Overpopulation Essay Wikipedia

"Overpopulate" and "Overpopulating" redirect here. For the general concept of overpopulation, see Overpopulation.

Human overpopulation (or population overshoot) occurs when the ecological footprint of a human population in a specific geographical location exceeds the carrying capacity of the place occupied by that group. Overpopulation can further be viewed, in a long term perspective, as existing if a population cannot be maintained given the rapid depletion of non-renewable resources or given the degradation of the capacity of the environment to give support to the population. Changes in lifestyle could reverse overpopulated status without a large population reduction.[1][2][3]

The term human overpopulation refers to the relationship between the entire human population and its environment: the Earth,[4] or to smaller geographical areas such as countries. Overpopulation can result from an increase in births, a decline in mortality rates, an increase in immigration, or an unsustainablebiome and depletion of resources. It is possible for very sparsely populated areas to be overpopulated if the area has a meagre or non-existent capability to sustain life (e.g. a desert). Advocates of population moderation cite issues like quality of life, carrying capacity, and risk of starvation as a basis to argue for population decline. Scientists suggest that the human impact on the environment as a result of overpopulation, profligate consumption and proliferation of technology has pushed the planet into a new geological epoch known as the Anthropocene.[5][6][7]

Overview[edit]

Human population has been rising continuously since the end of the Black Death, around the year 1350,[8] although the most significant increase has been since the 1950s, mainly due to medical advancements and increases in agricultural productivity. The rate of population growth has been declining since the 1980s, while the absolute total numbers kept increasing. Recent rate increases in several countries previously enjoying steady declines are also apparently contributing to continued growth in total numbers. The United Nations has expressed concerns on continued population growth in sub-Saharan Africa.[9] Recent research has demonstrated that those concerns are well grounded.[10] As of March 14, 2018 the world's human population is estimated to be 7.609 billion by the United States Census Bureau,[11] and over 7 billion by the United Nations.[12][13][14] Most contemporary estimates for the carrying capacity of the Earth under existing conditions are between 4 billion and 16 billion. Depending on which estimate is used, human overpopulation may or may not have already occurred. Nevertheless, the rapid recent increase in human population is causing some concern. The population is expected to reach between 8 and 10.5 billion between the years 2040[15][16] and 2050.[17] In 2017, the United Nations increased the medium variant projections to 9.8 billion for 2050 and 11.2 billion for 2100.[18]

The recent rapid increase in human population over the past three centuries has raised concerns that the planet may not be able to sustain present or future numbers of inhabitants. The InterAcademy Panel Statement on Population Growth, circa 1994, stated that many environmental problems, such as rising levels of atmospheric carbon dioxide, global warming, and pollution, are aggravated by the population expansion.[19] Other problems associated with overpopulation include the increased demand for resources such as fresh water and food, starvation and malnutrition, consumption of natural resources (such as fossil fuels) faster than the rate of regeneration, and a deterioration in living conditions. Wealthy but highly populated territories like Britain rely on food imports from overseas.[20] This was severely felt during the World Wars when, despite food efficiency initiatives like "dig for victory" and food rationing, Britain needed to fight to secure import routes. However, many believe that waste and over-consumption, especially by wealthy nations, is putting more strain on the environment than overpopulation.[21]

Most countries have no direct policy of limiting their birth rates, but the rates have still fallen due to education about family planning and increasing access to birth control and contraception.

History of concern[edit]

Concern about overpopulation is an ancient topic. Tertullian was a resident of the city of Carthage in the second century CE, when the population of the world was about 190 million (only 3–4% of what it is today). He notably said: "What most frequently meets our view (and occasions complaint) is our teeming population. Our numbers are burdensome to the world, which can hardly support us.... In very deed, pestilence, and famine, and wars, and earthquakes have to be regarded as a remedy for nations, as the means of pruning the luxuriance of the human race." Before that, Plato, Aristotle and others broached the topic as well.[22]

Throughout recorded history, population growth has usually been slow despite high birth rates, due to war, plagues and other diseases, and high infant mortality. During the 750 years before the Industrial Revolution, the world's population increased very slowly, remaining under 250 million.[23]

By the beginning of the 19th century, the world population had grown to a billion individuals, and intellectuals such as Thomas Malthus predicted that humankind would outgrow its available resources, because a finite amount of land would be incapable of supporting a population with a limitless potential for increase.[24]Mercantillists argued that a large population was a form of wealth, which made it possible to create bigger markets and armies.

During the 19th century, Malthus's work was often interpreted in a way that blamed the poor alone for their condition and helping them was said to worsen conditions in the long run.[25] This resulted, for example, in the English poor laws of 1834[25] and in a hesitating response to the Irish Great Famine of 1845–52.[26]

The UN Population Assessment Report of 2004 projects that the world population will plateau by 2050 and will remain stable until 2300.[27] A 2014 study published in Science challenges this projection, asserting that population growth will continue into the next century.[28][29] Adrian Raftery, a University of Washington professor of statistics and sociology and one of the contributors to the study, says: "The consensus over the past 20 years or so was that world population, which is currently around 7 billion, would go up to 9 billion and level off or probably decline. We found there's a 70 percent probability the world population will not stabilize this century. Population, which had sort of fallen off the world's agenda, remains a very important issue."[30] A more recent UN projection suggests the population could grow to as many as 15 billion by 2100.[31]

In 2017, more than a third of 50 Nobel prize-winning scientists surveyed by the Times Higher Education at the Lindau Nobel Laureate Meetings said that human overpopulation and environmental degradation are the two greatest threats facing humankind.[32] In November that same year, a statement by 15,364 scientists from 184 countries indicated that rapid human population growth is the "primary driver behind many ecological and even societal threats."[33]

Human population[edit]

History of population growth[edit]

Main article: World population

Population[9]
YearBillion
18041
19593
19744
19875
19996
20117
20207.7 (estimate)[34]

The human population has gone through a number of periods of growth since the dawn of civilization in the Holocene period, around 10,000 BCE. The beginning of civilization roughly coincides with the receding of glacial ice following the end of the last glacial period.[35] It is estimated that between 1–5 million people, subsisting on hunting and foraging, inhabited the Earth in the period before the Neolithic Revolution, when human activity shifted away from hunter-gathering and towards very primitive farming.[36]

Around 8000 BCE, at the dawn of agriculture, the population of the world was approximately 5 million.[37] The next several millennia saw a steady increase in the population, with very rapid growth beginning in 1000 BCE, and a peak of between 200 and 300 million people in 1 BCE.

