Overpopulation is a condition when an organism's numbers exceed the carrying capacity of its ecological niche. 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 use 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 management, and transportation. Negative impacts should also be considered including crowding stress and increased pollution. If addressing the environment as a whole, the survival and well-being of species other than humans must also be considered.
In the context of human societies, overpopulation occurs when the population density is so great as to actually cause an impaired quality of life, serious environmental degradation, or long-term shortages of essential goods and services. This is the definition used by popular dictionaries such Merriam-Webster. Overpopulation is not merely an imbalance between the number of individuals compared to the resources needed for survival, or a ratio of population over resources, or a function of the number or density of individuals, compared to the resources (ie. food production) they need to survive.
Some countries have managed to temporarily increase their carrying capacity by using technologies such as agriculture, desalination, and nuclear power. However most technologies decrease the long-term carrying capacity unless they are designed to be sustainable. 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. , , , , , , .
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 happening, 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 very large increase in available resources. The rise of colonialism meant European countries took food and essential materials from (and so displaced malnutrition and famine onto) poorer countries. His specific predictions for England therefore failed because he used a static analysis, and extrapolated his historical numbers into the future without considering unprecedented factors that could increase the resource base available to rich countries faster than he thought, (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).
Malthus noted that human population could double in 25 years with sufficient food. On a global scale, since the industrial revolution, human population growth has been constrained by food production increases as well as increasingly unequal access to food. 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.
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 come true.  (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 .
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). 
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.  However, Simon's predictions about the Earth being able to support quadrillions of people have been criticized by Hardin, Bartlett, Diamond and others; for example, Simon's predictions would lead to a density of ten persons per square foot of planet within 774 years. For more see .
Between 1950 and 1984, as the Green Revolution transformed agriculture around the globe, world grain production increased by 250%. 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. The oncoming peaking of global oil production (and subsequent decline of production), along with the peak of North American natural gas production will very likely 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. 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 most 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.
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
The theory of demographic transition, while unproven to apply to all world regions, holds that within a generation 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. 
A comparison of fertility rates in Italy and Sweden  suggest Italy is alleviating overpopulation more than Sweden due primarily to greater gender inequality and fewer social services, similar findings from the same source relate to Japan, Russia and Estonia. First and second world effects of social services and gender equality on overpopulation appear to be the opposite of those found in the third world.
Population projections from the 1900's 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 PDF. . 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
Source: Population Division of the Department of Economic and Social Affairs of the United Nation. World Population Prospects: The 2006 Revision.
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. This criticism of religious belief, however, has been disputed, as in this unofficial summary of Catholic Social Teaching On Population Growth.
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. 
On November 16, 2006 George W. Bush announced that the next Deputy Assistant Secretary for Population Affairs will be Dr. Eric Keroack. The U.S. Office of Population Affairs advises the Secretary and the Assistant Secretary for Health on reproductive health issues, including adolescent pregnancy, family planning, and sterilization, as well as other population issues. Keroack, an anti-abortion, anti-birth control obstetrician/gynecologist, is the medical director of A Woman's Concern, a Christian Crisis Pregnancy Center (CPC) in Massachusetts.
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" PDF. See also .
Some writers such as Julian Simon and Bjorn Lomborg and many of a conservative libertarian persuasion, on the other hand, believe that resources abound for a furtherance of population growth. And 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. See the Environment section below. See also .
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"  .
Additionally, other issues involving quality of life - would most people want to live in a world of tens of billions of 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 form 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 this kind of statistic PDF.
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.
Worldwide, 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." 
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. Unless population growth can be slowed quickly by investing heavily in female literacy and family planning services, there may not be a humane solution to the emerging world water shortage. Desalination is a real world, humane, 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.
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 in 2015 could be about half of what it was in 1990 – 92: a drop from 20 to 10 percent. 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
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 . "Well, the United Nations statistics are saying that 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 kilometer. Meanwhile, Israel has a whopping 302 people per square kilometer.  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's 10 times more densely populated than most other African countries, though at a total population of just 1,230,602 it sits at 46 out of 54 of Africa's nations for actual population numbers .  However, Mauritius does not have famine. On the contrary, it's a rich country with 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 2007 article form 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 story 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 successor 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.
