Latest Issue of Science News


Math Trek

Getting Old, Faster and Faster

The world population is aging fast, but is still younger than we tend to think

Sponsor Message

It's not so obvious how old a 60-year-old is. Ask most 60-year-olds these days and they'll say they still feel pretty young, since they're healthy and expect many active years to come. In 1900, though, a 60-year-old was, well, old.

This simple fact has big ramifications for demographers. Demographers have long known that on average people are getting older all around the world, and they have worked to assess the likely social impacts of that aging. For example, relatively few young people are around to support old people's pensions. But increased longevity counteracts those impacts by making people of any age in effect younger than they used to be, for example increasing the number of years they are capable of working. So it has been hard to assess how big the impact of an aging population is likely to be.

A trio of demographers has now developed new measures of age to fill this gap. Instead of analyzing people's chronological age, they've measured the number of additional years a person can expect to live, subtracting each person's age from the life expectancy at that point in time in the region they're living in. Even with this new measure, the demographers found that the world's population has grown older and will almost certainly continue to do so. In fact, the pace of aging will accelerate over the next 30 years.

"That's important because fastest aging is associated with the greatest adjustment costs," says Warren Sanderson of the International Institute for Applied Systems Analysis in Austria and the State University of New York at Stony Brook. "When things happen more slowly, the political processes can move slowly and more thoughtfully. When things happen fast, it's hard to adjust."

The researchers hope that the findings will encourage lawmakers to plan for an aging population now. In the United States, the minimum age for a full Social Security payment will soon rise to 67, for example. In the context of an aging society, further changes like this will almost certainly be necessary, the researchers say. "If it goes up gradually, the burden will not be very big," Sanderson says. Since aging is accelerating, problems that seem like mild irritants now will turn into major conundrums quickly, so a slow response may lead to abrupt—and difficult—adjustments.

The researchers found that the mean age of the world population is 30, with 44 years left to live on average. By the end of the century, the mean age is expected to be 45, with 41 years left. So both measures, mean age and average years of life remaining, show aging.

North America is a happy anomaly, though. The average age will go up through the end of the century, (from 37 to nearly 50), but the average years remaining also will go up (from 43 to 48). North America is the only region to show that pattern. Sanderson and his collaborators Wolfgang Lutz and Sergei Scherbov of the International Institute for Applied Systems Analysis in Laxenburg, Austria published their findings online Jan. 20 in Nature.

The increase in average age is caused by changes at both ends of life: People are living longer, and fewer babies are being born. In the United States, the population as a whole is getting older because of the aging of the baby boom generation and the decline in fertility after the baby boomers were born. In China, the one-child policy that was instituted in the 1979 lowered fertility rates, and, throughout the developing world, family planning efforts did the same. "One wave is piling on top of another worldwide to cause this," Sanderson says.

This new measure of the age of the population is especially informative because people make many decisions based on how many more years they expect to live, the researchers argue. For example, as longevity has increased, people have invested more in education since they'll have more time to reap the benefits.

These changes may soften the societal impact of the aging of the population. "If the younger generation is smaller, but they are better educated and can be more productive, that might be a good thing," Lutz says, since the young people, though fewer, would still be able to produce enough to support those too old to work. "Certainly the decline of population is desirable from an environmental perspective," he says. The team next plans to try to quantify these effects.

The other good news environmentally is that world population is likely to stop growing within the century. The researchers made this prediction two years ago, and they have now incorporated newer data that has corroborated it. Their model shows an 88 percent probability that world population growth will end within the century.


If you would like to comment on this article, please see the blog version.

Note: To comment, Science News subscribing members must now establish a separate login relationship with Disqus. Click the Disqus icon below, enter your e-mail and click “forgot password” to reset your password. You may also log into Disqus using Facebook, Twitter or Google.

X