Image copyright
Katharina M Miller
Sea ice is declining in the Arctic in both thickness and extent
Polar bears will be phased out by the end of the century unless more is done to combat climate change, a study predicts.
Scientists say some populations have already reached their survival limits as the Arctic sea ice shrinks.
Carnivores depend on sea ice from the Arctic Ocean to hunt seals.
As the ice breaks, animals are forced to roam long distances or toward the shore, where they struggle to find food and feed their cubs.
The bear has become the “son of the climate change poster,” said Dr. Peter Molnar of the University of Toronto in Ontario, Canada.
“Polar bears are already sitting on top of the world; if the ice goes, they have nowhere to go,” he said.
Polar bears are classified as vulnerable to extinction by the International Union for Conservation of Nature (IUCN), with climate change as a key factor in their decline.
Image copyright
International Polar Bear
Female polar bears need to store enough fat to feed their cubs
Studies show that decreasing sea ice is likely to decrease the number of polar bears, perhaps substantially. The new study, published in Nature Climate Change, sets a timeline for when that might happen.
By modeling the energy use of polar bears, the researchers were able to calculate their endurance limits.
Dr. Steven Amstrup, chief scientist at Polar Bears International, who was also involved in the study, told BBC News: “What we have shown is that, first, we will lose the survival of the cubs, so the cubs will be born but the females will not have enough body fat to produce milk to carry them through the ice-free season.
“Any one of us knows that we can only go without food for so long,” he added, “that’s a biological reality for all species.”
Image copyright
BJ Kirschhoffer
Polar bears rely on sea ice to catch prey
The researchers were also able to predict when these thresholds will be reached in different parts of the Arctic. This may have already happened in some areas where polar bears live, they said.
“Showing how imminent the threat is to different polar bear populations is another reminder that we must act now to avoid the worst of future problems we all face,” said Dr. Amstrup.
“The path we are on now is not a good one, but if society acts together, we have time to save polar bears. And if we do, we will benefit the rest of life on Earth, including ourselves.”
In a scenario of high greenhouse gas emissions, all but a few polar bear populations are likely to collapse by 2100, according to the study. And even if the moderate emission reduction targets are met, several populations will disappear.
The findings coincide with previous projections that polar bears are likely to persist until 2100 in only a few populations far north if climate change continues unabated.
Image copyright
International polar bears
Sea ice is frozen seawater that floats on the ocean surface, forming and melting with the polar seasons. Some persist year after year in the Arctic, providing vital wildlife habitat, such as polar bears, seals, and walruses.
Sea ice that remains in the Arctic for more than a year has decreased at a rate of about 13% per decade since satellite records began in the late 1970s.
Follow Helen on Twitter.
Follow Victoria on Twitter.
