El Nino has been a reoccurring phenomenon for centuries. What exactly is El Nino? "The term El Nino refers to a massive warming off the coastal waters of Peru and Equador that frequently extends more than 90 degrees of longitude. It is related to the Southern Oscillation, the atmospheric component of this phenomenon." (Gottschalk, 1998). Because El Nino and Southern Oscillation are often coupled, the term ENSO is used. (Garrison, 1999) This event usually last up to a year but can last up to three years. El Nino occurs every several years. The areas that are most affected by this event are all ocean areas at tradewind latitudes in both hemispheres. (Garrison, 1999) El Nino has been linked to flood and droughts all over the world. El Nino causes significant changes in biology and weather when it occurs.

             During an El Nino cycle there are many biological changes. During an El Nino thermocline is low and therefore there is less photosynthetic activity following in a decrease in the primary life forms. The warmer waters that are brought by El Nino hold less oxygen demanding the fish to go somewhere else. (Cook 1998) "Although upwelling may occur during an ENSO event, the source of upwelled water is nutrient-depleted water in the thickened surface layer approaching from the west"(Garrison, 1999). This does not help the fisherman to make money or eat during an ENSO event. This biological decrease also hurts the economy because the fishermen in the areas affected are not catching the right amount of fish to make money. Biological change is due to the climate and weather change during El Nino.

             The surface winds that move the ocean currents are a major controller in weather. During El Nino when the easterlies weaken and retract eastward during the early stages, the upwelling slows and the ocean warms along with the moist air above the ocean. The change in the ocean temperatures causes a major rain section over the western Pacific to move eastward.