Earth is no stranger to the disruptive forces of sudden climate change. Tree-ring data show that sudden drying in the American West from 900 to 1400 induced one of the most tenacious megadroughts on record, turning river basins into sheets of sand and contributing to the collapse of the agrarian Pueblo "cliff-dweller" civilization. Scientists suspect that increased greenhouse gases may be forcing another shift, but no computer model is yet capable of forecasting if, when, and how fast that shift might be happening. So with a $2-million-a-year investment by the U.S. Department of Energy, six national laboratories and a host of universities are joining forces in a prediction project called IMPACTS (Investigation of the Magnitudes and Probabilities of Abrupt Climate Transitions). Led by Collins, IMPACTS will pinpoint the mechanisms that drive abrupt climate change and add them to the Community Climate System Model (CCSM), one of the country's two leading computer climate models. Accurate predictions won't eliminate changes, but they might give us time to prepare.