Contrary to some earlier projections, the world’s population will soar through the end of the 21st century, thanks largely to sub-Saharan Africa’s higher-than-expected birth rates, experts said last week.

There is an 80 percent likelihood that the number of people on the planet, currently 7.2 billion, will increase to between 9.6 billion and 12.3 billion by 2100, the researchers said. They also saw an 80 percent probability that Africa’s population will rise to between 3.5 billion and 5.1 billion by 2100, from about 1 billion today.

The study, led by United Nations demographer Patrick Gerland and University of Washington statistician and sociologist Adrian Raftery and published in the journal Science, foresees only a 30 percent chance that Earth’s population will stop rising this century.

“Previous forecasts did indeed forecast a leveling off of the world population around 2050, and in some cases a decline,” Raftery said.

He said the new projections arise from data clearly establishing that birth rates in sub-Saharan Africa have not been decreasing as quickly as some experts had expected, a trend that was “not as clear when previous forecasts were made.”

(Raveen Dran/AFP/Getty Images)

Raftery said the researchers used data on population, fertility, mortality and migration from every country and then predicted future rates using new statistical models. Some of the figures, such as the median projection of the population hitting 10.9 billion by 2100, mirror a U.N. report published in 2013.

The world’s population reached 1 billion in the early 19th century, doubled to 2 billion in the 1920s and grew to 6 billion in the 1990s. It hit 7 billion in 2011. The findings underscore worries expressed for decades by some experts about a planet growing more crowded and humankind exhausting natural resources.

The researchers projected that Asia’s population, now 4.4 billion, will peak at around 5 billion people in 2050, then begin to decline. They forecast that the populations of North America, Europe and Latin America will stay below 1 billion each through 2100.