Every spring, the Alaskan village of Nenana (population 500) hosts the Nenana Ice Classic - a popular event that awards cash prizes to those lucky enough to guess when the annual ice breakup will occur on the nearby Tanana River. Winners must predict the exact minute that a specially constructed wooden tripod will crash through the icy surface.
Hundreds of thousands of people pay $2 a ticket to enter the contest. This year`s jackpot of $308,000 was divided among 18 winners who accurately predicted that the tripod would fall through the ice on Tuesday, May 8, at exactly 1 p.m.
For many Alaskans, the Ice Classic signifies the long-awaited arrival of spring. But for Stanford scientist Raphael Sagarin, the event is more than symbolic.
"What began as a wintertime diversion for railroad engineers has given us an unusual 84-year data set on the timing of river ice breakup," says Sagarin, a postdoctoral fellow at Stanford`s Hopkins Marine Station in Pacific Grove, Calif.
Writing in the Oct. 26 issue of Science, Sagarin and Fiorenza Micheli, assistant professor of biological sciences, explain how the Ice Classic and other historical records can serve as valuable tools for researchers studying global warming.
"Because scientists weren`t thinking about climate change 80 or 90 years ago, it`s really important that people kept these data," notes Sagarin, who has a keen interest in phenology - a branch of science that looks at the annual timing of natural events, such as bird migrations.
"Phenology used to be dismissed as a hobby of eccentric British naturalists, some of whom have family records dating back to the 1750s of when the first leaf appeared on a particular tree in spring," Sagarin says.
The Nenana Ice Classic was created in 1917 by engineers building a railroad bridge across the Tanana River, about 50 miles southwest of Fairbanks. When the river froze, the engineers had to stop work. According to Ice Classic historians, idle speculation about when the ice would break up is what led to the wagering.
To determine the contest winner, the engineers came up with an ingenious contraption still in use today. It consists of a tall tripod made of wooden logs painted with black-and-white stripes. A wire is attached from the top of the tripod to a clock on shore. When melting ice causes the tripod to move 100 feet, the clock stops automatically. The tripod and clock are monitored 24 hours a day by sharp-eyed villagers working in shifts.
"Contest records of the exact minute of ice breakup date back to 1917 and can be considered quite accurate, as the high stakes lead to constant vigilance at the time of breakup," write Sagarin and Micheli.
"The Nenana contest may be especially valuable because it is based on a more consistent definition of ice breakup than many records," they add.
The authors point out that river ice breakup is caused by a combination of thermal effects - when the ice "rots" or melts slowly - and dynamic effects - mechanical forces from upstream drift ice.
"Warmer climate would be expected to advance the time of breakup through both thermal effects and dynamic effects, due to thinning ice and increased snowmelt runoff into rivers," explain Sagarin and Micheli.
The authors analyzed the entire Ice Classic record and discovered that, on average, the Tanana River breakup occurs 5.5 days sooner than it did back in 1917. The earliest breakup on record took place on April 20, 1998; the latest on May 20, 1964.
"These results show that springtime is coming earlier," notes Sagarin. "This trend also matches up pretty well with historic temperature data from Nenana and Fairbanks."
He says that other phenological records from around the world documenting the springtime appearance of birds and new plant growth also reveal that spring is coming sooner - an indication that climate change is a reality that is affecting natural systems on Earth.
"This is nontraditional scientific knowledge, but simple observations are very important. For example, river ice breakup has direct economic consequences, because people who live along the Tanana rely on waterborne commerce," Sagarin says.
"Phenology was pooh-poohed until recently, but now it`s recognized as important data, because climate change is a relatively recent phenomenon that has caught scientists by surprise," he adds.
Sagarin says he might use his linear regression analysis to predict when the breakup will occur next spring.
His advice for those contemplating purchasing a ticket for the 2002 Ice Classic: "I wouldn`t enter a date that`s too late in the year."
-By Mark Shwartz-
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COMMENT: Raphael Sagarin, Department of Biological Sciences, Hopkins Marine Station (831) 655-6251; firstname.lastname@example.org
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