Most polar bears that spend the spring feeding in the peripheral seas of the Arctic Basin (such as the Beaufort, Chukchi, Kara, and Barents Seas) remain on the persistent pack ice of the central Arctic during the summer and this August, that refugium is still larger than Greenland. Most of these bears do not use this July-September Arctic Basin ice as a hunting platform unless they are very lucky: the few seals available are hard to catch. For the most part, polar bears fast or eat very little during the summer whether they are on land or on ice (see references in this post).
Since early June, sea ice experts have been wringing their hands over the melting of Arctic sea ice and offering breathless speculation that this year’s September minimum could be – gasp! – as low as or less than 2012 or even less. But now, as the graph of ice cover at 28 August shows below, that outcome is looking not just unlikely but virtually impossible (the blue line is 2019 extent, red dashed line is 2012, and the brown line is 2016):
As expected, the failure of the ice to remain on track to set a new record September low due to global warming is shrugged off with a reminder that summer ice extent “is sensitive to changes in daily weather conditions.”
Polar bear researchers just published a study that suggests polar bears have moved around the Arctic in direct response to recent sea ice changes — a conclusion I suggest you take with a grain of salt and a raised eyebrow.
That’s because they have also proposed, among other things, that the Svalbard Archipelago was a sea ice refugium during warm interglacial periods, and could be again if the Arctic warms as predicted. That they would accept and promote such a model-based conclusion, which has no relationship with reality, calls their scientific judgment into question.
Based on genetic model results, the Svalbard Archipelago (circled) has been proposed as a sea ice refugium for polar bears during previous warm Interglacial periods and during predicted sea ice declines in the future. Yet most years since 1979 (2014 was one exception), this region has been ice free during the summer, making Svalbard a decidedly poor candidate for retaining sea ice when it’s much warmer than today.
Posted in Population, Sea ice habitat
Tagged Canadian Arctic Archipelago, Cronin, DNA, extinction, gene flow, genetics, Hamilton, Miller, models, PBSG, Peacock, polar bear, Polyak, predictions, refugium, sea ice, warming Arctic
Last in a three-part series of my critique of Miller et al.’s (2012)
paper on the newest genetic evidence for the origin of polar bears. Part 1 here, Part 2 here.
Here is my final (I hope) comments on the claims made in that paper, suggesting why we might want to take them with a grain of salt.
These are the points regarding this paper that I think deserve a critical look. In this post, I’ll elaborate on Claims #3 and #4. [I’ve added one more to the original three listed].
Claim #1 Polar bears and brown bears (aka grizzlies) arose 4-5 million years old. [I countered with fossil evidence]
Claim #2 Hybridization in both directions occurred repeatedly throughout the evolutionary history of polar bears and brown bears. [I countered with full details on known hybrids]
Claim #3 Svalbard may have been an important refugium for polar bears during warm interglacial periods – and related sea ice issues related to the origin of polar bears as a species.
Claim #4 Polar bear population numbers (population size estimates) over the last one million years track changes in climate (warmer/colder periods).
Claim #3 Svalbard may have been an important refugium for polar bears during warm interglacial periods (and related sea ice issues related to the origin of polar bears as a species) [Which I’ll counter with evidence on paleo sea ice]