党英杰Map of countries by population density (See List of countries by population density.)
Areas of high population densities, calculated in 1994.Overpopulation is the condition of any organism's numbers exceeding the carrying capacity of its ecological niche. In common parlance, the term usually refers to the relationship between the human population and its environment, the Earth.
Overpopulation is not simply a function of the size or density of the population, but rather the number of individuals compared to the resources (for example, food production or water resources) needed for survival or well-being. Overpopulation can be determined using the ratio of population to available resources. If a given environment has a population of ten, but there is food or drinking water enough for only nine, then that environment is overpopulated; if the population is 100 individuals but there is food, shelter or water enough for 200, then it is not. Overpopulation can result from an increase in births, a decline in mortality rates due to medical advances, from an increase in immigration, a decrease in em
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igration, or from an unsustainable use and depletion of resources. It is possible for very sparsely-populated areas to be "overpopulated", as the area in question may have a very meager or non-existent capability to sustain human life (e.g. the middle of the Sahara desert or Antarctica).
The resources to be considered when evaluating whether an ecological niche is overpopulated include clean water, clean air, food, shelter, warmth, and other resources necessary to sustain life. If the quality of human life is addressed as well, there are then additional resources to be considered, such medical care, employment, money, education, fuel, electricity, proper sewage treatment, waste management, and transportation. Negative impacts should also be considered including crowding stress and increased pollution. If addressing the environment as a whole, the survival and well-being of species other than humans must also be considered.
Overpopulation is also related to issues of birth control, with some nations like China using strict measures in order to reduce birth rates, while religious and ideological opposit
ion to birth control has been cited as a factor contributing to overpopulation and poverty.[1]
Overpopulation predictions
Main article: Malthusian catastrophe
In An Essay on the Principle of Population (first published in 1798), Thomas Malthus proposed that while resources tend to grow linearly, population grows exponentially. He argued that, if left unrestricted, human populations continue to grow until they would become too large to be supported by the food grown on available agricultural land, causing starvation which then controls population growth. He argued that this had happened many times previously in human history and estimated that this would occur again by the middle of the 19th century. To avoid this happening, Malthus argued for population control through "moral restraint". While arguably he was right about human history up to his time, he made his prediction for the future exactly at the time the industrial revolution and a similar revolution in agriculture caused a very large increase in
available resources. His specific predictions therefore failed because he used a static analysis, and extrapolated his historical numbers into the future without considering factors that could increase the resource base available to humanity faster than he thought, (for example, the revolutions in agriculture at his time or later the Green Revolution), or factors which cause population growth to decline or reverse, (for example, the demographic transition).
On a global scale, since the industrial revolution, food production has grown faster than human population. However, it has been argued that other changes impacting earth's ability to function as a suitable habitat for human beings, such as global warming, desertification, overfishing and other environmental problems caused by industrialization, will eventually affect food production or factors necessary for well-being. Along with continued population growth, this may cause a Malthusian catastrophe.
Among the earlier best-known modern examples of such arguments are The Limits to Growth (1972) and The Population Bomb (1968). These reports have been subjected to c
riticism, and their predicted dates for such catastrophes have been proven false. The Limits to Growth stated that the world would run out of gold by 1981, mercury by 1985, tin by 1987, zinc by 1990, petroleum by 1992, and, copper, lead, and natural gas by 1993. The Population Bomb stated that that there would be a major food shortage in the United States in the 1970s and hundreds of millions of people were going to starve to death, leaving only some 20 million people alive in 1999. [2] [3]. (See Erlich's answer to his critics.)十一届
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名单 David Pimentel claims that population outcomes for the 22nd century range from 2 billion people (characterised as thriving in harmony with the environment), to 12 billion people (characterised as miserable and suffering difficult lives with limited resources and widespread famine). [4]
The book The Little Green Handbook reasons that in 2050 about 7.7 billion people would be expected to suffer from illness, lack of adequate sanitation, hunger, and extreme poverty,[2] provided that the high population estimates of year 2050 are realised.
In his recent book Collapse (2005), Jared Diamond argues that many earlier civilizations have collapsed due to environmental problems, and warns of current environmental problems. However, he also notes many situations in which humans have managed their natural resources well.
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