Traditionally El Nino refers to an increase of ocean surface temperatures over a large area of the South Pacific. The increase is only a matter of 2° to 7°C, but this is enough to upset the delicate balance that living organisms have with their environment. Scientifically, El Nino no longer refers just to this warming. Scientists have learned that these ocean changes are coupled with an atmospheric change which starts in the Indonesian area. This change is called the Southern Oscillation and refers to a reversal of the western Pacific trade winds which blow east to west during an El Nino. Normal Pacific trade winds in southern hemisphere blow west to east.

This ocean/atmosphere condition is called the El Nino/Southern Oscillation (ENSO for short) events. The winds of the ENSO event bring warm water to the eastern Pacific Ocean which creates a living environment that the organisms are not able to cope with. Increases of temperature, no matter how slight, can cause drastic results to little organisms that live in the sea. These events usually recur every 2 to 10 years, with an average of four years and individual events can last up to 2 years.