it has begun to be manifest. Examples include evacuation from areas stricken with flood or drought, food shipments or financial assistance to those remaining in such areas, and development of synthetic substitutes for products previously obtained from extinct species.5

Yet another type of response, sometimes called anticipatory adaptation, aims to improve the robustness of social systems, so that an unchecked environmental change would produce less reduction of values than would otherwise be the case.6 This type of intervention does not alter the rate of environmental change, but it lowers the cost of any adjustments that might become necessary. It can be distinguished, at least in theory, from type H mitigation in that it does not necessarily alter the driving forces of global change. An example is diversification in agricultural systems. Farmers, regions, and countries that rely on a range of crops with different requirements for growth may or may not produce less greenhouse or ozone-depleting gases than monoculturists. But polycultures are more robust in the face of drought, acid deposition, and ozone depletion. There may be crop failure, but only in some crops. Similarly, families and communities that have both agricultural and nonagricultural income are harmed less by the same threats than purely agricultural groups. They have other sources of income and can purchase crops from elsewhere.7

All social systems are vulnerable to environmental change, and modern industrial societies have different vulnerabilities from earlier social forms. Modem societies have built intricate and highly integrated support systems that produce unprecedented material benefits by relying critically on highly specialized outputs of technology, such as petrochemical fertilizers and biocides; hybrid seeds; drugs and vaccines; and the transmission of electricity, oil, and natural gas from distant sources. Although these complex sociotechnical systems contain great flexibility through the operation of global markets, they may have vulnerabilities that reveal themselves in the face of the changes that these systems have helped create. For instance, modern societies have become highly dependent on fossil fuels and vulnerable to a serious disruption of supply or distribution systems. They also support much larger and denser populations than ever before; such populations may be vulnerable to ecological changes affecting the viability of their food supplies.

Evidence from studies of disasters suggests that the poor, who lack diversified sources of income, political influence, and access to centralized relief efforts, tend to be worst off (Erikson, 1978;

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