The IUCN Red List of Threatened Species (hereafter Red List) provides standardized information on the taxonomy, distribution, and conservation status of plants, fungi, and animals around the globe. In 2015, members of the IUCN Polar Bear Specialist Group completed an updated Red List assessment, which resulted in the polar bear (Ursus maritimus) being categorized as Vulnerable. Vulnerable is the lowest of three “threatened” categories, and indicates a species that faces a high risk of extinction in the wild. The polar bear was also listed as Vulnerable during the previous assessment in 2008, and has held this designation in most years since 1982. The 2015 assessment relied on quantitative analyses and is the most rigorous assessment to date for the species.
Summary of the 2015 polar bear assessment
Loss of Arctic sea ice due to climate change is the most serious threat to Polar Bears throughout their circumpolar range (Obbard et al. 2010, Stirling and Derocher 2012, USFWS 2015). We performed a data-based sensitivity analysis with respect to this threat by evaluating the potential response of the global Polar Bear population to projected sea-ice conditions. Our analyses included a comprehensive assessment of generation length (GL) for Polar Bears; development of a standardized sea-ice metric representing important habitat characteristics for the species; and population projections, over three Polar Bear generations, using computer simulation and statistical models representing alternative relationships between sea ice and Polar Bear abundance.
Our analyses highlight the potential for large reductions in the global Polar Bear population if sea-ice loss continues, which is forecast by climate models and other studies (IPCC 2013). Our analyses also highlight the large amount of uncertainty in statistical projections of Polar Bear abundance and the sensitivity of projections to plausible alternative assumptions. Across six scenarios that projected polar bear abundance three generations forward in time using the median and 95th percentile of estimated GL, the median probability of a reduction in the mean global population size greater than 30% was approximately 0.71 (range 0.20-0.95). The median probability of a reduction greater than 50% was approximately 0.07 (range 0-0.35), and the probability of a reduction greater than 80% was negligible. The International Union for the Conservation of Nature Red List Guidelines suggests that assessors consider nearly the full range of uncertainty in potential outcomes, and adopt a precautionary but realistic attitude toward risk tolerance (Section 3.2.3, IUCN 2014). In light of the significant probability, across scenarios, of a reduction in mean global population size greater than 30%, and the relatively low probability of a reduction greater than 50%, we conclude that Polar Bears currently warrant listing as Vulnerable under criterion A3c (IUCN 2014).
History of polar bear redlisting by IUCN
1996 Lower Risk/conservation dependent
IPCC. 2013. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK.
IUCN Standards and Petitions Subcommittee. 2014. Guidelines for Using the IUCN Red List Categories and Criteria. Version 11.
Obbard, M.E., Thiemann, G.W., Peacock, E. and DeBruyn, T.D (eds). 2010. Polar Bears: Proceedings of the 15th Working Meeting of the IUCN/SSC Polar Bear Specialist Group, Copenhagen, Denmark, 29 June–3 July 2009. pp. 235. IUCN, Gland, Switzerland and Cambridge, UK.
Stirling, I. and Derocher, A.E. 2012. Effects of climate warming on polar bears: a review of the evidence. Global Change Biology 18: 2694-2706.
USFWS. 2015. Polar Bear (Ursus maritimus) Conservation Management Plan, Draft. U.S. Fish and Wildlife Service, Region 7, Anchorage, Alaska.