Starting up an El Niņo event:
The western Pacific Ocean warms and cools in cycles. Normally, east-to-west winds pile up warm water in the western Pacific, while cold water from deep in the ocean rises to the surface along the South American Coast. Every few years, the trade winds change, allowing the pool of warm water to move east where it blocks the rising cold water. These changes help trigger the global weather changes associated with El Niņo.