It’s still based on the same flawed ecological premise as all previous models – it assumes that sea ice was a naturally stable habitat until human-caused global warming came along. It also uses slight-of-hand maneuvers to correlate declining summer sea ice and declining polar bear population numbers.
Just because they keep repeating the same hype doesn’t make it true.
Here’s an excerpt from the USGS press release (issued 6/30/2015 1:30:00 PM), Greenhouse Gas Emissions Remain the Primary Threat to Polar Bears [Note this is not a peer-reviewed paper but an in-house generated USGS government document]
“Substantial sea ice loss and expected declines in the availability of marine prey that polar bears eat are the most important specific reasons for the increasingly worse outlook for polar bear populations,” said Todd Atwood, research biologist with the USGS, and lead author of the study. “We found that other environmental stressors such as trans-Arctic shipping, oil and gas exploration, disease and contaminants, sustainable harvest and defense of life takes, had only negligible effects on polar bear populations—compared to the much larger effects of sea ice loss and associated declines in their ability to access prey.”
Additionally, USGS researchers noted that if the summer ice-free period lengthens beyond 4 months – as forecasted to occur during the last half of this century in the unabated scenario – the negative effects on polar bears will be more pronounced. Polar bears rely on ice as the platform for hunting their primary prey – ice seals – and when sea ice completely melts in summer, the bears must retreat to land where their access to seals is limited. Other research this year has shown that terrestrial foods available to polar bears during these land-bound months are unlikely to help polar bear populations adapt to sea ice loss.”
As I’ve shown previously, polar bears eat little in summer regardless of whether they are on land or out on the sea ice – summer is a time of fasting for virtually all polar bears, and the suggestion that terrestrial foods will not save polar bears is a red herring argument.
This report (Atwood et al. 2014) was release at the end of 2014 and simply adds a few more “expert opinions” as to how polar bears might respond to summer sea ice declines predicted decades into the future – that’s about all. It’s an update to the prognostications of Amstrup et al. 2010, itself an update of Amstrup et al. 2008 and Amstrup et al. 2007. They’re all flawed models popped out of the same bent mold.
Here’s the section from my Arctic Fallacy paper where I discussed these flawed models and the Atwood et al. (2014) “second generation” model (see it for the references and footnotes, pdf of entire essay here):
Even though the USA possessed the smallest proportion of the world’s polar bear habitat, the Act pronounced a global endangerment finding. Supported by eight internal government reports commissioned by the US Fish and Wildlife Service and prepared by the US Geological Survey rather than peer-reviewed academic papers, the justification for this listing hinged on what are called ‘Bayesian Network’ model results.
The models relied upon the opinions of a single expert regarding how polar bears might respond to predicted sea ice changes. The same complex Bayesian Network model approach was recently used to assess walrus responses to predicted sea ice declines (Jay et al. 2011:1068; Oakley et al. 2012:4), using four expert opinions.
However, the use of such complex but data-poor Bayesian Network models has been strongly criticized for this purpose (Akçakaya et al. 2006; Karl et al. 2012) a point that will be discussed in more detail below.
The 2007 polar bear model has since been revised to include the expert opinions of four additional biologists (Atwood et al. 2014), but still does not include any population estimates, any discussion of naturally-occurring variations in population size, or changes in polar bear health due to naturally occurring shifts in sea-ice conditions, particularly in the critical spring season.
The complex ‘second generation’ model produced in 2014 by Atwood and colleagues assumes the only sea ice change that ‘threatens’ polar bear health or population size is the predicted decline in summer ice extent blamed on human-caused global warming. The well-documented variations in spring ice thickness in the Southern Beaufort, and their associated repercussions on seal and polar bear populations, have been glossed over in favor of spurious correlations with summer-ice declines (Fig. 5).
Negative effects on populations of short-term natural variations in spring sea ice or spring snow cover on ice have been entirely ignored in these predictions and the focus, both in academic reports and media stories, has been on summer ice extent.
More disturbing is that population declines that were clearly caused by thick sea ice conditions in spring are now blamed on summer sea-ice declines. I repeat, since this is such a critical point, population declines that were clearly caused by thick sea ice conditions in spring are now blamed on summer sea-ice declines. These claims are based on spurious statistical correlations, and are used as ‘evidence’ that the predicted declines of sea ice in the future will have more pronounced effects.”
Amstrup, S.C.,Marcot, B.G. and Douglas,D.C. 2007. Forecasting the rangewide status of polar bears at selected times in the 21st century. Administrative Report, US Geological Survey. Reston, Virginia.
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
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.
Atwood, T.C.,Marcot, B.G.,Douglas,D.C., Amstrup, S.C., Rode, K.D.,Durner, G.M. and Bromaghin, J.F. 2014. Evaluating and ranking threats to the long-termpersistence of polar bears. USGS Open-File Report 2014–1254. Abstract and pdf available for download here (8.5 MB).