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# Human population

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### Human population

The world population is the total number of living humans on Earth. As of today, it is estimated to number 7.171 billion by the United States Census Bureau (USCB).[1] The USCB estimates that the world population exceeded 7 billion on March 12, 2012.[2] According to a separate estimate by the United Nations Population Fund, it reached this milestone on October 31, 2011.[3][4][5]

The world population has experienced continuous growth since the end of the Great Famine and the Black Death in 1350, when it stood at around 370 million.[6] The highest rates of growth – global population increases above 1.8% per year – were seen briefly during the 1950s, and for a longer period during the 1960s and 1970s. The growth rate peaked at 2.2% in 1963, then declined to below 1.1% by 2012.[7] Total annual births were highest in the late 1980s at about 138 million,[8] and are now expected to remain essentially constant at their 2011 level of 134 million, while deaths number 56 million per year, and are expected to increase to 80 million per year by 2040.[9]

Current UN projections show a continued increase in population in the near future (but a steady decline in the population growth rate), with the global population expected to reach between 8.3 and 10.9 billion by 2050.[10][11] UN Population Division estimates for the year 2150 range between 3.2 and 24.8 billion;[12] mathematical modeling supports the lower estimate.[13] Some analysts have questioned the sustainability of further world population growth, highlighting the growing pressures on the environment, global food supplies, and energy resources.[14][15][16]

World population (millions)[17]
# Top ten most populous countries 1990 2008 2025*
1 China 1,141 1,333 1,458
2 India 849 1,140 1,398
3 United States 250 304 352
4 Indonesia 178 228 273
5 Brazil 150 192 223
6 Pakistan 108 166 226
8 Nigeria 94 151 208
9 Russia 148 142 137
10 Japan 124 128 126
World total 5,265 6,688 8,004
Top ten most populous (%) 60.0% 58.9% 57.5%
1 Asia 1,613 2,183 2,693
+ China 1,141 1,333 1,458
+ OECD Pacific* 187 202 210
2 Africa 634 984 1,365
3 Europe* 564 603 659
+ Russia 148 142 137
+ ex-Soviet Union* 133 136 146
4 Latin America 355 462 550
5 North America* 359 444 514
6 Middle East 132 199 272
Australia 17 22 28
European Union – 27 states 473 499 539
US + Canada 278 338 392
Ex-Soviet Union 289 285 289
Geographical definitions as in IEA Key Stats 2010 p. 66
Notes:
• Europe = OECD Europe + Non-OECD Europe and
excluding Russia and including Estonia, Latvia and Lithuania
• ex-Soviet Union (SU) = SU excluding Russia and Baltic states
• North America = US, Canada, Mexico
• OECD Pacific = Australia, Japan, Korea, New Zealand
• 2025 = with constant annual 2007/2008 growth until 2025

## Population by region

Six of Earth's seven continents are permanently inhabited on a large scale. Asia is the most populous continent, with its 4.2 billion inhabitants accounting for over 60% of the world population. The world's two most-populated countries alone, China and India, together constitute about 37% of the world's population. Africa is the second-most-populated continent, with around 1 billion people, or 15% of the world's population. Europe's 733 million people make up 11% of the world's population, while the Latin American and Caribbean regions are home to around 600 million (9%). Northern America, primarily consisting of the United States and Canada, has a population of around 352 million (5%), and Oceania, the least-populated region, has about 35 million inhabitants (0.5%).[18] Though it is not permanently inhabited by any fixed population, Antarctica has a small, fluctuating international population, based mainly in polar science stations. This population tends to rise in the summer months and decrease significantly in winter, as visiting researchers return to their home countries.[19]

