A female polar bear and her cubs rest on pack ice in northern Alaska’s Beaufort Sea. The bears specifically evolved to live on the ice, and do not thrive on land. With their habitat melting more rapidly than scientists anticipated, they are seriously threatened. “As far as rescuing polar bears before their habitat disappears, there really is no rescue,” expert Steven Amstrup says. Scientists say reduction of carbon dioxide emissions is urgent to save their habitat. (USFWS/AP Photo)