A team of researchers led by Dr John Wilmoth of the U.N. Department of Economic and Social Affairs announced yesterday in the journal Science that, according to their estimates, world population, now 7.2 billion, could hit 12.3 billion by 2100.
The top panel shows total world population projected to 2100; dotted lines are the range or error using the older scenario method, while shaded regions are the uncertainties using statistical methods; the darker shading is the 80 % confidence bars, and the lighter shading shows the 95 % confidence bars; at the bottom are the population projections for each continent. Image credit: Adrian Raftery / University of Washington.
World population projections are based mostly on two things: future life expectancy and fertility rates. Earlier techniques relied largely on expert opinion for how those trends were expected to change.
Dr Wilmoth’s team instead used statistical methods to combine government data and expert forecasts for such things as mortality rates, fertility rates and international migration.
The scientists found there’s an 80 % probability that world population in 2100 will be between 9.6 and 12.3 billion.
Most of the anticipated growth is in Africa, where population is projected to quadruple from around 1 billion today to 4 billion by 2100.
The main reason is that birth rates in sub-Saharan Africa have not been going down as fast as had been expected. There is an 80 % chance that the population in Africa at the end of the century will be between 3.5 billion and 5.1 billion people.
Other regions of the world are projected to see less change.
Asia, now 4.4 billion, is projected to peak at around 5 billion people in 2050 and then begin to decline.
Populations in North America, Europe, and Latin America and the Caribbean are projected to stay below 1 billion each.
“Earlier projections were strictly based on scenarios, so there was no uncertainty. This work provides a more statistically driven assessment that allows us to quantify the predictions, and offer a confidence interval that could be useful in planning,” said first author Dr Patrick Gerland, also of the U.N. Department of Economic and Social Affairs.
“Also, earlier reports represented uncertainty by using scenarios in which women would have 0.5 children more or less than the experts’ forecast. That method generates too great a range,” said co-author Prof Adrian Raftery of the University of Washington.
“In a given year and country the fertility rate might be half a child higher, but the probability that it would be half a child higher in all countries in all years in the future is very low.”
“Rising population could exacerbate world problems such as climate change, infectious disease and poverty, he said. Studies show that the two things that decrease fertility rates are more access to contraceptives and education of girls and women. Africa could benefit greatly by acting now to lower its fertility rate,” Prof Raftery concluded.
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Patrick Gerland et al. World population stabilization unlikely this century. Science, published online September 18, 2014; doi: 10.1126/science.1257469
