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The United States is the most overpopulated country in the world. Therefore The Americas is the most overpopulated continent in the world. European capitals are also overpopulated.
Overpopulation refers to when 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 is not simply a function of the size or density of the population. Overpopulation can be determined using the ratio of population to available sustainable resources. If a given environment has a population of ten, but there is food or drinking water enough for only nine, then that environment is overpopulated; if the population is 100 individuals but there is enough food, shelter, and water for 200 for the indefinite future, then it is not. Overpopulation can result from an increase in births, a decline in mortality rates due to medical advances, from an increase in immigration, a decrease in emigration, 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 very meager or non-existent capability to sustain human life (e.g. the middle of the Sahara desert or Antarctica).
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 as well, there are then additional resources to be considered, such as medical care, employment, money, education, fuel, electricity, proper sewage treatment, waste.
Some countries have managed to increase their carrying capacity by using technologies such as agriculture, desalination, and nuclear power. Some cornucopians have argued that poverty and famine are caused by bad government and bad economic policies, and that higher population density leads to more specialization and technological innovation, and that this leads to a higher standard of living.  . Others argue that overpopulation is an important cause of these problems.
- 1 Overpopulation predictions
- 2 Population growth
- 3 Resources
- 4 Environment
- 5 Cities
- 6 Overpopulation by world region
- 7 Effects of overpopulation
- 8 Current amount of overpopulation
- 9 See also
- 10 References
- 11 Further reading
- 12 External links
- Main article: Malthusian catastrophe
In An Essay on the Principle of Population (first published in 1798), Thomas Malthus proposed that while resources tend to grow linearly, population grows exponentially. He argued that, if left unrestricted, human populations continue to grow until they would become too large to be supported by the food grown on available agricultural land, causing starvation which then controls population growth. He noted that this had happened many times previously in human history and estimated that this would occur again by the middle of the 19th century. To avoid this outcome, Malthus argued for population control through "moral restraint". While arguably he was right about human history up to his time, he made his prediction for the future exactly at the time the industrial revolution and a similar revolution in agriculture caused a large increase in available resources. His specific predictions for England therefore may have erred because he used a static analysis, and extrapolated his historical numbers into the future without considering future factors that could increase the resource base more rapidly, (for example, the revolutions in agriculture at his time or later the Green Revolution), although he correctly predicted that population growth could decline or reverse with later marriages and "vices" like contraception (see for example, the demographic transition).
On a global scale, since the industrial revolution, food production has sometimes grown faster than human population. However, it has been argued that other changes impacting Earth's ability to function as a suitable habitat for human beings, such as global warming, desertification, overfishing, peak oil, soil degradation, deforestation, aquifer depletion and other environmental problems caused by industrialization, will significantly reduce food production or factors necessary for well-being. Given recent population growth, this may cause a Malthusian catastrophe.
Among the earlier best-known modern examples of such arguments are The Limits to Growth (1972) and The Population Bomb (1968) by Paul R. Ehrlich.
Paul Ehrlich "predicted", "The population of the U.S. will shrink from 250 million to about 22.5 million before 1999 because of famine and global warming", though it should be noted that between 1950 and 1984, as the Green Revolution transformed agriculture around the globe, world grain production increased by 250%, and the source of his quote, a 1969 short story called "Eco-catastrophe" reprinted from "Ramparts" Magazine, was apparently a work of science fiction. Ehrlich also predicted, "Before 1985, mankind will enter a genuine age of scarcity . . . in which the accessible supplies of many key minerals will be facing depletion."  According to The Skeptical Environmentalist by Bjørn Lomborg, Ehrlich's predictions did not materialise. (See Erlich's answer to his critics and The Ultimate Resource, by Julian Simon, which challenges Ehrlich's ideas.) Interestingly Simon himself once stated "We now have in our hands in our libraries, really the technology to feed, clothe, and supply energy to an ever-growing population for the next 7 billion years... We [are] able to go on increasing forever" (Myers and Simon, 1994, 65). These comments have subjected Simon himself to criticism.
In Facing the Limits to Growth the authors of the controversial 1972 study Limits to Growth tell of the difficulty in getting the idea of the necessity of limiting human population growth past "Entrenched political, economic, and religious cliques". And they acknowledge that revision has been necessary, "Because of the long time horizon involved in our studies, we always realized it would require several decades to get any perspective on the accuracy of our forecasts", however, "the basic conclusions are still the same. We have modified our model only a little to reflect some better data about the effects of technology on land yields and birth rates."
Between 1950 and 1984, as the Green Revolution transformed agriculture around the globe, world grain production increased by 250%. However, agricultural productivity has declined in many world regions in the past ten to 20 years due to overdrafting of groundwater (such as has occurred on the North Plain of China) , overgrazing, extensive slash-and-burn and resulting soil exhaustion and erosion. The energy for the Green Revolution was provided by fossil fuels in the form of fertilizers (natural gas), pesticides (oil), and hydrocarbon fueled irrigation. David Pimentel, professor of ecology and agriculture at Cornell University, and Mario Giampietro, senior researcher at the National Research Institute on Food and Nutrition (INRAN), place in their study Food, Land, Population and the U.S. Economy the maximum U.S. population for a sustainable economy at 200 million. To achieve a sustainable economy and avert disaster, the United States must reduce its population by at least one-third, and world population will have to be reduced by two-thirds, says the study. The authors of this study believe that the mentioned agricultural crisis will only begin to impact us after 2020, and will not become critical until 2050.
David Pimentel claims that population outcomes for the 22nd century range from 2 billion people (characterised as thriving in harmony with the environment), to 12 billion people (characterised as miserable and suffering difficult lives with limited resources and widespread famine).
The oncoming peaking of global oil production (and subsequent decline of production), along with the peak of North American natural gas production may precipitate this agricultural crisis much sooner than expected. Geologist Dale Allen Pfeiffer claims that coming decades could see spiraling food prices without relief and massive starvation on a global level such as never experienced before.
The book The Little Green Handbook reasons that in 2050 about 7.7 billion people would be expected to suffer from illness, lack of adequate sanitation, hunger, and extreme poverty, provided that the high population estimates of year 2050 are realised.
