World population

World population estimates from 1800 to 2100, based on UN 2010 projections (red, orange, green) and US Census Bureau historical estimates (black). According to the highest estimate, the world population may rise to 16 billion by 2100; according to the lowest estimate, it may decline to only 6 billion.

The world population is the total number of living humans on Earth. As of today, it is estimated to number 7.063 billion by the United States Census Bureau (USCB). The USCB estimates that the world population exceeded 7 billion on March 12, 2012. According to a separate estimate by the United Nations Population Fund, it reached this milestone on October 31, 2011.

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. 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, and had declined to 1.1% by 2011. Total annual births were highest in the late 1980s at about 138 million, 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.

Current 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 7.5 and 10.5 billion by 2050. Various longer-term estimates predict further growth, stagnation, or even overall decline in the global population by 2150. Some analysts have questioned the sustainability of further world population growth, citing the growing pressures on the environment, global food supplies, and energy resources.

World population (millions)
#	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
7	Bangladesh	116	160	198
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%). 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.

Population by continent

Continent name	Density (inhabitants/km2)	Population (2011)	Most populous country	Most populous city
Asia	86.7	4,140,336,501	China (1,341,403,687)	Tokyo (35,676,000)
Africa	32.7	994,527,534	Nigeria (152,217,341)	Cairo (19,439,541)
Europe	70	738,523,843	Russia (143,300,000; approx. 110 million in Europe)	Moscow (14,837,510)
North America	22.9	528,720,588	United States (313,485,438)	Mexico City/Metro Area (8,851,080 / 21,163,226)
South America	21.4	385,742,554	Brazil (190,732,694)	São Paulo (19,672,582)
Australia/Oceania	4.25	36,102,071	Australia (22,612,355)	Sydney (4,575,532)
Antarctica	0.0003 (varies)	4,490 (non-permanent, varies)	N/A	McMurdo Station (955)

Milestones by the billions

Main article: World population milestones

World population milestones (USCB estimates)

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		15		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. 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 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. 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 the one or two billion marks. 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.

History

See also: World population estimates and History of the world

Antiquity and Middle Ages

Main articles: Classical demography and Medieval demography

A dramatic population bottleneck is theorized for the period around 70,000 BC as a result of the Toba supervolcano eruption. From this time until the development of agriculture around the 11th millennium BC, it is estimated that the world population stabilized at about one million people, whose subsistence entailed 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. 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 which first emerged during the reign of Justinian caused Europe's population to drop by around 50% between 541 and the 8th century. 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 roughly 200 years for Europe's population to regain its 1340 level. China experienced a population decline from an estimated 123 million around 1200 to an estimated 65 million in 1393, which was presumably due to a combination of Mongol invasions and plague.

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 Spanish colonizers in the 16th century are believed to have contributed to population growth. Since being introduced by Portuguese traders in the 16th century, maize and cassava have replaced traditional African crops as that continent’s most important staple food crops. Alfred W. Crosby speculated that increased production of maize, cassava, and other American crops "...enabled the slave traders [who] drew many, perhaps most, of their cargoes from the rain forest areas, precisely those areas where American crops enabled heavier settlement than before."

The total population of the Americas in 1500 may have been between 50 and 100 million. The pre-Columbian North American population probably numbered somewhere between 2 million and 18 million. 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. Over the centuries, the Europeans had developed high degrees of immunity to these diseases, while the indigenous peoples had no such immunity.

Modern era

Map showing urban areas with at least one million inhabitants in 2006. Only 3% of the world's population lived in cities in 1800; this proportion had risen to 47% by 2000, and reached 50.5% by 2010. By 2050, the proportion may reach 70%.

During the 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 of European settlement comprised 36% of the world's population in 1900.

Population growth in the West became more rapid after the introduction of compulsory vaccination and improvements in medicine and sanitation. As living conditions and health care improved during the 19th century, the United Kingdom's population doubled every fifty years. 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. 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 Russia and the Soviet Union was marked by a succession of wars, famines and other disasters, each accompanied by large-scale population losses. By the end of World War II in 1945, the Russian population was about 90 million fewer than it could have been otherwise. In recent decades, Russia's population has declined significantly – from 148 million in 1991 to 143 million in 2012 – and may sink as low as 107 million by 2050, if current demographic trends continue.

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, 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; today, the region is home to over 1.2 billion people. The population of Java increased from about five million in 1815 to more than 130 million in the early 21st century. Mexico's population grew from 13.6 million in 1900 to about 112 million in 2009. Between the 1920s and 2000s, Kenya's population grew from 2.9 million to 37 million.