The Plague of Justinian caused Europe's population to drop by around 50% between 541 and the 8th century.[38] Steady growth resumed in 800 CE.[39] However, growth was again disrupted by frequent plagues; most notably, the Black Death during the 14th century. The effects of the Black Death are thought to have reduced the world's population, then at an estimated 450 million, to between 350 and 375 million by 1400.[40] The population of Europe stood at over 70 million in 1340;[41] these levels did not return until 200 years later.[42] England's population reached an estimated 5.6 million in 1650, up from an estimated 2.6 million in 1500.[43] New crops from the Americas via the Spanish colonizers in the 16th century contributed to the population growth.[44]

In other parts of the globe, China's population at the founding of the Ming dynasty in 1368 stood close to 60 million, approaching 150 million by the end of the dynasty in 1644.[45][46] The population of the Americas in 1500 may have been between 50 and 100 million.[47]

Encounters between European explorers and populations in the rest of the world often introduced local epidemics of extraordinary virulence. Archaeological evidence indicates that the death of around 90% of the Native American population of the New World was caused by Old World diseases such as smallpox, measles, and influenza.[48] Europeans introduced diseases alien to the indigenous people, therefore they did not have immunity to these foreign diseases.[49]

After the start of the Industrial Revolution, during the 18th century, the rate of population growth began to increase. By the end of the century, the world's population was estimated at just under 1 billion.[50] At the turn of the 20th century, the world's population was roughly 1.6 billion.[50] By 1940, this figure had increased to 2.3 billion.[51] Each subsequent addition of a billion humans took less and less time: 33 years to reach three billion in 1960, 14 years for four billion in 1974, 13 years for five billion in 1987, and 12 years for six billion in 1999.[52]

Dramatic growth beginning in 1950 (above 1.8% per year) coincided with greatly increased food production as a result of the industrialization of agriculture brought about by the Green Revolution.[53] The rate of human population growth peaked in 1964, at about 2.1% per year.[54] For example, Indonesia's population grew from 97 million in 1961 to 237.6 million in 2010,[55][56] a 145% increase in 49 years. In India, the population grew from 361.1 million people in 1951 to just over 1.2 billion by 2011,[57][58] a 235% increase in 60 years.

Continent1900 population[59]
Africa133 million
Asia904 million
Europe408 million
Latin America and Caribbean74 million
North America82 million

There is concern over the sharp population increase in many countries, especially in Sub-Saharan Africa, that has occurred over the last several decades, and that it is creating problems with land management, natural resources and access to water supplies.[60]

The population of Chad has, for example, grown from 6,279,921 in 1993 to 10,329,208 in 2009.[61]Niger, Uganda, Nigeria, Tanzania, Ethiopia and the DRC are witnessing a similar growth in population. The situation is most acute in western, central and eastern Africa.[10] Refugees from places like Sudan have further strained the resources of neighboring states like Chad and Egypt. Chad is also host to roughly 255,000 refugees from Sudan's Darfur region, and about 77,000 refugees from the Central African Republic, while approximately 188,000 Chadians have been displaced by their own civil war and famines, have either fled to either the Sudan, the Niger or, more recently, Libya.[62]

Projections of population growth[edit]

Main article: Projections of population growth

ContinentProjected 2050 population[63]
Africa1.8 billion
Asia5.3 billion
Europe628 million
Latin America and Caribbean809 million
North America392 million

According to projections, the world population will continue to grow until at least 2050, with the population reaching 9 billion in 2040,[64][65] and some predictions putting the population as high as 11 billion in 2050.[66] By 2100, the population could reach 15 billion.[31]Walter Greiling projected in the 1950s that world population would reach a peak of about nine billion, in the 21st century, and then stop growing, after a readjustment of the Third World and a sanitation of the tropics.[67]

In 2000, the United Nations estimated that the world's population was growing at the rate of 1.14% (or about 75 million people) per year and according to data from the CIA's World Factbook, the world human population currently increases by 145 every minute.[68]

According to the United Nations' World Population Prospects report:[69]

  • The world population is currently growing by approximately 74 million people per year. Current United Nations predictions estimate that the world population will reach 9.0 billion around 2050, assuming a decrease in average fertility rate from 2.5 down to 2.0.[70][71]
  • 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 by 44% from 2008 to 2050.[72]
  • 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,[73]Nigeria, Democratic Republic of the Congo, Bangladesh, Uganda, United States, 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 is expected to continue rising from 65 years in 2000–2005 to 75 years in 2045–2050. In the more developed regions, the projection is to 82 years by 2050. Among the least developed countries, where life expectancy today is just under 50 years, it is expected to increase to 66 years by 2045–2050.
  • The population of 51 countries or areas 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.
  • Birth rates are now falling in a small percentage of developing countries, while the actual populations in many developed countries would fall without immigration.[70]

Urban growth[edit]

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.[74] If the trend continues, the world's urban population will double every 38 years, according to 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.[75]

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.[76] One billion people, one-seventh of the world's population, or one-third of urban population, now live in shanty towns,[77] which are seen as "breeding grounds" for social problems such as unemployment, poverty, crime, drug addiction, alcoholism, and other social ills. In many poor countries, slums exhibit high rates of disease due to unsanitary conditions, malnutrition, and lack of basic health care.[78]

In 2000, there were 18 megacities – conurbations such as Tokyo, Beijing, Guangzhou, Seoul, Karachi, Mexico City, Mumbai, São Paulo, London 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 (at 34.1 million).[79]

According to the Far Eastern Economic Review, Asia alone will have at least 10 'hypercities' by 2025, that is, cities inhabited by more than 19 million people, including Jakarta (24.9 million people), Dhaka (25 million), Karachi (26.5 million), Shanghai (27 million) and Mumbai (33 million).[80]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.[81] Chinese experts forecast that Chinese cities will contain 800 million people by 2020.[82]

Causes[edit]

From a historical perspective, technological revolutions have coincided with population expansion. There have been three major technological revolutions – the tool-making revolution, the agricultural revolution, and the industrial revolution – all of which allowed humans more access to food, resulting in subsequent population explosions. For example, the use of tools, such as bow and arrow, allowed primitive hunters greater access to high energy foods (e.g. animal meat). Similarly, the transition to farming about 10,000 years ago greatly increased the overall food supply, which was used to support more people. Food production further increased with the industrial revolution as machinery, fertilizers, herbicides, and pesticides were used to increase land under cultivation as well as crop yields. Today, starvation is caused by economic and political forces rather than a lack of the means to produce food.[83][84]

Significant increases in human population occur whenever the birth rate exceeds the death rate for extended periods of time. Traditionally, the fertility rate is strongly influenced by cultural and social norms that are rather stable and therefore slow to adapt to changes in the social, technological, or environmental conditions. For example, when death rates fell during the 19th and 20th century – as a result of improved sanitation, child immunizations, and other advances in medicine – allowing more newborns to survive, the fertility rate did not adjust downward, resulting in significant population growth. Until the 1700s, seven out of ten children died before reaching reproductive age.[85] Today, more than nine out of ten children born in industrialized nations reach adulthood.[citation needed]

