Overpopulation is a condition where an organism's numbers exceed the carrying capacity of its habitat. In common parlance, the term usually refers to the relationship between the human population and its environment, the Earth.

Overpopulation does not depend only on the size or density of the population, but on the ratio of population to available sustainable resources. It also depends on the means of resources used and distributed throughout the population. If a given environment has a population of 10 individuals, but there is food or drinking water enough for only 9, then in a closed system where no trade is possible, that environment is overpopulated; if the population is 100 but there is enough food, shelter, and water for 200 for the indefinite future, then it is not overpopulated. Overpopulation can result from an increase in births, a decline in mortality rates due to medical advances, from an increase in immigration, or from an unsustainable biome and depletion of resources. It is possible for very sparsely-populated areas to be overpopulated, as the area in question may have a meager or non-existent capability to sustain human life (e.g. the middle of the Sahara Desert).

The resources to be considered when evaluating whether an ecological niche is overpopulated include clean water, clean air, food, shelter, warmth, and other resources necessary to sustain life. If the quality of human life is addressed, there may be additional resources considered, such as medical care, education, proper sewage treatment and waste disposal. Overpopulation places competitive stress on the basic life sustaining resources, leading to a diminished quality of life..

If resources required to sustain the organism are being consumed by the organism faster than the resource can be renewed, then the organism is overpopulated. For example, humans are destroying topsoil and consuming fossil fuels much faster than the planet can renew them and those resources are currently required to produce and distribute the necessary quantity of food to feed the population, and therefore humans are overpopulated on Earth.

Population growth

History

In order to better present the subject of overpopulation, it may be useful to first review the current population of the world in the context of human population from the dawn of civilization to date. Civilization began roughly 10,000 years ago, coinciding with:

• the final receding of ice following the end of the most recent glacial period and
• the start of the "Neolithic Revolution" when there was a shift in human activity away from “hunter-gathering” and towards very primitive farming.
• At the dawn of agriculture, about 8,000 BC, the population of the world was approximately 5 million.
• Minimal change in population for many thousands of years ending around 1,000BC.
• Steady growth began around 1,000BC which then plateaued (or alternatively peaked) around the year 0., at about 200 to 300 million.
• The trend for next 800 – 1000 years from around 800AD onwards was slow but steady growth, though with major disruption from frequent plagues (most notably the Black Death during the 14th century).
• New crops from the Americas increased the world population before the Industrial Revolution, from 1600 onward; significantly in parts of Asia, like China, where the population doubled from 60 to 150 million under the Ming dynasty.
• Yet faster growth from the start of the Industrial Revolution around 1700AD. About 1 billion persons estimated by 1804.
• At over 6.7 billion World Population is approximately 3 times higher in 2009 than it was at approximately 2.3 billion or less in 1939, despite loss of life during World War II (an upper estimate of which is some 72 million).
• Dramatic growth since around 1950 coinciding with greatly increased food production as a result of the heavy industrialisation of agriculture (known as the Green Revolution). Population is forecast to carry on growing to 8.9 billion, 9.2 billion, 9.5 billion or perhaps even 11 billion by 2050.

1900

• Africa - 133 million
• Asia - 946 million
• Europe - 408 million
• Latin America & Caribbean - 74 million
• Northern America - 82 million

Projections to 2050

United Nations reports, such as World Population Prospects state:

• World population is currently growing by approximately 74 million people per year. If current fertility rates continued, in 2050 the total world population would be 11 billion, with 169 million people added each year. However, global fertility rates have been falling for decades, and 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 2.05
• 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. An exception is the United States population, which is expected to increase 44% from 305 million in 2008 to 439 million in 2050.
• In 2000-2005, the average world fertility was 2.65 children per woman, about half the level 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. China would be higher still in this list were it not for its One Child Policy.
• 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.
• Birth rate are now falling in a small percentage of developing countries, while the actual populations in many developed countries would fall without immigration.
• By 2050 (Medium variant), India will have 1.6 billion people, China 1.4 billion, United States 400 million, Pakistan 309 million, Indonesia 280 million,Nigeria 259 million, Bangladesh 256 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.

2050

• Africa - 1.9 billion
• Asia - 5.2 billion
• Europe - 664 million
• Latin America & Caribbean - 769 million
• Northern America - 445 million

Demographic transition

The theory of demographic transition, while unproven to apply to all world regions, holds that, after the standard of living and life expectancy increase, family sizes and birth rates decline. Factors cited include such social factors as later ages of marriage, the growing desire of many women in such settings to seek careers outside 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 decline in birth rates in industrializing regions.

Another version of demographic transition is that of Virginia Abernethy in Population Politics, where she claims that the demographic transition occurs primarily in 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.

Many countries have high population growth rates but lower total fertility rates because high population growth in the past skewed the age demographic toward a young age, so the population still rises as the more numerous younger generation approaches maturity.

"Demographic entrapment" is a concept developed by Maurice King, who posits that this phenomenon 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. A breakdown by continent is as follows:

• 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 world 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 2.05.

