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From Skeptical Science and many other sources:

In conclusion, the reason polar bears have been classed as threatened comes from the impacts of future climate change on the bears’ habitat. Current analysis of subpopulations where data is sufficient clearly shows that those subpopulations are mainly in decline. Further habitat degradation will increase the threats to polar bears.

However, Susan Crockford is frequently named as collecting evidence for the claim that polar bears are doing well, despite a reduction in sea ice. Crockford is adjunct professor at the University of Victoria, Canada. For example, from her blog, Polar bears have not been harmed by sea ice declines:

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

These claims appear to be well-sourced with links to research, from blog posts such as this one and this one. Blog posts themselves are, of course, not peer-reviewed, but it does appear to contain a lot of links to peer reviewed science.

Do the claims by Susan Crockford and others make sense? Is there substantial evidence to support the claim that polar bears are doing well despite a decline in sea ice? Or is the evidence solid that sea ice decline does substantially theaten the survival of polar bears?

For reference, IPCC AR5 WG2, Section 28.3.2.2.2 (PDF, 7.0 MiB, 46 pages) states that projected extinction of polar bears is unlikely, so I'm not entirely sure to what extent the claims by Susan Crockford are in disagreement with scientific consensus as collected by IPCC, which is surprisingly short on polar bears.

gerrit
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  • I read a story on this somewhere. Instead of staying on the sea ice and eating seals, the polar bears return to land earlier in the year and eat nesting birds. The numbers of the birds have ballooned because of climate change in their winter habitat in the southern US. – GEdgar Mar 03 '15 at 16:35
  • @GEdgar I heard weeks ago (during a departmental seminar with to-be-published research) that eider duck population in the northern Hudson Bay area has significantly declined, exactly because of increased polar bear predation. But the claim ultimately challenged here is the one that polar bears are threatened due to climate change. As with other climate change contrarian claims, I expected to find a refutal in IPCC AR5 WG2, but was surprised to read that IPCC considers extinction of polar bears unlikely. – gerrit Mar 03 '15 at 16:38
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    @gerrit "the claim ultimately challenged here is the one that polar bears are threatened due to climate change." ... I think if that is the claim it should be reflected in the question. It seems to me substantially different than a question about polar bears' current status and recent population trends. – Larry OBrien Mar 03 '15 at 18:01
  • @LarryOBrien I don't think it is substantially different. The claim that reduced sea ice is due to climate change is not challenged in this question (nor by Susan Crockford). I'm not sure what evidence could test whether polar bears are threatened due to climate change, apart from measurable responses of polar bear populations to already observed climate change. – gerrit Mar 03 '15 at 18:43
  • @gerrit "I'm not sure what evidence could test whether polar bears are threatened due to climate change, apart from measurable responses...." I agree, but of course hypotheses about future trends are not nearly as easy to answer as questions about data. (Perhaps the shift in food sources is unsustainable?) So to me, "how *are* polar bears doing?" seems substantially different than "how *will* polar bears do?" – Larry OBrien Mar 03 '15 at 18:58
  • @LarryOBrien Ok. For the question, I will stick to the claim in the question — how are polar bears presently doing amid observed reduction in sea ice — and leave the implications for the future to be considered elsewhere. – gerrit Mar 03 '15 at 19:15
  • If polar bears adapt to a land-based diet, with darker coats to blend in (see peppered moth), so they don't look or act like current polar bears, would that count? Also, they'll interbreed with grizzlies. – Foo Bar Mar 04 '15 at 18:05
  • @FooBar I don't know. If there is any evidence of that happening, I would welcome it as an answer to support "it depends how you look at it". – gerrit Mar 04 '15 at 19:38
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    @Gerrit blog post on the subject here http://www.carbonbrief.org/blog/2015/03/what-does-the-science-say-about-polar-bears-and-climate-change . I haven't read it, but I noticed it mentioned on twitter and remembered this question. Hope it has some useful info. –  Mar 05 '15 at 08:07
  • I don't have the citations here- hence not an answer - just empirical observation. Get up to Svalbard and the bears are starving, having to fight amongst themselves for limited food as the retreating sea ice reduces their former hunting grounds. They are not doing very well at all. – glenatron Mar 05 '15 at 10:13
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    @DikranMarsupial Interesting blog post. I read that (1) *Apart from Western Hudson Bay area, few areas have been sufficiently studied* (2) *it's important not to draw conclusions about polar bears as a species from a single population*, and (3) *the IUCN designated polar bears as "vulnerable", meaning the global population has declined by more than 30 per cent in 40 years*. Could it be that both Crockford and IUCN extrapolate from too little data? But then again, of course, even a small probability of a serious decline implies a large risk, warranting the IUCN vulnerable status. – gerrit Mar 05 '15 at 16:34
  • How old are polar bears as a species? If that time is greater than the time since the last time the Arctic was ice free, then what did they do last time? Both from my reading and from some personal experience bears are smart and adaptable. – Sherwood Botsford Mar 09 '15 at 19:11
  • @SherwoodBotsford Good questions. Polar bears are apparently [150–600 kiloyears old](http://www.livescience.com/19785-ancient-polar-bears.html), but we have apparently no evidence of an Arctic Ocean free of sea ice for [700 kiloyears](https://en.wikipedia.org/wiki/Climate_change_in_the_Arctic#An_end_to_summer_sea_ice.3F) (which does not mean it didn't happen for a single summer). – gerrit Mar 09 '15 at 20:31
  • That's fairly fast evolution. This source: http://nsidc.org/arcticseaicenews/faq/#summer_ice says that the arctic may have been ice free during the holocene 8,000 years ago, and prior to that during the Eemian interglacial at 120,000 years ago. That would be within the time span of current polar bears. However the claim is that temperatures were warmer in the arctic during that period, but not that it was ice free. Given how fast the arctic has melted, it would be a good bet that it was ice free in the Eemian. – Sherwood Botsford Mar 10 '15 at 23:07
  • New item from 16 July 2015: [*Polar bears fail to adapt to lack of food in warmer Arctic*](http://www.bbc.co.uk/news/science-environment-33551569). Based on: [*Summer declines in activity and body temperature offer polar bears limited energy savings*](http://www.sciencemag.org/content/349/6245/295) (Science). – gerrit Jul 17 '15 at 11:19
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    "which is surprisingly short on polar bears" - we need more polar bears to become climate scientists! – Andrew Grimm Sep 23 '15 at 22:33

