Overpopulation is a condition where an organism's numbers exceed the carrying capacity of its habitat. In common parlance, the term usually refers to the relationship between the human population and its environment, the Earth.
Overpopulation does not depend only on the size or density of the population, but on the ratio of population to available sustainable resources. It also depends on the way resources are used and distributed throughout the population. If a given environment has a population of 10 individuals, but there is food or drinking water enough for only 9, then in a closed system where no trade is possible, that environment is overpopulated; if the population is 100 but there is enough food, shelter, and water for 200 for the indefinite future, then it is not overpopulated. Overpopulation can result from an increase in births, a decline in mortality rates due to medical advances, from an increase in immigration, or from an unsustainable biome and depletion of resources. It is possible for very sparsely-populated areas to be overpopulated, as the area in question may have a meager or non-existent capability to sustain human life (e.g. the middle of the Sahara Desert).
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, there may be additional resources considered, such as medical care, education, proper sewage treatment and waste disposal. Overpopulation places competitive stress on the basic life sustaining resources, leading to a diminished quality of life.
The rapid increase in human population over the course of the 20th century has raised concerns about the Earth's ability to sustain a large number of inhabitants. In 2009, the estimated annual growth rate was 1.10%, and the world population stood at roughly 6.7 billion. Current projections show a steady decline in the growth rate, and a population of around 9 billion by the year 2050. The scientific consensus is that the current population expansion and accompanying increase in usage of resources is linked to threats to the ecosystem. The InterAcademy Panel Statement on Population Growth, which was ratified by 58 member academies in 1994, called the expansion in human numbers "unprecedented", and stated that many environmental problems were aggravated by the population expansion. At the time, the world population stood at 5.5 billion, and optimistic scenarios predicted a peak of 7.8 billion by 2050, a number that current estimates show will be reached around 2030.
The human population has gone through a number of periods of different growth rates since the dawn of civilization in the Holocene period, roughly 10,000 years ago.
- The beginning of civilization coincides with the final receding of ice following the end of the most recent glacial period.
- This in turn coincides with the start of the Neolithic Revolution, when there was a shift in human activity away from hunter-gathering and towards very primitive farming.
- Around 8000 BC, at the dawn of agriculture, the population of the world was approximately 5 million.
- For around 7,000 years, there was minimal change in the world population.
- Beginning around 1000 BC, there was steady growth in the population, which plateaued (or alternatively, peaked) at around 1 BC, at about 200 to 300 million people.
- From around 800 AD onwards, the population once again grew steadily, though with major disruption from frequent plagues, most notably the Black Death during the 14th century.
- After the effects of the plagues had subsided during the 17th century, shortly before the Industrial Revolution, the world population began to grow once again. In parts of Asia, like China, the population doubled from 60 to 150 million under the Ming dynasty.
- After the start of the Industrial Revolution, during the 18th century, the rate of population growth began to increase. By the end of the century, the world's population was estimated at just under 1 billion.
- At the turn of the 20th century, the world's population was roughly 1.6 billion. By 1940, this figure had increased to 2.3 billion.
- Dramatic growth beginning in 1950 (above 1.8% per year) coincided with greatly increased food production as a result of the industrialisation of agriculture brought about by the Green Revolution. The rate of growth peaked in 1964, at about 2.2% per year.
- The world population is currently estimated to be 6,802,800,000, with unreported variability.
According to projections, the world population will continue to grow until at least 2050, with the population reaching 9 billion in 2040, and some predictions putting the population in 2050 as high as 11 billion.
The theory of demographic transition held that, after the standard of living and life expectancy increase, family sizes and birth rates decline. However, as new data has become available, it has been observed that after a certain level of development the fertility increases again. This means that both the worry the theory generated about aging populations and the complacency it bred regarding the future environmental impact of population growth are misguided.
There is wide variability both in the definition and in the proposed size of the Earth's carrying capacity, with estimates ranging from 1 to 1000 billion. Around two-thirds of the estimates fall in the range of 4 billion to 16 billion (with unspecified standard errors), with a median of about 10 billion.
In a study titled Food, Land, Population and the U.S. Economy, David Pimentel, professor of ecology and agriculture at Cornell University, and Mario Giampietro, senior researcher at the US National Research Institute on Food and Nutrition (INRAN), estimate the maximum U.S. population for a sustainable economy at 200 million. According to this theory, in order to achieve a sustainable economy and avert disaster, the United States would have to reduce its population by at least one-third, and world population would have to be reduced by two-thirds.
