Early sea ice thaw in W Hudson Bay due to ‘record breaking’ temperatures in 2023, not 2015? • Watts Up With That?
Dr. Susan Crockford
Based on International Polar Bear, the “3rd earliest” farewell date for West Hudson Bay was due to a “record-breaking” heat wave in May. West Hudson Bay sea ice hit the 30% coverage threshold used by the PBI to define “disruption” on June 17 of this year, sparking speculation about potential future impacts on life. and polar bears if the breakup had taken place earlier.
“This year’s farewell date of June 17 is the 3rd earliest in 45 years of satellite-based sea ice data from Western Hudson Bay, after 2015 and 2003..” [Flavio Lehner, PBI]
June 17, 2023 is the 168th Julian day used to graph the data in the image included in the PBI essay (see copy below). However, the data point for 2003 is about three days earlier, at 166 (June 14) and the point for 2015 is at 152 (June 1).
If the “record-breaking” heat caused the ice to melt early this year, what caused the ice to melt so soon? more than two weeks ago in 2015? May of that year was also warm along the west coast but clearly not a “record-breaking” warmth, because records were broken. This year. In fact, any warming that occurs only affects the melting of the ice in the western region, while the very thick ice cover in the rest of the bay resists the melting and allows the bears to come out. weeks later than usual.
Sea ice melt in 2023
The closest in my archives to June 17 is June 19 (but June 15 is not much different along the western part so it probably hasn’t changed much between 17 and 19). Notice how much ice is missing in the eastern bay.
Ice melt in 2015
Compare the above with June 1, 2015 (below), when same 30% ice coverage has clearly reached the threshold. Note that this is 30% of the Western Hudson Bay area in particular, not Hudson Bay in general. In fact, the 2015 ice melt pattern is quite unusual, with a lot of open water in the western region but thick, solid ice everywhere else against the melt. Although it dissipates early in West Hudson Bay, at August 13, 1992 only tapes remaining in the bay in general.
On July 20, 2015, more than half of all South Hudson Bay bears have necks was reported still far on the ice. On the same day (see tweet below), polar bear expert Andrew Derocher noted that only 2 out of 9 collared bears came ashore (one way via Hudson Strait), when predicting based on coverage 30% WH icebergs should have seen them all come ashore by June 30 (Cherry et al. 2013):
According to Cherry et al. (two thousand and thirteen):
“During the study, bears disembarked an average of 28.3 days (SE = 1.8) after 30% ice cover.”
Therefore, by Cherry’s criteria, this year we can expect most bears to come ashore in WH by July 15. However, as of June 27, only 6 bears have been tagged by WH. Andrew Derocher stayed ashore and the rest (27) remained in the sea with low ice density (see map below). Some of them are in the middle of the bay. Time will tell whether all of them will reach shore in the next two weeks or some will linger for a few more weeks on the remaining pieces of ice. seems to be the usual pattern In recent years.
All of this suggests that the 30% ice cover metric may not be a particularly good predictor of polar bear behavior. It’s not just my opinion: one of Derocher’s students conducted the same analysis and came to the same conclusion.
She More recent articles (Castro de la Guardia et al. 2017) found that the threshold of 50% ice coverage on WH is the best predictor of when polar bears come ashore in the summer:
“The most appropriate definition of a breakup is 50% ice concentration. There is a high positive correlation (r2 > 0.9, p = 0.07) between inshore migration and disintegration from 2006 to 2009, with polar bears migrating ashore about 20 days after parting.” [Castro de la Guardia et al. 2017, pg. 230, my emphasis]
If this more recent study, which uses more data and a 50% ice cover threshold to determine breakup, is the best predictor of when polar bears come ashore, why would the PBI representative use Using the 30% threshold? They don’t say, or even mention, that a different method has ever been used to gauge when polar bears come ashore. They also don’t mention it in general, at least since 2015, some bears simply don’t behave as expected and have stayed out. high-grade ice in late summer. Strange, that.
Bear problem on the shore
The first real Churchill polar bear warning report was issued (for week 2 of summer, June 19-25), only a few bears on the shore near town should be encouraged to go. play further.
Presenter
Castro de la Guardia, L., Myers, PG, Derocher, AE, Lunn, NJ, Terwisscha van Scheltinga, AD 2017. The sea ice cycle west of Hudson Bay, Canada, from a polar bear’s perspective. Flow of marine ecology 564: 225–233. http://www.int-res.com/abstracts/meps/v564/p225-233/
Cherry, SG, Derocher, AE, Thiemann, GW, Lunn, NJ 2013. Migration and seasonal fidelity of an arctic marine predator in relation to sea ice dynamics. Animal Ecology Magazine 82:912-921. http://onlinelibrary.wiley.com/doi/10.1111/1365-2656.12050/abstract
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