El Niño or male child in Spanish is the name given to a weather system that occurs off the western coast of Peru and affects the climate in the entire world. Among the consequences of El Niño are increased rainfall across the southern tier of the US and in Peru, which has caused destructive flooding, and drought in the West Pacific, sometimes associated with devastating brush fires in Australia It usually start around Christmas, thus the name El Niño, referring to the Christ child.

In normal, non-El Niño conditions, the trade winds blow towards the west across the tropical Pacific. These winds pile up warm surface water in the west Pacific, so that the sea surface is about 1/2 meter higher at Indonesia than at Ecuador. Temperatures are cooler off of South America as cold water moves up from deeper ocean levels. This cold water is filled with nutrients essential to marine life resulting in plenty of fish. Most rain occurs in the west where the moist air rises over the warmest water. The east Pacific is relatively dry.

El Niño starts when the trade winds decrease resulting in unusually warm water in the tropical water of the eastern Pacific off the coast of Peru. This warm water blocks the upwelling of nutrient-rich cold water and reduces the fish population. It also increases the rainfall in the area. Other far-removed areas of the world are affected by this shift of a major atmospheric effect. (Move cursor over map to see effect.)

Every 4 to 7 years (23 times in the last century) the change has been very dramatic and caused severe weather conditions. La Niña or girl child may follow a year of El Niño. In La Niña conditions, the warm waters off Peru become unusually cold. There are thus three conditions: normal weather, floods in Peru, and floods in Indonesia. Dry conditions prevail at the opposite end of the Pacific from the wet conditions.

Scientists from the University of Maine, studying the presence of a small mollusks shell in archaeological deposits, concluded the first El Niño occurred 5,800 years ago. The mollusks cannot live in the warm water brought on by El Niño and are absent from the layer laid down that year. At first, such layers appeared every 25 or 30 years. The beginning of El Niño coincides with the time the pre-Inca culture started building temples. Scientists postulate rituals and sacrifices were made and the next year La Niña occurred. These rituals lasted until about 3,000 years ago when El Niño started coming more frequently. At about the same time, the temples were abandoned. The two events may be connected. Scientists postulate that because sacrifices and rituals were no longer effective, the people abandoned the temples.

Centuries later, Inca priests went into the mountains above Machu Picchu each December and preformed rituals. When they returned they indicated when the rains would come and when planting should begin. It has been postulated they looked out over the Pacific Ocean and noted if any weather systems were developing. If they saw an El Niño, it meant early rain and lots of rain. Today, scientists maintain a vast array of temperature measuring buoys in the Pacific to detect the surface water temperature changes that signal the El Niño and La Niña conditions.