The UN calculates that there are more than 7 billion living humans on Earth, yet 200 years ago we numbered less than 1 billion.1 Recent estimates suggest that 6.5 percent of all people ever born are alive right now.2 This is the most conspicuous fact about world population growth: for thousands of years, population grew only slowly, but in recent centuries it has jumped dramatically. Between 1900 and 2000 the increase in world population was three times greater than the entire previous history of humanity– an increase from 1.5 to 6.1 billion in just 100 years.
A picture of world population in the very long-run fits the pattern of exponential growth (when a population grows exponentially the population increase is proportional to the size of the population). Yet an empirical observation of how growth rates have developed in the course of the last century reveals that this pattern no longer holds. The annual rate of population growth has recently been going down. A long historical period of accelerated growth has thus come to an end; the annual world population growth rate peaked in 1962, at around 2.1%, and has come down to almost half since.3
Based on these observations, world history can be divided into three periods marked by distinct trends in population growth. The first period (pre-modernity) was a very long age of very slow population growth. The second period, beginning with the onset of modernity (with rising standards of living and improving health) and lasting until 1962, had an increasing rate of growth. Now that period is over, and the third part of the story has begun; the population growth rate is falling and will likely continue to fall, leading to an end of growth towards the end of this century.
# Empirical View
# Key changes in population growth
In order to study how the world population changes over time it is useful to focus on the rate of change (rather than just levels). The following visualization presents the annual population growth rate, superimposed on the total world population, for the period 1750-2010 (plus projections up to 2100). This is the period in history when population growth changed most drastically. Before 1800 the world population growth rate was always well below 1%, while in the course of the first fifty years of the 20th century annual growth increase to up to 2.1% – the highest annual growth rate in history, recorded in 1962. After this point, it has been systematically going down with projections estimating an annual rate of growth of 0.1% for 2100.
This means that while the world population quadrupled in the 20th century it will not double in the 21st century.
World population, 1750-2015 and projections until 21004
# Long-run historical perspective: the big picture
Around 108 billion people have lived on our planet. This means that about 6.5% of all people ever born are alive right now.5 The following visualization plots estimates of the world population from 10,000 BCE to today. As it can be appreciated, before 1,000 CE the population slowly but steadily increased, going from about 2.4 million in 10,000 BCE to 295 million in 1,000 CE. By 1850, the world population had exceeded 1 billion people.
It is possible to add the projection of the UN (Medium Variant) to show the projected population increase until the end of the 21st century.
# Long-run historical perspective: country trends in the last 500 years
As has been already mentioned, for a long period of time (staring at the beginning of the 19th century and ending in the 1960s) total world population grew faster as the growth rate increased. This global pattern, however, masks a great deal of heterogeneity across countries; in reality growth started climbing at different points in time in each country. Data from the Clio Infra project allows a cross-country analysis. The following visualization shows total population by country in the last five centuries. Substantial differences are evident here: adding the U.S. to the graph reveals that, while the population in France roughly doubled in the period 1800-2000, in this same period the population in the U.S. increased almost 50-fold.
# Long-run historical perspective: regional shares
Differences at the regional level are also important. The estimates provided by the History Database of the Global Environment (HYDE) are shown in the following visualization that provides a break down of the world population by regions using this source. Asia is – and has been for a long time – the most populous region in the world.
# Recent history and projections
In terms of recent developments, the data from the UN Population Division provides consistent and comparable estimates (and projections) within and across countries and time, over the last century. This data starts from estimates for 1950, and is updated periodically to reflect changes in fertility, mortality and international migration (for more information see the Data Quality section at the end of this entry).
# Global population growth has peaked long ago
The chart below shows that global population growth has long peaked. The peak was in 1962 and 1963 with an annual growth rate of 2.2%; since then world population growth was halved.
For the last half century we are living in a world in which population growth is declining. The UN projects this decline to continue for the next decades.
# Population growth as determined by births and deaths
The map shows for each country of the world the rate of natural population growth. The rate of natural population increase is the population increase determined by births anddeaths. Migration flows are not taken into account.
We see that there are some countries today in which the natural population growth is slightly negative; the number of death exceeds the number of births. When we move the time slider to the past we see that this is a new phenomenon. Up to the 1970s there were no countries with negative natural population growth.
Worldwide we see population growth slowing – you can press play at the bottom of the chart to see the change over time.
# Population growth – country by country
The following visualization presents the rate of population growth by country – and now migration flows and population growth determined by births and deaths are both taken into account.
