Introduction | El Niño and La Niña (ENSO) | NAO and Artic Oscillation

El Niño and La Niña (ENSO)

All of a sudden one December…

…Peruvian fishermen find that many of the fish off their coast have died,
…Scuba divers in the Western Pacific find unhealthy coral reefs,
…giant thunderstorms bombard places from Tahiti to California,
…and drought and wildfires plague Indonesia.

Could all these events be connected? The answer is yes. During certain years the surface of the Pacific Ocean is warmed more than usual and wind patterns change. These changes cause the storms and drought and affect marine life like fish and corals. South American fisherman have given this phenomenon the name El Niño, which is Spanish for "The Christ Child," because it affects the planet at the same season, always around Christmas, the celebration of The Christ Child’s birth.

The 1997-1998 El Niño Event caused flooding in the town
of Lakeport, California. (Courtesy of FEMA)

Scientists call this phenomenon the El Niño/Southern Oscillation (or ENSO for short). El Niño refers to changes in the ocean and the Southern Oscillation refers to changes in the winds over the Pacific. Normally, strong winds blow across the Pacific from the east. The winds push water across the Pacific Ocean. During an ENSO event, the winds are not as strong in the western Pacific Ocean. Without the winds pushing, warm water from the western Pacific , which was piled up when the winds were blowing strongly, flows toward South America.

Every ENSO event is a bit different. Scientists are studying ENSO so that we can better understand how it changes the weather and how it might affect people and marine life.