It was an incredible week on the tundra in northern Canada. We sawn an estimated 31 polar bears in total from arrival on Sunday, November 12 through Saturday, November 19. But, the most recent aerial survey, done approximately every five years, showed a 27 percent decline in the Western Hudson Bay population: https://www.reuters.com/world/americas/canadas-hudson-bay-polar-bear-population-plummets-climate-change-warms-arctic-2022-12-23/
(Polar bear close inspection: Thursday, November 16 in Churchill, Manitoba)
Polar bears’ climate change threat come from the decline in the seasonal sea ice that is essential for them to hunt their primary food source, seals. While polar bears are excellent swimmers, seals are better so the ice acts as a hunting platform.
Temperatures have warmed several degrees here since the 1970s and 1980s.
This means the ice is developing later in the fall season and breaking up earlier in the summer, shrinking the time the bears can be on ice, eating. While on land, polar bears eat very little significant calories. Take a look at this comparison of the average freeze up from the 1970s and 80s compared to the modern average (1991-2020):
The freeze up is occurring at least 7 to 10 days later than it used to. Importantly, the frequency of very late freeze ups is increasing exponentially. Ice analyses are done every seven days so the latest data we have is from November 12. If we compare the percentage of Hudson Bay ice cover over 50 years we can see this :
This year’s amount of ice is the second lowest for this point in the season in 12 years. You can see just a small amount of ice on some of the western shores of Hudson Bay on the satellite image below. About three percent of Hudson Bay was covered in ice when we started the week (Nov. 12) compared to what should be about eight percent (modern average) and that value would have been 24 percent forty years ago.
November temperatures thus far have been several degrees above normal, at least +4 F in the Churchill area. There’s been a lack of consistent cold. Normal November lows should be in the single digits and subzero but there’s only been one or two nights matching that criteria. It finally did cool down at the end of last week.
Ice on the western parts of Hudson Bay has now doubled from three to about six percent over the past week thanks to the last several days of cold and a favorable northwest wind, but that’s still much less than the 1991-2020 average of about 16 percent. 40 years ago the average value by this date was 39 percent.
It’s certain that this year’s freeze up will be late. The ‘magic number’ appears to be about 30 percent. That’s the amount of ice cover on Hudson Bay where most bears end up on the ice. We’re still far from that but we could get there quickly with cold weather. It’s looking likely it will be a December freeze up. With warming over the recent decades it’s now ten times more likely than it was 40 years ago to see a December freeze up.
The late freeze up comes on the heels of an early ice out too. Temperatures in Churchill reached a staggering 90 degrees on June 30th, the tenth hottest recorded there.
That heat came at the worst possible time. The break up of ice on Hudson Bay usually is a process from late May into July. This year’s ice break up (defined by 50% ice cover) was reached 17 days earlier than the historical average date.
Every day matters for a polar bear. When they’re on land, not eating, they lose one kilogram (just over two pounds) of weight PER DAY. An adult that got plenty fat in the spring and summer can take that hit once in a while but polar bear cubs and subadults cannot. That’s why the population of Western Hudson Bay is seeing declines.
Let’s hope the polar bears of Hudson Bay can get on ice soon and that El Niño doesn’t have the devastating consequences on sea ice it has in recent decades.
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