Overshoot (population)

In environmental science, a population overshoots its local carrying capacity—the maximum population size that an ecosystem can sustainably support—when it exceeds the availability of resources needed for survival. This can lead to a population crash if resources are depleted faster than they can regenerate. Overshoot applies to humans as well as other animal populations: any species that relies on consumption of resources to survive. Environmental science studies to what extent human populations through their resource consumption have risen above the sustainable use of resources. For people, "overshoot" is that portion of their demand or ecological footprint which must be eliminated to be sustainable, or the delta between a sustainable population and what we currently have. Excessive demand leading to overshoot is driven by both consumption and population. Population decline due to overshoot is known as 'collapse'. The path taken by such a population is referred to as 'overshoot-and-collapse'. Collapse, like overshoot, can occur due to various factors, with the Malthusian catastrophe being a specific but not identical case. Overshoot can happen as a result of delayed impacts, where reproduction rates persistently surpass the death rate. This can lead to significant consequences, with entire ecosystems being profoundly impacted and sometimes simplified due to prolonged overshoot. An instance of this phenomenon took place in the Horn of Africa when smallpox was eradicated, causing a sudden increase in the population that exceeded the region's carrying capacity. For centuries, the land had sustained approximately 1 million pastoralists, but with the elimination of the disease, the population suddenly grew to 14 million people. Consequently, overgrazing occurred, leading to soil erosion. The most famous example of an overshoot-and-crash may be from St. Matthew Island. In 1944, 29 reindeer were introduced to the island, which by 1963 had grown to a peak population of roughly 6000 individuals — well past the estimated carrying capacity. At next count, in 1965, the population had plummeted and only 42 reindeer were left alive. Thomas Malthus (1766-1864) is perhaps the most well-known writer to have articulated the roots of the modern concept of human overshoot, with The Population Bomb (1967) by Paul Ehrlich reigniting the hotly-debated topic in more recent history. Daniel Quinn claims to have modernized the concept of human overpopulation in what are likely the most well-read volumes to have given it extensive treatment as a subject of ecology: The Story of B (1996) and My Ishmael (1997).

Human overshoot

The 1972 book The Limits to Growth discussed the limits to growth of society as a whole. This book included a computer-based model which predicted that 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. The model was based on five variables: "population, food production, industrialization, pollution, and consumption of non-renewable natural resources". This simulation modelled human populations after the overshoot and collapse seen in all unmoderated species. It was controversial and generally dismissed by economists. Sociologist William R. Catton, Jr. explored the connections between human societies and the natural environment in his book Overshoot published in 1980. Catton expressed his concerns about the global population exceeding Earth's sustainable limits, advocating that a reduction in population through natural means, such as mortality, was necessary. He argued that the predicament stemmed from both overpopulation, where the number of people surpassed what the planet could support, and overconsumption, referring to the excessive utilization of resources. Catton predicted that unless these issues were addressed, humanity would surpass the Earth's optimal carrying capacity, leading to potentially dire consequences. 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. In one study published in January 2021 in Frontiers in Conservation Science, the significance of overshoot is discussed. It says that alongside the growth of the global population, humanity's consumption relative to Earth's regenerative capacity has surged by 73% in 1960 to 170% in 2016, particularly in countries with higher incomes. These findings are based on recent ecological footprint studies. An article in Frontiers in Conservation Science also says ecological overshoot has been facilitated by the increasing reliance on fossil fuels. The widespread use of convenient energy sources has allowed human demand to detach from the limits of biological regeneration. Notably, fossil fuels account for 85% of commercial energy production, 65% of fiber production, and serve as the primary raw material for most plastics. As a possible cause for societal collapse, overshoot has been scholarly discussed, but has not been found having been the cause for historic cases of collapse.

Predictions of scarcity

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