Climate change is starving polar bears into extinction, according to research published Monday that predicts the apex carnivores could all but disappear within the span of a human lifetime. In some regions they are already caught in a vicious downward spiral, with shrinking sea ice cutting short the time bears have for hunting seals, scientists reported in Nature Climate Change.
Their dwindling body weight undermines their chances of surviving Arctic winters without food, the scientists added.
"The bears face an ever longer fasting period before the ice refreezes and they can head back out to feed," Steven Amstrup, who conceived the study and is chief scientist of Polar Bears International, told AFP.
On current trends, the study concluded, polar bears in 12 of 13 subpopulations analyzed will have been decimated within 80 years by the galloping pace of change in the Arctic, which is warming three times as fast as the planet as a whole.
"By 2100, recruitment" — new births — "will be severely compromised or impossible everywhere except perhaps in the Queen Elizabeth Island subpopulation," in Canada's Arctic Archipelago, said Amstrup.
That scenario foresees Earth's average surface temperature rising 3.3 degrees Celsius above the preindustrial benchmark. One degree of warming so far has triggered a crescendo of heatwaves, droughts and superstorms 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 Paris Agreement targets, but hugely ambitious all the same — it would probably only delay the polar bears' collapse.
The threat is not rising temperatures per se but the top-of-the-food-chain predators' inability to adapt to a rapidly shifting environment.
Half of Earth's land-based megafauna are classified as threatened with extinction, but only polar bears are endangered primarily by climate change.
But that status may not be unique for long, and should be seen as a harbinger of how climate will impact other animals in the coming decades, the authors warned.
The polar bear's "vulnerable" status on the IUCN Red List of endangered species — less severe than "endangered" or "critically endangered" — does not accurately reflect their plight, the authors argue.
Categories established by the International Union for the Conservation of Nature are based mainly on threats such as poaching and habitat encroachment that can be addressed with local action on the ground.
"But we cannot build a fence to protect sea ice from rising temperatures," said Amstrup.