From polar bear science
By Monday (July 19), more polar bears had landed near Churchill and on the banks of Wakusp National Park, but some are still in the bay. The pattern of ice breaking this year means that most bears come ashore far south of Churchill and migrate north in summer and fall. There have been two Churchill “problem” bear reports so far, but none for this week, so I’ll go ahead and post without them.
Note that the earliest average date on land for all bears (not the date the first bear hit the beach) for WH bears was June 9th (Julian Day 160), which happened in 1999 after which most bears had Ashore in mid-June (2003, 2011) [Day 180 is 29 June]. However, this means that the first bear on the beach on June 28 this year is far from “early”. From Castro de al. Guardia et al. 2017, which only lasts until 2015, which shows that the average date that bears were on land was late June-early July (but it’s been later since then, especially in recent years):
Three of Andrew Derocher’s six remaining collared females were ashore on Monday, so three are still offshore, along with all the other bears doing the same. The first came ashore two weeks ago, so there was hardly any rush. Note the two bears that appear to be in open water but are almost certainly ice that the satellites cannot “see” or have a concentration of <50%:
According to his map, there’s only a little bit of ice left in Hudson Bay. But even polar bear researchers know that satellites are notoriously bad at determining the correct amount of ice at this time of year and can underestimate the amount of ice in Hudson Bay by up to 50%. They’re usually forced to acknowledge this in their papers, but don’t care about social media or talking to reporters. The evidence that Andrew Derocher is aware of this comes, for example, from one of the work of a student on which he is co-author (Castro de la Guardia et al. 2017: 227) [my bold]:
In general, sea ice data from passive microwaves is associated with an underestimation error of up to 30% during breakup and freezing in the entire ice rim and seasonal ice regions of the northern hemisphere (e.g. Cavalieri et al. 1991, Comiso et al 1997, Markus & Dokken 2002). In Hudson Bay, passive microwave sea ice concentration can make sea ice concentration compared to CISDA. underestimate by up to 50% (Agnew & Howell 2003). Underestimated distortion of passive microwave data is associated with the presence of wet snow and melt ponds during breakup, and with areas covered by frazil ice and young ice during freezing (Agnew & Howell 2003).
In other words, contrary to predictions by polar bear specialists, some bears would rather deal with melt ponds and wet snow than go ashore, especially in Hudson Bay. Rather, this brings havoc with the latest predictive model using old Hudson Bay data – which was collected before this propensity to stay with waning ice was fully apparent – to predict a future of polar bear extinction worldwide (Castro de la Guardia et al. 2013; Molnar et al. 2020). And it means that there was likely a lot more ice in Hudson Bay for the week of July 19 than even the following table from the Canadian Ice Service suggests:
To me, it looks like the average land date for GH polar bears in 2021 will be around the first week of July, but it could be 10 years or more before we see dates appear in a publication. Funnily enough, some of these researchers seem to have lost their urge to publish data as soon as possible now that it no longer fits their narrative.
Churchill Problem Bear Reports
I note that this year there are no comments on the condition of the bears causing problems in Churchill (the same was the case last year). Strange compared to 2019 and 2017. Maybe I’m wrong, but I would assume that whoever authored these reports was advised that it is “not helpful” to let the public know that bears are in excellent State.
Castro de la Guardia, L., Derocher, AE, Myers, PG, Terwisscha van Scheltinga, AD and Lunn, NJ 2013. Future Sea Ice Conditions in Western Hudson Bay and Consequences for Polar Bears in the 21st Century. Biology of Global Change 19: 2675–2687. doi: 10.1111 / gcb.12272
Castro de la Guardia, L., Myers, PG, Derocher, AE, Lunn, NJ, Terwisscha van Scheltinga, AD 2017. Sea ice cycle in western Hudson Bay, Canada, as seen by a polar bear. Marine Ecology Progress Series 564: 225-233. http://www.int-res.com/abstracts/meps/v564/p225-233/
Molnár, PK, Bitz, CM, Holland, MM, Kay, JE, Penk, SR and Amstrup, SC 2020. The length of Lent sets time limits on the global persistence of polar bears. Nature climate change. https://doi.org/10.1038/s41558-020-0818-9