El Niño

History of Discovery

The term El Niño, or “Christ child” in Spanish, has been used for centuries by fishermen of the Northern Peru and Southern Ecuador littoral to describe a quasi-annual warming of coastal ocean waters shortly before Christmas, which persists for several months. Cold-water pelagic fish, such as anchovies and sardines, dominated and provided the basis of the regional maritime ecology, including guano birds, whose droppings constituted a large portion of the global fertilizer market, and the Peruvian economy before the advent of chemical fertilizers. The cold waters are the northernmost expression of the Chile, Peru, or Humboldt Current, flowing northward along the coast of Western South America from the sub-Antarctic Ocean and westward along the equator in a semipermanent feature called the “cold tongue.” Fishermen noted this seasonal change in the waters through the fluctuating size and composition of catches. Tremendous variability in the severity, onset, and duration of this phenomenon was also noted. On some occasions (“cold phase”) the losses were negligible, while other years (“warm phase”) brought a total collapse of the fishery and extensive deaths of guano birds and marine mammals. Colonial records from Peru indicate that the impacts of these changes were often exacerbated by contemporary devastating floods in the coastal Chira desert region and simultaneous droughts in the Altiplano.

Following a sequence of severe droughts, failed harvests, and millions of deaths resulting from the failure of the monsoon rains in India during the late 19th century, a leading British atmospheric scientist, Sir Gilbert Walker, was dispatched to determine their cause. Examining meteorological records from the subcontinent and surrounds, Walker noted a strong regional association in annual variations of atmospheric pressure over the area encompassing southeast Asia, particularly the Indonesian archipelago, and bordering the western equatorial Pacific and Australia, then another British dominion that was subject to severe and devastating climatic variability. Encouraged by this hemispheric-scale association in atmospheric pressure variations, Walker extended his analysis to the global scale and noted a strong negative correlation between the atmospheric pressure over Indonesia and Australia (Djakarta and Darwin) and the Central Pacific (Tahiti). Interannually, pressures above these two nodes appeared to rise and fall in lockstep with each other but in opposing directions. Walker coined the term Southern Oscillation to describe this observation. Further analysis of fluctuations in pressures at other locations around the world offered hope that the phenomenon might provide an explanation for variations in what Walker termed global weather.

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