However as Daniel Quinn points out in his book "The Story Of B": "When our population system is assessed as a whole, on a global scale, rather than country by country, there is no doubt whatever that, as a whole, our population is increasing catastrophically, so that studies conducted by international groups like the United Nations predict without reservation that there will be twelve billion of us here in forty years or so." However, a more recent report from the U.N. predicts that world population will reach 9.2 billion in the year 2050. 
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. Thus, desalinated water is very expensive only in places far from the sea, like New Delhi, or in high places, like Mexico City. Desalinated water is also 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" PDF.
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 or desertification. Global warming may cause flooding of many of the most productive agricultural areas. Thus, available useful land may become a limiting factor.
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 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. 
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.
Enthusiasts 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." PDF. 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 .
North Korea and South Korea have similar population densities and natural resources. But whereas North Korea is a poor, third world country suffering from terrible famine, South Korea is a rich, first world country where the people are well fed. 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 famine, no matter how high their population densities become. 
Once a country has industrialized and become wealthy, a combination of government regulation 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."
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".
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 Facing the Limits to Growth the authors of the influential 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."
|“||Occasionally, however, there arises the potential for catastrophic overshoot [overpopulation]. Growth in the globe's population and material economy confronts humanity with this possibility. It is the focus of this book. The potential consequences of this overshoot are profoundly dangerous. The situation is unique; it confronts humanity with a variety of issues never before experienced by our species on a global scale. We lack the perspectives, the cultural norms, the habits, and the institutions required to cope. And the damage will, in many cases, take centuries or millennia to correct. But the consequences need not be catastrophic. Overshoot can lead to two different outcomes. One is a crash of some kind. Another is a deliberate turnaround, a correction, a careful easing down. We explore these two possibilities as they apply to human society and the planet that supports it. We believe that a correction is possible and that it could lead to a desirable, sustainable, sufficient future for all the world's peoples. We also believe that if a profound correction is not made soon, a crash of some sort is certain. And it will occur within the lifetimes of many who are alive today.||”|
Actual examples can, in fact, be found of the results of human overpopulation. In Collapse How Societies Choose to Fail or SucceedJared Diamond pieces together the data to argue 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" .||”|
See also the book Easter Island, Earth Island (ISBN 0500050651).
Nuclear Power pros and cons
France is one of the world's most densely populated countries. According to a 2007 story broadcast on 60 Minutes, nuclear power gives France the cleanest air of any industrialized country, and the cheapest electricity in all of Europe. . France reprocesses its nuclear waste to reduce its mass and make more energy. . However, the article continues, "Today we stock containers of waste because currently scientists don't know how to reduce or eliminate the toxicity, but maybe in 100 years perhaps scientists will ... Nuclear waste is an enormously difficult political problem which to date no country has solved. It is, in a sense, the Achilles heel of the nuclear industry ... If France is unable to solve this issue, says Mandil, then 'I do not see how we can continue our nuclear program.'" Further, reprocessing itself has its critics PDF.
In the U.S., which does not reprocess nuclear waste, nuclear power has its own set of problems such as what to do with all the radioactive waste. "Already more than 80,000 tonnes of highly radioactive waste sits in cooling pools next to the 103 US nuclear power plants, awaiting transportation to a storage facility yet to be found. This dangerous material will be an attractive target for terrorist sabotage as it travels through 39 states on roads and railway lines for the next 25 years" . Even keeping track of it all has proved to be a problem . In fact fears have been expressed that terrorists could get ahold of some of it to make nukes . Additionally many point to the possibility of a catastrophic accident at one of these plants which could affect many thousands or even millions. Greenpeace has produced a report titled An American Chernobyl: Nuclear “Near Misses” at U.S. Reactors Since 1986 which "reveals that nearly two hundred “near misses” to nuclear meltdowns have occurred in the United States". At almost 450 nuclear plants in the world that risk is greatly magnified they say. This is not to mention numerous incidents , many unreported, that have occurred. Another report called Nuclear Reactor Hazards: Ongoing Dangers of Operating Nuclear Technology in the 21st Century concludes that risk of a major accident has increased in the past years. See also . For these reason many feel the risks outweigh the benefits.
