El Niño (pronounced el-NEEN-yo) is the name given to a change in the flow of water currents in the Pacific Ocean near the equator. El Niño—Spanish for "the child" because it often occurs around Christmas—repeats every three to five years. Although El Niño takes place in a small portion of the Pacific, it can affect the weather in large parts of Asia, Africa, Indonesia, and North and South America. Scientists have only recently become aware of the far-reaching effects of this phenomenon.
The rotation of Earth and the exchange of heat between the atmosphere and the oceans create wind and ocean currents. At the equator, trade winds blow westward over the Pacific, pushing surface water away from South America toward Australia and Indonesia. These strong trade winds, laden with moisture, bring life-giving monsoons to eastern Asia. As warm surface water moves west, cold, nutrient-rich water from deep in the ocean rises to replace it. Along the coast of Peru, this pattern creates a rich fishing ground.
Every three to five years, however, the trade winds slacken, or even reverse direction, allowing winds from the west to push warm surface water eastward toward South America. This change is called the Southern Oscillation (oscillation means swinging or swaying), and it is brought about by a shifting pattern of air pressure between the eastern and western ends of the Pacific Ocean. The warm water, lacking nutrients, kills marine life and upsets the ocean food chain. The warm, moist air that slams into the South American coast brings heavy rains and storms. At the same time, countries at the western end of the Pacific—Australia, Indonesia, and the Philippines—have unusually dry weather that sometimes causes drought and wildfires.
Another type of unusual weather that often follows an El Niño is called La Niña, which is Spanish for "the girl." El Niño and La Niña are opposite phases in the Southern Oscillation, or the back and forth cycle in the Pacific Ocean. Whereas El Niño is a warming trend, raising the water temperature as much as 10°F (5.6°C) above normal, La Niña is a cooling of the waters in the tropical Pacific, dropping the temperature of the water as much as 15°F (8°C) below normal.
Meteorologists believe the altered pattern of winds and ocean temperatures during an El Niño changes the high level winds, called the jet streams, that steer storms over North and South America. El Niños have been linked with milder winters in western Canada and the northern United States, as more severe storms are steered northward to Alaska. The jet streams altered by El Niño can also contribute to storm development over the Gulf of Mexico, which brings heavy rains to the southeastern United States. Similar rains may soak countries of South America, such as Peru and Ecuador, while droughts may affect Bolivia and parts of Central America.
El Niño also appears to affect monsoons, which are annual shifts in the prevailing winds that bring on rainy seasons. The rains of the monsoons are critical for agriculture in India, Southeast Asia, and portions of Africa. When the monsoons fail, millions of people are at risk of starvation. It appears that wind patterns associated with El Niños carry away moist air that would produce monsoon rains.
La Niña can bring cold winters to the Pacific Northwest, northern Plains states, Great Lakes states, and Canada, and warmer-than-usual winters to the southeastern states. In addition, it can bring drier-than-usual conditions to California, the Southwest, the Gulf of Mexico, and Florida, as well as drought for the South America coast and flooding for the western Pacific region.
Not all El Niños and La Niñas have equally strong effects on global climate; every El Niño and La Niña event is different, both in strength and length.
Jet streams: High velocity winds that blow at upper levels in the atmosphere and help to steer major storm systems.
Monsoon: An annual shift in the direction of the prevailing wind that brings on a rainy season and affects large parts of Asia and Africa.
According the National Oceanic and Atmospheric Administration (NOAA), 23 El Niños and 15 La Niñas took place in the twentieth century. Out of those, the four strongest occurred after 1980. Scientists are unsure if this is an indication that human activity is adversely affecting the weather or if it is simply a meaningless random clustering.
The El Niño event of 1982–83 was one of the most destructive of the twentieth century. It caused catastrophic weather patterns around the world. Devastating droughts hit Africa and Australia while torrential rains plagued Peru and Ecuador. In the United States, record snow fell in parts of the Rocky Mountains; drenching rains flooded Florida and the Gulf of Mexico's coast; and intense storms brought about floods and
mud slides in southern California. French Polynesia in the South Pacific was struck by its first typhoon in 75 years. It is estimated this particular El Niño killed 2,000 people and caused $13 billion worth of property damage.
Less than 15 years later, another destructive El Niño pattern developed. This one, however, was much more devastating than the 1982-83 event. In fact, it was the worst in recorded history. Beginning in late 1997, heavy rain and flooding overwhelmed the Pacific coast of South America, California, and areas along the Gulf Coast. Eastern Europe and East Africa were affected, as well. Australia, Central America, Mexico, northeastern Brazil, Southeast Asia, and the southern United States were all hit hard by drought and wildfires. In the United States, mudslides and flash floods covered communities from California to Mississippi. A series of hurricanes swept through the eastern and western Pacific. Southeast Asia suffered through its worst drought in fifty years. As a result, the jungle fires used to clear lands for farming raged out of control, producing smoke that created the worst pollution crisis in world history. At least 1,000 people died from breathing problems. By the time this El Niño period ended some eight months later in 1998, the unusual weather patterns it had created had killed approximately 2,100 people and caused at least $33 billion in property damage.