tional Research Council, 1990b). Other interdisciplinary efforts sponsored by the International Federation of Institutes for Advanced Studies, the International Social Science Council, and other groups have also involved social scientists in the study of global change.

In this book, we use the term social science to cover a broad range of research activities usually associated with disciplines such as economics, sociology, political science, psychology, anthropology, geography, and history and interdisciplinary fields such as policy science, human ecology, and management. Social science involves the systematic study of the behavioral processes of individuals and social groups, organizations, and institutions. Our use of the term includes activities that are sometimes characterized as behavioral science.

Natural scientists interested in global change sometimes harbor false expectations about the contributions social scientists can make to understanding of global change. But the important point is that the U.S. global change community is now remarkably receptive to input from the social sciences. It is consequently time for social scientists to take seriously the challenge of mapping a strategy to add to knowledge of global environmental change.

GLOBAL CHANGE AND ENVIRONMENTAL SYSTEMS

Global environmental changes are alterations in natural (e.g., physical or biological) systems whose impacts are not and cannot be localized. Sometimes the changes in question involve small but dramatic alterations in systems that operate at the level of the whole earth, such as shifts in the mix of gases in the stratosphere or in levels of carbon dioxide and other greenhouse gases throughout the atmosphere. We speak of global change of this sort as systemic in nature because change initiated by actions anywhere on earth can directly affect events anywhere else on earth. Other times, the changes in question result from an accretion of localized changes in natural systems, such as loss of biological diversity through habitat destruction and changes in the boundaries of ecosystems resulting from deforestation, desertification or soil drying, and shifting patterns of human settlement. Global changes of this sort we describe as cumulative in nature; we consider them global because their effects are worldwide, even if the causes can be localized (for further exposition of the concepts of systemic and cumulative global change, see Turner et al., 1991b). The boundary between systemic and cumulative change



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