Winds normally blow from east to west at the equator. As a result, warm water gets trapped deep in the western Pacific. During an El Niño event, however, the easterly winds go slack, allowing warm water to drift across the ocean from west to east. The warm water releases heat into the atmosphere, increasing Earth’s average temperature.
El Niño may trigger unusual weather worldwide: monsoons in the central Pacific, typhoons in Hawaii, torrential rains in South America, blizzards in the Rockies, warm winters in the northeastern United States, flooding in southern California, and severe droughts in southern Africa. Moreover, as warm water moves east, it prevents cold, nutrient-rich water below from rising to the surface (“upwelling”). The ecological consequences are grim. Fishes move to deeper, cooler waters; the animals that normally eat them may starve.