The image of a lonely polar bear floating on a tiny fragment of sea ice has become synonymous with the effects of climate change but now scientists have been able to quantify just how bad the issue of sea ice decline is for one of the planet’s most iconic species.
The researchers, based at Canada’s University of Toronto, Scarborough, studied a group of polar bears living in Canada’s Hudson Bay, taking over forty years’ of data and creating a bioenergetic model that reveals how sea ice loss is affecting the creatures. The bear population has declined by a massive 50% since the mid-1990s, falling from around 1,200 to just 600 individuals, they found.
Without sea ice platforms, seals outswim the bears
Published in Science journal, the results show that the reason the sea ice is so crucial to the bears’ survival is that it provides them with help in catching seals for food, acting as a platform. When polar bears try instead to hunt seals in open water, they have far less success in obtaining a meal, because the agile seals can simply outswim the large predators.
“If a bear tries to catch a seal in open water, the seal will outswim the bear pretty much every single time,” senior author and associate professor Péter Molnár said.
Bears who forage berries might as well eat nothing
With sea ice melting earlier in the spring and forming later in the winter due to the planet’s rising surface temperature, there is less sea ice available for polar bears to hunt on. That means polar bears are spending more time on land and three to four fewer weeks on sea ice than four decades ago. On land, they are forced to forage for berries or birds, but this intake, the scientists say, is an inefficient energy source. Bears who rely on foraging lose the same amount of energy as bears who simply eat nothing.
Polar bears are the largest bears. They’re enormous. They require a high-fat, high-energy diet.
Péter Molnár, Associate Professor at the University of Toronto
Mothers and cubs are among the worst affected by the shortened feeding season. Unable to feed as much on the blubber-rich seals, they struggle to produce enough milk for their cubs – one of the drivers for the dramatic drop in the polar bear population.
“They’re really tightly linked to the sea ice,” lead author Louise Archer said. “Their whole lifestyle depends on it.”
We need to act now
Worse, the scientists say the bears are merely a “bellwether” for the loss of an entire ecosystem driven by fossil-fuel-induced global warming. The lack of sea ice means algae is being lost and the seal population itself is affected too, as seals are dependent on the ice for a place to give birth.
The scientists warn that southern Arctic polar bear populations could disappear altogether if the current rate of greenhouse gas emissions and global warming continues, but they did offer a note of hope. “We, as a society, still have a chance to turn things around,” Molnár said. “But in order to do that, we need to act now and not decades from now.”