The chart shows the data for the period 1955-2015, plus projections for 2015-2100 using the UN Population Division data (switch to the map view in this chart for a wider cross-country comparison). As you can see, in most countries growth rates have been going down since the 1960s. Yet substantial differences remain across countries and regions. While Western Europe currently has close to zero annual growth rates, sub-Saharan Africa has rates that are still higher than 3% – that is, still higher than the peak growth rates recorded for the world at the beginning of the 1960s. Moreover, in many cases there has been divergence in growth rates. For instance, India and Nigeria had similar growth rates in 1960 (around 1.7%), but followed very different paths in the following years, and currently have populations that grow at very different rates (about 1.26% for India compared to 2.67% for Nigeria).
In the last century developed countries have had lower growth rates than developing countries. While some convergence is expected, large differences are projected to remain for the next century. The following visualization presents how the population growth rate has changed for ‘more developed’, ‘less developed’ and ‘least developed’ countries (UN categorization), together with the corresponding projections (UN Population Division estimates and projections from the 2012 revision).
Annual population growth rate by world regions, 1955-2010 and projections until 21006Full screen view Download Data
The above discussion also shows there are interesting patterns of population density: the most densely populated regions today have also been the most dense regions throughout modern history. India is a prime example of this. The following visualization shows population density patterns by country using the data from the History Database of the Global Environment (HYDE). Switch to the map view for a global perspective.
# World population by education level
The International Institute for Applied Systems Analysis (IIASA) is an interdisciplinary, highly-respected research institution near Vienna, Austria. The IIASA population projections are the most cited alternative to the UN work.
Interestingly their medium projection – which they consider most likely – stands in stark contrast to the UN projection. While the medium variant of the UN projection sees the world population growing continuously throughout the 21st century the IIASA medium (most likely) scenario sees the world population increase to 9.4 billion in 2070 and then begin a slow decline to below 9 billion by the end of the century.
As the IIASA researchers explain there are important methodological differences between the UN and IIASA projections. The UN uses probabilistic population projections to extrapolate populations for each country over the 21st century and is applying the same statistical methodology to all countries. The IIASA researchers in contrast have a country-specific approach that takes into account the knowledge of experts for each country separately.
The other important feature of the IIASA projection is that it takes into account the education of the population. As we show below in this entry there is a strong link between education and fertility – more educated women have fewer children. This link is taken into account in the model of the IIASA researchers and contributes to their projection of a much smaller total world population over the course of the 21st century.
The breakdown by education level is especially interesting: it shows that our world will be inhabited by more and more educated people. In the visualization below you see that in 1970 there were only around 700 million people in the world that had secondary or post-secondary education. By the end of this century the number of people with secondary or post-secondary education will have increased 10-fold and will reach 7 billion people (a similar number to the entire current world population)!
The projection also shows that the number of people with no education will decrease continuously and that by the end of this century virtually all people in the world will have received some level of education.
# Correlates, Determinants & Consequences
Perhaps the most direct and obvious determinant of population growth is fertility. In the following visualization we show the rate of fertility, defined as the average number of children that would be born to a woman over her lifetime if the woman were to experience the exact current age-specific fertility rates, and the woman were to survive from birth through the end of her reproductive life. This data comes from the UN Population Division. As we can see, fertility rates were stable across the world until the 1960s, with some differences in levels between ‘developed’ and ‘developing’ countries. After this point, fertility rates started dropping and levels began converging. This coincides with the decline in growth rates that has already been discussed. In the next section we explore the combined effects of changing fertility and mortality. You can read more about these factors in our fertility and life expectancy entries.
Total fertility, 1950-2010 and projections until 2100 (UN Population Division estimates and forecasts for medium fertility variant)7
# Demographic transition
The statistical office of Sweden – the Tabellverket (Office of Tables) – was established in 1749 when the Swedish population was 1,764,724; today it is more than five times higher (9,555,893 in 2012). This long record of population statistics makes Sweden a particularly interesting case to explore the mechanisms driving population changes.
Statistics Sweden – the successor of the Tabellverket – publishes data on both deaths and births since record-keeping began more than 250 years ago. These records suggest that around the year 1800 the death rate of the Swedes started falling, mainly due to improvements in health and living standards, especially for children.8 Yet while death rates were falling, birth rates remained at a constant pre-modern level until the 1860s. During this period and up until the first half of the 20th century, there was a sustained gap between the frequency of deaths and the frequency of births. It was because of this gap that the population of the Swedes increased. The following visualization supports these observations.
# The five-stage model of the demographic transition
The expansion of the Swedish population, caused by the widening gap between mortality rates and birth rates, has been observed in many other countries. Falling death rates succeeded by falling birth rates has been described by the model of the demographic transition. The essence of this model is synthesised in the graph below.
