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Human-caused global warming is poised to wipe out polar bears. The normally staid U.S. Geological Survey — studying whether the bear should be listed as a threatened species under the Endangered Species Act — concluded grimly last Friday:

Projected changes in future sea ice conditions, if realized, will result in loss of approximately 2/3 of the world’s current polar bear population by the mid 21st century. Because the observed trajectory of Arctic sea ice decline appears to be underestimated by currently available models, this assessment of future polar bear status may be conservative.

That’s right — this grim prediction is optimistic, a best-case scenario. In the next post, I’ll examine why polar bears are likely to go extinct by 2030 if not 2020. But first I need to dispense with a myth that polar bears are doing well — a myth propagated by people like Bjorn Lomborg in his new book, Cool It.

As an aside, Amazon.com amazingly invited Michael Crichton, the seriously confused global warming Denier, to be the book’s guest reviewer — perhaps Amazon.com should change its name to Deforestation.com. In his effusive review, Crichton repeats the myth:

Lomborg is only interested in real problems, and he has no patience with media fear-mongering; he begins by dispatching the myth of the endangered polar bears, showing that this Disneyesque cartoon has no relevance to the real world where polar bear populations are in fact increasing. Lomborg considers the issue in detail, citing sources from Al Gore to the World Wildlife Fund, then demonstrating that polar bear populations have actually increased five fold since the 1960s.

Uh, no. First off, if the Bush Administration’s USGS says the polar bear is facing devastation from global warming, you can safely say the claim has more credibility than anything Lomborg or Crichton write.

Second, global warming can temporarily boost polar bear populations. The 2004 study, “Polar Bears in a Warming Climate” in Integrative and Comparative Biology, explains:

In the short term, climatic warming may improve bear and seal habitats in higher latitudes over continental shelves if currently thick multiyear ice is replaced by annual ice with more leads, making it more suitable for seals.

Third, global warming can temporarily make it appear as if polar bear populations have increased. The 2006 study in Arctic, “Possible Effects of Climate Warming on Selected Populations of Polar Bears (Ursus maritimus) in the Canadian Arctic,” notes that for four of five polar bear populations in the Canadian Arctic:

… residents of coastal settlements have reported seeing more polar bears and having more problem bear encounters during the open-water season, particularly in the fall. In those areas, the increased numbers of sightings have been interpreted as indicative of an increase in population size, with the result that quotas for Inuit hunters were increased. However, in Western Hudson Bay, the decline in population size, condition, and survival of young as a consequence of earlier breakup of the sea ice brought about by climate warming have all been well documented (Stirling et al., 1999; Gagnon and Gough, 2005; Regehr et al., 2005; I. Stirling and N.J. Lunn, unpub. data [references in paper]). In Baffin Bay, the available data suggest that the population is being overharvested, so the reason for seeing more polar bears is unlikely to be an increase in population size.

What is the reason for seeing more polar bears, then?

… the sea ice is breaking up at progressively earlier dates, so that bears must fast for longer periods during the open-water season. Thus, at least part of the explanation for the appearance of more bears near coastal communities and hunting camps is likely that they are searching for alternative food sources in years when their stored body fat depots may be depleted before freeze-up, when they can return to the sea ice to hunt seals again.

So, no, there does not appear to be any evidence of a real or sustainable increase in polar bear population.

Fourth, some polar bear populations are clearly declining or on the verge of declining — not just in the Western Hudson Bay case noted above, but also in the Southern Beaufort Sea. A 2006 USGS study found an apparent decline in polar bears. The study also saw “declines in cub survival and physical stature” — the same trend that preceded “a significant decline in population size” in western Hudson Bay, Canada.

But what about the claim that “polar bear populations have actually increased five fold since the 1960s” and perhaps even risen slightly over the past two decades? This claim is well debunked by Dr. Andrew Derocher, Chair of the IUCN (World Conservation Union) SSC (Species Survival Commission) Polar Bear Specialist Group, which I will reprint at length here because this myth has gained new credibility thanks to Lumborg’s book:

The bottom line here is that it is an apples and oranges issue. The early estimates of polar bear abundance are a guess — there is no data at all for the 1950-60s. Nothing but guesses. We are sure the populations were being negatively affected by excess harvest (e.g., aircraft hunting, ship hunting, self-killing guns, traps, and no harvest limits). The harvest levels were huge and growing. The resulting low numbers of bears were due only to excess harvest but, again, it was simply a guess as to the number of bears.

After the signing of the International Agreement on Polar Bears in the 1970s, harvests were controlled and the numbers increased — there is no argument from anyone on this point. Some populations recovered very slowly (e.g., Barents Sea took almost 30 years) but some recovered faster. Some likely never were depressed by hunting that much, but the harvest levels remained too high and the populations subsequently declined. M’Clintock Channel is a good example. The population is currently down by over 60% of historic levels due only to overharvesting. Some populations recovered as harvests were controlled, but have since declined due to climate-related effects (e.g., Western Hudson Bay). In Western Hudson Bay, previously sustainable harvests cannot be maintained as the reproductive and survival rates have declined due to changes in the sea ice.

At this point, we lack quantitative data for an overall assessment of trend in Canada or Nunavut as a whole. There is, however, very strong evidence for a decline in Western Hudson Bay and the Southern Beaufort Sea based on quantitative studies. More recently, scientists working in the Southern Hudson Bay have reported a major decline in the condition of polar bears. A decline in condition was the precursor to the population decline in Western Hudson Bay. There is clear suggestion of a population decline due to over-harvest in Baffin Bay, Kane Basin and possibly Norwegian Bay.

The point is that you cannot simply summarize the status of polar bears-the information lies in the individual populations. You cannot put the various time periods together into a simplistic overview. Sea ice is declining but again, it is not declining the same everywhere. Some small areas of multi-year ice may improve habitat for polar bears. This latter point, however, does not mean that the habitat in all areas will improve and the predictions are very clear that the primary habitat of polar bears is at risk.

Dr. Derocher ends bluntly:

… no habitat, no seals; no seals, no bears. This never was an issue of polar bears alone. The only effective conservation approach is to protect the habitat and this is an issue of climate change. You can distort the issue any way you so desire. At the end of the day, the sea ice is disappearing. Take away the habitat and the species follows shortly thereafter (or before).

Comparing declines caused by harvest followed by recovery from harvest controls to declines from loss of habitat and climate warming are apples and oranges. Ignorant people write ignorant things.

The polar bear is at grave risk of extinction. Just when that extinction might come I will address in Part II.

This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.