September 26, 2023

How do El Niño and La Niña affect temperatures?

Nearly 100 million people in the US will experience triple-digit temperatures by the end of the week as a massive heat wave sweeps through the US Southwest

Recurring weather events play a vital role in the scorching heat and could contribute to making it worse. El Niño and La Niña – opposite extremes that alternate as sea surface temperatures, rainfall, air pressure and atmospheric circulation vary – play important roles in global temperatures.

What is El Nino?

This year marks the return of El Niño, a natural climate phenomenon that develops every two to seven years when the Pacific Ocean experiences “warmer-than-average” surface temperatures. NOAA explains that the event weakens trade winds as warm water is pushed toward America’s west coast, causing the Pacific Ocean’s jet stream to move south.

This transition will cause the northern US and Canada to experience drier and warmer weather than usual, while the Gulf Coast and southeastern US will see more precipitation and flooding.

What is La Nina?

La Nina is the equally impressive opposite of El Niño, causing trade winds to be “stronger than usual,” according to NOAA, and pushing warm water toward Asia. The colder waters in the Pacific Ocean are forcing the aforementioned jet stream further north, generally causing drought in the Southwestern U.S. while leading to more precipitation and flooding in the Pacific Northwest and Canada and a more intense Atlantic hurricane season.

Winters during these periods are generally warmer in the southern US and colder in the north.

NOAA's seasonal temperature outlook from July to September shows high heat across most of the US as El Nino rolls in.  /Credit: NOAA

NOAA’s seasonal temperature outlook from July through September shows high heat across most of the US as El Nino rolls in. /Credit: NOAA

How do El Niño and La Niña affect temperatures?

Both events could greatly affect temperatures around the world, especially when combined with climate change.

Michelle L’Heureux, a climate scientist at NOAA’s Climate Prediction Center, explained in June that El Niño “could lead to new records for temperatures, especially in areas already experiencing above-average temperatures during El Niño.”

On June 15, NOAA released a seasonal forecast that says the majority of the US is expected to see “above normal” average temperatures from July to September, particularly in the West, Gulf Coast and East regions. These temperatures already seem to be hitting these areas, as The Weather Channel described as a “scorching July” that doesn’t hit the US until the second week of July.

Many states are expected to see triple-digit numbers the week of July 10, Weather Channel meteorologist Stephanie Abrams said on “CBS Mornings.”

“By Friday it will feel like 100 degrees [Fahrenheit] or more for 90 million Americans, actually more than 90 million Americans here, in the South,” she said.

Maps show that about 53 million Americans already felt such temperatures on Monday, and that 98 million are expected to feel that kind of heat by Friday.

Phoenix, Arizona, has had its 10th consecutive day of heat at or above 110 degrees Fahrenheit, Abrams added, a record that could be broken if the spell is not broken. On Sunday, the National Weather Service warned of “prolonged dangerous heat,” saying that a “prolonged heat wave” will last at least until next Sunday.

How does climate change affect El Niño and La Niña?

The future of El Niño and La Niña is expected to be more intense than now.

In 2020, the American Geophysical Union published research on the cycle. Michael McPhaden, a senior scientist at NOAA’s Pacific Marine Environmental Laboratory and co-editor of the study, said events may change as concentrations of greenhouse gases in the atmosphere continue to rise. These gases are known to act as a sort of insulator for the sun’s radiation, raising Earth’s temperature as more of the gases — largely emitted from the burning of fossil fuels — fill the atmosphere.

“Extreme El Niño and La Niña events could increase in frequency from about one every 20 years to one every 10 years by the end of the 21st century under aggressive greenhouse gas emission scenarios,” McPhaden said, according to NOAA. “The strongest events can also become even stronger than they are now.”

NASA Chief Scientists and Senior Climate Adviser Kate Calvin told “Face the nationon Sunday that when La Niña was there last year, it was the “warmest La Niña year we’ve ever had,” tying for the fifth warmest year overall.

These events, which are determined by ocean heat, are likely to change as ocean heat changes. But oceans warm more slowly than land, meaning any additional heat brought by El Niño is likely to exacerbate the already excessive heat being felt.

“Oceans absorb a lot of heat, which is why we’re seeing an increase in ocean temperatures,” Calvin told Margaret Brennan. “But the thing to keep in mind is that oceans are actually — land is warming faster than oceans. So the places where we live are warming faster than the ocean. So while we’re seeing these increases in ocean temperatures, we’re also seeing temperature rises over land.”

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