Earth's population reaches 8-billion milestone, but this upward trend may not continue for long

On Tuesday, the United Nations officially marked the day the global population reached eight billion people.

It's not an exact science. It may have happened weeks or months ago or may not even have happened yet. But the fact is that humans are abundant on this planet and our population is on an upward trend. At least until the end of the century.

In the UN's World Population Prospects 2022 report, the international agency said that it expects the population to reach somewhere near 8.5 billion by 2030, 9.7 billion in 2050, 10.4 billion in the 2080s and remain at that level until 2100.

Between 1804 and 1927, the global population grew from one billion to two billion. It took 33 years after that to reach three billion. Since then, it's taken roughly 12.6 years to add another billion people.

But at least one population expert is skeptical about this projection by the UN.

"This is the last time we're probably going to have a conversation about reaching another billion marker," said Darrell Bricker, CEO at Ipsos Public Affairs and a fellow at the University of Toronto's Munk School of Global Affairs and Public Policy.

"Somewhere between eight and nine billion is where we're going to end up [by the end of the century]," said Bricker, who co-wrote Empty Planet: The Shock of Global Population Decline.

"The reason that it's not going to increase more than that is because … China now is recording its lowest birth rate in history. India has just dropped below replacement rate for its birth rate. That's 36 per cent of the entire global population that are now not replacing or not at replacement level birth rates."

And once it gets to eight or nine billion people, he said, it's likely it'll drop even lower.

Patrick Gerland, chief of the population estimates and projections section in the UN's population division, believes the agency's numbers are sound, but does agree that the population will level off some time in the relatively near future.

"If you look at some of the results from some of the alternative projections that some other research groups have produced, the alternative kind of future scenarios that different researchers have produced tend to be even more conservative, to expect this overall decline to happen a bit earlier, and eventually a bit faster than we anticipate," he said. 

Gerland said the 10.4-billion projection is more of an upper range than a lower one.

Why the discrepancy between what Bricker anticipates and the UN projections?

"The UN always seems to be playing a game of catch-up. And I'll give you a great example of this: They put out their last big recalculation of human fertility rates in 2017, so about five years ago. They have since revised down their population number from 11.2 billion people by the end of the century to 10.4 billion," Bricker said.