방법 비교

	Ecological Footprint Analysis	IPAT Decomposition
분야	Environmental Sociology	Environmental Sociology
계열	Process / pipeline	Process / pipeline
기원 연도	1996	1971
창시자	Mathis Wackernagel & William E. Rees	Paul R. Ehrlich & John P. Holdren (IPAT); Yoichi Kaya (Kaya identity)
유형	Bioproductive-area accounting pipeline for human demand versus biocapacity	Multiplicative accounting identity and decomposition of environmental impact
원전	Wackernagel, M., & Rees, W. E. (1996). Our Ecological Footprint: Reducing Human Impact on the Earth. New Society Publishers. ISBN: 9780865713123	Ehrlich, P. R., & Holdren, J. P. (1971). Impact of Population Growth. Science, 171(3977), 1212-1217.
별칭	Ecological Footprint Accounting, Footprint-Biocapacity Accounting, Wackernagel-Rees Footprint, EF Analysis	IPAT Identity, Ehrlich-Holdren Identity, Kaya Identity Decomposition, Impact Equation
관련	4	4
요약	Ecological footprint analysis measures human demand on nature by translating the resources a population consumes and the wastes it generates into the area of biologically productive land and sea required to supply them. Introduced by Mathis Wackernagel and William Rees in their 1996 book Our Ecological Footprint, the method expresses both demand (the footprint) and supply (biocapacity) in a common unit, the global hectare, so that the two can be compared directly. When a population's footprint exceeds the biocapacity available to it, the difference is an ecological deficit, and at the planetary scale a persistent deficit signals overshoot of the biosphere's regenerative capacity. The 2002 analysis by Wackernagel and colleagues operationalized this accounting at the global level, estimating that humanity moved from using about 70 percent of the biosphere's capacity in 1961 to roughly 120 percent by the late 1990s. The carbon component, the area of forest needed to sequester fossil-fuel emissions, is typically the largest and fastest-growing share. Footprint analysis is thus a sustainability accounting tool that renders an abstract idea, living within ecological limits, into a single comparable balance sheet.	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.