This summer, American scientists will be charting the sea floor north of Alaska on a Coast Guard icebreaker. Chief scientist Larry Mayer says that he’ll always remember two sights from last year’s voyage, when the ice had shrunk so much that the ship was able to research at least 100 miles farther north than was previously possible. He was excited by the first sight: the sea bottom captured on his computer screen. The floor was pocked with 300-foot-wide holes, an occurrence that usually indicates escaping natural gas.

The second sight occurred when Mayer was standing on deck. He spotted a lone polar bear drifting on a 30-foot-wide piece of ice. In the old days, the animal could have walked on solid ice back to land, but now it was bent and doomed. To Mayer, the two sights highlighted opportunity and tragedy in the least-mapped area of the world.