In demographics, the world population is the total number of humans currently living, and was estimated to have reached 7,800,000,000 people as of March 2020 . It took over 2 million years of human prehistory and history for the world's population to reach 1 billion, and only 200 years more to reach 7 billion.
The world population has experienced continuous growth following the Great Famine of 1315-1317 and the end of the Black Death in 1350, when it was near 370 million. The highest global population growth rates, with increases of over 1.8% per year, occurred between 1955 and 1975 – peaking at 2.1% between 1965 and 1970. The growth rate declined to 1.2% between 2010 and 2015 and is projected to decline further in the course of the 21st century.
The global population is still increasing, but there is significant uncertainty about its long-term trajectory due to changing rates of fertility and mortality. The UN Department of Economics and Social Affairs projects between 9-10 billion people by 2050, and gives an 80% confidence interval of 10-12 billion by the end of the 21st century.
Total annual births were highest in the late 1980s at about 139 million, and as of 2011 were expected to remain essentially constant at a level of 135 million, while deaths numbered 56 million per year and were expected to increase to 80 million per year by 2040. The median age of the world's population was estimated to be 30.4 years in 2018.
|World population (millions, UN estimates)|
|#||Top ten most populous countries||2000||2015||2030[A]|
Six of the Earth's seven continents are permanently inhabited on a large scale. Asia is the most populous continent, with its 4.64 billion inhabitants accounting for 60% of the world population. The world's two most populated countries, China and India, together constitute about 36% of the world's population. Africa is the second most populated continent, with around 1.34 billion people, or 17% of the world's population. Europe's 747 million people make up 10% of the world's population as of 2020, while the Latin American and Caribbean regions are home to around 653 million (8%). North America, primarily consisting of the United States and Canada, has a population of around 368 million (5%), and Oceania, the least populated region, has about 42 million inhabitants (0.5%).Antarctica only has a very small, fluctuating population of about 1200 people based mainly in polar science stations.
|Most populous country||Most populous city (metropolitan area)|
|Asia||104.1||4,641||1,439,323,000[note 1] - China||37,393,000/13,929,000 - Greater Tokyo Area/Tokyo Metropolis|
|Africa||44.4||1,340||Nigeria206,139,000 -||20,900,000 - Cairo|
145,934,000 - |
approx. 110 million in Europe
|16,855,000/12,537,000 - Moscow metropolitan area/Moscow|
|Latin America||24.1||653||Brazil212,559,000 -||22,043,000/12,176,000 - São Paulo Metro Area/São Paulo City|
|Northern America[note 2]||14.9||368||United States331,002,000 -||23,724,000/8,323,000 - New York metropolitan area/New York City|
|Oceania||5||42||Australia25,499,000 -||4,925,000 - Sydney|
|Antarctica||~0||0.004||N/A[note 3]||1,258 - McMurdo Station|
Estimates of world population by their nature are an aspect of modernity, possible only since the Age of Discovery. Early estimates for the population of the world date to the 17th century: William Petty in 1682 estimated world population at 320 million (modern estimates ranging close to twice this number); by the late 18th century, estimates ranged close to one billion (consistent with modern estimates). More refined estimates, broken down by continents, were published in the first half of the 19th century, at 600 million to 1 billion in the early 1800s and at 800 million to 1 billion in the 1840s.
It is difficult for estimates to be better than rough approximations, as even modern population estimates are fraught with uncertainties on the order of 3% to 5%.
Estimates of the population of the world at the time agriculture emerged in around 10,000 BC have ranged between 1 million and 15 million. Even earlier, genetic evidence suggests humans may have gone through a population bottleneck of between 1,000 and 10,000 people about 70,000 BC, according to the Toba catastrophe theory. By contrast, it is estimated that around 50-60 million people lived in the combined eastern and western Roman Empire in the 4th century AD.
