Why Is El Nino Harmful?

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Near the end of each calender year, along the west coast of South America, a warm current of nutrient-poor tropical water moves southward, replacing the cold, nutrient-rich surface waters off the coast of Peru. Because this condition frequently occurs around Christmas, local residents call it El Nino (Spanish for child), referring to the Christ child. In most years the warming lasts for only a few weeks. Occasionally—usually once every three to seven years—the warm waters don't leave. When they last for a year or two, it's called a major El Nino event.

During a major El Nino event, large numbers of fish and marine plants may die. Decomposition of the dead material depletes the water's oxygen supply, which leads to the bacterial production of huge amounts of smelly hydrogen sulfide. A greatly reduced fish (especially anchovy) harvest affects the world's fishmeal supply, leading to higher prices for poultry and other animals which normally eat fishmeal.

Studies reveal that El Nino is not an isolated occurrence, but is part of a pattern of change in the global circulation of the oceans and atmosphere. Specifically, the warming of the waters off the coast of Peru causes a decrease in air pressure over the eastern Pacific Ocean. As a result, the air pressure in the western Pacific rises (usually air pressure is higher over the eastern Pacific, near South America, and lower over the western Pacific, near Australia). This phenomenon of shifting air pressure across the Pacific is called the Southern Oscillation.

In "normal" years, when a major El Nino event and the Southern Oscillation do not occur, the difference in air pressure across the Pacific drives the trade winds (winds that blow throughout the tropics) westward, toward the equator. The trade winds influence surface water circulations and the sea level throughout the world. However, when the pressure differential fluctuates, the course of the trade winds is altered. As a result, weather patterns are disrupted throughout the Pacific region of the Southern Hemisphere, as well as into the Northern Hemisphere as far north as Alaska and northern Canada.

The 1982 to 1983 El Nino was one of the most severe climatic events of the twentieth century. It brought about devastating droughts, floods, and storms in many parts of the world. Australia was hit with its worst drought ever. Hawaii, Mexico, southern Africa, the Philippines, and Indonesia also experienced droughts. Meanwhile, extensive flooding was experienced in Louisiana, Florida, Cuba, Ecuador, Peru, and Bolivia.

The 1986 to 1987 El Nino may have contributed to making 1987 the warmest year in the last century.

Sources: Ahrens, C. Donald. Meteorology Today: An Introduction to Weather, Climate, and the ronment, 5th ed., p. 311; Engelbert, Phillis. The Complete Weather Resource, vol. 1, pp.72-74; Golob, Richard. Almanac of Science and Technology: What's New and What's Known, pp. 296-302.

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