Polar Bears International (PBI) is a non-profit organization dedicated to the conservation of polar bears, with a focus on saving their sea ice habitat through climate action. You can read more about them here: https://polarbearsinternational.org

Flavio has been volunteering with PBI since 2016 and since 2022 is acting as their Chief Climate Scientist, together with a fantastic and growing team.

Our work with PBI includes:

Useful scientific figures around Hudson Bay sea ice conditions

Length of ice-free season

The following figures show the annual sea ice break-up and freeze-up dates in Hudson Bay (Western and Southern Hudson Bay separately, WHB and SHB) as well as the number of “ice-free” days based on those dates. “Ice-free” in the following figures refers to 30% sea ice concentration (other thresholds are 20%, 30%, 40%, 50%). The data is from NASA satellites and available from 1979 (Source: https://nsidc.org/data/g02202/versions/4). The solid straight lines shows the long-term linear trends. The maps on the right show the sea ice concentration map at last year’s freeze-up and break-up dates.

Take away message: the length of the ice-free season varies considerably from year to year, but the long-term trend is consistently towards a longer ice-free season. The ice-free season has lengthened by about one month since 1979. A longer ice-free season means a longer period without access to food (seals) for polar bears.



Hudson Bay July average sea ice concentration

The month of July is typically when the sea ice breaks up and polar bears start to come on shore for the summer. A late ice break-up date can provide prolonged hunting opportunities, benefiting the well-being of polar bears, while an early break-up means an early start to the ice-free fasting season.


Difference in length of ice-free season between Western (WHB) and Southern Hudson Bay (SHB)

Sea ice tends to break up a few days later in the Southern Hudson Bay (SHB) than in the Western Hudson Bay (WHB) and this difference might prompt polar bears in a given year to migrate with the sea ice to stay with favorable hunting grounds as long as possible during the melt season, though this has been difficult to show conclusively in tracking data.

Below figure shows that there has been a tendency in recent years for sea ice to break up later in SHB than WHB, though that trend is not significant and can mostly be explained by year-to-year variations in wind: stronger westerly winds in a given year will transport more sea ice from WHB to SHB, where it piles up and becomes thick, thus taking longer to break up during the melting season. See this study for more details.

SHB freezes up about 10 days after WHB and there is currently no trend in that number over time. Below figure is for 30% sea ice threshold, other thresholds can be found here: 20%, 30%, 40%, 50%.



Toy model of polar bear movement during a winter season