In his recent book Collapse (2005), Jared Diamond argues that many earlier civilizations have collapsed due to environmental problems, and warns of current environmental problems. For example, he argues that it was overpopulation that led the now recovering inhabitants of Easter Island (a.k.a. Rapa Nui) to destroy their once beautiful island paradise.
|“||From circa AD 1000 to circa 1650/1700 AD, Rapa Nui's population increased significantly. Some estimate the population reached a high of 10,000 or even 15,000. Moai carving and transport were in full swing from 1400 to 1650, less than 100 years before the first recorded European visitors to the island. By the late nineteenth century the population had fallen to a low of 132. Deforestation, civil wars, European diseases and slave raiding all contributed to the population crash. Core sampling and archaeology from the island has revealed a slice of Rapa Nui history that speaks of deforestation, extinction of native bird populations, soil depletion, and erosion as well as loss of access to deep sea fish as wood became scarce. From this devastating ecological scenario it is not hard to imagine the resulting overpopulation, food shortages, and ultimate collapse of Rapa Nui society. Evidence of cannibalism at that time is present on the island, though very scant. Van Tilburg cautiously asserts, "The archaeological evidence for cannibalism is present on a few sites".||”|
However, he also notes many situations in which humans have managed their natural resources well.
Optimistic views on population
In The Skeptical Environmentalist, Bjørn Lomborg argues that, because of the falling rate of population growth in some parts of the world and because of new science and technologies, there is little problem with overpopulation. A rebuttal can be found here. Some of Lomborg's responses to his critics can be found here.
Julian Simon predicted that any poor country that chose to adopt property rights, science, technology, industrialization, modern agriculture, hydroponic farming, nuclear power, and desalination, would achieve a rich, first world standard of living, even if the Earth had tens of billions of people.
Similarly, in his 2007 book The Improving State of the World, Indur M. Goklany argues that there is little problem with overpopulation, as humanity's state is rapidly improving overall and environmental problems can be overcome. It proposes that in the early stages of economic and technological development, negative environmental impacts increase because securing access to such necessities as food, shelter, and energy is seen as more important than protecting the environment. As development continues and these supply problems are solved, environmental impact becomes a higher priority, and steps are then taken to reduce it. This pattern can be seen for many environmental indicators, such as air quality, availability of safe water, sanitation, and toxic residues (e.g., DDT and PCBs) in human tissues, which initially declined with increasing development but have more recently improved.
However, far from being the natural outcome of free markets that Goklany postulates, James Surowiecki argues in his review of the book that "The reality ... is that the fight over environmental regulation, at least in the United States, was -- and remains -- a fierce one and that environmental skeptics and businesses have done their best to prevent regulations such as the Clean Air and Clean Water Acts from ever becoming law. It is also the case that without those regulations, the 'cleaner planet' Goklany sees today would not exist.... The point is that far from being the inevitable product of a strong economy, environmental improvement is often the result of political struggles that could very easily have gone the other way."
The demographic transition
- Main article: Demographic transition
The theory of demographic transition, while unproven to apply to all world regions, holds that widespread empirical evidence shows that after the standard of living and life expectancy increases, family sizes start dropping. Factors cited in the decline of birth rates include such social factors as later ages of marriage, the growing desire of many women in such settings to seek careers outside of child rearing and domestic work, and the decreased need of children in industrialized settings. The latter factor stems from the fact that children perform a great deal of work in small-scale agricultural societies, and work less in industrial ones; it has been cited to explain the dropoff in birth rates worldwide in all industrializing regions.
Another version of demographic transition is that of Virginia Abernethy in Population Politics, in which she claims that the demographic transition is primarily in effect for nations where women enjoy a special status (see Fertility-opportunity theory). In strongly patriarchal nations, where she claims women enjoy few special rights, a high standard of living tends to result in population growth. She argues that foreign aid to poor countries must include significant components designed to improve the education, human rights, political rights, political power, and also to equalize the economic and sexual status and power of women.
Her theory runs counter to some of the available empirical evidence. For example Iran had a Total Fertility Rate of 1.82 children per couple in 2005, which is below the replacement rate of 2.1 to 2.3 children per couple needed to maintain population. Iran is widely perceived as a patriarchal nation, and yet any population growth that occurred there came not from increased birth rates, but from decreased mortality rates, and therefore not from a lack of reproductive rights.
"Demographic entrapment" is a concept developed by Maurice King that has not gained widespread acceptance. King argues that this occurs when a country has a population larger than its carrying capacity, no possibility of migration, and exports too little to be able to import food. This will cause starvation. He claims that for example many sub-Saharan nations are or will become stuck in demographic entrapment, instead of having a demographic transition.
For the world as a whole, the number of children born per woman decreased from 5.02 to 2.65 between 1950 and 2005. Europe 2.66 to 1.41. North America 3.47 to 1.99. Oceania 3.87 to 2.30. Central America 6.38 to 2.66. South America 5.75 to 2.51. Asia (excluding Middle East) 5.85 to 2.43. Middle East & North Africa 6.99 to 3.37. Sub-Saharan Africa 6.7 to 5.53. In 2050, the projected number of children born per woman is 2.05. Only the Middle East & North Africa (2.09) and Sub-Saharan Africa (2.61) will then have numbers greater than 2.
Population projections from the 1900s to 2050
The United Nations states that:
- Almost all growth will take place in the less developed regions, where today’s 5.3 billion population of underdeveloped countries is expected to increase to 7.8 billion in 2050. By contrast, the population of the more developed regions will remain mostly unchanged, at 1.2 billion. The world's population is expected to rise by 40% to 9.1 billion.
- World population is currently growing by approximately 75 million people per year. Net growth by mid-century is predicted by the United Nations to be 34 million per year in contrast to the roughly 76 million per year that was seen from 2000 to 2005.
- In 2000-2005, fertility at the world level stood at 2.65 children per woman, about half the level it had in 1950-1955 (5 children per woman). In the medium variant, global fertility is projected to decline further to 2.05 children per woman.
- During 2005-2050, nine countries are expected to account for half of the world’s projected population increase: India, Pakistan, Nigeria, Democratic Republic of the Congo, Bangladesh, Uganda, United States of America, Ethiopia, and China, listed according to the size of their contribution to population growth.
- Global life expectancy at birth, which is estimated to have risen from 46 years in 1950-1955 to 65 years in 2000-2005, is expected to keep rising to reach 75 years in 2045-2050. In the more developed regions, the projected increase is from 75 years today to 82 years by mid-century. Among the least developed countries, where life expectancy today is just under 50 years, it is expected to be 66 years in 2045-2050.
- The population of 51 countries or areas, including Germany, Italy, Japan and most of the successor States of the former Soviet Union, is expected to be lower in 2050 than in 2005.
