What is El Niño?
The oceanic and atmospheric phenomenon known as El Niño occurs in
the Pacific Ocean when the western coasts of Ecuador and Peru experience
unusually warm ocean conditions that cause climatic disturbances of
varying severity. The term is used to describe exceptionally intense and
persistent occurrences, although originally it described the warm
southerly current that appears in the region every December. These
extreme climatic conditions occur every three to seven years and can
affect climates around the world for more than a year. The name El Niño,
Spanish for "the child," refers to the infant Jesus Christ and is used
because the current usually begins during the Christmas season. The
phenomenon is know as the El Niño Southern Oscillation, or ENSO, because
El Niño is accompanied by a flux in air pressure and wind patterns in
the southern Pacific.
What happens during El Niño?
El Niño causes climatic disturbances when sea surface temperatures
in the southeastern tropical Pacific are abnormally high. Usually, the
warm waters are restricted to the western tropical Pacific, where
temperatures are higher than the eastern waters of coastal Peru and
Ecuador by more than 10 degrees Celsius. The air pressure is low over
the warmer waters and moist air rises, resulting in the clouds and heavy
rainfall typical of southeastern Asia, New Guinea, and northern
Australia. In the eastern Pacific, the water is cold and air pressure is
high, creating the characteristically arid conditions along coastal
South America. In the east cold water rises to the surface as warm
surface water is pushed westwards by the trade winds blowing from east
However, during El Niño, the easterly trade winds
subside and sometimes change direction. This causes a change in sea
surface temperatures and increases in wind and pressure changes. Sea
surface temperatures along the western coast of South America experience
a substantial increase while the warm water of the western Pacific flows
back eastward. As this happens, there is a shift in weather patterns -
wet weather conditions normal to the western Pacific move to the east,
and the arid conditions common in the east appear in the west.
What are its consequences?
The shift in normal weather conditions can result
in heavy rains in South America, and droughts in southern
Africa, southeastern Asia and India, as well as unusual weather
to parts of North America. El Niño also has economic
consequences, for example in coastal Peru and Ecuador many
industries and livelihoods are upset by the destruction of fish
and bird populations due to a shortage of nutrients in the
What is La Niña? La Niña is characterized by
unusually cold ocean temperatures in the Equatorial Pacific,
compared to El Niño, which is characterized by unusually warm
ocean temperatures in the Equatorial Pacific.
The 1997 El Niño observed by TOPEX/Poseidon. The white areas off
the tropical coasts of South and North America indicate the pool
of warm water.)