El Niño

El Niño (/ɛl ˈniːn.joʊ/; Spanish: ) is the warm phase of the El Niño–Southern Oscillation (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 the area off the Pacific coast of South America. The ENSO is the cycle of warm and cold 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. El Niño phases are known to occur close to four years, however, records demonstrate that the cycles have lasted between two and seven years. During the development of El Niño, rainfall develops between September–November. The cool phase of ENSO is La Niña, with SSTs in the eastern Pacific below average, and air pressure high in the eastern Pacific and low in the western Pacific. The ENSO cycle, including both El Niño and La Niña, causes global changes in temperature and rainfall. Developing countries that depend on their own agriculture and fishing, particularly those bordering the Pacific Ocean, are usually most affected. In American Spanish, the capitalized term El Niño means 'the boy'. In this phase of the Oscillation, the pool of warm water in the Pacific near South America is often at its warmest about Christmas. The original name of the phase, El Niño de Navidad, arose centuries ago, when Peruvian fishermen named the weather phenomenon after the newborn Christ. La Niña, chosen as the 'opposite' of El Niño, is American Spanish for 'the girl'. 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. Historically, El Niño events are thought to have been occurring for thousands of years. For example, it is thought that El Niño affected the Moche 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. Currently, each country has a different threshold for what constitutes an El Niño event, which is tailored to their specific interests. For example, the Australian Bureau of Meteorology looks at the trade winds, SOI, weather models and sea surface temperatures in the Nino 3 and 3.4 regions, before declaring an El Niño. The United States Climate Prediction Center (CPC) and the International Research Institute for Climate and Society (IRI) looks at the sea surface temperatures in the Niño 3.4 region, the tropical Pacific atmosphere and forecasts that NOAA's Oceanic Niño Index will equal or exceed +.5 °C (0.90 °F) for several seasons in a row. However, the Japan Meteorological Agency declares that an El Niño event has started when the average five month sea surface temperature deviation for the NINO.3 region, is over 0.5 °C (0.90 °F) warmer for six consecutive months or longer. The Peruvian government declares that a coastal El Niño is under way if the sea surface temperatures in the Niño 1 and 2 regions equal or exceed +.4 °C (0.72 °F) for at least three months. There is no consensus on if climate change will have any influence on the occurrence, strength or duration of El Niño events, as research supports El Niño events becoming stronger, longer, shorter and weaker. El Niño events are thought to have been occurring for thousands of years. For example, it is thought that El Niño affected the Moche in modern-day Peru, who sacrificed humans in order to try to prevent the rains. It is thought that there have been at least 30 El Niño events since 1900, with the 1982–83, 1997–98 and 2014–16 events among the strongest on record. Since 2000, El Niño events have been observed in 2002–03, 2004–05, 2006–07, 2009–10, 2014–16, and 2018-19.