- During 2005-2050, the net number of international migrants to more developed regions is projected to be 98 million. Because deaths are projected to exceed births in the more developed regions by 73 million during 2005-2050, population growth in those regions will largely be due to international migration.
- In 2000-2005, net migration in 28 countries either prevented population decline or doubled at least the contribution of natural increase (births minus deaths) to population growth. These countries include Austria, Canada, Croatia, Denmark, Germany, Italy, Portugal, Qatar, Singapore, Spain, Sweden, United Arab Emirates and United Kingdom.
- The updated United Nations figures project that the world population will reach 9.2 billion around 2050. This is the medium variant figure which assumes a decrease in average fertility from the present level of 2.5 down to 2.
- Birth rates are now falling in many developing countries, while the actual populations in many developed countries would fall without immigration.
- By 2050 (Medium variant), India will have almost 1.7 billion people, China 1.4 billion, United States 400 million, Indonesia 297 million, Pakistan 292 million, Nigeria 289 million, Bangladesh 254 million, Brazil 254 million, Democratic Republic of the Congo 187 million, Ethiopia 183 million, Philippines 141 million, Mexico 132 million, Egypt 121 million, Vietnam 120 million, Russia 108 million, Japan 103 million, Iran 100 million, Turkey 99 million, Uganda 93 million, Tanzania 85 million, and Kenya 85 million.
- Africa - 133 million
- Asia - 946 million
- Europe - 408 million
- Latin America & Caribbean - 74 million
- Northern America - 82 million
- Africa - 1.9 billion
- Asia - 5.2 billion
- Europe - 664 million
- Latin America & Caribbean - 769 million
- Northern America - 445 million
Overpopulation is also related to issues of birth control, with some nations like China using strict measures in order to reduce birth rates, while religious and ideological opposition to birth control has been cited as a factor contributing to overpopulation and poverty.
There are an estimated 350 million women in the poorest countries of the world who either did not want their last child, do not want another child or want to space their pregnancies, but they lack access to information, affordable means and services to determine the size and spacing of their families. In the developing world, some 514,000 women die of complications from pregnancy and abortion on a yearly basis. Additionally, 8 million infants die, many because of malnutrition or preventable diseases.
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".
These reflect the comments also of the United States Geological Survey in their paper The Future of Planet Earth: Scientific Challenges in the Coming Century. "As the global population continues to grow...people will place greater and greater demands on the resources of our planet, including mineral and energy resources, open space, water, and plant and animal resources".
On the other hand, some writers, such as Julian Simon, Bjorn Lomborg and others of a conservative Libertarian persuasion believe that resources abound for a furtherance of population growth. Population scientists have agreed with their assessments that there are indeed more resources left that would enable continued population growth. However, they warn, this will be at a high cost to the Earth - and thus to us, "the technological optimists are probably correct in claiming that overall world food production can be increased substantially over the next few decades...[however] the environmental cost of what Paul R. and Anne H. Ehrlich describe as 'turning the Earth into a giant human feedlot' could be severe. A large expansion of agriculture to provide growing populations with improved diets is likely to lead to further deforestation, loss of species, soil erosion, and pollution from pesticides and fertilizer runoff as farming intensifies and new land is brought into production". Since we are intimately dependent upon the living systems of the Earth, scientists have questioned the wisdom of further expansion.
According to the Millennium Ecosystem Assessment, a four-year research effort by 1,360 of the world’s leading scientists commissioned to measure the actual value of natural resources to humans and the world, "The structure of the world’s ecosystems changed more rapidly in the second half of the twentieth century than at any time in recorded human history, and virtually all of Earth’s ecosystems have now been significantly transformed through human actions". "Ecosystem services, particularly food production, timber and fisheries, are important for employment and economic activity. Intensive use of ecosystems often produces the greatest short-term advantage, but excessive and unsustainable use can lead to losses in the long term. A country could cut its forests and deplete its fisheries, and this would show only as a positive gain to GDP, despite the loss of capital assets. If the full economic value of ecosystems were taken into account in decision-making, their degradation could be significantly slowed down or even reversed". The MA blames habitat loss and fragmentation for the continuing disappearance of species.
Another study by the United Nations Environment Programme (UNEP) called the Global Environment Outlook  which involved 1,400 scientists and took five years to prepare comes to similar conclusions. It "found that human consumption had far outstripped available resources. Each person on Earth now requires a third more land to supply his or her needs than the planet can supply". It faults a failure to "respond to or recognise the magnitude of the challenges facing the people and the environment of the planet... 'The systematic destruction of the Earth's natural and nature-based resources has reached a point where the economic viability of economies is being challenged - and where the bill we hand to our children may prove impossible to pay'... The report's authors say its objective is 'not to present a dark and gloomy scenario, but an urgent call to action'. It warns that tackling the problems may affect the vested interests of powerful groups, and that the environment must be moved to the core of decision-making... '
Additionally, other issues involving quality of life - would most people want to live in a world of billions more people - and the basic right of other species to exist in their native environments come into play.
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 has steadily increased faster than population growth. World food production per person was considerably higher in 2005 than 1961.
As world population doubled from 3 billion to 6 billion, daily calorie consumption in poor countries increased from 1,932 to 2,650, and the percentage of people in those countries who were malnourished fell from 45% to 18%. This suggests that Third World poverty and famine are caused by underdevelopment, not overpopulation. However, others question these statistics.
The number of people who are overweight has surpassed the number who are malnourished. In a 2006 news story, MSNBC reported, "There are an estimated 800 million undernourished people and more than a billion considered overweight worldwide."
The Food and Agriculture Organization of the United Nations states in its report The State of Food Insecurity in the World 2006, that while the number of undernourished people in the developing countries has declined by about three million, a smaller percentage of the populations of developing countries is undernourished today compared with 1990–92: 17 percent against 20 percent. Furthermore, FAO’s projections suggest that the proportion of hungry people in developing countries could be halved from 1990-92 levels to 10 percent by 2015. The FAO also states "We have emphasized first and foremost that reducing hunger is no longer a question of means in the hands of the global community. The world is richer today than it was ten years ago. There is more food available and still more could be produced without excessive upward pressure on prices. The knowledge and resources to reduce hunger are there. What is lacking is sufficient political will to mobilize those resources to the benefit of the hungry." PDF
In Africa, if current trends of soil degradation and population growth continue, the continent might be able to feed just 25% of its population by 2025, according to UNU's Ghana-based Institute for Natural Resources in Africa.
