Polar bears have become the furry face of the climate crisis, with experts suggesting the animals could be all but extinct in a matter of the decades as the Arctic sea ice they hunt from melts away.
But now researchers say they have found a group of them in south-east Greenland who are surviving despite a lack of sea ice for much of the year.
The team say the polar bears – which appear to have been isolated from other groups for several hundred years – have clung on thanks to fresh water ice from glaciers that discharge into the sea.
The researchers add that despite expectations of a large decline in polar bear numbers in the Arctic, the discovery offers a glimmer of hope, not least as the conditions in south-east Greenland today are similar to those expected in the high Arctic towards the end of the century.
“I do think they can teach us something about where rare, small numbers of polar bears might be able to hang on in an ice-free Arctic,” said Dr Kristin Laidre, the first author of the study from the University of Washington who worked with the Greenland Institute of Natural Resources.
Writing in the journal Science, Laidre and colleagues report their studies of the movement, genetics and demographics of a sub-population of polar bears along the coastline of east Greenland revealed the presence of two distinct groups, one of which lives above 64 degrees north, and the other below, in the south-east of the island.
The team say the latter meets the criteria for a new sub-population of polar bears – raising the number identified to date from 19 to 20 – noting the animals are the most genetically isolated polar bears in the Arctic. Their movements are limited by features including the mountainous terrain and the Greenland ice sheet to the west, open water to the east and the lack of suitable habitat to the south.
“They’re geographically, genetically and demographically isolated, meaning they’re not interacting with other bears,” said Laidre, although she stressed the group is not evolving into a new species.
“Occasionally, there’s an immigrant that comes in and adds genetic diversity to the group,” Laidre added. “But because they are so geographically isolated, they don’t have a lot of genetic input from other polar bears from other parts of the Arctic.”
At first glance, the conditions of south-east Greenland may seem an unlikely habitat for polar bears, as sea ice is present for less than a third of a year. But as glaciers in the fjords move towards the ocean, the ice that breaks off can give rise not only to icebergs but aggregate in front of the glacier, providing what Laidre calls a “floating landscape” from which they can hunt year-round.
“What we know about polar bears is that having sea ice for about 100 days a year is just way too few for bears to survive,” she said. “The reason that they can make it in this isolated environment is that they have a supplemental ice platform.”
It is not the first time polar bears have been found to move along glacial fronts, but the team say the newly identified group – thought to be a few hundred strong – is unusual in that such features are essential for their survival.
However, Laidre said such habitats were rare and likely to change with global heating, while the small gene pool of the south-east Greenland bears may prove problematic should immigrant bears cease to turn up.
Prof Andrew Derocher, a polar bear expert at the University of Alberta who was not involved in the study, said the research showed polar bears in south-east Greenland comprised a distinct genetic group with isolation and inbreeding – although he said the lack of a fixed definition made it challenging to say if it was a new subpopulation.
“I suspect as the climate continues to warm in the Arctic, this study reflects a pattern that will emerge much more often: declining abundance coupled with low immigration will result in genetically distinct groups of polar bears scattered across the Arctic that with continued warming, will be extirpated over time,” he said.
“The low body condition and birth rate reported in south-east Greenland suggests this group of bears may already be living at the edge of persistence.”