El Nino & La Nina

El Nino is caused by the periodic shift in wind speed and direction in the tropical eastern Pacific which leads to changes in sea Surface temperatures. In what scientists call El Niño events, prevailing easterly winds weaken or give way to westerly winds, and the normal upwelling process, which brings cool, nutrient-rich waters up from lower levels of the ocean, stops.

This causes sea surface temperatures to rise, providing an unfavorable habitat for many sea animals and fish. The warmer ocean conditions can also lead to more rainfall and floods along the west coast of the Americas. A stronger easterly wind flow, on the other hand, can increase upwelling and make the sea surface temperatures even colder, producing La Nina. Both phenomena can have far-reaching weather effects. For example, strong El Niño events often result in a weak Atlantic Ocean hurricane season; La Nina events can spell drought, even for normally dry California.

People often confuse climate and weather - the two really are quite different.