Cuffey's first big discovery came when he was working on ice cores as a doctoral student at the University of Washington. Ice cores--long cylinders extracted from an ice sheet by drilling down a mile or farther--provide a physical record of annual snowfalls going back thousands of years. By analyzing the chemical composition of the ice, researchers determine when past temperature swings occurred. Cuffey wanted to know how big those swings were. After a thermometer was lowered into a borehole left by the removal of an ice core, he analyzed the temperatures of the ice layers within, adjusting for variables such as the diffusion of surface temperatures through the ice over time. He calculated that since the last ice age, about 10,000 years ago, the Greenland ice sheet has warmed a full 15C--and 10 of that warming occurred in just a decade. "Our impression of how volatile the climate is has changed quite dramatically," says Bernard Hallet, Cuffey's graduate adviser. "Kurt's work had a profound impact on the whole community." No one is prophesying tsunamis hitting the Statue of Liberty, as depicted in Hollywood's recent thriller The Day after Tomorrow, but coastal cities would be inundated, and droughts would descend on key agricultural areas.