Polar bears are having a rough time, according to research conducted by researchers at the University of Wyoming and the U.S. Geological Survey and published Tuesday.
The Arctic ice — on which polar bears hunt, sleep, play and raise their young — can be thought of as a treadmill. Currents and winds carry the ice westward, so polar bears wishing to remain in the same region must continually walk east, said Merav Ben-David, UW professor of zoology and physiology.
“They have to walk in order to remain in Alaska,” Ben-David said. “If they didn’t move, they would be drifting with the ice all the way to Russia, but we see that polar bears show high fidelity to (the) Alaskan coast.”
Climate change has accelerated the speed at which polar bears must walk east to remain in place and subsequently increases the amount they must hunt, according to the study, which was published in the journal Global Change Biology.
It is widely known the build-up of greenhouse gases in Earth’s atmosphere has, by warming the globe, reduced the extent of sea ice in the Arctic, Ben-David said. But climate change has also reduced the thickness of the ice and has actually diminished thickness more than extent.
“The ice — because it’s lighter and thinner and more broken — drifts now faster than it did when we started the satellite record in the eighties and nineties,” she said.
The team of researchers wondered if the increased pace of westward ice drift would be matched by an increased eastward pace of polar bear movement.
Shannon Albeke, ecoinformaticist and associate research scientist for the Wyoming Geographic Information Science Center, combined 77,000 data points, representing polar bear locations and movements, with information on ice drifts gathered from satellite imagery.
Ben-David and her fellow researchers found polar bears were working harder just to stay in place.
“We found that, indeed, polar bears have to move more — either walk faster or travel many more hours a day — to compensate for the higher drift,” Ben-David said. “Then what we did is calculate the energetic consequences and found that there was — as one would expect — an increase in the energy expenditure by polar bears and that translated into a need to hunt more seals.”
These climate change effects are a double whammy for the polar bears. It now takes more energy to stay in place. And to get that additional energy, bears must spend more time hunting. But they also need more time for walking. The result is a rougher, hungrier life for the Arctic’s bears.
The problem is further compounded by the decrease in the extent of Arctic ice.
With less ice to walk on, polar bears spend more time swimming to get where they are going. Swimming is more expensive, energy-wise, than walking, so this adds to the amount of time polar bears must spend hunting.
“Polar bears are ambush hunters, meaning they sit next to a breathing hole and wait for the seal to come up,” Ben-David said. “So, not only do they need to hunt more seals, they have less time to do that. So, most likely, their hunting success is lower because of this increased ice drift.”
According to the World Wildlife Fund, the world’s 22,000-31,000 polar bears spend roughly 50 percent of their time hunting. They must catch one to two of every 10 seals they try to hunt to stay alive.
Ben-David said the only way to save polar bears was by combating climate change. The government might have pulled out of the Paris climate agreement, but the American people should not, she said.
“We need to curb greenhouse gases,” Ben-David said. “That’s the only thing we can do. There are no other magic solutions to maintain polar bear populations. We just need to make sure that we can reverse the ice loss in the Arctic.”
Fortunately for polar bears and the people who care about them, Arctic ice loss is reversible, unlike so many other environmental disasters, Ben-David said. The ice over the Arctic Ocean experiences seasonal changes. It melts in the summer and refreezes in the winter. This seasonal instability in the Arctic ecosystem means that it has no stable state and is therefore more easily altered.
“It is a system that can be reversed,” Ben-David said. “There are many ecological systems that cannot be reversed once they change to a new stable state.”
But reversing the damaging effects of climate change requires immediate action, Ben-David said.
“If we get our act together and start reversing the trend, we will be able to save polar bears,” she said.