try? To what extent are multipliers such as annual income or annual distance traveled constant for a country, and to what extent are they contingent on other factors that may change over time, such as the manufacturing intensiveness or energy supply mix of the country's economy or the country's policies on income distribution or energy development?

ECONOMIC GROWTH

Global economic growth, defined as increases in the measured production of the world's goods and services, is likely to continue at a rapid rate well into the future. The human impulse to want more of the material things of life appears to be deep-seated, and the areas of the world in which people are most lacking in material goods are those with the greatest—and most rapidly increasing—population. Assuming United Nations and World Bank projections for world population to double to about 10 billion in about 50 years, with 90 percent or more of that growth occurring in the developing countries of Africa, Asia, and Latin America, and assuming that per capita income grows 2.5 percent and 1.5 percent annually in the developing and developed countries, respectively (a low projection, in both cases, by standards of the last several decades), global economic output would quadruple between 1990 and 2040.

Under these conditions the relative gap between per capita income in developing and developed countries would narrow, but the absolute gap would increase substantially. To the extent that per capita income aspirations in the developing countries are driven by comparison of their incomes with those in developed countries, aspirations for additional income growth in the developing countries may be even stronger in 50 years than they are now.

Increased income or economic activity as measured by such indicators as gross national product is not, of course, equivalent to increased well-being. There is considerable debate in the economic literature on how to measure welfare, focused on such questions as how to count things people value that are not traded in markets and whether expenditures for pollution control should be considered an addition or a subtraction from net welfare (e.g., Daly, 1986; Repetto et al., 1989). Although these questions are very important for analyzing human-environment interactions, most current analyses of the effects of economic growth and environmental quality are based on conventional definitions of economic activity.



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