Carrying capacity

There is wide variability both in the definition and in the proposed size of the Earth's carrying capacity, with estimates ranging from 1 to 1000 billion. Around two-thirds of the estimates fall in the range of 4 billion to 16 billion, with a median of about 10 billion.

In a study titled Food, Land, Population and the U.S. Economy, David Pimentel, professor of ecology and agriculture at Cornell University, and Mario Giampietro, senior researcher at the US National Research Institute on Food and Nutrition (INRAN), estimate the maximum U.S. population for a sustainable economy at 200 million. 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.

Steve Jones, head of the biology department at University College London, has said, "Humans are 10,000 times more common than we should be, according to the rules of the animal kingdom, and we have agriculture to thank for that. Without farming, the world population would probably have reached half a million by now."

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. In 2006, WWF's "Living Planet" report stated that in order for all humans to live with a high degree of luxury (European standards), we would be spending three times more than what the planet can supply.

But critics question the simplifications and statistical methods used in calculating ecological footprints. Some point out that a more refined method of assessing ecological footprint is to designate sustainable versus non-sustainable categories of consumption.

Resources

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." "Earth's natural wealth: an audit" by New Scientist magazine states that many of the minerals that we use for a variety of products are in danger of running out in the near future. "[no close quote follows.] A handful of geologists around the world have calculated the costs of new technologies in terms of the materials they use and the implications of their spreading to the developing world. All agree that the planet's booming population and rising standards of living are set to put unprecedented demands on the materials that only Earth itself can provide. Limitations on how much of these materials is available could even mean that some technologies are not worth pursuing long term.... "Virgin stocks of several metals appear inadequate to sustain the modern 'developed world' quality of life for all of Earth's people under contemporary technology".

On the other hand, some writers, such as Julian Simon and Bjorn Lomborg believe that resources exist for further population growth. However, critics warn, this will be at a high cost to the Earth: "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 [268842] 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.

Although all resources, whether mineral or other, are limited on the planet, there is a degree of self-correction whenever a scarcity or high-demand for a particular kind is experienced. For example in 1990 known reserves of many natural resources were higher, and their prices lower, than in 1970, despite higher demand and higher consumption. Whenever a price spike would occur, the market tended to correct itself whether by substituting an equivalent resource or switching to a new technology.

Fresh water

Fresh water supplies, on which agriculture depends, are running low worldwide. This water crisis is only expected to worsen as the population increases. Lester R. Brown of the Earth Policy Institute argues that declining water supplies will have future disastrous consequences for agriculture.

Fresh water can also be obtained from salt water by desalination. For example, Malta derives two thirds of its freshwater by desalination. A number of nuclear powered desalination plants exist, and some argue that there are billions of years of nuclear fuel available. But the high costs of desalination, especially for poor countries, make impractical the transport of large amounts of desalinated seawater to interiors of large countries. However, while desalinizing 1,000 gallons of water can cost as much as $3, the same amount of bottled water costs $7,945.

One study found that "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. 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 somewhat lower costs in places like Beijing, Bangkok, Zaragoza, Phoenix, and, of course, coastal cities like Tripoli." Thus while the study is generally positive about the technology for affluent areas that are proximate to oceans, it 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."

Israel is now desalinating water for a cost of 53 cents per cubic meter, Singapore at 49 cents per cubic meter. In the United States, the cost is 81 cents per cubic meter ($3.06 for 1,000 gallons).

Another problem of desalination is the "lethal byproduct of saline brine that is a major cause of marine pollution when dumped back into the oceans at high temperatures."

The world's largest desalination plant is the Jebel Ali Desalination Plant (Phase 2) in the United Arab Emirates, which can produce 300 million cubic meters of water per year, or about 2500 gallons per second. The largest desalination plant in the US is the one at Tampa Bay, Florida, which began desalinizing 25 million gallons (95000 m³) of water per day in December 2007. A January 17, 2008, article in the Wall Street Journal states, "Worldwide, 13,080 desalination plants produce more than 12 billion gallons of water a day, according to the International Desalination Association." After being desalinized at Jubail, Saudi Arabia, water is pumped inland though a pipeline to the capital city of Riyadh.

Food

Some argue there is enough food to support the world population, but other sources dispute this, particularly if sustainability is taken into account.

More than 100 countries now import wheat and 40 countries import rice. Egypt and Iran rely on imports for 40% of their grain supply. Algeria, Japan, South Korea and Taiwan import 70% or more. Yemen and Israel import more than 90%. And just 6 countries - Argentina, Australia, Canada, France, Thailand and the US - supply 90% of grain exports.

A 2001 United Nations report says population growth is "the main force driving increases in agricultural demand" but "most recent expert assessments are cautiously optimistic about the ability of global food production to keep up with demand for the foreseeable future (that is to say, until approximately 2030 or 2050)", assuming declining population growth rates.

However, the observed figures for 2007 show an actual increase in absolute numbers of undernourished people in the world, 923 million in 2007 versus 832 million in 1995.; the more recent FAO estimates point out to an even more dramatic increase, to 1.02 billion in 2009.