The Plague of Justinian, which first emerged during the reign of the Roman emperor Justinian, caused Europe's population to drop by around 50% between the 6th and 8th centuries AD. The population of Europe was more than 70 million in 1340. The Black Death pandemic of the 14th century may have reduced the world's population from an estimated 450 million in 1340 to between 350 and 375 million in 1400; it took 200 years for population figures to recover. The population of China decreased from 123 million in 1200 to 65 million in 1393, presumably from a combination of Mongol invasions, famine, and plague.
Starting in AD 2, the Han Dynasty of ancient China kept consistent family registers in order to properly assess the poll taxes and labor service duties of each household. In that year, the population of Western Han was recorded as 57,671,400 individuals in 12,366,470 households, decreasing to 47,566,772 individuals in 9,348,227 households by AD 146, towards the End of the Han Dynasty. At the founding of the Ming Dynasty in 1368, China's population was reported to be close to 60 million; toward the end of the dynasty in 1644, it may have approached 150 million. England's population reached an estimated 5.6 million in 1650, up from an estimated 2.6 million in 1500. New crops that were brought to Asia and Europe from the Americas by Portuguese and Spanish colonists in the 16th century are believed to have contributed to population growth. Since their introduction to Africa by Portuguese traders in the 16th century,maize and cassava have similarly replaced traditional African crops as the most important staple food crops grown on the continent.
The pre-Columbian population of the Americas is uncertain; historian David Henige called it "the most unanswerable question in the world." By the end of the 20th century, scholarly consensus favored an estimate of roughly 55 million people, but numbers from various sources have ranged from 10 million to 100 million. Encounters between European explorers and populations in the rest of the world often introduced local epidemics of extraordinary virulence. According to the most extreme scholarly claims, as many as 90% of the Native American population of the New World died of Old World diseases such as smallpox, measles, and influenza. Over the centuries, the Europeans had developed high degrees of immunity to these diseases, while the indigenous peoples had no such immunity.
During the European Agricultural and Industrial Revolutions, the life expectancy of children increased dramatically. The percentage of the children born in London who died before the age of five decreased from 74.5% in 1730-1749 to 31.8% in 1810-1829. Between 1700 and 1900, Europe's population increased from about 100 million to over 400 million. Altogether, the areas populated by people of European descent comprised 36% of the world's population in 1900.
Population growth in the West became more rapid after the introduction of vaccination and other improvements in medicine and sanitation. Improved material conditions led to the population of Britain increasing from 10 million to 40 million in the 19th century. The population of the United Kingdom reached 60 million in 2006. The United States saw its population grow from around 5.3 million in 1800 to 106 million in 1920, exceeding 307 million in 2010.
The first half of the 20th century in Imperial Russia and the Soviet Union was marked by a succession of major wars, famines and other disasters which caused large-scale population losses (approximately 60 million excess deaths). After the collapse of the Soviet Union, Russia's population declined significantly - from 150 million in 1991 to 143 million in 2012 - but by 2013 this decline appeared to have halted.
Many countries in the developing world have experienced extremely rapid population growth since the early 20th century, due to economic development and improvements in public health. China's population rose from approximately 430 million in 1850 to 580 million in 1953, and now stands at over 1.3 billion. The population of the Indian subcontinent, which was about 125 million in 1750, increased to 389 million in 1941; today, India, Pakistan and Bangladesh are collectively home to about 1.63 billion people.Java had about 5 million inhabitants in 1815; its present-day successor, Indonesia, now has a population of over 140 million. In just one hundred years, the population of Brazil decupled (x10), from about 17 million in 1900, or about 1% of the world population in that year, to about 176 million in 2000, or almost 3% of the global population in the very early 21st century. Mexico's population grew from 13.6 million in 1900 to about 112 million in 2010. Between the 1920s and 2000s, Kenya's population grew from 2.9 million to 37 million.
|World population milestones in billions (Worldometers estimates)|
It is estimated that the world population reached one billion for the first time in 1804. It was another 123 years before it reached two billion in 1927, but it took only 33 years to reach three billion in 1960. Thereafter, the global population reached four billion in 1974, five billion in 1987, six billion in 1999 and, according to the United States Census Bureau, seven billion in March 2012. The United Nations, however, estimated that the world population reached seven billion in October 2011.