1 Answers1

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We don't really know.

Despite the claims of a population boom, there is no definitive evidence to know how many polar bears there were "to begin with." One can't scientifically determine an end result with a variable starting point.

Polar Bears International asked Dr. Steven C. Amstrup, USGS polar bear project leader for 30 years the following question:

Q: Why all the fuss about polar bears? Aren't their populations increasing: in fact, booming?

A: One of the most frequent myths we hear about polar bears is that their numbers are increasing and have, in fact, more than doubled over the past thirty years. Tales about how many polar bears there used to be (with claims as low as 5,000 in the 1960s) are undocumented, but cited over and over again. Yet no one I know can come up with a legitimate source for these numbers.

PBI's official statement regarding a polar bear population boom:

A persistent myth to the contrary, polar bear numbers are NOT increasing.

An excellent article, by Peter Dykstra, in the Summer 2008 edition of Society of Environmental Journalists starts documenting all of the unfounded claims:

  • In a May 20 Los Angeles Times opinion piece, Jonah Goldberg took a whack at what he sees as quasi-religious overtones to conservation. Part of his backup? "Never mind that polar bears are in fact thriving — their numbers have quadrupled in the last 50 years."
  • James Taylor of the Heartland Institute cited a London Daily Telegraph article that "confirmed the ongoing polar bear population explosion" in a Sept 11, 2007, blog.
  • But the March 9, 2007, story that Taylor referenced actually makes no mention of global bear populations — quoting one scientist as observing strong growth in one local population, in Davis Strait; and another scientist reporting global warming-related declines in the local population in Hudson's Bay.
  • Taylor adds a new number into the mix from a March 26, 2008, posting at the Heartland site: "The global polar bear population has doubled since 1970, despite legal polar bear hunting."

  • A May 12 New York Post op-ed piece by S.T. Karnick introduces still another number — this time with a source:

    "The world polar-bear population is at a modern high — and growing. Mitch Taylor, a polar-bear biologist with Canada's Federal Provincial Polar Bear Technical Committee, notes that the bears now number about 24,000 — up about 40 percent from 1974, when fears arose about the bear's ability to survive overhunting by Canadian Eskimos and aboriginals."

  • From James Delingpole, a Times of London blogger, similar numbers, but different dates. And no source. "In 1950, let us not forget, there were about 5,000 polar bears. Now there are 25,000."

The article first extrapolates origins of the 5,000 number. Bjorn Lomborg's 2007 book, Cool It: The Skeptical Environmentalist's Guide to Global Warming." The book said, there were about 5,000. What was the footnote? "Krauss, 2006."

Clifford Krauss, a reporter for The New York Times, who wrote on May 27, 2006, about the conflict between polar bear protectors and trophy hunters: "Other experts see a healthier population. They note that there are more than 20,000 polar bears roaming the Arctic, compared to as few as 5,000 40 years ago." But he couldn't recall his source. He just said that number is widley accepted.

As we all know, Argumentum Ad Populum is a logical fallacy.

More commentary from Dr. Amstrup:

"How many bears were around then, we don't really know because the only studies of bears at that time were in their very early stages — people were just beginning to figure out how we might study animals scattered over the whole Arctic in difficult logistical situations. Some estimated that world population might have been as small as 5000 bears, but this was nothing more than a WAG. The scientific ability to estimate the sizes of polar bear populations has increased dramatically in recent years."

Ruut
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