Hudson Bay sea ice cover at early summer 2020 is similar to the 1980s

Don’t expect to hear this news from polar bear activists busy promoting the supposed threat to polar bears from declining Arctic sea ice but ice cover over Hudson Bay so far this summer has been very similar to what it was in the 1980s – often promoted as ‘the good old days’ for Western Hudson Bay polar bears. As of the end of June 2020, very concentrated ice (9/10-10/10) more than 1 metre thick still covered most of the bay and there was still no open water near Churchill along the west coast down into James Bay.

Polar bear activists don’t like to have current Hudson Bay sea ice reality ruin their social and news media narrative that ‘polar bears are all gonna die’, so they instead emphasize the obsolete ‘declining trend’ for Western Hudson Bay breakup dates that haven’t been updated since 2015 (e.g. Castro de la Guardia et al. 2017; Lunn et al. 2016). They do this despite the fact their colleagues admit polar bears don’t catch many seals after late June (regardless of sea ice conditions) because it is past the peak spring feeding period (Obbard et al. 2016; Lippold et al. 2019). Like in the 1980s, in 2015 and 2019 some bears stayed on the ice until early August and 2020 is shaping up to be another 1980’s-like summer.

Here is the same chart as above (last week in June) but in black and white (which was all the was available in the 1980s). These are harder to interpret but look at the over-all pattern and note that stippled areas (dots close together) represent open water:

And here is the chart for the same week in 1986:

And here is the same week in 1980:

How this will affect the dates that polar bears come ashore for the summer is unclear because there is always more of a lag between official WH ‘breakup’ dates and the dates that polar bears come ashore. Castro de la Guardia et al. (2017:230-231) found that WH polar bears come ashore approximately 20 days after sea ice ‘breakup’ hits a threshold of 50% sea ice concentration, which meant that in 1979-1989 most bears were off the ice about 31 July (±4 days) but from 2005-2015 most bears were ashore about 18 July (± 9 days), about 14 days earlier.

This year, all tagged WH polar bears were still on the ice as of early July, according to Andrew Derocher:

Last year, by 17 July most of Derocher’s bears (see below) were still out on the ice even though there didn’t appear to be much ice for them to access and at least half were still on the ice by the end of July (i.e. similar to the 1980s).

Hudson Bay #polarbears are coming ashore. Some tags haven't reported lately. Bears may be shifting behaviour to stay out longer on less ice. pic.twitter.com/XsPRDsby8V

— Andrew Derocher (@AEDerocher) July 17, 2017

In 2018, most bears were off the ice near Churchill by the third week in July (16-22) – only a week or so earlier than 2019 – with a few bears similarly reported off the ice the week before (9-15). And in 2017, most bears were off the ice near Churchill by the fourth week of July (24-30) and reported to be in “great shape”.  In 2016, most bears near Churchill were off the ice and in great shape by mid-July (11-17). However, 2015 appeared to be more like 2019: there were a few bears around Churchill by the third week of July (20-26) but like 2019, there was lingering ice on the bay until mid-August. Also like 2019, most of Derocher’s tagged bears were still on the ice at 15 July. I presume based on this information that most bears were not off the ice until the end of July (i.e. like they were in the 1980s and in 2019).

In other words, for 2020 sea ice breakup in Western Hudson Bay is looking very similar to the 1980s which means polar bears will likely not be ashore until the end of July or early August, as they were in the 1980s (and in 2015 and 2019).

In closing, I have copied below the chart for daily ice cover for Hudson Bay on 6 July, which shows a tiny patch of open water north of Churchill but still a lot of ice over the western half of Hudson Bay:

Last year at that time, when WH bears stayed on the ice into late July/early August, the ice looked like this:

References

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/

Lippold, A., Bourgeon, S., Aars, J., Andersen, M., Polder, A., Lyche, J.L., Bytingsvik, J., Jenssen, B.M., Derocher, A.E., Welker, J.M. and Routti, H. 2019. Temporal trends of persistent organic pollutants in Barents Sea polar bears (Ursus maritimus) in relation to changes in feeding habits and body condition. Environmental Science and Technology 53(2):984-995. https://pubs.acs.org/doi/10.1021/acs.est.8b05416

Lunn, N.J., Servanty, S., Regehr, E.V., Converse, S.J., Richardson, E. and Stirling, I. 2016. Demography of an apex predator at the edge of its range – impacts of changing sea ice on polar bears in Hudson Bay. Ecological Applications 26(5): 1302-1320. DOI: 10.1890/15-1256

Obbard, M.E., Cattet, M.R.I., Howe, E.J., Middel, K.R., Newton, E.J., Kolenosky, G.B., Abraham, K.F. and Greenwood, C.J. 2016. Trends in body condition in polar bears (Ursus maritimus) from the Southern Hudson Bay subpopulation in relation to changes in sea ice. Arctic Science 2: 15-32. DOI: 10.1139/AS-2015-0027