The odds are that the world's population won't double in the next century--but that its proportion of elderly people will, according to a new forecast. The findings, reported in tomorrow's issue of Nature, strengthen United Nations (UN) predictions that population growth will brake in most regions. Some of the poorest parts of the world could still see their populations triple over the next 50 years, however.
In the early 1970s, some prominent scientists warned that by 2000, humanity would outstrip Earth's ability to support it. Recent analyses, however, have found that birth control and other family planning measures have reduced fertility rates in the 1990s; the United Nations predicts that the world's population, now almost 6 billion people, will peak at about 11 billion by 2100.
Looking to refine such estimates, a team led by demographer Wolfgang Lutz of the International Institute for Applied Systems Analysis (IIASA) in Laxenburg, Austria, plugged into a computer model data on everything from fertility and mortality rates to patterns of food supply and the spread of infectious disease; the computer spit out probabilities for regional population growth. For instance, they found that growth is likely to triple in the Middle East and sub-Saharan Africa by 2050 and decrease in Eastern Europe. Overall, Lutz's team found, there is a two in three chance that the world's population will not double in the next century--but that the prospect of a rapidly graying population "is virtually certain," suggesting that the focus of public concern "will continue to shift from global population growth to population aging."
According to Shripad Tuljapurkar, a demographer at Mountain View Research in Los Altos, California, Lutz and his colleagues "make a persuasive case that global population growth is slowing down, which should soothe those who see population as the primary cause of the world's ills." Tuljapurkar says he's particularly struck by the firmness of the prediction that elderly numbers will double. "That's a strong statement," he says. Thanks to the rich database used in the study, adds Stanford biologist Anne Ehrlich, its predictions "are stronger than the UN figures."