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Is El Niño something unusual in the Earth’s climate?

El Niño has been occurring for thousands of years based on tree ring data and other paleoclimate evidence. In the 19th Century, some scientists started to make the link between the warm water in the Pacific and droughts in India and Australia. While the existence of El Niño has been known, interest began to increase after the strong El Niño of 1982-83. The occurrence of the very strong El Niño in 1997-98 was a watershed event in terms of monitoring of the prediction of the El Niño Southern Oscillation and its impact on weather around the world. 

How can something in the Pacific Ocean affect our weather here in the Midwest?

The unusually warm water associated with an El Niño causes large-scale changes in the atmosphere that affect jet stream patterns. The warm waters off the coast of South America tend to strengthen and broaden an upper level ridge of high pressure along the west coast of the U.S. This has potential effects on weather patterns in the Midwest. First, the high pressure ridge can deflect intrusions of Arctic air to the east and north of the Midwest, resulting in warmer than normal winters. In addition, storm tracks are often much farther south during El Nino winters.  This will lead to drier than normal winters in the Midwest as less moisture is transported into the region.

The four Ninñ regions
Typical impacts of El Niño across the globe.  Image Credit: NWS JetStream.

How are other parts of the continent and world affected by El Niño?

The large-scale changes during an El Niño result in rising and descending air in different areas, leading to wetter than normal weather in some areas and drought in others.  For example, rising air over the warmer eastern Pacific Ocean results in increased storm development and more rainfall. When the air rises over the eastern Pacific, it descends over the western Pacific and over eastern South America. Descending air inhibits the development of convection and its associated rainfall and can lead to drought conditions over these areas. The large-scale upper air wave patterns altered by El Niño propagate around the globe, inducing changes in local weather.

How well can forecasters predict the existence and intensity of an El Niño event?

After the 1982-83 strong El Niño event, more emphasis was placed on its prediction. Scientists were able to forecast sea surface temperatures months ahead of the 1997-98 El Niño, providing advanced warning of its occurrence. The vast impacts of the 1997-98 El Niño spurred monitoring and prediction efforts. Since that time, monitoring of Pacific Ocean sea surface temperatures has increased through the use of buoy, ship, and satellite data. Models are run by a variety of institutions to predict the probability of the occurrence of El Niño.

Is El Niño related to or affected by climate change?

Some research suggests that a warming climate will not affect the frequency of El Niño events but could increase the frequency of strong to very strong events. However, the link between climate change and El Niño is complicated by natural variability and the effects of other large scale phenomena such as the Pacific Decadal Oscillation (PDO) and the North Atlantic Oscillation (NAO), among others. Researchers are continuing to study and untangle these relationships.

What is the history behind the term “El Niño”?

Peruvian sailors named the warm north-flowing current "El Niño" (“the Boy”, referring to the Christ child) because it was most noticeable around Christmas. They had noted changes in biological activity coinciding with the periodic appearance of El Niño.