I = PAT

I = PAT is the lettering of a formula put forward to describe the impact of human activity on the environment.

I = P × A × T

In words:

Human Impact (I) on the environment equals the product of P= Population, A= Affluence, T= Technology. This describes how our growing population, affluence, and technology contribute toward our environmental impact.

The equation was developed in the 1970s during the course of a debate between Barry Commoner, Paul R. Ehrlich and John Holdren. Commoner argued that environmental impacts in the United States were caused primarily by changes in its production technology following World War II, while Ehrlich and Holdren argued that all three factors were important and emphasized in particular the role of human population growth. (PR Ehrlich, JP Holdren, Impact of population growth, Science, 1971).

The equation can aid in understanding some of the factors affecting human impacts on the environment.