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IPAT (I=P*A*T) describes how Population, Affluence, and Technology contribute to environmental Impact.

The equation was developed in the 1970's 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 population growth.[1]


I = Human Impact on the natural environment
P = Population
A = Affluence - consumption per capita
T = Technology - environmental impact per unit of consumption


The I, or impact, refers to the impacts of a given course of action or decision on the environment (locally, regionally or globally).

The P, or population, relates to the relevant human population for the environmental problem in question (locally, regionally or globally).

The A, or affluence, concerns the level of consumption of environmental resources per person.

The T, or technology, is a general term for technology and its environmental impact per unit of consumption. It can mean any human-created invention, system or organisation that has a consequence of either worsening or uncoupling the consumption from the environmental impact.

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  1. O'Neill et al. 2004. Population, Greenhouse Gas Emissions and Climate Change. Essay in book: Lutz W. et al (editors). 2004. The End of Population Growth in the 21st Century London: Earthscan