Polar bears could become extinct by the end of the century because of melting sea ice unless more is done to tackle climate change, a study claims.
The study, published in Nature Climate Change, shows how declining sea ice caused by global warming is drastically decreasing polar bear numbers.
It is the first time scientists have predicted for the first time when, where and how polar bears are likely to become extinct.
“It’s been clear for some time that polar bears are going to suffer under climate change,” said Peter Molnar, a biologist at the University of Toronto Scarborough and lead author of the study.
“But what was not fully clear was when we would expect major declines in the survival and reproduction of polar bears that could ultimately lead to their extirpation.
"We didn’t know whether that would happen early or later in this century.”
The animals, which are already considered to be endangered, need the ice to catch seals for food because they are not sufficiently skilled as swimmers to capture them in open water.
"Ultimately, the bears need food and in order to have food, they need ice," Mr Molnar said.
"But in order for them to have ice, we need to control climate change."
Models were used to determine the bears’ energy needs while fasting and thresholds that would make survival difficult, as well as one predicting the future number of days without ice.
The data was then used to estimate when survival thresholds would be passed for 13 Arctic sub-populations that represent 80 per cent of polar bears.
Researchers said that if humans failed to reduce greenhouse gas emissions, most populations of the species could struggle to survive beyond 2100.
They said many of the polar bears would begin to experience reproductive failure, leading to local extinctions as early as 2040.
Scientists estimate there are fewer than 26,000 polar bears left in the world, in regions such as Hudson Bay in north-east Canada and the Svalbard Archipelago in Norway.
But Mr Molnar said there was a chance that some could be saved with “aggressive” cuts to greenhouse gas emissions.
"I'm well aware that the story we're telling is a grim one," Mr Molnar said.
"But there is also an element of hope that they are not completely doomed if we change our behaviour."
Last year was one of the worst years on record for Greenland’s ice sheet, which shrank by hundreds of billions of tonnes in a high-pressure environment brought on by unusually clear skies and warmer temperatures, a study found in April.
The ice sheet, the second largest in the Arctic, lost about 600 million tonnes last year.