To estimate the potential effects of global warming on the world's food system, agronomists and economists linked the output of climate models to crop yield and economic models.⁸ Figure 7.1 shows several important results of these studies, including the sensitivity of impact assessments to the results of different climate models, the considerable potential for adaptation to alter the impact of climate change, and the relative vulnerability of developing countries.

Also important to the IPCC and other assessments are efforts to calculate the costs and benefits of various mitigation strategies, such as carbon taxes and carbon sequestration through reforestation, including estimates of nonmarket values. For example, the estimated costs of a carbon tax to achieve a 20 percent reduction in CO₂ emissions ranged from $50 to $330 per ton of carbon in the IPCC study,⁹ depending on the economic assumptions and model used. Forest plantations and forest management have the potential to sequester up to 75 billion tons of carbon a year.¹⁰ Studies of the economic feasibility of this strategy have been used as a basis for discussions in the negotiations for the Framework Convention on Climate Change and have informed debate on strategies such as joint implementation of carbon reductions through aid for forest and energy efficiency projects.

Also considered by the IPCC was the issue of deforestation in Amazonia, where human dimensions research has informed policy decisions in Amazonian nations, especially Brazil, and in international organizations such as the World Bank. In the late 1980s international attention focused on Amazonia, where rapid deforestation was linked to climate change, loss of biodiversity, and threats to indigenous peoples.¹¹ Human dimensions research revealed the causes of forest destruction; for example, the building of highways opened the forest to migrants, many of whom did not know how to farm cleared land or manage forests sustainably.¹² Biases in agricultural subsidies, tax incentives, and high inflation promoted extensive land clearing for ranching.¹³ Detailed social and spatial analyses of relationships among deforestation, secondary growth, and demo-