Causes of Overpopulation
NB: (This is taken from some sources on the internet. Too long ago I can't remember the link). In fact, this is collected by some students as mentioned at the end of the reading. Thank you.
Pls read this and write an essay on population
Overpopulation is one of the most serious threats to mankind. It's high time we identify and understand the causes of overpopulation and take steps to avoid it. To know more about the causes of overpopulation, read on…
By definition, overpopulation is the condition where the number of organisms exceeds the carrying capacity of their habitat. We are facing the effects of overpopulation in our daily lives. Overpopulation has impacted the life of common man and has proved to be one of the gravest difficulties that have to be fought. Overpopulation implies scarcity of resources and economic inflation; these are the monsters which can make life miserable. Living through the negative effects of overpopulation have made us realize serious problems associated with it. It is high time we wake up and find the causes of overpopulation and work on them.
Causes of Overpopulation
Decline in the Death Rate: The fall in death rates that is decline in mortality rate is one fundamental causes of overpopulation. Owing to the advancements in medicine, man has found cures to the previously fatal diseases. The new inventions in medicine have brought in treatments for most of the dreadful diseases. This has resulted in an increase in the life expectancy of individuals. Mortality rate has declined leading to an increase in population. Owing to modern medications and improved treatments to various illnesses, the overall death rate has gone down. The brighter side of it is that we have been able to fight many diseases and prevent deaths. On the other hand, the medical boon has brought with it, the curse of overpopulation.
Rise in the Birth Rate: Thanks to the new discoveries in nutritional science, we have been able to bring in increase in the fertility rates of human beings. Medicines of today can boost the reproductive rate in human beings. There are medicines and treatments, which can help in conception. Thus, science has led to an increase in birth rate. This is certainly a reason to be proud and happy but advances in medicine have also become a cause of overpopulation.
Migration: Immigration is a problem in some parts of the world. If the inhabitants of various countries migrate to a particular part of the world and settle over there, the area is bound to suffer from the ill effects of overpopulation. If the rates of emigration from a certain nation do not match the rates of immigration to that country, overpopulation makes its way. The country becomes overly populated. Crowding of immigrants in certain parts of the world, results in an imbalance in the density of population.
Lack of Education: Illiteracy is another important cause of overpopulation. Those lacking education fail to understand the need to prevent excessive growth of population. They are unable to understand the harmful effects that overpopulation has. They are unaware of the ways to control population. Lack of family planning is commonly seen in the illiterate lot of the world. This is one of the major factors leading to overpopulation. Due to ignorance, they do not take to family planning measures, thus contributing to a rise in population.
Viewing the issue of increasing population optimistically, one may say that overpopulation means the increase in human resources. The increase in the number of people is the increase in the number of productive hands and creative minds. But we cannot ignore the fact that the increase in the number producers implies an increase in the number of consumers. Greater number of people requires a greater number of resources.
Not every nation is capable of providing its people with the adequate amount of resources. The ever-increasing population will eventually leave no nation capable of providing its people with the resources they need to thrive. When the environment fails to accommodate the living beings that inhabit it, overpopulation becomes a disaster.
By Manali Oak
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, and on the means of resource use and distribution used by that 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 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, 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.
Some countries have managed to increase their carrying capacity by using technologies such as modern agriculture, desalination, and nuclear power. Not everyone agrees that overpopulation is a bad thing. In his book The Ultimate Resource, economist Julian Simon argued that higher population density leads to more specialization and technological innovation, and that this leads to a higher standard of living. But most sociologists see overpopulation as a serious problem.
 Population growth
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 8,000BC, 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.
• The trend for next 800 - 900 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).
• Yet faster growth from the start of the Industrial Revolution around 1700AD.
• 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 the start of the Green Revolution around 1950 and continuing to the present day. Forecast to carry on growing to 8.9 billion, 9.2 billion, 9.5 billion or perhaps even 11 billion by 2050.
Clearly, an inspection of the graphs above reveals the unusual and very pronounced negative skewing. In this case that means after many thousands of years of minimal population there has, for the first time in human history, been a period of consistently rapid population increase followed more recently by a spectacular and unprecedented increase.
 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.
• 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. 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.
• 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 rates 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 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
 Demographic transition
United Nation's population projections by location.
Main article: 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.[original research?]