There is a strong correlation between overpopulation and poverty.[86] In contrast, the invention of the birth control pill and other modern methods of contraception resulted in a dramatic decline in the number of children per household in all but the very poorest countries.[87]

Agriculture has sustained human population growth. This dates back to prehistoric times, when agricultural methods were first developed, and continues to the present day, with fertilizers, agrochemicals, large-scale mechanization, genetic manipulation, and other technologies.[88]

Humans have historically exploited the environment using the easiest, most accessible resources first. The richest farmland was plowed and the richest mineral ore mined first. Ceballos, Ehrlich and Ehrlich said that overpopulation is demanding the use of ever more creative, expensive and/or environmentally destructive means in order to exploit ever more difficult to access and/or poorer quality natural resources to satisfy consumers.[89]

Demographic transition[edit]

Main articles: Demographic transition and Sub-replacement fertility

The theory of demographic transition held that, after the standard of living and life expectancy increase, family sizes and birth rates decline. However, as new data has become available, it has been observed that after a certain level of development (HDI equal to 0.86 or higher) the fertility increases again.[90] This means that both the worry that the theory generated about aging populations and the complacency it bred regarding the future environmental impact of population growth are misguided.

Factors cited in the old theory included 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 for 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.

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, Honorary Research Fellow at the University of Leeds, 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.[91]

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 region 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 2.49
  • 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

Excluding the observed reversal in fertility decrease for high development, the projected world number of children born per woman for 2050 would be around 2.05. Only the Middle East & North Africa (2.09) and Sub-Saharan Africa (2.61) would then have numbers greater than 2.05.[92]

Carrying capacity[edit]

Main article: Carrying capacity

This article appears to contradict the article Carrying capacity. Please see discussion on the linked talk page. Please do not remove this message until the contradictions are resolved.(August 2017)

Some groups (for example, the World Wide Fund for Nature[93][94] and 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 the current consumption patterns of Europeans, we would be spending three times more than what the planet can renew.[95] Humanity as a whole was using, by 2006, 40 percent more than what Earth can regenerate.[96] However, Roger Martin of Population Matters states the view: "the poor want to get rich, and I want them to get rich," with a later addition, "of course we have to change consumption habits,... but we've also got to stabilise our numbers".[97] Another study by the World Wildlife Fund in 2014 found that it would take the equivalent of 1.5 Earths of biocapacity to meet humanity's current levels of consumption.[98]

But critics question the simplifications and statistical methods used in calculating Ecological Footprints. Therefore, Global Footprint Network and its partner organizations have engaged with national governments and international agencies to test the results – reviews have been produced by France, Germany, the European Commission, Switzerland, Luxembourg, Japan and the United Arab Emirates.[99] Some point out that a more refined method of assessing Ecological Footprint is to designate sustainable versus non-sustainable categories of consumption.[100][101] However, if yield estimates were adjusted for sustainable levels of production, the yield figures would be lower, and hence the overshoot estimated by the Ecological Footprint method even higher.

Other studies give particular attention to resource depletion and increased world affluence.[further explanation needed][102][103]

In a 1994 study titled Food, Land, Population and the U.S. Economy, David Pimentel and Mario Giampietro estimated the maximum U.S. population for a sustainable economy at 200 million.[104] And in order to achieve a sustainable economy and avert disaster, the United States would have to reduce its population by at least one-third, and world population would have to be reduced by two-thirds.[105]

Many quantitative studies have estimated the world's carrying capacity for humans, that is, a limit to the world population.[106] A meta-analysis of 69 such studies suggests a point estimate of the limit to be 7.7 billion people, while lower and upper meta-bounds for current technology are estimated as 0.65 and 98 billion people, respectively. They conclude: "recent predictions of stabilized world population levels for 2050 exceed several of our meta-estimates of a world population limit".[107]

Effects of human overpopulation[edit]

Further information: Overconsumption and Human impact on the environment

Some more problems associated with or exacerbated by human overpopulation and over-consumption are:

  • Inadequate fresh water[108] for drinking as well as sewage treatment and effluent discharge. Some countries, like Saudi Arabia, use energy-expensive desalination to solve the problem of water shortages.[109][110]
  • Depletion of natural resources, especially fossil fuels.[111]
    World energy consumption & predictions, 1970–2025.
  • Increased levels of air pollution, water pollution, soil contamination and noise pollution.
  • Changes in atmospheric composition and consequent global warming.[112][113][114]
  • Loss of arable land and increase in desertification.[115] Deforestation and desertification can be reversed by adopting property rights, and this policy is successful even while the human population continues to grow.[116]
  • Mass species extinctions and contracting biodiversity[117][118][119][120][121] 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.[122] As of February 2011, the IUCN Red List lists a total of 801 animal species having gone extinct during recorded human history,[123] although the vast majority of extinctions are thought to be undocumented.[122] Biodiversity would continue to grow at an exponential rate if not for human influence.[124] Sir David King, former chief scientific adviser to the UK government, told a parliamentary inquiry: "It is self-evident that the massive growth in the human population through the 20th century has had more impact on biodiversity than any other single factor."[125][126]Paul and Anne Ehrlich said population growth is one of the main drivers of the Earth's extinction crisis.[127]
  • High infant and child mortality.[129] High rates of infant mortality are associated with poverty. Rich countries with high population densities have low rates of infant mortality.[130]
  • 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 viruses that infect humans.
  • Increased chance of the emergence of new epidemics and pandemics.[131] 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.[132]
  • Starvation, malnutrition[133] or poor diet with ill health and diet-deficiency diseases (e.g. rickets). However, rich countries with high population densities do not have famine.[134]
  • 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.[135]
  • Low life expectancy in countries with fastest growing populations.[136]
  • Unhygienic living conditions for many based upon water resource depletion, discharge of raw sewage[137] 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.[138]
  • Elevated crime rate due to drug cartels and increased theft by people stealing resources to survive.[139]
  • Conflict over scarce resources and crowding, leading to increased levels of warfare.[140]
  • Less personal freedom and more restrictive laws. Laws regulate and shape politics, economics, history and society and serve as a mediator of relations and interactions between people. The higher the population density, the more frequent such interactions become, and thus there develops a need for more laws and/or more restrictive laws to regulate these interactions and relations. It was even speculated by Aldous Huxley in 1958 that democracy is threatened due to overpopulation, and could give rise to totalitarian style governments.[141]

Many of these problems are explored in the dystopic science fiction film Soylent Green, where an overpopulated Earth suffers from food shortages, depleted resources and poverty and in the documentary "Aftermath: Population Overload".

