Polar bears, fat and ice: there are fewer and fewer of them in the Arctic due to climate change

In search of polar bears where the Churchill River flows into the vast Hudson Bay, Canadabiologist Geoff York observes a region that has a low-fat diet and ice due to the climate change.

And there are fewer polar bears, too.

There are now about 600 polar bears in western Hudson Bay, one of the most endangered of the 20 populations of the white beasts. That’s nearly half as many as there were 40 years ago, says York, director of research and policy for Polar Bears International. His most recent study, with a team of scientists from several specialties, shows that if the world doesn’t further reduce emissions of heat-trapping gases, “we could lose this population entirely by the end of the century,” he says.

It’s not just polar bears that are threatened in this shifting gateway to the Arctic, where warmer waters melt sea ice earlier in the year and open ocean persists longer. Given what grows, lives and, above all, what is eaten in this region, it is as if the foundations of a house were moving. “The entire marine ecosystem is linked to the seasonality of that sea ice cover”said University of Manitoba sea ice scientist Julienne Stroeve.

When sea ice melts earlier, the overall water temperature warms and algae blooms change, which in turn changes the plankton that feed on the algae, which changes the fish, all the way to beluga whales, seals and polar bears, scientists say.

“What we’re seeing is the transformation of an Arctic ecosystem into a more southern open ocean,” York explains from a 12-foot Zodiac inflatable boat. “We’re seeing a transformation from high-fat plankton leading to things like beluga whales and polar bears to low-fat plankton leading to the bottom of the food chain, which is jellyfish.”

“To live in the Arctic you have to be fat, or live off fat, or both,” said Kristin Laidre, a marine mammal scientist at the University of Washington who specializes in Arctic species.

The polar bear, a symbol of climate change and a region that is warming four times faster than the rest of the planet, is the king of fat. When mother polar bears nurse their cubs — as an Associated Press team witnessed on the rocks outside Churchill, Manitoba, known as the polar bear capital of the world — what comes out in the milk is 30 percent fat, York says.

“If you think of the thickest whipped cream, it would be like drinking it,” York says. “That’s why there are puppies that are born the size of my fist in January and by March they’re already 20 to 25 pounds.”

Fewer of these pups are born or survive the first year because their mothers are not fat or strong enough to become pregnant, York says.

Polar bears are feeding like crazy in the ice-covered spring. They use the sea ice shelves as bases to hunt their favourite prey, the fat seals, especially the pups.

In Hudson Bay, unlike other areas where polar bears live, sea ice naturally disappears in the summer. So polar bears lose their food supply. This has always happened, but now it happens earlier in the year and the ice-free area lasts longer, York and Stroeve say.

So most polar bears are starving. Recent studies have shown that even hunting on land — caribou, birds, human garbage — requires so much energy that bears who do it don’t actually gain any more calories than those who just sit and starve.

“Here in Hudson Bay, we know from long-term research that today’s bears spend up to a month longer on shore than their parents or grandparents did. That’s 30 more days without access to food, and that’s on average,” York explains.

Some years, bears approach the 180-day starvation threshold. Polar bears can fast for less than that and do just fine, mostly because they’re so good at collecting and storing fat for these lean periods, York says. During that lean period, researchers monitoring the bears found that 19 out of 20 lost 47 pounds in just three weeks — about 7% of their body weight.

Arctic sea ice has declined by about 13% per decade since 1979according to the National Snow and Ice Data Center. While Arctic sea ice hit its fourth-lowest extent on record in late August, in western Hudson Bay unusual winds have meant ice lasts longer than usual, but it’s a temporary and very localized respite.

A study by Stroeve and York this year looked at sea ice levels, that 180-day hunger threshold, and climate simulations based on different levels of carbon pollution. The researchers found that once the Earth warms another 1.3 or 1.4 degrees Celsius (2.3 to 2.5 degrees Fahrenheit) from now, polar bears will likely cross that point of no return. The bears will be too hungry and this population is likely to become extinct.

Studies, including those of the United Nationswhich analyze current efforts to reduce carbon dioxide emissions, project warming of about 1.5 to 1.7 °C (2.7 to 3.1 °F) between now and the end of the century.

“The populations are definitely not going to make it,” Stroeve said.

There are about 4,500 polar bears in the three Hudson Bay populations and 55,000 beluga whales. Together, that’s more than 63 million kilograms (141 million pounds) of huge, fat mammals. That sounds huge, but those white beasts are losing a battle against an even bigger weight: the amount of heat-trapping carbon dioxide the world spews into the air.

Laidre, of the University of Washington, said some scientists believe the smallest aquatic zooplankton, called copepods, are the most important animals in the Arctic. They are fat, heavy and the staple food of bowhead whales.

But copepods live in the plankton of smaller plants, which is changing. The timing of when copepods can thrive is changing and new species are coming in, “and they are not as lipid-rich,” Laidre explains.

“It’s not that there’s nothing living out there,” York says, looking out over the bay. “It’s just that the things that live up north are changing and are looking a lot more like the south.”

What’s happening in Hudson Bay is a preview of what’s coming further northsaid Stroeve, the ice scientist.

For her, there is something special about polar bears: “It really makes you happy to see them, to see an animal living in such a harsh environment. And somehow they have survived. And we are going to make them not survive? That makes me sad.”