This May, polar explorers Lonnie Dupre and Eric Larsen will begin a four-month journey across the Arctic Ocean -- the first time a summer crossing will have been attempted. They will travel by slac, a combined sled/canoe, and expect to be in the water at least 30% of the time. Or perhaps even more: summer ice depth in the Arctic Ocean is less than half of what it was in the 1960s, and the ice fields have become sufficiently clear that even the long-sought "northwest passage" may soon be open. Dupre and Larsen intend to use the summer crossing as a way to draw attention to environmental disruption and the effects of global warming, and will be collecting snow samples every 50 miles to be analyzed for pollutants.