El Nino

The El Nino-Southern Oscillation (ENSO) phenomenon is a global mechanism that is caused by the large-scale interaction between the ocean and the atmosphere. The Southern Oscillation (a more recent discovery) refers to an oscillation in the surface pressure (atmospheric mass) between the southeastern tropical Pacific and the Australian-Indonesian regions. When the waters in the eastern Pacific are abnormally warm—referred to as an El Niño event—sea level pressure drops in the eastern Pacific and rises in the west. The reduction in the pressure gradient is accompanied by a weakening of the low-latitude easterly trades. This enables warm water near Australia and Indonesia (the eastern Pacific) to travel eastward toward Peru and Ecuador (South America). Normally, the trade winds move warm water westward, piling warm surface water in the west Pacific so that the sea surface is roughly 1.6 feet (0.5 m) higher at Indonesia than at Ecuador. The sea surface temperature is about 13°F (8°C) higher in the western Pacific than the east. This causes the upward movement of deeper, colder water to the surface off the coast of South America. This is called upwelling, and it is an extremely important process because it

Large hail collects on streets and grass during a severe thunderstorm. The larger ice stones are two to three inches (5-7 cm) in diameter. These storms can be very destructive to homes, cars, and yards.

(NOAA, National Severe Storms Laboratory)

Storms can cause tornadoes as a result of El Niño. This photo shows a tornado touching ground in Cordell, Oklahoma, on May 22, 1981.

brings up rich nutrients that make it a very rich, productive fishing area. The upwelling process feeds the plankton, which in turn feed the fish. El Niño, however, spreads warm water eastward toward South America and it covers the cold upwellings with about 500 feet (152 m) of water keeping it warmer than average, which plays havoc with marine ecosystems. The Southern Oscillation (the SO in ENSO) is the atmospheric component of the cycle.

El Niño has widespread impacts on a global scale. The area of warm water, and its associated energy, is enormous. Flooding, damage to ecosystems, increased spreading of infectious diseases, drought, wildfires, crop failures, and starvation are some effects of El Niño. It also causes increased tropical storms and hurricane activity.

In 1997, Hurricane Linda, which made landfall on the coast of Mexico, was a result of El Niño. It was one of the fiercest eastern Pacific storms ever recorded, with winds that reached 185 miles per hour (298 km/hr). El Niño can also cause intense rainfall and mudslides. California is especially vulnerable to mudslides and debris slides triggered by El Niño. Because many of California's urban areas are built on steep, coastal mountain slopes, when the soil becomes saturated, the entire slope can fail, bringing entire houses down.

Ice storms are another extreme weather effect from El Niño. When warm air flows over a freezing surface, a heavy layer of ice can form. The ice can become so heavy when it is deposited on surfaces that it can cause extreme damage. It can break trees, damage homes, and bring down power lines, leaving homes without electricity for long periods of time.

El Niño has also been credited with causing tornadoes across many areas of the United States. In 1998, Florida suffered the worst series of tornadoes in the state's recorded history. It was reported that 800 homes were completely destroyed and 700 were left uninhabitable. Forty-two people lost their lives and damages exceeded $60 million.

El Niño can also cause a die-off of marine life or reduce the survival rate of the young. It has also been known to devastate popula-

Changes in the conditions of marine systems can endanger the survival rate of sea lion pups. (Captain Budd Christman, NOAA)

Specific regions will be affected by El Niño. Some areas will have an excess of rain, others drought. Some areas will be warmer than usual, others cooler.

tions of seabirds off Peru by reducing the fish stock that they feed off. Some scientists believe that if El Niños were to become more frequent the overall composition of marine life would change.

Today, there is some debate in the scientific community as to whether there is a connection between El Niño and global warming. According to the National Oceanic and Atmospheric Administration (NOAA), some climatologists say that the series of warm climate events during the 1990s are evidence that a general warming trend is starting to change the weather; yet others say that the variations are within the normal limits. One of the major problems at this point is that scientists have not been documenting El Niño events long enough—in order to draw reliable scientific conclusions, they need to be able to document events over a long period of time, the longer the better (hundreds to thousands of years, or more).

El Niño Time Line




First El Niño event historically recorded







Stronger than previous occurrences




Multiple El Niños occurred during this time interval


This El Niño was stronger than previous occurrences




This was the first El Niño to receive recognition by scientists worldwide





Extremely strong El Nino whose climatic effects were felt worldwide in the form of drought, flooding, and other responses




El Niño Time Line



This El Niño event went down in the history books as the largest one on record


This El Niño event was comparable in intensity to that of 1982-83. During this series, the United States experienced one of the warmest winters on record


Very strong, similar to 1982-83


Very strong, similar to 1982-83


This El Niño event was the strongest one in the 20th century


Very strong


Very strong


Very strong

Source: NOAA

Even so, there is a fairly large group of experts at NOAA, National Aeronautics and Space Administration (NASA), and the U.S. Geological Survey (USGS) who believe that El Niño events have become not only more frequent, but more intense during the past 100 years. During the 20th century, there were 23 El Niños. The four strongest of these all occurred after 1980. According to the Intergovernmental Panel on Climate Change (IPCC), the frequency and intensity of El Niño events have increased since 1970 compared with the previous 100 years. They state that since 1976 El Niños have become more frequent, persistent, and intense.

Although there is still debate about whether global warming causes El Niño, it is accepted that El Niños do produce more heat, which is carried out of the Tropics and raises global temperatures. Scientists predict that if global warming increases El Niños will also increase.

Computer models have been an extremely powerful tool in helping climatologists predict climatic conditions. By inputting field-collected data along with physical laws of the ocean and atmospheric general circulation patterns, systems can be modeled.

Models are built on the basis of present observations. Then, in order to check their reliability, they are tested using past real-world observations to see if they can derive the same results and match what happened in reality. Once this has been successfully achieved, the models can then be used to predict the future. Models to predict El Niño are currently being improved so that they can predict an upcoming event a year or more in advance.

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