### Population by continent

Continent Density
(inhabitants/km2)
Population
(2011)
Most populous country Most populous city
Asia 86.7 4,140,336,501 Template:Flagu (1,341,403,687) Tokyo (35,676,000)
Africa 32.7 994,527,534 Template:Flagu (152,217,341) Cairo (19,439,541)
Europe 70 738,523,843 Template:Flagu (143,300,000;
approx. 110 million in Europe)
Moscow (14,837,510)
North America 22.9 528,720,588 Template:Flagu (313,485,438) Mexico City/Metro Area (8,851,080 / 21,163,226)
South America 21.4 385,742,554 Template:Flagu (190,732,694) São Paulo (19,672,582)
Oceania 4.25 36,102,071 Template:Flagu (22,612,355) Sydney (4,575,532)
Antarctica 0.0003
(varies)
4,490
(non-permanent, varies)[20]
N/A[note 1] N/A

## History

### Antiquity and Middle Ages

Until the development of agriculture around the 11th millennium BC, it is estimated that the world population stabilized at about three million people,[21] who subsisted through hunting and foraging – a lifestyle that by its nature ensured a low population density. The total world population probably never exceeded 15 million inhabitants before the invention of agriculture.[22] 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.[23]

The plague which first emerged during the reign of Justinian caused Europe's population to drop by around 50% between 541 and the 8th century.[24] The population of Europe was more than 70 million in 1340.[25] 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;[26] it took roughly 200 years for Europe's population to regain its 1340 level.[27] China experienced a population decline from an estimated 123 million around 1200 to an estimated 65 million in 1393,[28] which was presumably due to a combination of Mongol invasions and plague.[29]

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.[30] England's population reached an estimated 5.6 million in 1650, up from an estimated 2.6 million in 1500.[31] New crops that were brought to Asia and Europe from the Americas by Spanish colonists in the 16th century are believed to have contributed to population growth.[32][33] Since their introduction by Portuguese traders in the 16th century,[34] maize and cassava have replaced traditional African crops as that continent’s most important staple food crops.[35]

Pran Nath, in his book, the study of Economic conditions of Ancient India, estimated that, around 300 B.C., the population of Ancient India was between 100 million and 140 million. Kingsley Davis is also inclined to agree with this figure.[36] Estimates made by W. H. Moreland, noted historian, reveal that, in 1600 A.D., the population of India was around 100 million. Hence from 300 B.C., to 1600 A.D. India's population was more or less stationary.[37]

The total population of the Americas in 1500 may have been between 50 and 100 million.[38] The pre-Columbian North American population probably numbered somewhere between 2 million and 18 million.[39] Encounters between European explorers and populations in the rest of the world often introduced local epidemics of extraordinary virulence.[40] 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.[41] Over the centuries, the Europeans had developed high degrees of immunity to these diseases, while the indigenous peoples had no such immunity.[42]

### Modern era

During the European Agricultural and Industrial Revolutions, the life expectancy of children increased dramatically.[45] 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.[46][47] Between 1700 and 1900, Europe’s population increased from about 100 million to over 400 million.[48] Altogether, the areas of European settlement comprised 36% of the world's population in 1900.[49]

Population growth in the West became more rapid after the introduction of compulsory vaccination and improvements in medicine and sanitation.[50] As living conditions and health care improved during the 19th century, the United Kingdom's population doubled every fifty years.[51] By 1801, the population of England had grown to 8.3 million, and by 1901 it had reached 30.5 million; the population of the United Kingdom reached 60 million in 2006.[52] The United States saw its population grow from around 5.3 million in 1800 to 106 million in 1920, exceeding 307 million in 2010.[53]

The first half of the 20th century in Russia and the Soviet Union was marked by a succession of wars, famines and other disasters, each accompanied by large-scale population losses.[54] Stephen J. Lee estimates that, by the end of World War II in 1945, the Russian population was about 90 million fewer than it could have been otherwise.[55] In recent decades, Russia's population has declined significantly – from 148 million in 1991 to 143 million in 2012[56] – but as of 2013 this decline appears to have halted.[57]

