“Not only do the bears have to fast for longer and need more energy to get through this, they also have a harder time to accumulate this energy,” he said. While fasting, bears move as little as possible to conserve energy. But sea-ice loss and population declines create new problems — having to expend more energy searching for a mate, for example — that could further affect survival. Even under more modest warming projections, in which greenhouse gas emissions peak by 2040 and then begin to decline, many of the subgroups would still be wiped out, the research showed. Over the years, polar bears have become a symbol both for those who argue that urgent action on global warming is needed and for those who claim that climate change is not happening or, at best, that the issue is overblown.