there is a need to be especially supportive of studies dealing with time scales of decades to centuries. Studies oriented to time scales of a decade or less are likely to focus on factors such as short-term fluctuations in public opinion, the impact of business cycles, and the introduction of particular public policies (for example, favorable tax treatment accorded to ranchers in Brazil). Studies framed in terms of time scales of decades to centuries, by contrast, will focus on different classes of events, such as the Industrial Revolution, long-term patterns of urbanization, and the gradual evolution of systems of private property rights. We believe that studies of shorter-term phenomena have an important place in improving understanding of the human dimensions of global change. Nonetheless, we are convinced that there is a compelling case for devoting more attention to the longer time scales in analyzing the human dimensions of global change. By and large, modern work in the social sciences has paid far more attention to short time scales. Yet global change is intrinsically a historical phenomenon that calls for an examination of long-term changes in human systems as well as environmental systems.

1e: There is a need to support studies that compare interventions at different points in the cycle of human-environment relationships and make empirical assessments of their relative effects. Human responses to global changes vary on several important dimensions. There are significant differences, for example, between responses to actual and anticipated changes and between deliberate and incidental responses. In addition, there are numerous points in the cycle of interactions between human systems and environmental systems at which humans can intervene to protect their values. Chapter 4 differentiates among three types of mitigation and among blocking, adjustment, and efforts to enhance the robustness of social systems. Research on the human dimensions of global change should seek both to identify the factors that determine when humans will opt for one or another of these responses and to assess the benefits, costs, and unanticipated effects of different types of responses in a variety of socioeconomic and political settings.

1f: Research should make a systematic effort to compare and contrast human responses at different levels of social organization. Responses to changes in environmental systems by individuals, corporations, communities, and countries may vary in terms of both the ease with which they are initiated and the consequences of pursuing them. Different types of responses may also be available at various levels of social organization. There is

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