Thursday, June 8, 2023

Season’s unwanted guest: Dirty La Nias keep popping up

There is something strange with La Nia, a natural but powerful weather phenomenon associated with more droughts and wildfires and more Atlantic hurricanes in the western United States. It is becoming the country’s unwanted weather guest and meteorologists said the West’s megadrought will not be far away until La Nia arrives.

The current double-dip La Nia set a record for strength last month and a rare but absolutely unprecedented third straight winter is unlikely to be around. And it’s not just that. Scientists are seeing that the world is getting more La Nias in the past 25 years than ever before and this is in stark contrast to their best computer model simulations of what happens with human-caused climate change.

“They (La Nias) don’t know when to leave,” said Michel L’Herreux, head of the National Oceanic and Atmospheric Administration’s Forecast Office for La Nia and its more famous flip side, El Nio.

An Associated Press statistical analysis of winter La Nias shows that they used to be about 28% of the time from 1950 to 1999, but over the past 25 winters, they’ve been ripening for about half the time. There’s a small chance that this effect could be random, but if La Nia sticks around this winter, as forecast, it will further push the trend to a statistically significant line, which is important in science, L. ‘ said Heureux. Their own analysis shows that La Nia-like conditions are occurring more frequently in the past 40 years. Other new studies are showing similar patterns.

What is troubling many scientists is that their go-to climate simulation models, which get the correct conditions for the rest of the world, predict more El Nios, not La Nias, and that may lead to climate change. Controversy is brewing in the community about what to believe according to Colombia. University climate scientist Richard Seeger and MIT hurricane scientist Kerry Emanuel.

What Seeger and other scientists say is happening is that the eastern equatorial Atlantic is not warming as fast as the western equatorial Atlantic or even with climate change in the rest of the world. And it is not the amount of warming that matters but the difference between West and East. The greater the difference, the lower the probability of a La Nia, the smaller the difference, the greater the likelihood of an El Nio. Scientists speculate that it may be related to another natural cycle, called the Pacific Decadal Oscillation, or it may be caused by human-caused climate change, or both.

“At this point we just don’t know,” L’Heureux said. “Scientists are watching and, I know, actively studying. But it’s really important because of the regional conditions. We need to get it right.”

La Nia is a natural and cyclical cooling of parts of the equatorial Pacific that changes weather patterns around the world in contrast to a warming El Nio. Due to frequent more Atlantic storms, less rain and more wildfires in the west, and agricultural losses in the middle of the country, studies have shown that La Nia is more costly for the United States than El Nio. El Nio, La Nia, and neutral conditions are called ENSO, which stands for El Nio Southern Oscillation, and they are one of the largest natural impacts on climate, sometimes amplifying the major effects of human-caused climate change. and reduce the second time. By the burning of coal, oil and gas, the scientists said.

They have a “very, very strong” effect indeed, said Azhar Ehsan, lead research scientist at Columbia University’s El Nio/La Nia forecast. “So for the third time in a row, a La Nia is not a welcome thing.”

He said that dangerous heat in India and Pakistan this month and in April is associated with La Nina.

The current La Nia was formed in the late summer of 2020 when the Atlantic set a record for the number of named storms. It strengthened in the winter as the West’s drought worsened and weakened so much in early summer 2021 that NOAA said conditions were neutral. But that stagnation lasted only a few months and the La Nia returned in early 2021, causing this double decline.

Ahsan said that usually the second years of La Nia are weak, but in April this La Nia surprised meteorologists by setting a record of intensity in April, which is based on sea surface temperature.

“These are very impressive prices for April,” L’Heureux said. Nevertheless, because La Nias have historically weakened in summer and there are slight signs that it may ease slightly, there is a small but growing possibility that this La Nia will be considered neutral in late summer. may be hot enough.

La Nia has the greatest impact in winter and that is when it is a problem for the west as it is the rainy season which is supposed to recharge the reservoirs. But the West is in a major 22-year drought, about the same period of increasing La Nia frequency.

UCLA climate scientist Danielle Swain said three factors — ENSO, climate change and randomness — are a huge trigger for large-scale wildfires when it comes to drought. Without climate change, La Nia and bad luck would have made the drought the worst in 300 years, but with climate change it is the worst in at least 1,200 years, said UCLA climate hydrologist Park Williams.

La Nia is “a very important player; This could be the key player,” said Swain, who has a blog on western weather. “It may account for a third, perhaps half of the terms given if it is pronounced adequately.”

“It is very unlikely that the southwest will at least partially improve from the megadrought during La Nia,” Swain said.

A La Nia “increases your Atlantic storms” but reduces them in the Pacific, said hurricane researcher Phil Klotzbach of Colorado State University.

It winds about 6 to 7 miles (10 to 12 kilometers) above the water’s surface. One of the major factors in the development of a hurricane is whether there is wind shear, which are changes in wind from high to low altitude. Wind shear can head or tip hurricanes, making them difficult to strengthen and sometimes even sticking. Wind shear can also allow dry air into storms that choke them.

When El Nio happens, there is a lot of Atlantic wind shear and it is difficult for a hurricane to go. But La Nia means less wind in the Atlantic, which makes it easier for storms to intensify and do so quickly, said University of Albany hurricane researcher Kristen Corbosiero.

“It’s a really huge factor,” Corbosiero said.

“Whatever the cause, the increasing incidence of La Nias may be behind the rising storm,” said MIT’s Emanuel.

Some regions, such as eastern Australia and the dry Sahel region of Africa, perform better with more rainfall during La Nia. India and Pakistan, even though they get extra spring heat, also receive much needed rain in La Nias, Colombia’s Ehsan said.

A 1999 economic study found that a La Nia drought cost United States agriculture between $2.2 billion and $6.5 billion, far more than the $1.5 billion cost of an El Nio. A neutral ENSO is best for agriculture.

Colombia’s Seeger said that even though there may be some chance and some natural cycles behind changes in La Nia, as climate change is likely to be a factor, he thinks there will probably be more of them.

, . Follow up on Associated Press’s climate coverage


Follow Seth Borenstein on Twitter @borenbears


Associated Press climate and environmental coverage is supported by a number of private foundations. See more about Associated Press’s climate initiative here. Associated Press is solely responsible for all content.


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