What is El Niño?

Weather phenomenon can wreak havoc

By Brandon Miller and Nick Thompson, CNN
NOAA

NOAA graphic of typical impacts to North America during El Niño.

(CNN) - The weather phenomenon called El Niño largely became a part of the public vernacular more than 20 years ago. In 1997, it caused devastating flooding in the Western United States and drought in Indonesia. It also was blamed for deadly virus outbreaks in Africa and rising coffee prices around the world.

El Niño even became personified as Chris Farley on "Saturday Night Live."

Pure chaos. But what is El Niño? Let us explain.

What is El Niño? And what causes one?

El Niño is a warming of the eastern Pacific Ocean, mainly along the Equator.

These warmer waters are usually confined to the western Pacific by winds that blow from east to west, pushing the warmer water toward Indonesia and Australia.

El Niño is back

But during an El Niño, the winds slow down and can even reverse direction, allowing the warmer water to spread eastward all the way to South America.

El Niños occur every two to seven years in varying intensity, and the waters of the eastern Pacific can be up to 4 degrees Celsius (7 degrees Fahrenheit) warmer than usual.

What happens when there's an El Niño?

A strong El Niño heats up the atmosphere and changes circulation patterns around the globe, especially the jet stream over the Pacific, which becomes stronger and dumps more frequent and intense storms over the Western United States, especially California. It also means more rain for the west coast of South America.

But the atmosphere is somewhat of a zero-sum game. More rain in North and South America comes at the expense of normally rainy Southern Asia and Australia, which become abnormally dry and experience droughts.

A strong El Niño also influences cyclone seasons around the planet. The warmer the East Pacific is, the more hurricanes it gets. The Atlantic Ocean sees fewer hurricanes, however, a result of increased upper level winds that prevent these storms from developing. That proved true for the 2015 hurricane season -- the Atlantic saw a relatively quiet year then, while the Pacific broke a number of records.

The weather isn't the only thing that's affected. Warmer surface waters in the eastern Pacific drive away the coldwater fish that are the backbone of the fishing industry in much of Latin America. It was here that the phenomenon was first noticed by fishermen, who named it "El Niño" -- meaning "little boy" or "Christ child" in Spanish -- since it would often appear around Christmas.

Which areas are typically affected?

Like snowflakes, no two El Niños are exactly alike, and they're only one of many different large-scale weather patterns acting in tandem to influence global weather. The presence of "the blob," as it has become known -- an area of warmer water in the Northern Pacific during the 2014-2016 event -- wasn't there during the 1997 El Niño.

Nevertheless typically during El Niño years -- more rain falls in the Southwestern and Southeastern United States -- while the North experiences much drier and warmer weather.

It has been known to cause intense flooding across eastern sections of Africa, leading to landslides, an increase in waterborne diseases and even food shortages, while northern and southern parts of the continent experience severe drought.

El Niño is also known to leave much of the West Pacific, Australia and Asia warmer and drier than usual.

An El Niño will reduce hurricane development in the Atlantic by creating more wind shear across the region. However, it has the opposite effect on the West Pacific, allowing for more typhoon development.

Does climate change have anything to do with it?

The influence of climate change on El Niño is a matter of debate. Some research suggests that while the overall number of El Niños is unlikely to increase, the number of "super" El Niños are twice as likely to occur.

Other recent studies show that climate change could make the impact from El Niños worse.

One of the most likely byproducts of global warming is more extreme precipitation events as warmer temperatures can hold more water vapor in the atmosphere. It could make El Niño-induced floods even more devastating.

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