Monthly Archives: March 2013

Polar bear-sea ice relationships: what biologists knew in ’72

1972 – a bit over 40 years ago. Seven years before we had reliable sea ice extent data from satellites and the year before the international agreement was signed by Arctic nations to protect polar bears from overhunting.

In 1972, a bear biologist by the name of Jack Lentfer was working for the Alaska Department of Fish and Game, stationed at the Naval Arctic Research Lab in Barrow. Lentfer was one of the founding delegates of the Polar Bear Specialist Group, where he represented US interests until 1981.

In the proceedings of the 1972 PBSG meeting (Lentfer 1972a), Lentfer stated the following in his report to the group:

“Long term warming and cooling trends occur in the Arctic and probably affect polar bear distribution and numbers. Climatic trends should be considered when assessing bear distributions and population data on a long term basis.” [my bold]

Warming and cooling, not just warming.

He also had a paper published that year (Lentfer 1972b), entitled “Polar bear: Sea ice relationships.” Forty years on, I thought it was worth having a look at what Lentfer told his fellow polar bear biologist colleagues back then. Continue reading

Polar bears cavorting with ABC brown bears not supported by geological and fossil evidence

The authors of a new paper out in PLoS Genetics (Cahill et al. 2013, entitled “Genomic Evidence for Island Population Conversion Resolves Conflicting Theories of Polar Bear Evolution”) propose to explain how and why the brown bears (aka grizzlies) of the ABC islands of southeast Alaska (Admiralty, Baranof, and Chicagof – see previous post here), got to be so genetically distinct from brown bears on the Alaska mainland and so surprisingly similar (genetically) to polar bears. The authors determined (using a model) that this genetic pattern could be explained by an ancient hybridization event resulting from female polar bears cavorting with male brown bears in SE Alaska.

I had some issues with the way the paper was promoted by some of the co-authors, which I dealt with separately here. More importantly, I found the scenario these geneticists offered to explain how hybridization might have occurred to be patently implausible. Geological and fossil evidence from SE Alaska largely refutes their scenario, although another explanation may be more tenable. It is not impossible, in my opinion, that hybridization occurred in SE Alaska during the last Ice Age, but if it did, it almost certainly did not happen the way Cahill and colleagues suggest.

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Sea ice maximum reached March 15: what it means for polar bears

On Monday, March 25, the National Snow and Ice Data Center (NSIDC) announced that March 15 2013 was likely the maximum extent reached this winter. Note that just a few days ago, I discussed the relationship between maximum extent of sea ice and the global distribution of polar bears around the Arctic (see March 20th post here).

NSIDC says: “Arctic sea ice extent on March 15 was 15.13 million square kilometers (5.84 million square miles). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole.”

NSIDC says: “Arctic sea ice extent on March 15 was 15.13 million square kilometers (5.84 million square miles). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole.” Click to enlarge.

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Polar bear spin reaches new heights as geneticists promote their work

A new paper out in the journal PLoS Genetics proposes that a hybridization event between female polar bears and male brown bears (aka grizzlies) occurred in Southeast Alaska at the end of the last ice age. I’ll get to a discussion of the paper itself (coming in a day or two) but first I have a few things to say about the global warming hyperbole generated by the people promoting the paper. I found it simply mind-boggling.

While the paper itself (Cahill et al. 2013: “Genomic Evidence for Island Population Conversion Resolves Conflicting Theories of Polar Bear Evolution”) contains only one short phrase that could possibly be interpreted as linking the results to future scenarios of catastrophic global warming, some of the co-authors have made statements (for the press release and in media interviews) that spin the global warming mantra right over the top. Continue reading

Polar bears of W. Hudson Bay came ashore in 2009 as late as in 1992

It’s like pulling teeth, getting up-to-date information on breakup dates of Hudson Bay sea ice. You’d think with the importance of this seasonal event to the polar bears of Hudson Bay (some of which, we’re told, face the most perilous future of all polar bears worldwide), we’d get a press release every summer alerting us to the precise date of sea ice breakup and the subsequent arrival of the bears onshore. I’m thinking of something similar to the dispatches we get from the National Snow and Ice Data Center (NSIDC) when Arctic sea ice reaches its yearly maximum (e.g. March 2012) and its yearly minimum extent (e.g. September 2012).