David Attenborough described the level of human population on the planet as a multiplier of all other environmental problems.[142] In 2013, he described humanity as "a plague on the Earth" that needs to be controlled by limiting population growth.[143]

Most biologists and sociologists see overpopulation as a serious threat to the quality of human life.[144][145] Some deep ecologists, such as the radical thinker and polemicist Pentti Linkola, see human overpopulation as a threat to the entire biosphere.[146]

The effects of overpopulation are compounded by overconsumption. According to Paul R. Ehrlich:

Rich western countries are now siphoning up the planet’s resources and destroying its ecosystems at an unprecedented rate. We want to build highways across the Serengeti to get more rare earth minerals for our cellphones. We grab all the fish from the sea, wreck the coral reefs and put carbon dioxide into the atmosphere. We have triggered a major extinction event ... A world population of around a billion would have an overall pro-life effect. This could be supported for many millennia and sustain many more human lives in the long term compared with our current uncontrolled growth and prospect of sudden collapse ... If everyone consumed resources at the US level – which is what the world aspires to – you will need another four or five Earths. We are wrecking our planet’s life support systems.[147]

Some economists, such as Thomas Sowell[148] and Walter E. Williams[134] argue that third world poverty and famine are caused in part by bad government and bad economic policies.

Resources[edit]

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 how resources are managed and distributed throughout the population.

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, waste disposal and energy supplies. Overpopulation places competitive stress on the basic life sustaining resources,[150] leading to a diminished quality of life.[145]

Directly related to maintaining the health of the human population is water supply, and it is one of the resources that experience the biggest strain. With the global population at about 7.5 billion, and each human theoretically needing 2 liters of drinking water, there is a demand for 15 billion liters of water each day to meet the minimum requirement for healthy living (United). Weather patterns, elevation, and climate all contribute to uneven distribution of fresh drinking water. Without clean water, good health is not a viable option. Besides drinking, water is used to create sanitary living conditions and is the basis of creating a healthy environment fit to hold human life. In addition to drinking water, water is also used for bathing, washing clothes and dishes, flushing toilets, a variety of cleaning methods, recreation, watering lawns, and farm irrigation. Irrigation poses one of the largest problems, because without sufficient water to irrigate crops, the crops die and then there is the problem of food rations and starvation. In addition to water needed for crops and food, there is limited land area dedicated to food production, and not much more that is suitable to be added. Arable land, needed to sustain the growing population, is also a factor because land being under or over cultivated easily upsets the delicate balance of nutrition supply. There are also problems with location of arable land with regard to proximity to countries and relative population (Bashford 240). Access to nutrition is an important limiting factor in population sustainability and growth. No increase in arable land added to the still increasing human population will eventually pose a serious conflict. Only 38% of the land area of the globe is dedicated to agriculture, and there is not room for much more. Although plants produce 54 billion metric tons of carbohydrates per year, when the population is expected to grow to 9 billion by 2050, the plants may not be able to keep up (Biello). Food supply is a primary example of how a resource reacts when its carrying capacity is exceeded. By trying to grow more and more crops off of the same amount of land, the soil becomes exhausted. Because the soil is exhausted, it is then unable to produce the same amount of food as before, and is overall less productive. Therefore, by using resources beyond a sustainable level, the resource become nullified and ineffective, which further increases the disparity between the demand for a resource and the availability of a resource. There must be a shift to provide adequate recovery time to each one of the supplies in demand to support contemporary human lifestyles. [151][152][153]

David Pimentel 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."[154][155]

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.[156] 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.[156] 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".[157]

On the other hand, some cornucopian researchers, such as Julian L. Simon and Bjørn Lomborg believe that resources exist for further population growth. In a 2010 study, they concluded that "there are not (and will never be) too many people for the planet to feed" according to The Independent.[158] Some 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."[159] Since we are intimately dependent upon the living systems of the Earth,[160][161][162] some 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 prominent 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."[163] "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."[164][165]

Another study was done by the United Nations Environment Programme (UNEP) called the Global Environment Outlook.

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.[166]

Fresh water[edit]

Further information: Water crisis

Fresh water supplies, on which agriculture depends, are running low worldwide.[167][168] This water crisis is only expected to worsen as the population increases.[169]

Potential problems with dependence on desalination are reviewed below, however, the majority of the world's freshwater supply is contained in the polar icecaps, and underground river systems accessible through springs and wells.

Fresh water can 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;[170][171] however, the high costs of desalination, especially for poor countries, make impractical the transport of large amounts of desalinated seawater to interiors of large countries.[172]

Graph of human population from 10000 BCE to 2000 CE. It shows exponential rise in world population that has taken place since the eighteenth century.
Areas of high population densities, calculated in 1994
Human population growth rate in percent, with the variables of births, deaths, immigration, and emigration – 2013
Net annual human population increase by country – 2016.
Urban areas with at least one million inhabitants in 2006. 3% of the world's population lived in cities in 1800, rising to 47% at the end of the twentieth century.

Youth unemployment is also soaring, with the economy unable to absorb the spiraling numbers of those seeking to enter the work force. Many young people do not have the skills to match the needs of the Egyptian market, and the economy is small, weak and insufficiently industrialized... Instead of being something productive, the population growth is a barrel of explosives. —Ofir Winter, an Egypt specialist at the Institute for National Security Studies[149]

An industrial area, with a power plant, south of Yangzhou's downtown, China

The world population explosion: causes, backgrounds and projections for the future

J. Van Bavel

J. Van Bavel, Centre for Sociological Research / Family & Population Studies (FaPOS), Faculty of Social Sciences, University of Leuven, Parkstraat 45 bus 3601, 3000 Leuven, Belgium.

Correspondence at: eb.nevueluk.cos@levaBnaV.naJ

Author information ►Copyright and License information ►

Copyright : © 2013 Facts, Views & Vision

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Facts Views Vis Obgyn. 2013; 5(4): 281–291.

This article has been cited by other articles in PMC.

Abstract

At the beginning of the nineteenth century, the total world population crossed the threshold of 1 billion people for the first time in the history of the homo sapiens sapiens. Since then, growth rates have been increasing exponentially, reaching staggeringly high peaks in the 20th century and slowing down a bit thereafter. Total world population reached 7 billion just after 2010 and is expected to count 9 billion by 2045. This paper first charts the differences in population growth between the world regions. Next, the mechanisms behind unprecedented population growth are explained and plausible scenarios for future developments are discussed. Crucial for the long term trend will be the rate of decline of the number of births per woman, called total fertility. Improvements in education, reproductive health and child survival will be needed to speed up the decline of total fertility, particularly in Africa. But in all scenarios, world population will continue to grow for some time due to population momentum. Finally, the paper outlines the debate about the consequences of the population explosion, involving poverty and food security, the impact on the natural environment, and migration flows.

