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An extreme lack of sea ice in Canada this winter should serve as a “wake-up call” for the risk climate change poses to polar bears, say conservationists.

Ice normally starts building up across Hudson Bay in November, but the area has remained almost entirely ice-free in the face of temperatures 6°C above average. In the north-western part of the bay, ice extent . In an average year, 70 to 80 per cent of this part of the bay is covered in ice by this stage in the year.

That has left polar bears standing by the shore, waiting for the ice to form so they can hunt seals. Temperatures in recent days have begun dropping and the US . But the agency says the current low is “extreme” and, across the bay as a whole, second only to 2010 for this time of year.

“It’s very unusual. It’s very low,” says at WWF Canada. “I don’t think this is panic and everything is collapsing, but it’s indicative of the broader trend [of sea ice loss].”

Climate change has .

“It’s not good [for the bears],” says , an ecologist at the British Antarctic Survey. “The longer they don’t have sea ice, they get a gradual loss in condition. A lot will survive it [this year]. But it tips the balance towards stress-related mortality. Fewer will survive.”

Research suggests that almost all the world’s remaining 26,000 polar bears will be pushed to the edge of their fasting limits by the end of the century due to climate change. Laforest says that while bears in the high Arctic are currently doing fine, the sub-population in the Hudson Bay area are the canaries in the coal mine. 

“They are the first to go through these broad implications of climate change,” he says. “We need to take these warning signals for what they are. It’s a wake-up call.”

The remote nature of the region in which the bears hunt, and the cost of tracking them, means it will be hard to measure precisely what impact this year’s late freeze has on the animals. In the meantime, Laforest says there may be more human-wildlife conflict as hungry bears wander into Inuit communities in search of food. The late ice is also impacting people in the region, he says, as they cannot access their usual hunting grounds. 

The National Snow and Ice Data Center says the picture for the Arctic as a whole is mixed, with sea ice extent only the tenth lowest on record for November. On the Russian side of the Arctic, sea ice growth has been above average in the Bering Sea, trapping ships in ice and disrupting supplies to Siberian cities.