As Arctic warms, scientists wrestle with its climate ‘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.