Thursday, August 22, 2013

Polar Bears Have Not Been Harmed by Sea Ice Declines in Summer - The Evidence

A new review paper from SPPI by Dr. Susan J. Crockford finds polar bear numbers are increasing and that they have not been harmed by a decline of Arctic sea ice:

[Illustrations, footnotes and references available in PDF version]
The polar bear biologists and professional activists of the IUCN Polar Bear Specialist Group (PBSG) continue to insist that since 1979 increasingly smaller amounts of Arctic sea ice left at the end of summer (the September ice minimum) have already caused harm to polar bears. They contend that global warming due to CO2 from fossil fuels (“climate warming” in their lexicon) is the cause of this decline in summer ice.
I’ve spent the last year examining their evidence of on-going harm, but in addition, I’ve looked at the evidence (much of it not mentioned in the Stirling and Derocher paper1) that polar bears have either not been harmed by less sea ice in summer or have thrived in spite of it.
This is a summary of my findings. I’ve provided links to my original essays on individual topics, which are fully referenced and illustrated. You are encouraged to consult them for complete details. This synopsis (pdf with links preserved,pdf with links as footnotes) complements and updates a previous summary, “Ten good reasons not to worry about polar bears” (pdf with links preserved; pdf with a foreword by Dr. Matt Ridley, with links as footnotes).
1) Polar bear numbers overall have increased, despite the appearance of a ‘stable’ global population since 2001 and significant declines in Arctic sea ice coverage in summer.  ...
As the monthly sea ice extent graphs for 1979 to 2012/2013 in Fig. 3 (below) show, while concern over the “Arctic ice death spiral” focuses on the dramatic changes in September values, there has been much less difference over time for March, June and November values. These months are far more relevant to polar bear health and survival than September, since November through June is when polar bears really need sea ice — especially during the critical feeding period, which runs from March through June in all regions.
While the decline in ice extent is greatest in September, all evidence suggests this is the least important month of the year for polar bears – the yearly ice minimum in September occurs after the critical spring/summer feeding periodafter the spring/summer mating period and well before the winter birth of cubs.

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