Global perspective

The amounts of natural resources in this context are not necessarily fixed, and their distribution is not necessarily a zero-sum game. For example, due to the Green Revolution and the fact that more and more land is appropriated each year from wild lands for agricultural purposes, the worldwide production of food had steadily increased up until 1995. World food production per person was considerably higher in 2005 than 1961.

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. From 1950 to 1984, as the Green Revolution transformed agriculture around the world, grain production increased by over 250%. The world population has grown by about four billion since the beginning of the Green Revolution and most believe that, without the Revolution, there would be greater famine and malnutrition than the UN presently documents.

The number of people who are overweight has surpassed the number who are undernourished. In a 2006 news story, MSNBC reported, "There are an estimated 800 million undernourished people and more than a billion considered overweight worldwide." The U.S. has one of the highest rates of obesity in the world. 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 proportion of the populations of developing countries is undernourished today than in 1990–92: 17% against 20%. Furthermore, FAO’s projections suggest that the proportion of hungry people in developing countries could be halved from 1990-92 levels to 10% 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."

As of 2008, the price of grain has increased due to more farming used in biofuels, world oil prices at over $100 a barrel, global population growth, climate change, loss of agricultural land to residential and industrial development, and growing consumer demand in China and India Food riot have recently taken place in many countries across the world. An epidemic of stem rust on wheat caused by race Ug99 is currently spreading across Africa and into Asia and is causing major concern. A virulent wheat disease could destroy most of the world’s main wheat crops, leaving millions to starve. The fungus has spread from Africa to Iran, and may already be in Afghanistan and Pakistan.

It is becoming increasingly difficult to maintain food security in a world beset by a confluence of "peak" phenomena, namely peak oil, peak water, peak phosphorus, peak grain and peak fish. Growing populations, falling energy sources and food shortages will create the "perfect storm" by 2030, according to the UK government chief scientist. He said food reserves are at a 50-year low but the world requires 50% more energy, food and water by 2030. The world will have to produce 70% more food by 2050 to feed a projected extra 2.3 billion people and as incomes rise, the United Nations' Food and Agriculture Organisation (FAO) warned.

Africa

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. 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. In 2001, 46.4% of people in sub-Saharan Africa were living in extreme poverty.

According to the BBC, the famine in Zimbabwe was caused by government seizure of farmland. However drought has also played a major role. Drought in southern Africa now threatens 13 million people with famine, 6 million of whom live in Zimbabwe. The current food shortages are projected to worsen. Prior to this combination of drought and seizure of farmland, Zimbabwe exported 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 there are normally 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. Although it is undoubtedly true that bad governance has exacerbated the famine, the article notes that "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 vandalized and looted. A 2006 BBC article about the 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."

Compared to Zimbabwe's population density of 33 people per square kilometre, Israel has 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 for this is that its government encourages farmers to use modern agriculture and irrigation to grow huge amounts of food. Another possible reason is that Israel is a net importer of food. It must also be noted that the high productivity of modern agriculture depends on the unsustainable use of fossil fuels to produce fertilizer and pesticide and to drive farming machinery. Although economic aid has been decreasing from the US it still remains the top receiver.

Asia

In China, only 8% of children are underweight. According to a 2004 article from the BBC, China, the world's most populous country, suffers 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.

Nearly half of India's children are malnourished, according to recent government data. Japan may face a food crisis that could reduce daily diets to the austere meals of the 1950s, believes a senior government adviser.

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 all other animals, human populations predictably grow and shrink according to their available food supply – populations grow in an abundance of food, and shrink in times of scarcity.

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 have 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 when one limits their scope to the population living within a given political boundary, human populations do not always grow to match the available food supply. Additionally, many of these countries are major exporters of food.

Nevertheless, on the global scale the world population is increasing, as is the net quantity of human food produced - a pattern that has been true for roughly 10,000 years, since the human development of agriculture. That some countries demonstrate negative population growth fails to discredit the theory. Food moves across borders from areas of abundance to areas of scarcity. Additionally, this hypothesis is not so simplistic as to be rejected by a single case study, as in Germany's recent population trends - clearly other factors are at work: contraceptive access, cultural norms and most importantly economic realities differ from nation to nation.

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) owing to widespread overdrafting beyond sustainable yields. Other countries affected include Pakistan, Iran, and Mexico. This overdrafting is already leading to water scarcity and cutbacks in grain harvest. Even with the overpumping of its aquifers, China has developed a grain deficit. This effect has contributed in driving 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 soon turn to the world market for grain.

Land

World Resources Institute states that "Agricultural conversion to croplands and managed pastures has affected some 3.3 billion [hectares] — roughly 26 percent of the land area. All totaled, agriculture has displaced one-third of temperate and tropical forests and one-quarter of natural grasslands." Energy development may also require large areas; hydroelectric dams are one example. Usable land may become less useful through salinization, deforestation, desertification, erosion, and urban sprawl. Global warming may cause flooding of many of the most productive agricultural areas. Thus, available useful land may become a limiting factor. By most estimates, at least half of cultivable land is already being farmed, and there are concerns that the remaining reserves are greatly overestimated.

