How Warming Affects Arctic Sea Ice, Polar Bears

Photo: Kerstin Langenberger, Svalbard, Norway

By Seth Borenstein, Camille Fassett and Kati Perry, Associated Press

Majestic, increasingly hungry and at risk of disappearing, the polar bear is dependent on something melting away on our warming planet: sea ice.

In the harsh and unforgiving Arctic, where frigid cold is not just a way of life but a necessity, the polar bear stands out. But where it lives, where it hunts, where it eats — it’s disappearing underfoot in the crucial summertime.

“They have just always been a revered species by people, going back hundreds and hundreds of years,” said government polar bear researcher Steve Amstrup, now chief scientist for Polar Bear International. “There’s just something special about polar bears.”

Scientists and advocates point to polar bears, marked as “threatened” on the endangered species list, as the white-hot warning signal for the rest of the planet — “the canary in the cryosphere.” As world leaders meet in Glasgow, Scotland, to try to ramp up efforts to curb climate change, the specter of polar bears looms over them.

The State of Sea Ice

Arctic sea ice — frozen ocean water — shrinks during the summer as it gets warmer, then forms again in the long winter. How much it shrinks is where global warming kicks in, scientists say. The more the sea ice shrinks in the summer, the thinner the ice is overall, because the ice is weaker first-year ice.

Julienne Stroeve, a University of Manitoba researcher, says summers without sea ice are inevitable. Many other experts agree with her.

The warming already in the oceans and in the air is committed — like a freight train in motion. So no matter what, the Earth will soon see a summer with less than 1 million square miles of sea ice scattered in tiny bits across the Arctic.

The big question is when the Arctic will “look like a blue ocean,” said Mark Serreze, director of the National Snow and Ice Data Center.

Maybe as early as the 2030s, most likely in the 2040s and almost assuredly by the 2050s, experts say.

The Polar Bear Connection

Photo: Polar Bears International

There are 19 different subpopulations of polar bears in the Arctic. Each is a bit different. Some are really in trouble, especially the southernmost ones, while others are fairly close to stable. But their survival from place to place is linked heavily to sea ice.

“As you go to the Arctic and see what’s happening with your own eyes … it’s depressing,” said University of Washington marine biologist Kristin Laidre, who has studied polar bears in Baffin Bay.

Shrinking Sea Ice Means Polar Bears Shrink, Too

In the summertime, polar bears go out on the ice to hunt and eat, feasting and putting on weight to sustain them through the winter. They prefer areas that are more than half covered with ice because it’s the most productive hunting and feeding grounds, Amstrup said. The more ice, the more they can move around and the more they can eat.

Just 30 or 40 years ago, the bears feasted on a buffet of seals and walrus on the ice. But with ice loss, the bears haven’t been doing as well, Amstrup said.

One sign: A higher proportion of cubs are dying before their first birthdays.

Polar bears are land mammals that have adapted to the sea. The animals they eat — seals and walruses mostly — are aquatic.

The bears fare best when they can hunt in shallow water, which is typically close to land. Recently, however, the sea ice has retreated far offshore in most summers. That has forced the bears to drift on the ice into deep waters that are devoid of their prey, Amstrup said.

The Future

Even as leaders meet in Scotland to try to ratchet up the effort to curb climate change, the scientists who monitor sea ice and watch the polar bears know so much warming is already set in motion.

There’s a chance, if negotiators succeed and everything turns out just right, that the world will once again see an Arctic with significant sea ice in the summer, experts said. But until then “that door has been closed,” said Twila Moon, a National Snow and Ice Data Center scientist.

So hope is melting too.

“It’s near impossible for us to see a place where we don’t reach an essentially sea ice-free Arctic, even if we are able to do the work to create much, much lower emissions” of heat-trapping gases, Moon said. “Sea ice is one of those things that we’ll see hit some pretty devastating lows along that path. And we can already see those influences for polar bears.”


For more on this important topic, explore the following:

More In-Depth Interactive Associated Press Article

Polar Bears International website

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