Unwanted Weather Guest: Nasty La Nina Keeps Popping Up

Something weird is happening with La Nina, the natural but powerful weather event linked to more drought and wildfires in the western United States and more hurricanes in the Atlantic. It becomes the country’s unwelcome weather guest and meteorologists have said the Western mega-drought won’t go away until La Nina does.

The current double dip La Nina set a strength record last month and should be here for a rare but not quite unprecedented third winter in a row. And it’s not just this one. Scientists note that over the past 25 years the world appears to have more La Ninas than before and this is the complete opposite of what their best computer model simulations would expect to happen with man-made climate change ..

“They (La Ninas) don’t know when to leave,” said Michelle L’Heureux, chief of the National Oceanic and Atmospheric Administration’s forecast office for La Nina and its most famous setback, El Nino.

A statistical analysis of the La Ninas winter from the Associated Press shows that they occurred about 28% of the time from 1950 to 1999, but in the past 25 winters they have brewed nearly half the time. There’s a small chance that this effect is random, but if La Nina persists this winter, as expected, it would push the trend above the statistically significant line, which is critical in science, L’Heureux said. His own analysis shows that La Nina-like conditions are occurring more often over the past 40 years. Other new studies show similar trends.

What bothers many scientists is that their baseline climate simulation models that tend to get the conditions right over the rest of the globe are predicting more El Ninos, not La Ninas, and that’s causing conflict in the climate community on what to believe, according to Columbia. University climatologist Richard Seager and MIT hurricane specialist Kerry Emanuel.

What Seager and other scientists have said 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, but the difference between West and East. The bigger the difference, the more likely a La Nina, the smaller the difference, the more likely an El Nino. Scientists think it could be linked to another natural cycle, called the Pacific Decadal Oscillation, or it could be caused by human-induced 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 is really important due to regional conditions. We have to do it right.

La Nina is a natural, cyclical cooling of parts of the equatorial Pacific that alters weather patterns around the world, as opposed to El Nino warming. Often leading to more hurricanes in the Atlantic, less rain and more wildfires in the West and agricultural losses in the middle of the country, studies have shown that La Nina costs more in the United States than El-Nino. Together, El Nino, La Nina and the Neutral Condition are called ENSO, which stands for El Nino Southern Oscillation, and they have one of the most significant natural effects on the climate, sometimes increasing and sometimes mitigating the significant effects of climate change d human origin. from burning coal, oil and gas, the scientists said.

“They really have a very, very strong effect,” said researcher Azhar Ehsan, who leads Columbia University’s El Nino/La Nina forecasts. “So a third straight La Nina is not a welcome thing at all.”

He said the dangerous heat in India and Pakistan this month and April is connected to La Nina.

The current La Nina formed in late summer 2020 when the Atlantic set a record for the number of named storms. It strengthened in winter when the western drought worsened and by early summer 2021 weakened enough for NOAA to declare conditions neutral. But that hiatus only lasted a few months, and by early fall 2021, La Nina was back, making it a double dip.

Normally, the second years of La Nina tend to be weaker, but in April, La Nina surprised meteorologists by setting an April intensity record, which is based on sea surface temperatures, Ehsan said. .

“Those are very impressive values ​​for April,” L’Heureux said. Still, because La Ninas historically weakens over the summer and there are slight signs that this may be easing a bit, there is a small but growing chance that this La Nina could warm just enough to be considered neutral in late summer.

La Nina has its greatest effect in the winter and this is where it is a problem for the West as it is the rainy season which is supposed to recharge the reservoirs of the areas. But the West is in a 22-year mega-drought, about the same period of increasing La Nina frequency.

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

La Nina “is quite an important player; maybe it’s the dominant player,” said Swain, who blogs about western weather. “He could be responsible for a third, maybe half of the given conditions if pronounced enough.”

“The Southwest is much less likely to experience at least a partial recovery from the mega-drought during La Nina,” Swain said.

La Nina “amplifies your storms in the Atlantic” but diminishes them in the Pacific, said Phil Klotzbach, a hurricane researcher at Colorado State University.

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 storms is whether or not there is wind shear, that is, changes in the wind from high to low altitudes. Wind shear can decapitate or topple hurricanes, making them difficult to bolster and sometimes even stay. Wind shear can also leave dry air in hurricanes that suffocates them.

When there’s an El Nino, there’s a lot of wind shear in the Atlantic and it’s hard for hurricanes to get going. But La Nina means little wind shear in the Atlantic, which makes it easier for storms to intensify and get faster, said University of Albany hurricane researcher Kristen Corbosiero.

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

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

Some areas like eastern Australia and the arid Sahel region of Africa do better with more rain during La Nina. India and Pakistan, while getting extra spring heat, are also getting more rain needed in La Ninas, said Ehsan from Colombia.

A 1999 economic study found that the La Nina drought cost US agriculture between $2.2 billion and $6.5 billion, which is far more than the $1.5 billion cost of El Nino. A neutral ENSO is best for agriculture.

Columbia’s Seager said that while there may be chance and natural cycles behind the changes in La Nina, because there is likely a climate change factor, he thinks there will likely be more.


Follow AP’s climate coverage at https://apnews.com/hub/climate


Follow Seth Borenstein on Twitter at @borenbears


The Associated Press’s climate and environmental coverage receives support from several private foundations. Learn more about AP’s climate initiative here. The AP is solely responsible for all content.


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