Human overpopulation (or human population overshoot) describes a concern that human populations may become too large to be sustained by their environment or resources in the long term. The topic is usually discussed in the context of world population, though it may concern individual nations, regions, and cities.
Since 1804, the global human population has increased from 1 billion to 8 billion due to medical advancements and improved agricultural productivity. Annual world population growth peaked at 2.1% in 1968, and has since dropped to 1.1%. According to the most recent United Nations' projections, "[t]he global population is expected to reach 9.7 billion in 2050 and 10.4 billion in 2100." The UN's projections report predicts that the human population will peak at around 10.4 billion people, before decreasing, noting that fertility rates are falling worldwide. Other models agree that the population will stabilize before or after 2100.
Early discussions of overpopulation in English were spurred by the work of Thomas Malthus. Discussions of overpopulation follow a similar line of inquiry as Malthusianism and its Malthusian catastrophe, a hypothetical event where population exceeds agricultural capacity, causing famine or war over resources, resulting in poverty and depopulation. More recent discussion of overpopulation was popularized by Paul Ehrlich in his 1968 book The Population Bomb and subsequent writings. Ehrlich described overpopulation as a function of overconsumption, arguing that overpopulation should be defined by a population being unable to sustain itself without depleting non-renewable resources.
The belief that global population levels will become too large to sustain is a point of contentious debate. Those who believe global human overpopulation to be a valid concern, argue that increased levels of resource consumption and pollution exceed the environment's carrying capacity, leading to population overshoot. The population overshoot hypothesis is often discussed in relation to other population concerns such as population momentum, biodiversity loss, hunger and malnutrition, resource depletion, and the overall human impact on the environment.
Critics of the belief note that human population growth is decreasing and the population will likely peak, and possibly even begin to decrease, before the end of the century. They argue the concerns surrounding population growth are overstated, noting that quickly declining birth rates and technological innovation make it possible to sustain projected population sizes. Other critics claim that the concept is too narrowly focused, ignores more pressing issues, like poverty, and places an undue burden on the global south.
Overview
Modern proponents of the concept have suggested that overpopulation, population growth and overconsumption are interdependent and collectively are the primary drivers of human-caused environmental problems such as climate change and biodiversity loss. Many scientists have expressed concern about population growth, and argue that creating sustainable societies will require decreasing the current global population. Advocates have suggested implementation of population planning strategies to reach a proposed sustainable population.
Overpopulation hypotheses are controversial, with many demographers and environmentalists disputing the core premise that the world cannot sustain the current trajectory of human population. Additionally, many economists and historians have noted that sustained shortages and famines have historically been caused by war, price controls, political instability, and repressive political regimes (often employing central planning) rather than overpopulation, and that population growth historically has led to greater technological development and advancement of scientific knowledge that has enabled the engineering of substitute goods and technology that better conserves and more efficiently uses natural resources, produces greater agricultural output with less land and less water, and addresses human impacts on the environment due to there being greater numbers of scientists, engineers, and inventors and subsequent generations of scientists overturning scientific paradigms maintained by previous generations of scientists. Instead, social scientists argue that disputes between themselves and biologists about human overpopulation are over the appropriateness of definitions being used (and often devolve into social scientists and biologists simply talking past each other).