population growth

File:Human population since 1800.png

File:Population curve.svg to 2000 CE]]

World population has been rising continuously since the end of the Black Death, around the year 1350.{{cite web|url=http://www.abc.net.au/science/articles/2008/01/29/2149185.htm |title=Black death 'discriminated' between victims |website=Australian Broadcasting Corporation |date=29 January 2008 |access-date=3 November 2008 |url-status=live |archive-url=https://web.archive.org/web/20161220120404/http://www.abc.net.au/science/articles/2008/01/29/2149185.htm |archive-date=20 December 2016 }} Population began growing rapidly in the Western world during the industrial revolution. The most significant increase in the world's population has been since the 1950s, mainly due to medical advancements{{cite journal |title=The contribution of vaccination to global health: past, present and future |publisher=Philosophical Transactions of the Royal Society |date=19 June 2014|pmc=4024226 |last1=Greenwood |first1=B. |journal=Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences |volume=369 |issue=1645 |pages=20130433 |doi=10.1098/rstb.2013.0433 |pmid=24821919 }} and increases in agricultural productivity.Armelagos, George J., Alan H. Goodman, and Kenneth H. Jacobs. "The origins of agriculture: Population growth during a period of declining health." Population and Environment 13.1 (1991): 9-22.Taiz, Lincoln. "[https://www.scielo.br/j/txpp/a/TWxQX34RrdtTmTPpDPtgNhS/?format=pdf&lang=en Agriculture, plant physiology, and human population growth: past, present, and future]." Theoretical and Experimental Plant Physiology 25 (2013): 167-181.

{{Main|Haber process#Economic and environmental aspects}}

Due to its dramatic impact on the human ability to grow food, the Haber process, named after one of its inventors, the German chemist Fritz Haber, served as the "detonator of the population explosion", enabling the global population to increase from 1.6 billion in 1900 to 7.7 billion by November 2019.{{cite journal |last1=Smil |first1=Vaclav |year=1999 |title=Detonator of the population explosion |url=http://www.vaclavsmil.com/wp-content/uploads/docs/smil-article-1999-nature7.pdf |journal=Nature |volume=400 |issue=6743 |page=415 |doi=10.1038/22672 |bibcode=1999Natur.400..415S |s2cid=4301828 |archive-date=2021-01-22 |access-date=2019-07-04 |archive-url=https://web.archive.org/web/20210122190517/http://vaclavsmil.com/wp-content/uploads/docs/smil-article-1999-nature7.pdf |url-status=dead }}

Some of the reasons for the "Modern Rise of Population"{{Cite book|title=The Modern Rise of Population|last=McKeown|first=Thomas|publisher=Edward Arnold|year=1976|isbn=9780713159868|location=London, UK}} were particularly investigated by the British health scientist Thomas McKeown (1912–1988). In his publications, McKeown challenged four theories about the population growth:

1. McKeown stated that the growth in Western population, particularly surging in the 19th century, was not so much caused by an increase in fertility, but largely by a decline of mortality particularly of childhood mortality followed by infant mortality,{{Cite journal|vauthors=McKeown T, Brown RG |date=1955|title=Medical evidence related to English population changes in the eighteenth century|journal=Population Studies|volume=9|issue=2|pages=119–141|doi=10.1080/00324728.1955.10404688|jstor=2172162}}{{Cite journal|vauthors=McKeown T, Brown RG, Record RG |date=1972|title=An interpretation of the modern rise of population in Europe|journal=Population Studies |volume=26 |issue=3|pages=345–382|doi=10.1080/00324728.1972.10405908|jstor=2173815|pmid=11630563}}
2. The decline of mortality could largely be attributed to rising standards of living, whereby McKeown put most emphasis on improved nutritional status,
3. McKeown questioned the effectiveness of public health measures, including sanitary reforms, vaccination and quarantine,{{Cite journal|vauthors=McKeown T, Record RG |date=1962

|title=Reasons for the Decline of Mortality in England and Wales during the Nineteenth Century

|journal=Population Studies|volume=16|issue=2|pages=94–122

|doi=10.2307/2173119|jstor=2173119}}

1. The “McKeown thesis" states that curative medicine measures played little role in mortality decline, not only prior to the mid-20th century but also until well into the 20th century.{{Cite journal|vauthors=McKeown T, Record RG, Turner RD |date=1975

|title=An Interpretation of the Decline of Mortality in England and Wales during the Twentieth Century

