Christina Wu at the Urban Times (July 3, 2014) recently asked this question. She came up with a surprisingly balanced argument but some predictable responses from IUCN Polar Bear Specialist Group (PBSG) biologists. As a consequence, she overlooked some critical facts that make a big difference to the answer.
Figure 1. Predictions of polar bear population declines by 2050 are being used by the Center for Biological Diversity, WWF and Polar Bears International to solicit donations.
UPDATED 18 May 2015 – see below.
Wu stated that, for the populations for which we have numbers (see my discussion here), polar bear populations have been increasing overall since the 1970s. She then asked:
“So if polar bear populations are increasing, what’s all the fuss about?”
She went to PBSG biologists for answers. She talked to Elizabeth (Lily) Peacock, now a medical student, and Geoff York, who is employed full time for the World Wildlife Fund (WWF). Apparently, they did not correct her conclusion that polar bear numbers are currently increasing but brought up their concerns about the future instead.
Wu quoted Peacock as saying:
“Some populations appear to be doing OK now, but what’s frightening is what might happen in the very near future.”
“Frightening” is a pretty loaded word for a scientist to use. And notice the “might” – rain might be predicted two weeks from now but that doesn’t mean it’s guaranteed to rain.
Regarding the models used to predict the future for polar bears, remember that Steven Amstrup, who is now a full time spokesperson for Polar Bears International [“Save our sea ice”], was the only polar bear expert consulted about how polar bears might respond to the sea ice changes generated by climate models. As I’ve pointed out previously (here and here), Amstrup appears to have been wrong, at least as far as his predictions on polar bear responses to declines in summer sea ice (July-September) are concerned.
Wu then repeats some so-called “facts” about Western Hudson Bay bears we’ve heard time and again from biologists:
“The number of cubs observed in Hudson Bay is significantly lower than what it used to be, and while older bears are fat enough to survive a few lean years, younger bears are weaker. These low numbers undermine the idea that increasing numbers of bears are the result of overall population growth.”
I expect, like most people, Wu does not realize that none of this information is published – the results of the research upon which these statements are based are not available for anyone to look at.
These data are critical evidence in support of the claim that polar bears are already being harmed by sea ice declines attributed to anthropogenic global warming – they are the most widely cited claims. Yet, the biologists responsible for the research haven’t bothered to get it published, even in preliminary form (see previous posts here and here). Why not? The logical conclusion is that the data actually don’t support their claims, but until we see the reports, no one will know for sure.
The PBSG acknowledged this missing data in their latest (14 February 2013) population status report (pdf here) for the Western Hudson Bay subpopulation. They say it will be forthcoming in 2014, but we haven’t seen it yet.
UPDATE [18 May 2015]: An internal government report has finally been released on recent (2005-2011) WHB mark-recapture work (PDF HERE; discussed here) but it contains a population estimate only. It has no figures on changes (if any) on number of cubs, size of litters, or condition of bears over time for 1984-2011 (previous study period ended in 2004). The authors (Lunn et al. 2013:18) calculated a new estimate for the population at 2004 (previous count), using the same method they used for their new count in 2011; this generated an estimate of 742 (630-872) for 2004, vs. the 806 (653-984) estimated for 2011. This indicates that there has been no decline in population numbers since the last estimate was calculated in 2004.
In addition, Lunn and colleagues (see pg 15) found no significant trend in either breakup or freeze-up dates over the period 2001-2010 (using a definition of 50% ice cover, rather than polar bear-relevant definitions of 30%/10% determined by Seth Cherry and colleagues in 2013, discussed in detail here). They also acknowledged that they did not cover a significant portion of the WHB population territory in their 2005-2011 mark-recapture surveys and this likely accounted for the difference between their estimate and the one calculated from an aerial survey in 2011.
As a consequence, the PBSG updated their population status table in late January 2015. They listed the WHB subpopulation estimate as “1030” and its trend as “stable,” in agreement with Environment Canada’s recent assessment.
Geoff York then makes a point for Wu that’s a classic strawman tactic:
“The thing to remember is the vast range of the polar bear and the utter size of the Arctic. Impacts from warming are unfolding at different rates and different time scales.”
Wu, presumably echoing the rest of York’s answer, compares future Southern Hudson Bay habitat (including James Bay) to habitat in the High Arctic Archipelago in central Canada:
“And while we reiterate the fact that global warming could prove to be catastrophic by reducing available ice in the southern reaches of the bears’ range, higher north, such an increase of open waters could actually make hunting easier.“
That statement is certainly true – that’s what the models predict. But what York didn’t tell her is that recent research contradicts a number of assumptions about polar bear responses to reduced summer sea ice that has already happened. Talking abstractly about possible future habitat differences is deliberate obfuscation of the pertinent facts from contemporary research that contradict the predictions that have been made.
