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An equation (I = P × A × T) that was developed by Paul Ehrlich and John Holdren in 1972 to describe how impact (I) or environmental change is a function of population size (P), affluence (A), and technology (T). Although the I = PAT formula is a useful way of studying the relationship between factors that govern environmental change, critics have pointed to two important weaknesses in this sort of approach. First, the factors contributing to any particular impact can vary a great deal, depending on the environmental impact in question (for example, different factors contribute to depletion of the ozone layer and to loss of biodiversity). Secondly, the equation suggests that the three factors (P, A, and T) operate independently, whilst in reality they may well interact with each other.

Subjects: Environmental Science.

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