David Pimentel, Professor Emeritus at Cornell University, has stated that "With the imbalance growing between population numbers and vital life sustaining resources, humans must actively conserve cropland, freshwater, energy, and biological resources. There is a need to develop renewable energy resources. Humans everywhere must understand that rapid population growth damages the Earth’s resources and diminishes human well-being."
Fresh water supplies, on which agriculture depends, are running low worldwide. This water crisis is only expected to worsen as the population increases. Lester R. Brown of the Earth Policy Institute argues that declining water supplies will have future disastrous consequences for agriculture.
Studies agree that there is enough food to support the world population, but critics dispute this, particularly if sustainability is taken into account.
The amounts of natural resources in this context are not necessarily fixed, and their distribution is not necessarily a zero-sum game. For example, due to the Green Revolution and the fact that more and more land is appropriated each year from wild lands for agricultural purposes, the worldwide production of food had steadily increased up until 1995. World food production per person was considerably higher in 2005 than 1961.
Thinkers such as David Pimentel, a professor from Cornell University, Virginia Abernethy, Alan Thornhill, Russell Hopffenberg and author Daniel Quinn propose that like all other animals, human populations predictably grow and shrink according to their available food supply – populations grow in an abundance of food, and shrink in times of scarcity.
World Resources Institute states that "Agricultural conversion to croplands and managed pastures has affected some 3.3 billion hectares — roughly 26 percent of the land area. All totaled, agriculture has displaced one-third of temperate and tropical forests and one-quarter of natural grasslands." Energy development may also require large areas; hydroelectric dams are one example. Usable land may become less useful through salinization, deforestation, desertification, erosion, and urban sprawl. Global warming may cause flooding of many of the most productive agricultural areas. Thus, available useful land may become a limiting factor. By most estimates, at least half of cultivable land is already being farmed, and there are concerns that the remaining reserves are greatly overestimated.
There has also been increasing development in extracting renewable energy, such as solar, wind, and tidal energy. If used on a wide scale, these could theoretically fulfill most, if not all, of the energy needs currently being filled by non-renewable resources. Some of these renewable resources also have ecological footprints, although they may be different or smaller than some non-renewable resources.
Modern agriculture uses large amounts of fertilizer. Since much of this fertilizer is made from petroleum, the problem of peak oil is of concern. According to articles in Discover Magazine (in 2003 and a 2006), it is possible to use the process of thermal depolymerization to manufacture fertilizer out of garbage, sewage, and agricultural waste.
The United Nations indicates that about 850 million people are malnourished or starving, and 1.1 billion people do not have access to safe drinking water. Some argue that Earth may support 6 billion people, but only if many live in misery. The proportion of the world's population living on less than $1 per day has halved in 20 years, but these are inflation-unadjusted numbers and likely misleading.
While the current world trends are not indicative of any realistic solution to human overpopulation during the 21st century, there are several mitigation measures that have or can be applied to reduce the adverse impacts of overpopulation.
Overpopulation is related to the issue of birth control; some nations, like the People's Republic of China, use strict measures to reduce birth rates. Religious and ideological opposition to birth control has been cited as a factor contributing to overpopulation and poverty. Some leaders and environmentalists (such as Ted Turner) have suggested that there is an urgent need to strictly implement a China-like one-child policy globally by the United Nations, because this would help control and reduce population gradually and most successfully as is evidenced by the success and resultant economic-growth of China due to reduction of poverty in recent years.
One option is to focus on education about overpopulation, family planning, and birth control methods, and to make birth-control devices like male/female condoms,pills and intrauterine devices easily available.
In the 1970s, Gerard O'Neill suggested building space habitats that could support 30,000 times the carrying capacity of Earth using just the asteroid belt and that the solar system as a whole could sustain current population growth rates for a thousand years. Marshall Savage (1992, 1994) has projected a human population of five quintillion throughout the solar system by 3000, with the majority in the asteroid belt. Arthur C. Clarke, a fervent supporter of Savage, argued that by 2057 there will be humans on the Moon, Mars, Europa, Ganymede, Titan and in orbit around Venus, Neptune and Pluto. Freeman Dyson (1999) favours the Kuiper belt as the future home of humanity, suggesting this could happen within a few centuries. In Mining the Sky, John S. Lewis suggests that the resources of the solar system could support 10 quadrillion (1016) people.
Many philosophers, including Thomas Malthus, have said at various times that when humankind does not check population-growth, nature takes its course. But this course might not result in the death of humans through catastrophes; instead it might result in infertility. German scientists have reported that a virus called Adeno-associated virus might have a role in male infertility, but is otherwise harmless to humans. Thus, if this or similar viruses mutate, they might cause infertility on a large-scale, causing a mass scale viral epidemic and thus resulting in a natural human population-control over time.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)