Many countries in the developing world have experienced rapid population growth over the past century. China's population rose from approximately 430 million in 1850 to 580 million in 1953,[58] and now stands at over 1.3 billion. The population of the Indian subcontinent, which stood at about 125 million in 1750, reached 389 million in 1941;[59] today, India and its surrounding countries are home to about 1.6 billion people.[60] The population of Java increased from about five million in 1815 to more than 130 million in the early 21st century.[61] Mexico's population grew from 13.6 million in 1900 to about 112 million in 2010.[62][63] Between the 1920s and 2000s, Kenya's population grew from 2.9 million to 37 million.[64]

### Milestones by the billions

Main article: World population milestones
World population milestones (USCB estimates)[1]
Population
(in billions)
1 2 3 4 5 6 7 8 9
Year 1804 1927 1960 1974 1987 1999 2012 2027 2046
Years elapsed between milestones 123 33 14 13 12 13 16 19

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.[65] 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.[1] The United Nations, however, estimated that the world population reached seven billion in October 2011.[3][4][5]

According to current projections, the global population will reach eight billion by 2030, and will likely reach around nine billion by 2050. Alternative scenarios for 2050 range from a low of 7.4 billion to a high of more than 10.6 billion.[66] 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.[66] 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.[12][67]

There is no estimation for the exact day or month the world's population surpassed one or two billion. The days of three and four billion were not officially noted, but the International Database of the United States Census Bureau places them in July 1959 and April 1974. The United Nations did determine, and celebrate, the "Day of 5 Billion" on July 11, 1987, and the "Day of 6 Billion" on October 12, 1999. The "Day of 7 Billion" was declared by the Population Division of the United Nations to be October 31, 2011.[68]

## Global demographics

Main article: Demographics of the world

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 gender imbalances evident in the Indian and Chinese populations.[69][70] 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.[69] At the beginning of 2012, 50.5% of the world's population was under 30;[71] as of the end of 2012, the median age of the human race is about 30 years. The global average life expectancy is 67.07 years,[69] with women living an average of 69 years and men approximately 65 years.[69] In 2010, the global fertility rate was estimated at 2.52 children per woman.[67] In June 2012, British researchers calculated the total weight of Earth's human population as 287 million tonnes, with the average person weighing 62 kilograms (137 lb).[72]

