• The consequences of environmental change depend as much on the social systems that produce vulnerability as on the biophysical systems that cause environmental change.

  • The consequences of environmental change are strongly dependent on the ability of people and social systems to adapt; consequently, access to economic resources is a key mediator between environmental changes and their impacts.

  • Climate models can be linked to crop models to provide early warnings of famine.

  • Human health may be an important area affected by climate change.

Knowledge is not yet adequate to achieve several goals critical to anticipating the likely consequences of future environmental changes, such as:

  • Developing indicators of vulnerability that are sensitive to regional and social variations.

  • Projecting vulnerability estimates into the future.

  • Linking mesoscale outputs of climate models to regional impacts, taking into account vulnerability and the ability of vulnerable individuals and social systems to adapt.

Impacts of Past and Present Climate Variability

The most noticeable and perhaps most serious effects of long-term climate change may not be slow changes in average temperature or precipitation but rather such extreme events as storms, droughts, heat waves, floods, and wildfires; in some climate change scenarios, epidemics may be the most serious of all the dangers. Because of the importance of such episodes to society, environmental scientists are increasingly attempting to predict changes in the frequency of extreme weather events and to identify the boundary conditions for the spread of disease. Social scientists have explored the impacts of climate variability in historical and archeological studies and in research on the human impacts of climatic natural disasters. These studies have highlighted the importance of understanding vulnerability and adaptation.

Several recent studies suggest links between drought and the collapse of civilizations in Asia and Latin America. For example, the abandonment of settlements in the Andean altiplano and Amazon River basin has been shown to correlate with paleoenvironmental evidence of severe El Niño events.72 A large body of work examines the influence of climatic variations on European and North Atlantic history,73 showing the effects of the Little Ice Age and cooler periods associated with volcanic eruptions and the vulnerabilities of different social systems to those changes. As scientists gain new insights into paleoclimatic variability, rapid climate change, and shifts in decadal circulation patterns, social

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