The term El Niño is part of a broader phenomenon called El Niño-Southern Oscillation, or ENSO. It’s a recurring climate pattern involving changes in sea surface temperatures across the central and eastern tropical Pacific.

The phenomenon has three phases: the warm phase is El Niño, the cool phase is La Niña, and between the two lies a neutral or transitional phase, when neither dominates clearly. The changes occur in the tropical region of the Pacific Ocean, within 700 miles of the equator.