According to current projections, the global population will reach eight billion by 2024, and is likely to reach around nine billion by 2042. Alternative scenarios for 2050 range from a low of 7.4 billion to a high of more than 10.6 billion. Projected figures vary depending on underlying statistical assumptions and the variables used in projection calculations, especially the fertility variable. Long-range predictions to 2150 range from a population decline to 3.2 billion in the "low scenario", to "high scenarios" of 24.8 billion. One extreme scenario predicted a massive increase to 256 billion by 2150, assuming the global fertility rate remained at its 1995 level of 3.04 children per woman; however, by 2010 the global fertility rate had declined to 2.52.
There is no estimation for the exact day or month the world's population surpassed one or two billion. The points at which it reached three and four billion were not officially noted, but the International Database of the United States Census Bureau placed them in July 1959 and April 1974 respectively. The United Nations did determine, and commemorate, the "Day of 5 Billion" on 11 July 1987, and the "Day of 6 Billion" on 12 October 1999. The Population Division of the United Nations declared the "Day of 7 Billion" to be 31 October 2011.[needs update]
As of 2012, the global sex ratio is approximately 1.01 males to 1 female. The greater number of men is possibly due to the significant sex imbalances evident in the Indian and Chinese populations. Approximately 26.3% of the global population is aged under 15, while 65.9% is aged 15-64 and 7.9% is aged 65 or over. The median age of the world's population was estimated to be 29.7 years in 2014, and is expected to rise to 37.9 years by 2050.
According to the World Health Organization, the global average life expectancy is 71.4 years as of 2015, with women living an average of 74 years and men approximately 69 years. In 2010, the global fertility rate was estimated at 2.52 children per woman. In June 2012, British researchers calculated the total weight of Earth's human population as approximately 287 million tonnes, with the average person weighing around 62 kilograms (137 lb).
The CIA estimated nominal 2013 gross world product at US$74.31 trillion, giving an annual global per capita figure of around US$10,500. Around 1.29 billion people (18.4% of the world population) live in extreme poverty, subsisting on less than US$1.25 per day; approximately 870 million people (12.3%) are undernourished. 83% of the world's over-15s are considered literate. In June 2014, there were around 3.03 billion global Internet users, constituting 42.3% of the world population.
The Han Chinese are the world's largest single ethnic group, constituting over 19% of the global population in 2011. The world's most-spoken first languages are Mandarin Chinese (spoken by 12.4% of the world's population), Spanish (4.9%), English (4.8%), Arabic (3.3%) and Hindi (2.7%). The world's largest religion is Christianity, whose adherents account for 31.4% of the global population;Islam is the second-largest religion, accounting for 24.1%, and Hinduism the third, accounting for 13.8%. In 2005, around 16% of the global population were reported to be non-religious.
|Rank||Country||Population||% of world||Date||Source|
(official or UN)
|1||China||1,406,865,320||17.9%||1 Mar 2021||National population clock|
|2||India||1,373,943,255||17.5%||1 Mar 2021||National population clock|
|3||United States||331,250,024||4.22%||1 Mar 2021||National population clock|
|4||Indonesia||269,603,400||3.43%||1 Jul 2020||National annual projection|
|5||Pakistan||220,892,331||2.81%||1 Jul 2020||UN Projection|
|6||Brazil||212,806,242||2.71%||1 Mar 2021||National population clock|
|7||Nigeria||206,139,587||2.63%||1 Jul 2020||UN Projection|
|8||Bangladesh||170,245,378||2.17%||1 Mar 2021||National population clock|
|9||Russia||146,748,590||1.87%||1 Jan 2020||National annual estimate|
|10||Mexico||127,792,286||1.63%||1 Jul 2020||National annual projection|
Approximately 4.45 billion people live in these ten countries, representing around 57% of the world's population as of September 2020.
The tables below list the world's most densely populated countries, both in absolute terms and in comparison to their total populations.
