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A Malthusian catastrophe (also known as Malthusian check) is a prediction of a forced return to subsistence-level conditions once population growth has outpaced agricultural production. ==Thomas Malthus== In 1779, Thomas Malthus wrote: Notwithstanding the apocalyptic image conveyed by this particular paragraph, Malthus himself did not subscribe to the notion that mankind was fated for a "catastrophe" due to population overshooting resources. Rather, he believed that population growth was generally restricted by available resources: ==Neo-Malthusian theory== After World War II, mechanized agriculture produced a dramatic increase in productivity of agriculture and the Green Revolution greatly increased crop yields, expanding the world's food supply while lowering food prices. In response, the growth rate of the world's population accelerated rapidly, resulting in predictions by Paul R. Ehrlich, Simon Hopkins,〔 〕 and many others of an imminent Malthusian catastrophe. However, populations of most developed countries grew slowly enough to be outpaced by gains in productivity. By the early 21st century, many technologically developed countries had passed through the demographic transition, a complex social development encompassing a drop in total fertility rates in response to lower infant mortality, increased urbanization, and a wider availability of effective birth control, causing the demographic-economic paradox. On the assumption that the demographic transition is now spreading from the developed countries to less developed countries, the United Nations Population Fund estimates that human population may peak in the late 21st century rather than continue to grow until it has exhausted available resources.〔(【引用サイトリンク】title=2004 UN Population Projections, 2004. )〕 Historians have estimated the total human population back to 10,000 BC. The figure on the right shows the trend of total population from 1800 to 2005, and from there in three projections out to 2100 (low, medium, and high).〔 The graph of annual growth rates (at the top of the page) shows the annual growth rate over the same period. If population growth were exactly exponential, then the growth rate would be a flat line. The fact that it was increasing from 1920 to 1960 indicates faster-than-exponential growth over this period. However, the growth rate has been decreasing since then, and is projected to continue decreasing. The United Nations population projections out to 2100 (the red, orange, and green lines) show a possible peak in the world's population occurring by 2040 in the first scenario, and by 2100 in the second scenario, and never ending growth in the third. The graph of annual growth rates (at the top of the page) does not appear exactly as one would expect for long-term exponential growth. For exponential growth it should be a straight line at constant height, whereas in fact the graph from 1800 to 2005 is dominated by an enormous hump that began about 1920, peaked in the mid-1960s, and has been steadily eroding away for the last 40 years. The sharp fluctuation between 1959 and 1960 was due to the combined effects of the Great Leap Forward and a natural disaster in China.〔 Also visible on this graph are the effects of the Great Depression, the two world wars, and possibly also the 1918 flu pandemic. Though short-term trends, even on the scale of decades or centuries, cannot prove or disprove the existence of mechanisms promoting a Malthusian catastrophe over longer periods, the prosperity of a major fraction of the human population at the beginning of the 21st century, and the debatability of ecological collapse made by Paul R. Ehrlich in the 1960s and 1970s, has led some people, such as economist Julian L. Simon, to question its inevitability.〔Simon, Julian L, "(More People, Greater Wealth, More Resources, Healthier Environment )", ''Economic Affairs: J. Inst. Econ. Affairs'', April 1994.〕 A 2004 study by a group of prominent economists and ecologists, including Kenneth Arrow and Paul Ehrlich〔Arrow, K., P. Dasgupta, L. Goulder, G. Daily, P. Ehrlich, G. Heal, S. Levin, K. Mäler, S. Schneider, D. Starrett and B. Walker, "Are We Consuming Too Much" ''Journal of Economic Perspectives'', 18(3), 147-172, 2004.〕 suggests that the central concerns regarding sustainability have shifted from population growth to the consumption/savings ratio, due to shifts in population growth rates since the 1970s. Empirical estimates show that public policy (taxes or the establishment of more complete property rights) can promote more efficient consumption and investment that are sustainable in an ecological sense; that is, given the current (relatively low) population growth rate, the Malthusian catastrophe can be avoided by either a shift in consumer preferences or public policy that induces a similar shift. However, some contend that the Malthusian catastrophe is not imminent. A 2002 study〔(World agriculture 2030: Global food production will exceed population growth ) August 20, 2002.〕 by the UN Food and Agriculture Organization predicts that world food production will be in excess of the needs of the human population by the year 2030; however, that source also states that hundreds of millions will remain hungry (presumably due to economic realities and political issues). 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「Malthusian catastrophe」の詳細全文を読む スポンサード リンク
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