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Ecology

The Phenomenon El Niño

During December, warm and cold currents meet on the coasts of South America, causing water to evaporate and leading to the formation of clouds that hold a vast amount of rain. This phenomenon can last up to a year.

Text and photos : Javier A. Pinzón

What is the El Niño Phenomenon?

El Niño is an oceanic and atmospheric phenomenon that occurs when the waters in the central and eastern parts of the tropical Pacific Ocean warm, causing weather alterations of various magnitudes in several places across the globe.

For a long time it was believed that El Niño was a local phenomenon that took place in Peru and Ecuador. However, the measuring campaigns conducted during the International Geophysical Year of 1957-58, which coincided with an important El Niño, revealed that the phenomenon takes place across the entire Pacific Ocean. This pattern, which according to Arthur Strahler repeats every three to eight years, is generated when the winds in the central and western parts of the Pacific Ocean weaken, increasing the temperature of the ocean’s surface to between 37.4 and 44.6 ºF.

How did it get its name?

Peruvian fishermen in the port of Paita in northern Peru gave the phenomenon the name El Niño after observing that the water that runs from the southern coast of Chile from south to north, off the northern Peruvian coast, would warm up around Christmas Eve and the shoals or schools of fish would disappear from the ocean’s surface. This took place around Christmas, so it was called El Niño in reference to the baby Jesus.

How does it form?

According to Dr. Kevin Trenberth of the Climate Analysis Section at the National Center for Atmospheric Research in New Zealand, the changing ocean surface temperatures alter the rain and surface winds, which in turn influence oceanic currents and surface temperatures. These interactions produce a positive feedback loop, in which each change tends to produce more changes.

Under normal conditions, the trade winds push the warm water westward, crossing the Pacific toward Asia and Australasia, while the cold water moves toward the Pacific coast of Central and South America.

This displacement of surface water makes it possible for deep, cold water to surface near the South American coast (Humboldt Current). This current drags nutrients from the bottom, increasing fish populations. That’s why this area is very rich in fishery. But when the temperatures of the eastern (South America) and central parts of the Pacific Ocean are consistently higher than normal, some 37.4 to 44.6 ºF, a wave of wind from the west (Asia) arises. This generates a large current of warm water that moves slowly towards South America, giving rise to the El Niño phenomenon. During the month of December, both streams (warm and cold) are found along the coasts of South America, causing water to evaporate and form clouds that hold a vast amount of rain. This phenomenon can last up to a year.

What affect does this phenomenon have on the world?

One of the greatest effects of El Niño is the change in global rain patterns. The trade winds in the Pacific are weakened, so the warm water from the west (Asia) moves eastward (South America), transporting heat to the atmosphere and generating clouds that will carry rain to the east. In other words, there will be more rain in areas where it usually does not rain and less rain where it usually rains a lot.

The changes associated with El Niño, which include droughts, floods, heat waves, and others, come at a hefty price in many parts of the world. The extreme droughts or floods affect agriculture and the change in the marine currents affect fishing because the cold currents that usually drag nutrients from the bottom to the surface, necessary for feeding fish stocks, do not surface. There are also serious effects on health, energy demands, and air quality, in addition to an increase in the risk of forest fires.

The El Niño Record

The 2015-16 phenomenon was one of the strongest registered to date. It affected global temperatures, making 2016 the hottest year ever recorded. In addition to the heat, the event also caused droughts in Africa, which caused food production to plummet in many African countries. South America experienced floods in Brazil, Argentina, Paraguay, Peru, and Uruguay. It also experienced droughts in northern Colombia, Venezuela, Brazil, Bolivia, Chile and Central America, and snowstorms in the United States. Indonesia suffered an intense drought, as did Australia. The Pacific corals experienced one of the worst recorded bleaching events.

El Niño and Global Warming

According to Dr. Trenberth, global warming aggravates the effects of El Niño. These two phenomena determine regional weather patterns and when they work together in the same direction, they produce the strongest effects and records are broken.