People may finally be nearing their limit.
Despite a growth burst that more than doubled the global human population over the past 50 years, a study released today predicts it will peak at 9 billion by the year 2070 and then begin to decline.
"People thought for many years that we would breed ourselves out of existence," says Warren Sanderson, a professor of economics and history at State University of New York at Stonybrook and co-author of the study appearing in this week's Nature. "They thought we'd produce so many children, there would be no standing room left on the planet. But now it seems our population will peak.
"And that's an optimistic message."
The study is the first to pinpoint an end to the burgeoning population. The scientists estimate there is an 85 percent chance the species will taper to about 8.4 billion by the year 2100. The current world population is counted at 6.1 billion.
Previous demographic studies by the United Nations had projected higher populations of 9.32 billion by the year 2050, with no decline in growth. Part of the reason for the different predictions is the new study anticipates the number of children born per woman will go down.
Forecasts Never Certain
Like the weather, population is tricky to predict since it is dependent on so many independent factors, including disease, wars and social trends. Demographers in the 1930s, for example, never predicted the post-World War II baby boom that caused populations to spike in the United States. Later, they also missed that U.S. birth rates would drop significantly by the 1970s.
In order to reflect the uncertainty of population prediction, the researchers, based at the International Institute for Applied Systems Analysis in Laxenburg, Austria, framed their findings in probabilities.
The team determined there is a 20 percent chance the population will peak by the year 2050, a 55 percent chance it will peak by 2075 and an 85 percent chance numbers will reach their limit in the next century. Sanderson says this method can provide policy makers with a more precise estimate of what to expect.
But others argue the predictions could be dangerously misleading even though they are framed in probabilities.
"It's a mistake to think we can stop worrying about population growth," says Robert Engelman, vice president for research for Population Action International, a Washington-based advocacy group. "The population growth problem isn't solved until we've solved it."
While most developed countries, particularly in Europe, have shown signs of declining, or soon-to-be declining populations, developing nations in sub-Saharan Africa and in western Asia still have high population growth. According to U.N. findings, Chad's population is growing by 3.3 percent every year, Yemen's population is expanding at the same rate and Madagascar is growing by 3 percent annually.
Part of the reason, says Engelmen, is women in these countries often have many children, starting at a young age. He argues it's important for the United States and other countries to promote family planning programs around the world in order to encourage lower global birth rates.
The Population Divide
In order to maintain a stable population, women must average 2.1 children each, a figure known as the replacement fertility rate. Two children replace the woman and her partner and the 0.1 figure reflects infant mortality rates.