tipping point

For Arctic scientists, the summer of 2007 changed everything. That’s when, for the first time in history, record warmth melted the Northwest Passage, nearly opening it to shipping; turned a portion of the East Siberian Sea the size of Mexico into open ocean; and shrank the polar ice cap to a size never before reached so early in the March-to-September melt season, as documented by satellite since 1979. Jim Overland is interviewed.