I = PAT is the lettering of a formula put forward to describe the impact of human activity on the environment.I = P × A × TIn words:Human Impact on the environment equals the product of Population, Affluence, and Technology. This shows how the population, affluence and technology produce an impactThe equation was developed in the 1970s during the course of a debate between Barry Commoner, Paul R. Ehrlich and John Holdren.