However, some people claim that the problems of nuclear waste do not come anywhere close to approaching the problems of fossil fuel waste. , . A 2004 article from the BBC states: "The World Health Organization (WHO) says 3 million people are killed worldwide by outdoor air pollution annually from vehicles and industrial emissions, and 1.6 million indoors through using solid fuel."  In the U.S. alone, fossil fuel waste kills 20,000 people each year.  A coal power plant releases 100 times as much radiation as a nuclear power plant of the same wattage.  In addition, fossil fuel waste causes global warming, which leads to increased deaths from hurricanes, flooding, and other weather events. 
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.
Overpopulation by world region
Petén region of Guatemala
This region is inhabited by mostly indigenous peoples. The resource base is stretched thin by deforestation and inability of the fragile tropical forest soils to provide high yield agriculture. Decades of non-sustainable agriculture including considerable slash-and-burn activity by native peoples have left the region unable to feed or support the present population (in terms of food, drinking water, sanitation and other factors).
Despite sustained domestic and international efforts to improve economic and demographic prospects, Bangladesh remains a developing nation, in part due to its large population. Its per capita income in 2006 was US$2300, compared to the world average of $10,200.
Recent (2005-2007) estimates of Bangladesh's population range from 142 to 159 million, making it the 7th most populous nation in the world. With a land area of 144,000 square kilometers (55,600 sq mi (144,000 km²), ranked 94th), the population density is remarkable. A striking comparison is offered by the fact that Russia's population is only slightly smaller. Indeed, Bangladesh boasts the highest population density in the world, excluding a handful of city-states. Bangladesh's population growth was among the highest in the world in the 1960s and 1970s, when the count grew from 50 to 90 million, but with the promotion of birth control in the 1980s, the growth rate slowed. The total fertility rate is now 3.1 children per woman, compared with 6.2 three decades ago. The population is relatively young, with the 0–25 age group comprising 60%, while 3% are 65 or older.
Bangladesh remains among the poorest nations in the world. Many people are landless and forced to live on and cultivate flood-prone land. Nearly half of the population lives on less than 1 US$ per day.
Massive deforestation with resulting desertification, water resource degradation and soil loss has affected approximately ninety percent of Madagascar's previously biologically productive lands. Most of this loss has occurred since independence from the French, and is the result of local people trying merely to subsist. The country is currently unable to provide adequate food, fresh water and sanitation for its population.
Madagascar does not have secure property rights.
Madagascar's long isolation from the neighboring continents (it is the oldest island in the world, isolated for at least 65 million years) has resulted in a unique mix of plants and Malagasy fauna, many found nowhere else in the world; some ecologists refer to Madagascar as the "eighth continent". Unfortunately, Madagascar has lost 95% of its rainforests during the last 50 years.
Its environmental problems are caused especially by rapid population growth. Extensive deforestation has taken place in parts of the country. Slash-and-burn activity, locally called tavy, has occurred in the eastern and western dry forests as well as the on the central high plateau, reducing certain forest habitat and applying pressure to some endangered species. Slash-and-burn is a method sometimes used by shifting cultivators to create short-term yields from marginal soils. When practiced repeatedly, or without intervening fallow periods, the nutrient-poor soils may be exhausted or eroded to an unproductive state. The resulting increased surface runoff from burned lands has caused significant erosion and resulting high sedimentation to western rivers. 
Some members of the Australian environmental movement, notably the organisation Sustainable Population Australia, believe that as the driest inhabited continent, Australia cannot continue to sustain its current rate of population growth without becoming overpopulated. The UK-based Optimum Population Trust supports the view that Australia is overpopulated, and believes that to maintain the current standard of living in Australia, the optimum population is 10 million (rather than the present 20.86 million), or 21 million with a reduced standard of living.
India also has enormous problems with overpopulation. The current population is over a billion, but India does not have much land mass such as China. India is experiencing major problems with declining water tables due to over-extraction beyond sustainable yield. India is building desalination plants to solve this problem.  Because India has the same population density as Japan, some have claimed that India's poverty is caused by underdevelopment, not overpopulation. , .
The Worldwatch Institute said the booming economies of China and India are planetary powers that are shaping the global biosphere. The State of the World 2006 report said the two countries' high economic growth hid a reality of severe pollution. The report states:
- The world's ecological capacity is simply insufficient to satisfy the ambitions of China, India, Japan, Europe and the United States as well as the aspirations of the rest of the world in a sustainable way.
