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Sustainable population refers to a proposed sustainable human population of Earth or a particular region of Earth, such as a nation or continent.

When evaluating global population, estimates vary widely, with estimates based on different figures ranging from 0.65 billion people to 98 billion, with 8 billion people being a typical estimate. Projections of population growth, evaluations of overconsumption and associated human pressures on the environment have led to some to advocate for what they consider a sustainable population. Proposed policy solutions vary, including sustainable development, female education, family planning and broad human population planning.

Estimates

Many studies have tried to estimate the world's sustainable population for humans, that is, the maximum population the world can host.[1] A 2004 meta-analysis of 69 such studies from 1694 until 2001 found the average predicted maximum number of people the Earth would ever have was 7.7 billion people, with lower and upper meta-bounds at 0.65 and 98 billion people, respectively. They conclude: "recent predictions of stabilized world population levels for 2050 exceed several of our meta-estimates of a world population limit".[2] A 2012 United Nations report summarized 65 different estimated maximum sustainable population size and the most common estimate was 8 billion.[3][4]

Advocates of reduced population often put forward much lower numbers. Paul R. Ehrlich stated in 2018 that the optimum population is between 1.5 and 2 billion.[5] Geographer Chris Tucker estimates that 3 billion is a sustainable number.[6] The Georgia Guidestones recommend 500 million. There are other estimates, often of a number less than 8 billion.[7][8]

Critics of overpopulation criticize the basic assumptions associated with these estimates. For example, Jade Sasser believes that calculating a maximum of number of humanity which may be allowed to live while only some, mostly privileged European former colonial powers, are mostly responsible for unsustainably using up the Earth, is wrong.[9]

Overshoot

Main articles: Overshoot (population) § Human overshoot, Overconsumption, Human overpopulation, and Malthusian catastrophe

Predictions of scarcity

See also: Water scarcity
Greater Los Angeles lies on a coastal mediterranean savannah with a small watershed that is able to support at most one million people on its own water; as of 2015, the area has a population of over 18 million. Researchers predict that similar cases of resource scarcity will grow more common as the world population increases.[10]

In his 1798 work An Essay on the Principle of Population, the British scholar Thomas Malthus incorrectly predicted that continued population growth would exhaust the global food supply by the mid-19th century. Malthus wrote the essay to refute what he considered the unattainable utopian ideas of William Godwin and Marquis de Condorcet, as presented in Political Justice and The Future Progress of the Human Mind. In 1968, Paul R. Ehrlich reprised Malthus' argument in The Population Bomb, predicting that mass global famine would occur in the 1970s and 1980s.[11]

The predictions of Ehrlich and other neo-Malthusians were vigorously challenged by a number of economists, notably Julian Lincoln Simon, and advances in agriculture, collectively known as the Green Revolution, forestalled any potential global famine in the late 20th century. Between 1950 and 1984, as the Green Revolution transformed agriculture around the world, grain production increased by over 250%.[12] The world population has grown by over four billion since the beginning of the Green Revolution, but food production has so far kept pace with population growth. Most scholars believe that, without the Revolution, there would be greater levels of famine and malnutrition than the UN presently documents.[13] However, neo-Malthusians point out that fossil fuels provided the energy for the Green Revolution, in the form of natural gas-derived fertilizers, oil-derived pesticides, and hydrocarbon-fueled irrigation, and that many crops have become so genetically uniform that a crop failure in any one country could potentially have global repercussions.[14]

In May 2008, the price of grain was pushed up severely by the increased cultivation of biofuels, the increase of world oil prices to over $140 per barrel ($880/m3),[15] global population growth,[16] the effects of climate change,[17] the loss of agricultural land to residential and industrial development,[18][19] and growing consumer demand in the population centres of China and India.[20][21] Food riots subsequently occurred in some countries.[22][23] However, oil prices then fell sharply. Resource demands are expected to ease as population growth declines, but it is unclear whether mass food wastage and rising living standards in developing countries will once again create resource shortages.[24][25]

David Pimentel, professor of ecology and agriculture at Cornell University, estimates that the sustainable agricultural carrying capacity for the United States is about 200 million people; its population as of 2015 is over 300 million.[26] In 2009, the UK government's chief scientific advisor, Professor John Beddington, warned that growing populations, falling energy reserves and food shortages would create a "perfect storm" of shortages of food, water, and energy by 2030.[10][27] According to a 2009 report by the United Nations Food and Agriculture Organization (FAO), the world will have to produce 70% more food by 2050 to feed a projected extra 2.3 billion people.[28]

The observed figures for 2007 showed an actual increase in absolute numbers of undernourished people in the world, with 923 million undernourished in 2007, versus 832 million in 1995.[29] The 2009 FAO estimates showed an even more dramatic increase, to 1.02 billion.[30]

Human impact on the environment

Illegal slash-and-burn agriculture in Madagascar, 2010

A number of scientists have argued that the looming human impact on the environment and accompanying increase in resource consumption threatens the world's ecosystem and the survival of human civilization.[31][32][33][34] The InterAcademy Panel Statement on Population Growth, which was ratified by 58 member national academies in 1994, states that "unprecedented" population growth aggravates many environmental problems, including rising levels of atmospheric carbon dioxide, global warming, and pollution.[35] Indeed, some analysts claim that overpopulation's most serious impact is its effect on the environment.[36]

