Compare methods

	IPAT Decomposition	Social Metabolism Analysis
Field	Environmental Sociology	Environmental Sociology
Family	Process / pipeline	Process / pipeline
Year of origin	1971	1998
Originator	Paul R. Ehrlich & John P. Holdren (IPAT); Yoichi Kaya (Kaya identity)	Marina Fischer-Kowalski (Vienna School of Social Ecology)
Type	Multiplicative accounting identity and decomposition of environmental impact	Biophysical accounting pipeline for society's material and energy flows
Seminal source	Ehrlich, P. R., & Holdren, J. P. (1971). Impact of Population Growth. Science, 171(3977), 1212-1217.	Fischer-Kowalski, M. (1998). Society's Metabolism: The Intellectual History of Materials Flow Analysis, Part I, 1860-1970. Journal of Industrial Ecology, 2(1), 61-78.
Aliases	IPAT Identity, Ehrlich-Holdren Identity, Kaya Identity Decomposition, Impact Equation	Societal Metabolism Analysis, Material and Energy Flow Analysis (MEFA), Socio-Economic Metabolism, Social Metabolism Accounting
Related	4	4
Summary	IPAT decomposition expresses environmental impact as the product of three factors, population, affluence, and technology, providing a simple accounting framework for attributing degradation to its proximate human drivers. The identity was crystallized in the debate between Paul Ehrlich, John Holdren, and Barry Commoner around 1971, with Ehrlich and Holdren's Science article on the impact of population growth a foundational statement. In the equation, affluence is output per person and technology is impact per unit of output, so the three factors multiply back exactly to total impact, making IPAT a definitional identity rather than an empirical claim. Its best-known specialization, the Kaya identity, decomposes carbon emissions into population, GDP per capita, energy intensity of output, and carbon intensity of energy, and underpins much emissions-scenario work. By taking growth rates, IPAT also yields a clean additive decomposition that apportions the change in impact among its drivers. Because the identity assumes each factor contributes proportionally, it was the stimulus for the stochastic STIRPAT model, in which Dietz and Rosa relaxed that assumption to test the drivers statistically.	Social metabolism analysis studies a society as if it were a living organism that takes in materials and energy from nature, transforms them, builds up stocks, and excretes wastes and emissions, characterizing this biophysical throughput through systematic accounting. The concept and its intellectual lineage were synthesized by Marina Fischer-Kowalski and colleagues at the Vienna School of Social Ecology in their two-part 1998 history of materials flow analysis, which traced the metabolism metaphor from nineteenth-century thinkers to its modern, quantitative form. The method draws a boundary around a socio-economic system, a country, region, or city, and accounts for the materials and energy entering it through domestic extraction and imports, the stocks accumulated in buildings and infrastructure, and the outputs released as wastes, emissions, and exports. Mass and energy balances ensure the accounts are internally consistent, yielding indicators such as domestic material consumption and per-capita material flow that describe the scale and structure of a society's resource use. By comparing throughput to economic output over time, the analysis examines whether economies are decoupling growth from material and energy use. Social metabolism is a foundational framework in social ecology and industrial ecology for assessing biophysical sustainability.