What is the El Nino phenomenon, why does it occur and what impacts can it cause?

(CNN) — El Nino is a natural weather pattern in the tropical Pacific Ocean that causes sea surface temperatures to be warmer than average and has a major impact on climate around the world, affecting billions of people.

The warmest waters of the oceans are generally confined to the western Pacific by winds blowing from east to west, which push warm waters toward Indonesia and Australia.

Scientists are still looking for answers as to why this happens, but these slow winds can last for weeks or months.

El Niño events occur every two to seven years in varying intensities, and the waters of the eastern Pacific can become up to 4 °C warmer than normal.

El Nino is the opposite of the La Nina weather pattern.

What happens when El Nino occurs?

A strong El Niño warms the atmosphere and changes circulation patterns around the world, particularly the jet stream over the Pacific Ocean, which becomes stronger and brings more frequent and intense hurricanes to the western US, especially California. Is. It also means more rain for the west coast of South America.

This can particularly affect the jet stream, a narrow band of fast air in the upper atmosphere of the Pacific Ocean, which becomes stronger and more frequent over the western US, especially California and the west coast of South America. Gives rise to intense storms.

But the atmosphere is like a zero-sum game. More rain falls over North and South America at the expense of normally rainy South Asia and Australia, which become unusually dry and experience drought.

El Nino is believed to have caused severe flooding in eastern parts of Africa, leading to landslides, increased waterborne diseases and even food shortages, while northern and southern parts of the continent experience drought. Serious.

A strong El Niño also affects cyclone season across the planet. The warmer the Pacific Ocean, the more storms or typhoons it forms, while fewer storms form in the Atlantic Ocean because increased upper-level winds prevent them from developing. This occurred during the 2015 hurricane season, when the Pacific broke records while the Atlantic experienced a relatively calm year.

Which areas are usually most affected?

Like snowflakes, no two El Niños are exactly alike. For example, an area of ​​warm water in the North Pacific that was known as “the Blob” during the 2014–2016 El Niño event was not there during the 1997 El Niño.

But during typical El Niño years, the southwestern and southeastern United States receive more rainfall, while the north experiences drier and warmer weather.

And weather isn’t the only thing that affects El Niño. Warm surface waters in the eastern Pacific drive away cold-water fish that are the backbone of the fishing industry in much of Latin America. In fact, fishermen there first observed the phenomenon and called it “the boy” or “Baby Jesus” because it often appeared around Christmas.

Does climate change have anything to do with it?

The impact of climate change on El Niño is a matter of debate. Some research suggests that the overall magnitude of El Niño is unlikely to increase, but that a “Super El Niño” is twice as likely to increase.

Some recent studies suggest that climate change could worsen the effects of El Niño. And while the total number of El Niño events is unlikely to increase as the planet warms, the likelihood of a so-called “Super El Niño” will double, other research suggests.

One of the most likely byproducts of global warming is more extreme precipitation, as warmer temperatures can trap more water vapor in the atmosphere. This could make El Nino-induced floods even more devastating.

editor’s Note: This article was originally published in October 2023.

With information from Helen Regan.