Graph on polar bear population uses unreliable data
A graph circulating on social media purports to show the polar bear population is growing in spite of global warming. This is misleading; experts say the chart uses outdated, unreliable data -- and that human-driven climate change poses a threat to polar bears.
"Polar bear population increasing / But doesn't fit climate narrative, so info cancelled," says a January 4, 2023 Facebook post from Bjorn Lomborg, author of "The Skeptical Environmentalist."
The graph shared in the post shows an increase in polar bears from 1965 to 2021. It cites data from the Polar Bear Specialist Group (PBSG), part of the International Union for the Conservation of Nature (IUCN).
"Reality: Polar bears were intensely hunted / 1976 world banned much hunting / Polar bear population recovered and now at its highest in 6 decades," Lomborg added.
Climate skeptics often point to the growth of certain bear populations to downplay the role of humans in driving global warming, as AFP has previously reported.
But experts told AFP the data used in the graph shared online are incomplete. The IUCN says on its red list of threatened species that the population trend for polar bears is "unknown."
Conservation group Polar Bears International, on behalf of AFP, asked 17 experts to assess the claim in the graphic. All 17 responded to the online questionnaire saying that they did not agree with its conclusions.
"Data from the 50's and 60's are at best highly unreliable guesstimates that cannot be compared to the modern polar bear population monitoring methods we use today," said Thea Bechshoft, a staff scientist at Polar Bears International.
Sian Henley, an academic specializing in the polar ocean at Edinburgh University, agreed. "The apparent increase in polar bear numbers is more likely to reflect the increase in our understanding and the reliability of the data, rather than an actual increase in numbers," she said.
The graph's footnote indicates the curve rests on eight sets of data, including six from the PBSG's latest status report in 2021. The other data are from the proceedings of two meetings: one held by the PBSG in 1981 and one by a precursor group in 1965.
The graph shows a rise from 1965 to 1981 coinciding with an international ban on polar bear hunting, which started in 1973 with exceptions for some indigenous communities.
However, former PBSG chairman Dag Vongraven of the Norwegian Polar Institute told AFP the 1965 and 1981 estimates are not valid due to limitations in tracking polar bears at the time.
The 1965 figures come from a paragraph in a scientific meeting report and are based on three estimates. Two are extrapolations of bear counts in Alaska in 1959 and Canada in 1964; the other is a 1961 global range estimate from a Soviet scientist.
"This is guesswork, pure and simple. You can't trust these at all," Vongraven said.
Polar bears are hard to track, roaming the ice in remote regions of the Arctic where they blend into the white landscape. Researchers monitor them using aerial flyovers and tagging.
But Vongraven said collars for satellite-tracking polar bears were introduced in the late 1960s. And the 19 distinct subpopulations of polar bears, which enable accurate counting, were not yet delineated by 1981.
The data from that year's report are likewise unreliable for creating a global graph, Vongraven said. The figures are based on estimates from 17 zones dating back as far as 1969.
"These surveys are on really random bits of area because at that time we didn't know (where) the populations (were delineated), so these are approximations, guesstimates, guesswork ... really coarse methods," Vongraven said. "You just can't use these. There's very little data behind them."
Steven Amstrup, chief scientist at Polar Bears International, said the apparent upward curve of the graph shared online reflects "improved knowledge" of the polar population, not an overall rise.
Polar bear numbers are derived from a combination of estimates for well-studied areas and "educated guesses" for less well-known areas. The latter is based in part on knowledge of sea ice and habitats, Amstrup said.
"A global estimate, therefore, is a combination of some really good numbers and others about which we are much less confident," he told AFP in an email.
Of the 19 discrete polar bear subpopulations, some are more accessible for monitoring than others. For example, more is known about the bears in the western and southern Hudson Bay in Canada than in more remote areas.
"As we've learned more, we've realized that in some of these areas, previous estimates were too low and we now believe there are more bears there than we previously thought," Amstrup said.
"If you plot estimated global population over time, it may look like a rising curve. This plotting of estimated numbers over time however reflects improved estimates rather than growth in numbers."
More recent data for certain areas are more detailed, but still not enough to give a precise global picture.
The PBSG says in its status report that monitoring for change in 10 of the 19 subpopulations was "data deficient" over the past generation of polar bears, or about 11.5 years.
Of the nine others, two were estimated to have "likely increased" and four were "likely stable." Three were estimated to have "likely decreased."
Looking back over two or more generations, there was insufficient data for 16 of the 19 subpopulations that make up the headcount.
The PBSG's most recent estimate for the global polar bear population is 26,000 -- an average from a range of 22,000 to 31,000. Precise numbers for four of the subregions are listed as "unknown."
"For the Russian populations there's no data whatsoever ... and for the polar basin nothing, no studies, because it's way too remote and too expensive," said Vongraven of the Norwegian Polar Institute.
"So in half the area that polar bears reside in, we know nothing."
The PBSG said in its 2021 report, cited at the bottom of the graph, that it has adjusted estimates since 1993.
"Although better information is now available for several subpopulations, some estimates remain missing, outdated, or include large uncertainty," the document says.
Vongraven said it is "logical to think that this whole population increased in the years after" the 1973 hunting ban. But "carrying capacity" -- the number of bears that a given environment can sustain -- has held those numbers in check.
"In the last decades with climate change, it's pretty evident that carrying capacity has decreased quite enormously," Vongraven said.
Polar bears rely on sea ice to forage for the seals that they eat. The ice has been disappearing, with the far north warming up to four times faster than the rest of the world, according to an August 2022 study published in Nature.
Most of the 17 experts polled for AFP cited sea ice loss as the principal threat to the bears.
"Intense Arctic warming, caused by emissions of greenhouse gases by human activity has already caused, and is continuing to cause, dramatic reductions in sea ice coverage," said Sian Henley of Edinburgh University. "This loss of polar bear habitat is the most significant threat to the survival of the species."
A 2021 regional government aerial survey, published in December 2022, indicated the number of polar bears in the Western Hudson Bay had fallen by more than a quarter in five years. The report said the decline could be due in part to bears migrating to neighboring areas.
The United Nations has documented melting sea ice, and its latest climate change report details how humans contribute to global warming by burning fossil fuels.
Numerous studies have shown how climate change and shrinking sea ice pose a threat to polar bears and their habitat. A 2020 study indicated the length of the yearly ice-free period in some areas may have passed crucial thresholds for the bears' survival.
"The data from places we know best are unequivocal in showing that sea ice decline ultimately means declines in polar bear numbers and distribution," said Amstrup of Polar Bears International.
"The fact that some populations are not yet affected by declining ice, and that we now feel some of these subpopulations are larger than we previously thought is good news. But it is good only in a temporary sense if societies don't halt global warming."
Read all of AFP's climate-related fact checks here.
February 13, 2023 This story was updated with responses from additional polar bear experts, including quotes from Thea Bechshoft and Sian Henley.