The IPAT equation is a thought model that expresses how humans (negatively) impact the environment. The precise equation has been debated by notable thinkers and environmentalists, but it is generally agreed that impact is some function of population, affluence, and technology where the definition of the terms for population, affluence, and technology have also been debated. Historically, the IPAT equation was used to direct attention towards one of the key causes of impact, thereby highlighting a single political solution e.g. Ehrlich and Holdren thought that population is the key driver of impact and therefore limiting population growth is central to mitigating impact. As of 2000 (when this review article was written), the IPAT equation had instead led to a singular focus on technology innovation to pursue sustainability.
This singular focus on technology innovation has been described as technological optimism, or the belief that technological improvements is central to long-term sustainability. The IPAT equation suggests that impact is a function of population, affluence, and technology; it is then inferred that population will continue to increase and so will affluence. This inference is reinforced by 1) the fact that population is ever-increasing, and 2) the idea that greater affluence is (bluntly) associated with improved quality of life, and in general, improving quality of life for all is assumed to be a good thing. If we then take for granted that both terms population (P) and affluence (A) are increasing, then we are left to minimize technology (T) to mitigate impact (I). But is this technological optimism, or technological resignation?
Technological optimism is the basis of industrial ecology. Industrial ecology adopted a variant of the IPAT equation as its “master equation,” where the T term is expressed as “environmental impact per unit of per capita GDP.” In industrial ecology, emphasis has been placed in minimizing the environmental impact per unit of per capita GDP, or by improving the productivity of resources used in the economy. This emphasis on technological efficiency is best characterized by the conversations around Factor X, which is the idea that innovation can improve the economic productivity of natural resources by some factor (e.g. 4, 10, 50). The Factor X conversations have only a theoretical basis, but still have influenced policy decisions in various European countries.
While industrial ecology sought mitigation of impact through technological innovation, there has been a general lack of focus in mitigating impact through management of affluence because of potential ethical considerations. One can (should?) easily idealize the pursuit of a basic quality of life for all. It is this idealization that has justified a lack of emphasis in mitigating impact via the affluence term, GDP per capita, in the IPAT equation even thought it has also been acknowledged that GDP is a totally inadequate term for measuring quality of life. The IPAT equation could be a constructive way to discuss the environmental impact of inequity, consumerism, and capitalism – but only if the affluence term were disaggregated into separate terms that better describe a basic quality of living and everything else supplementary to that basic standard.
Analogous to the rise of industrial ecology to address the role of technology in sustainable development, did the Ehrlich/Holdren-Commoner debate lead to work on managing population and affluence in the social sciences? If no, should it have?
Chertow, M.R. (2000). “The IPAT Equation and Its Variants.” Journal of Industrial Ecology. 4 (4):13-20