|journal=Population Studies|volume=29|issue=3|pages=391–422

|doi=10.1080/00324728.1975.10412707|jstor=2173935|pmid=11630508}}

Although the McKeown thesis has been heavily disputed, recent studies have confirmed the value of his ideas.{{cite journal |last1=Korotayev |first1=A. V. |last2=Malkov |first2=A. S. |year=2016 |url=https://www.academia.edu/35548090 |title=Compact Mathematical Model of the World System Economic and Demographic Growth, 1 CE–1973 CE |journal=International Journal of Mathematical Models and Methods in Applied Sciences |volume=10 |pages=200–209}} His work is pivotal for present day thinking about population growth, birth control, public health and medical care. McKeown had a major influence on many population researchers, such as health economists and Nobel prize winners Robert W. Fogel (1993) and Angus Deaton (2015). The latter considered McKeown as "the founder of social medicine".{{Cite book|title=The Great Escape. Health, wealth, and the origins of inequality|last=Deaton|first=Angus|publisher=Princeton University Press|year=2013|isbn=978-0-691-15354-4|location=Princeton and Oxford|pages=91–93|quote=McKeown's views, updated to modern circumstances, are still important today in debates between those who think that health is primarily determined by medical discoveries and medical treatment and those who look to the background social conditions of life.}}

The "population growth rate" is the rate at which the number of individuals in a population increases in a given time period, expressed as a fraction of the initial population. Specifically, population growth rate refers to the change in population over a unit time period, often expressed as a percentage of the number of individuals in the population at the beginning of that period. This can be written as the formula, valid for a sufficiently small time interval:

:$Population\backslash \; growth\backslash \; rate\; =\; \backslash frac\{\; P(t\_2)\; -\; P(t\_1)\}\; \{P(t\_1)(t\_2-t\_1)\}$

A positive growth rate indicates that the population is increasing, while a negative growth rate indicates that the population is decreasing. A growth ratio of zero indicates that there were the same number of individuals at the beginning and end of the period—a growth rate may be zero even when there are significant changes in the birth rates, death rates, immigration rates, and age distribution between the two times.[http://www.apheo.ca/index.php?pid=61 Association of Public Health Epidemiologists in Ontario] {{webarchive|url=https://web.archive.org/web/20080522092307/http://www.apheo.ca/index.php?pid=61 |date=22 May 2008 }}

A related measure is the net reproduction rate. In the absence of migration, a net reproduction rate of more than 1 indicates that the population of females is increasing, while a net reproduction rate less than one (sub-replacement fertility) indicates that the population of females is decreasing.

Most populations do not grow exponentially, rather they follow a logistic model. Once the population has reached its carrying capacity, it will stabilize and the exponential curve will level off towards the carrying capacity, which is usually when a population has depleted most its natural resources.{{Cite book|title=Campbell Biology|last1=Reece|first1=Jane|last2=Urry|first2=Lisa|last3=Cain|first3=Michael|last4=Wasserman|first4=Steven|last5=Minorsky|first5=Peter|last6=Jackson|first6=Robert|publisher=Pearson|year=2014}} In the world human population, growth may be said to have been following a linear trend throughout the last few decades.

File:Logistic growth graph (population ecology).JPG

The growth of a population can often be modelled by the logistic equation{{Cite book|title=Brief Applied Calculus|last1=Stewart|first1=James|last2=Clegg|first2=Daniel|publisher=Brooks/Cole Cengage Learning|year=2012}}

:$\backslash frac\{dP\}\{dt\}=rP\backslash left(1-\backslash frac\{P\}\{K\}\backslash right),$

where

• $P(t)$ = the population after time t;
• $t$ = time a population grows;
• $r$ = the relative growth rate coefficient;
• $K$ = the carrying capacity of the population; defined by ecologists as the maximum population size that a particular environment can sustain.

As it is a separable differential equation, the population may be solved explicitly, producing a logistic function:

:$P(t)=\backslash frac\{K\}\{1+Ae^\{-rt\}\}$,

where $A=\backslash frac\{K-P\_0\}\{P\_0\}$ and $P\_0$ is the initial population at time 0.