Global demographics

Main article: Demographics of the world

Chart showing geographic distribution of world population in 2005.

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. 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. At the beginning of 2012, 50.5% of the world's population was under 30; 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, with women living an average of 69 years and men approximately 65 years. In 2010, the global fertility rate was estimated at 2.52 children per woman. 83% of the world's over-15s are considered literate. 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 (140 lb).

The nominal 2011 gross world product was estimated at US$69.11 trillion, giving an annual global per capita figure of around US$9,900. 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 925 million people (13.2%) are malnourished. In December 2011, there were around 2.26 billion global Internet users, constituting 32.7% of the world population.

The Han Chinese are the world's largest single ethnic group, constituting over 19% of the global population, while the second-largest single ethnicity, the Bengali people, account for around 4.8%. 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 Hindi-Urdu (2.68%). 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%. In 2005, around 16% of the global population were reported to be non-religious.

Largest populations by country

Further information: List of countries by population

A map of the world's countries by total population, with darker shading indicating larger populations.

The 10 countries with the largest total population:

Rank	Country / Territory	Population	Date	% of world population	Source
1	China	1,355,240,000	January 6, 2013	19.2%
2	India	1,210,193,422	March 2011	17%
3	United States	315,068,000	January 6, 2013	4.46%
4	Indonesia	237,641,000	May 2010	3.36%
5	Brazil	197,530,000	January 6, 2013	2.8%
6	Pakistan	181,701,000	January 6, 2013	2.57%
7	Nigeria	170,123,740	July 2012	2.41%
8	Bangladesh	161,083,804	July 2012	2.28%
9	Russia	141,927,297	January 1, 2010	2.009%
10	Japan	127,547,000	June 1, 2012	1.81%

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

Further information: List of countries and dependencies by population density

The tables below list the world's most densely populated countries, both in absolute terms and in comparison to their total populations.

Population density (people per km²) map of the world in 1994. Red and pink areas denote regions of highest population density.

10 most densely populated countries (with population above 1 million)

Rank	Country/Region	Population	Area (km2)	Density (Pop. per km2)
1	Singapore	5,183,700	710	7301
2	Bahrain	1,234,596	750	1646
3	Bangladesh	152,518,015	147,570	1034
4	Taiwan	23,293,593	36,190	644
5	Mauritius	1,288,000	2,040	631
6	South Korea	50,004,441	99,538	502
7	Lebanon	4,292,000	10,452	411
8	Rwanda	10,718,379	26,338	407
9	Netherlands	16,775,273	41,526	404
10	Belgium	11,139,292	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	1,223,250,000	3,287,240	372	Growing country
Bangladesh	152,518,015	147,570	1034	Growing country
Japan	127,547,000	377,873	338	Declining in population
Philippines	94,013,200	300,076	313	Fast-growing country
Vietnam	85,789,573	331,689	259	Growing country
United Kingdom	62,262,000	243,610	256	Growing country
South Korea	50,004,441	99,538	502	Steady in population
Taiwan	23,293,593	36,190	644	Declining in population
Sri Lanka	20,277,597	65,610	309	Growing country
Netherlands	16,830,000	41,526	405	Steady in population

Fluctuation

Main article: Population growth

Estimates of population evolution in different continents between 1950 and 2050, according to the United Nations. The vertical axis is logarithmic and is in millions of people.

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.

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), 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.

A world map showing global variations in fertility rate per woman, according to the CIA World Factbook's 2012 data.

  7–8 Children

  6–7 Children

  5–6 Children

  4–5 Children

  3–4 Children

  2–3 Children

  1–2 Children

  0–1 Children

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.

In some countries, there is negative population growth (i.e. net decrease in population over time), especially in Central and Eastern Europe – this is mainly due to low fertility rates. During the 2010s, Japan and some countries in Western Europe are also expected to encounter negative population growth, due to sub-replacement fertility rates.

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.

• 

  Estimated world population figures, 10,000 BC–2000 AD.

• 

  Estimated world population figures, 10,000 BC–2000 AD (in log y scale).

• 

  World population figures, 1950–2000.

• 

  Estimated global growth rates, 1950–2050.

• 

  Estimated and projected populations of the world and its continents (except Antarctica) from 1950 to 2100. The shaded regions correspond to the range of projections by the United Nations Department of Economic and Social Affairs.

