Most polar bears could disappear from Arctic by 2100 due to global warming, study says

Most of the Arctic's polar bear population will struggle to survive by 2100 due to melting sea ice, a new study claims.

A loss of the ice caused by global warming will force the animals on to land, where they must rely on fat reserves due to a lack of food, researchers from the University of Toronto in Canada said.

The study, published in Nature Climate Change, said "aggressive" cuts to greenhouse gas emissions are needed now to save the animals from extinction as they rely on the ice, which forms above the open waters, to reach their prey.

Modelling was used to determine a polar bear's energy requirements while fasting and the thresholds that would limit their survival, alongside a model predicting the future number of days without ice.

The researchers used this to then estimate when the survival thresholds would be surpassed for 13 Arctic sub-populations that represent 80% of all polar bears.

Under a high greenhouse gas emissions scenario, the researchers found the bears' survival would be "unlikely" in much of the Arctic due to reduced sea ice.

But if there was a "moderate emissions scenario" more sub-populations could survive this century.

"Ultimately, aggressive greenhouse gas emissions mitigation will be required to save polar bears from extinction," the study said.

Cubs would be most at risk from fasting, while solitary adult females would be the least affected, researchers found.

They also found survival thresholds may have already been reached in several polar bear sub-populations.

"Our model captures demographic trends observed during 1979 to 2016, showing that recruitment and survival impact thresholds may already have been exceeded in some (polar bear) sub-populations," study author Peter Molnar and his colleagues said.

"It also suggests that, with high greenhouse gas emissions, steeply declining reproduction and survival will jeopardise the persistence of all but a few high-Arctic sub-populations by 2100."

The authors said their study was limited by the use of a single "earth systems model", which is used to determine how sea ice will be affected, and because of uncertainties and variations in bear behaviour and energy usage among different sub-populations.

Most polar bears live north of the Arctic Circle in the North Pole but there are some populations south of the Arctic Circle in Hudson Bay, Canada.