Human population projections

[11] Other organizations project lower levels of population growth in Africa, based particularly on improvement in women's education and successful implementation of family planning.

The main driver of long-term future population growth on this planet is projected to be the continuing evolution of fertility and mortality.

In 1831, president of Yale college Jeremiah Day included a United States population estimate as an example of an exponential equation.

[14] 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.

[18] 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.

[20] 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.

[21] Another 2014 paper by demographers from several universities, using data from the UN's 2014 report and their own statistical methods, forecast that the world's population would reach about 10.9 billion in 2100 and continue growing thereafter.

[20][7][25] Jose Rimon of Johns Hopkins University suggested, "We have been underestimating what is happening in terms of fertility change in Africa.

"[25] The population of a country or area grows or declines through the interaction of three demographic drivers: fertility, mortality, and migration.

With longevity trending towards uniform and stable values worldwide, the main driver of future population growth will be the evolution of the fertility rate.

Belarus, Estonia, Germany, Hungary, Italy, Japan, Russia, Serbia, and Ukraine have experienced a net inflow of migrants over the decade, helping to offset population losses caused by a negative natural increase (births minus deaths).

The projections in the report assume this with no upper limit, though at a slowing pace depending on circumstances in individual countries.

The hypothetical feasibility (and wide availability) of life extension by technological means would further contribute to long term (beyond 2100) population growth.

[34][35][36] Evolutionary biology also suggests the demographic transition may reverse itself and global population may continue to grow in the long term.

[40] From 2024 to 2050, the eight highlighted countries are expected to account for about half of the world's projected population increase: India, Nigeria, the Democratic Republic of the Congo, Pakistan, Ethiopia, Tanzania, Egypt, and Indonesia.

[40] Large urban areas are hubs of economic development and innovation, with larger cities underpinning regional economies and local and global sustainability initiatives.

[41] The following 101 metropolitan areas with the largest population projections for the years 2025, 2050, 2075, and 2100, according to professors Daniel Hoornweg and Kevin Pope, are listed below.