Population size fluctuates at differing rates in differing regions. Nonetheless, population growth is the long-standing trend on all inhabited continents, as well as in most individual states. During the 20th century, the global population saw its greatest increase in known history, rising from about 1.6 billion in 1900 to over 6 billion in 2000. A number of factors contributed to this increase, including the lessening of the mortality rate in many countries by improved sanitation and medical advances, and a massive increase in agricultural productivity attributed to the Green Revolution.
In 2000, the United Nations estimated that the world's population was growing at an annual rate of 1.1% (equivalent to around 75 million people), down from a peak of 88 million per year in 1989. By 2000, there were approximately ten times as many people on Earth as there had been in 1700. Globally, the population growth rate has been steadily declining from its peak of 2.2% in 1963, but growth remains high in Latin America, the Middle East, and Sub-Saharan Africa.
In 2006, the United Nations stated that the rate of population growth was visibly diminishing due to the ongoing global demographic transition. If this trend continues, the rate of growth may diminish to zero by 2050, concurrent with a world population plateau of 9.2 billion. However, this is only one of many estimates published by the UN; in 2009, UN population projections for 2050 ranged between around 8 billion and 10.5 billion. An alternative scenario is given by the statistician Jorgen Randers, who argues that traditional projections insufficiently take into account the downward impact of global urbanization on fertility. Randers' "most likely scenario" reveals a peak in the world population in the early 2040s at about 8.1 billion people, followed by decline. Adrian Raftery, a University of Washington professor of statistics and of sociology, states that "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."
Estimated world population figures, 10,000 BC-AD 2000
Estimated world population figures, 10,000 BC-AD 2000 (in log y scale)
|Latin America[Note 1]||40||20||10||16||24||38||74||167||508||577||590||603||784||912|
|Northern America[Note 1]||6||3||2||2||7||26||82||172||312||337||345||351||433||398|
|Latin America[Note 1]||6.8||3.0||1.4||2.0||2.5||3.0||4.5||6.6||8.5||8.6||8.6||8.6||8.1||9.4|
|Northern America[Note 1]||1.0||0.5||0.3||0.3||0.7||2.1||5.0||6.8||5.2||5.0||5.0||5.0||4.5||4.1|
The following table gives estimates, in millions, of population in the past. The data for 1750 to 1900 are from the UN report "The World at Six Billion" whereas the data from 1950 to 2015 are from a UN data sheet.
|70,000 BC||< 0.015||0||0|||
Using the above figures, the change in population from 2010 to 2015 was:
Long-term global population growth is difficult to predict. The United Nations and the US Census Bureau both give different estimates - according to the UN, the world population reached seven billion in late 2011, while the USCB asserted that this occurred in March 2012. The UN has issued multiple projections of future world population, based on different assumptions. From 2000 to 2005, the UN consistently revised these projections downward, until the 2006 revision, issued on 14 March 2007, revised the 2050 mid-range estimate upwards by 273 million.
Average global birth rates are declining fast, but vary greatly between developed countries (where birth rates are often at or below replacement levels) and developing countries (where birth rates typically remain high). Different ethnicities also display varying birth rates. Death rates can change rapidly due to disease epidemics, wars and other mass catastrophes, or advances in medicine.
2012 United Nations projections show a continued increase in population in the near future with a steady decline in population growth rate; the global population is expected to reach between 8.3 and 10.9 billion by 2050. 2003 UN Population Division population projections for the year 2150 range between 3.2 and 24.8 billion. One of many independent mathematical models supports the lower estimate, while a 2014 estimate forecasts between 9.3 and 12.6 billion in 2100, and continued growth thereafter. The 2019 Revision of the UN estimates gives the "medium variant" population as; nearly 8.6 billion in 2030, about 9.7 billion in 2050 and about 10.9 billion in 2100. In December 2019, the German Foundation for World Population projected that the global population will reach 8 billion by 2023 as it increases by 156 every minute. In a modelled future projection by the Institute for Health Metrics and Evaluation the global population was projected to peak in 2064 at 9.73 billion people and decline to 8.79 billion in 2100. Some analysts have questioned the sustainability of further world population growth, highlighting the growing pressures on the environment, global food supplies, and energy resources.
