El Niño is a climate pattern that describes the unusual warming of surface waters in the eastern tropical Pacific Ocean. It is the “warm phase” of a larger phenomenon called the El Niño-Southern Oscillation (ENSO), while La Niña is the “cool phase” of ENSO. During an El Niño event, westward-blowing trade winds weaken along the Equator, causing warm surface water to move eastward along the Equator, from the western Pacific to the coast of northern South America. El Niño 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 and beyond. El Niño events occur irregularly at two- to seven-year intervals, but they are not a regular cycle and are not predictable in the sense that ocean tides are. Some of the effects of El Niño include:

• Weather: El Niño can affect weather significantly. The warmer waters cause the Pacific jet stream to move south of its neutral position, leading to dryer and warmer than usual conditions in areas in the northern U.S. and Canada. In contrast, the U.S. Gulf Coast and Southeast experience wetter than usual periods with increased flooding.

• Ecosystems: El Niño can bring tropical species, like yellowtail and albacore tuna, into areas that are normally too cold.

• Economy: El Niño can have significant economic impacts, such as reducing the productivity of fisheries and agriculture in some regions.

El Niño events are defined by their wide-ranging teleconnections, which are large-scale, long-lasting climate anomalies or patterns that are related to each other and can affect much of the globe.