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I = PAT is the lettering of a formula put forward to describe the impact of human activity on the environment. :I = P × A × T In words: :Human Impact on the environment equals the product of Population, Affluence, and Technology. This shows how the population, affluence and technology produce an impact The equation was developed in the 1970s 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 human population growth. The equation can aid in understanding some of the factors affecting human impacts on the environment, but it has also been cited as one of the primary factors underlying many of the dire environmental predictions of the 1970s by Paul Ehrlich, George Wald, Denis Hayes, Lester Brown, René Dubos, and Sidney Ripley that did not come to pass.〔R Bailey (2000) ''Earth day then and now'', Reason 32(1), 18-28〕 Neal Koblitz classified equations of this type as "mathematical propaganda" and criticized Ehrlich's use of them in the media (e.g. on The Tonight Show) to sway the general public.〔N Koblitz (1981) "Mathematics as Propaganda", in ''Mathematics Tomorrow'', ed. Lynn Steen, pp 111-120.〕 The Kaya identity is closely related to the I = PAT equation. The I = PAT equation is more general, describing an abstract "impact". The Kaya identity describes more clearly the impact of human activity on CO2 emissions. ==Population== In the I=PAT equation, the variable P represents the population of an area, such as the world. Since the rise of industrial societies, human population has been increasing exponentially. This has caused Thomas Malthus and many others to postulate that this growth would continue until checked by widespread hunger and famine (see Malthusian growth model). The United Nations and the US Census Bureau project that world population will increase from 7.0 billion today to about 9.2 billion by 2050.〔(US Census Bureau international popopulation statistics and projections 1950 to 2050 )〕〔(United Nations population projections )〕 These projections take into consideration that population growth has slowed in recent years as women are having fewer children. This phenomenon is believed to be a result of demographic transition in developed nations. As a result, the UN believes that human population might stabilize around 9 billion by 2100.〔 However, since the world population is set to keep rising for the next few decades, this factor of the I=PAT equation will likely keep increasing human impact on the environment for the near future. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「I = PAT」の詳細全文を読む スポンサード リンク
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