High crop yield vegetables like potatoes and lettuce use less space on 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, and new advances are 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 argue that not all arable land will remain productive if used for agriculture because 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 the United Arab Emirates and particularly the Emirate of Dubai have constructed large artificial islands, or have created large dam and dike systems, like the Netherlands, which reclaim land from the sea to increase their total land area. Some scientists have said that in the future, densely populated cities will use vertical farming to grow food inside skyscrapers.

The space taken by a humans themselves is not a problem. A number of thinkers who deny that overpopulation is a problem have noted that the whole world population could live on land with the area of Texas. The resources that are likely to run out first are good cropland, timber and fresh water.

Energy

Population optimists 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..." Earth has enough uranium to provide humans with all of their electricity needs until the sun blows up in 5 billion years, assuming that we develop large-scale breeder reactors.

There has also been increasing development in extracting renewable energy, such as solar, wind, and tidal energy. If used on a wide scale, these could theoretically fulfill most, if not all, of the energy needs currently being filled by non-renewable resources. Some of these renewable resources also have ecological footprints, although they may be different or smaller than some non-renewable resources.

Fertilizer

Modern agriculture uses large amounts of fertilizer. Since much of this fertilizer is made from petroleum, the problem of peak oil is of concern. According to articles in Discover Magazine (in 2003 and a 2006), it is possible to use the process of thermal depolymerization to manufacture fertilizer out of garbage, sewage, and agricultural waste.

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. Some argue that Earth may support 6 billion people, but only if many live in misery. The proportion of the world's population living on less than $1 per day has halved in 20 years, but these are inflation-unadjusted numbers and likely misleading.

The UN Human Development Report of 1997 states: "During the last 15-20 years, more than 100 developing countries, and several Eastern 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 1930s. 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". Similarly, although the proportion of "starving" people in sub-Saharan Africa has decreased, the absolute number of starving people has increased due to population growth. The percentage dropped from 38% in 1970 to 33% in 1996 and was expected to be 30% by 2010. But the region’s population roughly doubled between 1970 and 1996. To keep the numbers of starving constant, the percentage would have dropped by more than half.

Opponents of birth control sometimes argue that overpopulation is unrelated to extreme poverty.

The chart to the right is illuminating. As of 2004, there were 108 countries in the world with more than five million people. None of these in which women have, on the average, more than 4 children in their lifetime, have a per capita GDP of more than $5000. Conversely, in all but two of the countries with a per capita GDP of more than $5,000, women have, on the average, 2 or fewer children in their lifetime. Israel and Saudi Arabia are the only outliers, with per capita GDP between $15,000 and $25,000, and average lifetime births per woman between 2 and 4.

As their income increases, women are liberated and tend to have fewer "quality kids", like two in place of six.

The correlation does not imply cause and effect, and can be linked to the interplay of birth rates, death rates and economic development.

Environment

Overpopulation has substantially adversely impacted the environment of Earth starting at least as early as the 20th century. There are also economic consequences of this environmental degradation in the form of ecosystem services attrition. Beyond the scientifically verifiable harm to the environment, some assert the moral right of other species to simply exist rather than become extinct. Environmental author Jeremy Rifkin has said that "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 the American Association for the Advancement of Science (AAAS) 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."

Further, even in countries which have both large population growth and major ecological problems, it is not necessarily true that curbing the population growth will make a major contribution towards resolving all environmental problems. However, as developing countries with high populations become more industrialized, pollution and consumption will invariably increase.

The Worldwatch Institute said the booming economies of China and India are planetary powers that are shaping the global biosphere. 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

It said that if China and India were to consume as much resources per capita as United States or Japan in 2030 together they would require a full planet Earth to meet their needs. In the longterm these effects can lead to increased conflict over dwindling resources and in the worst case a Malthusian catastrophe.

Cities

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. Projections indicate that most 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.

In 2000, there were 18 megacities – conurbations such as Tokyo, Seoul, Mexico City, Mumbai, São 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 (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 the increase in population density within cities (and the emergence of megacities), UN Habitat states in its reports that urbanization may be the best compromise in the face of global population growth. Cities concentrate human activity within limited areas, limiting the breadth of environmental damage. But this mitigating influence can only be achieved if urban planning is significantly improved and city services are properly maintained.