Key words: Fertility, family planning, world population, population growth, demographic transition, urbanization, population momentum, population projections.

Keywords: Fertility, family planning, world population, population growth, demographic transition, urbanization, population momentum, population projections

Introduction

In the year 1900, Belgium and the Philippines had more or less the same population, around 7 million people. By the year 2000, the population of the Western European monarchy had grown to 10 million citizens, while the South East Asian republic at the turn of the century already counted 76 million citizens. The population of Belgium has since then exceeded 11 million citizens, but it is unlikely that this number will rise to 12 million by the year 2050. The population of the Philippines on the other hand will continue to grow to a staggering 127 million citizens by 2050, according to the demographic projections of the United Nations (UN 2013).

The demographic growth rate of the Philippines around the turn of the century (2% a year) has already created enormous challenges and is clearly unsustainable in the long term: such growth implies a doubling of the population every 35 years as a consequence of which there would be 152 million people by 2035, 304 million by 2070, and so on. Nobody expects such a growth to actually occur. This contribution will discuss the more realistic scenarios for the future.

Even the rather modest Belgian demographic growth rate around the turn of this century (0.46%) is not sustainable in the long term. In any case, it exceeds by far the average growth rate of the human species (homo sapiens sapiens) that arose in Africa some 200.000 years ago. Today, earth is inhabited by some 7 billion people. To achieve this number in 200.000 years, the average yearly growth rate over this term should have been around 0.011% annually (so 11 extra human beings per 1.000 human beings already living on earth). The current Belgian growth rate would imply that our country would have grown to 7 billion in less than 1500 years.

The point of this story is that the current growth numbers are historically very exceptional and untenable in the long term. The demographic growth rates are indeed on the decline worldwide and this paper will attempt to explain some of the mechanisms behind that process. That doesn’t change the fact, however, that the growth remains extraordinarily high and the decline in some regions very slow. This is especially the case in Sub Saharan Africa. In absolute numbers, the world population will continue to grow anyway for quite some time as a result of demographic inertia. This too will be further clarified in this paper.

The evolution of the world population in numbers

In order to be sustainable, the long term growth rate of the population should not differ much from 0%. That is because a growth rate exceeding 0% has exponential implications. In simple terms: if a combination of birth and growth figures only appears to cause a modest population growth initially, then this seems to imply an explosive growth in the longer term.

Thomas R. Malthus already acquired this point of view by the end of the 18th century. In his famous “Essay on the Principle of Population” (first edition in 1789), Malthus argues justly that in time the growth of the population will inevitably slow down, either by an increase of the death rate or by a decrease of the birth rate. On a local scale, migration also plays an important role.

It is no coincidence that Malthus’ essay appeared in England at the end of the 18th century. After all, the population there had started to grow at a historically unseen rate. More specifically the proletariat had grown immensely and that worried the intellectuals and the elite. Year after year, new demographic growth records were recorded.

At the beginning of the 19th century, the number of 1 billion people was exceeded for the first time in history. Subsequently growth accelerated and the number of 2 billion people was already surpassed around 1920. By 1960, another billion had been added, in 40 instead of 120 years time. And it continued to go even faster: 4 billion by 1974, 5 billion by 1987, 6 billion by 1999 and 7 billion in 2011 (Fig. 1).

Fig. 1

Historical growth of the world population since year 0

This will certainly not stop at the current 7 billion. According to the most recent projections by the United Nations, the number of 8 billion will probably be exceeded by 2025, and around 2045 there will be more than 9 billion people1. The further one looks into the future, the more uncertain these figures become, and with demography on a world scale one must always take into account a margin of error of a couple of tens of millions. But according to all plausible scenarios, the number of 9 billion will be exceeded by 2050.

Demographic growth was and is not equally distributed around the globe. The population explosion first occurred on a small scale and with a relatively moderate intensity in Europe and America, more or less between 1750 and 1950. From 1950 on, a much more substantial and intensive population explosion started to take place in Asia, Latin America and Africa (Fig. 2). Asia already represented over 55% of the world population in 1950 with its 1.4 billion citizens and by the year 2010 this had increased to 4.2 billion people or 60%. Of those people, more than 1.3 billion live in China and 1.2 billion in India, together accounting for more than one third of the world population.

Fig. 2

Evolution of the population size by continent, 1950-2050*.

In the future, the proportion of Asia will come down and that of Africa will increase. Africa was populated by some 230 million people around 1950, or 9% of the world population. In 2010 there were already more than 1 billion Africans or 15% of the world population. According to UN projections, Africa will continue to grow at a spectacular rate up to 2.2 billion inhabitants in 2050 or 24% of the world population. The proportion of Europe, on the other hand, is evolving in the opposite direction: from 22% of the world population in 1950, over 11% in 2010 to an expected mere 8% in 2050. The population of Latin America has grown and is growing rapidly in absolute terms, but because of the strong growth in Asia and especially Africa, the relative proportion of the Latin American population is hardly increasing (at most from 6 to 8%). The proportion of the population in North America, finally, has decreased slightly from 7 to 5% of the world population.

What these figures mainly come down to in practice is that the population size in especially the poor countries is increasing at an unprecedented rate. At the moment, more than 5.7 billion people, or more than 80% of humanity, are living in what the UN categorise as a developing country. By 2050, that number would – according to the projections – have increased to 8 billion people or 86% of the world population. Within this group of developing countries, the group of least developed countries, the poorest countries so to speak, is growing strongly: from 830 million now, up to an expected 1.7 billion in 2050. This comprises very poor countries such as Somalia, Sudan, Liberia, Niger or Togo in Africa; Afghanistan, Bangladesh or Myanmar in Asia; and Haiti in the Caribbean.

The growth of the world population goes hand in hand with global urbanisation: while around the year 1950 less than 30% of people lived in the cities, this proportion has increased to more than 50%. It is expected that this proportion will continue to grow to two thirds around 2050. Latin America is the most urbanised continent (84%), closely followed by North America (82%) and at a distance by Europe (73%). The population density has increased intensely especially in the poorest countries: from 9 people per square km in 1950 to 40 people per square km in 2010 (an increase by 330%) in the poorest countries, while this figure in the rich countries increased from 15 to 23 people per square km (a 50% growth). In Belgium, population density is 358 people per square km and in the Netherlands 400 people per square km; in Rwanda this number is 411, in the Palestinian regions 666 and in Bangladesh an astonishing 1050.