Scientists contend that human overpopulation, continued human population growth and overconsumption, particularly by the wealthy, are the primary drivers of mass species extinction.[37][38][39][40] By 2050 population growth, along with profligate consumption, could result in oceans containing more plastic than fish by weight.[39] In November 2017, the World Scientists' Warning to Humanity: A Second Notice, signed by 15,364 scientists from 184 countries, asserted that rapid human population growth is the "primary driver behind many ecological and even societal threats."[41] African wildlife populations are declining significantly as growing human populations encroach on protected ecosystems, such as the Serengeti.[42] The Global Assessment Report on Biodiversity and Ecosystem Services, released by IPBES in 2019, states that human population growth is a factor in biodiversity loss.[43][44] According to a 2020 World Wildlife Fund Living Planet Report and its Living Planet Index, global wildlife populations have plummeted by 68% since 1970 as a result of overconsumption, population growth and intensive farming, which experts assert is further evidence that humans have unleashed a sixth mass extinction event on earth.[45][46]

According to influential biologist E. O. Wilson, who asserts that human population growth and the forces it multiplies, including habitat destruction, pollution and overharvesting, are destructive to the planet's biodiversity:

The pattern of human population growth in the 20th century was more bacterial than primate. When Homo sapiens passed the six billion mark, we had already exceeded perhaps as much as 100 times the biomass of any large animal species that had ever existed on the land. We and the rest of life cannot afford another 100 years like that.[47]

Having one less child, on average, saves 58.6 tonnes of CO2 equivalent per year.

A July 2017 study published in Environmental Research Letters argued that the most significant way individuals could mitigate their own carbon footprint is to have fewer children, followed by living without a vehicle, foregoing air travel, and adopting a plant-based diet.[48] According to said study, having one less child would save 24 times more CO2e than living car free.

Human population planning

A government sign in China: "For a prosperous, powerful nation and a happy family, please practice family planning."

Human population planning is the practice of intervening to alter the rate of population growth. Historically, human population control has been implemented by limiting a region's birth rate, by voluntary contraception or by government mandate. It has been undertaken as a response to factors including high or increasing levels of poverty, environmental concerns, and religious reasons. The use of abortion in some population control strategies has caused controversy,[49] with religious organizations such as the Roman Catholic Church explicitly opposing any intervention in the human reproductive process.[50]

The University of Nebraska publication Green Illusions argues that population control to alleviate environmental pressures need not be coercive. It states that "Women who are educated, economically engaged, and in control of their own bodies can enjoy the freedom of bearing children at their own pace, which happens to be a rate that is appropriate for the aggregate ecological endowment of our planet."[51] The book Fatal Misconception by Matthew Connelly similarly points to the importance of supporting the rights of women in bringing population levels down over time.[52] Paul Ehrlich also advocates making "modern contraception and back-up abortion available to all and give women full equal rights, pay and opportunities with men," noting that it could possibly "lead to a low enough total fertility rate that the needed shrinkage of population would follow. [But] it will take a very long time to humanely reduce total population to a size that is sustainable." Ehrlich places the optimum global population size at 1.5 to 2 billion people.[53]

Other academicians and public figures have pointed to the role of agriculture and agricultural productivity of increasing human carrying capacity, which results in population overshoot, as with any other species when their food supply experiences an increase, which in turn results in resource depletion and mass poverty and starvation in the case of humans.[54][55][56][57]

Carrying capacity

Urbanization in Seattle, Washington, United States

Talk of economic and population growth leading to the limits of Earth's carrying capacity for humans are popular in environmentalism.[58] The potential limiting factor for the human population might include water availability, energy availability, renewable resources, non-renewable resources, heat removal, photosynthetic capacity, and land availability for food production.[59] The applicability of carrying capacity as a measurement of the Earth's limits in terms of the human population has not been very useful, as the Verhulst equation does not allow an unequivocal calculation and prediction of the upper limits of population growth.[58] Carrying capacity has been used as a tool in Neo-Malthusian arguments since the 1950s.[60] The concept of carrying capacity has been applied to determining the population limits in Shanghai, a city faced with rapid urbanization.[61]

The application of the concept of carrying capacity for the human population, which exists in a non-equilibrium, is criticized for not successfully being able to model the processes between humans and the environment.[58][62] In popular discourse the concept has largely left the domain of academic consideration, and is simply used vaguely in the sense of a "balance between nature and human populations".[62]

In human ecology a popular definition from 1949 states "the maximum number of people that a given land area will maintain in perpetuity under a given system of usage without land degradation setting in". Sociologists have criticized this for numerous reasons. Aside from the fact that humans are able to adopt new customs and technology, some common critiques are 1.) an assumption an equilibrium population exists, 2.) difficulties in measuring resources, 3.) inability to account for human tastes and how much labour they will expend, 4.) assumption of full usage of resources, 5.) assumption of landscape homogeneity, 6.) assumption that regions are isolated from each other, 7.) contradicted by history, and 8.) the standard of living is ignored.[62]

Romanian American economist Nicholas Georgescu-Roegen, a progenitor in economics and a paradigm founder of ecological economics, has argued in 1971 that the carrying capacity of Earth — that is, Earth's capacity to sustain human populations and consumption levels — is bound to decrease sometime in the future as Earth's finite stock of mineral resources is presently being extracted and put to use.[63]: 303  Leading ecological economist and steady-state theorist Herman Daly, a student of Georgescu-Roegen, has propounded the same argument.[64]: 369–371 

See also

References

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