Study: Polar bears are disappearing Global warming is being blamed for a rise in the death of polar bear cubs. GLOBAL warming is being blamed for a rise in the death of polar bear cubs. A NEW US-Canada study says a key polar bear population fell by almost half in the past decade, with scientists seeing a dramatic increase in young cubs dying. Researchers chiefly blame shrinking sea ice from global warming. Scientists from the US Geological Survey and Environment Canada tagged and released polar bears in the southern Beaufort Sea from 2001 to 2010. The bear population shrank to about 900 in 2010, down from about 1,600 in 2004. Study lead author Jeff Bromaghin said only two of 80 polar bear cubs the team tracked between 2004 and 2007 survived. Normally about half of cubs live. He thinks the cubs starved because there was a lack of summer sea ice and they couldn't get to seals. The study is in the journal Ecological Applications.