Ecological footprint by world region

As set forth on page 18 of WWF's Living Planet report, the regions of the world with the greatest ecological footprint are ranked as follows as of 2003:

1. Northern America
2. Europe (European Union countries)
3. Middle-East and Central Asia
4. Asia and Pacific Islands
5. Africa
6. Europe (Non-European Union countries)
7. Latin-America and the Caribbean

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. As of 2008, the IUCN Red List lists a total of 717 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. [268843]
• Intensive factory farming to support large populations. It results in human threats including the evolution and spread of antibiotic resistant bacteria diseases, excessive air and water pollution, and new virus that infect humans.
• Increased chance of the emergence of new epidemic and pandemics For many environmental and social reasons, including overcrowded living conditions, malnutrition and inadequate, inaccessible, or non-existent health care, the poor are more likely to be exposed to infectious disease.
• Starvation, malnutrition or poor diet with ill health and diet-deficiency diseases (e.g. rickets). However, 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. However, this problem can be reduced with the adoption of sewers. For example, after Karachi, Pakistan installed sewers, its infant mortality rate fell substantially.
• 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
• Less Personal Freedom / More Restrictive Laws. Laws regulate interactions between humans. Law "serves as a primary social mediator of relations between people." [268844] The higher the population density, the more frequent such interactions become, and thus there develops a need for more laws to regulate these interactions.

Some economists, such as Thomas Sowell and Walter E. Williams have argued that third world poverty and famine are caused by bad government and bad economic policies, and not by overpopulation. Most biologists and sociologists see overpopulation as a serious problem.

Mitigation measures

While the current world trends are not indicative of any realistic solution to human overpopulation during the 21st century, there are several mitigation measures that have or can be applied to reduce the adverse impacts of overpopulation.

Birth regulations

Overpopulation is related to the issue of birth control; some nations, like the People's Republic of China, use strict measures to reduce birth rates. Religious and ideological opposition to birth control has been cited as a factor contributing to overpopulation and poverty. Some leaders and environmentalists (such as Ted Turner) have suggested that there is an urgent need to strictly implement a China-like one-child policy globally by the United Nations, because this would help control and reduce population gradually and most successfully as is evidenced by the success and resultant economic-growth of China due to reduction of poverty in recent years.

Indira Gandhi, late Prime Minister of India, implemented a forced sterilization programme in the 1970s. Officially, men with two children or more had to submit to sterilization, but many unmarried young men, political opponents and ignorant men were also believed to have been sterilized. This program is still remembered and criticized in India, and is blamed for creating a wrong public aversion to family planning, which hampered Government programmes for decades.

Urban designer Michael E. Arth has proposed a "choice-based, marketable birth license plan" he calls "birth credits." Birth credits would allow any woman to have as many children as she wants, as long as she buys a license for any children beyond an average allotment that would result in zero population growth (ZPG). If that allotment was determined to be one child, for example, then the first child would be free, and the market would determine what the license fee for each additional child would cost. Extra credits would expire after a certain time, so these credits could not be hoarded by speculators. Another advantage of the scheme is that the affluent would not buy them because they already limit their family size by choice, as evidenced by an average of 1.1 children per European woman. The actual cost of the credits would only be a fraction of the actual cost of having and raising a child, so the credits would serve more as a wake-up call to women who might otherwise produce children without seriously considering the long term consequences to themselves or society.

Education and empowerment

One option is to focus on education about overpopulation, family planning, and birth control methods, and to make birth-control devices like male/female condoms and pills easily available. Some 80 million pregnancies – nearly 40% of the total each year – are unplanned. An estimated 350 million women in the poorest countries of the world 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 annually of complications from pregnancy and abortion. Slightly more than one half of the maternal deaths occurred in the sub-Saharan Africa region, followed by South Asia. Additionally, 8 million infants die, many because of malnutrition or preventable diseases, especially from lack of access to clean drinking water. In the United States, in 2001, almost half of pregnancies were unintended.

Egypt announced a program to reduce its overpopulation by family planning education and putting women in the workforce. It was announced in June 2008 by the Minister of Health and Population Hatem el-Gabali. The government has set aside 480 million Egyptian pounds (about 90 million U.S. dollars) for the program.

Extraterrestrial settlement

In the 1970s, Gerard O'Neill suggested building space habitats that could support 30,000 times the carrying capacity of Earth using just the asteroid belt and that the solar system as a whole could sustain current population growth rates for a thousand years. Marshall Savage (1992, 1994) has projected a human population of five quintillion throughout the solar system by 3000, with the majority in the asteroid belt. Arthur C. Clarke, a fervent supporter of Savage, argued that by 2057 there will be humans on the Moon, Mars, Europa, Ganymede, Titan and in orbit around Venus, Neptune and Pluto. Freeman Dyson (1999) favours the Kuiper belt as the future home of humanity, suggesting this could happen within a few centuries. In Mining the Sky, John S. Lewis suggests that the resources of the solar system could support 10 quadrillion (10¹⁶) people.

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 for the human species.

Many authors, including Carl Sagan, Arthur C. Clarke, and Isaac Asimov have argued that shipping the excess population into space is no solution to human overpopulation. According to Clarke, "the population battle must be fought or won here on Earth". The problem for these authors is not the lack of resources in space (as shown in books such as Mining the Sky), but the physical impracticality of shipping vast numbers of people into space to "solve" overpopulation on Earth. However, Gerard O'Neill's calculations show that Earth could offload all new population growth with a launch services industry about the same size as the current airline industry.

