Officials raised the alarm last week for a near guarantee that the world will face its hottest year on record within the next five years.
A double whammy of human-induced climate change and the return of ElNiño are expected “to push global temperatures into uncharted territory,” said World Meteorological Organization Secretary-General Petteri Taalas in anews release.
“There’s really high confidence that we will get an El Niño event,” said John O’Brien, a climate scientist at Lawrence Berkeley National Laboratory. “I think what we don’t know right now is what kind of El Niño we’re going to get.”
The El Niño events of 1982-83 and 1997-98 resulted in winters with record-breaking snow and rain in California. This year the state has already seen flooding due to historic precipitation, in places like Pajaro (Monterey County) and Corcoran (Kings County). These and other communities are still recovering, with the potential for even more wet weather down the road.
The Chronicle spoke with six scientists and asked about how the upcoming El Niño could unfold, and the magnitude of impacts it could bring to the West Coast.
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“That’s the million-dollar question,” O’Brien said.
Signs of ElNiño
ElNiño involves warmer-than-normal water temperatures around the equator in the eastern and central Pacific Ocean. This drives moisture-laden air to rise over ocean waters and lead to storms over parts ofthe western United States, as well as Central and Southern America.
Surface temperatures of the water in the eastern Pacific, off the coast of Peru, soared over the past several months— as high as10 degrees higher than usual.
“That’s a big deal for fisheries and regional impacts in South America,” said Kris Karnauskas, a climate scientist at the University of Colorado Boulder.
The warm waters energized torrential downpours and devastating floods that putover half a million people in Peru in urgent need of humanitarian aid, according to the United Nations Office for the Coordination of Humanitarian Affairs.
While the warm waters off the coast of South America are unusual, such a rise isn’t completely unprecedented.
Monthly temperatures were even higher in the region during 1982-83 and 1997-98. Those years may sound familiar because they both produced incredibly strong ElNiños— defined by warmer-than-normal sea surface temperatures in waters closer to the International Date Line, in the east-central equatorial Pacific. Theincessant rains of the 1997-98 El Niño produced devastating landslides and debris flows across the Bay Area.
That said, there were also years, like 2017, where warm sea surface temperatures in the equatorial Pacific didn’t result in a similar rise in the east-central Pacific.
“But this one feels a little different,” said MichelleL’Heureux, a climate scientist with the National Oceanic and Atmospheric Administration’s Climate Prediction Center. “Just in the last several weeks, we’re starting to see the intensity spread to the west. And we think that will eventually lead to a shift in the winds and the convection patterns that will allow us to declare El Niño.”
Computer models are pointing to rising sea surface temperatures across the equatorial Pacific in the coming months. There is a greater than 90% chance that ElNiño will form and persist through the Northern Hemisphere winter, according to the National Oceanic and Atmospheric Association’s Climate Prediction Center.
But there are limitations to the models.
“The models are known to be overconfident,” saidShang-Ping Xie, a climate scientist at UC San Diego’s Scripps Institution of Oceanography. “They are not as chaotic as nature is.”
What El Niño means for California weather
ElNiño conditions tilt the odds for wetter conditions in California, especially the southern parts of the state, scientists say.
“More rain on the coast, potentially more snowfall in the Sierra Nevada,” said Chronicle meteorologist Gerry Díaz.
This link between water in the equatorial Pacific and West Coast weather is what scientists call a teleconnection.
“Imagine throwing a rock in the water and then the waves ripple out,” O’Brien said. “That’s essentially what’s happening with El Niño.”
The warm water results in rising air that produces waves in the atmosphere, which can alter the path of the jet stream such that storms veer further south than normal, toward California.
But that doesn’t guarantee that California will see a repeat of past wet winters, even with a strong El Niño. That’s one of the biggest misconceptions, scientists say, pointing out that El Niño conditions just increase the chances that California will see more precipitation than normal.
On top of that, each event occurs over a unique background of varying atmospheric conditions.
“No two ElNiños look the same,” said Tom Di Liberto, a climate scientist with the National Oceanic and Atmospheric Administration.
For example, even though the 2015-2016 ElNiño brought extremely warm waters to the equatorial Pacific, it brought far less precipitation than expected.
“A lot of people call it the failed El Niño,” O’Brien said.
Part of the reason that the event didn’t pan out as expected, O’Brien says, is because the traditional index used to define El Niño, based on sea surface temperatures in the east-central equatorial Pacific, doesn’t provide a complete picture. The 2015-2016 El Niño involved extremely warm waters, but the consequent moist air rose closer to the central equatorial Pacific. The resulting shift in storm track didn’t steer wet weather in California.
By contrast, moreimpactful events, like those in 1982-83 and 1997-98, arose further east. There is another index that captures longitude information that O’Brien said does a better job at predicting how El Niño events affect California weather. But this is a relatively new approach, he added, and used less frequently in the scientific community.
ElNiño also doesn’t control the weather alone— there’s an “alphabet soup” of other patterns, L’Heureux said, like the Pacific North American pattern, or PNA, and the Arctic Oscillation, or AO. These can have stronger effects on the weather than El Niño, but scientists can’t predict them months in advance.
“Climate scientists are still trying to work out what makes them tick,”L’Heureux said.
Links between climate change and ElNiño
Scientists expect human-induced climate change to produce warmer temperatures worldwide. But how that warmer atmosphere will influence ElNiño’s effect on weather remains an open question.
One complication is that climate change has many impacts,Di Liberto said. If you think of El Niño as a light bulb controlled by a hundred dimmer switches, “climate change is like a bratty kid going in and slightly changing” all of the switches, he explained.
But there is a strong link between climate change and storm activity. A warmer atmosphere can hold more water, meaning future storms will likely pack a stronger punch. On the flip side, warmer temperatures could also make droughts more intense.
“Even beyond ElNiño, extremes should get more extreme with climate change,” Karnauskas said.
These effects are already occurring, L’Heureux added, which makes the process of accurately forecasting ElNiño impacts extremely challenging.
“We have to always be mindful that we’re dealing with both climate change and El Niño, and that they can work together,” L’Heureux said.
Reach Jack Lee: firstname.lastname@example.org
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