World population forecast to peak before 2100

An end to the once seemingly unstoppable growth in world population is in sight, say scientists who have laid odds on when the number of humans will peak.

An end to the once seemingly unstoppable growth in world population is in sight, say scientists who have laid odds on when the number of humans will peak.

There is about a four-to-one chance the world population of 6.1 billion will level off at about 8.4 billion by the end of the century, about a billion fewer than United Nations predictions.

The study of human numbers, in the journal Nature today, foresees the end of an era of unrelenting population growth during which the billion mark was passed in 1804. It took just 123 years more to double to two billion and less than half that time to reach five billion, in 1987. Giving odds on the accuracy of population growth predictions will enable policy makers to make better informed judgements about future needs, the scientists say.

The study found birth rates would continue to fall faster than expected in many parts of the world, leading to a likely end to population growth before the century is out.

"There has been enormous concern about the consequences of human population growth for the environment and for social and economic development," say the researchers, led by Wolfgang Lutz of the University of Groningen in The Netherlands. "But this growth is likely to end in the foreseeable future."

Using statistical analyses of fertility and life expectancy for different regions of the world, the scientists demonstrated that there is an 85 per cent chance of population growth grinding to a halt by 2100, and a 60 per cent chance that it will not exceed 10 billion.

But the scientists warn there are uncertainties that could throw these projections off course, resulting in, for instance, the number of people at the end of the century topping 12.1 billion. By contrast, there is a 15 per cent chance that the population then might be less than it is today.

The scientists say there is definitely going to be a radical shift in demography over the next 100 years, with a far greater proportion of the population being older and more infirm. "A stabilised or shrinking population will be a much older population," they say. "At the global level, the proportion above age 60 is likely to increase from 10 per cent to around 22 per cent in 2050. This is higher than it is in western Europe today. By the end of the century it will increase to around 34 per cent, and extensive population ageing will occur in all world regions."

Even in sub-Saharan Africa, which will continue to have some of the fastest rates of population growth, the number of older people will rise, with the population at the end of the century being older than in western Europe today. In Japan, where the demographic time bomb is likely to hit the hardest, as much as half the population in 2100 will be 60 or over, putting considerable strain on the economy.

The scientists emphasise that populations in some of the most vulnerable regions will continue to growth. "[But] the prospect of an end to world population growth is welcome news for efforts towards sustainable development."

However, demographers have become increasingly concerned about the accuracy of their forecasts since they failed to predict a decline in fertility in many western countries during the Seventies, which led to lower than expected population growth. The rapid reduction in mortality after the Second World War was not foreseen, which meant the age structures of many countries were far older than was anticipated.

Nico Keilman, a demographer at the University of Oslo in Norway, said the study was an important contribution to assessing the risks of population growth. "The demographic future of any human population is uncertain, but some of the many possible trajectories are more probable than others," Dr Keilman said. "Those who use forecasts should be informed about the accuracy of historical predictions. But more important is the expected accuracy of the forecast."