Over the years, the fate of polar bears has become highly politicized. Groups including the Cato Institute, a libertarian research organization that challenges aspects of climate change, have called concerns about the bears overblown, arguing that some research shows that the animals have survived repeated warm periods. But scientists say during earlier warm periods the bears probably had significant alternative food sources, notably whales, that they do not have today.
Poignant images of bears on isolated ice floes or roaming land in search of food have been used by conservation groups and others to showcase the need for action to reduce warming. Occasionally, though, these images have been shown to be not what they seem.
After a video of an emaciated bear picking through garbage cans in the Canadian Arctic was posted online by National Geographic in 2017, the magazine acknowledged that the bear’s condition might not be related to climate change. Scientists had pointed out that there was no way of knowing what was wrong with the bear; it might have been sick or very old.
The new study did not include projections in which emissions were reduced drastically, said Cecilia M. Bitz, an atmospheric scientist at the University of Washington and an author of the study. The researchers needed to be able to determine, as precisely as possible, the periods when sea ice would be gone from a particular region. “If we had wanted to look at many models we wouldn’t have been able to do that,” Dr. Bitz said.
Andrew Derocher, a polar bear researcher at the University of Alberta who was not involved in the study, said the findings “are very consistent with what we’re seeing from empirical studies like monitoring work in the field.”
“The study shows clearly that polar bears are going to do better with less warming,” he added. “But no matter which scenario you look at, there are serious concerns about conservation of the species.”
Of the 19 subpopulations, little is known about some of them, particularly those in the Russian Arctic. Of subpopulations that have been studied, some — generally those in areas with less ice loss — have shown little population decline so far. But others, notably in the southern Beaufort Sea off northeastern Alaska, and in the western Hudson Bay in Canada, have been severely affected by loss of sea ice.