The nominal 2012 gross world product was estimated at US$71.83 trillion by the CIA, giving an annual global per capita figure of around US$10,000.[73] Around 1.29 billion people (18.4% of the world population) live in extreme poverty, subsisting on less than US$1.25 per day;[74] approximately 925 million people (13.2%) are malnourished.[75] 83% of the world's over-15s are considered literate.[69] In June 2012, there were around 2.4 billion global Internet users, constituting 34.2% of the world population.[76] The Han Chinese are the world's largest single ethnic group, constituting over 19% of the global population in 2011. [77] The world's most-spoken first languages are Mandarin Chinese (spoken by 12.44% of the world's population), Spanish (4.85%), English (4.83%), Arabic (3.25%) and Hindustani (2.68%).[69] The world's largest religion is Christianity, whose adherents account for 33.35% of the global population; Islam is the second-largest religion, accounting for 22.43%, and Hinduism the third, accounting for 13.78%.[69] In 2005, around 16% of the global population were reported to be non-religious.[78] ## Largest populations by country Further information: List of countries by population 10 most populous countries Rank Country / Territory Population Date % of world population Source 1 China[note 2] 1,365,140,000 June 21, 2014 19% [79] 2 India 1,210,193,422 March 2011 17% [80] 3 United States 318,515,000 June 21, 2014 4.44% [81] 4 Indonesia 237,641,000 May 2010 3.31% [82] 5 Brazil 200,069,000 21 June 2014 2.79% [83] 6 Pakistan 186,792,000 June 21, 2014 2.6% [84] 7 Nigeria 174,507,539 July 2013 2.37% [85] 8 Bangladesh 163,654,860 July 2013 2.25% [86] 9 Russia 143,347,100 January 1, 2013 1.98% [87] 10 Japan 127,547,000 June 1, 2012 1.78% [88] Approximately 4.06 billion people live in these ten countries, representing around 58% of the world's population as of November 2012. ### Most densely populated countries The tables below list the world's most densely populated countries, both in absolute terms and in comparison to their total populations. 10 most densely populated countries (with population above 1 million) Rank Country/Region Population Area (km2) Density (Pop. per km2) 1 Singapore 5,312,400 710 7482 2 Bahrain 1,234,571 750 1646 3 Bangladesh 152,518,015 147,570 1034 4 Taiwan 23,324,092 36,190 644 5 Mauritius 1,288,000 2,040 631 6 South Korea 50,004,441 99,538 502 7 Lebanon 4,324,000 10,452 414 8 Netherlands 16,817,333 41,526 404 9 Rwanda 10,537,222 26,338 400 10 Belgium 11,151,495 30,528 365 Countries ranking highly in terms of both total population (more than 15 million people) and population density (more than 250 people per square kilometer): Country Population Area (km2) Density (Pop. per km2) Notes India 1,245,660,000 3,287,240 379 Growing country Bangladesh 152,518,015 147,570 1034 Growing country Japan 127,360,000 377,873 338 Declining in population[89] Philippines 94,013,200 300,076 313 Growing country Vietnam 88,780,000 331,689 268 Growing country United Kingdom 62,262,000 243,610 256 Growing country[90] South Korea 50,004,441 99,538 502 Steady in population[91] Taiwan 23,293,593 36,190 644 Declining in population[92][93] Sri Lanka 20,277,597 65,610 309 Growing country Netherlands 16,840,000 41,526 406 Steady in population[94] ## Fluctuation Main article: Population growth 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. According to the United Nations, population growth on Earth's inhabited continents between 2000 to 2005 totalled: • 227,771,000 in Asia; • 92,293,000 in Africa; • 38,052,000 in Latin America; • 16,241,000 in Northern America; • 3,264,000 in Europe; • 1,955,000 in Oceania; • 383,047,000 overall. 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. This increase was due to a number of factors, 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.[95][96][97] In 2000, the United Nations estimated that the world's population was growing at an annual rate of 1.14% (equivalent to around 75 million people),[98] 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. According to data from the CIA's 2005–2006 World Factbooks, the world population increased by an average of 203,800 people every day in the mid-2000s. The World Factbook increased this estimate to 211,090 people every day in 2007, and again to 220,980 people every day in 2009. Globally, the population growth rate has been steadily declining from its peak of 2.19% in 1963, but growth remains high in Latin America, the Middle East and Sub-Saharan Africa.