Home Sciences Scientists worry: ‘La Niña’ stays longer and creates more hurricanes

Scientists worry: ‘La Niña’ stays longer and creates more hurricanes

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Something strange is happening with La Niña, the powerful natural weather phenomenon linked to droughts and wildfires in the western United States and more hurricanes in the Atlantic. Contrary to what has happened so far, is becoming an almost permanent weather guest in many Atlantic countries and the Pacific. Forecasters believe that the megadrought in the West will not go away until La Niña does.

The current presence of La Niña has broken all intensity records and is considered very likely to be present for the third consecutive winter., something uncommon but not entirely unknown, especially in recent decades. In fact, scientists are noticing that in the last 25 years the world seems to have more La Niña episodes than normal and that is just the opposite of what should be happening with human-caused climate change, simulations show. informatics.

“The girl doesn’t know when to leave” explained Michelle L’Heureux, head of the National Oceanic and Atmospheric Administration (NOAA) forecast office for La Niña and its famous counterpart, El Niño.

A statistical analysis by the Associated Press of the La Niña winter shows that these phenomena used to occur about 28% of the time between 1950 and 1999, but in the last 25 winters they have been occurring for almost half the time. There’s a small chance this effect is random, but if La Niña continues this winter, as predicted, it would lift the trend above the statistically significant line, which is key science, L’Heureux said.

Their own analysis shows that La Niña conditions are occurring more frequently in the last 40 years. Other recent studies also show similar patterns.

Confusion among scientists

But there is one fact that puzzles scientists. And it is that their climate simulation models predict that there should be more episodes of El Niño, not La Niña, and that is causing controversy in the climate community.

Climatologist Richard Seager and other scientists believe that what is happening is that the eastern equatorial Atlantic is not warming as fast as the western equatorial Atlantic (or even the rest of the world) with climate change. And in this case it is not the amount of warming that matters, but the difference between the west and the east. The larger the difference, the more likely La Niña will be, and the smaller the difference, the more likely El Niño will be.

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Scientists speculate that it could be related to another natural cycle, called the Pacific Decadal Oscillation, or it could be caused by human-caused climate change, or both.

“Right now we just don’t know; scientists are investigating,” L’Heureux said.

La Niña is a natural, cyclical cooling of parts of the equatorial Pacific that changes weather patterns around the world, unlike the warming of El Niño. It often leads to more hurricanes in the Atlantic, less rain and more wildfires in the west, and agricultural losses in the center of the country. Studies have shown that La Niña is more costly to the United States than El Niño. Together, El Niño, La Niña, and the neutral condition are called ENSO, which stands for El Niño Southern Oscillation, and they have one of the largest natural effects on climate, sometimes enhancing and sometimes dampening the larger effects of climate change. man-made from burning coal, oil and gas, scientists said.

“They really have a very, very strong effect,” said research scientist Azhar Ehsan, who heads Columbia University’s El Niño/La Niña forecast. “So a third La Niña in a row is not very welcome,” he added.

He also stated that the extreme heat in India and Pakistan experienced this month and in April is related to La Niña.

It was formed in 2020

The current La Niña formed in late summer 2020 when the Atlantic set a record for the number of storms assigned with their own name. It strengthened in the winter as the western drought worsened, and in early summer 2021 it weakened enough for NOAA to say conditions were already neutral. But that hiatus only lasted a few months, and by early fall 2021, La Niña was back, making it a double dip.

Normally, second La Niña years tend to be weaker, but in April, La Niña surprised forecasters by setting a record intensity. “These are very impressive values ​​for April,” L’Heureux said. Still, because La Niña historically weakens during the summer and there are faint signs that it may be abating, there is a small but growing chance that La Niña will get hot enough to become neutral by late summer.

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La Niña has its greatest effect in winter and that is when it is a problem for the West, because the rainy season is the one that recharges the reservoirs and aquifers of that region. But The West is experiencing a 22-year megadrought, roughly the same length of time that La Niña has increased in frequency.

Three factors — ENSO, climate change, and randomness — matter most when it comes to drought, which itself is a big trigger for massive wildfires, said UCLA climate scientist Daniel Swain. Without climate change, La Niña and bad luck might have made the drought the worst in 300 years, but with climate change it is the worst in at least 1,200 years, said Park Williams, a climate hydrologist at UCLA.

La Niña “is a pretty big player; it can be the dominant player,” said Swain, who blogs about western weather. “He could be responsible for a third, maybe a half of the given conditions.”

La Niña triggers storms in the Atlantic

La Niña “increases storms in the Atlantic” but decreases them in the Pacific, said Phil Klotzbach, a hurricane researcher at Colorado State University.

These are winds of 10 to 12 kilometers above the surface of the water. One of the key factors in the development of storms is if there is the so-called ‘wind shear’, which are changes in the wind at a certain altitude. wind shear can decapitate hurricanes, making them difficult to strengthen and sometimes even to stay. Wind shear can also let dry air into hurricanes and suffocate them.

When there’s an El Niño, there’s a lot of wind shear in the Atlantic and it’s hard for hurricanes to get going. But La Niña means little shear in the Atlantic, making it easier for storms to intensify and do it quickly, said Kristen Corbosiero, a hurricane researcher at the University at Albany. “That’s a really huge factor,” Corbosiero said.

“Whatever the cause, the increasing incidence of La Niña may be behind the increase in hurricanes,” said MIT’s Emanuel.

Reference article: https://phys.org/news/2022-05-weather-unwanted-guest-nasty-la.html

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