Ordinarily, that causes the Pacific to be a few inches higher on its western end. During an El Nino, however, the equatorial trade winds slacken. The warm surface water that is normally pushed up against the western side begins to slide eastward. When this happens a chain reaction follows. Cool, nutrient-filled waters along the west coast of the Americas, which support an abundance of fish and marine life, never make it to the surface, and marine life dies or migrates to other waters.
Peruvian fishermen come in with empty nets.
As the plume of warm water spreads eastward, the currents of air that rise from warm water in effect suck the trade winds back eastward even more. The rising, moisture-laden air breeds thunderstorms over the eastern Pacific, while the reversal of the normal wind patterns depresses the formation of thunderclouds that ordinarily dump vast quantities of rain on the western Pacific. A complex change in high-level winds, meanwhile, brings strong air streams 40,000 feet aloft whipping across Central America to the Atlantic and on toward Africa. Md. Exactly what triggers an El Nino cycle remains a mystery. But one basic lesson scientists have learned from watching the El Nino cycle is that to understand weather, they must look beyond the sky.