Washington Post: For scientists, global warming is a disaster movie, its opening scenes set at the poles of Earth. The epic already has started. And it’s not fiction. The scenes are playing, at the start, in slow motion: The relentless grip of the Arctic Ocean that defied man for centuries is melting away. The sea ice reaches only half as far as it did 50 years ago. In the summer of 2006, it shrank to a record low; this summer the ice pulled back even more, by an area nearly the size of Alaska. Where …