The El Niño phenomenon: a model of global ocean disruption

By Jean-René VANNEY

L’Atlas Bleu / Exploring

Extent of the phenomenon

carte, el nino, océan global, courant océanique

The two diagrams, with an obvious exaggeration in scale, represent the vertical and longitudinal wave-like motions caused by the back and forth movement of the warm water layer (known as the ‘suprathermoclinal’ layer) during the course of the El Niño phenomenon, which occurs at intervals of several years.The map shows the average area covered by its route between the eastern (South American Pacific) and western (northern Australia) Pacific.

It is an exaggerated oscillation of a natural wave of heat and desalination (due to the convective rainfall it triggers) that periodically crosses the ocean. El Niño reaches catastrophic proportions when brought about by an exceptional forcing to the east. The amplified wave, shifted toward the west by the trade winds, is stored there for several months. A reversed wave, or return wave, then forms there that, by moving towards the east, gradually pushes the warm layer higher. This warm layer finishes by against the arid coast of America, where it spreads out, bringing equatorial rains, generally accompanied by catastrophic phenomena (see p.15). The last time such an event occurred was in 1998. Neither the frequency nor possible relationships of El Niño with global warming are presently known.

Principle of disruption

The El Niño event in 1982-1983, off South America

The penultimate oceanic catastrophe brought about by an El Niño event occurred in the south-eastern Pacific from the middle of 1982 to the end of 1983, with two peak phases (December 82-January 83 and March-April 83) with the following devastating consequences:

1) rise in surface levels (m): +0.50 (Peru), +0.40 (Galápagos), +0.25 (northern Chile);

2) rise in temperature: between 2° and 5°C above normal values;

3) thermocline deepening (up to 150 m in the Galápagos) and heat diffusion up to 1000 m;

4) reversal of the South Equatorial Current, powerful transfer of warm (29°-30°C) and desalinated water towards South American coasts;

5) unusually high rainfall offshore, torrential rain on arid coasts, reaching beyond the tropic;

6) coastal destruction: gullying due to runoff, cliff erosion due to waves, thermal and chemical degradation of coral reefs, etc.;

7) ecological disasters: stifling of coastal upwelling, coral bleaching, reduced primary production and biomass, massive fish mortality, biochemical pollution, exodus of marine birds and mammals, cold water fishery crises, prosperity of warm water fisheries.

Jean-René VANNEY, géographe océanographe (décédé le 29 janvier 2019)

Il a été Professeur à  l’Institut de Géographie à l’Université Paris IV-Sorbonne. Il est notamment l’auteur de plusieurs ouvrages de référence en géographie physique des océans (

Jean-René VANNEY, « Un modèle de dérèglement de l’océan Global : le phénomène El Niño », L’atlas Bleu, Revue cartographique des mers et des littoraux. Mis en ligne le 11 janvier 2020,

(version digitale adaptée d’après l’article paru dans L’Atlas Permanent de la Mer et du Littoral n°7 « Risques littoraux et maritimes ». Ed. LETG-Nantes, 2015. pp.14-15)


DOI : 10.35109/atlasbleu-eng.10021