World numbers 'may peak by 2100'

The future will be less crowded than expected - and older

By BBC News Online's environment correspondent Alex Kirby

Researchers say the world's population could stop growing sooner than expected.

They suggest it could peak within the next 70 years, and then decline.

By the end of the century, they believe, the number of people alive could be 8.4 billion - about one billion fewer than the United Nations has predicted.

But there will be wide regional variations, and far more elderly people than there are today.

The scientists, whose work is reported in the magazine Nature, say: "There has been enormous concern about the consequences of human population growth for the environment and for social and economic development.

Slow decrease

"But this growth is likely to come to an end in the foreseeable future."

Included among their forecasts are:

• an 85% chance that global population will stop growing before 2100
• a 60% probability that numbers will not exceed 10 billion before the end of the century, and "around a 15% probability" that the world's population by then will be lower than it is today
• about a 75% chance that the peak population of the European part of the former Soviet Union had already been reached in 2000.

The median value of the researchers' projections reaches a peak around 2070 at nine billion people, and then slowly decreases to 8.4 billion by 2100.

Absolute numbers will still grow

But while they say the median population sizes over the next two decades are already declining in eastern Europe and the European part of the old USSR, elsewhere the picture is very different.

"The populations of north Africa and sub-Saharan Africa are likely to double" over the same period, the authors say, "even when we take into account the uncertainty about future HIV trends.

"Owing to an earlier fertility decline, the China region is likely to have around 700 million fewer people than the south Asia region by the middle of the century.

"This absolute difference in population size is likely to be maintained over the entire second half of the century and illustrates the strong impact of the timing of fertility decline on eventual population size."

Ageing world

There will also be pronounced differences in population structure, the authors believe.

"At the global level the proportion above age 60 is likely to increase from its current level of 10% to around 22% in 2050.

"By the end of the century it will increase to around 34%, and extensive population ageing will occur in all world regions."

The scientists base their projections on several variables, including assumptions on the speed of fertility decline, the subsequent fertility level, and life expectancy.

Except in Africa, where they say HIV/AIDS will lower it in the early part of the century, they assume life expectancy will rise everywhere.

Physical pressures should be less than forecast

Dr Med Bouzidi, of the International Planned Parenthood Federation (IPPF), told BBC News Online: "I think the report is credible.

"It 's encouraging - it shows family planning has been more successful than we'd have expected 30 or 50 years ago.

"But many of the women who need it are not using any reliable and safe family planning.

Scarce resources

"The poorest of the poor still don't have access to contraception."

Professor Norman Myers, of Green College, Oxford, UK, told BBC News Online: "A lot of other population projections show big variations, though not as big as this one.

"It is possible - there've been all sorts of surprises in the recent demographic past.

"But one pivotal variable is the environmental resource base - whether people will have enough to live on - and I'm not sure the authors have taken that into account."