### Exponential growth model

Population growth is the change in a population over time, and can be quantified as the change in the number of individuals of any species in a population using "per unit time" for measurement. In biology, the term population growth is likely to refer to any known organism, but this article deals mostly with the application of the term to human populations in demography.

In demography, population growth is used informally for the more specific term population growth rate (see below), and is often used to refer specifically to the growth of the human population of the world.

Simple models of population growth include the Malthusian Growth Model and the logistic model.

The world population grew from 1 billion to 7 billion from 1800 to 2011. During the year 2011, according to estimates, 135 million people were born and 57 million died, for an increase in population of 78 million.[1]

Population[1]
Years Passed Year Billion
- 1800 1
127 1927 2
33 1960 3
14 1974 4
13 1987 5
12 1999 6
12 2011 7
14 2025* 8
18 2043* 9
40 2083* 10
* UNFPA
United Nations Population Fund
estimate 31.10.2011

## Determinants of population growth

Four factors determine population growth for a given geographical area - births (B), deaths (D), immigration rate (I), and emigration rate (E):

growth rate of population = (B-D)+(I-E)

In other words, the population growth of a period can be calculated in two parts, natural growth of population (B-D) and mechanical growth of population (I-E), in which mechanical growth of population is mainly affected by social factors, e.g. advanced economies may grow faster while backward economies grow slowly or even experience negative growth. (Growth can be both positive or negative i.e. growth can increase or decrease.)

## Population growth rate

In demographics and ecology, the "population growth rate" is the rate at which the number of individuals in a population increases in a given time period 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:

$pop\ growth\ rate = \frac\left\{ P\left(t_2\right) - P\left(t_1\right)\right\} \left\{P_1\right\}$

The most common way to express population growth is as a percentage. That is:

$\mathrm\left\{percentage\ growth\right\} = \mathrm\left\{pop\ growth\ rate\right\} \times 100.$

A positive growth ratio (or rate) indicates that the population is increasing, while a negative growth ratio indicates the population is decreasing. A growth ratio of zero indicates that there were the same number of people at the two times—net difference between births, deaths 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.[2]

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

## Excessive growth and decline

Main articles: Overpopulation and Population decline

Population exceeding the carrying capacity of an area or environment is called overpopulation. It may be caused by growth in population or by reduction in capacity. Spikes in human population can cause problems such as pollution and traffic congestion, these might be resolved or worsened by technological and economic changes. Conversely, such areas may be considered "underpopulated" if the population is not large enough to maintain an economic system (see population decline). Between these two extremes sits the notion of the optimum population.

## Human population growth rate

Globally, the growth rate of the human population has been declining since peaking in 1962 and 1963 at 2.20% per annum. In 2009, the estimated annual growth rate was 1.1%.[4] The CIA World Factbook gives the world annual birthrate, mortality rate, and growth rate as 1.89%, 0.79%, and 1.096% respectively.[5] The last 100 years have seen a rapid increase in population due to medical advances and massive increase in agricultural productivity[6] made possible by the Green Revolution.[7][8][9]

The trend is shown in the graph at right. Actual measured data are given to 2010 and extrapolated estimates beyond that. If the linear trend holds and growth rate continues to decline, population growth rate will fall to zero in about 2080. Population will peak and begin declining thereafter. The Malthus exponential model, modified to reflect the linear growth rate trend, suggests that world population will peak at about 10.3 billion. This, of course, is speculative but is consistent with other models showing a population peak in the latter part of the 21st century.

The actual annual growth in the number of humans fell from its peak of 88.0 million in 1989, to a low of 73.9 million in 2003, after which it rose again to 75.2 million in 2006. Since then, annual growth has declined. In 2009, the human population increased by 74.6 million, which is projected to fall steadily to about 41 million per annum in 2050, at which time the population will have increased to about 9.2 billion.[4] Each region of the globe has seen great reductions in growth rate in recent decades, though 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.[10]

Some countries experience negative population growth, 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 HIV-related deaths. Some Western Europe countries might also encounter negative population growth.[11] Japan's population began decreasing in 2005.[12] The United Nations Population Division expects world population to peak at over 10 billion at the end of the 21st century but Sanjeev Sanyal has argued that global fertility will fall below replacement rates in the 2020s and that world population will peak below 9 billion by 2050 followed by a long decline.[13]

## Growth by country

According to United Nations population statistics, the world population grew by 30%, or 1.6 billion people, between 1990 and 2010.[14] In number of people the increase was highest in India 350 million and China 196 million. Population growth was among highest in the United Arab Emirates (315%) and Qatar (271%).[14]