Although the world population will continue to grow in absolute figures for some time – a following paragraph will explain why – the growth rate in percentages in all large world regions is decreasing. In the richer countries, the yearly growth rate has already declined to below 0.3%. On a global scale, the yearly growth rate of more than 2% at the peak around 1965 decreased to around 1% now. A further decline to less than 0.5% by 2050 is expected. In the world’s poorest countries, the demographic growth is still largest: at present around 2.2%. For these countries, a considerable decrease is expected, but the projected growth rate would not fall below 1.5% before 2050. This means, as mentioned above, a massive growth of the population in absolute figures in the world’s poorest countries.

Causes of the explosion: the demographic transition

The cause of, first, the acceleration and, then, the deceleration in population growth is the modern demographic transition: an increasingly growing group of countries has experienced a transition from relatively high to low birth and death rates, or is still in the process of experiencing this. It is this transition that is causing the modern population explosion. Figure 3 is a schematic and strongly simplified representation of the modern demographic transition.

Fig. 3

Schematic representation of the modern demographic transition.

In Europe, the modern demographic transition started to take place in the middle of the 18th century. Until then, years of extremely high death rates were quite frequent. Extremely high crisis mortality could be the consequence of epidemic diseases or failed harvests and famine, or a combination of both. As a consequence of better hygiene and a better transportation infrastructure (for one, the canals and roads constructed by Austria in the 18th century), amongst other reasons, crisis mortality became less and less frequent. Later on in the 19th century, child survival began to improve. Vaccination against smallpox for example led to an eradication of the disease, with the last European smallpox pandemic dating from 1871. This way, not only the years of crisis mortality became less frequent, but also the average death rate decreased, from an average 30 deaths per 1000 inhabitants in the beginning of the 19th century to around 15 deaths per 1000 citizens by the beginning of the 20th century. In the meantime, the birth rate however stayed at its previous, high level of 30-35 births per 1000 inhabitants.

The death rate went down but the birth rate still didn’t: this caused a large growth in population. It was only near the end of the nineteenth century (a bit earlier in some countries, later in others) that married couples in large numbers started to reduce their number of children. By the middle of the 20th century, the middle class ideal of a two children household had gained enormous popularity and influence. The reaction by the Church, for example in the encyclical Humanae Vitae (1968), came much too late to bring this evolution to a halt.

As a consequence of widespread family planning – made even easier in the sixties by modern hormonal contraceptives – the birth rate started declining as well and the population tended back towards zero growth. Nowadays the end of this transition process has been more than achieved in all European countries, because the fertility has been below replacement level for several decades (the replacement level is the fertility level that would in the long term lead to a birth rate identical to the death rate, if there would be no migration)2.

That the population explosion in the developing countries since the second half of the 20th century was so much more intense and massive, is a consequence of the fact that in those countries, the process of demographic transition occurred to a much more extreme extent and on a much larger scale. On the one hand, mortality decreased faster than in Europe. After all, in Europe the decline in mortality was the result of a gradual understanding of the importance of hygiene and afterwards the development of new medical insights. These insights of course already existed at the start of the demographic transitions in Asian, Latin American and African regions, whereby the life expectancy in these regions could grow faster. On the other hand, the total fertility – the average number of children per woman – at the start of the transition was a lot higher in many poor regions than it initially was in Europe. For South Korea, Brasil and the Congo, for example, the total fertility rate shortly after the Second World War (at the start of their demographic transition) is estimated to be 6 children per woman. In Belgium this number was close to 4.5 children per woman by the middle of the nineteenth century. In some developing regions, the fertility and birth rate decreased moderately to very fast, but in other regions this decline took off at an exceptionally sluggish pace – this will be further explained later on. As a consequence of these combinations of factors, in most of these countries the population explosion was much larger than it had been in most European countries.

Scenarios for the future

Nonetheless, the process of demographic transition has reached its second phase in almost all countries in the world, namely the phase of declining fertility and birth rates. In a lot of Asian and Latin American countries, the entire transition has taken place and the fertility level is around or below the replacement level. South Korea for example is currently at 1.2 children per woman and is one of the countries with the lowest fertility levels in the world. In Iran and Brasil the fertility level is currently more or less equal to Belgium’s, that is 1.8 to 1.9 children per woman.

Crucial to the future evolution of the population is the further evolution of the birth rate. Scenarios for the future evolution of the size and age of the population differ according to the hypotheses concerning the further evolution of the birth rate. The evolution of the birth rate is in turn dependent on two things: the further evolution of the total fertility rate (the average number of children per woman) in the first place and population momentum in the second. The latter is a concept I will later on discuss in more detail. The role of the population momentum is usually overlooked in the popular debates, but is of utmost importance in understanding the further evolution of the world population. Population momentum is the reason why we are as good as certain that the world population will continue to grow for a while. The other factor, the evolution of the fertility rate, is much more uncertain but of critical importance in the long term. The rate at which the further growth of the world population can be slowed down is primarily dependent on the extent to which the fertility rates will continue to decline. I will further elaborate on this notion in the next paragraph. After that, I will clarify the notion of population momentum.

Declining fertility

Fertility is going down everywhere in the world, but it’s going down particularly slowly in Africa. A further decline remains uncertain there. Figure 4 shows the evolution per world region between 1950 and 2010, plus the projected evolution until 2050. The numbers before 2010 illustrate three things. First of all, on all continents there is a decline going on. Secondly, this decline is not equal everywhere. And thirdly: the differences between the continents remain large in some cases. Asia and Latin America have seen a similar decline in fertility: from 5.9 children per woman in 1950 to 2.5 at the start of the 21st century. Europe and North America had already gone through the largest part of their demographic transition by the 1950’s. Their fertility level has been below replacement levels for years. Africa has indeed seen a global decrease of fertility, but the average number of children is still at an alarmingly high level: the fertility merely decreased from 6.7 to 5.1 children per woman.

Fig. 4

Evolution of the total fertility rate by world region: 1950-2050

These continental averages hide a huge underlying diversity in fertility paths. Figure 5 attempts to illustrate this for a number of countries. Firstly let us consider two African countries: the Congo and Niger. As was often the case in Europe in the 19th century, fertility was first on the rise before it started declining. In the Congo this decrease was more extensive, from around 6 children in 1980 to 4 children per woman today, and a further decline to just below three is expected in the next thirty years. Niger is the country where the fertility level remains highest: from 7 it first rose to an average of just below 8 children per woman in the middle of the 1980’s, before decreasing to just above 6.5 today. For the next decades a decline to 4 children per woman is expected. But that is not at all certain: it is dependent on circumstances that will be further explained in a moment. The demographic transition is after all not a law of nature but the result of human actions and human institutions.