In Stage 1 there is no increase of the population. Birth rates are high, but only few children – around 2 per woman – reach adulthood because the death rate is also high. We see the resulting population pyramid in the bottom left corner of the chart.
In Stage 2 the death rate starts falling and because of the birth rate, which is still high, the population increases rapidly.
In Stage 3 the birth rate starts to follow the death rate and the population increase slows down.
In Stage 4 the birth rate and the death are low and get so close to each other that the size population hardly changes.
There is increasing evidence that this transition is followed by Stage 5 when the birth rate starts to increase again in very well developed countries.9
# The five stages of the demographic transition
The following visualization depicts the Swedish pattern of demographic transition vis-a-vis other countries.
Demographic transition in 5 countries, 1820-201010
# Health improvements
The high fertility of families in poor health environments is widely considered to be a consequence of families attempting to ensure that enough children survive. As health improves, families tend to adapt to the new situation by lowering their expectations of how many children to have. Better child health has thus two opposing effects on population growth. In the first instance, the effect of improving health is lower mortality – a driver initially pushing population growth up. But later on health improvements result in lower fertility – a driver pushing growth in the opposite direction.
Since virtually all countries in the world have already achieved historically low child mortality rates, it is natural to think that the latter effect currently dominates the global landscape. The following visualization presents the correlation between population growth and child mortality across the world. Indeed, countries with high child mortality rates tend to grow faster. This is important, since it suggests that health improvements are effective at curbing population growth – and that, by the same token, failing to tackle child mortality may actually foster faster population growth.
(Taking also migration flows into account it looks like this https://ourworldindata.org/grapher/population-growth-vs-child-mortality)
# Data Quality & Measurement
# Data on the population of the ancient world
Kremer (1993) provides estimates of the total world population over the last 1 million years.11 He puts together UN estimates for the period 1920-1990, as well as estimates from McEvedy and Jones (1978)12 for the period 10,000 BCE-1900 CE, and Deevey (1960)13 for the period 1,000,000 BCE-10,000 BCE.
The estimates from McEvedy and Jones (1978) after 200 BCE were obtained by aggregating population estimates for individual geographic regions taken from other authors (see references therein), and these in turn were based primarily on historical sources such as Roman and Chinese censuses. Their estimates of population prior to 200BCE were based on archaeological and anthropological evidence.
Many studies not considered in Kremer (1993) provide competing estimates of world population over long historial periods (Kremer (1993) mentions Clark (1977)14 and Durand (1977)15, but there are more). The following two graphs provide a sense of the dispersion of different estimates. All long-run estimates appear to be fairly close.
Comparison of different estimates of world population for the last million years – Figure 1 in DeLong (1998)16
# Data quality of recent world population estimates
The most discussed estimates from the last century are those from the UN Population Division. These are revised periodically and aim to be consistent and comparable within and across countries and time.
The methodology used by the UN to produce their estimates and projections is discussed extensively in the World Population Prospects’ Methodology Report. As noted in this report, estimates are produced “by starting with a base population by age and sex for 1 July 1950 and advancing the population through successive 5-year time intervals using the cohort-component method, based on age-specific estimates of the components of population change (fertility, mortality, and international migration).” Population counts by age and sex from periodic censuses are used as benchmarks.
The process of ‘revising’ the estimates involves incorporating new information about the demography of each country. The following diagram explains the process used to ensure consistency.
# Process for generating UN population revisions – Table I.4. in the UN World Population Prospects Methodology Report17
The main implication of this cohort-component framework by demographic trends is that it sometimes leads to marked inconsistencies with official country statistics. The following map, showing the coverage of births through civil registration, speaks to this issue: many countries, particularly those in the least developed regions of the world, have limited census data. For countries with no data in one or two decades before each revision, UN estimates are derived by extrapolating trends from countries in the same region with a socio-economic profile considered close to the country in question.
Civil registration coverage of births (in percent) using 2014 data from the WHO18
# Uncertainty of future projections
The most discussed projections of population growth are also those from the UN Population Division.19 Keilman (2001)20 provides an assessment of the forecasts of world population published by the UN between 1951 and 1998. This comparisons of projected versus actual population levels suggests that UN forecasts are fairly accurate. The following visualization shows this.
Since projecting fertility is a fundamental part of the forecasting exercise, future estimates are usually presented for different variants. The following visualization presents world population projections under different fertility assumptions. As you might expect, projections are highly sensitive to changes in the assumptions made about fertility.Full screen viewDownload Data
# Data Sources
# Estimates of ancient population
As it was discussed in the previous section, there are a number of studies providing historic population data. The most commonly cited source is McEvedy and Jones (1978).
