Hudson Bay has been oddly slow to freeze this year, which has led to a predictable bit of hand-wringing from certain biologists reiterating prophesies of polar bear population collapse. However, since 2009, the last time that freeze-up was anywhere near this late was 2016. In other words, far from this years’ late freeze-up being a picture of ‘the new normal,’ conditions in 2021 are actually unusual compared to the last twelve years.
Moreover, considering that 2021 fall ice formation for the Arctic in general is well ahead of 2016 (and every year since, except 2018), it’s hard to see why human-caused global warming caused by ever-increasing CO2 emissions explains the slow freeze-up of Hudson Bay. Timing of Hudson Bay freeze-up has always been highly variable from one year to the next (Castro de la Guardia et al. 2017: Fig. 3, copied below). The average freeze-up date in the 1980s was 16 November ± 5 days, while from 2005-2015 this had shifted about a week to 24 November ± 8 days (Castro de la Guardia et al. 2017:230). This year freeze-up was later than usual but last year and the three years before that the ice froze as early as it did in the 1980s. Cue the zombie apocalypse.
UPDATE 11 December 2021: see chart below from Andrew Derocher on the position of tagged WH bears at 10 December.
According to an article in The Guardian last week: ‘No easy fix’: polar bear capital of the world turns to electric buggies to save the bears (3 December 2021):
“We’re not getting the good years of sea ice formation that we used to have. We’re getting bad years and OK years,” said Andrew Derocher, a professor of biology at the University of Alberta. “When you do that over a long enough period of time, you can expect that your population is going to decline.”
However, Derocher grossly mischaracterizes the long-term freeze-up data for Western Hudson Bay. The most recent published data (Castro de la Guardia et al. 2017) soundly refutes his statement to The Guardian. Moreover, Derocher has not updated this information in the scientific literature since 2015 even though he must calculate it every year. All I can do is publicly document the phenomenon based on sea ice charts and reports from local observers.
Based on published and privately recorded daily sea ice data (Castro de la Guardia et al. 2017: Fig. 3, copied below), there have been one or two late freeze-up years (‘bad’ in Derocher-parlance) each decade since 1979: 1981, 1994, 1998, 2009, 2010, 2016, 2021. The frequency of bad years has never been higher than twice per decade and has not increased over time. ‘OK’ years would have bears leaving the ice by the last week of November, which happened in 2010-2015 last decade. 2016 was ‘bad’: freeze-up was quite late. However, in 2017, 2018, and 2019, bears left shore about the same time they did in the 1980s (by the second week of November or so), which by Derocher standards are ‘good’ years. That’s three good years in the 2010s, six OK years and one bad year; for the 2020s so far, one good year and one bad. Even the 1980s had one bad year and two OK years among the good years.
In other words, the most recent full decade can most honestly be described as a mix of good and OK years similar to the 1980s.
While freeze-up in 2016 was late and bears didn’t leave until the second week of December, virtually all bears came ashore in very good condition in July, which meant the extra wait for fall ice was not a problem.
The Guardian piece later stated:
It had been 156 days since most of the bears last ate. At 180 days, starvation begins to set in.
Ice is also breaking up earlier in the season, meaning bears are forced to return to land weeks earlier than normal and have a smaller window for hunting.
Over the last decade, the bears have lost nearly a total of 12 days of ice on either end of the season.
“We’ve always been concerned about an early break-up with a really late freeze-up,” said Derocher. “And that would be the worst-case scenario for polar bears.”
Let’s look at that scary-sounding claim of number of days onshore and starvation. According to Derocher and colleagues, 3 December marked 167 days ashore for WH bears, which means the average date ashore at breakup for all bears in 2021 was Day 170 or 19 June. In the fall, all indications are that some bears had left shore by 26 November and virtually all had left by 4 December. If we call it 168 days, that’s definitely a longer sojourn on land than the 1980s but no longer than it was in the late 1990s and early 2000s (see graph above, panel C).
UPDATE 11 December 2021: In a tweet late in the day 10 December, Derocher posted an ice chart with the position of bears he had tagged earlier this year (‘Blue & orange are adult females tracked by satellite collars. Purple are a mix of adult males, adult females & subadults tracked with eartag radios. Collars last 1 year with 6 locations/day. Eartags last < 6 months with 1 location/day.’). The last similar chart he posted was on 1 December, showing a few bears on ice but most lined up along the coast ready to head off – but nothing in between, so that we can’t determine from his data exactly when most bears left and he can claim that freeze-up was ‘very late’. In other words, there is nothing here to contradict my suggestion that most bears (there are always some stragglers) had left by 4 December. Some bears that were still on shore at 10 December may have been making short foraging trips from land or caught a seal days earlier near shore and feel disinclined to leave immediately. However, Derocher seems to suggest the ice near them is not thick enough for them to move, which seems an implausible explanation. Backup ice chart for 10 December here and for 1 December here.