Hunger and malnutrition kill nearly 6 million children a year, and more people are malnourished in sub-Saharan Africa this decade than in the 1990s, according to a report released by the Food and Agriculture Organization Tuesday. In sub-Saharan Africa, the number of malnourished people grew to 203.5 million people in 2000-02 from 170.4 million 10 years earlier says The State of Food Insecurity in the World report.
According to the BBC, the famine in Zimbabwe was caused by government seizure of farmland. However drought has also played a major role. Thirteen-million people are threatened by famine, in light of the drought in southern Africa. Six-million of them live in Zimbabwe. So that is a contingent of fully half of those potentially threatened by the current food shortages, if indeed they get worse, as is projected.  Prior to this combination of drought and seizure of farmland, Zimbabwe had been exporting so much food that it was called "the breadbasket of southern Africa." So other countries were also harmed by these farm seizures. People who study the Zimbabwean famine claim that normally there are more than enough natural resources to feed the people. Some claim that the dams and rivers in Zimbabwe are full, and that the famine has nothing to do with drought. And though it's undoubtedly true that bad governance has exacerbated the famine, still notes the article, "Four weeks without rain at the critical germination phase has led to the failure of [the villagers] small crops. There will be no harvest again until next June."
Prior to President Robert Mugabe's seizure of the farmland in Zimbabwe, the farmers had been using irrigation to deal with drought, but during the seizures of the farmland, much of the irrigation equipment was either vandalized or looted. A 2006 BBC article about Mugabe's seizure of farmland states, "Critics say the reforms have devastated the economy and led to massive hunger. Much of the formerly white-owned land is no longer being productively used - either because the beneficiaries have no experience of farming or they lack finance and tools. Many farms were wrecked when they were invaded by government supporters."
Zimbabwe only has 33 people per square kilometre. Meanwhile, Israel has a whopping 302 people per square kilometre. Although Israel is a desert country with frequent drought and very high population density, it does not have famine. One possible reason why Israel does not have famine is because its government respects the property rights of farmers, and encourages them to use modern agriculture and irrigation to grow huge amounts of food.
Mauritius is the most densely populated country in Africa. It is 10 times more densely populated than most other African countries, though at a total population of just 1.23 million, it sits 46th out of Africa's 54 nations for actual population numbers. However, Mauritius does not have famine; on the contrary, it enjoys a First World standard of living. The reason that Mauritius is doing so well is because it has strong protection of property rights, and because it uses science, technology, industrialization, and modernization.
According to a 2004 article from the BBC, China, the world's most populous country, is suffering from an obesity epidemic. More recent data indicate China's grain production peaked in the mid 1990s, due to overextraction of groundwater in the North China plain.
According to a 2007 article from the BBC, scientists at Columbia University have theorized that in the future, densely populated cities such as New York City may use vertical farming to grow food on each floor of 30-storey skyscrapers.
Population as a function of food availability
Thinkers such as David Pimentel, a professor from Cornell University, Virginia Abernethy, Alan Thornhill, Russell Hopffenberg and author Daniel Quinn propose that like any 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.
Proponents of this theory argue that every time food production is increased, the population grows. Some human populations throughout history support this theory. Populations of hunter-gatherers fluctuate in accordance with the amount of available food. Population increased after the Neolithic Revolution and an increased food supply. This was followed by subsequent population growth after subsequent agricultural revolutions.
Critics of this idea point out that birth rates are lowest in the developed nations, which also has the highest access to food. In fact, some developed countries have both a diminishing population and an abundant food supply. The United Nations projects that the population of 51 countries or areas, including Germany, Italy, Japan and most of the states of the former Soviet Union, is expected to be lower in 2050 than in 2005. This shows that human populations do not always grow to match the available food supply; also, many of these countries are major exporters of food. Nevertheless, at the global scale the world population is increasing.
As a result of water deficits
Water deficits, which are already spurring heavy grain imports in numerous smaller countries, may soon do the same in larger countries, such as China or India. The water tables are falling in scores of countries (including Northern China, the US, and India) due to widespread overpumping using powerful diesel and electric pumps. Other countries affected include Pakistan, Iran, and Mexico. This will eventually lead to water scarcity and cutbacks in grain harvest. Even with the overpumping of its aquifers, China is developing a grain deficit. When this happens, it will almost certainly drive grain prices upward. Most of the 3 billion people projected to be added worldwide by mid-century will be born in countries already experiencing water shortages. One suggested solution is for population growth to be slowed quickly by investing heavily in female literacy and family planning services. Desalination is also considered a viable and effective solution to the problem of water shortages.
After China and India, there is a second tier of smaller countries with large water deficits — Algeria, Egypt, Iran, Mexico, and Pakistan. Four of these already import a large share of their grain. Only Pakistan remains self-sufficient. But with a population expanding by 4 million a year, it will also likely soon turn to the world market for grain.
- Further information: Water crisis
Despite advances in agriculture, the fresh water supplies that it depends on are running low worldwide. Some argueTemplate:Weasel-inline that 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 could well have future disastrous consequences for agriculture.
However, the amount of freshwater is not necessarily limited to what is currently available in nature. Malta derives two thirds of its freshwater from desalination of salt water. This is an energy intensive process. One possible solution is large expansion of nuclear powered desalination plants. Such plants already exist. Some argue that there are billions of years of nuclear fuel available. Critics point to the high costs of desalination technologies, especially for poor third world countries, the impracticability and cost of transporting or piping massive amounts of desalinated seawater throughout the interiors of large countries, and the "lethal byproduct of saline brine that is a major cause of marine pollution when dumped back into the oceans at high temperatures".
One study of the costs of desalination and its transport says that "Indeed, one needs to lift the water by 2000 m, or transport it over more than 1600 km to get transport costs equal to the desalination costs.[How to reference and link to summary or text]. Desalinated water is expensive in places that are both somewhat far from the sea and somewhat high, such as Riyadh and Harare. In other places, the dominant cost is desalination, not transport. This leads to relatively low costs in places like Beijing, Bangkok, Zaragoza, Phoenix, and, of course, coastal cities like Tripoli." Still, the study, while generally positive about the technology for affluent areas that are proximate to oceans, concludes that "Desalinated water may be a solution for some water-stress regions, but not for places that are poor, deep in the interior of a continent, or at high elevation. Unfortunately, that includes some of the places with biggest water problems". 
Newer agricultural technologies do not always require more water usage; for example hydroponics and green houses require less.
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, like for hydroelectric dams. 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.
