El Niño and La Niña
El Niño and La Niña (Encyclopedia of Environmental Issues, Revised Edition)
Ecuadoran and Peruvian fishermen gave the name El Niño to a warm, southward-flowing ocean current that would occur off the west coasts of their countries every year around Christmastime (El Niño is Spanish for “the little boy” or, more specifically, “the Christ child”). Originally used to describe a brief, localized, annual phenomenon, the term later became associated with unusually strong ocean warming in this area that occurred every few years, disrupting local fish and bird populations. “Anti-El Niño” ocean cooling events were called either La Niña (the little girl) or El Viejo (the old man).
The term “El Niño” has come to be associated with the large warm-water anomalies covering extensive portions of the tropical Pacific Ocean off the coast of Latin America that persist for many months, and with the related weather effects noted around the globe. It has been known for many years that when warm water appears off the coast of Peru, atmospheric pressure drops over the eastern Pacific and rises over Australia and the Indian Ocean. Because of this relationship, major El Niño events are usually associated with other global weather phenomena, including drought in Africa and Australia and the failure of the Indian monsoon. Scientists know the atmospheric component of this global pattern as the Southern Oscillation. The coupled global oceanic-atmospheric system is called El Niño-Southern Oscillation (ENSO). El...
(The entire section is 364 words.)
Causes and Prediction (Encyclopedia of Environmental Issues, Revised Edition)
When an El Niño condition develops in the eastern Pacific, the sea surface temperature and rainfall in the eastern tropical Pacific are at their seasonal peaks. Major El Niño occurrences are closely tied to global weather patterns and the circulation of currents in the Pacific Ocean. Variations in Indian monsoon circulation sometimes precede variations in the Southern Oscillation, indicating that there is a possible feedback mechanism linking these phenomena. The period of the Southern Oscillation is irregular, with a return period of about three to four years, so about two El Niños occur per decade. The amplitude of the Southern Oscillation is highly irregular. If some global atmospheric perturbation contributes to the amplitude of the Southern Oscillation while an El Niño is developing, a major El Niño might be expected to occur. However, if a global perturbation subtracts from the amplitude of the Southern Oscillation, the El Niño might be weak.
The point at which scientists decide that a major El Niño condition is occurring has been historically contentious. A network of buoys has been established to augment satellite monitoring of sea surface temperatures in the Pacific Ocean. This network played a key role in the early detection of the 1997-1998 El Niño. When sea surface temperatures reach 3 to 5 degrees Celsius (5.4 to 9.0 degrees Fahrenheit) above normal for the season in the eastern equatorial Pacific,...
(The entire section is 596 words.)
Environmental Consequences (Encyclopedia of Environmental Issues, Revised Edition)
When unusually warm water appears off the coast of Peru, the local anchovy fishing industry falters. Sportfishing off Baja California, California, and Oregon, in contrast, enjoys a boom, as marlin and other highly prized fish usually found in more tropical southern waters move north. Other marine ecosystems around the globe may also be affected by El Niño conditions. Factors such as increased sea surface temperature, decreased sea level, and salinity changes related to high rainfall affect the algae that protect coral reefs, causing the coral to bleach and die. This, in turn, has negative impacts on fish and plant life within reef ecosystems. The 1997-1998 El Niño event was marked by coral reef bleaching in the Indo-Pacific region, the Caribbean, and the Florida Keys. Extensive coral bleaching also occurred around the globe in association with the 2009-2010 El Niño.
During El Niño episodes, the intertropical convergence zone, a band of major tropical convection circling the globe, moves southward. This southward shift in precipitation patterns causes torrential rains in some places that are normally dry and dry conditions in places that are usually wet. In the Galápagos Islands, El Niño brings much higher than normal precipitation in March, April, and May. During major El Niños, Peru and Ecuador experience torrential rains and flooding. In Guayaquil, Ecuador, El Niño was blamed for causing more than 3...
(The entire section is 657 words.)