Other approaches and effects

Many philosophers, including Thomas Malthus, have said at various times that when humankind does not check population-growth, nature takes its course. But this course might not result in the death of humans through catastrophes; instead it might result in infertility. German scientists have reported that a virus called Adeno-associated virus might have a role in male infertility, but is otherwise harmless to humans. Thus, if this or similar viruses mutate, they might cause infertility on a large-scale, causing a mass scale viral epidemic and thus resulting in a natural human population-control over time.

See also

• Birth Credits
• Eugenics
• Georgia Guidestones
• One-child policy
• Human migration
• Fertility and intelligence
• List of most highly-populated countries
• Medieval demography
• Over-consumption
• Overpopulation in companion animals
• Agriculture and population limits
• Population ageing
• Population control
• Population reduction
• Rientrodolce, an Italian interest group which lobbies against overpopulation
• Risks to civilization, humans and planet Earth
• Sustainability
• Tragedy of the commons
• Sustainable fertility rate

References

1. Global food crisis looms as climate change and population growth strip fertile land
2. Ron Nielsen, The Little Green Handbook: Seven Trends Shaping the Future of Our Planet, Picador, New York (2006) ISBN 978-0312425814
3. "What was the population of the world in the past?", World-o-meters
4. World Population Summary, U.S. Census Bureau
5. Historical Estimates of World Population, U.S. Census Bureau
6. Microsoft Word - WorldPOP2300.doc
7. United Nations Population Division Home Page, United Nations Department of Economic and Social Affairs
8. US Census Bureau estimates and news release.of AUG. 14, 2008
9. http://www.un.org/News/Press/docs/2005/pop918.doc.html
10. World Population Prospects: The 2006 Revision
11. World Resources Institute
12. Eating Fossil Fuels | EnergyBulletin.net
13. Leading geneticist Steve Jones says human evolution is over, The Times, October 7, 2008
14. Bloomberg.com: Canada
15. WWF - Living Planet Report 2006
16. Global Footprint Network :: HOME - Ecological Footprint - Ecological Sustainability
17. WWF LIving planet report
18. http://www.tinbergen.nl/discussionpapers/98105.pdf
19. Planning and Markets: Peter Gordon and Harry W. Richardson
20. Cornell University Entomology - David Pimentel
21. David Pimentel, et al. "Will Limits of the Earth's Resources Control Human Numbers?", Dieoff.org
22. Worldwatch Briefing: Sixteen Dimensions of the Population Problem, Worldwatch Institute, September 24, 1998
23. Earth's natural wealth: an audit
24. Misleading Math about the Earth: Scientific American
25. NASA Earth Science Data and Services: Checking Earth's Vital Signs
26. Ecosystem Change: Scientific Facts on Ecosystem Change
27. USGS OFR 02-349: Human Impact on the Planet: An Earth Science Perspective and Ethical Considerations
28. Correcting myths from Bjørn Lomborg, Info-pollution.com
29. 1. How have ecosystems changed?
30. Ecosystem Change: Scientific Facts on Ecosystem Change
31. 3. How have ecosystem changes affected human well-being and poverty alleviation?
32. Global Environment Outlook: environment for development (GEO-4)
33. Population Outrunning Water Supply as World Hits 6 Billion | Worldwatch Institute
34. Amazon.com: When the Rivers Run Dry: Water-The Defining Crisis of the Twenty-First Century: Books: Fred Pearce
35. Amazon.com: Outgrowing the Earth: The Food Security Challenge in an Age of Falling Water Tables and Rising Temperatures: Books: Lester R. Brown
36. Nuclear Desalination
37. http://www.sustainablenuclear.org/PADs/pad11983cohen.pdf
38. Who Owns Water?
39. The Arid West—Where Water Is Scarce - Desalination—a Growing Watersupply Source, Library Index
40. Evaluating the costs of desalination and water transport. Yuan Zhoua,b, Richard S.J. Tolb,c,d
41. Desalination gets a serious look, Las Vegas Sun, March 21, 2008
42. 100 Largest Desalination Plants Planned, in Construction, or in Operation—January 1, 2005
43. Applause, At Last, For Desalination Plant, The Tampa Tribune, December 22, 2007
44. Water, Water, Everywhere..., The Wall. St Journal, January 17, 2008
45. Desalination is the Solution to Water Shortages, redOrbit, May 2, 2008
46. Michael Haynes, Rumy Husan 2000 “National inequality and the catch-up period: Some "growth alone" scenarios” Journal of Economic Issues. 34:3 “In a world that now produces more food than is necessary to feed all its population [UN 1994], there is no excuse for hunger and starvation.”
47. Bernard Gilland “World population and food supply can food production keep pace with population growth in the next half-century?” Food Policy 27 (2002) 47–63
48. http://www.globalchange.umich.edu/globalchange2/current/lectures/food_supply/food.htm
49. Food and Agriculture Organization Economic and Social Development Department. “The State of Food Insecurity in the World, 2008 : High food prices and food security - threats and opportunities”. Food and Agriculture Organization of the United Nations, 2008, p. 2.
