El Niño Southern Oscillation (ENSO)

A major El Niño began in April of 1997 and continued until May 1998. It has been labeled by some as the ‘El Niño of the century’ as it was certainly the biggest on record by several measures. It brought with it many weather extremes and unusual weather patterns around the world. Moreover, the event was predicted by climate scientists and received unprecedented news coverage, so that the term ‘El Niño’ became part of the popular vernacular. Many things were blamed on El Niño, and some of them indeed were influenced by El Niño, although in some instances, the connection was, at best, tenuous. Although El Niño may be relatively new to the public, it has been known to scientists, at least in some respects, for decades and even centuries. El Niño refers to the exceptionally warm sea temperatures in the tropical Pacific, but it is linked to major changes in the atmosphere through the phenomenon known as the Southern Oscillation (SO), in particular, so that the whole phenomenon is called El Niño–Southern Oscillation (ENSO) by scientists. This article outlines the current understanding of ENSO and the physical connections between the tropical Pacific and the rest of the world.