[99] In some countries, there is negative population growth (i.e. a net decrease in population over time), especially in Europe – this is mainly due to low fertility rates. During the 2010s, Japan and some countries in Europe began to encounter negative population growth, due to sub-replacement fertility rates.[89] 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.[100] 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.[101] ### Projections Main articles: World population estimates and Projections of population growth Long-term global population growth is difficult to predict. The United Nations and the US Census Bureau both give different estimates – according to the latter, the world population reached seven billion in March 2012,[102] while the UN asserted that this occurred in late 2011.[103] 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 March 14, 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. UN (medium variant – 2012 revision) and US Census Bureau (June 2012) estimates[104][105] Year UN est. (millions) Difference USCB est. (millions) Difference 2005 6,514 6,474 2010 6,916 402 6,864 390 2015 7,324 408 7,250 386 2020 7,717 393 7,628 378 2025 8,083 366 7,984 356 2030 8,425 342 8,315 331 2035 8,743 318 8,619 304 2040 9,039 296 8,899 280 2045 9,308 269 9,154 255 2050 9,551 243 9,383 229 UN 2012 estimates and medium variant projections (in millions)[104] Year World Asia Africa Europe Latin America/Caribbean Northern America Oceania 2010 6,916 4,165 (60.2%) 1,031 (14.9%) 740 (10.7%) 596 (8.6%) 347 (5.0%) 37 (0.5%) 2015 7,324 4,385 (59.9%) 1,166 (15.9%) 743 (10.1%) 630 (8.6%) 361 (4.9%) 39 (0.5%) 2020 7,717 4,582 (59.4%) 1,312 (17.0%) 744 (9.6%) 662 (8.6%) 376 (4.9%) 42 (0.5%) 2025 8,083 4,749 (58.8%) 1,468 (18.2%) 741 (10.1%) 691 (9.2%) 390 (4.8%) 45 (0.6%) 2030 8,425 4,887 (58.0%) 1,634 (19.4%) 736 (8.7%) 717 (8.5%) 403 (4.8%) 47 (0.6%) 2035 8,743 4,997 (57.2%) 1,812 (20.7%) 730 (8.3%) 739 (8.5%) 415 (4.8%) 50 (0.6%) 2040 9,039 5,080 (56.2%) 1,999 (22.1%) 724 (8.0%) 757 (8.4%) 426 (4.8%) 52 (0.6%) 2045 9,308 5,136 (55.2%) 2,194 (23.6%) 717 (7.7%) 771 (8.3%) 436 (4.7%) 55 (0.6%) 2050 9,551 5,164 (54.1%) 2,393 (25.1%) 709 (7.4%) 782 (8.2%) 446 (4.7%) 57 (0.6%) 2055 9,766 5,168 (52.9%) 2,595 (26.6%) 700 (7.2%) 788 (8.1%) 456 (4.7%) 59 (0.6%) 2060 9,957 5,152 (51.7%) 2,797 (28.1%) 691 (6.9%) 791 (7.9%) 465 (4.7%) 61 (0.6%) 2065 10,127 5,120 (50.6%) 2,998 (29.6%) 681 (6.7%) 791 (7.8%) 474 (4.7%) 63 (0.6%) 2070 10,277 5,075 (49.4%) 3,195 (31.1%) 673 (6.5%) 788 (7.6%) 482 (4.7%) 64 (0.6%) 2075 10,409 5,019 (48.2%) 3,387 (32.5%) 665 (6.4%) 783 (7.5%) 490 (4.7%) 66 (0.6%) 2080 10,524 4,957 (47.1%) 3,570 (33.9%) 659 (6.3%) 776 (7.4%) 496 (4.7%) 67 (0.6%) 2085 10,626 4,894 (46.1%) 3,742 (35.2%) 653 (6.1%) 767 (7.2%) 502 (4.7%) 68 (0.6%) 2090 10,717 4,833 (45.1%) 3,903 (36.4%) 649 (6.1%) 757 (7.1%) 506 (4.7%) 69 (0.6%) 2095 10,794 4,773 (44.2%) 4,051 (37.6%) 644 (6.0%) 747 (6.9%) 510 (4.7%) 69 (0.6%) 2100 10,854 4,712 (43.4%) 4,185 (38.6%) 639 (5.9%) 736 (6.8%) 513 (4.7%) 70 (0.6%) ### Population growth by region The table below shows historical and predicted regional population figures in millions.[103][106][107] The availability of historical population figures varies by region. World historical and predicted populations (in millions)[108][109] Region 1500 1600 1700 1750 1800 1850 1900 1950 1999 2008 2050 2150 World 458 580 682 791 978 1,262 1,650 2,521 5,978 6,707 8,909 9,746 Africa 86 114 106 106 107 111 133 221 767 973 1,766 2,308 Asia 243 339 436 502 635 809 947 1,402 3,634 4,054 5,268 5,561 Europe 84 111 125 163 203 276 408 547 729 732 628 517 Latin America and the Caribbean[Note 1] 39 10 10 16 24 38 74 167 511 577 809 912 Northern America[Note 1] 3 3 2 2 7 26 82 172 307 337 392 398 Oceania 3 3 3 2 2 2 6 13 30 34 46 51 World historical and predicted populations by percentage distribution[108][109] Region 1500 1600 1700 1750 1800 1850 1900 1950 1999 2008 2050 2150 World 100 100 100 100 100 100 100 100 100 100 100 100 Africa 18.8 19.7 15.5 13.4 10.9 8.8 8.1 8.8 12.8 14.5 19.8 23.7 Asia 53.1 58.4 63.9 63.5 64.9 64.1 57.4 55.6 60.8 60.4 59.1 57.1 Europe 18.3 19.1 18.3 20.6 20.8 21.9 24.7 21.7 12.2 10.9 7.0 5.3 