Works in Progress: Nenana Ice Classic

Each year Alaskans wager when a frozen river will thaw, and science is the winner.

By Karen Wright
May 1, 2002 5:00 AMMay 9, 2023 4:59 PM


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In 1917 railroad engineers in Nenana, Alaska, started a betting contest only the snowbound and bored could invent. They wagered on the exact moment when a tall wooden tripod stationed on the frozen Tanana River would drift 100 feet downriver during the spring melt. The Nenana Ice Classic has drawn gamblers every year since: Several hundred thousand entrants from around the world will compete for a jackpot of more than $300,000 this year.

The winning bet best predicts when the tripod frozen into the Tanana River will drift 100 feet downriver. The earliest ice breakup was April 5, 1998. The latest was May 20, 1964.Photograph courtesy of Rasmuson Library/University of Alaska Fairbanks

Climatologists are betting the Ice Classic will have a scientific jackpot, too. Last year Stanford University scientists used contest records to gauge the impact of temperature increases over the 84 years since the event began. The analysis shows that, on average, ice on the Tanana breaks up five and a half days earlier than it once did—a shift that is bound to have significant consequences for plankton, fish, and birds, as well as human traffic. "It shows what I expected, that the ice breakup is occurring earlier each spring," says Raphael Sagarin of Stanford's Hopkins Marine Station in Pacific Grove, California. "And I suspected that because I was aware of the evidence from other nontraditional data sets."

In recent years, ecologists have sought unconventional sources, ranging from the trading logs of fur trappers to the diaries of wine makers, to get a better handle on the effects of climate change on living things. Subtle shifts in the timing of ecological events, such as when beavers breed or the first bluebirds land, can confirm suspected patterns of past climate variations or act as proxies when meteorological data isn't available. They can also herald more profound ecological disruptions.

"People around the world kept records of these events long before scientists became interested in them," says John Magnuson, a limnologist at the University of Wisconsin in Madison. "Sometimes it was for religious reasons, sometimes for practical ones, but mostly it was just out of basic curiosity."

Magnuson organized an international conference several years ago to review amateur accounts of lake and river ice cover in the Northern Hemisphere. Colleagues from across the United States, as well as those from Japan, Russia, Finland, Germany, Switzerland, and Canada compared notes on nontraditional records dating back to the ninth century. Two churches on either side of Lake Constance in central Europe, for example, kept meticulous logs of freeze-ups. When the lake froze over completely, villagers carried a statue of the Madonna from one church across the ice to the other, where it would stay until the next big freeze. No one knows why the Madonna crossed the lake, but her travels could be an indication that the last few centuries have been getting warmer.

Magnuson is mainly interested in the past 150 years, when industrialization is thought to have brought on global warming. He and his colleagues compared the freeze and thaw records of 26 bodies of water, from the Angara River in central Russia to Wisconsin's Lake Mendota, just outside Magnuson's window. Almost all revealed the same long-term trend toward freezing later in the year and thawing earlier. On average, freeze-ups happened almost six days later each century, and thaws happened about six days earlier. The changes correspond to an increase in air temperature of more than 2 degrees Fahrenheit each century.

"We wondered at first whether we should even use [these nontraditional records]," says Magnuson. "We had no way of going back and checking their methods. But the results were so consistent. It seemed inconceivable that they'd all be biased in the same way."

So Sagarin was not surprised when the Nenana records echoed Magnuson's findings. Sagarin read about the Ice Classic in a guidebook he bought while studying tidal pools on the Alaskan coast. "I instantly thought, 'Well, that would be a great historical record of climate change,'" he says. "What made me trust it is the almighty dollar, knowing how many eyes are trained on that tripod each year. There's almost no reason to believe that the recording of the time of the breakup has been manipulated."

Nenana natives start taking bets on each year's classic in February. Near the end of that month, they put the black-and-white painted poles of the tripod into holes drilled into the Tanana's ice. A flagged wire runs from the top of the tripod to a clock on shore. It's rigged so the wire snaps and the clock stops when the tripod moves 100 feet or more. As breakup time nears—between April 20 and May 20—designated tripod sentinels take shifts watching, too. On sunny weekends, people like to drive from Fairbanks and Anchorage and set up lawn chairs on the banks of the Tanana in hopes of catching the moment when the ice goes.

Every year, the organizers of the betting event, the Nenana Ice Classic, create a new poster. In 1917 the jackpot was $800. In 2001 it was $308,000. Tickets are $2 each and bets must be placed before April 5. In 2001 some 18 winners split the jackpot.Posters courtesy of the Nenana Ice Classsics

"I really like watching the earth go through this whole rebirthing thing," says Julie Coghill, a Fairbanks resident who has made the trek for most of the last 30 years. "The swans, the geese, the cranes, they're all coming back up north. It's cheap entertainment."

Sagarin never made it to Nenana. But he talked to the event's organizers to determine whether the tripod's position or criteria for breakup times had changed significantly over the decades. They hadn't, and the results of each year's contest, to the minute, are posted on the Ice Classic Web site ( When Sagarin checked local meteorological records, on the other hand, he found large gaps and inconsistencies. The Ice Classic register seemed more reliable than the professional logs, and it reflected global climate trends gleaned from other sources. "It corresponds almost perfectly with a cool period in that part of the world" from 1940 to 1970, he says.

Some amateur databases are problematic, in part because they're compiled by untrained observers, and in part because the observation of biological events—judging when, for example, a cherry blossom has fully opened—can be subjective. But veterans like Magnuson develop standards governing which records are accurate. Anyway, he points out, there aren't many alternative methods for tracing the annual effects of historical climate trends. Tree rings may be the only available records that aren't kept by human beings.

"I'm sure there are other data sets out there that we haven't seen yet," says Magnuson, who has already examined hundreds of amateur records. French investigators recently correlated the dates of 175 years of grape harvests with weather conditions caused by air currents over the Atlantic Ocean. Terry Root, of the University of Michigan, has consulted amateur birdwatchers' reports to see how Midwest wildfowl respond to changes in wetland conditions. Based on 41 years of data, she has predicted that droughts caused by global warming might cut pond populations in half in this century.

Sagarin's favorite analysis compares recent observations of bird arrivals and flower blooms in Wisconsin with notes kept by conservationist Aldo Leopold more than 65 years ago. The analysis suggests that some plants and animals are more flexible than others in responding to climate upheavals: Rose-breasted grosbeaks arrived earlier as temperatures increased, for example, but eastern towhees stuck to the same schedule. Information like that can be tough to uncover but remarkably rewarding. Magnuson says it's "like searching for gold."

To learn more about the Nenana Ice Classic, visit

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