# McEvedy and Jones (1978)
- Data Source: McEvedy, Colin and Richard Jones (1978), “Atlas of World Population History,” Facts on File, New York, pp. 342-351; relying on archeological and anthropological evidence, as well as historical documents such as Roman and Chinese censuses
- Description of available measures: Population
- Time span: 400BCE-2,000CE
- Geographical coverage: Global by country and regions
This source is an input to produce, among other, the data from the HYDE project. Further references to this source are available in Goldewijk, K. K., Beusen, A., & Janssen, P. (2010). Long-term dynamic modelling of global population and built-up area in a spatially explicit way: HYDE 3.1. The Holocene.
# History Database of the Global Environment (HYDE)
- Data Source: History Database of the Global Environment project, using estimates from McEvedy and Jones (1978), Livi-Bacci (2007)21, Maddison (2001)22, and Denevan (1992)23
- Description of available measures: Geographic distribution of the world population
- Time span: 10,000BCE-2,000CE
- Geographical coverage: Global at a 5 arc-minute spatial resolution
- Link: http://themasites.pbl.nl/
The data from the HYDE project is in turn the basis for the population series published by the ‘Clio-Infra’ project
- Data Source: HYDE project and UN Population Division
- Description of available measures: Population
- Time span: 1,500-2,000CE
- Geographical coverage: Global by country
- Link: www.clio-infra.eu/datasets/indicators
# Estimates of population in recent history and projections
# UN Population Database
- Data Source: UN Population Division based on ‘cohort-component’ framework by demographic trends (see Data Quality section)
- Description of available measures:
◦ Population, by Five-Year Age Group and Sex
◦ Population Sex Ratio (males per 100 females)
◦ Median Age
◦ Population Growth Per Year
◦ Crude Birth Rate
◦ Crude Death Rate
◦ Net Reproduction Rate
◦ Total Fertility Rate
◦ Life Expectancy at Birth by Sex
◦ Net Migration Rate
◦ Sex ratio at birth
◦ Births by Age-group of Mother
◦ Age-specific Fertility Rates
◦ Women Aged 15-49
◦ Deaths by Sex
◦ Infant Mortality
◦ Mortality Under Age 5
◦ Dependency Ratios
◦ Population by Age: 0-4, 0-14, 5-14, 15-24, 15-59, 15-64, 60+, 65+, 80+
- Time span: 1950-2015
- Geographical coverage: Global by country
- Link: http://esa.un.org/unpd/wpp/
# Gridded Population of the World (GPW)
- Data Source: Center for International Earth Science Information Network (CIESIN), published by the Socioeconomic Data and Applications Center (SDAC) based on census data
- Description of available measures: Population
- Time span: 1990-2010
- Geographical coverage: Global at a 2.5 arc-minute spatial resolution
- Link: http://sedac.ciesin.columbia.edu/data/collection/gpw-v3
- Notes: Within the CIESIN, the Anthropogenic Biomes map the distribution of the world population at different points in time: 1700, 1800, 1900, 2000. These maps focus on the varying impact of humans on the environment.
- Data Publisher: University of Iowa (originally developed by the Oak Ridge National Laboratory (ORNL) for the Department of Defense, U.S.)
- Data Source: Annual mid-year national population estimates from the Geographic Studies Branch, US Bureau of Census
- Description of available measures: Population and ‘ambient population’ (a measure of person-hours accounting for varying presence throughout the day in commercial areas)
- Time span: 1998-2012, but authors warn of inter-temporal comparability issues
- Geographical coverage: Global at 30 arc-second grid spatial resolution (highest population resolution available)
- Link: http://sedac.ciesin.columbia.edu/data/collection/gpw-v3
# World Development Indicators
- Data Publisher: World Bank
- Data Source: UN Population Division
- Description of available measures: Population growth (annual %)
- Time span: 1981-2015
- Geographical coverage: Global by country
- Link: http://data.worldbank.org/indicator/
# Compilations of census data and other sources
Historical population data on a sub-national level – including their administrative divisions and principal towns – is collected by Jan Lahmeyer and published at his website www.populstat.info.
The Minnesota Population Center publishes various high-quality datasets based on census data beginning in 1790. At the time of writing this source was online at www.pop.umn.edu/index.php. It focuses on North America and Europe.
The Data & Information Services Center (DISC) Archive at University of Wisconsin-Madison provides access to census data and population datasets (mostly for the Americas). At the time of writing this source was online at http://www.disc.wisc.edu.
The International Database published by the U.S. Census Bureau provides data for the time 1950-2100. At the time of writing this source was online at http://www.census.gov/population/international/.
The Atlas of the Biosphere publishes data on Population Density. At the time of writing this source was online at www.sage.wisc.edu/atlas/maps.