Climate has shaped the course of history. Subtle variability in climate often dictates when there is famine and when there is plentitude. This is conveyed most strongly when normal patterns suddenly change. In Peru, for example, farmers have historically recognized años de abundancia (years of abundance) every 2 to 7 years. Unusually warm temperatures are accompanied by heavy rains, turning the coastal desert to abundant pasture. Crops and livestock thrive in regions where they typically languish. However, the sea, usually teeming with fish, becomes anomalously warm and dormant. This phenomenon, called El Niño (Little Boy or Christ Child) by Peruvians for its tendency to begin around Christmas, is now recognized as a disruption of the ocean-atmosphere system in the tropical waters of the Pacific with consequences felt around the globe. El Niño has received widespread attention because the interplay between winds and ocean currents affects not only the climate but also fisheries, marine biology, and, ultimately, human welfare.