La Niña (Encyclopedia of Environmental Issues, Revised Edition)
As the warm-water anomalies in the eastern Pacific fade, scientists know that El Niño is ending. When a large body of colder-than-average water establishes itself off the coast of Peru, along with a strong ridge of high pressure, meteorologists announce that a La Niña event is occurring. A La Niña may follow closely on the heels of an El Niño, as was the case with the 2010-2011 La Niña, or occur after a year or two of neutral conditions. During a La Niña, the Pacific sea surface height in the eastern Pacific is measurably lower than when an El Niño is occurring. The westerly trade winds are also stronger than normal. During a La Niña, the average temperature of the tropical troposphere may be 1 degree Celsius (1.8 degrees Fahrenheit) lower than during an El Niño. La Niñas tend to be much more variable in strength than El Niños.
During periods when the waters of the eastern Pacific have been observed to be anomalously cold, the Pacific Northwest tends to be wetter and cooler than normal, especially during winter. During a La Niña year, winter temperatures in the southern and southeastern United States are often warmer than normal. In the United States, some link La Niña years to very hot summers; the summer of 1988, which was very hot and dry, is the prototype summer for this weather phenomenon. Tropical cyclones are more common on the northern Australian coast during La Niña events. Widespread flooding in eastern...
(The entire section is 300 words.)
Further Reading (Encyclopedia of Environmental Issues, Revised Edition)
Changnon, Stanley Alcide, ed. El Niño, 1997-1998: The Climate Event of the Century. New York: Oxford University Press, 2000.
Clarke, Allan J. An Introduction to the Dynamics of El Niño and the Southern Oscillation. San Diego, Calif.: Academic Press, 2008.
D’Aleo, Joseph S., and Pamela G. Grube. The Oryx Resource Guide to El Niño and La Niña. Westport, Conn: Oryx Press, 2002.
Glantz, Michael H. Currents of Change: Impacts of El Niño and La Niña on Climate and Society. 2d ed. New York: Cambridge University Press, 2001.
_______. La Niña and Its Impacts: Facts and Speculation. Tokyo: United Nations University Press, 2002.
Philander, S. George. Our Affair with El Niño: How We Transformed an Enchanting Peruvian Current into a Global Climate Hazard. Princeton, N.J.: Princeton University Press, 2006.
Rosenzweig, Cynthia, and Daniel Hillel. Climate Variability and the Global Harvest: Impacts of El Niño and Other Oscillations on Agroecosystems. New York: Oxford University Press, 2008.
(The entire section is 157 words.)
El Niño and La Niña
Definition (Encyclopedia of Global Resources)
El Niño is signaled by a warm current of water off the Peruvian coast in contrast to the normally cold waters that rise to the surface. This change alters the circulation pattern of the Pacific Ocean, which in turn causes changes in climate. La Niña creates an opposite effect by extending and deepening the impact of the normal circulation pattern in the Pacific because of colder water than normal in the eastern Pacific.
(The entire section is 75 words.)
Overview (Encyclopedia of Global Resources)
Peruvian and Ecuadorian fishermen have long noted that for a few weeks in December the waters off their coasts grow warmer, an effect they called El Niño (“the boy child”) because of the event’s proximity to Christmas. In some years this warming is more significant in both its temperature and its duration and can have worldwide impact.
Sir Gilbert Walker, in his study of Asian monsoons, was the first to document the normal pattern of Pacific Ocean circulation. Walker realized there was a yearly cyclical variation in the atmosphere over the southwest Pacific Ocean, which he termed the “Southern Oscillation.” The Pacific Ocean is normally characterized by strong equatorial currents and trade winds driven by rising cool water off the coast of Peru that moves toward the equator and heads westward, setting up a circulation cell effect. This Southern Oscillation circulation results in warm water and an area of low pressure producing wet conditions in the South Pacific and correspondingly relatively dry conditions on the west coasts of the Americas. The rising cool water off Peru also brings nutrients to the surface that attract plankton, which in turn sustain an anchovy population that proves a stable food source for many marine creatures, birds, and humans. The birds furnish a steady supply of guano, a source for fertilizer.
El Niño entirely reverses this circulation model within the Pacific Ocean with dramatic...
(The entire section is 420 words.)