Nigeria is the most populous country in Africa. The 2006 census gave a population of 140 million and country is projected to have a population of 289 million by 2050. According to the United Nations, Nigeria has been undergoing explosive population growth and one of the highest growth and fertility rates in the world. By UN projections, Nigeria will be one of the countries in the world that will account for most of the world's total population increase by 2050. Health, health care, and general living conditions in Nigeria are poor. Life expectancy is 47 years (average male/female) and just over half the population has access to potable water and appropriate sanitation. Nigeria, like many developing countries, suffers from a polio crisis as well as periodic outbreaks of cholera, malaria, and sleeping sickness. Between 1990 and 2005, the Nigeria lost a staggering 79% of its old-growth forests.
Nigeria is losing 1,355 square miles of rangeland and cropland to desertification each year. About 35 million people in northern Nigeria are currently suffering from the effects of desertification. While Nigeria’s human population was growing from 33 million in 1950 to 140 million in 2006, a fourfold expansion, its livestock population grew from 6 million to 66 million, an 11-fold increase. With the food needs of its people and land and the forage needs of cattle, sheep and goats exceeding the carrying capacity of its grasslands, the country is slowly turning to desert and Nigeria’s fast-growing population is being squeezed into an ever-smaller area.
Ethiopia has more fertile land per person than the United Kingdom. In the 1970s, the Ethiopian government seized the farmland from the farmers. This contributed to a 1984 - 1985 famine in Ethiopia. Ethiopia's famine is aggravated by high population growth, bad governance, inefficient agricultural policies, misplaced budgetary priorities, abject poverty, poor infrastructure, lack of access to fertilizers and pesticides, the HIV/AIDS pandemic, and internal conflicts. High population growth is a major factor.
Ethiopia's population has grown from 18 million in 1950 to an estimated 77 million today and is projected to be about 170 million by 2050. FAO estimated on January 6, 2006, that more than 11 million people in the Horn of Africa countries may be affected by an impending widespread famine, largely attributed to a severe drought, and exacerbated by military conflicts in the region. These conditions of drought, together with other factors including high cereal prices, overpopulation in the region, and conflict, lead to 2006 Horn of Africa food crisis.
In a 2005 interview with the BBC, Ethiopian prime minister Meles Zenawi said, "There is a lot of fertile land in the low lands of Ethiopia which is not being utilised."  A 2005 article in The Economist states, "The state owns all the land in Ethiopia... One of two newly formed opposition groups, the Coalition for Unity and Democracy (CUD), offered a liberal alternative: campaigning, among other things, for land to be privatised." 
The combination of decades of drought, desertification, and fast population growth are among the causes of the Darfur conflict, because the Arab Baggara nomads searching for water have to take their livestock further south, to land mainly occupied by non-Arab farming communities.
In Niger, people cutting down trees for firewood contributed to problems of deforestation and desertification. But then the country changed its economic policy, and started to allow private ownership of trees. Once the trees were treated as private property, people had an incentive to take care of them. People could now make more money by caring for the trees and selling the fruit, instead of cutting the trees down for firewood. As a result, the deforestation was reversed, and the forest grew bigger. This happened, despite the fact that the human population was growing. By adopting property rights, the environment benefitted, and the people became wealthier and better fed, even while the human population was growing.
2005-06 Niger food crisis was caused by an early end to the 2004 rains, desert locust damage to some pasture lands, high food prices, and chronic poverty. The food shortage impacts some 3.3 million people — including 800,000 children under age five — in some 3,815 villages. In January 16, 2006, the UN directed an appeal for US$ 240 million of food aid for West Africa to feed at least 10 million people affected by the food crisis, with Niger being the worst-affected country.
Haiti averages approximately 250 people per square kilometre (650 per sq. mi.). Fertility rate (TFR) in Haiti is 4.86 lifetime births per woman (2007 est.). In 1925, Haiti was a lush tropical paradise, with 60% of its original forest covering the lands and mountainous regions. Since then, the population has cut down all but 2% of its forest cover, and in the process has destroyed fertile farmland soils, while contributing to desertification. Haiti remains one of the least-developed countries in the Western Hemisphere. Haiti now ranks 154th of 177 countries in the UN’s Human Development Index (2006). According to the CIA World Factbook, about 80% of the population lives in poverty. Haiti is the only country in the Americas on the WHO list of Least Developed Countries. Unemployment staying high, rising sharply in the mid to late 90's peaking at 70% in 1999 (2000 CIA World Factbook is the source for that number), and then decreasing to the usual rates of around 50% in recent years.
