Decades ago, powerful images like these came to represent the wrath of climate change. They tell a compelling story: Global warming is melting Arctic sea ice, which polar bears need to survive. Without it, they’ll perish.
This is a true story. In the last two decades, the Arctic has lost about a third of its winter sea ice, and it continues to melt at a rate of about 13 percent each decade. As a result, polar bears are at risk of extinction. One 2020 study found that if polluters don’t curb their greenhouse gas emissions — the primary driver of modern global warming — all but a few populations of polar bears will vanish by the end of the century.
But there is a very small glimmer of hope for these iconic predators, revealed today in a study published in the journal Science. It finds that a newly documented population of polar bears in Greenland seems to be surviving without much sea ice for most of the year. Instead of hunting only on ice that forms in the sea, these bears are also using ice that breaks off of glaciers that flow into fjords from land, which is available year-round. Not many studies have documented this behavior before.
The authors suggest that in a warming world, regions with glacial ice might be strongholds for the species, helping them hang on.
“These areas might see polar bears persist for longer,” said Steven Amstrup, the chief scientist at Polar Bears International, who is not affiliated with the new study. If the bears didn’t have abundant glacial ice, he said, “we wouldn’t have polar bears in that area right now.”
This is big news for an animal with so much symbolism, but experts warn that it’s not exactly good news. Instead, it foreshadows the final act of a tragedy, revealing where the last remnants of a species could live.
Polar bears need fat, and so they also need sea ice
The life of a polar bear depends on fat. They need body fat to stay warm in the frigid Arctic, and they also need fat to stay hydrated. Because most of the freshwater around them is frozen for much of the year, they often rely, instead, on metabolic water — a byproduct of the breakdown of the fat they consume.
That’s why seals are an ideal food source — they’re basically one big pile of calorie-dense blubber. Polar bears hunt them nearly exclusively for food, and can chow down on 100 pounds of blubber in a single sitting.
But there’s a catch: This fatty feast is typically only possible when there’s sea ice. The bears snatch seals when they come onto the ice to molt or have babies, or when seals poke their heads through it to breathe.
In a typical year, Arctic sea ice shrinks during the summer (when bears in some regions will fast) and then forms again in the winter (allowing the bears to hunt). Climate change, however, is blasting the Arctic with heat — it has warmed about twice as fast as the global average — drastically shortening the number of days available to hunt.
“There’s no food without ice,” said Andrew Derocher, a professor and polar bear expert at the University of Alberta, who is also not affiliated with the paper.
The new study doesn’t contradict any of this. “As Arctic sea ice goes away, we see consequences for polar bears,” said Kristin Laidre, the paper’s lead author and an associate professor at the University of Washington. But the study does suggest that some populations of bears might be less sensitive to shrinking sea ice.
Scientists documented an unusual population of polar bears in Greenland
It’s hard to imagine an animal more challenging to study than the polar bear, especially in a place like Greenland. Beyond a tolerance for cold weather, researchers often need a helicopter or two just to find the animals, which have evolved to remain hidden so they can sneak up on prey.
That’s one reason why this study is such a big deal: It reveals a never-before-documented population of polar bears in southeast Greenland, which is largely distinct from populations in the northeast. It’s the most genetically distinct polar bear population in the world, Laidre says, suggesting that it’s been isolated for a while.
The most intriguing results, however, have more to do with these animals’ lifestyles than with their genetics. In this part of Greenland, sea ice is especially scarce. There’s no usable sea ice for more than 250 days of the year, the authors write, and polar bears can’t fast that long. They lose about two pounds of body fat per day of fasting, Derocher said.
Yet this population of bears has survived for hundreds of years, Laidre says, so clearly they’re finding food. The question is, how?
First, a pedantic yet important breakdown of ice: There’s sea ice, which is frozen seawater, but there are also glaciers, which are made of snow (freshwater) compressed over time into large sheets of ice that flow like a slow-moving river.
In a few parts of the world home to polar bears — including Svalbard and southeast Greenland — large glaciers run into the sea, where they crumble into pieces. They’re a bit like conveyer belts, said Twila Moon, a study co-author and scientist at the National Snow and Ice Data Center. As one piece breaks off into the sea, there’s another to replace it.
What the researchers found is that polar bears in southeast Greenland can use these glacial chunks to hunt seals, even though icebergs are much more varied and jagged than sea ice. The finding suggests that these bears can hunt on any ice surface if there’s food underneath. (Some polar bears in northern Europe likely also use glaciers to live and hunt, for at least part of the year, Derocher said.)
And this approach may be key to their survival. Even in the summer, there’s still plenty of glacial ice available after the sea ice has melted away. The glaciers here are huge and incredibly thick, Moon said, so although they melt, they continue to dump ice into the fjords. That’s the glimmer of hope: Habitats with glacial ice could be refuges for polar bears in a warming world.
No polar bears are safe as the planet heats up
Despite the new evidence, Derocher, of the University of Alberta, doesn’t see this study as good news. For one, there aren’t many polar bear habitats that have glacial ice, he said. So even if these habitats become refuges, they won’t be able to support many bears. (And as of yet, researchers don’t have plans to ship polar bears to these regions.)
Plus, glaciers are melting quickly, too — including the ones in Greenland, which is home to one of only two ice sheets on the planet. The country is losing roughly 234 billion tons of its glacial ice sheet per year, which is melting seven times faster than it was in the 1990s. (Remarkably, melting Greenland ice alone contributes to roughly 0.5 millimeters of sea-level rise globally.)
It’s also not clear that the polar bears in the study are thriving, Derocher says. The researchers found that female bears have a lower birth rate and less body mass compared to some other populations — those are “red flags,” he said. Because the bears are so isolated, they could also be at risk of genetic problems that arise from inbreeding, he added.
“If the bears are not in a very good condition in southeast Greenland already, that’s an indicator of potential vulnerability to warming,” he said.
Laidre explains that we don’t know much about the health of these bears — after all, her team only just documented them. “I think people are tempted to give it a hopeful spin, but we just don’t know how they’re doing,” she said. The logical next step, she added, is to monitor the new population to determine whether it’s healthy and stable or in decline, such as from a lack of food.
Ultimately, as many wildlife stories go, the only way to save this species is by quickly cutting back carbon emissions, experts say. Those images of polar bears seemingly suffering as the ice melts are dramatic, but they’re not wrong. The benefit of glacial ice complicates but doesn’t change the story of their plight.
“Glacial ice is something that we have to consider when we think about where polar bears might be in an ice-free Arctic,” Laidre said. Southeast Greenland might be something of a stronghold, she said, but “these bears are subject to climate warming, just like all of the other bears.”