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The scientists assessed the risk of extinction of polar bears because of global warming

Scientists found out that by 2100 most subpopulations of polar bears in the Arctic are under threat of extinction due to reduction of sea ice caused by global warming. The study is published in the journal Nature Climate Change.

Polar bears Ursus maritimus species use sea ice to hunt with him on seals. In the summer, during the melting of coastal ice animals move on land where they have virtually no food and are funded by accumulated fat. Since the warm season in the Arctic lengthened, and the area of sea ice decreases in response to warming, polar bears each year have to be on the mainland more and more time

Canadian and American scientists under the direction of Peter Molnar (Péter Molnár) from the University of Toronto have built the model changes in the ice cover of the Arctic seas over the period 1979 to 2016 and calculated thresholds of the duration of the summer fasting of polar bears, in days, after which dramatically increases the risk of reducing animal numbers due to the decrease in the survival of pups and adults.

The researchers broke the population of white polar bears in the 19 subpopulations, grouped into four Ecoregion. In the southern Ecoregion seasonal ice covering the North-East coast of Canada and West coast of Greenland, where the summer before was no ice, the bears are accustomed to wait for warm season on the coast, vykarmlivaya young and saving energy.

In other regions polar bears and the summer is traditionally used ice floes to hunt with them. Now, here along the Arctic coasts of Russia, Greenland and Alaska — in the summer the ice is virtually absent, and bears from these subpopulations have been particularly vulnerable.

It is known that polar bears can go without food for quite a long time, but a specific threshold was until recently unknown. Now scientists have determined them for each Ecoregion separately, using a model of dynamic energy balance based on the determination of the animal's needs in energy in various dynamic modes.

The results obtained, the authors combined data from the climate models, which predict the number of days without ice in subsequent years.

It turned out that by 2100, the threshold value is exceeded for 13 subpopulations that represent about 80 percent of all polar bears. According to researchers, the greatest risk due to prolonged fasting could be the cubs, and the smallest single adult females.

The authors assessed the risk of extinction of polar bears for two different climate scenarios. The results showed that under the scenarios RCP8.5. with high level of greenhouse gas emissions by 2100 will disappear virtually all polar bears in the Arctic and scenario RCP4.5, which provides a moderate level of emissions, part of the subpopulations will be able to keep.

Scientists rule out possibility of adaptation of polar bears to life on land. As an example, they cite the cold period of the late Pleistocene, when polar bears live throughout the ice-covered Baltic sea, and when after Holocene warming, the eternal ice retreated, the animals just disappeared from the region.

According to the researchers, their findings should be another incentive for the adoption of measures to combat global warming.