Americans constitute approximately 5% of the world's population, but they produce roughly 25% of the world’s CO2, consume about 25% of world’s resources, including approximately 26% of the world's energy, although having only around 3% of the world’s known oil reserves, and generate approximately 30% of world’s waste.  The average American's impact on the environment is approximately 250 times greater than the average Sub-Saharan African's. 
U.S. Census Bureau figures show the U.S. population grew by 2.8 million between July 1, 2004, and July 1, 2005. If current birth rate and immigration rates were to remain unchanged for another 60 to 70 years, US population would double to approximately 600 million people. The Census Bureau's latest estimates actually go as high as predicting that there will be 1 billion Americans in 2100. United States had approximately one million people in 1700, and approximately five million in 1800.
Some people, such as Julian Simon, counter this with the claim that through innovation, science, and technology, the United States creates more resources than it uses.  Likewise, in an article in The New York Times, John Tierney said that all of the garbage produced in the United States fills up less than 10 square miles of landfill per year, and that after the landfills are full, much of that land gets turned into parks. 
Paul Ehrlich made the point that a state or nation may have a large land area or considerable wealth (which implies, by conventional wisdom, that overpopulation should not be at play), and yet be overpopulated. The U.S. state of Arizona, for example, has enormous land area, but has neither the carrying capacity of arable land or potable water to support its population. While it imports food, using its wealth to offset this shortfall, that only serves to illustrate that it has insufficient carrying capacity. The only way that Arizona (and Southern California) obtains sufficient water is by extraction of water from the Colorado River beyond its fair share (and beyond its own carrying capacity of innate water resources), based on international standards of fair use per lineal mile of river. Recently Arizona has considered expensive desalination as a way to eliminate water shortages. 
According to the California Department of Water Resources, if more supplies aren’t found by 2020, residents will face a shortfall nearly as great as the amount consumed today. Los Angeles is a coastal desert able to support at most 1 million people on its own water; the Los Angeles basin now is the core of a megacity that spans 220 miles from Santa Barbara to the Mexican border. The region’s population is expected to reach 22 million by 2020, 28 million in 2035, and 33 million in 2050. The population of California continues to grow by more than a half million a year and is expected to reach 48 million in 2030. Water shortage issues are likely to arise well before then. California is considering using energy-expensive desalination to solve this problem., , , 
Uganda had a population of approximately seven million people at independence in 1962, and in 45 years the population of Uganda has grown to 30 million. By 2050, there will be a projected 130 million Ugandans, making Uganda the 12th most populated country in the world, with more people than Russia or Japan. Its population will have increased 18-fold in less than 90 years. Many people think that population growth is no longer a problem, and many consider it is politically incorrect to discuss it. In 1968, when Paul Ehrlich produced his book The Population Bomb, overpopulation was seen by many as the gravest long-term threat facing the human race, but now it scarcely gets a mention, even in discussions on climate change: as if the number of people producing and consuming on this planet had no relevance to the magnitude of stress on the environment.
Uganda has 120 people per square km. By comparison, Denmark has 126, Switzerland has 176, Italy has 193, Germany has 232, The United Kingdom has 246, Israel has 302, Japan has 333, Belgium has 341, the Netherlands has 392, South Korea has 480, and Mauritius has 610 - and all of those other countries have a rich, first world standard of living. This suggests that Uganda's problems are aggavated by underdevelopment. 
It should be noted that if developing countries were to consume resources and produce pollution at the current U.S. per-capita level, it would require several planet Earths just to sustain their economies.
During the late 20th century, farmers in Zimbabwe were growing enough food to feed the country. The country also grew enough extra food for export that it was known as "the breadbasket of southern Africa."  Since that time period, President Robert Mugabe seized the farmland and exiled white and foreign farmers from the country  , labelling white farmers as "enemies of the state."  This later resulted in severe famine. However, the population growth of Zimbabwe is lower than many other African nations  , thus the famine is more often attributed to poor governing, underdevelopment, corruption and other factors rather than overpopulation.
