLIMATE CHANGE

Recommendation 1. Research programs should be initiated to collect data to improve understanding of thresholds and nonlinearities in geophysical, ecological, and economic systems. Geophysical efforts should focus especially on modes of coupled atmosphere-ocean behavior, oceanic deepwater processes, hydrology, and ice. Economic and ecological research should focus on understanding nonmarket and environmental issues, initiation of a comprehensive



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