El Niño, La Niña, and the Southern Oscillation

El Niño-Southern Oscillation, ENSO, is a dominant mode of climate variability affecting the earth. Occurring every 2–7 years, ENSO arises due to air–sea interactions in the tropical Pacific Ocean and is marked by anomalously warm or cool sea-surface temperatures in the central-to-eastern equatorial Pacific. Warm events in the eastern equatorial Pacific are called El Niño events, and cool events are called La Niña events. Climate and weather phenomena associated with ENSO include floods, droughts, heat waves, and tropical cyclones, which can lead to effects on fisheries, agriculture, health, and air quality.