El Nino
El Niño is a climate pattern that describes the unusual warming of surface waters along the tropical west coast of South America. El Nino has an impact on ocean temperatures, the speed and strength of ocean currents, the health of coastal fisheries, and local weather from Australia to South America. El Niño events occur irregularly at two- to seven-year intervals. However, it is not a regular cycle, or strictly predictable in the sense that ocean tides are. El Niño has long been recognized by fishers off the coast of Peru as the yearly appearance of unusually warm water in the Pacific Ocean. The name El Niño, meaning the "little boy" in Spanish, was used because the phenomenon often arrived around Christmas. Peruvian scientists later noted that more intense climatic changes occurred at intervals of several years, shifting the meaning of El Niño to describe these irregular and intense events rather than the annual warming of coastal surface waters. Led by the work of Sir Gilbert Walker in the 1930s, climatologists determined that El Niño occurs simultaneously with the Southern Oscillation. The Southern Oscillation is a change in atmospheric pressure over the tropical eastern and western Pacific Ocean. When coastal waters become warmer in the eastern tropical Pacific (El Niño), atmospheric pressure decreases in the eastern Pacific and increases in the western Pacific (Southern Oscillation). Climatologists define these linked phenomena as El Nino-Southern Oscillation (ENSO). Today, most scientists use the terms El Niño and ENSO interchangeably. Scientists use the Oceanic Nino Index (ONI) to measure deviations from normal sea-surface temperatures. El Niño events are indicated by sea-surface temperature increases of more than .5 degrees Celsius (.9 Fahrenheit) for at least five successive three-month seasons. The intensity of El Niño events varies from weak temperature increases about 2-3 degrees Celsius (4-5 degrees Fahrenheit) with only