{{Further|Total fertility rate|Estimates of historical world population|Population dynamics}}

{{See also|Human overpopulation|Overshoot (population)}}

File:Countriesbyfertilityrate.svg per woman according to the CIA World Factbook's 2021 data

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File:World population (UN).svgs between 1950 and 2050 according to the United Nations. The vertical axis is logarithmic and is in millions of people. (2011)]]

File:World population growth rate 1950–2050.svg

The world population growth rate peaked in 1963 at 2.2% per year and subsequently declined. In 2017, the estimated annual growth rate was 1.1%.{{cite web|url=http://www.un.org/en/development/desa/population/publications/index.shtml|title=World Population Prospects 2017|archive-url=https://web.archive.org/web/20170711042851/http://www.un.org/en/development/desa/population/publications/index.shtml|archive-date=11 July 2017|url-status=dead}} The CIA World Factbook gives the world annual birthrate, mortality rate, and growth rate as 1.86%, 0.78%, and 1.08% respectively.{{cite web|url=https://www.cia.gov/the-world-factbook/countries/world/|title=The World Factbook|date=20 November 2015|access-date=4 January 2016}} The last 100 years have seen a massive fourfold increase in the population, due to medical advances, lower mortality rates, and an increase in agricultural productivity made possible by the Green Revolution.{{cite news|url=http://news.bbc.co.uk/1/hi/world/south_asia/4994590.stm|title=BBC NEWS - South Asia - The end of India's green revolution?|date=29 May 2006}}

The annual increase in the number of living humans peaked at 88.0 million in 1989, then slowly declined to 73.9 million in 2003, after which it rose again to 75.2 million in 2006. In 2017, the human population increased by 83 million. Generally, developed nations have seen a decline in their growth rates in recent decades, though annual growth rates remain above 2% in some countries of the Middle East and Sub-Saharan Africa, and also in South Asia, Southeast Asia, and Latin America.{{cite web |url=https://www.census.gov/ipc/www/idb/worldpop.php |title=International Programs |url-status=dead |archive-url=https://web.archive.org/web/20090701122431/http://www.census.gov/ipc/www/idb/worldpop.php |archive-date=1 July 2009 }}

In some countries the population is declining, especially in Eastern Europe, mainly due to low fertility rates, high death rates and emigration. In Southern Africa, growth is slowing due to the high number of AIDS-related deaths. Some Western Europe countries might also experience population decline.{{Cite web |url=http://esa.un.org/unpp/index.asp?panel=2 |title=UN population projections |access-date=23 May 2009 |archive-date=14 September 2010 |archive-url=https://web.archive.org/web/20100914023416/http://esa.un.org/UNPP/index.asp?panel=2 |url-status=dead }} Japan's population began decreasing in 2005.{{cite news|url=https://www.theguardian.com/world/2009/jan/02/japan-population|title=Japan sees biggest population fall|newspaper=the Guardian|date=2 January 2009|agency=Associated Press}}

The United Nations Population Division projects world population to reach 11.2 billion by the end of the 21st century.

The Institute for Health Metrics and Evaluation projects that the global population will peak in 2064 at 9.73 billion and decline to 8.89 billion in 2100.

{{cite journal

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|journal=Lancet

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A 2014 study in Science concludes that the global population will reach 11 billion by 2100, with a 70% chance of continued growth into the 22nd century.{{cite news|author=Carrington, Damien|date= 18 September 2014|url=https://www.theguardian.com/environment/2014/sep/18/world-population-new-study-11bn-2100 |title=World population to hit 11bn in 2100 – with 70% chance of continuous rise|newspaper=The Guardian|access-date= 19 December 2016}}{{Cite journal | doi = 10.1126/science.1257469| pmid = 25301627| title = World population stabilization unlikely this century| journal = Science| volume = 346| issue = 6206| pages = 234–7| date = 14 September 2014| issn = 1095-9203| last1 = Gerland | first1 = P.| last2 = Raftery | first2 = A. E.| last3 = Ev Ikova | first3 = H.| last4 = Li | first4 = N.| last5 = Gu | first5 = D.| last6 = Spoorenberg | first6 = T.| last7 = Alkema | first7 = L.| last8 = Fosdick | first8 = B. K.| last9 = Chunn | first9 = J.| last10 = Lalic | first10 = N.| last11 = Bay | first11 = G.| last12 = Buettner | first12 = T.| last13 = Heilig | first13 = G. K.| last14 = Wilmoth | first14 = J.| pmc=4230924| bibcode = 2014Sci...346..234G}} The German Foundation for World Population reported in December 2019 that the global human population grows by 2.6 people every second, and could reach 8 billion by 2023.{{cite news |last=Hook |first=Chris |date=20 December 2019 |title=Earth's population set to soar to 7.75 billion people by New year's Eve|url=https://7news.com.au/news/social/world-population-at-775-bln-by-year-end-c-616688|work=Seven News|access-date=2 January 2020}}{{cite news |last= Silk |first=John |date=21 December 2019|title=World's population to hit 7.75 billion in 2019 |url=https://www.dw.com/en/worlds-population-to-hit-775-billion-in-2019/a-51758905 |work=Deutsche Welle |access-date=14 March 2021}}