Latin America and the Caribbean[Note 1] 8.5 1.7 1.5 2.0 2.5 3.0 4.5 6.6 8.5 8.6 9.1 9.4 Northern America[Note 1] 0.7 0.5 0.3 0.3 0.7 2.1 5.0 6.8 5.1 5.0 4.4 4.1 Oceania 0.7 0.5 0.4 0.3 0.2 0.2 0.4 0.5 0.5 0.5 0.5 0.5 Note: in the table below, the figures for North America only refer to post-European contact settlers, and not native populations from before European settlement. Estimated world and regional populations at various dates (in millions) Year World Africa Asia Europe Latin America[Note 1] Northern America Oceania Notes 70,000 BC < 0.015 [110] 10,000 BC 1 9000 BC 3 8000 BC 5 [111] 7000 BC 7 6000 BC 10 5000 BC 15 4000 BC 20 3000 BC 25 2000 BC 35 1000 BC 50 [111] 500 BC 100 [111] AD 1 200 [112] 1000 310 1750 791 106 502 163 16 2 2 1800 978 107 635 203 24 7 2 1850 1,262 111 809 276 38 26 2 1900 1,650 133 947 408 74 82 6 1950 2,519 221 1,398 547 167 172 12.8 1955 2,756 247 1,542 575 191 187 14.3 1960 2,982 277 1,674 601 209 204 15.9 1965 3,335 314 1,899 634 250 219 17.6 1970 3,692 357 2,143 656 285 232 19.4 1975 4,068 408 2,397 675 322 243 21.5 1980 4,435 470 2,632 692 361 256 22.8 1985 4,831 542 2,887 706 401 269 24.7 1990 5,263 622 3,168 721 441 283 26.7 1995 5,674 707 3,430 727 481 299 28.9 2000 6,070 796 3,680 728 520 316 31.0 2005 6,454 888 3,917 725 558 332 32.9 2010 6,972 1,022 4,252 732 580 351 35.6 ## Mathematical approximations In 1975, Sebastian von Hoerner proposed a formula for population growth which represented hyperbolic growth with an infinite population in 2025.[114] 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.[115] The transition from hyperbolic growth to slower rates of growth is related to the demographic transition. According to Sergei Kapitsa,[116] the world population grew between 67,000 BC and 1965 according to the following formula: $N = \frac\left\{C\right\}\left\{\tau\right\} \arccot \frac\left\{T_0-T\right\}\left\{\tau\right\}$ where • N is current population • T is the current year • C = (1.86±0.01)•1011 • T0 = 2007±1 • $\tau$ = 42±1 ### Years for world population to double Using linear interpolation and extrapolation of UNDESA population estimates, the world population has doubled, or will double, in the following years (with two different starting points). Note how, during the 2nd millennium, each doubling took roughly half as long as the previous doubling, fitting the hyperbolic growth model mentioned above. However, after 2025 it is unlikely that there will be another doubling of the global population in the 21st century.[117] Starting at 500 million Population (in billions) 0.5 1 2 4 8 Year 1500 1804 1927 1974 2025 Years elapsed 304 123 47 51 Starting at 375 million Population (in billions) 0.375 0.75 1.5 3 6 Year 1171 1715 1881 1960 1999 Years elapsed 544 166 79 39 ## Overpopulation Main article: Overpopulation ### Predictions of scarcity In his 1798 work An Essay on the Principle of Population, as it affects the future improvement of society with remarks on the speculations of Mr. Godwin, M. Condorcet, and other writers; the British scholar Thomas Malthus incorrectly predicted that continued population growth would exhaust the global food supply by the mid-19th century. The essay was written to refute what Malthus called, the unattainable Utopian ideas of William Godwin and Marquis de Condorcet; presented in Political Justice and The Future Progress of the Human Mind. In 1968, Paul R. Ehrlich reprised this argument in The Population Bomb, predicting that mass global famine would occur in the 1970s and 1980s.[118] 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%.[119] 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.[120] However, neo-Malthusians point out that the energy for the Green Revolution was provided by fossil fuels, 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 could potentially have global repercussions.[121] 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),[122] global population growth,[123] the effects of climate change,[124] the loss of agricultural land to residential and industrial development,[125][126] and growing consumer demand in the population centres of China and India.[127][128] Food riots subsequently occurred in some countries.[129][130] However, oil prices then fell sharply, and remained below$100/barrel until around 2010. 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.[131][132]

