Is the climate changing? You bet. Or residents of Nenana, Alaska do, anyway. For the last 84 years, the folks in Nenana, 230 miles north of Anchorage, have been placing bets on when the ice would break up on the nearby Tanana River. The annual guessing game, known locally as the Nenana Ice Classic, allowed a team of Stanford University researchers to conclude, in an article published this week in the journal Science, that the breakup is occurring an average of 5.5 days earlier in recent years than it did in 1917. Scientists used to dismiss this kind of amateur data-gathering, but nowadays, with the push to prove that the climate is changing, many are taking it seriously. So are Ice Classic participants, who stand to win upwards of $300,000 if they guess right.