The El Niño–Southern Oscillation (ENSO) is a naturally occurring climate pattern involving fluctuations in sea-surface temperatures and atmospheric pressure across the tropical Pacific Ocean, affecting weather and climate in many parts of the world.
ENSO has three main phases: El Niño, La Niña, and ENSO-neutral. During El Niño, sea-surface temperatures in the central and eastern equatorial Pacific are warmer than usual. During La Niña, they are cooler than usual. During ENSO-neutral conditions, neither phase is established.
ENSO influences the movement of heat and moisture through the atmosphere, changing rainfall patterns, temperatures, and atmospheric circulation. Depending on the phase and location, these changes can increase the likelihood of droughts, floods, heat extremes, or changes in storm activity. ENSO can also affect agriculture, water availability, ecosystems, and human health.
ENSO is monitored using oceanic and atmospheric observations. Its phases develop over months and can persist for several seasons, although their duration and strength vary.
QUICK FACT
ENSO is a coupled ocean–atmosphere system: its behavior depends on interactions between the ocean and the atmosphere, not just changes in sea-surface temperature.
COMMONLY CONFUSED WITH
- El Niño: The warm phase of ENSO.
- La Niña: The cool phase of ENSO.
- ENSO-neutral: Conditions in which neither El Niño nor La Niña is present.
- Climate change: Long-term changes in climate patterns that can result from natural processes and human activities. ENSO is a recurring natural climate pattern that operates within the broader climate system.
SEE ALSO