Betting on global warming
Gambling has never been considered a science, but one long-standing wager has given scientists in Alaska highly accurate data on climate change.
The Nenana Ice Classic, where contestants place money on the exact minute they predict the ice on the Tenana River will break up, has been running for 84 years.
The records from this competition have been analysed and compared to climatic data, showing that the river is breaking up on average 5.5 days sooner, supporting the theory that the seasons are changing, reports the latest issue of Science.
"Contest records of the exact minute of ice breakup date back to 1917," they write in their paper. "They can be considered quite accurate, as the high stakes lead to constant vigilance at the time of breakup."
The researchers compared the records with climactic data for Nenana. The data included daily precipitation, snowfall and upper and lower air temperatures. Nenana is a small town of only 500 people, so the climate is unlikely to be affected by heat-island effects due to urbanisation. Any gaps in the records were filled by data from Fairbanks, 90km away.
The analysis shows that there is a definite trend towards earlier breakup of the ice. But over the years the timing has fluctuated. "The records show a warm period from 1920 to 1940, a cooling period until 1970, and resumed warming until the late 1990s," the paper states.
The bet began in 1917 as a diversion for railroad engineers who were forced to stop work as the river froze over. They bet on when the ice would break up and they could start work again.
The engineers devised a wooden tripod with black stripes to be used as the marker and the same design is still in use today. The time is recorded by the simple device of a wire reaching from the top of the tripod to a clock on shore. If the tripod moves, the clock stops automatically.
The prize was $800 in the first year. Today, hundreds of thousands of people pay $2 a ticket to enter the contest. This year, 18 people accurately predicted the tripod would fall through the ice on Tuesday May 8 at exactly 1pm. They shared the $308,000 jackpot.
The tripod is placed in the same area of the river each year. The location changed slightly before the 1970's because a close railroad bridge began to experience heavier and more frequent train traffic. The new location is still in the same straight section of the river that has not altered course substantially since the competition began.
Anecdotal evidence from the residents of Nenana indicates that in recent years, thermal breakups, where the ice under the tripod 'rots' away, have been more common than a dynamic breakup, where the ice cracks apart because of upstream mechanical forces.