El Niño Southern Oscillation (ENSO)

Sometimes, the trade winds across the equatorial Pacific shift, either becoming stronger or weaker. This leads to changes in ocean circulation, which causes changes in the temperature of the ocean. The El Niño Southern Oscillation, also known as ENSO, is the term used to describe these changes in the ocean temperatures and atmospheric conditions seen off the west coast of South America. ENSO has three phases: warm (El Niño), cold (La Niña), and neutral.

Source: NASA Examines Global Impacts of the 2015 El Niño | NASA