Growth rates of the world's most populous countries
Rank Country Population
2010
Population
1990
Growth (%)
1990–2010
World 6,895,889,000 5,306,425,000 30.0%
1  China 1,341,335,000 1,145,195,000 17.1%
2  India 1,224,614,000 873,785,000 40.2%
3  United States 310,384,000 253,339,000 22.5%
4  Indonesia 239,871,000 184,346,000 30.1%
5  Brazil 194,946,000 149,650,000 30.3%
6  Pakistan 173,593,000 111,845,000 55.3%
7  Nigeria 158,423,000 97,552,000 62.4%
9  Russia 142,958,000 148,244,000 -3.6%
10  Japan 128,057,000 122,251,000 4.7%

### 1960s to 2010 table of population growth

Population growth 1990–2008 (%)[15]
Africa 55%
Middle East 51%
Asia 35%
Latin America 30%
OECD North America 24%
OECD Europe 9%
OECD Pacific 8%
Former Soviet Union −1%
Non-OECD Europe −11%

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 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,[16] further straining its resources. Vietnam, Mexico, Nigeria, Egypt, Ethiopia, and the DRC are witnessing a similar growth in population.

The situation was most acute in northern, western and central Africa. Refugees from places like the Sudan have helped further strain the resources of neighbouring states like Chad and Egypt. The nation is also host to roughly 255,000 refugees from Sudan's Darfur region, and about 77,000 refugees from the Central African Republic, while approximately 188,000 Chadians have been displaced by their own civil war and famines, have either fled to either the Sudan, the Niger, or more recently, Libya.

