“The bears face an increasingly long period of fasting before the ice sets in and they can return to feed,” Steven Amstrup, who designed the study and is chief scientist, told AFP. by Polar Bears International.Based on current trends, the study concluded that polar bears in 12 of the 13 subpopulations analyzed will have been wiped out within 80 years by the rapid pace of change in the Arctic, which is like the planet as a whole.
“By 2100, recruitment” – new births – “will be severely compromised or impossible anywhere except perhaps in the Queen Elizabeth Island subpopulation,” in Canada’s Arctic Archipelago, Amstrup said.
This scenario predicts an increase in the average Earth’s surface temperature of 3.3 degrees Celsius above the pre-industrial baseline. So far, a degree of warming has triggered a crescendo of heatwaves, droughts and super-storms made more destructive by rising seas.
But even if humanity were able to cap global warming at 2.4 degrees Celsius – about half a degree above the Paris Agreement targets, but extremely ambitious nonetheless – it would likely only delay. the collapse of the polar bears.
“The Arctic is warming at 3 times the global average due to man-made climate change … and as a result, the arctic landscape is changing at a tremendous rate,” said meteorologist and climate specialist from CBS News Jeff Berardelli. “We are running out of time to limit the damage caused by climate change. There is no doubt that we will lose vital species forever. The question is how much are we willing to sacrifice? It will depend on how quickly and boldly we act to limit climate change and habitat destruction. ”
The threat is not rising temperatures per se, but the inability of predators at the top of the food chain to adapt to a rapidly changing environment.
“If somehow, by magic, the sea ice could be maintained even as temperatures rise, the polar bears might be fine,” Amstrup said by email.
“The problem is, their habitat is literally melting. ”
Half of Earth’s terrestrial megafauna is listed as endangered, but only polar bears are primarily threatened by.
But this status may not be unique for long, and should be seen as a harbinger of the impact of climate on other animals in the coming decades, the authors warned.
About 25,000 Urus maritimus remain in the wild today.
The challenge of their survival has long been understood, but the new study – building on Amstrup’s pioneering work ten years ago – is the first to establish a timeline for their likely demise.
The new approach covers two sets of data.
One is the expanding fasting period, which varies from region to region and can last six months or more.
The other is a pair of climate change projections that follow the decline of sea ice through the turn of the century, based on scenarios from the UN’s IPCC Climate Science Advisory Committee.
“By estimating the thinness and fat of polar bears, and modeling their energy consumption, we were able to calculate the threshold number of days that polar bears can fast before pup and adult survival rates begin. to drop, ”said lead author Peter Molnar. , professor at the University of Toronto.
A male bear, for example, in the Western Hudson Bay population whose body weight is 20% less than its normal body weight at the onset of the fast, will only have enough stored energy to survive. about 125 days instead of 200 days.
Newborn cubs are even more at risk, according to the study, especially when mothers have not gained enough weight to provide nourishing milk.
Females without offspring, however, have the greatest ability to endure long periods without food.
The “vulnerable” status of the polar bear on the IUCN Red List of Endangered Species – less serious than “endangered” or “critically endangered” – does not accurately reflect their plight, say the authors.
The categories established by the International Union for the Conservation of Nature are primarily based on threats such as poaching and habitat encroachment that can be addressed through local action on the ground.
“But we can’t build a fence to protect sea ice from rising temperatures,” Amstrup said.