EXPLAINER: How warming affects Arctic sea ice, polar bears

Majestic, more and more hungry and susceptible to disappearing, the polar bear relies on one thing melting away on our warming planet: sea ice.

Within the harsh and unforgiving Arctic, the place frigid chilly is not only a lifestyle however a necessity, the polar bear stands out. However the place it lives, the place it hunts, the place it eats — it’s disappearing underfoot within the essential summertime.

“They’ve simply all the time been a revered species by individuals, going again a whole lot and a whole lot of years,” stated longtime authorities polar bear researcher Steve Amstrup, now chief scientist for Polar Bear Worldwide. “There’s simply one thing particular about polar bears.”

Scientists and advocates level to polar bears, marked as “threatened” on the endangered species listing, because the white-hot warning sign for the remainder of the planet — “the canary within the cryosphere.” As world leaders meet in Glasgow, Scotland, to attempt to ramp up efforts to curb local weather change, the specter of polar bears looms over them.

United Nations Setting Program head Inger Andersen used to steer the Worldwide Union for the Conservation of Nature, which screens and classifies species in bother. She asks: “Do we actually wish to be the era that noticed the tip of the power of one thing as majestic because the polar bear to outlive?”


Arctic sea ice — frozen ocean water — shrinks in the course of the summer season because it will get hotter, then varieties once more within the lengthy winter. How a lot it shrinks is the place international warming kicks in, scientists say. The extra the ocean ice shrinks in the summertime, the thinner the ice is total, as a result of the ice is weaker first-year ice.

Julienne Stroeve, a College of Manitoba researcher, says summers with out sea ice are inevitable. Many different consultants agree along with her.

Former NASA chief scientist Waleed Abdalati, now a high College of Colorado environmental researcher, is one in every of them.

“That’s one thing human civilization has by no means identified,” Abdalati stated. “That’s like taking a sledgehammer to the local weather system and doing one thing enormous about it.”

The warming already within the oceans and within the air is dedicated — like a freight prepare in movement. So, it doesn’t matter what, the Earth will quickly see a summer season with lower than 1 million sq. kilometers of sea ice scattered in tiny bits throughout the Arctic.

The massive query is when the Arctic will “appear to be a blue ocean,” stated Mark Serreze, director of the Nationwide Snow and Ice Information Middle.

Possibly as early because the 2030s, almost certainly within the 2040s and virtually assuredly by the 2050s, consultants say.

The Arctic has been warming twice as quick as the remainder of the world. In some seasons, it has warmed 3 times quicker than the remainder of the globe, stated College of Alaska at Fairbanks scientist John Walsh.

That’s due to one thing known as “Arctic amplification.” Basically, white ice within the Arctic displays warmth. When it melts, the darkish sea absorbs rather more warmth, which warms the oceans much more shortly, scientists say.


There are 19 totally different subpopulations of polar bears within the Arctic. Every is a bit totally different. Some are actually in bother, particularly the southernmost ones, whereas others are fairly near secure. However their survival from place to put is linked closely to sea ice.

“As you go to the Arctic and see what’s taking place with your individual eyes … it’s miserable,” stated College of Washington marine biologist Kristin Laidre, who has studied polar bears in Baffin Bay.

Shrinking sea ice means shrinking polar bears, actually.

Within the summertime, polar bears exit on the ice to hunt and eat, feasting and placing on weight to maintain them by the winter. They like areas which are greater than half coated with ice as a result of it’s the best looking and feeding grounds, Amstrup stated. The extra ice, the extra they will transfer round and the extra they will eat.

Simply 30 or 40 years in the past, the bears feasted on a buffet of seals and walrus on the ice.

Within the Eighties, “the males have been enormous, females have been reproducing repeatedly and cubs have been surviving nicely,” Amstrup stated. “The inhabitants appeared good.”

With ice loss, the bears haven’t been doing as nicely, Amstrup stated. One signal: The next proportion of cubs are dying earlier than their first birthdays.

Polar bears are land mammals which have tailored to the ocean. The animals they eat — seals and walruses largely — are aquatic.

The bears fare greatest once they can hunt in shallow water, which is usually near land.

“When sea ice is current over these near-shore waters, polar bears could make hay,” Amstrup stated.

However in recent times the ocean ice has retreated far offshore in most summers. That has compelled the bears to float on the ice into deep waters — generally almost a mile deep — which are devoid of their prey, Amstrup stated.

Off Alaska, the Beaufort Sea and Chukchi Sea polar bears present a telling distinction.

Go 30 to 40 miles offshore from Prudhoe Bay within the Beaufort Sea “and also you’re in very unproductive waters,” Amstrup stated.

Additional south within the Chukchi, it’s shallower, which permits bottom-feeding walruses to thrive. That gives meals for polar bears, he stated.

“The bears within the Chukchi appear to be faring fairly nicely due to that extra productiveness,” Amstrup stated. However the bears of the Beaufort “give us an actual good early warning of the place that is all coming to.”


At the same time as world leaders meet in Scotland to attempt to ratchet up the trouble to curb local weather change, the scientists who monitor sea ice and watch the polar bears know a lot warming is already set in movement.

There’s an opportunity, if negotiators succeed and all the things seems excellent, that the world will as soon as once more see an Arctic with vital sea ice in the summertime late this century and within the twenty second century, consultants stated. However till then “that door has been closed,” stated Twila Moon, a Nationwide Snow and Ice Information Middle scientist.

So hope is melting too.

“It’s close to not possible for us to see a spot the place we don’t attain an basically sea ice-free Arctic, even when we’re capable of do the work to create a lot, a lot decrease emissions” of heat-trapping gases, Moon stated. “Sea ice is a kind of issues that we’ll see attain some fairly devastating lows alongside that path. And we will already see these influences for polar bears.”


The Related Press Well being and Science Division receives help from the Howard Hughes Medical Institute’s Division of Science Schooling. The AP is solely answerable for all content material.

Fassett, an information journalist based mostly in Oakland, California, is a corps member for The Related Press/Report for America Statehouse Information Initiative. Report for America is a nonprofit nationwide service program that locations journalists in native newsrooms to report on under-covered matters.

Seth Borenstein, Camille Fassett And Kati Perry, The Related Press

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