Melting Sea Ice And Starvation Could Push Polar Bears To Extinction By 2100

Without ice, polar bears' fat stores fall too low to support cubs or even survive. Bogorodskiy/Shutterstock

Experts warn we could be closer than we realize to losing polar bears as rising temperatures and melting sea ice drive them onto land where food sources for these voracious predators are scarce. Starvation in adults has a catastrophic impact on the survival rates of future generations of bears, as mothers are scarcely able to stay alive or produce sufficient fatty milk for their cubs. New research published in Nature Climate Change predicts that without intervention populations could disappear completely by 2100 and so scientists are making a push for greater efforts to rapidly curb carbon emissions or else this species will be lost to the history books.

A polar bear’s favorite meal is seals, whose insulating blubber serves as a much-needed source of fat to keep the bears themselves well-fed and better able to cope with the icy conditions of the Arctic. However, in order to hunt for seals, polar bears need ice to keep themselves hidden while they close in on a seal.

In recent years, Arctic sea ice has been melting at an unprecedented rate due to warming temperatures as a result of climate change. The knock-on effect for polar bears is that they’re forced back onto the land where there’s not much for a bear to eat. The longer they go without food, the lower their fat supplies fall until they cross a threshold where adults can barely support themselves, let alone any cubs. This threshold has already been crossed in several subpopulations where cub numbers have fallen dramatically as a result.

Polar bear cubs are reliant on a supply of fatty milk from their mother if they're to survive long enough to begin hunting for themselves. AndreAnita/Shutterstock

To arrive at their estimates, lead researcher Péter Molnár and colleagues used dynamic energy budget models to establish the energy needs of fasting polar bears and at what stage starvation would likely lead to the death of their cubs and eventually the bears themselves. This information was combined with an Earth Systems Model that uses previous data to predict the number of future ice-free days in this region. The findings showed that thresholds would be surpassed for 13 subpopulations of polar bears, representing 80 percent of their entire population. The researchers estimate that this could lead to the end of the species by the turn of the century.

It’s not all bad news however, as when the model was run again in a moderate emissions scenario (RCP4.5), more subpopulations were able to survive, showing hope for the species beyond 2100. While shocking, the researchers note that the models are limited in their capacity to make predictions as adequate energy budget data wasn’t available for several subpopulations of polar bears. But the results emphasize the desperate need for urgent action on climate change in order to halt sea ice melting before it drives these creatures beyond a threshold from which they can’t return.

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