"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
Main article: Carrying capacity
Estimates of the carrying capacity of Earth range between 1 billion and 1 trillion people, depending on the values used in calculations. The variability of estimates has grown larger since 1950, compared to earlier estimates.
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.
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. "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  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.
 Fresh water
Further information: Water crisis
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 200 miles (320 km) inland though a pipeline to the capital city of Riyadh. 
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 - the US, Canada, France, Australia, Argentina and Thailand - supply 90% of grain exports. The US alone supplies almost half of world 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.
 Global perspective
Growth in food production has been greater than population growth. Food per person increased during the 1961-2005 period.
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.
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 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." PDF
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 riots 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.
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.
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 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. 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[original research?] 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.
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.
According to a 2007 article from the BBC, scientists at Columbia University have theorized that in the future, densely populated cities such as Mexico City, Los Angeles, and New York City, which are the largest in North America, 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 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.
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 apt to run out first are good cropland and fresh water.
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..." Plug-in electric cars such as the Tesla Roadster suggest that Gore's prediction will come true. 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. Most renewable energy forms rely on an oil-based economy to produce, i.e. you cannot make a wind turbine without the oil-run machinery to begin with, making the whole process moot. Some of these renewable resources also have ecological footprints, although they may be different or smaller than some non-renewable resources.
Modern agriculture uses large amounts of fertilizer. Since much of this fertilizer is made from petroleum, the problem of peak oil is of concern. According to articles in Discover Magazine (in 2003 and a 2006), it is possible to use the process of thermal depolymerization to manufacture fertilizer out of garbage, sewage, and agricultural waste.
 Wealth and poverty
As the world's population has grown, the percentage of the world's population living on less than $1 per day (adjusted for inflation) has halved in 20 years. The graph shows the 1981-2001 period.
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 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.
wealth per capita graphed against fertility rate.
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.
Overpopulation has greatly impacted the environment of Earth starting at least as early as the 20th century. There are indirect 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. Says environmental author Jeremy Rifkin, "our burgeoning population and urban way of life have been purchased at the expense of vast ecosystems and habitats. ... It's no accident that as we celebrate the urbanization of the world, we are quickly approaching another historic watershed: the disappearance of the wild."
Says Peter Raven, former President of 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."
A 2001 United Nations report has postulated that, although human activity can be blamed for much of the environmental degradation in the last century, overpopulation is not a major cause, but rising per-capita production and consumption and the use of particular technologies used in such production are more likely major factors. 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.
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.
In 2000, there were 18 megacities – conurbations such as Tokyo, Mexico City, Mumbai (Bombay), 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 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. North America
2. Europe (European Union countries)
3. Middle-East and Central Asia
4. Asia and Pacific Islands
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 2007, the IUCN Red List lists a total of 698 animal species having gone extinct during recorded human history.
• High infant and child mortality. High rates of infant mortality are caused by poverty. Rich countries with high population densities have low rates of infant mortality. 
• Increased chance of the emergence of new epidemics and pandemics 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 diseases.
• 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
 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
See also: Criticism of the Roman Catholic Church#Opposition to contraception
Overpopulation is related to issue of birth control; some nations, like 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 (including 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. Because such a policy would be uniformly and unanimously implemented globally and would be implemented by a reputable central-global organization (United Nations), it would face little political and social opposition from individual countries.
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. 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. 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 (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 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, and that "the population battle must be fought or won here on Earth". (Clarke, 1999) 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 in O'Neill, Gerard K. (1981). 2081: A Hopeful View of the Human Future. Simon and Schuster. ISBN 0-671-44751-3..
 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, thus resulting in a natural and harmless human population-control over time.
Some[who?] propose that governments around the world should stop spending funds on child vaccination because children would and should survive naturally by principle of "survival of the fittest", rather than artificially through vaccination, and argue that humans survived even before the introduction of modern vaccination. They suggest that the funds saved from vaccination should instead be better spent on providing free-of-cost primary and higher education to everyone, particularly the meritorious but needy scholars and students. Alternatively, they argue that it was only the introduction of modern vaccination that led to the growth in world population from less than 1 billion people to more than 6 billion people in the 20th century only. They argue that saving children who are unable to get proper education leads to unemployment and that such uneducated children gradually become a burden to society and to their nations, and many of them resort to becoming criminals
Contributed by NguyenDucNam as part of his homework. Thanks Nam.