I = impact on the environment
P = number of people
A = amount of resources consumed by each person (or per capita affluence)
T = environmental damage caused by producing or extracting those resources ("T" for technology)
Thus, human impact on the environment is a function of the population size, the level of resource use, and the environmental impacts associated with obtaining and using those resources. This formulation (described in the article by Daily and Ehrlich on the supplementary readings list in the Study Guide ) suggests that no one factor alone is responsible for our environmental problems. The relative importance of the various factors will differ depending on the particular problem.
Optional excercise: think of environmental problems for which each term is predominant. For example, for the case of damage wrought by a nuclear explosion, the environmental impact is fairly independent of the number of people living in the area and of their affluence, with the "T" term predominant. Which terms do you think are most important for the impact of the United States on the global environment? How about that of India?
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