Recent research by Julienne Stroeve and colleagues, published in Communications Earth & Environment, projects that global warming would extend the Hudson Bay’s ice-free period, shortening the resident polar bears’ hunting season.
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The authors indicate that if temperatures rise by more than 2.1 degrees Celsius, the ice-free period in most of Hudson Bay may exceed the maximum fasting time that adult polar bears can tolerate.
Hudson Bay, located in the Arctic Ocean off the coast of northern Canada, is covered in sea ice during the season and is home to roughly 1,700 polar bears. Polar bears spend the winter on the sea ice, hunting seals, their preferred prey. When the ice melts in the spring, they come ashore and fast during the ice-free summer before returning to the sea ice in the melts.
Over the last three decades, the Hudson Bay area has warmed by more than one degree Celsius, extending the ice-free period from around 120 to 150 days. Polar bears in the bay rely on sea ice to hunt. Therefore, an extending ice-free period could affect both their survival rate during the fasting period and their reproductive success during the following hunting season.
In the western and southern Hudson Bay regions, where losses in polar bear populations have already been noted, Julienne Stroeve and colleagues estimated projected changes to the ice-free time by analyzing predictions from the IPCC's Coupled Model Intercomparison Project 6 (CMIP6) models. It is believed that polar bears could comfortably endure 183–218 days of ice-free time.
The authors calculated that if global warming surpasses 2.1 degrees Celsius and 2.6 degrees Celsius, respectively, the ice-free period might last longer than the 183-day limit in the western and southern Hudson Bay regions.
Furthermore, they predict that seasonal ice melt will probably happen sooner in the spring. Since cubs are usually born between November and January, this might decrease the bears' nursing time, which could lower their reproductive success.
The scientists emphasize that if global warming is kept to 2 degrees Celsius over pre-industrial levels, the Hudson Bay polar bear population has a strong chance of survival.
Journal Reference:
Stroeve, J., et al. (2024) Ice-free period too long for Southern and Western Hudson Bay polar bear populations if global warming exceeds 1.6 to 2.6 °C. Communications Earth & Environment. doi:10.1038/s43247-024-01430-7