According to Polar Bears International, the “3rd-earliest” breakup date for Western Hudson Bay was caused by a “record breaking” heat wave in May. Western Hudson Bay sea ice hit the 30% coverage threshold used by PBI to define “breakup” on 17 June this year, prompting speculation about potential future impacts on polar bear survival should breakup come even earlier.
“This year’s break-up date of June 17 is the 3rd earliest in the 45 years of satellite-based sea ice data from Western Hudson Bay, after 2015 and 2003.” [Flavio Lehner, PBI]
17 June 2023 is day 168 on the Julian calendar 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, on day 166 (14 June) and the point for 2015 is on day 152 (1 June).
If “record-breaking” heat caused this year’s early ice retreat, what caused the ice to retreat more than two weeks earlier in 2015? May was warm that year along the west coast as well but obviously not “record-breaking” warmth, because the records were broken this year. In fact, whatever warmth that occurred only affected ice melt in the western sector, while very thick ice over the rest of the bay resisted melt and allowed bears to stay out many weeks later than usual.Continue reading