WEDNESDAY, Aug. 1, 2001 (HealthDayNews) -- Ever since the 1968 publication of Paul Erlich's The Population Bomb, which painted a dark picture of a densely populated future, policy makers have worried about the planet's burgeoning number of humans.
But now, a new study by American, Dutch and Austrian researchers predicts the human population will stop growing before the end of this century, then gradually decline. The study appears in the Aug. 2 issue of Nature.
There's an 85 percent chance the global population will stop growing by 2100, and it may peak by 2070, says study co-author Warren C. Sanderson, professor of economics and history at State University of New York at Stony Brook. By the end of the century, he predicts a peak global population of 8.4 billion people.
Sanderson says the predictions are based on changes in global fertility rates, prompted mostly by the education of females.
Scientists say, on average, a woman needs a fertility rate of at least 2.1 children to insure continuing her lineage. Fertility rates generally are dropping in the developing world, although some regions, such as sub-Saharan Africa, still have high rates. However, in many developed nations, the rates are well below 2.1.
Sanderson says United Nations' prediction of 9.7 billion people by 2150 are very unlikely.
He says the U.N. prediction assumes high fertility levels in developing countries eventually will fall to a minimum of 2.1 children per woman and eventually will rise to 2.1 in developed nations. This would mean every country would have the same fertility rate, and the global population would stabilize.
"There's no evidence for this whatsoever," says Sanderson.
His study describes how population changes would affect several world powers. For example, declining fertility rates and a sharp reduction in male longevity mean the European portion of Russia already has reached its population peak.
Sanderson and his colleagues predict that in China, the first country to surpass 1 billion people, the population will start shrinking in the second quarter of this century; however, the U.S. population will continue to rise during that time.
The findings also suggest a trend that could fundamentally alter national demographics. The data indicates a dramatic aging of the population. In China, the proportion of people over 60 is expected to triple in the next 50 years, increasing to 30 percent of that country's population.
Japan will see the most significant impact. By 2100, Sanderson says at least 49 percent of that country's population will be over 60. And he says, "Every place in the world over the course of the century is going to become considerably older."
"That means that public policy with regards to older people, who usually are also people who are sicker, is going to have to be rethought," says Sanderson. "You really have to think about providing medical care in very different ways.
The per-capita costs of this health care are likely to be increasing quite considerably over time."
However, another population expert says the new predictions may be no more accurate than the U.N. figures.
Rodolfo A. Bulatao, a demographer and co-editor of Beyond Six Billion: Forecasting the World's Population, says Sanderson and his colleagues are working with the same 30 years of historical population data as the United Nations did.
"A lot of the error in projections comes from the base data that you use," he says.
Bulatao also says the study's predictions vary widely by 2100, ranging between roughly 4 billion and 14 billion people.
"[It's] a huge spread. It's not a very concrete projection," he says.
Still, Bulatao says most demographers would probably agree the world's population growth is likely to slow down, stop or even peak in the next century.
Sanderson says Erlich, who believed the human race would "breed itself into oblivion," would be horrified by the findings.
"In a way, our study is optimistic. Humans are not going to breed themselves out of existence," says Sanderson. "That means that we need to pay attention to living sustainably with the people we're going to have."
What To Do
Check the population clocks from the U.S. Census Bureau, or visit the Population and Development Division of the United Nations.
You can also read about Erlich at this companion site to a PBS documentary.
