Every spring, Nenana, Alaska, hosts a contest in which participants try to guess the exact minute that a wooden tripod placed on the frozen Tanana River will fall through the breaking ice. The contest started in 1917 as a diversion for railroad engineers, with a jackpot of $801 for the closest guess. It has grown into an event in which hundreds of thousands of entrants enter their guesses on the internet and vie for more than $300,000.

Because so much money and interest depends on the time of the ice breakup, it has been recorded to the nearest minute with great accuracy since 1917 (ch18_MCSP_Global_Warming). And because a standard measure of breakup has been used throughout this time, the data are consistent. An article in Science ([2001, October], Climate change in nontraditional data sets, Science, 294, 811) used the data to investigate global warming. Researchers are interested in the following questions: What is the rate of change in the date of breakup over time (if any)? If the ice is breaking up earlier, what is your conclusion? Does this necessarily suggest global warming? What could be other reasons for this trend? What is the predicted breakup date for the year 2015? (Be sure to include an appropriate prediction or confidence interval.) Write up a short report with your answers.