WHAT WAS CLAIMED
Polar bear numbers have increased from 5000 in the 1950s to up to 31,000 in 2015.
OUR VERDICT
Misleading. While polar bear populations appear to have grown, experts say estimates from the 1950s to 1970s were largely inaccurate.
AAP FACTCHECK - Claims suggesting polar bear numbers are increasing don't tell the full story about the Arctic's enormous carnivores.
Experts say early estimates of polar bear populations were just the tip of the iceberg and underestimated due to poor methods.
Social media posts have floated the decades-old claim that polar bear numbers are growing, using it as evidence for climate change denialism.
"Polar Bears defy the doomsday predictions," one Facebook post reads.
"When Al Gore was born, there were only 5,000 polar bears. Now, due to the ravages of Global Warming, only 30,000 polar bears remain!"
The post also features a graphic with polar bear population estimates from the Foundation for Economic Education, an American conservative think tank.
The graphic states that in the 1950s there were 5000 polar bears, a number that doubled between 1965 and 1970 and more than doubled again to 25,000 in 1984.
It then states estimates in 2005 were 20,000 to 25,000 and then grew to between 22,000 and 31,000 in 2015.
However, the claim that polar bear numbers have increased since the 1950s rests on thin ice, according to experts.
The largest of the bear species, polar bears are officially listed as "vulnerable" on the International Union for Conservation of Nature's Red List of Threatened Species, and defined as "threatened" under the US Endangered Species Act.
Polar bear experts told AAP FactCheck early estimates are no longer plausible.
Steven Amstrup, chief scientist for Polar Bears International, said that until the late 1980s, scientists had limited ability to estimate polar bear numbers accurately.
While some early estimates suggested a global population of about 5000, he said, few took the number seriously.
"These claims about global population growth from something like 5000 bears to 25,000-plus, which have been repeated since the early 2000s, are wrong," Dr Amstrup said.
"What appears to be population growth is really increased knowledge about the bears."
He described early polar bear tracking methods, such as aerial surveys, as "crude", failing to account for the quantity of, and variation in, habitats or the difficulties of finding white creatures in a white environment.
By the 1980s, Dr Amstrup said, capture-mark-recapture had become the gold standard of assessing numbers and trends, a method many of the current best estimates rely on, though scientists also use other methods.
However, getting accurate global estimates is complex "due to the inaccessibility of their location and budget limitations", Dr Amstrup explained.
"This means that the global population estimate is composed of a mixture of solid estimates, OK estimates, and poor estimates."
Scientists now have a higher quality educated guess of about 25,000-26,000 polar bears worldwide, he said.
University of Alberta biologist Andrew Derocher, who studies polar bears, agreed early population guesses were made with no scientific basis, and the first reliable estimates come from the 1980s.
In the 1950s and 1960s, he added, polar bear populations were depleted by unregulated hunting - which is mentioned in the Facebook post.
Numbers increased in the 1970s, after they were protected from excessive hunting by the international Agreement for the Conservation of Polar Bears.
"Today, we have a mix of status. Some have now declined from earlier higher abundance, some are stable, and a few might still be increasing," Professor Derocher said.
This is because the habitats of the 20 subpopulations of polar bears vary widely based on sea ice loss.
"The threat posed by climate change and loss of polar bear sea ice habitat has not changed over the last decade," he said.
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