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In environmentalism, the concept of overshoot is the belief that the human population, or its resource consumption patterns, has or in the future may rise above the sustainable use of resources. The "overshoot" is that proportion of the population or environmental footprint which must be eliminated in order for human society on Earth to be sustainable.
A decline in population as a consequence of overshoot has been termed 'collapse'. The trajectory undergone by such a population is often termed 'overshoot-and-collapse'.
Overshoot can occur due to lag effects. Reproduction rates may remain high relative to the death rate. Entire ecosystems may be severely affected and sometimes reduced to less-complex states due to prolonged overshoot. The eradication of disease can trigger overshoot when a population suddenly exceeds the land's carrying capacity. An example of this occurred on the Horn of Africa when smallpox was eliminated. A region that had supported around 1 million pastoralists for centuries was suddenly expected to support 14 million people. The result was overgrazing, which led to soil erosion.
Dennis Meadows and Donella Meadows presented their computer-based model of the future of the human population in their 1972 book The Limits to Growth. This study predicted the Earth would reach a carrying capacity of ten to fourteen billion people after some two hundred years, after which the human population would collapse. This simulation modelled human populations after the overshoot and collapse seen in yeast cells in a petri dish. It was highly controversial and generally dismissed as nonsense.
William R. Catton, Jr., a sociologist, wrote about relationships between human societies and their environment, as well as his beliefs that there were too many people and more needed to die, in his 1980 book Overshoot: The Ecological Basis of Revolutionary Change. He wrote that humanity would overshoot Earth's carrying capacity, due to both overpopulation and overconsumption.
The Global Footprint Network purports to be able to measure how much the human economy demands against what the Earth can renew. The Optimum Population Trust (now called Population Matters) has listed what they believe is the overshoot (overpopulation) of a number of countries, based on the above.
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