As climate change causes the retreat of glaciers and ice sheets, the population of polar bears could drop by 30 percent, experts warn.

The recently released assessment by the International Union for Conservation of Nature, confirmed that polar bears are included in the 2015 Red List of Threatened Species. This means that the changes posed by global warming have detrimental effects on the survival of one of the largest bears in the world.

The assessment predicts that the current population estimate of 26,000 polar bears would decrease by 30 percent in the next 35 years. With the current data gathered by the agency, the reassessment placed polar bears as 'vulnerable' species. This category is just a step away from being 'endangered'.

"There is a high risk of extinction and the threat is serious," Dena Cator of the IUCN's species survival commission said.

"You could consider polar bears to be a canary in the coal mine. They are an iconic and beautiful species that is extremely important to indigenous communities. But changes to their sea ice habitat are already being seen as a result of climate change," she added.

On Sept. 11, 2015, the Arctic sea ice has reached its fourth lowest extent in a satellite record.Experts estimated sea ice at 1.70 million square miles, the fourth lowest extent recorded. With an annual decline in glaciers, polar bears would have a difficult time hunting for food.

These bears rely much on sea ice for food hunting. The retreating ice sheets and emergence of ice-free land for a longer time would force them to fast longer than usual. Starvation could pose detrimental health effects to bears and their reproductive ability is also affected.

Female polar bears usually enter dens near sea ice in preparation for birth. They could fast for up to eight months during pregnancy until their cubs are born, which is the longest period of food deprivation for any mammal. However, with the trend of retreating sea ice, they can't feed much as hunting becomes a daunting task.

Polar bear cubs are at most risk of death in the first year of their life, because the probability of cub survival is largely determined by maternal condition. Mother polar bears with more fat stored are more likely to have bigger and healthier cubs. Thus, cub mortality is also affected by climate change as polar bears starve longer than usual due to longer ice-free season.

Polar bears are not the only species threatened by drastic changes in the environment. The updated Red List spans to about 79,837 assessed species wherein 23,250 are threatened with extinction.

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