Sadly, this is not the case.

So I was intrigued to see that a new paper just out in the Journal of Animal Ecology, by Seth Cherry (a Ph.D. student of Andrew Derocher) and colleagues, dealt with Hudson Bay breakup dates. I was hoping for some data beyond 2007, which has been the limit of information provided so far by polar bear biologists (see previous posts here and here). Unfortunately, because the methods for determining breakup dates in this paper are so different from previous ones (more detail below), the new data (1991-2009) can’t be compared to earlier studies that go back to 1979. But there is some good news.

Although you wouldn’t know it by the author’s conclusion, the results of the study confirm for this region my previously stated contention that polar bears need spring and early summer ice (March through June) for gorging on young, fat seals and documented declines in sea ice have rarely impinged on that critical feeding period – by which I meant, bears have seldom, if ever, been forced off the ice of Hudson Bay as early as June.

The study also confirms that there has not been any kind of spectacular retreat of sea ice breakup dates – coming earlier and earlier in the season – over the last 19 years and that polar bears did not arrive on shore in 2009 until very late – approximately 22 August – the same date they came ashore in 1992.

Below are two figures from the paper: one (the map) necessary to understand the new “Cherry method” of calculating breakup dates for Hudson Bay (no disrespect intended) and the other (the graph), which presents the data collected. The table with my converted breakup dates is below them. A few quotes from the study and some comments on it follows.

UPDATE (March 21 2013; 6:12 PM PST). A typo in the table has been fixed (2001 is Jun 21 not Jul 21) and the post amended accordingly.
UPDATE 2 (July 7, 2013) The Cherry et al. paper is now in print, the references have been updated accordingly.

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Polar bear distribution shows they are limited by winter ice extent

I’ve said it before but it’s worth saying again now that the sea ice in the Arctic is approaching its seasonal maximum extent and thickness: polar bears are limited by winter sea ice extent (Fig.1), not by the minimum extent of ice in the summer. Otherwise, their distribution would resemble the summer sea ice minimum (Fig. 2), not the winter maximum.

Despite the hue and cry about “declining sea ice,” polar bears are still as well distributed throughout their available winter habitat as they were in 1979, when detailed sea ice records began – see the map below. See further details on polar bear distribution here.

Figure 1. Polar bear distribution map (adapted from the one provided by the PBSG) compared to sea ice concentration at Feb 28 (at or near the seasonal maximum extent) 1979 and 2013. I can’t see a difference – can you see a difference? The only place there is consistently sea ice in winter but not polar bears is the Sea of Okhotsk, but there is no evidence that polar bears have ever lived there despite the presence of seals. Click to enlarge

Figure 1. Polar bear distribution map (adapted from the one provided by the PBSG) compared to sea ice concentration at Feb 28 (at or near the seasonal maximum extent) 1979 and 2013. I can’t see a difference – can you see a difference? The only place there is consistently sea ice in winter but not polar bears is the Sea of Okhotsk, but there is no evidence that polar bears have ever lived there despite the presence of seals. Click to enlarge

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Matt Ridley’s foreword to my “10 good reasons not to worry” list – “We should be listening to Susan Crockford”

Benny Peiser over at the Global Warming Policy Foundation has just posted an essay by well-known author Matt Ridley (including “The Rational Optimist”), entitled “We should be listening to Susan Crockford” which is included as a foreword to a pdf of my earlier post, “Ten good reasons not to worry about polar bears.”

This stand-alone pdf is especially suitable for sharing with friends and policy makers.

I encourage you to have a look.