I = PAT

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I = (PAT) is the mathematical notation of a formula put forward to describe the impact of human activity on the environment.

I = P × A × T

The expression equates human impact on the environment to a function of three factors: population (P), affluence (A) and technology (T).^[1] It is similar in form to the Kaya identity, which applies specifically to emissions of the greenhouse gas carbon dioxide.

The validity of expressing environmental impact as a simple product of independent factors, and the factors that should be included and their comparative importance, have been the subject of debate among environmentalists. In particular, some have drawn attention to potential inter-relationships among the three factors; and others have wished to stress other factors not included in the formula, such as political and social structures, and the scope for beneficial, as well as harmful, environmental actions.