Such a toll has a 71 per cent likelihood of occurring, the study states, a prediction determined by averaging three possible scenarios of polar bear reactions to melting sea ice. Three were needed because polar bears are divided into 19 subpopulations across the region and are not all reacting to ice melt in the same way. Some subpopulations have shown declines, some show nutritional stress while others have been observed as being either productive or simply stable.
‘The data used in our study were obtained from long-term research programs on polar bears across their range,’ explains Kristin Laidre, a principal scientist at the Polar Science Center, University of Washington who contributed to the report. One of the three scenarios projected a proportional decline of bears with sea ice. The other two projected losses out of already observed changes to 11 of the 19 subpopulations. ‘Finally, we also used satellite data from NASA to look at the sea ice trends in each subpopulation,’ she says.
Polar bears use platforms of sea ice to hunt for seals. Because they hunt little else, reductions in sea ice can seriously impact their nutrition and the survival rate of cubs. The satellite data revealed that ice cover has declined in all 19 of these subpopulation ranges over the last 35 years. ‘Anthropogenic climate change is the primary threat to the species because, over the long-term, global temperatures will increase and Arctic sea ice will decrease as long as atmospheric greenhouse gas concentrations continue to rise,’ the report states.
It concludes that its results are consistent with the polar bear having an IUCN listing of ‘vulnerable’.