Causes Of El Nino

What causes the El Nino phenomenon?

Expert Answers
Michael Ugulini eNotes educator| Certified Educator

The El Nino phenomenon, which occurs every three to five years, is caused by warmer water in the eastern Pacific Ocean. This water is warmer because as trade winds lessen or reverse their direction, winds from the west push warm surface water to the east in the direction of the continent of South America. Therefore, there is less cold water pulled up from below as a result of this increase in warmer water.

In essence, an El Nino is caused by the interaction between the surface layers of the tropical Pacific Ocean and the atmosphere over the tropical Pacific Ocean.

This warming of Pacific Ocean tropical water affects global weather. Typically, in the United States, the most significant effect of El Nino is wetter weather and cooler-than-average temperatures across the southern portion of the country. The northern sector of the country usually experiences warmer weather and drier-than-average conditions.

A dual effect is caused by El Nino. The warm and moist air that descends upon the South American coastline brings storms and heavy downpours of rain. The opposite effect takes place in Australia, Indonesia, and the Philippines, where very dry weather conditions occur. This can lead to drought and destructive wildfires.

An El Nino is a warming trend. A La Nina can follow an El Nino. A La Nina is a cooling trend. It is a cooling of Pacific Ocean tropical waters