Sometimes I wonder how the polar bear became the poster animal for climate change. These are ferocious beasts—they’ve even be known to engage in a little cannibalism when food gets tight. They’re far from the only animals that may be suffering because of climate change—just ask the Panamanian golden frog—and few of us will ever meet one outside the Arctic exhibit at the local zoo.
But those little white cubs are just so cute.
Of course, the real reason that polar bears have become a symbol of climate change is that they live among the Arctic sea ice—and the rapid melting of that ice is one of the clearest effects of the planet’s warming over the past several decades. Lose the sea ice, and the polar bears lose their habitat. It’s as simple as that. Polar bears can swim, but they can’t swim forever.
Now scientists have come out with a study that confirms the deadly effect retreating sea ice can have on the polar bear. A team of researchers led by Anthony Pagano of the U.S. Geological Survey found that polar bear cubs who were forced to swim longer distances because of melting sea ice had higher rates of mortality than those cubs who did not need to take long swims. The study, presented today at the International Bear Association Conference in Ottawa, is the first to identify a multi-year trend in increased long-distance swimming for polar bears—earlier work had only reported on the occasional marathon swim. As co-author Geoff York of the World Wildlife Fund told Reuters:
Climate change is pulling the sea ice out from under polar bears’ feet, forcing some to swim longer distances to find food and habitat.
Between 2004 and 2009 Pagano and his co-authors data from 68 GPS collars placed on adult female bears and combined that with satellite imagery of the changing ice, which allowed them to identify when bears needed to swim more than 30 miles at a time. During those years they found 50 long-distance swimming events, with one swim as long as 426 miles and lasting as long as 12.7 days.
Those long-distance swims took a toll on cubs accompanying the mothers, in part because young polar bears don’t have much fat and can’t cope with being in the cold water for long periods of time. Cubs forced to swim suffered a 45% mortality rate during the years of the study, while only 18% of the cubs not forced to make long swims died.
With Arctic sea ice at its lowest extent this past June since satellite records began in 1979—and sea ice volume down 47% from that year—the future does not look very good for polar bears. Which means—among other things—we may need to find a new poster animal for climate change, something that really grabs out attention. Perhaps human beings.