El Niño and La Niña
For almost five centuries, coastal residents of Peru noted and recorded a strange feature of the eastern Pacific Ocean waters that border their home. In the first months of each year, a warm southward current usually modified the normally cool waters. But every few years, this warming started earlier—in December. It was far stronger than usual, and it lasted as long as a year or two. Torrential rains fell on the arid land; as one early observer put it, "The desert becomes a garden." However, warm waters flowing south also shut off the deeper, cooler waters that are crucial to sustaining the region's marine life.
El Niño Visualizations
This is El Niño, "The Baby Boy," so named by the Peruvians because of its typical appearance around Christmas time. Once thought to affect only a narrow strip of water off Peru, El Niño is now recognized as a large-scale oceanic warming that affects most of the tropical Pacific. The weather impacts related to El Niño and its counterpart, La Niña (a cooling of the eastern tropical Pacific), extend throughout the Pacific Rim to eastern Africa and beyond.
El Niño is normally accompanied by a change in atmospheric circulation called the Southern Oscillation. The ENSO phenomenon (standing for El Niño–Southern Oscillation) is one of the main sources of interannual, or year-to-year, variation in weather and climate around the world.
Since recognizing some 30 years ago that the oceanic and atmospheric parts of ENSO are strongly linked, scientists have moved steadily toward a deeper understanding of El Niño. Climate forecasters have taken the first steps toward predicting the onset of El Niño and La Niña events months in advance.
NCAR scientists have been at the forefront of research placing El Niño in a global context, analyzing ENSO and its manifestations around the world.
In the 1970s and 1980s, social scientists at NCAR were among the first to examine how the phenomenon affected the people of South America and other regions. They have since collaborated on international projects involving dozens of nations in examining how forecasts of El Niño and La Niña could improve their citizens' lives.
Groundbreaking climate simulations have shown the occurrence of El Niño as far back as the last ice age. And NCAR scientists have demonstrated how El Niño, La Niña, and other regional cycles of the ocean and atmosphere can influence weather and climate thousands of miles away.
Computer models disagree on how El Niño and La Niña will be affected by long-term climate change. One possibility is a steady-state warming in the central Pacific that would have some characteristics of El Niño.
El Niño and Long-term Climate Change
Computer models disagree on how El Niño and La Niña will be affected by long-term climate change. One possibility is a steady-state warming in the central Pacific that would have some characteristics of El Niño. This schematic shows areas that have a consistent change in precipitation pattern linked to the first year of an El Niño event. The months in which the effect is seen are grouped by their first initials (for example, OND is October, November, December). (Illustration courtesy Kevin Trenberth, NCAR.).
