Record low May sea ice rings alarm bells for Canada's Hudson Bay polar bears

By Gloria Dickie

(Reuters) - The extent of sea ice covering Canada's Hudson Bay hit a record low for May, intensifying concern on the fate of the some 4,000 polar bears that live there, as new research adds to a growing scientific consensus that the region's bears are on track to disappear within decades.

Three of the world's remaining 19 polar bear populations live in and around Canada's vast Hudson Bay, which connects to the Arctic and Atlantic oceans.

The region is unique compared to the Arctic as the Bay thaws out entirely in summer, forcing bears to come ashore while they wait for the ice to return. The bears do not eat during this time, as they need sea ice to hunt seals.

While the Bay normally remains covered in ice in May, this year the eastern portion of Hudson Bay opened up, the National Snow and Ice Data Service said, as strong winds shifted ice westward. This led Hudson Bay to register its lowest extent of ice for May in the satellite record dating back to 1979, at 205,000 square kilometres (79,000 square miles) below average.

"It's a very unusual situation," said polar bear biologist Andrew Derocher of the University of Alberta. "There are fewer bears in eastern Hudson Bay, but there is much less known about where they come from."

Bears using the area, he added, probably moved out as the ice shifted this year. "But if they got stuck on the offshore islands, they'll likely be in trouble as the ice disappeared from that area and hasn't come back," he said.

Derocher said the bears he observed during spring fieldwork in Western Hudson Bay appeared to be in good condition, but that will not continue as climate change upends the bears' habitat.

LOCAL EXTINCTION

A study published in the journal Nature Communications Earth and Environment on Thursday highlighted the peril facing the world's southernmost polar bear populations.

If the world were to breach the U.N. Paris Agreement target of limiting global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) above preindustrial temperatures, the research suggests polar bears in Western Hudson Bay and Southern Hudson Bay would be in serious trouble.

Under current emissions policies, the world is on track to surpass 1.5 C of warming in the 2030s.

"The disappearance of the Southern Hudson Bay polar bears is imminent, with Western Hudson Bay not far behind," said study lead author Julienne Stroeve of the University of Manitoba.

"If we go over the 2 C of warming, we can't really hope that those bears will still stay there."

The Western Hudson Bay polar bear population has already fallen by half since 1987.

The research, which used warming projections from 20 climate models, determined Western Hudson Bay would become an unsuitable habitat for polar bears at around 2.2 C (4 F) of warming.

Southern Hudson Bay would no longer be able to support bears at between 1.6 C and 2.1 C (2.9 F and 3.8 F) of warming, as the lengthened open water period would force bears to fast beyond the point of survival.

While previous studies have made similar projections, the new research factored in sea ice thickness for the first time. Even if sea ice is present, it may not be thick enough to support the weight of an adult bear.

Past studies assessing future polar bear survival, Stroeve said, may have underestimated how long polar bears will be forced to go without hunting by around 50 days when only examining sea ice extent.

(Reporting by Gloria Dickie in London, editing by Deepa Babington)