concern responses to actual or anticipated global changes. What will humans do in anticipation of global change to keep it from harming what they value? How will humans respond to actual global changes? What is the likelihood that humans will take no organized action at all in response to particular global changes, and what would be the consequent effects on human welfare? To answer such questions, natural and social scientists need to work together.

HUMAN CAUSES OF GLOBAL CHANGE

Almost all human activity has some potential relevance to global change. Researchers in a number of fields have studied human-environment interactions, usually within the boundaries of single disciplines and almost always below the global level. They have demonstrated that a complex of social, political, economic, technological, and cultural variables, sometimes referred to as driving forces, influences the human activities that proximately cause global change. The driving forces can be roughly classified as follows:

  • Population Growth Each person makes some demand on the environment for the essentials of life—food, water, clothing, shelter, and so on. If all else is equal, the greater the number of people, the greater the demands placed on the environment for the provision of resources and the absorption of waste and pollutants. However, all else is not equal. For example, a new individual with the standard of living and technological base of an average North American would use about 35 times as much energy as an individual living at India's average standard—with a roughly proportional impact on the global environment.

  • Economic Growth For the first time in human history, economic activity is so extensive that it produces environmental change at the global level; the prospect of further economic growth arouses concern about the quality of the global environment. Economic growth necessarily stresses the environment, but the amount of stress from a given amount of economic growth depends, among other things, on the pattern of goods and services produced, the population and resource base for agricultural development, forms of national political organization, and development policies.

  • Technological Change Technology can influence environmental change by finding new ways to discover and exploit natural resources or by changing the volume of resources required—or the



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