However, there were no reports of especially thin or starving bears this year (most summer photos were of bears in good condition) or any reports of cannibalism: I’m absolutely sure that if there had been, Derocher would have said so. Body condition of bears when they come ashore matters: the conundrum of 1983 was that breakup wasn’t early that year yet most bears came ashore in less than good condition and by mid-November, many were very thin and likely struggled to make it through the winter (Ramsay and Stirling 1988).
The article states that “at 180 days, starvation sets in”. This is a gross misrepresentation of the model prediction to which it refers (Molnár et al. 2010). The model predicts that 9-21% of adult males would be at risk of starvation at 180 days (6 months) ashore, up from 3-6% of males at risk of starvation at 120 days (4 months) ashore (which was routine for WH bears in the 1980s).
Starvation is therefore not a given at 180 days, but a possibility. So far, there has never yet been a year where the population spent 180 days ashore, so there are no data, only the model prediction. While 2003 was close to that ‘starvation risk’ threshold, there is nothing in the literature about 2003 being a year of starving adult bears: that honor goes to 1983 (Ramsay and Stirling 1988).
Further on, the Guardian article had even more comments from Derocher:
Already, the bears are showing warning signs.
The weight of pregnant polar bears has declined over the years, as have new births. Bears typically lose one kilogram of weight each day they remain on the tundra instead of ice – further adding pressure on the population.
The bear population has dropped by nearly 30% since 1987. If current trends hold, the bears are predicted to undergo a reproductive failure by 2040, accelerating the species’ demise.
“Eventually, you’ll pretty much have like a zombie population of polar bears that just can’t sustain themselves and it’s a matter of time before they’re extirpated. When? That’s the million-dollar question,” Derocher said.
I recently pointed out that a claim by polar bear researcher Nick Lunn that unpublished data on weights of pregnant WH polar bears had declined 15% between 1980 and 2019 actually meant that bears in 2019 were heavier than they were in the 1990s and early 2000s. I’ve also commented at length on this claim about a 30% decline in WH numbers since 1987, which is a deliberate misrepresentation of the data (Crockford 2019, 2021; Dyck et al. 2017). Furthermore, the 2020 model mentioned by Derocher that predicts WH reproductive failure by 2040 uses implausible ‘business as usual’ sea ice projections that shouldn’t be taken seriously by anyone (Hausfather and Peters 2020; Molnár et al. 2020).
Finally, as for the suggestion of an imminent ‘zombie’ polar bear population in Western Hudson Bay, isn’t it funny that Derocher failed to point out that the slower-than-usual freeze-up of Hudson Bay this year is likely to be beneficial for polar bears? A slow freeze-up allows the bears an extended period of ice-edge fall seal hunting before the extreme cold and darkness of winter makes that activity extremely difficult, and almost certainly forestalls impending starvation. No, he wouldn’t want to mention that: it would kill the zombies.
Castro de la Guardia, L., Myers, P.G., Derocher, A.E., Lunn, N.J., Terwisscha van Scheltinga, A.D. 2017. Sea ice cycle in western Hudson Bay, Canada, from a polar bear perspective. Marine Ecology Progress Series 564: 225–233. http://www.int-res.com/abstracts/meps/v564/p225-233/
Crockford, S.J. 2021. The State of the Polar Bear Report 2020. Global Warming Policy Foundation Report 48, London. pdf here.
Dyck, M., Campbell, M., Lee, D., Boulanger, J. and Hedman, D. 2017. 2016 Aerial survey of the Western Hudson Bay polar bear subpopulation. Final report, Nunavut Department of Environment, Wildlife Research Section, Iglolik, NU. http://www.gov.nu.ca/environnement/information/wildlife-research-reports#polarbear
Hausfather, Z. and Peters, G.P. 2020. Emissions – the ‘business as usual’ story is misleading [“Stop using the worst-case scenario for climate warming as the most likely outcome — more-realistic baselines make for better policy”]. Nature 577: 618-620
Molnár, P.K., Derocher, A.E., Thiemann, G.W. and Lewis, M.A. 2010. Predicting survival, reproduction and abundance of polar bears under climate change. Biological Conservation 143:1612−1622.
Molnár, P.K., Bitz, C.M., Holland, M.M., Kay, J.E., Penk, S.R. and Amstrup, S.C. 2020. Fasting season length sets temporal limits for global polar bear persistence. Nature Climate Change. https://doi.org/10.1038/s41558-020-0818-9
Ramsay, M.A. and Stirling, I. 1988. Reproductive biology and ecology of female polar bears (Ursus maritimus). Journal of Zoology London 214:601-624. http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1988.tb03762.x/abstract