How warming impacts Arctic sea ice, polar bears

Majestic, more and more hungry and vulnerable to disappearing, the polar bear depends on one thing melting away on our warming planet: sea ice.
In the tough and unforgiving Arctic, the place frigid chilly isn’t just a lifestyle however a necessity, the polar bear stands out. But the place it lives, the place it hunts, the place it eats — it’s disappearing underfoot within the essential summertime.
“They have just always been a revered species by people, going back hundreds and hundreds of years,” mentioned longtime authorities polar bear researcher Steve Amstrup, now chief scientist for Polar Bear International. “There’s just something special 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 in 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 Environment Program head Inger Andersen used to guide the International Union for the Conservation of Nature, which screens and classifies species in bother. She asks: “Do we really want to be the generation that saw the end of the ability of something as majestic as the polar bear to survive?”
The state of sea ice
Arctic sea ice — frozen ocean water — shrinks through the summer time 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 general, as a result of the ice is weaker first-year ice.
Julienne Stroeve, a University of Manitoba researcher, says summers with out sea ice are inevitable. Many different specialists agree along with her.
Former NASA chief scientist Waleed Abdalati, now a high University of Colorado environmental researcher, is one in every of them.
“That’s something human civilization has never known,” Abdalati mentioned. “That’s like taking a sledgehammer to the climate system and doing something huge 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 time 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 “look like a blue ocean,” mentioned Mark Serreze, director of the National Snow and Ice Data Center.
Maybe as early because the 2030s, most probably within the 2040s and virtually assuredly by the 2050s, specialists say.
The Arctic has been warming twice as quick as the remainder of the world. In some seasons, it has warmed 3 times sooner than the remainder of the globe, mentioned University of Alaska at Fairbanks scientist John Walsh.
That’s due to one thing known as “Arctic amplification.” Essentially, white ice within the Arctic displays warmth. When it melts, the darkish sea absorbs far more warmth, which warms the oceans much more rapidly, scientists say.
The polar bear connection
There are 19 totally different subpopulations of polar bears within the Arctic. Each is a bit totally different. Some are actually in bother, particularly the southernmost ones, whereas others are fairly near steady. But their survival from place to position is linked closely to sea ice.
“As you go to the Arctic and see what’s happening with your own eyes … it’s depressing,” mentioned University of Washington marine biologist Kristin Laidre, who has studied polar bears in Baffin Bay.
Shrinking sea ice means shrinking polar bears, actually.
In {the summertime}, polar bears exit on the ice to hunt and eat, feasting and placing on weight to maintain them by way of the winter. They desire areas which can be greater than half coated with ice as a result of it’s the best looking and feeding grounds, Amstrup mentioned. The extra ice, the extra they’ll transfer round and the extra they’ll eat.
Just 30 or 40 years in the past, the bears feasted on a buffet of seals and walrus on the ice.
In the Nineteen Eighties, “the males were huge, females were reproducing regularly and cubs were surviving well,” Amstrup mentioned. “The population looked good.”
With ice loss, the bears haven’t been doing as properly, Amstrup mentioned. 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 often near land.
“When sea ice is present over those near-shore waters, polar bears can make hay,” Amstrup mentioned.
But lately the ocean ice has retreated far offshore in most summers. That has pressured the bears to float on the ice into deep waters — generally practically a mile deep — which can be devoid of their prey, Amstrup mentioned.
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 you’re in very unproductive waters,” Amstrup mentioned.
Further south within the Chukchi, it’s shallower, which permits bottom-feeding walruses to thrive. That gives meals for polar bears, he mentioned.
“The bears in the Chukchi seem to be faring pretty well because of that additional productivity,” Amstrup mentioned. But the bears of the Beaufort “give us a real good early warning of where this is all coming to.”
The future
Even as world leaders meet in Scotland to attempt to ratchet up the hassle 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 every thing seems good, that the world will as soon as once more see an Arctic with important sea ice in the summertime late this century and within the twenty second century, specialists mentioned. But till then “that door has been closed,” mentioned 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’re able to do the work to create much, much lower emissions” of heat-trapping gases, Moon mentioned. “Sea ice is one of those things that we’ll see reach some pretty devastating lows along that path. And we can already see those influences for polar bears.”