In the Part 2 of my look at Ashley Cooper’s photographs of global warming published in The Guardian on June 3rd I concentrate on the single image of a dead, emaciated, polar bear.
The caption reads
A male polar bear that starved to death as a consequence of climate change. Polar bears need sea ice to hunt their main prey, seals. Western fjords of Svalbard which normally freeze in winter, remained ice free all season during the winter of 2012/13, one of the worst on record for sea ice around the island archipelago. This bear headed hundreds of miles north, looking for suitable sea ice to hunt on before it finally collapsed and died.
The US National Snow and Ice Data Center (NSIDC) has monthly maps of sea ice extent. The Western Fjords were indeed ice free during the winter of 2012/13, even in March 2013 when the sea ice reaches a maximum. In March 2012 Western Fjords were also ice free, along with most of the North Coast was as well. The maps are also available for March of 2011, 2010, 2009 and 2008. It is the earliest available year that seems to have the minimum extent. Screen shots of Svarlbard are shown below.
As the sea ice extent has been diminishing for years, maybe this had impacted on the polar bear population? This is not the case. A survey published late last year, showed that polar bear numbers has increased by 42% between 2004 and 2015 for Svarlbard and neighbouring archipelagos of Franz Josef Land and Novaya Zemlya.
Even more relevantly, studies have shown that the biggest threat to polar bear is not low sea ice levels but unusually thick spring sea ice. This affects the seal population, the main polar bear food source, at the time of year when the polar bears are rebuilding fat after the long winter.
Even if diminishing sea ice is a major cause of some starvation then it may have been a greater cause in the past. There was no satellite data prior to the late 1970s when the sea ice levels started diminishing. The best proxies are the average temperatures. Last year I looked at the two major temperature data sets for Svarlbard, both located on the West Coast where the dead polar bear was found. It would appear that there was a more dramatic rise in temperatures in Svarlbard in the period 1910-1925 than in period since the late 1970s. But in the earlier warming period polar bear numbers were likely decreasing, continuing into later cooling period. Recovery in numbers corresponds to the warming period. These changes have nothing to do with average temperatures or sea ice levels. It is because until recent decades polar bears were being hunted, a practice that has largely stopped.
The starvation of this pictured polar bear may have a more mundane cause. Polar bears are at the top of the food chain, relying on killing fast-moving seals for food. As a polar bear gets older it slows down, due to arthritis and muscles not working as well. As speed and agility are key factors in catching food, along with a bit of luck, starvation might be the most common cause of death in polar bears.