Fig. 5

Evolution of the total fertility rate in some countries between 1950 and 2010, and projected evolution until 2050.

Around 1950, Pakistan and Iran had more or less the same fertility level as Niger, but both countries have seen a considerable decline in the meantime. In Pakistan the level decreased slowly to the current level of 3 children per woman. In Iran the fertility decreased more abruptly, faster and deeper to below the replacement level – Iran today has one of the lowest fertility levels in the world, and a further decline is expected. The Iranian Revolution of 1978 played a crucial role in the history of Iran (Abassi-Shavazi et al., 2009): it brought better education and health care, two essential ingredients for birth control.

Brasil was also one of the countries with very high fertility in the 1950’s – higher than the Congo, for example. The decrease started earlier than in Iran but happened more gradually. Today both countries have the same total fertility, below the replacement level.

Child mortality, education and family planning

Which factors cause the average number of children to go down? The literature concerning explanations for the decrease in fertility is vast and complex, but two factors emerge as crucial in this process: education and child survival.

Considering child survival first: countries combining intensive birth control with very high child mortality are simply non-existent. The statistical association between the level of child mortality and fertility is very tight and strong: in countries with high child mortality, fertility is high, and vice versa. This statistical correlation is very strong because the causal relation goes in both directions; with quick succession of children and therefore a lot of children to take care for, the chances of survival for the infants are lower than in those families with only a limited number of children to take care of – this is a fortiori the case where infrastructure for health care is lacking. A high fertility level thus contributes to a high child mortality. And in the other direction: where survival chances of children improve, the fertility will go down because even those households with a lower number of children have increasing confidence in having descendants in the long term.

It is crucial to understand that the decline in child mortality in the demographic transition always precedes the decline in fertility. Men, women and families cannot be convinced of the benefits of birth control if they don’t have confidence in the survival chances of their children. Better health care is therefore essential, and a lack of good health care is one of the reasons for a persistently high fertility in a country like Niger.

Education is another factor that can cause a decline in fertility. This is probably the most important factor, not just because education is an important humanitarian goal in itself (apart from the demographic effects), but also because with education one can kill two birds with one stone: education causes more birth control but also better child survival (recently clearly demonstrated by Smith-Greenaway (2013), which in its turn will lead to better birth control. The statistical correlation between level of education and level of fertility is therefore very strong.

Firstly, education enhances the motivation for birth control: if parents invest in the education of their children, they will have fewer children, as has been demonstrated. Secondly, education promotes a more forward-looking lifestyle: it will lead people to think on a somewhat longer term, to think about tomorrow, next week and next month, instead of living for the day. This attitude is necessary for effective birth control. Thirdly, education also increases the potential for effective contraception, because birth control doesn’t just happen, especially not when efficient family planning facilities are not or hardly accessible or when there are opposing cultural or family values.

The influence of education on birth control has been demonstrated in a vast number of studies (James et al., 2012). It starts with primary education, but an even larger effect can be attained by investment in secondary education (Cohen, 2008). In a country like Niger, for example, women who didn’t finish primary school have on average 7.8 children. Women who did finish primary school have on average 6.7 children, while women who finished secondary school “only” have 4.6 children (Fig. 6). The fertility of Niger would be a lot lower if more women could benefit from education. The tragedy of that country is that too many people fall in the category of those without a degree of primary school, with all its demographic consequences.

Fig. 6

Association between level of education and total fertility rate in some poor countries.

One achieves with education therefore a plural beneficial demographic effect on top of the important objective of human emancipation in itself. All this is of course not always true but depends on which form of “education”; I assume that we’re talking about education that teaches people the knowledge and skills to better take control of their own destiny.

It is one thing to get people motivated to practice birth control but obtaining actual effective contraception is quite another matter. Information concerning the efficient use of contraceptives and increasing the accessibility and affordability of contraceptives can therefore play an important role. There are an estimated 215 million women who would want to have contraception but don’t have the means (UNFPA, 2011). Investments in services to help with family planning are absolutely necessary and could already have great results in this group of women. But it’s no use to put the cart before the horse: if there is no intention to practice birth control, propaganda for and accessibility of contraception will hardly have any effect, as was demonstrated in the past. In Europe the lion’s share of the decline in fertility was realized with traditional methods, before the introduction of hormonal contraception in the sixties. There is often a problem of lack of motivation for birth control on the one hand, as a result of high child mortality and low schooling rates, and a lack of power in women who may be motivated to limit fertility but are confronted with male resistance on the other (Blanc, 2011; Do and Kurimoto, 2012). Empowerment of women is therefore essential, and education can play an important role in that process as well.

Population momentum

Even if all the people would suddenly practice birth control much more than is currently considered possible, the world population would still continue to grow for a while. This is the consequence of population momentum, a notion that refers to the phenomenon of demographic inertia, comparable to the phenomenon of momentum and inertia in the field of physics. Demographic growth is like a moving train: even when you turn off the engine, the movement will continue for a little while.

The power and direction of population momentum is dependent on the age structure of the population. Compare the population pyramids of Egypt and Germany (Fig. 7). The one for Egypt has a pyramidal shape indeed, but the one for Germany looks more like an onion. As a consequence of high birth rates in the previous decades, the largest groups of Egyptians are to be found below the age of forty; the younger, the more voluminous the generation. Even if the current and future generations of Egyptians would limit their fertility strongly (as is indeed the case), the birth rate in Egypt would still continue to rise for quite some time, just because year after year more and more potential mothers and fathers reach the fertile ages. Egypt therefore clearly has a growth momentum.

Fig. 7

Population pyramids of Egypt (left) and Germany (right).

Germany on the other hand has a negative or shrinking momentum: even if the younger generations of Germans would have a larger num ber of children than the generation of their own parents, the birth rate in Germany would still continue to decrease because fewer and fewer potential mothers and fathers reach the fertile ages.

The population momentum on a global scale is positive: even if fertility would decrease overnight to the replacement level, the world population would continue to grow with 40% (from 7 billion to 9.8 billion). Only the rich countries have a shrinking momentum, that is -3%. For Europe the momentum is -7%. The population momentum for the poorest countries in the world is +44%, that of Sub Saharan Africa +46% (Espenshade et al., 2011).

Consequences of the population explosion

The concerns about the consequences of population explosion started in the sixties. Milestone publications were the 1968 book The Population bomb by biologist Paul Ehrlich, the report of the Club of Rome from 1972 (The Limits to Growth) and the first World Population Plan of Action of the UN in 1974 among others.

