<P> El Niño / ɛl ˈniːnjoʊ / (Spanish pronunciation: (el ˈniɲo)) is the warm phase of the El Niño Southern Oscillation (commonly called ENSO) and is associated with a band of warm ocean water that develops in the central and east - central equatorial Pacific (between approximately the International Date Line and 120 ° W), including off the Pacific coast of South America . El Niño Southern Oscillation refers to the cycle of warm and cold temperatures, as measured by sea surface temperature, SST, of the tropical central and eastern Pacific Ocean . El Niño is accompanied by high air pressure in the western Pacific and low air pressure in the eastern Pacific . The cool phase of ENSO is called "La Niña" with SST in the eastern Pacific below average and air pressures high in the eastern and low in western Pacific . The ENSO cycle, both El Niño and La Niña, cause global changes of both temperatures and rainfall . </P> <P> Developing countries that are dependent upon agriculture and fishing, particularly those bordering the Pacific Ocean, are usually most affected . In American Spanish, the capitalized term "El Niño" refers to "the little boy", so named because the pool of warm water in the Pacific near South America is often at its warmest around Christmas . The original name, "El Niño de Navidad", traces its origin centuries back to Peruvian fishermen, who named the weather phenomenon in reference to the newborn Christ . "La Niña", chosen as the' opposite' of El Niño, literally translates to "the little girl". </P> <P> Originally the term El Niño applied to an annual weak warm ocean current that ran southwards along the coast of Peru and Ecuador at about Christmas time . However, over time the term has evolved and now refers to the warm and negative phase of the El Niño Southern Oscillation and is the warming of the ocean surface or above - average sea surface temperatures in either the central and eastern tropical Pacific Ocean . This warming causes a shift in the atmospheric circulation with rainfall becoming reduced over Indonesia and Australia, while rainfall and tropical cyclone formation increases over the tropical Pacific Ocean . The low - level surface trade winds, which normally blow from east to west along the equator, either weaken or start blowing from the other direction . </P> <P> Historically, El Niño events are thought to have been occurring for thousands of years . For example, it is thought that El Niño affected the Inca Empire in modern - day Peru, who sacrificed humans in order to try to prevent the rains . Scientists have also found the chemical signatures of warmer sea surface temperatures and increased rainfall caused by El Niño in coral specimens that are around 13,000 years old . In around 1525 when Francisco Pizarro made landfall on Peru, he noted rainfall occurring in the deserts which subsequently became the first written record of the impacts of El Niño . Modern day research and reanalysis techniques have managed to find at least 26 El Niño events since 1900, with the 1982 - 83, 1997--98 and 2014--16 events among the strongest on record . </P>

When was el nino and la nina discovered