14th June 2013

World population could reach 11 billion by 2100

A new statistical analysis by the United Nations, in a report released yesterday, shows that global population could reach nearly 11 billion by the end of this century. That's about 800 million, or 8 percent, more than the previous projection of 10.1 billion, issued in 2011.

The projected rise is mostly due to fertility in Africa, where the U.N. had expected birth rates to decline more quickly than they have. The current population on the continent is about 1.1 billion and is now expected to reach 4.2 billion, nearly a fourfold increase, by 2100.

"The fertility decline in Africa has slowed down or stalled to a larger extent than we previously predicted, and as a result the African population will go up," said Adrian Raftery, a University of Washington professor of statistics and sociology.

The new U.N. estimates use statistical methods developed by Raftery and his colleagues at the UW Center for Statistics and the Social Sciences. The group's improved fertility forecasting methods – combined with updated data from the U.N. – were used to project long-term consequences of fertility change in Africa since the last population estimate in 2011.

New to this year's projection are finer-tuned statistics that anticipate the life expectancies of men and women across the 21st century. At the global level, life expectancy is projected to reach 76 in the period 2045-2050, and 82 in 2095-2100. People in developed countries could live on average to 89 by 2100, compared to about 81 in developing regions. This is assuming no radical breakthrough in longevity treatments, however.

By far the largest expected population increase is in Nigeria, projected to rise from 184 million now, to 914 million in 2100. Eight of the top ten increases are in Africa, with India in second place. The United States is eighth.

In other areas of the world, few significant changes are expected. Europe may see a small decline because of fertility continuing below replacement level, while other nations around the globe may see modest increases due to longer life expectancies, Raftery said.

There's no end in sight to the increase of world population, he added, yet the topic has gone off the agenda in favour of other pressing global issues, including poverty and climate – both of which have ties to world population.

"These new findings show that we need to renew policies, such as increasing access to family planning and expanding education for girls, to address rapid population growth in Africa," Raftery said.

The UN gives high and low variants of its projections, assuming that women have an average of half a child more or less than the best projection. That leaves a large uncertainty, from 7 billion to nearly 17 billion, in the range for potential world population by the end of this century.

By contrast, the UW research group has developed probabilities of future population levels to be coupled with best forecasts. "Our probability intervals are much tighter, ranging from 9 billion to 13 billion in 2100," Raftery said.

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