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. 
- The chronic inability of many of these countries to escape from the "Malthusian trap" via economic growth exceeding population growth. Many Third World countries simply lack the economic or infrastructural base to provide a rising standard of living for most of their people, especially in Africa, the Arab world, and parts of Latin America.
- 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. 
- Illegal (and legal) immigration to the developed world on an unprecedented scale, creating an unprecedented demographic and political problem in Europe and the United States. Even the controlled and legal migration of talented and well-educated people from the Third World to the developed world denudes it of its limited skills base.
- 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 incidence of hemorrhagic fevers and other infectious diseases from crowding, lack of adequate sanitation and clean potable water, and scarcity of available medical resources.
- 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 birth weight due to the inability of mothers to get enough resources to sustain a fetus from fertilization to birth
- 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
- Over-utilization of infrastructure, such as mass transit, highways, and public health systems
- Higher land prices
Extraterrestrial population projections
- "The germs of existence contained in this spot of earth, with ample food, and ample room to expand in, would fill millions of worlds in the course of a few thousand years."
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 population of five quintillion throughout the solar system by 3000, with the majority in the asteroid belt. Inhabitants of the asteroid belt may risk disaster caused by their home world colliding with other asteroids. Arthur C. Clarke, a fervent supporter of Savage, now argues 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 staggering resources of the solar system could support 10 quadrillion (10^16) people.
K. Eric Drexler, famous inventor of the futuristic concept of Molecular Nanotechnology, has suggested in Engines of Creation that colonizing space will mean breaking the Malthusian limits to growth forever for the human species.
Many authors (eg. Carl Sagan, Arthur C. Clarke, Isaac Asimov) have argued that shipping the excess population into space is no solution to human overpopulation, saying that (Clarke, 1999) "the population battle must be fought or won here on Earth." It is not the lack of resources in space that they see as the problem (as books such as Mining the sky demonstrate); it is the sheer physical impracticality of shipping vast numbers of people into space to "solve" overpopulation on Earth that these authors and others regard as absurd. However, Gerard O'Neill's calculations show that the Earth could offload all new population growth with a launch services industry about the same size as the current airline industry in O'Neill, Gerard K. (1981). 2081: A Hopeful View of the Human Future. Simon and Schuster. ISBN 0-671-44751-3..
Overpopulation in fiction
In 1729, Jonathan Swift wrote the satirical essay A Modest Proposal where he suggests one solution for both the problem of overpopulation and the growing numbers of undernourished people in Ireland: cannibalism, particularly the raising of infants as food.
Science fiction writers have frequently made famous predictions in which they portrayed dystopian futures in which the world has become massively overpopulated. This became a major theme in the 1950s and 1960s. One of the first depictions of future megacities was The Caves of Steel by Isaac Asimov (1954). The 1960s saw increasing anxiety about the prospect of the exponential growth of world population, underscored by the publication of Paul R. Ehrlich's non-fiction The Population Bomb, in 1968. The 1969 Star Trek: The Original Series episode entitled The Mark of Gideon dealt with a race of overpopulated aliens who abducted Captain Kirk to solve their population problem.
In the same year, John Brunner's science-fictional Stand on Zanzibar was published. This is perhaps the definitive overpopulation novel to date, though Harry Harrison's Make Room! Make Room! also became a powerful film (Soylent Green). Logan's Run is a novel by William F. Nolan and George Clayton Johnson (1967), describing a dystopian future society in which the population is kept young by euthanizing everyone who reaches a certain age, thus neatly avoiding the problem of overpopulation. A 1972 film called Z.P.G. featured an overpopulated, very polluted future Earth, whose world government practices Zero Population Growth, executing persons who violate the 30-year ban on procreation. Another 1971 film, called The Last Child also took a stub at laws in the future where families are only allowed to have 1 child and people over 65 are forbidden medical care.
J. G. Ballard's story Billennium pictures a future in which every individual has four, then just three, square meters of living space. Frederik Pohl in The Space Merchants described a future in which even public staircases are rented out as living spaces. Robert Silverberg's The World Inside imagines a future with mile high towers holding a million people each. James Blish and Norman L. Knight in A Torrent of Faces imagine a nightmarish future of 1,000 billion living in just 100,000 cities on Earth.
