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The climate crisis might have contributed to the weekend’s deadly tornadoes

Looking out from the destroyed Dawson Village Apartments in Dawson Springs, Ky., where a tornado flattened much of the town Friday night.William Widmer/NYT

A historic series of at least 38 tornadoes slammed six midwestern states over the weekend, killing dozens and creating nightmarish scenes across the region. The twisters crushed an Amazon warehouse near St. Louis, tore an Arkansas nursing home apart, and leveled entire towns.

Experts are now working to examine what effect the climate crisis may have had on the disaster.

“This event was shockingly unusual,” Jennifer Marlon, a climate scientist at Yale’s School of Environment, wrote in an email.

Winter twisters are relatively uncommon. From 1991 to 2015, the US saw only 27 December tornadoes in an average year, while May saw a mean of 269 tornadoes annually.


This was also no ordinary December tornado outbreak: It was likely the deadliest one on record.

For tornadoes to travel as far north as Kentucky this late in the year is also abnormal. Usually, the state sees its worst ones in spring.

“Something like this is an unusual event for the month of December. It’s typically our quietest month for tornadoes, especially in Kentucky,” ABC News meteorologist Rob Marciano said on “Good Morning America” on Saturday.

One of the storms that struck on Friday night, dubbed the “Quad-State Tornado,” wreaked havoc in four states, traveling 240 miles. It appears to have been the longest continuous tornado in US history, breaking the previous record, which was set in 1925. In the town of Mayfield, Kentucky, the Quad-State storm’s winds thrust debris more than 30,000 feet into the air — comparable to a commercial airplane’s cruising height, and one of the greatest heights for tornado debris on record.

Tornadoes form inside thunderstorms, which occur when cool, dense, dry air meets warmer, more humid air. As the hot air rises, cool air falls. During an ordinary thunderstorm, the falling cool air brings precipitation with it. But sometimes, this also causes air currents to start violently spinning in various speeds and directions, forming a tornado.


It can be difficult to determine exactly how the climate crisis might have affected any individual tornado because tornadoes require a vast array of conditions to form including warm and moist conditions at the ground level, cool and dry winds clashing with those conditions, and a condition known as wind shear wherein winds vary in speed and direction at different altitudes. All of those can be impacted by global warming.

In addition, tornadoes occur over a much smaller area than other extreme weather events. That means they require much more granular climate models to study.

“The widest tornado ever recorded was only two and a half miles wide. That’s huge for a tornado, but our model simulations can’t resolve that fine of resolution,” said Stephen Strader, a meteorologist at Villanova University.

It’s clear, though, that the climate crisis is impacting the environmental backdrop against which tornadoes are forming. For instance, warm air temperatures don’t always lead to tornadoes, but they are a necessary precondition for them to start.. And there is clear evidence that the climate crisis is pushing up winter air temperatures.

At the end of last week, the Midwest was certainly warmer than average. Air temperatures in the impacted region soared into the high 70s on Friday, 20 to 30 degrees above normal temperatures.

“Tornadoes need a complex mix of conditions to form, but warm, moist air is one key ingredient,” said Marlon. “Memphis had 79 degree heat — 26 degrees above average! That is not normal.” Indeed, those Memphis temperatures broke a 103-year record.


La Niña, a natural weather pattern which formed this past autumn wherein Pacific Ocean surface temperatures drop and winds blow warmer waters to the west, almost definitely played a part in last week’s warm weather and therefore hurricane formation. But higher winter temperatures are also a key hallmark of climate change.

Strader says that scientists have not yet seen any evidence that the frequency of tornadoes has increased over time. But research does indicate that the locations where they’re forming is shifting. One 2018 study found that in the past 40 years, tornadoes have become more frequent in the m idwest and Southeast, but less common in parts of the Great Plains.

“There is some evidence that this shift is linked to global warming,” said Marlon.

There is also some evidence that tornado activity is shifting eastward, towards the Tennessee and Mississippi River Valleys. The shift is extremely subtle, but it could make tornado activity more frequent in New England. What’s changing more rapidly, though, is our built environment. More buildings, Strader said, “means that there’s more targets for tornadoes to hit, putting more people in danger.”

More research is required to determine how the climate crisis is impacting tornadoes. But Strader said we shouldn’t wait to prepare by making buildings stronger and more resilient to the elements.


He said the Amazon warehouse and nursing home destroyed this weekend, for instance, were likely built with “minimum standards for cost saving measures.” He likened commercial buildings to “glorified sheds.”

“If we build better we can save lives,” he said. “The evidence is that climate change is working against us when it comes to extreme weather, but we can improve conditions now.”

Dharna Noor can be reached at dharna.noor@globe.com. Follow her on Twitter @dharnanoor.