|Year||World||Asia||Africa||Europe||Latin America/Caribbean||Northern America||Oceania|
|2000||6,144||3,741 (60.9%)||811 (13.2%)||726 (11.8%)||522 (8.5%)||312 (5.1%)||31 (0.5%)|
|2005||6,542||3,978 (60.8%)||916 (14.0%)||729 (11.2%)||558 (8.5%)||327 (5.0%)||34 (0.5%)|
|2010||6,957||4,210 (60.5%)||1,039 (14.9%)||736 (10.6%)||591 (8.5%)||343 (4.9%)||37 (0.5%)|
|2015||7,380||4,434 (60.1%)||1,182 (16.0%)||743 (10.1%)||624 (8.5%)||357 (4.8%)||40 (0.5%)|
|2020||7,795||4,641 (59.5%)||1,341 (17.2%)||748 (9.6%)||654 (8.4%)||369 (4.7%)||43 (0.6%)|
|2025||8,184||4,823 (58.9%)||1,509 (18.4%)||746 (9.1%)||682 (8.3%)||380 (4.6%)||45 (0.6%)|
|2030||8,549||4,974 (58.2%)||1,688 (19.8%)||741 (8.7%)||706 (8.3%)||391 (4.6%)||48 (0.6%)|
|2035||8,888||5,096 (57.3%)||1,878 (21.1%)||735 (8.3%)||726 (8.2%)||401 (4.5%)||50 (0.6%)|
|2040||9,199||5,189 (56.4%)||2,077 (22.6%)||728 (7.9%)||742 (8.1%)||410 (4.5%)||53 (0.6%)|
|2045||9,482||5,253 (55.4%)||2,282 (24.1%)||720 (7.6%)||754 (8.0%)||418 (4.4%)||55 (0.6%)|
|2050||9,735||5,290 (54.3%)||2,489 (25.6%)||711 (7.3%)||762 (7.8%)||425 (4.4%)||57 (0.6%)|
|2055||9,958||5,302 (53.2%)||2,698 (27.1%)||700 (7.0%)||767 (7.7%)||432 (4.3%)||60 (0.6%)|
|2060||10,152||5,289 (52.1%)||2,905 (28.6%)||689 (6.8%)||768 (7.6%)||439 (4.3%)||62 (0.6%)|
|2065||10,318||5,256 (51.0%)||3,109 (30.1%)||677 (6.6%)||765 (7.4%)||447 (4.3%)||64 (0.6%)|
|2070||10,459||5,207 (49.8%)||3,308 (31.6%)||667 (6.4%)||759 (7.3%)||454 (4.3%)||66 (0.6%)|
|2075||10,577||5,143 (48.6%)||3,499 (33.1%)||657 (6.2%)||750 (7.1%)||461 (4.4%)||67 (0.6%)|
|2080||10,674||5,068 (47.5%)||3,681 (34.5%)||650 (6.1%)||739 (6.9%)||468 (4.4%)||69 (0.7%)|
|2085||10,750||4,987 (46.4%)||3,851 (35.8%)||643 (6.0%)||726 (6.8%)||474 (4.4%)||71 (0.7%)|
|2090||10,810||4,901 (45.3%)||4,008 (37.1%)||638 (5.9%)||711 (6.6%)||479 (4.4%)||72 (0.7%)|
|2095||10,852||4,812 (44.3%)||4,152 (38.3%)||634 (5.8%)||696 (6.4%)||485 (4.5%)||74 (0.7%)|
|2100||10,875||4,719 (43.4%)||4,280 (39.4%)||630 (5.8%)||680 (6.3%)||491 (4.5%)||75 (0.7%)|
In 1975, Sebastian von Hoerner proposed a formula for population growth which represented hyperbolic growth with an infinite population in 2025. The hyperbolic growth of the world population observed until the 1970s was later correlated to a non-linear second order positive feedback between demographic growth and technological development. This feedback can be described as follows: technological advance -> increase in the carrying capacity of land for people -> demographic growth -> more people -> more potential inventors -> acceleration of technological advance -> accelerating growth of the carrying capacity -> faster population growth -> accelerating growth of the number of potential inventors -> faster technological advance -> hence, the faster growth of the Earth's carrying capacity for people, and so on. The transition from hyperbolic growth to slower rates of growth is related to the demographic transition.
