Polar bears in southern Hudson Bay could go extinct as early as the 2030s because the sea ice that helps them forage for food is thinning, a new study suggests.
“We already knew that the loss of Arctic sea ice would spell disaster for polar bears, so this could be the first subpopulation to disappear,” said Julian Stroeve, lead author of the study, which was published Thursday in the journal Science. Communications Earth and Environment.
Last month, the eastern half of Hudson Bay, home to the world’s most studied polar bears, No ice A month earlier than usual.
Polar bears are accustomed to an ice-free season of about four months, during which they rely on their fat reserves until the ice forms again and they can hunt blubber-rich seals from the pack ice. But the presence of sea ice does not guarantee that polar bears can hunt; the ice must be thick enough to support them.
although Early research To study sea ice coverage to determine the species’ ability to survive, Dr. Stroeve and her colleagues used climate models from the Intergovernmental Panel on Climate Change. Latest Report Predict when the remaining ice will become too thin for bears to hunt successfully.
While there is no consensus on how much ice is needed to support an adult male polar bear, this study relied on field studies to establish a baseline of about 10 centimeters (just under 4 inches).
Polar bears are good at making do with minimal resources on the ice. They crawl. They swing their bodies on their bellies. They stretch their limbs as far as they can to distribute their weight more evenly across the ice. Sometimes they still fall through. This isn’t usually a problem for polar bears, who are good swimmers, but it can be a problem if they’re preying on seals. Breaking the ice acts as an alarm, alerting the seals to the presence of a predator.
Polar bears need thick ice to run fast and catch seals, said Geoffrey York, senior director of research and policy at the Polar Bear Institute and co-author of the study. Sea ice is high in salt and more plastic and elastic than glassy freshwater ice. But other experts say 10 centimeters is excessive.
“We always try to find a metric that works,” said Andrew Derocher, a professor of biological sciences at the University of Alberta. “But 10 centimeters is too thin. I can’t land a helicopter on that ice. It needs to be about twice as thick for a polar bear to actually use it.”
Elisabeth Kruger, Arctic manager for the World Wildlife Fund, said the models were not predicting as much warming in the Arctic as had been thought. “It’s actually pretty daunting,” she said.
The ice-free season is now about a month longer than the one polar bears are accustomed to. research shows When there is no ice Extended to six monthseven the hardiest Hudson Bay bears, generally healthy adult males, struggle to survive.
Polar bears are so-called indicator species, meaning they can predict the health and viability of the entire Arctic ecosystem. The loss of sea ice and reduced snow cover has severely impacted their preferred food, ringed seals, which have a hard time raising their pups in their maternity dens if snow levels fall below 32 centimeters.
Last year, global temperatures temporarily reached 1.5 degrees Celsius above pre-industrial levelsUnder the Paris climate agreement, countries agreed to work to limit global warming to that level or below to avoid the worst impacts of global warming. While the temperature rise is not permanent, Dr. Stroeve and other scientists say polar bears in the region will not be able to survive if temperatures rise by 2.1 degrees Celsius above pre-industrial benchmarks.
Today, there are approximately Polar bear population halved The situation in western Hudson Bay remains the same as it was in 1987.
“Our best analysis is that polar bears will still be around until the end of the century,” Dr. Desrocher said, referring to the 19 subpopulations that live in the Arctic. “But in Hudson Bay, that’s unlikely to happen.”
Hudson Bay bears are unlikely to leave their range, even if conditions become untenable. At some point, First Nations and Inuit communities may have to change their traditional polar bear hunting practices to protect bear numbers. Towns may have to find ways to discourage bears from seeking human food during times of distress to minimize human-bear conflict. Long-term possibilities could include distributing polar bear feed, but Dr. DeRocher said that approach is unlikely to sustain a subpopulation indefinitely.
“There are no viable alternatives to tackling greenhouse gas emissions to manage populations in the long term,” Dr Desrocher said.
