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Why the link between tornadoes and climate change is so hard to draw: NPR

Mayfield, Ky., was one of the places that suffered terrible tornadoes over the weekend.

Brendan Smialowski / AFP via Getty Images


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Brendan Smialowski / AFP via Getty Images


Mayfield, Ky., was one of the places that suffered terrible tornadoes over the weekend.

Brendan Smialowski / AFP via Getty Images

Dozens of tornadoes – including one major hurricane that tore through more than 200 miles – hit Kentucky, Tennessee, Arkansas, Illinois, Missouri and Mississippi on Friday and Saturday, killing at least 14 people in four states and dozens of others just in Kentucky.

Those who follow devastating news out of the region may wonder: (How) are hurricanes related to climate change?

After all, most extreme weather events have dominated the headlines lately – from Wildfires in America arrive Historical floods in Western Europe – has a clear link to high temperatures, record rainfall and other effects of a warming planet.

However, the same cannot be said exactly for tornadoes.

Scientists know that warm weather is a major contributor to tornadoes, and that climate change is altering the environment in which these types of storms form. But they can’t connect those dots directly, because research into the link between climate and tornadoes is still far behind that of other extreme weather events like hurricanes and wildfires.

That’s at least in part due to a lack of data – even though the US World leader in tornadoes, averaging about 1,200 a year.

Harold Brooks, a tornado scientist at the National Severe Storms Laboratory, says less than 10 percent of severe thunderstorms produce tornadoes, which makes it difficult to draw firm conclusions about the processes. leading to them and how they may be affected by climate change. told the Associated Press.

Other factors that make climate change attribution difficult include the quality of the observational record and the ability of models to simulate certain weather events. The National Oceanic and Atmospheric Administration said that was the case for tornadoes.

“Observational records are inconsistent and relatively short, models are still inconclusive regarding the reproduction of cyclone activity, and only we understand on how global warming and climate change will affect the various atmospheric processes that produce cyclones (wind shear, for example) are more limited,” read page on its website.

While scientists may not be able to precisely connect tornado frequency or intensity to human-caused climate change, they say there are signs pointing in that direction.

Here’s what they know:

What are tornadoes and when do they happen?

NOAA identify tornado as narrow, violently rotating columns of air extending from a thunderstorm to the ground (while the wind portion is invisible, tornadoes can form condensate funnels of water droplets, dust, and debris). They can be one of the most devastating natural disasters, tearing down homes, tearing down infrastructure and blowing debris away.

Tornadoes can strike in any part of the United States at any time of the year.

Historically, they have been associated with the Great Plains, although experts argue that the idea of ​​the so-called “Typhoon Alley” can be misleading because the tornado threat is a moving target. It moves from the Southeast during the cooler months of the year, toward the Southern and Central Plains in May and June, and the northern and Midwest Plains in early summer.

When people talk about “tornado season,” they’re usually referring to the time of year that the United States sees the most tornadoes — peaking in May and June in the Southern Plains and then in the Southern Plains. Northern Plains and Upper Midwest. This weekend’s tornadoes aren’t outside the typical tornado season, but experts say that’s not uncommon in itself.

What conditions caused this weekend’s storm

Meteorologists are pointing to two contributing factors: warm temperatures and strong winds.

Thunderstorms occur when drier, denser cold air is pushed through warmer, moist air, and a gust is created as warm air rises. Changes in wind speed and/or direction (called “wind shear”) can cause the wind to rotate, setting the stage for a tornado.

There’s usually not a lot of unsettled wind in the winter as the air is usually not warm or humid – but that’s not the case on weekends.

States in the Midwest and South experienced spring-like temperatures on Friday. Memphis, Tenn., saw one record high of nearly 80 degrees Fahrenheit, for example.

“The atmosphere didn’t know it was December – temperatures in the 70s and 80s,” the Mississippi-based tweeted. meteorologist Craig Ceecee.

It could be the product of many things, from La Niña . climate model bring warmer-than-average conditions to the southern United States, to above average water temperature of the Gulf of Mexico, to warm winter weather that is increasingly common as the planet warms.

In any case, that high temperature creates warm, humid air that helps form thunderstorms. And once a hurricane forms, experts believe strong wind shear (which often occurs in winter) will prolong its tornadoes.

Victor Gensini, a professor of meteorology at Northern Illinois University, told the AP that while tornadoes typically lose energy within minutes, this weekend’s tornadoes lasted for hours.

The US is likely to see more tornadoes outside of their usual time and place

Experts say climate change is impacting tornado formation conditions and could lead to changes in when and where the United States sees them.

John T. Allen, a professor of meteorology at Central Michigan University, wrote in a USA Today opinion column that while the relationship to climate change remains uncertain, there appears to have been an “eastward shift in tornado frequency” and an increasing frequency of tornado outbreaks over the past few decades.

“Climate projections for the end of the 21st century have suggested that conditions are favorable for the development of severe storms that produce tornadoes. will increase across North America, and the impact is likely to be greatest in winter and fall,” he added.

Brooks, of the National Severe Storms Laboratory, said the US is likely to see more tornadoes in the winter (and fewer in the summer) as national temperatures rise above the long-term average. .

And Gensini said to Axios projections show an increase in major outbreaks in the central and southeastern regions. He also compared the tornado-climate change distribution to baseball’s steroid era, as Axios put it: “Pinting an individual home run using steroids is very difficult, he said. , but overall the trend is clear.”

A version of this story first appeared inside Morning version live blogs.

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