A similar point, from the opposite point of view, is made by Ursula K. LeGuin in the utopian part of her novel Always Coming Home, in which the visiting anthropologist recognises that one of the reasons for the success and stability of the Kesh culture is simply that there are fewer of them (in the post-apocalyptic future) than previously.
From the 1980s on, there has been an evident lessening of such fears in science fiction. Cyberpunk fiction, such as that of William Gibson, often depicts huge, sprawling cities. Yet these are as remarkable for their energy and diversity as for their more dystopian characteristics.
One of the reasons for this may be the rise of environmental fiction with The End of Nature (1990) by Bill McKibben, the environmental trilogy Ishmael (1992), The Story of B (1996), and My Ishmael (1997) by Daniel Quinn. With the host of environmental problems caused by overpopulation, almost by definition, talking about one is talking about the other.
- How peak oil could lead to starvation
- Eating Fossil Fuels | EnergyBulletin.net
- 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
- Ron Nielsen, The Little Green Handbook: Seven Trends Shaping the Future of Our Planet, Picador, New York (2006) ISBN 978-0312425814
- 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)
- "Averting a world food shortage: tighten your belts for CAIRO II". British Medical Journal. October 19 1996. Check date values in:
- World Population Prospects: The 2006 Revision
- "Birth rates 'must be curbed to win war on global poverty'". The Independent. 31 January 2007. Check date values in:
- 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
- "Domesticating the World: Conversion of Natural Ecosystems". World Resources Institute. September 2000.
- "Grasslands in Pieces: Modification and Conversion Take a Toll". World Resources Institute. December 2000.
- 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)
- 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
- Rifkin, Jeremy (December 24 2006). "The risks of too much city in a crowded world". Toronto Star. Retrieved 2006-12-24. Check date values in:
- "Limits to Growth: The 30-Year Update". Chelsea Green Publishing.
- 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
- Cèsar Barrientos, Asociacion para la Recuperacion, Manejo y Sana Emiento Ambiental and Victor Hugo Fernandez, Guatemala Case Study
- "Reproductive Health and Rights is Fundamental for Sound Economic Development and Poverty Alleviation," United Nations Population Fund. Retrieved 17 July 2007.
- "World Health Report 2005". World Health Organization.
- "Congressional Budget Justification - FY 2005". USAID.
- Peter Tyson. The Eighth Continent: Life, Death, and Discovery in the Lost World of Madagascar. ISBN 0380975777.
- Impact of Population and Poverty on Rainforests
- Deforestation in Madagascar
- population.org.au :: Sustainable Population Australia
- Optimum Population Trust
- Booming nations 'threaten Earth'
- As Consumerism Spreads, Earth Suffers, Study Says
- China and India Key to Ecological Future of the World, Says Report
- UN predicts huge migration to rich countries
- UN Press Release: World Population Increase
- "Nigerian state thwarts polio push". BBC News. March 22, 2004. Retrieved 2006-09-07. Check date values in:
- Nigeria: Environmental Profile
- Protecting Cropland - Advancing Deserts
- Desertification Threatens Economy, Food Security
- Ethiopia rejects war criticism
- Humanitarian Crises in Ethiopia and Eritrea
- Country Report - Ethiopia
- Countries with highest population for 1950, 2005 and 2050
- Ethiopia: Struggling to end food aid dependency
- Millions of people are on the brink of starvation in the Horn of Africa, Food and Agriculture Organization (FAO) news release, 6 January 2006
- Looking to water to find peace in Darfur
- Niger food crisis timeline
- Haiti Total fertility rate - Demographics
- "Forestry". Retrieved 2006-09-18.
