ABSTRACT

The impact an economy has on the environment depends on the number of people, what and how much each one consumes, and the natural resources required for the production of the goods and services consumed. Ecological economists use the so-called IPAT equation in order to highlight the impact as a function of these three variables, all of which have changed dramatically during the last 200 years. The IPAT equation is also called the Commoner-Ehrlich equation after two pioneers – Paul Ehrlich and Barry Commoner – who at the beginning of the 1970s discussed the environmental impact of different factors: What was the role of population growth, economic growth, and changes in technology? The equation is:

I = P × A × T

where:

I stands for environmental impact P stands for population A stands for consumption per capita or affl uence T stands for throughput – natural resources – used per unit of consumption; it is largely dependent on the technology used in the production of goods and services

Population is measured in numbers. Affl uence is usually measured as income or consumption in monetary units per capita. Throughput is measured in physical units – e.g. tonnes, cubic feet, hectares – of natural resources that are used up in relation to income or consumption.