Something strange is happening with La Nina, the natural but powerful weather event related to more drought and wildfires in the western United States and more Atlantic hurricanes. He is becoming the country’s unwanted weather guest and meteorologists said the Western mega-drought will not go away until La Nina does.
The current double fall of La Nina set a record high last month and is expected to be possible for a rare but unprecedented third consecutive winter. And it’s not just that. Scientists are realizing that in the last 25 years the world seems to be receiving more La Nina than before, and this is the complete opposite of what its best computer model simulations say should happen to human-induced climate change.
“They (La Ninas) don’t know when to leave,” said Michelle L’Heureux, head of the forecast office for La Nina’s National Oceanic and Atmospheric Administration and her most famous face, El Nino.
A statistical analysis by the Associated Press of La Nina d’hivern shows that they used to spend 28% of their time between 1950 and 1999, but in the last 25 winters, they have done almost half the time. There is a small possibility that this effect may be random, but if La Nina stays this winter, as expected, this would push the trend above the statistically significant line, which is key in science, said L’Heureux . His own analysis shows that conditions similar to La Nina are occurring more frequently in the last 40 years. Other new studies show similar patterns.
What bothers scientists is that their climate simulation models, which tend to have the right conditions in the rest of the world, predict more El Niños, not La Nina, and this is causing controversy in the climate community about what to believe, according to Columbia. . University climate scientist Richard Seager and MIT hurricane scientist Kerry Emanuel.
What Seager and other scientists said 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 it’s not the amount of warming that matters, it’s the difference between west and east. The more difference, the more likely it is a La Nina, the less difference, the more likely it is an El Nino. Scientists speculate that it could be related to another natural cycle, called the Pacific Decadal Oscillation, or it could be caused by man-made climate change or both.
“At the moment we just don’t know,” L’Heureux said. “Scientists look and I know, they’re actively studying. But it’s very important for regional conditions. We have to do it right.”
La Nina is a natural, cyclical cooling of parts of the equatorial Pacific that changes weather patterns around the world, unlike the warming of El Nino. Often causing more Atlantic hurricanes, less rain, and more wildfires in the west and agricultural losses in the middle of the country, studies have shown that La Nina is more expensive in the United States than El Nino. Together, El Nino, La Nina and the neutral condition are called ENSO, which means El Nino Southern Oscillation, and have one of the greatest natural effects on the climate, sometimes increasing and sometimes dampening the great effects of climate change caused for man. of burning coal, oil and gas, scientists said.
“They really have a very, very strong effect,” said research scientist Azhar Ehsan, who directs Columbia University’s El Nino / La Nina forecast. “Therefore, a third consecutive La Nina is not at all welcome.”
He said the dangerous heat in India and Pakistan this month and in April is connected to La Nina.
The current La Nina was formed in the late summer of 2020 when the Atlantic set a record number of so-called storms. It intensified in the winter when the drought in the West worsened and in the early summer of 2021 it weakened enough because NOAA said conditions were neutral. But this break lasted only a few months and in the early fall of 2021 La Nina returned, doing a double dive.
Normally, the second years of La Nina are usually weaker, but in April this La Nina surprised meteorologists by setting a record intensity in April, which is based on sea surface temperatures, he said. Ehsan.
“These are very impressive values for April,” L’Heureux said. However, as La Nina has historically weakened over the summer and there are slight indications that it may be declining slightly, there is a small but growing possibility that this La Nina will heat up enough to be considered neutral by the end. of summer.
La Nina has its greatest effect in winter and that is when it is a problem for the West because it is the rainy season that is supposed to recharge the reservoirs in the areas. But the West is in a 22-year-old mega-drought, roughly the same time period of increasing the frequency of La Nina.
Three factors (ENSO, climate change, and randomness) are more important when it comes to drought, which in itself is a major trigger for massive forest fires, said UCLA climate scientist Daniel Swain. Without climate change, La Nina and bad luck could have made 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.
Nina “is a very important player; he could be the dominant player, “said Swain, who has a blog on Western climate.” He could be responsible for a third, maybe half of the given conditions if he pronounces himself enough. “
“The Southwest is much less likely to see at least a partial recovery from the mega-drought during La Nina,” Swain said.
Nina “amplifies your Atlantic storms,” but lessens them in the Pacific, said Colorado State University hurricane researcher Phil Klotzbach.
These are winds 6 to 7 miles (10 to 12 kilometers) above the surface of the water. One of the key factors in the development of the storm is whether there is wind shear, which are changes in wind from high to low elevations. Wind shear can decapitate or overturn hurricanes, making them difficult to strengthen and sometimes even stay. Wind shear can also allow dry air to enter the hurricanes that suffocate them.
When there is an El Nino, there is a lot of shear from the Atlantic wind and it is difficult for the hurricanes to start. But La Nina means little wind shear in the Atlantic, making it easier for storms to intensify and do so quickly, said Albany University hurricane researcher Kristen Corbosiero.
“That’s a very important factor,” Corbosiero said.
“Whatever the cause, the growing incidence of La Ninas may be behind the increase in hurricanes,” said Emanuel of MIT.
Some areas such as eastern Australia and the arid Sahel region of Africa do better with more rain during La Nina. India and Pakistan, while receiving more spring heat, are also receiving more necessary rainfall in La Ninas, Columbia Ehsan said.
A 1999 economic study found that the La Nina drought cost U.S. agriculture $ 2.2 billion to $ 6.5 billion, which is much more than El Nino’s $ 1.5 billion. A neutral ENSO is best for agriculture.
Columbia’s Seager said that while there may be some possibility and some natural cycles behind the changes in La Nina, because there is likely to be a climate change factor, he believes there will probably be more.
___
Follow AP’s weather coverage at https://apnews.com/hub/climate
___
Follow Seth Borenstein on Twitter at @borenbears
___
Associated Press’ environmental and climate coverage is supported by a number of private foundations. See more information on the AP Climate Initiative here. The AP is solely responsible for all content.