Reposted by Polar Bear Science
Published on November 25, 2020 |
Sea ice formation is ahead in some regions and lagging behind in other regions, but overall, sea ice habitat is so abundant for this time of year that virtually all polar bears in the Arctic are back to sea ice hunting seals.
Overall, there was more sea ice on November 24, 2020 than the same day in 2016. This was the final year that a number of polar bear subpopulations were surveyed, including western and southern Hudson Bay, southern Beaufort and Chukchi Sea ( Crockford) 2019, 2020), see graphic below from NSIDC Masie:
Northern hemisphere sea ice on November 24, 2016-2020.
UPDATE November 27, 2020: The Problem Bear Report released today (for week 13, November 16-22) has been added below.
EASTERN CANADIAN ARCTIC
Ice is rapidly forming over Hudson Bay a little earlier than usual, but the Davis Strait off southern Baffin Island is still sparsely covered.
The pattern of ice formation over Hudson Bay was somewhat unusual this year as the winds blew much of the ice off the coast during the freezing process. Plus, the freezing came earlier than normal. Aside from the fact that a bear with a chase collar was on the ice on November 16, polar bear researcher Andrew Derocher remained silent about the locations of the rest of the collar bears until this morning when he published a map dated November 23rd. Half of the eight bears, who are unlikely to be pregnant women is on the ice (see below). The other four will stay ashore in caves to have their young later this year.
Of course, knowing that these bears are all offshore doesn't tell us when they actually left the coast – as far as we know, they hit the ice on November 17th (one day after Derocher's first announcement). Regardless, Derocher falsely implied in his tweet this morning that the November 23 situation supported his claim that this was "not an early freeze".
Aside from the fact that for all independent actions, including ice maps, on-the-spot reports, and photos of bears hunting on the ice, the freeze was early this year even for the 1970s and 1980s (Castro de la Guardia et al. 2017); Stirling et al. 1977). Many bears (but not all) hunted ice in the first few days of November (see table below), which would have been earlier than usual in the 1980s (when the average bear departure day was November 16). A few stragglers stayed behind, including Derocher's bear neck bears, apparently with no apparent rush to get onto the ice.
The Canadian Ice Service Deviation From Normal map for Hudson Bay shows that there is much more ice than usual in the center of the bay and south in James Bay (so blue!). In contrast, there is much less ice than usual in northern Hudson Bay and Davis Strait (off southern Baffin Island), which is shown in red and pink.
A study by Castro de la Guardia and colleagues (2017: Figure 3) found that the The earliest freeze dates for Western Hudson Bay since 1979 were November 6, 1991 and 1993. As the ice maps from the CIS archives (below) show, in the first week of November in 1991 there was roughly as much ice off the coast of Western Hudson Bay as there was this year (graphic above). In other words, Derocher says this wasn't an early freeze year, don't do it that way.
In 1993 (below) there was much more ice in the north of Hudson Bay than in early November, but no longer on the west coast where polar bears gather and wait for the ice to form:
Two weeks later, the ice cover over Hudson Bay is impressive for this time of year, as evidenced by the ice for the week of November 23 (below). This graph shows the actual ice cover rather than the anomaly. The ice forms quickly.
So it's no wonder polar bear experts haven't released official polar bear segregation / freezing dates since 2015 (Castro de la Guardia et al. 2017) – freezing was average (2017) or earlier than average (2017) 2018-2020) , for four years in a row. Although the freezing was very late in 2016, we know that there was occasional very late freezing year, as was the case in 1983, even before it was claimed that man-made climate change was the regulator of all Arctic ice (Ramsay and Stirling 1988 )).
The last two reports from the Polar Bear Alert Program at Churchill (for weeks 11 and 12, November 2-8, and November 9-15) were finally published online today, but neither mention the state of the ice. Given that no report appears to have been released this week, and the small number of incidents in Week 12 (4 "Incidents") and the number of bears in the holding facility (PBHF) late last week (0), it looks like this the November 9-15 report (below) was the last of the season.
UPDATE 27 November 2020: The Problem Bear Report released today (for week 13, November 16-22) is added below, indicating that despite their abundance, some bears are still not on the ice.
To compare with the above, see the last 2017 Problem Report Report (below):
WESTERN ARCTIC INCLUDING RUSSIAN FAR EAST
The Beaufort Sea has been largely ice-covered since the third week of October (in contrast, this was not the case until mid-November in 2012). Currently, coastal ice is rapidly forming on the shores of the Bering Sea, but the ice from the Chukchi Sea has not yet moved south through the Bering Strait. Wrangel Island, where many female Chukchi polar bears have their cubs, was reached by the advancing ice pack on November 11th.
Chukchi Bering Sea, NSIDC Masie Ice Cream Menu for November 24, 2020 (Day 329).
CENTRAL RUSSIAN COAST
On the Russian coast, the Laptev and East Siberian Seas have been completely covered with ice since the beginning of November (below), after coastal ice had formed quickly this autumn and the pack ice was slowly advancing.
Russian Arctic, NSIDC Masie November 4, 2020.
BARENTE AND KARA SEA
After a slow return of the Arctic ice bag, the Franz Josef Land in the eastern Barents Sea now has a considerable ice cover. However, the Svalbard Archipelago in the western Barents is still ice-free, as it has been for many years at this point in autumn (except last year). As a result, most of the pregnant female polar bears in the Barents Sea choose to set up their maternity shelters on the mobile pack ice in the north or on one of the islands of Franz Josef Land.
Barents and Kara Seas, NSIDC Masie, November 24, 2020 (Day 329).
At this time of the season there is little ice in the Eastern Kara Sea, especially around Novaya Zemlya. However, this has been the case in this region at least since the late 1990s. A diagram of the ice cover over Lake Kara over the past five years (NSIDC Masie, below) shows that 2020 was only the second lowest in the last few years after 2016.
Kara sea ice on November 24, 2016-2020, NSIDC Masie.
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's perspective. Marine Ecology Progress Series 564: 225-233. http://www.int-res.com/abstracts/meps/v564/p225-233/
Crockford, S.J. 2019. The polar bear disaster that never happened. Global Warming Policy Foundation, London. Available in paperback and e-book formats.
Crockford, S.J. 2020. Polar Bear Condition Report 2019. Global Warming Policy Foundation Report 39, London. pdf here.
Ramsay, M. A. and Stirling, I. 1988. Reproductive biology and ecology of female polar bears (Ursus maritimus). Journal of Zoology London 214:601-624.
Stirling I, Jonkel C., Smith P., Robertson R., Cross D. 1977. The ecology of the polar bear (Ursus maritimus) along the west coast of Hudson Bay. Canadian Wildlife Service Occasional Paper No. 33. pdf here.