Did This Polar Bear Die Because of Climate Change?
AUGUST 11, 2015 2:15 PM ET // BY KIERAN MULVANEY
This skinny polar bear was photographed off the north coast of Alaska. KIERAN MULVANEY
Over the past couple of days, a photograph of a dead polar bear has made the viral rounds online, its fame accentuated by a number of different articles which claim the bear in question was "killed by climate change." But is that claim true?
The photograph was taken by Sebastian Copeland, and is featured in his book Arctica: The Vanishing North; but the first thing to note is, over-enthusiastic headlines to the contrary, he didn't in fact claim that climate change killed the bear. Rather, he noted a warming Arctic would make that kind of death more likely.
"The frozen remains of this young bear point to starvation," he is quoted as saying. "The faster retreat of the sea ice, a bear's favored spot for seal hunting, leads to longer fasting periods and the demise of more animals from starvation." That, say polar bear experts, is quite accurate.
"It's difficult if not impossible to attribute a cause of death from a photo or link a specific death to global climate change," Geoff York, senior conservation director for Polar Bears International, said in an email to Discovery News from the North Slope of Alaska, where he is surveying polar bear dens. "It is fair to say that this is what a changing climate looks like. This is what scientists mean by increased bears in poor condition and decreased survival."
That sentiment was shared by Andrew Derocher, professor of biological sciences at the University of Alberta.
"Looking at the picture, it’s not a big bear," he told Discovery News --and smaller, younger bears tend to have higher mortality rates than adults, which polar bear expert Ian Stirling has described as seeming "virtually immortal. Subadults are inexperienced hunters, don't kill seals often and may find the kills they do make are taken from them by large, mature males.
That’s one reason why starvation is, said Derocher, the No. 1 cause of polar bear mortality. "And ultimately there’s something behind starvation," he continued. "It could just be an individual that fails to thrive, sometimes it may be an individual of low quality. It could be diseases, it could be parasites, it could be bad luck -- we don’t like to talk about luck in an evolutionary context, but sometimes that’s what it is. Sometimes it can be incredibly hard to tell what's caused the mortality, even if the animal’s dying in front of you."
All that said, Derocher is at pains to underline York's point that, even while nobody can point to a specific dead bear and say climate change killed it, it is important "to not discount the climate change aspect. We are seeing more bears perishing from starvation in relation to changing sea ice conditions. We’ve changed the rules under which polar bears are living in much of their range, and one of the consequences is that they’re not getting as much energy intake and we’re quite often asking them to expend more energy working and living in that environment. So the net result is bears become in poorer condition, bears get stuck away from sea ice or their prey, and therefore we are seeing what you could call climate change-related mortality, which usually manifests as starvation."
At issue is not just a decline in the area of polar bear's sea ice habitat, but also changes in its quality -- "you could have 100 percent sea ice cover, and it might not be polar bear habitat, because it could be too thin," Derocher noted -- and also the time available for polar bears to hunt on the ice.
"The ice-free period is increasing in much of the polar bear’s range," Derocher said. "It’s what we see in western Hudson Bay, the Beaufort Sea and many other parts. Svalbard is just a mess this year, as well. It’s pretty grim." On average, Hudson Bay for example is ice-free one extra day each year: That's one more day every year that polar bears go without hunting, and over time, that adds up.
"The way that climate change is manifested in any polar bear population is: The first thing we see is a change in sea ice," explained Derocher. "The second thing we see is a change in the body condition of polar bears. When we see that change in body condition, the next things are changes in survival rates and changes in reproductive output. Ultimately, those two factors result in a population decline, which is hard and expensive to document."
So no, there is no smoking (or warming) gun to pin the death of that one bear on climate change. But there is more than enough evidence to suggest global warming is making polar bear starvation more common, and will do so even more in the future -- which appears to be the point that Copeland was trying to make in the first place.