Satellite image shows Hudson Bay sea ice breaking up earlier than usual

Warm weather has accelerated the breakup of sea ice in Hudson Bay this year, according to data from the Canadian Ice Service, part of a growing trend of summer sea ice coverage shrinking every decade.

Hudson Bay freezes and melts each year. Although it’s part of the Arctic Ocean, it is completely free of sea ice for a brief period in summer and autumn, before freezing over again in winter.

The melt is not unusual, but this process is starting earlier and earlier, leaving polar bears stranded and sending warning signs about the pace of climate change, according to experts.

An image of the bay, taken on June 28 by a camera on the NOAA-20 satellite, shows a strip of sea ice drifting along its southwestern shore, the edges visibly hazy and fractured, appearing more similar to a puff of smoke than solid ice.

According to NASA’s Earth Observatory, which posted the picture as Image of the Day on Wednesday, it demonstrates how fractured the ice was at the time, an indicator that it would not stay solid for long.

That prediction seems to be coming true. 

An animation on Environment and Climate Change Canada’s website, compiled using data from the Canadian Ice Service, shows the ice in Hudson Bay shrinking rapidly between July 7 and July 16. The largest drop occurs between July 12 and July 13, with a large swathe of thinner ice appearing to vanish completely off of the map overnight.

The speedy break-up of ice that used to remain solid for weeks into July has lasting impacts, experts say.

Andrew Derocher, professor of biological sciences at the University of Alberta, has been studying polar bears for 40 years and is part of a research group that monitors polar bear populations using GPS satellite collars. He has been posting updates through his Twitter account, displaying the movements of polar bears in Hudson Bay as they deal with this summer’s early ice break-up.

In a July 5 post, he noted that there were more polar bears from the Hudson Bay area coming in from the ice to land than usual, with “many north of Churchill than normal,” and that the bears that remained on the ice were “hanging on at extraordinarily low ice levels.”

In another tweet Saturday, accompanied by a map showing the signals of polar bears which researchers are tracking, he wrote that there were still a few polar bears out on the ice.

“Very unusual behaviour that we’ll be analyzing over the coming months,” he said. “Shifting behaviour in response to shifting sea ice phenology may be involved. To be clear, it’s not adaptation but existing plasticity. It won’t help in the long term.”

According to experts, when polar bears have to travel off of the sea ice and onto land earlier in the summer than usual, it means they have to stretch their fat reserves for longer, potentially leading to higher mortality rates for polar bear populations.

The amount of summer sea ice coverage in Canada has been trending downwards for decades, observers note.

Between 1968 and the mid-1990s, summer sea ice coverage had more predictable ups and downs, and even at its lowest amount of coverage, there were still around 1.2 million square kilometres covered by sea ice in northern Canadian waters. But over the past few decades, summer sea ice has been decreasing at higher rates.

The last time the sea ice coverage reached 1.2 million square kilometres was in 2018 — the highest amount of sea ice coverage Canada had seen in its northern waters since 2004.

Since 1968, northern Canada’s sea ice coverage during the summer has declined at a rate of 7.1 per cent per decade, according to a report published this March. The Hudson Bay area in particular has seen a loss of 69,000 square kilometres between 1968 and 2022 — a decline of 8.8 per cent per decade.

“Human-induced warming from greenhouse gas emissions and climate variability has resulted in an unprecedented loss of sea ice over the last 50 years,” the report noted.