Forecasts

Main article: World population estimates

UN (medium variant – 2010 revision) and US Census Bureau (December 2010) estimates

Year	UN est. (millions)	Difference	USCB est. (millions)	Difference
2000	6,123	–	6,090	–
2010	6,896	773	6,852	763
2020	7,657	761	7,593	740
2030	8,321	665	8,249	656
2040	8,874	553	8,801	552
2050	9,306	432	9,256	456

In the long run, future 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, while the UN asserted that this occurred in late 2011.

Average global birth rates are declining slightly, 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 unexpectedly due to disease, war and other mass catastrophes, or advances in medicine.

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.

UN 2008 estimates and medium variant projections (in millions)

Year	World	Asia	Africa	Europe	Latin America	Northern America	Oceania
2000	6,115	3,698 (60.5%)	819 (13.4%)	727 (11.9%)	521 (8.5%)	319 (5.2%)	31 (0.5%)
2005	6,512	3,937 (60.5%)	921 (14.1%)	729 (11.2%)	557 (8.6%)	335 (5.1%)	34 (0.5%)
2010	6,909	4,167 (60.3%)	1,033 (15.0%)	733 (10.6%)	589 (8.5%)	352 (5.1%)	36 (0.5%)
2015	7,302	4,391 (60.1%)	1,153 (15.8%)	734 (10.1%)	618 (8.5%)	368 (5.0%)	38 (0.5%)
2020	7,675	4,596 (59.9%)	1,276 (16.6%)	733 (9.6%)	646 (8.4%)	383 (5.0%)	40 (0.5%)
2025	8,012	4,773 (59.6%)	1,400 (17.5%)	729 (9.1%)	670 (8.4%)	398 (5.0%)	43 (0.5%)
2030	8,309	4,917 (59.2%)	1,524 (18.3%)	723 (8.7%)	690 (8.3%)	410 (4.9%)	45 (0.5%)
2035	8,571	5,032 (58.7%)	1,647 (19.2%)	716 (8.4%)	706 (8.2%)	421 (4.9%)	46 (0.5%)
2040	8,801	5,125 (58.2%)	1,770 (20.1%)	708 (8.0%)	718 (8.2%)	431 (4.9%)	48 (0.5%)
2045	8,996	5,193 (57.7%)	1,887 (21.0%)	700 (7.8%)	726 (8.1%)	440 (4.9%)	50 (0.6%)
2050	9,150	5,231 (57.2%)	1,998 (21.8%)	691 (7.6%)	729 (8.0%)	448 (4.9%)	51 (0.6%)

Population growth by region

The table below shows historical and predicted regional population figures in millions. The availability of historical population figures varies by region.

World historical and predicted populations (in millions)

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	39	10	10	16	24	38	74	167	511	577	809	912
Northern America	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

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	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	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	Northern America	Oceania	Notes
70,000 BC	< 0.015
10,000 BC	1
9000 BC	3
8000 BC	5
7000 BC	7
6000 BC	10
5000 BC	15
4000 BC	20
3000 BC	25
2000 BC	35
1000 BC	50
500 BC	100
AD 1	200
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

Hoerner (1975) 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 has recently been correlated to a non-linear second order positive feedback between demographic growth and technological development. This feedback can be described as follows: technological growth → increase in the carrying capacity of land for people →demographic growth → more people → more potential inventors → acceleration of technological growth →accelerating growth of the carrying capacity – faster population growth →accelerating growth of the number of potential inventors →faster technological growth → hence, the faster growth of the Earth's carrying capacity for people, and so on.

According to Kapitsa (1997), the world population grew between 67,000 BC and 1965 according to the following formula:

$N = \frac{C}{\tau} \arccot \frac{T_0-T}{\tau}$

where

• N is current population
• T is the current year
• C = (1.86±0.01)•10¹¹
• T₀ = 2007±1
• $\tau$ = 42±1

The transition from hyperbolic growth to slower rates of growth is related to the demographic transition.

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.

Historic chart showing the periods of time the world population has taken to double, from 1700 to 2000.

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

The scientific consensus is that the current population expansion and accompanying increase in usage of resources is linked to threats to the global ecosystem. 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. Indeed, some analysts claim that overpopulation's most serious impact is its effect on the environment. 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.

