Scientists have first predicted when, where, and how polar bears are likely to disappear, warning that if greenhouse gas emissions remain on their current trajectory, all but a few polar bear populations in the Arctic will likely they will disappear by the year 2100.
As early as 2040, it is highly likely that many polar bears will begin to experience reproductive failure, leading to local extinctions, according to a study published in Nature Climate Change.
The study examines how bears will be affected in two different greenhouse gas emission scenarios. The researchers found that, in an emissions scenario as usual, polar bears will likely only remain in the Queen Elizabeth Islands, the northernmost group in Canada’s Arctic archipelago, at the turn of the century. And even if greenhouse gases are moderately mitigated, the majority of polar bear populations in the Arctic are likely to experience reproductive failure by 2080.
Scientists estimate that fewer than 26,000 polar bears remain, spread across 19 different subpopulations ranging from the ice landscapes of Svalbard, Norway, to the Hudson Bay in Canada and the Chukchi Sea between Alaska and Siberia. Polar bears cannot find enough livelihood on land and depend on sea ice to hunt. They often rethink the seal’s breathing holes in the ice, waiting hours for a fatty meal to surface. But as sea ice declines due to climate change, so will polar bears.
“It has been clear for some time that polar bears will suffer under climate change,” said Péter Molnár, a biologist at the University of Toronto Scarborough, and lead author of the study. “But what was not entirely clear was when we would expect large declines in the survival and reproduction of polar bears that could lead to their removal.” We didn’t know if that would happen earlier or later in this century. “
Polar bears draw on the energy reserves accumulated during the winter hunting season to spend the summer months on land or the time they spend on ice in unproductive waters. Although bears are used to fasting for months, their body condition, reproductive capacity, and survival will eventually decrease if they are forced to go too long without eating. In the Beaufort Sea population of southern Alaska, biologists have already seen the number of polar bears drop from 25 to 50% during periods of low ice, when bears have been forced to fast for too long. And in western Hudson Bay, one of the southernmost polar bear habitats, the population has declined approximately 30% since 1987.
To determine when the bears could reach their critical physiological limit, Molnár and his colleagues estimated how lean and fat polar bears can be and modeled the animals’ energy use to obtain the threshold number of days they can fast before their declines decrease. pup and adult survival rates. They then combined those thresholds with the projected number of future sea ice-free days to determine how populations in different parts of the Arctic will be affected.
“Even if we mitigate emissions, we will still see that some subpopulations will die out before the end of the century,” said Molnár. This includes polar bears in the southernmost and vulnerable ice areas of western Hudson Bay, the Davis Strait, and southern Hudson Bay. “But we would have substantially more populations that would persist by the end of the century, even with reduced reproduction, compared to a business broadcast scenario.”
The study examined 13 of the world’s 19 polar bear subpopulations, representing 80% of the species’ total population. Bears inhabiting an area known as the Archipelago ecoregion in the Canadian Arctic were not included as the geography of the area (islands and narrow channels) made it too difficult to predict the future extent of the ice.
Of those populations studied, polar bears in southern Hudson Bay and the Davis Strait in Canada are “very likely” to experience reproductive failure by 2040 in an unmitigated emissions scenario. Polar bears across much of Alaska and Russia will be in serious trouble by 2080. And by 2100, it is inevitable that these populations will experience reproductive failure, leading to extinction if countries do not dramatically reduce heat-trapping gas emissions. .
“It is important to note that these projections are probably conservative,” said Steven Amstrup, chief scientist at Polar Bears International and co-author of the study. The models, he explained, can assume a better body condition than the reality of bears at the beginning of fasting periods. And the team used a cautious benchmark estimate of how much energy a bear uses to maintain its body condition. “The impacts we project are likely to occur more quickly than the document suggests.”
Unlike other species threatened by hunting or deforestation, polar bears can only be saved if their habitat is protected, which requires addressing global climate change. Previous research has shown that even if we reduce greenhouse gas emissions tomorrow, it will still take another 25 to 30 years for the extent of sea ice to stabilize due to all the carbon dioxide already in the atmosphere. It is important for the public to understand the urgency of the problem, Amstrup said. But a timeline for possible extirpation was also an important tool for managers of northern communities living alongside polar bears.
“It shows where we would expect to see further conflict between humans and bears,” said Andrew Derocher, a biology professor at the University of Alberta who runs the Polar Bear Science Laboratory and is not affiliated with the study. Not all Arctic communities have programs to deal with more polar bears in their localities. And there is a moral question of whether humans should help struggling bears.
“With something like polar bears, where you’re not going to regain their habitat, it’s not clear if we’re going to try to keep these populations everywhere. If we start to see a large number of bears on earth dying of hunger, what kind of interventions would we enter?
Derocher said polar bear managers needed to determine whether they would provide supplemental food for the bears or relocate them to regions that still had ice.
“You look at the consequences of a video of a hungry bear. Well, imagine going to Churchill, Manitoba, a polar bear tourism hub, and seeing 50 bears walking like this. The public outcry will be intense and managers need to think about what their policies will be now. ”
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