Human population projections

Human population projections are attempts to show how human populations might change in the future. These projections are an important input to forecasts of the population's impact on the planet and humanity's future well-being. Models of population growth take trends in human development and apply projections into the future. These models use trend-based-assumptions about how populations will respond to economic, social and technological forces to understand how they will affect fertility and mortality, and thus population growth. The 2022 projections from the United Nations Population Division (UN) (chart #1) show that annual world population growth peaked at 2.2% per year in 1964, has since dropped to 0.9% in 2023, equivalent to about 74 million people each year, and could drop even further to minus 0.1% by 2100. Based on this, the UN projected that the world population, 8 billion as of 2023, would peak around the year 2084 at about 10.3 billion, and then start a slow decline, assuming a continuing decrease in the global average fertility rate from 2.5 births per woman during the 2015–2020 period to 1.8 by the year 2100 (the medium-variant projection). However, estimates outside of the United Nations have put forward alternative models based on additional downward pressure on fertility (such as successful implementation of education and family planning goals in the United Nations' Sustainable Development Goals) which could result in peak population during the 2060–2070 period rather than later. According to the UN, all of the predicted growth in world population between 2020 and 2050 will come from less developed countries and more than half will come from sub-Saharan Africa. Half of the growth will come from just eight countries, five of which are in Africa. The UN predicts that the population of sub-Saharan Africa will double by 2050. The Pew Research Center observes that 50% of births in the year 2100 will be in Africa. Other organizations project lower levels of population growth in Africa, based particularly on improvement in women's education and successful implementation of family planning.

During the remainder of this century, some countries will see population growth and some will see population decline. For example, the UN projects that Nigeria will gain about 340 million people, about the present population of the US, to become the third most populous country, and China will lose about half of its population. Even though the global fertility rate continues to fall, chart #2 shows that because of population momentum the global population will continue to grow, although at a steadily slower rate, until the mid 2080s (the median line). The main driver of long-term future population growth is projected to be the continuing evolution of fertility and mortality.

History of population projections Projections of global human population are generally based on birth rates and death rates, and since these are difficult to predict very far into the future, forecasts of global population numbers and growth rates have changed over time.

20th century Walter Greiling projected in the 1950s that world population would reach a peak of about nine billion in the 21st century and then stop growing after an improvement in public health in less developed countries. In 1983, astrophysicist Brandon Carter developed the Doomsday Argument, a probabilistic argument that postulates it is unlikely for humans born today to be randomly selected at an early position in the ordering of all humans who will ever live. In the original formulation, there is a 95% chance that the total number of humans will be less than 1.2 trillion and that extinction will occur before the year 9120. In 1992, the United Nations published five projections of long-term world population growth. According to their medium projection, the world population would grow to 10.0 billion by 2050, 11.2 billion by 2100, and 10.8 billion by 2150.

21st century

Estimates published in the early 2000s tended to predict that the population of Earth would stop increasing around 2070. For example in a 2004 long-term prospective report, the United Nations Population Division projected that world population would peak at 9.2 billion in 2075 and then stabilize at a value close to 9 billion out to as far as the year 2300. Jørgen Randers, one of the authors of the seminal 1972 long-term simulations in The Limits to Growth, offered an alternative scenario in a 2012 book, arguing that traditional projections insufficiently take into account the downward impact of global urbanization on fertility. Randers' "most likely scenario" predicted a peak in world population in the early 2040s at about 8.1 billion people, followed by decline. In 2012, the UN changed its prediction to the effect that no maximum would likely be reached in the 21st century, and that by the year 2100 world population would increase to somewhere in the range 9.6 to 12.3 billion with 10.9 billion being the midpoint of that range. The main reason for the revision was a recognition that the high fertility rate in Africa was not declining as fast as had been previously assumed.

… excerpt ends here. Continue reading the full article.