Forecasts of scarcity

In 1798, the economist Thomas Malthus incorrectly predicted that continued population growth would exhaust the global food supply by the mid-19th century. In 1968, Paul R. Ehrlich reprised this argument in The Population Bomb, predicting mass global famine in the 1970s and 1980s. The dire predictions of Ehrlich and other neo-Malthusians were vigorously challenged by a number of economists, notably Julian Lincoln Simon. Agricultural research already under way, such as the Green Revolution, led to dramatic improvements in crop yields. Food production has so far kept pace with population growth, but neo-Malthusians point out that the Green Revolution relies heavily on petroleum-based fertilizers, and that many crops have become so genetically uniform that a crop failure could potentially have global repercussions. Food prices in the early 21st century are rising sharply on a global scale, and causing serious malnutrition to spread widely.

Graph of the global human population from 10,000 BC to 2010 AD, from the US Census Bureau. The graph shows the extremely rapid growth in the world population that has taken place since the 18th century.

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

The potential peaking of world oil production may test the critics of Malthus and Ehrlich, as oil is of crucial importance to global transportation, power generation and agriculture. 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, and remained below $100/barrel until around 2010. Resource demands are expected to ease as population growth declines, but it is unclear whether rising living standards in developing countries will once again create resource shortages.

Richard C. Duncan claims the that the world population will decline to about 2 billion around 2050. 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 2011 is over 310 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" 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. 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.

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.

Population control

Main article: Human 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, with 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.

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; the updated figure totalled approximately 106 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". Given an estimated global population of 6.2 billion in 2002, it could be inferred that about 6% of all people who had ever existed were alive in 2002. 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.

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 limited size of the world population in prehistoric times (as compared to its current size) makes this source of 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 people for purposes of taxation or military service. 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 should be in the billions, or even tens of billions of people.

Another critical factor for such an estimate is life expectancy. Using an average figure of twenty years and the population estimates above, one can compute a total of about 58 billion. Using a figure of forty yields around 30 billion. However, life expectancy varies greatly when taking into account children who died before their first birthday, a number very difficult to estimate for earlier times. Haub states that "life expectancy at birth probably averaged only about ten years for most of human history". His estimates for infant mortality suggest that around 40% of those who have ever lived did not survive beyond their first birthday.

United Nations population agencies

The United Nations operates several organisations with various population-related competencies, including the Commission on Population and Development, the United Nations Population Division, and the United Nations Population Fund.

See also

• Birth control
• Demographic transition
• Depopulation
• Doomsday argument
• Family planning
• Food security

• Megacity
• Coastal population
• Natalism
• One-child policy
• Two-child policy
• World's largest cities

Historical:

• Historical demography
• National Commission for the Observance of World Population Year 1974

Lists:

• List of religious populations
• List of countries by past and future population
• List of countries by population in 1900
• List of countries by population density
• List of countries by population growth rate
• List of countries by fertility rate
• Lists of organisms by population – for non-human global populations

External links

Further reading

• World Population Prospects, the 2010 Revision (United Nations Population Division).
• Symptoms of The Global Demographic Decline
• Central Intelligence Agency (2012). CIA World Factbook 2012. Retrieved 6 November 2012.
• The World in Balance Transcript of two-part PBS' Nova on World Population
• The Environmental Politics of Population and Overpopulation A University of California, Berkeley summary covering historical and contemporary population dynamics, forecasts, resource scarcity, population control, and environmental concerns

Organizations

• Optimum Population Trust
• The Day of 6 Billion official homepage
• World Population Day United Nations: July 11
• United Nations (2001). United Nations Population Info
• Population Reference Bureau www.prb.org – News and issues related to population.
• Berlin Institute for Population and Development "English". Berlin-institut.org. March 23, 2010. http://www.berlin-institut.org/index.php?id=48.

Statistics and maps

• World population statistics presented in a treemap interface
• World Population Map, Statistical Graph
• Year-by-Year World Population Estimates: 10,000 BC to AD 2007
• United States Census Bureau (2004). Historical Estimates of World Population
• The AfriPop Project, showing African population statistics
• PopulationData.net (2005). PopulationData.net – Information and maps about populations around the world
• GeoHive GeoHive.com – World Statistics including population and future predictions.
• World maps, including maps of population from 1 AD to 2300 AD
• World countries mapped by population size
• World Population from the US Census Bureau in an interactive Excel dashboard
• Trendalyzer: interactive population graphs

Population clocks

• U.S. Census Bureau – World Population Clock
• Population Counter
• World Population
• World Population Counter
• Live World Population
• (French) World Population Clock (2005). WorldPopClock.com – World population clock.