The intensity of El Niño events varies from weak temperature increases (about 4–5° F) with only moderate local effects on weather and climate to very strong increases (14–18° F) associated with worldwide climatic changes. El Niño events are indicated by sea surface temperature increases of more than 0.9° Fahrenheit for at least five successive three-month seasons.
Scientists use the Oceanic Nino Index (ONI) to measure deviations from normal sea-surface temperatures. Today, most scientists use the terms El Niño and ENSO interchangeably. Climatologists define these linked phenomena as El Niño-Southern Oscillation (ENSO).
When coastal waters become warmer in the eastern tropical Pacific (El Niño), the atmospheric pressure above the ocean decreases. The Southern Oscillation is a change in air pressure over the tropical Pacific Ocean. Led by the work of Sir Gilbert Walker in the 1930s, climatologists determined that El Niño occurs simultaneously with the Southern Oscillation. El Niño soon came to describe irregular and intense climate changes rather than just the warming of coastal surface waters. When capitalized, El Niño means the Christ Child, and was used because the phenomenon often arrived around Christmas. We have no real record of what indigenous Peruvians called the phenomenon, but Spanish immigrants called it El Niño, meaning “the little boy” in Spanish. However, El Niño is not a regular cycle, or predictable in the sense that ocean tides are.Įl Niño was recognized by fishers off the coast of Peru as the appearance of unusually warm water. El Niño events occur irregularly at two- to seven-year intervals. El Niño and La Niña are considered the ocean part of ENSO, while the Southern Oscillation is its atmospheric changes.Įl Niño has an impact on ocean temperatures, the speed and strength of ocean currents, the health of coastal fisheries, and local weather from Australia to South America and beyond. La Niña, the “cool phase” of ENSO, is a pattern that describes the unusual cooling of the region’s surface waters. El Niño is the “warm phase” of a larger phenomenon called the El Niño-Southern Oscillation (ENSO). El Niño is a climate pattern that describes the unusual warming of surface waters in the eastern tropical Pacific Ocean.
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