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Now 20 years with no trend in ice breakup dates for Western Hudson Bay polar bears

Straight from the horse’s mouth: all polar bear females tagged by researchers around Churchill in Western Hudson Bay last year were still on the ice as of 25 June. With plenty of ice still remaining over the bay, spring breakup will be no earlier this year than it has been since 1999. Contrary to predictions of ever-declining ice cover, the lack of a trend in sea ice breakup dates for Western Hudson Bay is now twenty years long (a hiatus, if you will) and yet these bears are repeatedly claimed to have been seriously harmed in recent years by a loss of sea ice.

Derocher 2019 WHB collared females 25 June all bears still on the ice

In fact, WH bears have faced relatively few ‘early’ years of sea ice breakup and breakup has never come before the 15th of June. The earliest recent spring breakup date did not come in 2012 – when sea ice hit a summer record low – but in 1999, when Hudson Bay sea ice suddenly began to melt by late June rather than mid-July (Cherry et al. 2013; Castro de la Guardia et al. 2017; Lunn et al. 2016). And this year, as has been the case since 1999, breakup looks to be about two weeks later (give or take a week or so, at around 1 July), than was the case in the 1980s and early 1990s.

In other words, there has been no escalation of breakup dates since 1999: there has been no declining trend in breakup dates for Western Hudson Bay polar bears for 20 years (and no trend in fall freeze-up dates either).

UPDATE 26 June 2019: Here is the latest sea ice chart for the week of 24 June 2019 from the Canadian Ice Service (all that dark green is thick first year ice >1 m thick):

Hudson Bay weekly stage of development 2019 June 24
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