Did Climate Change Fuel Deadly Twisters? Probably, Scientists Say

ACROSS AMERICA — The deadly cluster of twisters that tore across multiple states Friday, killing at least 88 people, may be the latest example of extreme weather wrought by the warming of the planet, climate scientists say.

The storm, which killed 74 people in Kentucky alone, had already been called one of the deadliest and longest lasting in U.S. history. More than 30 tornadoes cut a path of destruction about 250 miles long; and if viewed as a single tornado event, it would be the longest on record in the United States.

That alone doesn’t mean the storm system was spawned by climate change, but tornado expert and Northern Illinois University professor Victor Gensini told CNN that an analysis of the data is likely to support that.

“When you start putting a lot of these events together, and you start looking at them in the aggregate sense, the statistics are pretty clear that not only has there sort of been a change — a shift, if you will — of where the greatest tornado frequency is happening,” Gensini told the cable news network. “But these events are becoming perhaps stronger, more frequent and also more variable.”

Tornadoes form when warm, humid air collides with cold, dry air during thunderstorms. These conditions cause spinning within thunderclouds, and the spinning currents can drop down from a cloud and become a twister.

Gensini, whose research spans four decades, said tornadoes are becoming more frequent in large swaths of the Midwest and Southeast, while decreasing in frequency in the area known as “Tornado Alley,” parts of the central and southern Great Plains.

That study, published in 2018, examined the frequency of EF1 or greater tornadoes over 40 years from Louisiana to Missouri eastward, especially south of the Ohio River and east of the Mississippi.

Some of the deadliest and most destructive tornadoes of the 21st century have occurred in the region from Louisiana north to Missouri and eastward, especially south of the Ohio River, east of the Mississippi and west of the Appalachians. That includes the Super Outbreak of 2011, a cluster of tornadoes between April 25-28 that caused about $12 billion in damage (in 2021 dollars) and killed 321.

Part of the eastward shift, Gensini told CNN, can be explained by a La Niña weather pattern.

“It's also very common when you have La Niña in place to see this eastward shift in highest tornado frequency,” he said. “But if you look at the past 40 years, the research I've done ... has shown that places like Nashville, Tennessee, for example — or Mayfield, Kentucky, that we saw got hit — their frequency of tornadoes, their risk of having a tornado has increased over the last 40 years.”

But meteorologists and climate scientists just aren’t sure yet.

The link between tornadoes and climate change is more nuanced than for other extreme weather phenomena, such as heat waves, droughts, hurricanes and wildfires.

Scientists at Yale University say climate change “may be involved in some noteworthy recent shifts in the location and seasonal timing of the tornado threat,” but they haven’t found evidence a human-warmed climate makes twisters more frequent or violent.

One reason it’s so difficult for climate scientists to draw a connection: Climate change effects are typically seen as broad regional shifts, such as depleting sea ice; each tornado is a brief, episodic and localized events, making it difficult to discern long-term trends in their behavior and distinguish them from normal ups and down.

Jennifer Marlon, a climate scientist at the Yale School of Environment, told CNN there are “some really important signatures” that suggest a link between Friday’s tornadoes and climate change. Scientists, she said, are “observing changes in the outbreaks, not just the severity of individual outbreaks and tornadoes, but also quiet periods.”

December tornadoes are rare, with most occurring during the spring and summer, and that’s also fueling questions about how climate change may have influenced the deadly outbreak.

“In my 40 years as a meteorologist, this was one of the most shocking weather events I've ever witnessed,” says Jeff Masters, a meteorologist at Yale Climate Connections. “Watching these storms on Friday night, my thought was, ‘Is no season safe?’ Extreme tornadoes in December. That was mind-blowing to me.”

A new study presented Monday at the American Geophysical Union conference in New Orleans suggests that in a warming world, winter tornadoes are likely to be stronger, stay on the ground longer and cut a wider swath of destruction.

The study, which isn’t yet peer-reviewed, was conducted before last weekend’s tornado outbreak. It suggests stronger winds will make winter tornadoes that are killers now nine times more powerful by the end of the century if carbon dioxide levels continue to rise, The Associated Press reported.

“There is a potential for events in the future that are more intense that would not have been as intense in the current climate,” said study author Jeff Trapp, head of atmospheric sciences at the University of Illinois, Urbana-Champaign. “Bearing in mind that these high-end events are still going to be rare.”

He compared data from two large tornadoes in 2013 — the Hattiesburg, Mississippi, tornado in February that had winds of up to 170 mph and injured 82 people, and the Moore, Oklahoma, tornado in May that killed 24 people and had winds of up 210 mph.

The winter storm had significantly wider and longer paths, and wind speeds were about 14 percent higher than the springtime events.

Scientists attending the conference were intrigued but not entirely convinced.

“I’m not 100 percent sold on the technique, but it’s a very interesting approach,” Harold Brooks, a scientist at the National Severe Storms Laboratory in Norman, Oklahoma, told the AP. “To me the really interesting result seems to be the longer-tracks for the cool season.”

Gensini told National Geographic that given the different ways the warming climate has already affected weather patterns, it makes that sense tornadoes would be affected, too.

“Instead of asking: ‘Did climate change cause this tornado?’ it’s better to operate under the assumption that climate change did play a role,” he told National Geographic. “Start from the premise that every extreme event is being affected by climate change."