The long-awaited 2015 IUCN Red List assessment for polar bears was released today (Wiig et al. 2015) and it includes some rather astonishing details − including the fact that the population trend is unknown.
1) It confirms the global population size I published in May 2015 (20,129-32,558; average 26,344). See the graph below, now amended to reflect this point. If global numbers do decline over the next 35 years, it will be from a high point not previously acknowledged by the IUCN Polar Bear Specialist Group (PBSG).
2) The current population trend is listed as: ? Unknown. [NOT declining – if anyone claims it is, send them here: IUCN Red List U. maritimus]
3) It puts the generation time for polar bears at 11.5 years (range 9.8-13.6), a huge drop from the 15 years used in previous predictive models. This change makes a big difference to the model results: three generations (the minimum period needed to show a trend) are now 35 years rather than 45 years.
4) It states there is a 70% chance of a 30% decline in polar bear numbers by 2050 and a 7% probability of a reduction > 50% if sea ice declines as predicted, but noted the large amount of uncertainty in these projections. That means there is a greater chance that numbers will not decline by 30% in the next 35 years (a 30% chance) than that the numbers will decline by 50% or more by 2050. That sounds like good news to me.
5) It will continue to list polar bears as Vulnerable. PBSG biologists managed to prevent polar bears from being listed as Least Concern or perhaps Near Threatened. But they had to give up a lot to get it.
6) The report supplement (Wiig et al. 2015 supppl.) explained why they did not calculate extinction probabilities and extinction is not mentioned at all on the IUCN Red List polar bear assessment page. This assessment only considers the probabilities of a decline in population size by 2050.
Yet, a spokesperson for the IUCN apparently stated (The Guardian, Climate change is ‘single biggest threat’ to polar bear survival; 19 November 2015 ) that:
“There is a high risk of extinction and the threat is serious,” said Dena Cator of the IUCN’s species survival commission. “You could consider polar bears to be a canary in the coal mine. They are an iconic and beautiful species that is extremely important to indigenous communities. But changes to their sea ice habitat are already being seen as a result of climate change.”
Apparently Dena Cator does not expect that people will read the report or find the assessment page on the IUCN Red List website – or she’s giving her personal opinion rather than explaining the report results. More on the points above and links to the report supplement pdf below, with quotes.
1) The assessment includes subpopulation size estimates previously demoted to zero by the IUCN Polar Bear Specialist Group because they were deemed not scientific enough. The Chukchi Sea is considered to have approximately 2,000 bears; East Greenland 2,000 bears; Kara Sea 3,200 bears; Laptev Sea 1,000 bears. The IUCN Red List folks insisted they be included, vindicating my continued objections that removing these estimates from the total were unscientific and misleading. Only the Arctic Basin subpopulation was not given a population estimate (Wiig et al. 2015 Supplement, Table 3).
2) The status pronouncement that Google offers up first at the top of the page (see below) when you search for “IUCN Red List Ursus maritimus” (based on info from the “Encyclopedia of Life” which Google apparently thinks is an authority, NOW NEEDS TO BE CHANGED. THE POPULATION TREND IS UNKNOWN.
3) In the Wiig et al. 2015 supplement file, it has this to say about comparing this new analysis, with its tightened analytical methods, to previous predictions:
“However, different analytical frameworks and approaches to interpreting outcomes make comparison of our analysis with a Bayesian Network difficult. Furthermore, Atwood et al. (2015) considered a large suite of potential stressors for Polar Bears, and interactions among stressors, whereas our approach included only statistical (i.e., non-mechanistic) relationships between abundance and sea ice.” [my bold]
And regarding the uncertainty of predicting future polar bear population changes:
“Our findings represent a sensitivity analysis based on limited data and several plausible but un-tested assumptions…
Overall, our analysis highlights the potential for large reductions in Polar Bear abundance if sea-ice loss continues over the long-term, which is forecasted by climate models and other studies (IPCC 2013). It also highlights the large amount of uncertainty in even simple statistical projections of Polar Bear subpopulations, and the sensitivity of these projections to plausible alternative assumptions.” [my bold]
6) The 2015 IUCN Red List assessment did not calculate an extinction risk estimate for polar bears in part because for many subpopulations, only two population estimates are available over a relatively short period of time (see pg. 14 in the Wiig et al. 2015 supplement file). In other words, it would have been unscientific to do so.
Citation for the report:
Wiig, Ø., Amstrup, S., Atwood, T., Laidre, K., Lunn, N., Obbard, M., Regehr, E. & Thiemann, G. 2015. Ursus maritimus. The IUCN Red List of Threatened Species 2015: e.T22823A14871490. Published online here;
PDF copy of that report page: 2015 IUCN Red List Ursus maritimus (Polar Bear) – www_iucnredlist_org_Nov 18 2015
PDF of supplement, as issued: 2015 IUCN Red List report 22823_Ursus_maritimus; PDF of supplement, marked by SJC: 2015 IUCN Red List report MARKED 22823_Ursus_maritimus
You must be logged in to post a comment.