High crop yield vegetables like potatoes and lettuce do not waste space with inedible plant parts, like stalks, husks, vines, and inedible leaves. New varieties of selectively bred and hybrid plants have larger edible parts (fruit, vegetable, grain) and smaller inedible parts; however, many of the gains of agricultural technology are now historic, with new advances being more difficult to achieve. With new technologies, it is possible to grow crops on some marginal land under certain conditions. Aquaculture could theoretically increase available area. Hydroponics and food from bacteria and fungi, like Quorn, may allow the growing of food without having to consider land quality, climate, or even available sunlight, although such a process may be very energy-intensive.
Some claim that not all arable land will remain productive if used for agriculture, as they argue that some marginal land can only be made to produce food by unsustainable practices like slash-and-burn agriculture. Even with the modern techniques of agriculture, the sustainability of production is in question.
Some scientists have said that in the future, densely populated cities will use vertical farming to grow food inside skyscrapers.
Some countries, such as Dubai have constructed large artificial islands, or have created large dam and dike systems, like the Netherlands, which reclaim land from the water to increase their total land area.
The space taken by a the human being itself is not a problem. It has been noted by a number of thinkers - like noted philosopher Justin West who deny that overpopulation is a problem - that the entire population of the world could live in Texas (or a land mass the size of Texas). Texas has a total surface area of 261,914 square miles, which is 7.30174326 × 10^12 square feet. Divided by 7 billion (slightly larger than the current population of the world) would yield an average of 1,043 sq feet per person. Were everyone allotted space thusly, a family of 4 would have roughly a 4000 square foot home. This is assuming, of course, single floor houses. Compacted this way, the rest of North America, and all of South America, Europe, Asia, Africa, Australia and Antarctica would be left vacant of human beings and open to farming.
Some groups (for example, the World Wide Fund for Nature and the Global Footprint Network) have stated that the carrying capacity for the human population has been exceeded as measured using the ecological footprint. Critics question the simplifications and statistical methods employed in calculating ecological footprints. Some argue that there is nothing intrinsically negative about using more land to improve living standards. On the other hand, proponents would counter that there are many moral dilemmas inherent in geopolitically and temporally inequitable distribution of resources.
Population optomists have also been criticized for failing to account for future shortages in fossil fuels, currently used for fertilizer and transportation for modern agriculture. (See Hubbert peak and Future energy development.) They counter that there will be enough fossil fuels until suitable replacement technologies have been developed, for example hydrogen in a hydrogen economy.
In his 1992 book Earth in the Balance, Al Gore wrote, "... it ought to be possible to establish a coordinated global program to accomplish the strategic goal of completely eliminating the internal combustion engine over, say, a twenty-five-year period..." Plug in electric cars such as the Tesla Roadster suggest that Gore's prediction will come true. The Earth has enough uranium to provide humans with all of their electricity needs until the sun blows up in 5 billion years.
There has also been increasing development in renewable energy resources, such as solar, wind, and tidal energy, which, if used on a wide scale, could supplement most, if not all, of the energy needs currently being filled by non-renewable resources. However, it should be noted that some of these renewable resources also have ecological footprints, though 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 a 2003 article in Discover magazine, it is possible to use the process of thermal depolymerization to manufacture fertilizer out of garbage, sewage, and agricultural waste. A follow up article from 2006 gave more information.
Wealth and poverty
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. Thus some argue that the Earth may support 6 billion people, but only on the condition that many live in misery. Others posit that poverty was worse in the past when the population was smaller, and that worldwide poverty is declining as the population grows. The percentage of the world's population living on less than $1 per day has halved in twenty years; these are inflation adjusted numbers. Furthermore, a 2007 article from Investor's Business Daily suggests that the population explosion has been accompanied by an increase in worldwide living standards. The article states, "On a per-person basis, real average incomes have more than tripled since 1950 worldwide. And in once-poor areas with the greatest trade liberalization — like East Asia — growth has been even greater, soaring 5,675% from 1950 to 2003.".
However states the UN Human Development Report from 1997 "During the last 15-20 years, more than 100 developing countries, and several East European countries, have suffered from disastrous growth failures. The reductions in standard of living have been deeper and more long-lasting than what was seen in the industrialised countries during the depression in the 1930´es. As a result, the income for more than one billion people has fallen below the level that was reached 10, 20 or 30 years ago." How do some massage the numbers to come up with a rosy picture for the third world? Says Pimm and Harvey "Lomborg’s great optimism about humanity’s future shows up in the way he presents statistics. In sub-Saharan Africa, 'starving people' constituted '38 percent in 1970 … [but only] '33 percent … in 1996. [The percentage is] expected to fall even further to 30 percent in 2010.' The absolute numbers of starving are curiously missing from these paragraphs. Roughly, the region’s population doubled between 1970 and 1996. To keep the numbers of starving constant, the percentage would have had to have dropped by more than half.". In other words, the percentages Lomborg presents would indeed be impressive in an environment with no population growth, but in one wherein the population has doubled the absolute numbers has actually risen dramatically.
For example, North Korea and South Korea have similar population densities, natural resources, and even parallel cultures (ethnically based in Korean) sharing the same peninsular homeland; but, whereas North Korea is a poverty-stricken, socialist country where its people are suffering from terrible famine and are destitute, South Korea is a prosperous, capitalist country where the people are well nourished and materially/economically secure (without just a small portion of the entire poulation benefiting from the wealth [as do North Korea's Communist Party officials with the little wealth their country has] but all the nation's people benefitting from their economic successes) despite the fact that South Korea's poulation is double that of North Korea's population with a higher fertility rate (hence a faster growing population) as well. This suggests that it is bad economic polices, not "overpopulation," that causes famine. Various Indices of Economic Freedom suggest that countries with a strong level of economic freedom never have famines or even food shortages, regardless of how high their population densities.
Once a country has industrialized and become wealthy, a combination of government regulation (as one possible choice for effective action) and technological innovation may cause air pollution to decline substantially, even as its population continues to grow. For example, in the United States between 1970 and 2006, the population increased by 42%, inflation adjusted GNP grew by 195%, the number of automobiles more than doubled, and the total number of miles driven increased by 178%. However, according to the Environmental Protection Agency, during that same time period, there were substantial reductions in total annual emissions of carbon monoxide, nitrogen oxides, sulfur dioxide, particulates, and lead.
