World population unlikely to stabilize this century

The world's population is unlikely to stabilize this century but instead keeps growing and could reach 11 billion by 2100, a new study using modern statistical tools said Thursday.

That represents about 2 billion more people than was forecast in some previous research, but it largely supports the 2013 UN projections that see an increase to 10.9 billion by 2100.

"The consensus over the past 20 years or so was that world population, which is currently around 7 billion, would go up to 9 billion and level off or probably decline," said corresponding author Adrian Raftery, a statistician at the University of Washington, in a statement.

"We found there's a 70 percent probability the world population will not stabilize this century. Population, which had sort of fallen off the world's agenda, remains a very important issue."

The new study, published in the U.S. journal Science, showed there is an 80 percent likelihood that the population in 2100 will be between 9.6 billion and 12.3 billion.

Most of the anticipated growth is in Africa, where population is projected to quadruple from around 1 billion today to 4 billion by the end of the century.

"For Africa, the main reasons are higher fertility in history and a recent slowdown in fertility decline," co-author Li Nan of the United Nations Population Division (UNPD) told Xinhua.

There is an 80 percent chance that the population in Africa at the end of the century will be between 3.5 billion and 5.1 billion people, the study projected.

Other regions of the world may see less change. Asia, now 4.4 billion, is projected to peak at around 5 billion people in 2050 and then begin to decline. Populations in North America, Europe, and Latin America and the Caribbean are projected to stay below 1 billion each.

"These projections indicate that there is little prospect of an end to world population growth this century without unprecedented fertility declines in most parts of Sub-Saharan Africa still experiencing fast population growth," the researchers wrote in their paper.

Every two years, the UNPD publishes revised World Population Prospects (WPP), using the most recent data, but these projections were based on scenarios and have been criticized for lacking a probabilistic basis, according to the study.

The new article introduces the first probabilistic population statistics issued by the UNPD in July, known as Bayesian statistics, that combines all available information to generate better predictions.

"We found the uncertainty to be much smaller than that in previous projections," Li said.

"In WPP2012, for example, the uncertainty is described as 'If on average each woman has half less or half more children', then the total population of the world in 2100 would be 6.75 billion or 16.64 billion, in which the probability of having half less or half more children is unknown."

Li said populous countries, especially those with unsustainable growth potential, should have their own population projections that could take into account internal population change and that could best inform decision makers of their own population issues.

"Along this line, China is doing well, and is helping some developing countries such as Brazil, Kenya, and India," he said.

"This south-south collaboration was introduced as a side event at the 2014 Commission on Population and Development of the United Nations."