According to linear interpolation and extrapolation of UNDESA population estimates, the world population has doubled, or will double, in the years listed in the tables below (with two different starting points). During the 2nd millennium, each doubling took roughly half as long as the previous doubling, fitting the hyperbolic growth model mentioned above. However, after 2024, it is unlikely that there will be another doubling of the global population in the 21st century.
In his 1798 work An Essay on the Principle of Population, the British scholar Thomas Malthus incorrectly predicted that continued population growth would exhaust the global food supply by the mid-19th century. Malthus wrote the essay to refute what he considered the unattainable utopian ideas of William Godwin and Marquis de Condorcet, as presented in Political Justice and The Future Progress of the Human Mind. In 1968, Paul R. Ehrlich reprised Malthus' argument in The Population Bomb, predicting that mass global famine would occur in the 1970s and 1980s.
The predictions of Ehrlich and other neo-Malthusians were vigorously challenged by a number of economists, notably Julian Lincoln Simon, and advances in agriculture, collectively known as the Green Revolution, forestalled any potential global famine in the late 20th century. Between 1950 and 1984, as the Green Revolution transformed agriculture around the world, grain production increased by over 250%. The world population has grown by over four billion since the beginning of the Green Revolution, but food production has so far kept pace with population growth. Most scholars believe that, without the Revolution, there would be greater levels of famine and malnutrition than the UN presently documents. However, neo-Malthusians point out that fossil fuels provided the energy for the Green Revolution, in the form of natural gas-derived fertilizers, oil-derived pesticides, and hydrocarbon-fueled irrigation, and that many crops have become so genetically uniform that a crop failure in any one country could potentially have global repercussions.
In May 2008, the price of grain was pushed up severely by the increased cultivation of biofuels, the increase of world oil prices to over $140 per barrel ($880/m3), global population growth, the effects of climate change, the loss of agricultural land to residential and industrial development, and growing consumer demand in the population centres of China and India.Food riots subsequently occurred in some countries. However, oil prices then fell sharply. Resource demands are expected to ease as population growth declines, but it is unclear whether mass food wastage and rising living standards in developing countries will once again create resource shortages.
David Pimentel, professor of ecology and agriculture at Cornell University, estimates that the sustainable agricultural carrying capacity for the United States is about 200 million people; its population as of 2015 is over 300 million. In 2009, the UK government's chief scientific advisor, Professor John Beddington, warned that growing populations, falling energy reserves and food shortages would create a "perfect storm" of shortages of food, water, and energy by 2030. According to a 2009 report by the United Nations Food and Agriculture Organization (FAO), the world will have to produce 70% more food by 2050 to feed a projected extra 2.3 billion people.
The observed figures for 2007 showed an actual increase in absolute numbers of undernourished people in the world, with 923 million undernourished in 2007, versus 832 million in 1995. The 2009 FAO estimates showed an even more dramatic increase, to 1.02 billion.
A number of scientists have argued that the current global population expansion and accompanying increase in resource consumption threatens the world's ecosystem. The InterAcademy Panel Statement on Population Growth, which was ratified by 58 member national academies in 1994, states that "unprecedented" population growth aggravates many environmental problems, including rising levels of atmospheric carbon dioxide, global warming, and pollution. Indeed, some analysts claim that overpopulation's most serious impact is its effect on the environment.
Scientists contend that human overpopulation, continued human population growth and overconsumption, particularly by the wealthy, are the primary drivers of mass species extinction. By 2050 population growth, along with profligate consumption, could result in oceans containing more plastic than fish by weight. In November 2017, a statement by 15,364 scientists from 184 countries asserted that rapid human population growth is the "primary driver behind many ecological and even societal threats." African wildlife populations are declining significantly as growing human populations encroach on protected ecosystems, such as the Serengeti. The Global Assessment Report on Biodiversity and Ecosystem Services, released by IPBES in 2019, states that human population growth is a factor in biodiversity loss. According to a 2020 World Wildlife Fund Living Planet Report and its Living Planet Index, global wildlife populations have plummeted by 68% since 1970 as a result of overconsumption, population growth and intensive farming, which experts assert is further evidence that humans have unleashed a sixth mass extinction event on earth.
