Europe's population has aged to such a degree that it will likely continue to shrink, even if birthrates rebound to a one-for-one replacement level, a new study suggests. A major part of this trend is due to the fact that women have been postponing childbirth for increasing lengths of time, the authors have found. Their research appears in the journal Science, published by the American Association for the Advancement of Science (AAAS).
The year 2000 marked a key turning point for Europe, reports the research team, led by Wolfgang Lutz of the Austrian Academy of Science, in Vienna, and the International Institute for Applied Systems Analysis, in Laxenburg, Austria.
That year, the population's "momentum" flipped from positive to negative, a measure that reflects the age structure of the population. In Europe, where older generations are larger than younger ones, negative momentum arises as subsequent generations have fewer potential mothers. Thus, even if women begin having more children, a tendency to decline can persist for decades, simply because there are fewer women of childbearing age.
"Negative momentum has not been experienced on a large scale in world history so far. It is now like sailing against a current running toward population shrinkage and aging," Lutz said.
Two factors are responsible for Europe's negative population momentum. The first is well-known: that women are having fewer than two children, on average.
The second factor, whose future impact hasn't been addressed directly until now, the authors say, is that women's average age at childbirth has been increasing over time. This so-called "tempo effect" matters because it reduces the number of children born in a given year, boosting the average age at which women have children.
Using data from the European Demographic Observatory, the researchers estimated how these two factors might affect Europe's population in future decades. They found that approximately 40 percent of potential future population declines caused by low fertility were related to the postponing of births.
"We've found that the timing of childbearing can actually have a major impact on future demographic trends," said co-author Brian O'Neill of the International Institute for Applied Systems Analysis and Brown University.
The current birthrate rate in Europe is 1.5 children per woman. According to the Science authors, after adjusting for the tempo effect (estimating how many babies would be born in a given period of time if no births were postponed), the rate increases to 1.8.
To pinpoint the future effects of changes in fertility rates and the timing of childbirth, the researchers assumed that other possible influences would promote stability--that is, mortality rates wouldn't change, and there would be no immigration.
"In reality we expect continued immigration into Europe, but here we wanted to identify these two mechanisms which we think are new and important insights into the nature of population dynamics. To sharpen the focus on them, we had to eliminate other effects like migration in the calculations," Lutz said.
According to the researchers' calculations, if women's average age at childbirth continues to increase for another 10 to 40 years, there will be a built-in tendency for population size to decline by 55 million, to 144 million by 2100.
Lutz and his co-authors suggested that governments concerned about population aging and the potential for population decline could consider policies that give women more options in planning when to have children.
"The choices young couples make depend on the conditions around them," Lutz said.
Possible starting points for consideration might address childcare, labor laws, part-time work options, or subsidized housing for young parents, according to Lutz.
"Giving women more choices is easier said than done," Lutz said. "It would involve revamping the career pattern that's structured around the male life course with no room for a baby break. This male-oriented career pattern needs to be changed."
"In thinking about what different policy options are out there for addressing aging and the possibility of population decline, one that has not been considered before is that there may be a demographic as well as a health benefit to providing more options to women in how to arrange their life-course, and when to have children," said O'Neill.
The continuing decline in Europe's population size, and the shift to an older population, will likely pose challenges for social security and health systems, according to Lutz and his co-authors. These trends may also lead to reduced productivity gains, the researchers propose, ultimately affecting global competitiveness and economic growth.
Lutz's co-authors are Brian C. O'Neill at the International Institute for Applied Systems Analysis in Laxenburg, Austria, and Brown University, in Providence, RI; and Sergei Scherbov at the Austrian Academy of Science, in Vienna, Austria, and the International Institute for Applied Systems Analysis, in Laxenburg, Austria.
The American Association for the Advancement of Science (AAAS) is the world's largest general scientific society, and publisher of the journal, Science (www.sciencemag.org). AAAS was founded in 1848, and serves some 265 affiliated societies and academies of science, serving 10 million individuals. Science has the largest paid circulation of any peer-reviewed general science journal in the world, with an estimated total readership of one million. The non-profit AAAS (www.aaas.org) is open to all and fulfills its mission to "advance science and serve society" through initiatives in science policy; international programs; science education; and more. For the latest research news, log onto EurekAlert!, www.eurekalert.org, the premier science-news Web site, a service of AAAS.