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 2013 is over 310 million.[133] 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" by 2030. Beddington claimed that food reserves were at a fifty-year low, and that the world would require 50% more energy, food and water by 2030.[134][135] According to a 2009 report by the United Nations Food and Agriculture Organisation (FAO), the world will have to produce 70% more food by 2050 to feed a projected extra 2.3 billion people.[136]

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.[137] The 2009 FAO estimates showed an even more dramatic increase, to 1.02 billion.[138]

### Environmental impacts

A number of scientists have argued that the current global population expansion and accompanying increase in resource consumption threatens the world's ecosystem, as well as straining humanity's ability to feed itself.[139][140] The InterAcademy Panel Statement on Population Growth, which was ratified by 58 member national academies in 1994, called the growth in human numbers "unprecedented", and stated that many environmental problems, such as rising levels of atmospheric carbon dioxide, global warming, and pollution, were aggravated by the population expansion.[141] Indeed, some analysts claim that overpopulation's most serious impact is its effect on the environment.[15] At the time of the 1994 IAP statement, the world population stood at 5.5 billion, and lower-bound scenarios predicted a peak of 7.8 billion by 2050, a number that current estimates state will be reached in the late 2020s.

### Population control

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, religious reasons, and overpopulation. The use of abortion in some population control strategies has caused controversy,[142] with organizations such as the Roman Catholic Church explicitly opposing any intervention in the human reproductive process.[143]

The

## Number of humans who have ever lived

Further information: Paleodemography

An estimate of the total number of humans who have ever lived was prepared by Carl Haub of the nonprofit Population Reference Bureau in 1995, and was subsequently updated in 2002 and 2011; the 2011 figure was approximately 107 billion.[146][147][148] 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".[147] Various estimates published in the first decade of the 21st century give figures ranging from approximately 100 billion to 115 billion. In the 1970s, claims emerged alleging that 75% of all the people who had ever lived were alive at that time. This view was eventually debunked as unscientific; given an estimated global population of 7 billion in 2011, it could be inferred from Haub's 2011 calculation that about 6.5% of all people who had ever existed were alive in 2011.[148]

### Estimation methodologies

An accurate estimate of the number of humans who have ever lived is difficult to produce for numerous reasons. Firstly, the set of specific characteristics that define a "human" is a matter of definition, and it is open to debate which members of early Homo sapiens and earlier or related species of Homo to include in the estimate (see also Sorites paradox). Even if the scientific community reached a broad consensus regarding which characteristics distinguished human beings, it would be nearly impossible to pinpoint the time of their first appearance to even the nearest millennium, due to the scarcity of fossil evidence. However, the very small size of the world population in prehistoric times (as compared to its current size) makes this uncertainty of limited importance.

More importantly, 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.[149] All claims of population sizes preceding the 18th century are imprecise estimates, and thus the margin of error for the total number of humans who have ever lived may be in the billions, or even tens of billions, of people.

Another critical factor for such an estimate is life expectancy, which depends critically on infant mortality rates; these figures are very difficult to estimate for ancient times. Haub's numbers suggest that around 40% of those who have ever lived did not survive beyond their first birthday.[147] Haub also stated that "life expectancy at birth probably averaged only about ten years for most of human history".[147]