In the world population debate, the general concerns involve mainly three interconnected consequences of the population explosion: 1) the growing poverty in the world and famine; 2) the exhaustion and pollution of natural resources essential to human survival; and 3) the migration pressure from the poor South to the rich North (Van Bavel, 2004).

Poverty and famine

The Malthusian line of thought continues to leave an important mark on the debate regarding the association between population growth and poverty: Malthus saw an excessive population growth as an important cause of poverty and famine. Rightfully this Malthusian vision has been criticized a lot. One must after all take the reverse causal relation into account as well: poverty and the related social circumstances (like a lack of education and good health care for children) contribute to high population growth as well.

Concerning famine: the production of food has grown faster since 1960 than the world population has, so nowadays the amount of food produced per person exceeds that which existed before the population explosion (Lam, 2011). The problem of famine isn’t as much an insufficient food production as it is a lack of fair distribution (and a lack of sustainable production, but that’s another issue). Often regions with famine have ecological conditions permitting sufficient production of food, provided the necessary investments in human resources and technology are made. The most important cause of famine is therefore not the population explosion. Famine is primarily a consequence of unequal distribution of food, which in turn is caused by social-economic inequality, lack of democracy and (civil) war.

Poverty and famine usually have mainly political and institutional causes, not demographic ones. The Malthusian vision, that sees the population explosion as the root of all evil, therefore has to be corrected (Fig. 8). Rapid population growth can indeed hinder economical development and can thus pave the way for poverty. But this is only part of the story. As mentioned, poverty is also an underlying cause of rapid population growth. Social factors are at the base of both poverty and population growth. It’s those social factors that require our intervention: via investments in education and (reproductive) health care.

Fig. 8

Connections between social factors, poverty and population growth.

Impact on the environment

The impact of the population explosion on the environment is unquestionably high, but the size of the population represents only one aspect of this. In this regard it can be useful to keep in mind the simple I=PAT scheme: the ecological footprint or impact on the environment (I) can be regarded as the product of the size of the population (P), the prosperity or consumption level (A for affluence) and the technology used (T). The relationship between each of these factors is more complex than the I=PAT scheme suggests, but in any case the footprint I of a population of 1000 people is for example dependent on how many of those people drive a car instead of a bike, and of the emission per car of the vehicle fleet concerned.

The ecological footprint of the world population has increased tremendously the past decades and the growth of the world population has obviously played an important role in this. The other factors in the I=PAT scheme have however played a relatively bigger role than the demographic factor P. The considerable increase in the Chinese ecological footprint of the past decades for example, is more a consequence of the increased consumption of meat than of population growth (Peters et al., 2007; Liu et al., 2008). The carbon dioxide emission of China grew by 82% between 1990 and 2003, while the population only increased by 11% in that same period. A similar story exists for India: the population grew by less than 23% between 1990 and 2003, while the emission of carbon dioxide increased by more than 83% (Chakravarty et al., 2009). The consumption of water and meat in the world is increasing more rapidly than the population3. The consumption of water per person is for example threefold higher in the US than in China (Hoekstra and Chapagain, 2007). The African continent has at present the same number of inhabitants as Europe and North America together, over 1 billion. But the total ecological footprint of Europeans and Americans is many times higher than that of Africans (Ewing et al., 2010). Less than 18% of the world population is responsible for over 50% of the global carbon dioxide emission (Chakravarty et al., 2009).

If we are therefore concerned about the impact of the world population on the environment, we can do something about it immediately by tackling our own overconsumption: it’s something we can control and it has an immediate effect. In contrast, we know of the population growth that it will continue for some time anyhow, even if people in poor countries would practice much more birth control than we consider possible at present.

Migration

The population explosion has created an increasing migration pressure from the South to the North – and there is also important migration within and between countries in the South. But here as well the message is: the main responsibility doesn’t lie with the population growth but with economic inequality. The primary motive for migration was and is economic disparity: people migrate from regions with no or badly paid labour and a low standard of living to other regions, where one hopes to find work and a higher standard of living (Massey et al., 1993; Hooghe et al., 2008; IMO, 2013). Given the permanent population growth and economical inequality, a further increasing migration pressure is to be expected, irrespective of the national policies adopted.

It is sometimes expected that economic growth and increasing incomes in the South will slow down the migration pressure, but that remains to be seen. After all, it isn’t usually the poorest citizens in developing countries that migrate to rich countries. It is rather the affluent middle class in poor countries that have the means to send their sons and daughters to the North – an investment that can raise a lot of money via remittances to the families in the country of origin (IMO, 2013). There is after all a considerable cost attached to migration, in terms of money and human capital. Not everyone can bear those costs: to migrate you need brains, guts and money. With growing economic development in poor countries, an initial increase in migration pressure from those countries would be expected; the association between social-economic development and emigration is not linearly negative but follows the shape of a J turned upside down: more emigration at the start of economic development and a decline in emigration only with further development (De Haas, 2007).

7 Billion and counting… What is to be done?

A world population that needed some millennia before reaching the number of 1 billion people, but then added some billions more after 1920 in less than a century: the social, cultural, economic and ecological consequences of such an evolution are so complex that they can lead to fear and indifference at the same time. What kind of constructive reaction is possible and productive in view of such an enormous issue?

First of all: we need to invest in education and health care in Africa and elsewhere, not just as a humanitarian target per se but also because it will encourage the spread of birth control. Secondly, we need to encourage and support the empowerment of women, not just via education but also via services for reproductive health. This has triple desirable results for demographics: it will lead to more and more effective birth control, which in itself has a positive effect on the survival of children, which in turn again facilitates birth control.

Thirdly: because of the positive population momentum, the world population will certainly continue to grow in absolute figures, even though the yearly growth rate in percentages is already on the decline for several years. The biggest contribution we could make therefore, with an immediate favourable impact for ourselves and the rest of the world, is to change our consumption pattern and deal with the structural overconsumption of the world’s richest countries.

Footnotes

(1)Unless otherwise specified, all figures in this paragraph are based on the United Nations World Population Prospects, the 2012 Revision, http://esa.un.org/wpp/. Concerning projections for the future, I reported the results of the Medium Variant. Apart from this variant, there are also high and low variants (those relying on scenarios implying respectively an extremely high and extremely low growth of the population) and a variant in which the fertility rates are fixed at the current levels. It is expected that the actual number will be somewhere between the highest and lowest variant and will be closest to the medium variant. That’s why I only report this latter value.

(2)In demography, the term «fertility» refers to the actual number of live births per women. By contrast, the term fecundity refers to reproductive capacity (irrespective of actual childbearing), see Habbema et al. (2004).

(3)See http://www.unwater.org/water-cooperation-2013/water-cooperation/facts-and-figures

References

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