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.
This is the last sentence of paper’s abstract:
“This process of genome erosion and conversion may be a common outcome when climate change or other forces cause a population to become isolated and then overrun by species with which it can hybridize.”
This is the only statement in the entire paper that could be construed as referring to predicted catastrophic global warming – if you wanted to see it that way. It could also mean natural climate change, which is perhaps how it was intended to be interpreted.
But this is what co-author of the paper Beth Shapiro said, according to a CBC news item (March 15):
“We’ve seen that polar bears are hybridizing with brown bears now, at the edge of their range in Canada. I guess it means if we destroy all their habitat, and the only habitat that’s left for polar bears looks like brown bear habitat, then they’re just going to hybridize with brown bears and turn into brown bears.” [my emphasis]
And the same day, in the Windsor Star, there was another similar quote from Shapiro:
How polar bears got their white coat remains a scientific mystery, but newly published research suggests a way they could turn brown again.
One of the study’s authors says that’s what might eventually happen to some groups of modern bears as climate change alters their habitat.
“It’s not something that happened in the past and might happen in the future – it’s happening today,” said Beth Shapiro, one of the authors of the study published in the journal PLOS Genetics. [my bold]
Let’s be clear about the facts of recent hybridization between polar bears and brown bears: hybridization has occurred over the last 10 years or so in the western Arctic (see previous post here) because a few male brown bears invaded polar bear habitat. Male brown bears (grizzlies) wandered out over the sea ice in spring, when the ice was as thick as it gets all season and the landscape was the epitome of polar bear habitat. This recent hybridization did not happen because we destroyed polar bear habitat.
And surely even Shapiro knows that even the most pessimistic scenarios devised by climate modelers do not predict the total loss of winter sea ice in the Arctic – which is what any rational biologist would mean by “polar bear habitat.”
Similarly, in the press release, we have another co-author, Ed Green, suggesting that their research results portend a dire future for polar bears:
The findings suggest that continued climate warming and loss of arctic sea ice may lead to the same thing happening more broadly, said coauthor Richard E. (Ed) Green, an assistant professor of biomolecular engineering in UCSC’s Baskin School of Engineering. “As the ice melts in the Arctic, what is going to happen to the polar bears? In the ABC Islands, the polar bears are gone. They’re brown bears now, but with polar bear genes still present in their genomes,” he said. [my bold]
Apparently Ed Green thinks that the sea ice extent at the height of the last Ice Age (26,000 or so years ago), when it was so much colder than today that polar bears were forced out of the Arctic and onto ice that extended thousands of miles south into the northeast Pacific, is an appropriate analogy for “normal” polar bear habitat. And that the extremely rapid warming of the climate as the ice age ended, which caused the sea ice in the North Pacific to retreat completely, even in winter, is an appropriate analogy for the loss of summer sea ice decades from now predicted by some computer models.
Talk about drama queens – these two take the cake.
Stay tuned for a discussion of some of the science in the paper itself.
Cahill JA, Green RE, Fulton TL, Stiller M, Jay F, et al. 2013. Genomic Evidence for Island Population Conversion Resolves Conflicting Theories of Polar Bear Evolution. PLoS Genetics 9(3): e1003345. doi:10.1371/journal.pgen.1003345