Every spring, residents of the town of Nenana in Alaska buy lottery tickets. They write down the day and minute when the ice on the Tanana River will break. A tripod stands on the ice, connected by a rope to a clock on the shore. When the ice breaks up, the tripod falls and stops the clock. That moment is the winner. The lottery has been running since 1917, and its tickets have turned into a climate thermometer.
El Niño is an abnormal warming of water in the tropical Pacific Ocean. It changes weather across the planet. But in Alaska, thousands of kilometers from the tropics, its influence is usually weak. To see it, you need a very long series of observations. The Nenana lottery provided 90 years of daily records.
Scientists compared river breakup dates in El Niño years with those in other years. In El Niño years, the ice broke up on average 3.4 days earlier. The difference is small but statistically significant. A test that randomly selected 14 years out of 90 showed that the probability of getting such a deviation by chance is only 1.1%. This means the connection is real. The reason is clear from meteorological data: in El Niño years, Alaska is warmer and has less snow, so the ice melts faster.
The Nenana Ice Classic lottery has existed since 1917, and its top prize in some years exceeded 300 thousand dollars. The tripod placed on the ice is connected to a clock on the shore: when the ice moves, the tripod falls and stops the mechanism. Residents guess not only the day but also the minute of the event.