Here are just a few of those facts:
1) Changes to Western Hudson Bay sea ice conditions over the last 30 years have been virtually identical to Southern Hudson Bay, yet between 1998 and 2004, Southern Hudson Bay bear population numbers remained stable while those in Western Hudson Bay declined (details here and here). UPDATE – see note above regarding updated WHB sea ice and population size data.
2) Davis Strait sea ice habitat declined almost as much over the last 30 years as it did in Hudson Bay, yet its polar bear population almost doubled (details here and here). UPDATE – see posts here and here regarding Davis Strait sea ice coverage for spring 2015.
3) Over the last 30 years, sea ice habitat in the Chukchi Sea (north of the Bering Sea, between Alaska and Russia) has declined more than almost any other region in the Arctic yet a recent study showed polar bears there are in excellent condition and reproducing well (details here, here, and here) – two hallmarks of a healthy population and the opposite of the predictions made by Amstrup and colleagues (see References, below, including Amstrup et al. 2007). UPDATE – see also this recent post: If summer ice was critical for S. Beaufort polar bears, 2012 would have decimated them.
Wu ends with a surprising note:
“Finally, to make things a little more complex, having too many bears may lead to higher competition for resources, which would then decrease the health of the entire population, and which is why limited hunting of bears has been seen as a potential way of increasing overall health.”
This statement reflects suggestions made in the literature (discussed previously here and here) that some polar bear populations (e.g., Barents Sea, Western Hudson Bay, Davis Strait) have grown so much since they were protected by international treaty in 1973 that they may have reached their maximum sustainable size. Biologists have admitted that it is probably not yet possible to separate the effects of summer sea ice declines from those of increased population size on polar bear population health, that attribution of blame is complicated.
So, are polar bears really threatened with extinction? All the evidence says they are not in any trouble right now: the classification of polar bears as ‘threatened with extinction’ is based completely on predictions made by computer models about what might happen by 2050. However, the results of recent polar bear research have disproved, or called into question, many of the assumptions used to make those models work. That leads me to conclude that polar bears are not endangered.
See Wu’s entire article here.
References
Amstrup, S.C. 2011. Polar bears and climate change: certainties, uncertainties, and hope in a warming world. Pgs. 11-20 in R.T. Watson, T.J. Cade, M. Fuller, G. Hunt, and E. Potapov (eds.), Gyrfalcons and Ptarmigan in a Changing World, Volume 1. The Peregrine Fund, Boise, Idaho. http://dx.doi.org/10.4080/gpcw.2011.0100
Amstrup, S.C., DeWeaver, E.T., Douglas, D.C., Marcot, B.G., Durner, G.M., Bitz, C.M., and Bailey, D.A. 2010. Greenhouse gas mitigation can reduce sea-ice loss and increase polar bear persistence. Nature 468:955-958. http://www.nature.com/nature/journal/v468/n7326/abs/nature09653.html
Amstrup, S.C., Marcot, B.G., Douglas, D.C. 2007. Forecasting the range-wide status of polar bears at selected times in the 21st century. USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision, U.S. Geological Survey Administrative Report, USGS, Reston, Virginia. http://www.usgs.gov/newsroom/special/polar_bears/
Amstrup, S.C., Marcot, B.G., Douglas, D.C. 2008. A Bayesian network modeling approach to forecasting the 21st century worldwide status of polar bears. Pgs. 213-268 in Arctic Sea Ice Decline: Observations, Projections, Mechanisms, and Implications, E.T. DeWeaver, C.M. Bitz, and L.B. Tremblay (eds.). Geophysical Monograph 180. American Geophysical Union, Washington, D.C. http://onlinelibrary.wiley.com/doi/10.1029/180GM14/summary and http://alaska.usgs.gov/science/biology/polar_bears/pubs.html
Cherry, S.G., Derocher, A.E., Thiemann, G.W., Lunn, N.J. 2013. Migration phenology and seasonal fidelity of an Arctic marine predator in relation to sea ice dynamics. Journal of Animal Ecology 82(4):912-921.
http://onlinelibrary.wiley.com/doi/10.1111/1365-2656.12050/abstract
Durner, G.M., Douglas, D.C., Nielson, R.M., Amstrup, S.C., McDonald, T.L. and 12 others. 2009. Predicting 21st-century polar bear habitat distribution from global climate models. Ecological Monographs 79:25-58. http://www.esajournals.org/doi/abs/10.1890/07-2089.1
Lunn, N.J., Regehr, E.V., Servanty, S., Converse, S., Richardson, E. and Stirling, I. 2013. Demography and population assessment of polar bears in Western Hudson Bay, Canada. Environment Canada Research Report. 26 November 2013. PDF HERE
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