A comprehensive study of climate change in the Arctic, released Monday, does what few people anywhere in the debate have managed: it puts a face on global warming. Among the first victims, the study predicts, will be polar bears. That is because unbroken sea ice serves as a kind of herder for seals, concentrating them around breathing holes and other small openings, where they become polar bears' favorite prey. The study concludes that by 2070, the top of the world is likely to be mainly open blue water in the summer.