Overpopulation has had a major impact on the environment of Earth starting at least as early as the 20th century. Many posit that the human population has expanded, enabled by over-exploiting natural resources, with resultant adverse impacts upon biodiversity, aquifer sustainability, climate change and even human health. There are also indirect economic consequences of this environmental degradation in the form of ecosystem services attrition. Beyond the scientifically verifiable harm to the environment, some argue the moral right of other species to simply exist, protected from human exploitation. Says environmental author Jeremy Rifkin, "our burgeoning population and urban way of life have been purchased at the expense of vast ecosystems and habitats. ... It's no accident that as we celebrate the urbanization of the world, we are quickly approaching another historic watershed: the disappearance of the wild."
Says Peter Raven, former President of AAAS (the American Association for the Advancement of Science) in their seminal work AAAS Atlas of Population & Environment, "Where do we stand in our efforts to achieve a sustainable world? Clearly, the past half century has been a traumatic one, as the collective impact of human numbers, affluence (consumption per individual) and our choices of technology continue to exploit rapidly an increasing proportion of the world's resources at an unsustainable rate. ... During a remarkably short period of time, we have lost a quarter of the world's topsoil and a fifth of its agricultural land, altered the composition of the atmosphere profoundly, and destroyed a major proportion of our forests and other natural habitats without replacing them. Worst of all, we have driven the rate of biological extinction, the permanent loss of species, up several hundred times beyond its historical levels, and are threatened with the loss of a majority of all species by the end of the 21st century".
In 1800 only 3% of the world's population lived in cities. By the 20th century's close, 47% did so. In 1950, there were 83 cities with populations exceeding one million; but by 2007, this had risen to 468 agglomerations of more than one million. If the trend continues, the world's urban population will double every 38 years, say researchers. The UN forecasts that today's urban population of 3.2 billion will rise to nearly 5 billion by 2030, when three out of five people will live in cities.
The increase will be most dramatic in the poorest and least-urbanised continents, Asia and Africa. Surveys and projections indicate that all urban growth over the next 25 years will be in developing countries. One billion people, one-sixth of the world's population, or one-third of urban population, now live in shanty towns, which are seen as "breeding grounds" for social problems such as crime, drug addiction, alcoholism, poverty and unemployment. In many poor countries slums exhibit high rates of disease due to unsanitary conditions, malnutrition, and lack of basic health care. By 2030, over 2 billion people in the world will be living in slums.
In 2000, there were 18 megacities – conurbations such as Tokyo, Mexico City, Mumbai(Bombay), Sao Paulo and New York City – that have populations in excess of 10 million inhabitants. Greater Tokyo already has 35 million, more than the entire population of Canada.
By 2025, according to the Far Eastern Economic Review, Asia alone will have at least 10 hypercities, those with 20 million or more, including Jakarta (24.9 million people), Dhaka (25 million), Karachi (26.5 million), Shanghai (27 million) and Mumbai (with a staggering 33 million). Lagos has grown from 300,000 in 1950 to an estimated 15 million today, and the Nigerian government estimates that city will have expanded to 25 million residents by 2015. Chinese experts forecast that Chinese cities will contain 800 million people by 2020.
Despite this increase in population density within the cities and the rise of more megacities, UN Habitat stated in its reports that if these 2 matters do not negate the fact that city living can be the best solution for dealing with the rising population numbers (and thus still be a good approach on dealing with overpopulation). This however can only be achieved if urban planning is improved and if the city services are properly maintained.
Overpopulation by world region
- Further information: List of most overpopulated countries
As can be seen on page 18 of WWF's Living Planet report, the most overpopulated regions in the world are as follows:
- North America
- Latin America and the Caribbean
- Europe (EU-countries)
- Europe (non-EU-countries
- Middle-East and Central Asia
- Latin-America and the Caribbean
- Asia Pacific
In depth information per country may be found at List of most overpopulated countries. This is an incomplete list of most overpopulated countries.
Effects of overpopulation
Some problems associated with or exacerbated by human overpopulation:
- Inadequate fresh water for drinking water use as well as sewage treatment and effluent discharge. Some countries, like Saudi Arabia, use energy-expensive desalination to solve the problem of water shortages.
- Depletion of natural resources, especially fossil fuels
- Increased levels of air pollution, water pollution, soil contamination and noise pollution. Once a country has industrialized and become wealthy, a combination of government regulation and technological innovation causes pollution to decline substantially, even as the population continues to grow.
- Deforestation and loss of ecosystems that sustain global atmospheric oxygen and carbon dioxide balance; about eight million hectares of forest are lost each year.
- Changes in atmospheric composition and consequent global warming
- Irreversible loss of arable land and increases in desertification Deforestation and desertification can be reversed by adopting property rights, and this policy is successful even while the human population continues to grow.
- Mass species extinctions. from reduced habitat in tropical forests due to slash-and-burn techniques that sometimes are practiced by shifting cultivators, especially in countries with rapidly expanding rural populations; present extinction rates may be as high as 140,000 species lost per year. The IUCN Red List lists a total of 698 animal species having gone extinct during recorded human history.
- High infant and child mortality. High rates of infant mortality are caused by poverty. Rich countries with high population densities have low rates of infant mortality. 
- Increased chance of the emergence of new epidemics and pandemics
- Starvation, malnutrition or poor diet with ill health and diet-deficiency diseases (e.g. rickets). Famine is aggravated by poverty. Rich countries with high population densities do not have famine.
- Poverty coupled with inflation in some regions and a resulting low level of capital formation. Poverty and inflation are aggravated by bad government and bad economic policies. Many countries with high population densities have eliminated absolute poverty and keep their inflation rates very low.
- Low life expectancy in countries with fastest growing populations
- Unhygienic living conditions for many based upon water resource depletion, discharge of raw sewage and solid waste disposal
- Elevated crime rate due to drug cartels and increased theft by people stealing resources to survive
- Conflict over scarce resources and crowding, leading to increased levels of warfare
Current amount of overpopulation
In 2006, WWF's "Living Planet" report stated that if we all want to live with a high degree of luxury (European standards), we would be spending three times more than what the planet can supply. In other reports, such as the one cited in the The Planet-documentary, it is mentioned that we already consume five times more than that the planet can supply, giving the current population numbers and our standard of living. Although there is still no real consensus, it is expected that the amount of overpopulation currently lies within this range.