50. “One sixth of humanity undernourished - more than ever before”. Food and Agriculture Organization of the United Nations, 2009
51. # World Resources Institute
52. By invitation | The truth about the environment | Economist.com
53. http://www.nicholas.duke.edu/people/faculty/pimm/publications/pimmreprints/170_Pimm_Harvey_Nature.pdf
54. " The limits of a Green Revolution?". BBC News. March 29, 2007.
55. " Feed the world? We are fighting a losing battle, UN admits". The Guardian. February 26, 2008.
56. Nearly 1 in 5 Chinese overweight or obese - Diet and nutrition - MSNBC.com
57. 2008: The year of global food crisis
58. The global grain bubble
59. Food crisis will take hold before climate change, warns chief scientist
60. Global food crisis looms as climate change and fuel shortages bite
61. Experts: Global Food Shortages Could ‘Continue for Decades'
62. Has Urbanization Caused a Loss to Agricultural Land?
63. The World's Growing Food-Price Crisis
64. The cost of food: Facts and figures
65. Riots and hunger feared as demand for grain sends food costs soaring
66. Already we have riots, hoarding, panic: the sign of things to come?
67. Feed the world? We are fighting a losing battle, UN admits
68. Millions face famine as crop disease rages
69. IRAN: Killer fungus threatens wheat production in western areas
70. " World faces 'perfect storm' of problems by 2030, chief scientist to warn". The Guardian. March 18, 2009.
71. " Global crisis 'to strike by 2030'". BBC News. March 19, 2009.
72. " Global food production will have to increase 70% for additional 2.3 billion people by 2050". Finfacts.com. September 24, 2009.
73. Africa may be able to feed only 25% of its population by 2025
74. " Birth rates 'must be curbed to win war on global poverty'". The Independent. January 31, 2007.
75. BBC NEWS | World | Africa | Zimbabwe opposition leader held
76. Famine disaster threat to 6 m in southern Africa - Telegraph
77. MUGABE'S MAN-MADE FAMINE - 2002-09-03
78. Mugabe's Famine - Timothy Terrell - Mises Institute
79. Famine becomes Mugabe weapon | International | The Observer
80. Stricken by hunger among the lush fields - Telegraph
81. News: Southern Africa Humanitarian Crisis, Zimbabwe: Mugabe admits chaotic land reforms to blame for food shortages
82. Mugabe strikes his final blow against white farmers - Telegraph
83. BBC NEWS | World | Africa | Zimbabwe 'asks farmers to return'
84. http://en.wikipedia.org/wiki/List_of_countries_by_population_density
85. Seeking life in the desert, on the desert's terms
86. ISRAEL21c
87. Food troubles are here to stay - Haaretz - Israel News
88. Eating fossil fuels http://www.fromthewilderness.com/free/ww3/100303_eating_oil.html
89. Survey Says Nearly Half of India's Children Are Malnourished, CBS News
90. BBC NEWS | Asia-Pacific | Chinese concern at obesity surge
91. Global Water Shortages May Lead to Food Shortages--Aquifer Depletion
92. Japan warned of food shortage, The Australian
93. 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
94. Abernathy, Virginia, Population Politics ISBN 0765806037
95. Food Production & Population Growth, video with Daniel Quinn and Alan Thornhill
96. Hopfenberg, Russell, "Human Carrying Capacity Is Determined by Food Availability," Population & Environment, vol. 25, no. 2, November 2003, pp. 109-117
97. Quinn, Daniel, Ishmael ISBN 0-553-07875-5
98. Daniel Quinn in his book, "The Story Of B"
99. Asia Times Online :: South Asia news - India grows a grain crisis
100. Global Water Shortages May Lead to Food Shortages-Aquifer Depletion
101. EJP | News | France | French-run water plant launched in Israel
102. Black & Veatch-Designed Desalination Plant Wins Global Water Distinction
103. The Food Bubble Economy
104. John Houghton, Global Warming: The Complete Briefing, Cambridge University Press, 2009 ISBN 9780521709163
105. Meet the first resident of Dubai's palm-shaped man-made island | the Daily Mail
106. BBC NEWS | Americas | Vertical farming in the big Apple
107. Economics, Macroeconomic Resources - Articles
108. We Will Never Run Out of Oil
109. Al Gore's Vision of Global Salvation
110. Anything Into Oil | Alternative Energy | DISCOVER Magazine
111. Anything Into Oil | Alternative Energy | DISCOVER Magazine
112. 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
113. I.A. Shiklomanov, Appraisal and Assessment of World Water Resources, Water International 25(1): 11-32 (2000)
114. The World Bank Group
115. 3. How have ecosystem changes affected human well-being and poverty alleviation?
116. The New Economy of Nature: The Quest to Make Conservation Profitable (ISBN 1-55963-945-8), Gretchen C. Daily and Katherine Ellison
117. " Booming nations 'threaten Earth'". BBC News. January 12, 2006.
118. " State of the World 2006: China and India Hold World in Balance". Worldwatch Institute. 11 January 2006.
119. " Effects of Over-Consumption and Increasing Populations". 26 September 2001. Retrieved on 19 June 2007