{{Main|List of countries by population growth rate}}

File:Comparing Population Growth By Country's Development, 2002.svg

According to United Nations population statistics, the world population grew by 30%, or 1.6 billion humans, between 1990 and 2010.{{cite web|url=http://esa.un.org/unpd/wpp/unpp/Panel_profiles.htm|title=World Population Prospects - Population Division - United Nations|access-date=28 May 2012|archive-url=https://web.archive.org/web/20110507035406/http://esa.un.org/unpd/wpp/unpp/Panel_profiles.htm|archive-date=7 May 2011|url-status=dead}} In number of people the increase was highest in India (350 million) and China (196 million). Population growth rate was among highest in the United Arab Emirates (315%) and Qatar (271%).

Many of the world's countries, including many in Sub-Saharan Africa, the Middle East, South Asia and South East Asia, have seen a sharp rise in population since the end of the Cold War. The fear is that high population numbers are putting further strain on natural resources, food supplies, fuel supplies, employment, housing, etc. in some of the less fortunate countries. For example, the population of Chad has ultimately grown from 6,279,921 in 1993 to 10,329,208 in 2009, further straining its resources. Vietnam, Mexico, Nigeria, Egypt, Ethiopia, and the DRC are witnessing a similar growth in population.

The following table gives some example countries or territories:

;Notes

:* Eritrea left Ethiopia in 1991.

:† Split into the nations of Sudan and South Sudan during 2011.

:‡ Japan and the Ryukyu Islands merged in 1972.

:# India and Sikkim merged in 1975.

{{Excerpt|Projections of population growth|paragraphs=1|only=paragraphs}}

• Demographic history
• Demographic transition
• Density dependence
• Ecological overshoot
• Epidemiological transition
• Human population planning
• Irruptive growth
• Overshoot (population)
• Population ageing
• Population decline
• Population density
• World population
• Estimates of historical world population
• Zero population growth

{{reflist|30em}}

{{externalvideo|video1=[https://www.youtube.com/watch?v=8bSJEUmAnlQ Food Production and Population Growth - Daniel Quinn]}}

• {{cite web|url=https://esa.un.org/unpd/wpp/index.html|title=World Population Prospects|publisher=Website of the United Nations Population Division|archive-url=https://web.archive.org/web/20170711032459/https://esa.un.org/unpd/wpp/index.html|archive-date=11 July 2017}}
• {{cite web|url=https://www.ecofuture.org/pop/revs/quinn_pop_video.html|title=Food Production and Population Growth|work=Daniel Quinn, Alan D. Thornhill, PhD|publisher=Ecofuture. Population and Sustainability Media, Non-fiction}}
• {{cite web|url=http://esa.un.org/unpd/ppp/index.html|title=Probabilistic Population Projections, 2nd Revision|publisher=Website of the United Nations Population Division|archive-url=https://web.archive.org/web/20131004212919/http://esa.un.org/unpd/ppp/index.html|archive-date=4 October 2013}}
• {{cite web|url=https://populationinstitutecanada.ca/pic-resources/population-growth-and-the-food-supply/|title=Population Growth and the Food Supply|publisher=Population Institute of Canada}}
• {{cite web|url=http://www.census.gov/ipc/www/idb/worldpopinfo.php|title=World population growth and trends 1950-2050|publisher=US Census|archive-url=https://web.archive.org/web/20100707175239/http://www.census.gov/ipc/www/idb/worldpopinfo.php|archive-date=7 July 2010}}
• {{cite web|url=https://www.cambridge.org/tz/academic/subjects/life-sciences/natural-resource-management-agriculture-horticulture-and/feeding-ten-billion-plants-and-population-growth?format=PB&isbn=9780521646857|title=Feeding the Ten Billion-Plants and Population Growth|publisher=PGR Newsletter FAO-Bioversity L.T. Evans. 2000. Cambridge University Press. ISBN 0-521-64685-5}} Published in Issue No. 125, page 39 to 40 - (5802) characters

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