- Behavioral sink
- Birth control
- List of overpopulated countries
- Environmental attitudes
- Environmental stress
- Group behavior
- Group size measures
- Overpopulation in wild animals
- Social density
- Social issues
- Global food crisis looms as climate change and population growth strip fertile land
- The Ultimate Resource 2 Julian Simon
- Population control nonsense Walter Williams, Feb. 24, 1999
- A world of good newsJeff Jacoby, May 14, 2007
- Overpopulation and Standard of Living
- Thomas Sowell Julian Simon, combatant in a 200-year warThomas Sowell, February 12, 1998
- Overpopulation.Com FAQ
- Too Many People? JACQUELINE R. KASUN
- Ron Nielsen, The Little Green Handbook: Seven Trends Shaping the Future of Our Planet, Picador, New York (2006) ISBN 978-0312425814
- E.O. Wilson, The Future of Life
- Overpopulation and Standard of Living
- Jeff Jacoby
- Eating Fossil Fuels
- Best SF : 1969
- washingtonpost.com: Greener Than You Think
- Correcting myths from Julian Simon
- Limits to Growth: The 30-Year Update. Chelsea Green Publishing.
- How peak oil could lead to starvation
- Eating Fossil Fuels | EnergyBulletin.net
- Ecologist Says Unchecked Population Growth Could Bring Misery
- Peak Oil: the threat to our food security
- Agriculture Meets Peak Oil
- Record rise in wheat price prompts UN official to warn that surge in food prices may trigger social unrest in developing countries
- NOVA Online | Secrets of Easter Island | First Inhabitants
- M. Wackernagel, C. Manfreda and D. Deumling, Ecological Footprint of Nations, November 2002 Update: How Much Nature do they Use? How Much Nature do they Have?, Redefining Progress, San Francisco, Ca. (2002)
- Cite error: Invalid
<ref>tag; no text was provided for refs named
- Averting a world food shortage: tighten your belts for CAIRO II. British Medical Journal.
- World Resources Institute
- United Nations Population Division Home Page
- World Population Prospects: The 2006 Revision
- includeonly>"Birth rates 'must be curbed to win war on global poverty'", The Independent, 31 January 2007.
- Q: should the United Nations support more family-planning services for poor countries? | Insight on the News | Find Articles at BNET.com
- Cornell University Entomology - David Pimentel
- Will Limits Of The Earth'S Resources Control Human Numbers?
- Worldwatch Briefing: Sixteen Dimensions of the Population Problem | Worldwatch Institute
- Misleading Math about the Earth: Scientific American
- NASA Earth Science Data and Services: Checking Earth's Vital Signs
- Ecosystem Change: Scientific Facts on Ecosystem Change
- USGS OFR 02-349: Human Impact on the Planet: An Earth Science Perspective and Ethical Considerations
- 1. How have ecosystems changed?
- Ecosystem Change: Scientific Facts on Ecosystem Change
- 3. How have ecosystem changes affected human well-being and poverty alleviation?
- Global Environment Outlook: environment for development (GEO-4)
- # World Resources Institute
- By invitation | The truth about the environment | Economist.com
- Nearly 1 in 5 Chinese overweight or obese - Diet and nutrition - MSNBC.com
- Africa may be able to feed only 25% of its population by 2025
- BBC NEWS | World | Africa | Zimbabwe opposition leader held
- Famine disaster threat to 6m in southern Africa - Telegraph
- MUGABE'S MAN-MADE FAMINE - 2002-09-03
- Mugabe's Famine - Timothy Terrell - Mises Institute
- Famine becomes Mugabe weapon | International | The Observer
- Stricken by hunger among the lush fields - Telegraph
- News: Southern Africa Humanitarian Crisis, Zimbabwe: Mugabe admits chaotic land reforms to blame for food shortages
- Mugabe strikes his final blow against white farmers - Telegraph
- BBC NEWS | World | Africa | Zimbabwe 'asks farmers to return'
- Seeking life in the desert, on the desert's terms
- Index of Economic Freedom
- BBC NEWS | Asia-Pacific | Chinese concern at obesity surge
- BBC NEWS | Americas | Vertical farming in the big Apple
- Hopfenberg, Russell and Pimentel, David, "Human Population Numbers as a Function of Food Supply," Environment, Development and Sustainability, vol. 3, no. 1, March, 2001, pp. 1-15
- Abernathy, Virginia, Population Politics ISBN 0765806037
- Food Production & Population Growth, video with Daniel Quinn and Alan Thornhill
- Hopfenberg, Russell, "Human Carrying Capacity Is Determined by Food Availability," Population & Environment, vol. 25, no. 2, November 2003, pp. 109-117
- Quinn, Daniel, Ishmael ISBN 0-553-07875-5
- Daniel Quinn in his book, "The Story Of B"
- Asia Times Online :: South Asia news - India grows a grain crisis
- Global Water Shortages May Lead to Food Shortages-Aquifer Depletion
- EJP | News | France | French-run water plant launched in Israel
- Black & Veatch-Designed Desalination Plant Wins Global Water Distinction
- The Food Bubble Economy
- Population Outrunning Water Supply as World Hits 6 Billion | Worldwatch Institute
- Amazon.com: When the Rivers Run Dry: Water-The Defining Crisis of the Twenty-First Century: Books: Fred Pearce
- Amazon.com: Outgrowing the Earth: The Food Security Challenge in an Age of Falling Water Tables and Rising Temperatures: Books: Lester R. Brown
- Nuclear Desalination
- Facts from Cohen
- Who Owns Water?
- Evaluating the costs of desalination and water transport. Yuan Zhoua,b, Richard S.J. Tolb,c,dPDF (430 KiB)
- Domesticating the World: Conversion of Natural Ecosystems. World Resources Institute.
- Grasslands in Pieces: Modification and Conversion Take a Toll. World Resources Institute.
- Is there really spare land? A critique of estimates of available cultivable land in developing countries. Environment, Development, and Sustainability.
- Meet the first resident of Dubai's palm-shaped man-made island | the Daily Mail
- Bloomberg.com: Canada
- WWF - Living Planet Report 2006
- Global Footprint Network :: HOME - Ecological Footprint - Ecological Sustainability
- Planning and Markets: Peter Gordon and Harry W. Richardson
- Economics, Macroeconomic Resources - Articles
- We Will Never Run Out of Oil
- Al Gore's Vision of Global Salvation
- Anything Into Oil | Alternative Energy | DISCOVER Magazine
- Anything Into Oil | Alternative Energy | DISCOVER Magazine
- Food and Agriculture Organization of the United Nations. 2001. Food Insecurity: When People Live With Hunger and Fear Starvation. The State of Food insecurity in the World 2001. Italy: FAO
- I.A. Shiklomanov, Appraisal and Assessment of World Water Resources, Water International 25(1): 11-32 (2000)
- The World Bank Group
- IBDeditorials.com: Editorials, Political Cartoons, and Polls from Investor's Business Daily - Free-Trade Fraud
- 3. How have ecosystem changes affected human well-being and poverty alleviation?