- Global Warming
- Illinois Recycling Association Recycling Facts
- SEI: Energy Consumption
- NRDC: Reducing U.S. Oil Dependence
- Alarm sounds on US population boom - The Boston Globe
- Consumption Industrialized, Commercialized, Dehumanized, and Deadly
- October 4, 2006: U.S. Population Reaches 300 Million, Heading for 400 Million: No Cause for Celebration
- US population to pass 300 million milestone
- 1 billion Americans
- Balancing ACT - population growth E: The Environmental Magazine
- Paul Ehrlich, The Population Bomb, Buccaneer Books; Reprint edition (December 1995) ISBN 1568495870
- Colorado River Water Users Association: Arizona
- Stakeholders in the Colorado River
- Allocation by U.S. of Colorado River use beyond fair share
- John F. Kennedy Library, Ralph A. Dungen #8.6 White House Files, Washington DC
- Abernethy, C. L., ed. Intersectoral Management of River Basins. Proceedings of an International Workshop on "Integrated Water Management in Water-Stressed River Basins in Developing Countries: Strategies for Poverty Alleviation and Agricultural Growth," Loskop Dam, South Africa, 1621 October 2000. Colombo, Sri Lanka: IWMI and German Foundation for International Development (DSE), 2001.; Mostert, E., ed. River Basin Management. Proceedings of the International Workshop, The Hague, 2729 October. UNESCO, 1999
- Mexico's small share of Colorado River extraction
- State of the World 2006: China and India Hold World in Balance
- Human consumption straining earth's resources
- I.A. Shiklomanov, Appraisal and Assessment of World Water Resources, Water International 25(1): 11-32 (2000)
- "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)
- 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)
- 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
- 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)
- *The High Frontier (1976, 2000) Gerard O'Neill, Apogee Books ISBN 1-896522-67-X
- Marshall Savage, (1992, 1994) The Millennial Project: Colonizing the Galaxy in Eight Easy Steps. Little, Brown. ISBN 0-316-77163-5
- *Reader's Digest February 2001
- Freeman Dyson, The Sun, The Genome, and The Internet (1999) Oxford University Press. ISBN 0-19-513922-4
- Greetings, Carbon-Based Bipeds! (1999) Arthur C. Clarke, Voyager ISBN 0-00-224698-8
- The Good Earth Is Dying (1971) Isaac Asimov (published in Der Spiegel)
- Mining the Sky (1996) John S. Lewis. Addison Wesley. ISBN 0-201-47959-1
- 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)
- National Security Study Memorandum 200 (a U.S. NSS document from the 1970s)
- Rientrodolce (an Italian interest group which lobbies against overpopulation)
- World Population Foundation
- The Ultimate Resource, a work by Julian Simon challenging the perceived dangers of overpopulation
- Food security
- Global warming
- Immigration reduction
- Medical advances
- Urban sprawl
- Transmigration program
- Water crisis
- Holocene extinction event
- Green Revolution
- White flight
- List of famines
- Medieval demography
- List of countries by fertility rate
- World energy consumption
- Causes of hypothetical future disasters
|Wikiquote has quotations related to: Overpopulation|
- The Population Project
- Chart: World Population Growth Through History
- AAAS Atlas of Population and Environment
- U.S. Population Reaches 300 Million, Heading for 400 Million -- No Cause for Celebration
- Earth Policy Institute Resources on POPULATION and HEALTH
- DIE OFF - a population crash resource page
- VOA News - World Population Growth to be Concentrated in Developing Nations
- Map over population density
- Population Research Institute
- Population-Environment Balance (organization)
- Ecofuture.org Population and Sustainability Website
- A Crusade Against Overpopulation
- Is World Population a Concern? Robert Heilbroner, Thomas Malthus, and the Application of Both
- The Food Bubble Economy
- Agriculture - how peak oil could lead to starvation
- Overpopulation and Happiness
- Eating Fossil Fuels
- Lecture on population growth over human history
- Negative Population Growth (organization)
- LAND, ENERGY AND WATER (ideal US population size)
- Overpopulation.com: Overpopulation FAQ
- Planned Parenthood mission and population stance
- Sustainable Population Australia
- Population Action International (organization)
- Population Connection (formerly Zero Population Growth; organization)
- Appeal to Marco Pannella on overpopulation
- Humanity has no enemies apart from itself (English and Lithuanian)
- Sierra Club's Population Campaign (organization)
- SUSPS (concerned with the Sierra Club's immigration policy; organization)
- Voluntary Human Extinction Movement
- World population projections by the United Nations "World Population to 2300"
- World Population Balance (organization)
- Article about overpopulation
- Introduction to Social Macrodynamics
- MOBUTOBE by art group monochrom. A satirical art activism initiative for the "accomplishment of total population".
- 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
- National Geographic article on overpopulation