A July 2017 study published in Environmental Research Letters argued that the most significant way individuals could mitigate their own carbon footprint is to have fewer children, followed by living without a vehicle, foregoing air travel, and adopting a plant-based diet.
Human population control is the practice of intervening to alter the rate of population growth. Historically, human population control has been implemented by limiting a region's birth rate, by voluntary contraception or by government mandate. It has been undertaken as a response to factors including high or increasing levels of poverty, environmental concerns, and religious reasons. The use of abortion in some population control strategies has caused controversy, with religious organizations such as the Roman Catholic Church explicitly opposing any intervention in the human reproductive process.
The University of Nebraska publication Green Illusions argues that population control to alleviate environmental pressures need not be coercive. It states that "Women who are educated, economically engaged, and in control of their own bodies can enjoy the freedom of bearing children at their own pace, which happens to be a rate that is appropriate for the aggregate ecological endowment of our planet." The book Fatal Misconception by Matthew Connelly similarly points to the importance of supporting the rights of women in bringing population levels down over time.Paul Ehrlich also advocates making "modern contraception and back-up abortion available to all and give women full equal rights, pay and opportunities with men," noting that it could possibly "lead to a low enough total fertility rate that the needed shrinkage of population would follow. [But] it will take a very long time to humanely reduce total population to a size that is sustainable." Ehrlich places the optimum global population size at 1.5 to 2 billion people.
Other academicians and public figures have pointed to the role of agriculture and agricultural productivity of increasing human carrying capacity, which results in population overshoot, as with any other species when their food supply experiences an increase, which in turn results in resource depletion and mass poverty and starvation in the case of humans.
Estimates of the total number of humans who have ever lived range is estimated to be of the order of 100 billion. Such estimates can only be rough approximations; as even modern population estimates are subject to uncertainty of around 3% to 5%. Kapitza (1996) cites estimates ranging between 80 and 150 billion. Haub (1995) prepared another figure, updated in 2002 and 2011; the 2011 figure was approximately 107 billion. Haub characterized this figure as an estimate that required "selecting population sizes for different points from antiquity to the present and applying assumed birth rates to each period".
Robust population data only exist for the last two or three centuries. Until the late 18th century, few governments had ever performed an accurate census. In many early attempts, such as in Ancient Egypt and the Persian Empire, the focus was on counting merely a subset of the population for purposes of taxation or military service. Thus, there is a significant margin of error when estimating ancient global populations. Pre-modern infant mortality rates are another critical factor for such an estimate; these rates are very difficult to estimate for ancient times due to a lack of accurate records. Haub (1995) estimates that around 40% of those who have ever lived did not survive beyond their first birthday. Haub also stated that "life expectancy at birth probably averaged only about ten years for most of human history", which is not to be mistaken for the life expectancy after reaching adulthood. The latter equally depended on period, location and social standing, but calculations identify averages from roughly 30 years upward.
Driving these threats are the growing human population, which has doubled since 1970 to 7.6 billion, and consumption. (Per capita of use of materials is up 15% over the past 5 decades.)
The overarching driver of species extinction is human population growth and increasing per capita consumption.
Much less frequently mentioned are, however, the ultimate drivers of those immediate causes of biotic destruction, namely, human overpopulation and continued population growth, and overconsumption, especially by the rich. These drivers, all of which trace to the fiction that perpetual growth can occur on a finite planet, are themselves increasing rapidly.
The report blames humans alone for the "dire" state of the planet. It points to the exponential growth of human consumption, population, global trade and urbanization over the last 50 years as key reasons for the unprecedented decline of Earth's resources - which it says the planet is incapable of replenishing.
Statistics and maps