Example nation 1st Population total. 2nd Population total. 3rd Population total. 4th Population total. 5th Population total. Life expectancy in years. Total population growth from 1st Pop. Total to 5th Pop. Total.
Eritrea* N/A* N/A* 3,437,000(1994)[17] 4,298,269 (2002) 5,673,520 (2008)[18] 61 (2008)[19] 2,236,520 (since independence)
Ethiopia* 23,457,000(1967)*[20] 50,974,000(1990)* [21] 54,939,000(1994) [17] 67,673,031(2003) 79,221,000(2008)[22] 55(2008)[19] 55,764,000
Sudan** 14,355,000(1967)**[20] 25,204,000(1990)** [21] 27,361,000 (1994)**[17] 38,114,160 (2003)** 42,272,000(2008)**[23] 50(2008)**[19] 27,917,000
Chad 3,410,000(1967)[20] 5,679,000(1990) [21] 6,183,000 (1994)[17] 9,253,493(2003) 10,329,208 (2009)[16] 47(2008)[19] 6,919,205
Niger 3,546,000(1967)[20] 7,732,000(1990) [21] 8,846,000(1994)[17] 10,790,352 (2001) 15,306,252 (2009)[24] 44 (2008)[19] 11,760,252
Nigeria 61,450,000(1967)[20] 88,500,000(1990) [21] 108,467,000 (1994)[17] 129,934,911 (2002) 158,259,000 (2008)[25] 47(2008)[19] 96,809,000
Mali 4,745,000(1967)[20] 8,156,000(1990),[21] 10,462,000(1994)[17] 11,340,480(2002) 14,517,176(2010).[26] 50(2008)[19] 9,772,176
Mauritania 1,050,000(1967)[20] 2,025,000(1990) [21] 2,211,000 (1994)[17] 2,667,859 (2003) 3,291,000 (2009)[16] 54(2008)[19] 2,241,000
Senegal 3,607,000(1967)[20] 7,327,000(1990) [21] 8,102,000 (1994) [17] 9,967,215(2002) 13,711,597 (2009)[27] 57(2008)[19] 10,104,597
Gambia 343,000(1967)[20] 861,000(1990) [21] 1,081,000 (1994)[17] 1,367,124 (2000) 1,705,000(2008)[25] 55(2008)[19] 1,362,000
Algeria 11,833,126 (1966)[20] 25,012,000 (1990) [21] 27,325,000 (1994) [17] 32,818,500 (2003) 34,895,000[22][28](2008) 74 (2008)[19] 23,061,874
The DRC/Zaire 16,353,000(1967)[20] 35,562,000 (1990) [21] 42,552,000 (1994) [17] 55,225,478 (2003) 70,916,439 (2008) [22][29] 54(2008)[19] 54,563,439
Egypt 30,083,419 (1966)[20] 53,153,000 (1990) [21] 58,326,000 (1994) [17] 70,712,345 (2003) 79,089,650 [30][30] (2008) [22] 72 (2008)[19] 49,006,231
Réunion (French colony) 418,000 (1967)[20] N/A (1990) [21] N/A (1994)[17] 720,934 (2003) 827,000 (2009) [28] N/A (2008)[19] 409,000
The Falkland Islands (UK Territory) 2,500(1967)[20] N/A (1990) [21] N/A (1994)[17] 2,967 (2003) 3,140(2010)[16] N/A (2008)[19] 640
Chile 8,935,500(1967)[20] 13,173,000 (1990) [21] 13,994,000(1994)[17] 15,116,435 (2002) 17,224,200 (2011) 77 (2008)[19] 8,288,700
Colombia 19,191,000(1967)[20] 32,987,000(1990) [21] 34,520,000(1994)[17] 41,088,227 (2002) 45,925,397(2010)[31] 73 (2008)[19] 26,734,397
Brazil 85,655,000(1967)[20] 150,368,000 (1990) [21] 153,725,000 (1994)[17] 174,468,575 (2000) 190,732,694(2010) [32] 72(2008)[19] 105,077,694
Mexico 45,671,000(1967)[20] 86,154,000(1990) [21] 93,008,000(1994)[17] 103,400,165 (2000) 112,322,757(2010)[33] 76(2008)[19] 66,651,757
Fiji 476,727 (1966)[20] 765,000(1990) [21] 771,000 (1994)[17] 844,330 (2001) 849,000[28] (2010) 70 (2008)[19] 372,273
Nauru 6,050(1966)[20] 10,000(1990) [21] N/A (1994)[17] 12,329 (2002) 9,322 (2011)[34] N/A (2008)[19] 3,272
Jamaican 1,876,000 (1967)[20] 2,420,000 (1990) [21] 2,429,000 (1994)[17] 2,695,867 (2003) 2,847,232[35](2010) 74 (2008)[19] 971,232
Australia 11,540,764 (1964)[20] 17,086,000 (1990) [21] 17,843,000 (1994)[17] 19,546,792 (2003) 23,618,241[36] (2010) 82 (2008)[19] 11,066,508
Albania 1,965,500(1964)[20] 3,250,000 (1990) [21] 3,414,000 (1994)[17] 3,510,484 (2002) 2,986,952 (July 2010 est.)[16][37] (2010) 78 (2008)[19] 1,021,452
Poland 31,944,000(1967)[20] 38,180,000 (1990) [21] 38,554,000 (1994)[17] 38,626,349 (2001) 38,192,000(2010)[38] 75 (2008)[19] 6,248,000
Hungary 10,212,000(1967)[20] 10,553,000 (1990) [21] 10,261,000 (1994)[17] 10,106,017 (2002) 9,979,000(2010)[39] 73 (2008)[19] -142,000
Bulgaria 8,226,564(1965)[20] 8,980,000 (1990) [21] 8,443,000 (1994)[17] 7,707,495(2000) 7,351,234 (2011)[40] 73 (2008)[19] -875,330
UK 55,068,000 (1966)[20] 57,411,000 (1990) [21] 58,091,000 (1994) [17] 58,789,194 (2002) 62,008,048 (2010)[41] 79(2008)[19] 7,020,048
Ireland/Éire 2,884,002(1966)[20] 3,503,000(1990) [21] 3,571,000 (1994)[17] 3,840,838 (2000) 4,470,700 [42] (2010) 78 (2008)[19] 1,586,698
The PRC/China 720,000,000(1967)[20] 1,139,060,000(1990) [21] 1,208,841,000 (1994)[17] 1,286,975,468 (2004) 1,339,724,852(2010)[43] 73 (2008)[19] 619,724,852
Japan*** 98,274,961(1965)[20] 123,537,000(1990) [21] 124,961,000 (1994)[17] 127,333,002 (2002) 127,420,000 (2010)[44] 82(2008)[19] 28,123,865
Ryukyu Islands (Once occupied by the US)*** 934,176(1965)[20]
India# 511,115,000 (1967)[20] 843,931,000 (1990) [21] 918,570,000 (1994)[17] 1,028,610,328 (2001) 1,210,193,422(2011)[45] 69 (2008)[19] 699,078,422
Notes
* Eritrea left Ethiopia in 1991.
** Split into the nations of Sudan and Southern Sudan during 2011.
*** Merged in 1972.
# Merged in 1975.

## Into the future

Main article: Projections of population growth

According to UN's 2010 revision to its population projections, world population will peak at 10.1bn in 2100 compared to 7bn in 2011.[46] However, some experts dispute the UN's forecast and have argued that birthrates will fall below replacement rate in the 2020s. According to these forecasters, population growth will be only sustained till the 2040s by rising longevity but will peak below 9bn by 2050.[47]