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Ranking topics: Largest populations: 2040 forecast

The world’s population may never grow as large as many had previously assumed. In a new paper, researchers at the Institute of Health Metrics and Evaluation at the University of Washington project that the global population will top out in 2064 and then fall steadily. Current estimates by the UN’s Population Division reckon it will continue to grow until at least 2100. As a result, the IHME estimates a total population of 8.9bn in 2100; the UN places the number at about 10.9bn.

The huge discrepancy is largely accounted for by differing views on two issues. First, the IHME study’s central scenario assumes that improvements in access to education and contraceptives in sub-Saharan Africa—and a concomitant fall in fertility—will result in a population there of just under 3.1bn in 2100, compared with 3.8bn in the UN study. Accounting for mortality, this means 890m fewer African births on a cumulative basis in the remainder of the century. However, even the IHME’s conservative projections still have sub-Saharan Africa as the only continent with a growing population by the end of the century.

Other demographers have also argued that better education could cause the global population to peak before the end of the century. Last year The Economist reported on projections by Wolfgang Lutz, a demographer at the International Institute for Applied Systems Analysis in Austria. If recent progress in education in sub-Saharan Africa was maintained, estimated Mr Lutz, the world’s population would peak at 9.4bn in 2075 and decline to 8.9bn by 2100 (as IHME also estimates). Brisker progress would imply an earlier peak, at 9bn, and a fall to 7bn by the end of the century.

The second reason for the discrepancy between the IHME’s and the UN’s figures is that the former is more conservative about what will happen to populations when fertility rates fall below the replacement level of 2.1 births per woman. The UN assumes that in many countries with low rates, such as Taiwan, where the fertility rate is just over 1, they will increase again—not all the way to 2.1, but to around 1.75. The IHME believes that 1.4 is a more likely outcome. The difference yields a substantial gap in population projections.

Should these outcomes come to pass, they would be broadly positive for the environment and the fight against climate change, at least relative to the UN’s expectations. Fewer people, other things being equal, ought to mean lower carbon emissions and lower demand for food and water—although rising living standards may have a countervailing effect. Having fewer adults of working age would mean fewer taxpayers. Without increases in productivity, or increases in working lives, would also mean slower economic growth. Social security and welfare systems would come under ever greater stress. And labour would become scarcer—and so perhaps better paid. 

This extract is from our Graphic detail section.