120. Principal Agglomerations of the World
121. Megacities Of The Future
122. Nigeria: Lagos, the mega-city of slums
123. Half of humanity set to go urban
124. Planet of Slums - The Third World’s Megacities
125. The world goes to town
126. Planet of Slums by Mike Davis
127. Lagos, Nigeria facts - National Geographic
128. China's urban population to reach 800 to 900 million by 2020: expert
129. UN Habitat calling urban living 'a good thing
130. National Geographic Magazine; Special report 2008: Changing Climate (Village Green-article by Michelle Nijhuis)
131. UN Habitat calling to rethink urban planning
132. WWF Living Planet Report 2006
133. Hubbert, M.K. Techniques of Prediction as Applied to Production of Oil and Gas, US Department of Commerce, NBS Special Publication 631, May 1982
134. The Wall Street Journal Online - Outside the Box
135. * Wilson, E.O., 2002, The Future of Life, Vintage ISBN 0-679-76811-4
136. International Energy Outlook 2000, Energy Information Administration, Office of Integrated Analysis and Forecasting, U.S. Department of Energy, Washington D.C. (2000)
137. The world in 2050:Impact of global growth on carbon emissions
138. UNEP, Global Environmental Outlook 2000, Earthscan Publications, London, UK (1999)
139. Trees and crops reclaim desert in Niger - International Herald Tribune
140. Leakey, Richard and Roger Lewin, 1996, The Sixth Extinction : Patterns of Life and the Future of Humankind, Anchor, ISBN 0-385-46809-1
141. S.L. Pimm, G.J. Russell, J.L. Gittleman and T.M. Brooks, The Future of Biodiversity, Science 269: 347-350 (1995)
142. IUCN Red List
143. U.S. National Research Council, Commission on the Science of Climate Change, Washington D.C. (2001)
144. "Emerging Infectious Diseases" by Mark E.J. Woolhouse and Sonya Gowtage-Sequeria
145. WHO Infectious Diseases Report
146. Population control nonsense, Walter Williams, February 24, 1999
147. Index of Economic Freedom
148. 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)
149. Wastewater Pollution in China
150. Clean water could save millions of lives, the-spark.net, November 27, 2006
151. American Council for the United Nations University (2002)
152. Heidelberger Institut fur International Konfliktforschung, Konfliktbarometer 2003: 12. Jarlickhe Konfliktanalyse University of Heidelberg, Germany (2004)
153. Julian Simon, combatant in a 200-year war, Thomas Sowell, February 12, 1998
154. Population control nonsense, Walter Williams, Feb. 24, 1999
155. E.O. Wilson, The Future of Life
156. Ted Turner: Global warming could lead to cannibalism, Atlanta Journal-Constitution, April 3, 2008
157. Ted Turner: World Needs a 'Voluntary' One-Child Policy for the Next Hundred Years, Jones Report
158. Vinay Lal. Indira Gandhi, UCLA College of Letters and Science
159. http://www.corrupt.org/act/interviews/michael_e_arth/ Interview: City Architect and Reconstructor Michael E. Arth by Alex Birch
160. http://laborsofhercules.org/ The Labors of Hercules Modern Solutions to 12 Herculean Problems-Labor II: Overpopulation
161. " Population growth driving climate change, poverty: experts". Agence France-Presse. September 21, 2009.
162. " Netherlands Again Number One Donor to United Nations Population Fund". United Nations Population Fund (UNFPA).
163. " Maternal mortality ratio falling too slowly to meet goal". WHO. October 12, 2007.
164. Q: should the United Nations support more family-planning services for poor countries? | Insight on the News | Find Articles at BNET.com
165. IOL: Population woes weigh down Egypt
166. *The High Frontier (1976, 2000) Gerard O'Neill, Apogee Books ISBN 1-896522-67-X
167. Marshall Savage, (1992, 1994) The Millennial Project: Colonizing the Galaxy in Eight Easy Steps. Little, Brown. ISBN 0-316-77163-5
168. *Reader's Digest February 2001
169. Freeman Dyson, The Sun, The Genome, and The Internet (1999) Oxford University Press. ISBN 0-19-513922-4
170. Greetings, Carbon-Based Bipeds! (1999) Arthur C. Clarke, Voyager ISBN 0-00-224698-8
171. The Good Earth Is Dying (1971) Isaac Asimov (published in Der Spiegel)
172. Mining the Sky (1996) John S. Lewis. Addison Wesley. ISBN 0-201-47959-1
173. http://www.newscientist.com/article.ns?id=dn1483
174. http://news.bbc.co.uk/1/hi/health/1620174.stm

Further reading

• 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.
• F. L. Lucas, The Greatest Problem (1960); an early wake-up call on over-population, by a distinguished Cambridge academic
• 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, 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)

External links

• United Nations world population site. Projections and historical information.
• UN Online databases with selectable variants, either basic or detailed information.
• "Bursting at the seams", Jeffrey Sachs's lectures on overpopulation
• 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
• 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
• Optimum Population Trust
• Populous Planet FLYP Media story on the photography of overpopulation