Forecast Sees Halt to Population Growth by End of Century

John Roach
for National Geographic News
August 6, 2001

The foreboding threat of world disaster from explosive population growth could turn out to be overly alarmist, say the authors of a new demographic study.

Their forecast shows there's a high chance that the world's population will stop growing before the end of the 21st century. It suggests that the total number of people may peak in 70 years or so at about 9 billion people, compared with 6.1 billion today.

The scientists say their prediction is more reliable than other population forecasts because they employed non-traditional but more rigorous methods of analysis. The study was conducted by the International Institute for Applied Systems Analysis (IIASA) in Laxenburg, Austria.

In their report, published in the August 2 issue of Nature, the authors attribute the rosier-than-usual outlook to successful efforts in the last few decades to curb fertility rates.

Now, they say, the time has come for society to think seriously about how to meet the needs of a stable but considerably larger world population in the decades ahead.

"We are going to have a stable population. So we have to make sure we have a sustainable environment and a sustainable economy to go with the sustainable population," said Warren Sanderson of IIASA, a co-author of the report.

The figures obtained in the new study are roughly in line with future population scenarios released by the United Nations in 1998.

But some population experts are at odds with IIASA's conclusions, arguing there is no guarantee that population growth will stabilize before the end of the 21st century.

"In the '60s we were panicked about population growth and did something about it," said Carl Haub of the Population Reference Bureau in Washington, D.C. "We find ourselves about halfway to this point of stable population growth. We will get there, but to call the game over in fifth inning isn't quite right."

Calculating Probable Outcomes

Determining accurately what the world's population will be in the distant future is impossible because fertility, mortality, and migration rates are highly uncertain. Because of this, some demographers who do population forecasting have adopted an approach—called probabilistic analysis—that helps account for uncertainty. "We don't know what future fertility will be, we don't know future life expectancy, but we can gather information about the ranges [of possible outcomes] they might be in," said Sanderson. From this, demographers calculate the probability, or likelihood, of certain trends or events occurring.

According to IIASA's forecast, there is an 85 percent probability that the world's population will have stopped growing by the year 2100, and a 60 percent probability that it will not have exceeded 10 billion before then.

Continued on Next Page >>


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