amount or kind of wastes produced—per unit of output. Technologies may either increase or decrease the impact of human activity on the environment, depending on the other driving forces, which determine which technologies are developed and used.

  • Political-Economic Institutions The global environment responds to the actions of markets, governments, and the international political economy. Markets are always imperfect, and the impact of economic activity on the environment depends on which imperfect-market method of environmental management is being used. Governmental structure and policies can also have significant environmental consequences, both intentional and inadvertent. And the international political economy, with its global division of labor and wealth, can promote environmental abuses, particularly in the Third World. The effects depend on policy at the national level and on the behavior of particular economic actors.

  • Attitudes and Beliefs Beliefs, attitudes, and values related to material possessions and the relation of humanity and nature are often seen as lying at the root of environmental degradation. Such attitudes and beliefs probably have their greatest independent effects over the long-term, on the time scale of human generations or more. Within single lifetimes, attitudes and beliefs can have significant influence on resource-using behavior, even when social-structural and economic variables are held constant.

Although each of these driving forces is important at certain times and under certain conditions, much remains unknown about what determines their relative importance, how they affect each other, and how the driving forces in particular places combine to produce global effects. For example, various combinations of social conditions may lead to a single outcome, such as deforestation.

Single-factor explanations of the anthropogenic sources of global environmental change are apt to be misleading, because the driving forces of global change generally act in combination with each other and the interactions are contingent on place, time, and level of analysis. Understanding the linkages is a major scientific challenge that will require developing new interdisciplinary teams. The research effort should include studies at both global and lower geographic levels, with strong emphasis on comparative studies at local or regional levels with worldwide representation. Research should address the same question at different time scales, examine the links between levels of analysis and between time scales, and explore the ways that the human forces that cause environmental change may also be affected by it.

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