Geoscience Reference
In-Depth Information
Box 2El Niño‒Southern Oscillation
One of the most important and mysterious elements in global climate is the periodic
switching of the direction and intensity of ocean currents and winds in the Pacific.
Originally known as El Niño ('Christ child' in Spanish), as it usually appears at
Christmas, and now more normally known as ENSO (El Niño-Southern Oscillation),
this phenomenon typically occurs every three to seven years. It may last from several
months to more than a year. The 1997-8 El Niño conditions were the strongest on re-
cord and caused droughts in the southern USA, East Africa, northern India, north-east
Brazil, and Australia. In Indonesia, forest fires burned out of control in the very dry
conditions. In California, parts of South America, Sri Lanka, and East Central Africa,
there were torrential rains and terrible floods.
ENSO is an oscillation between three climates: 'normal' conditions, La Niña, and 'El
Niño'. El Niño conditions have been linked to changes in the monsoon, storm patterns,
and occurrence of droughts all over the world. The state of the ENSO has also been
linked to the position and occurrence of hurricanes in the Atlantic. For example, it is
thought that the poor prediction of where Hurricane Mitch made landfall was because
the ENSO conditions were not considered and the strong trade winds helped drag the
storm south across Central America instead of west as predicted.
Predicting El Niño events is very difficult but getting steadily easier. For example,
there is now a large network of both ocean and satellite monitoring systems over the
Pacific Ocean, primarily aimed at recording sea-surface temperature, which is the ma-
jor indicator of the state of the ENSO. By using this climatic data in both computer
circulation models and statistical models, predictions are made of the likelihood of an
El Niño or La Niña event. We are really still in the infancy stage of developing our un-
derstanding and predictive capabilities of the ENSO phenomenon.
There is also considerable debate over whether ENSO has been affected by climate
change. The El Niño conditions generally occur every three to seven years and in the
last 30 years this has continued by with no discernable pattern. As El Niño conditions
occurred in 1987-8, 1991-2, 1994-5, 1997-8, 2003-4, and 2010-11 representing gaps
of four, three, three, six, and seven years, respectively. While La Niña events occurred
in 1989-90, 1997-8, 1999-2000, 2000-1, 2008-9, 2011-12, and 2012-13, represent-
