is El Nino?

Phytoplankton bloomDuring normal years, when there is a steep thermocline tilt, the cold, deep currents flowing from Antarctica up the west coast of South America are allowed to upwell, bringing essential nutrients that would otherwise lie at the bottom. Phytoplankton living near the surface depend upon these nutrients for survival. In turn, fish and mammals depend upon phytoplankton as the very foundation of the marine food chain. As previously explained, the warm surface waters of an El Niño prevent this upwelling, effectively starving the phytoplankton population there and those animals higher up the food chain that depend upon it. Fishermen in Peru and Ecuador generally suffer heavy losses in their anchovy and sardine industries.

At Christmas Island, as a result of the sea level rise during the 1982-83 El Niño, sea birds abandoned their young and flew out over a wide expanse of ocean in a desperate search for food. Along the coast of Peru during that same time period, 25 percent of the adult fur seal and sea lion populations starved to death, and all of the pups in both populations died. Similar losses were experienced in many fish populations.

Meanwhile, over a six-month period about 100 inches of rainfall fell in Ecuador and northern Peru--ordinarily a desert region. Vegetation thrived and the region grew lush with grasslands and lakes, attracting swarms of grasshoppers and, subsequently, birds and frogs that fed on the grasshoppers. Many fish that had migrated upstream during the coastal flooding became trapped in the drying lakes and were harvested by local residents. Shrimp harvests were also very high in some of the coastal flood regions, but so too was the incidence of malaria cases due to thriving mosquito populations.

El Niño's impacts on weather patterns
El Niño's effects are not limited to the tropical regions off the western coasts of Peru and Ecuador. Its effects are felt all over the world, where the disruption of normal local weather patterns can have tragic and/or profound economic consequences. As warm water migrates eastward, increased heat and moisture rises into the atmosphere, altering the weather patterns in neighboring regions, which in turn can ripple out to affect still other region weather patterns around the globe. For instance, a severe El Niño will enhance the jet stream over the western Pacific and shift it eastward, leading to stronger winter storms over California and the southern United States, with accompanying floods and landslides. In contrast, El Niño can also cause severe droughts over Australia, Indonesia, and parts of southern Asia.

While El Niño is known to lower the probability of hurricanes in the Atlantic, it increases the chances of cyclones and typhoons in the Pacific. The 1982-83 El Niño is estimated by NOAA to have caused some $8 billion in damages due to floods, severe storms, droughts and fires around the world.

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This animation shows sea surface temperature across the equatorial Pacific Ocean (top) during the 1997-98 El Niño. The lift-out shows a higher-resolution image of ocean color in the region surrounding the Galapagos Islands. Play the animation several times and note the transitions that occur between May 10 and May 25, 1998. As the El Niño recedes, surface temperatures cool allowing colder, nutrient-rich currents to upwell. There is a large, almost immediate bloom of phytoplankton in response to the replenished food source. (Courtesy of Greg Shirah, Goddard SVS) (853k)


What is El Niño?
El Niño: a temperature anomaly
El Niño's impacts on the biosphere

What is La Niña?

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El Niño/La Niña Updates

El Niño: A temperature anomaly El Niño's impacts on the biosphere |

What is El Nino? Fact Sheet

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