Sea ice looks low for this time of year but how does it compare to 2007, when summer ice habitat for polar bears hit a record-breaking low? What can the impact of 2007 ice levels on polar bears tell us about what to expect this year?
By this date in 2007 (8 August, Day 220, NSIDC Masie map below), there was almost 1 million km2 less ice than there is this year (map above). However, look which polar bear subpopulations not only survived, but thrived, through the 2007 low ice summer: Chukchi Sea, Southern Beaufort, Barents Sea, Davis Strait, Foxe Basin, Western Hudson Bay, and Southern Hudson Bay. That’s all of the subpopulations for which we have recent data.
There is more than a month left in the melt season, of course. However, while 2012 finished with a lower minimum ice extent due to a massive mid-August storm that broke up a lot of ice (Simmonds and Rudeva 2012), by the end of the first week of August (i.e, the 8th), there was more ice in 2012 than in 2007 and a bit less than this year (2012, 6.3 mkm2; 2007, 5.6 mkm2; 2015, 6.5 mkm2).
This means if less summer ice for a longer period of time impacts polar bear health and survival, conditions in 2007 should have had a noticeable impact on polar bears around the world. They didn’t. That suggests even if this September sea ice minimum is as low as 2007, it won’t have any negative impact on polar bear health or survival. The most profoundly negative documented impacts have come from thick sea ice in spring or suboptimal spring snow levels (Crockford 2015) and the evidence shows that variation in the extent of summer ice is simply irrelevant to polar bears.