- The Wall Street Journal Online - Outside the Box
- Ron Nielsen, The Little Green Handbook: Seven Trends Shaping the Future of Our Planet, Picador, New York (2006) ISBN 978-0312425814
- The New Economy of Nature: The Quest to Make Conservation Profitable (ISBN 1-55963-945-8), Gretchen C. Daily and Katherine Ellison
- includeonly>Rifkin, Jeremy. "The risks of too much city in a crowded world", Toronto Star, December 24 2006. Retrieved on 2006-12-24.
- Principal Agglomerations of the World
- Megacities Of The Future
- Nigeria: Lagos, the mega-city of slums
- Half of humanity set to go urban
- Planet of Slums - The Third World’s Megacities
- State of World Population 2007
- The world goes to town
- Planet of Slums by Mike Davis
- Lagos, Nigeria facts - National Geographic
- China's urban population to reach 800 to 900 million by 2020: expert
- UN Habitat calling urban living 'a good thing
- Un Habitat calling to rethink urban planning
- WWF Living Planet Report 2006
- French-run water plant launched in Israel.
- Black & Veatch-Designed Desalination Plant Wins Global Water Distinction.
- Hubbert, M.K. Techniques of Prediction as Applied to Production of Oil and Gas, US Department of Commerce, NBS Special Publication 631, May 1982
- * Wilson, E.O., 2002, The Future of Life, Vintage ISBN 0-679-76811-4
- Worldwide Deforestation Rates.
- International Energy Outlook 2000, Energy Information Administration, Office of Integrated Analysis and Forecasting, U.S. Department of Energy, Washington D.C. (2000)
- UNEP, Global Environmental Outlook 2000, Earthscan Publications, London, UK (1999)
- Trees and crops reclaim desert in Niger - International Herald Tribune
- Leakey, Richard and Roger Lewin, 1996, The Sixth Extinction : Patterns of Life and the Future of Humankind, Anchor, ISBN 0-385-46809-1
- S.L. Pimm, G.J. Russell, J.L. Gittleman and T.M. Brooks, The Future of Biodiversity, Science 269: 347-350 (1995)
- U.S. National Research Council, Commission on the Science of Climate Change, Washington D.C. (2001)
- "Emerging Infectious Diseases" by Mark E.J. Woolhouse and Sonya Gowtage-Sequeria
- Walter Williams
- Cite error: Invalid
<ref>tag; no text was provided for refs named
- G. McGranahan, S. Lewin, T. Fransen, C. Hunt, M. Kjellen, J. Pretty, C. Stephens and I. Virgin, Environmental Change and Human Health in Countries of Africa, the Caribbean and the Pacific, Stockholm Environment Institute, Stockholm, Sweden (1999)
- Wastewater Pollution in China
- American Council for the United Nations University (2002)
- Heidelberger Institut fur International Konfliktforschung, Konfliktbarometer 2003: 12. Jarlickhe Konfliktanalyse University of Heidelberg, Germany (2004)
- WWF LIving planet report
- Virginia Abernethy, professor (emerita) of psychiatry and anthropology, Population Politics, (1993)
- Albert Bartlett, emeritus professor of physics, Arithmetic, Population, and Energy: The Forgotten Fundamentals of the Energy Crisis, (1978)
- Joel E. Cohen, Chair, Laboratory of Populations at the Rockefeller University, How Many People Can the Earth Support? (1996)
- Barry Commoner, American biologist and college professor Making Peace with the Planet (1990)
- Herman Daly, professor at the School of Public Policy at the University of Maryland, College Park Ecological Economics and the Ecology of Economics (1999)
- Paul R. Ehrlich, Bing Professor of Population Studies, The Population Bomb, (1968) The Population Explosion, (1990) The Population Bomb, (1995) reprint
- Garrett Hardin, 1941 Stanford University - Ph.D. Microbiology, Living Within Limits, (1995) reprint
- Steven LeBlanc, Constant battles: the myth of the peaceful, noble savage, (2003) ISBN 0312310897 argues that local overpopulation has been the major cause of warfare since paleolithic times.
- Bjørn Lomborg, Masters in political science at the University of Aarhus in 1991, The Skeptical Environmentalist: Measuring the Real State of the World, (2001)
- Andrew Mason, Professor, head of the University of Hawaii's population studies program, Population change and economic development in East Asia: Challenges met, opportunities seized (2001)
- Donella Meadows, lead author Ph.D. in biophysics from Harvard, Jorgen Randers, professor of policy analysis at the Norwegian School of Management, Dennis Meadows, director of the Institute for Policy and Social Science Research Limits to Growth: The 30-Year Update (Paperback) (2004)
- Thomas Malthus, English demographer and political economist, An Essay on the Principle of Population, (1798)
- Julian Lincoln Simon, professor of Business Administration The Ultimate Resource 2, (1998)"
- Ben J. Wattenberg, senior fellow at the neoconservative American Enterprise Institute, The Birth Dearth (1989) ??? Fewer: How the New Demography of Depopulation Will Shape Our Future, (2005)
- Daniel Quinn, author The Story of B, pp 304-305 (1996)
- World population projections by the United Nations "World Population to 2300"
- "Bursting at the seams", Jeffrey Sachs's lectures on overpopulation
- AAAS Atlas of Population and Environment
- Optimum Population Trust resources on enivironmentally sustainable population
- U.S. Population Reaches 300 Million, Heading for 400 Million -- No Cause for Celebration
- Earth Policy Institute Resources on POPULATION and HEALTH
- Chart: World Population Growth Through History
- VOA News - World Population Growth to be Concentrated in Developing Nations
- Map over population density
- Is World Population a Concern? Robert Heilbroner, Thomas Malthus, and the Application of Both
- Agriculture - how peak oil could lead to starvation
- Overpopulation: What you can do.
- National Geographic article on overpopulation
- Population and the Environment: The Global Challenge
- World Scientists' Warning to Humanity
- Too Many People? By Dr Jacqueline Kasun
- Catholic Social Teaching On Population Growth An unofficial summary
- Theories of population - from the Catholic Encyclopedia
- Article about overpopulation
- Lecture on population growth over human history
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