The series of weekend tornadoes that ripped through the parts of the US this weekend adds to another stretch of deadly and potentially unprecedented weather disasters that plagued the planet this year. Meteorologists and climate scientists say the latest outbreak is historic.
And as these extreme weather events intensify, occur more often and exacerbate the country’s growing economic toll, science is running to keep up to answer emerging questions of whether climate change is intensifying every single disaster. With this weekend’s tornadoes, climate researchers say it’s too early to determine the link, but the uncertainty doesn’t mean it is unlikely.
In Kentucky, the series of tornadoes uprooted trees, tore down homes and infrastructure, and killed at least 74 people. Gov. Andy Beshear said at a news conference that the tornado event reached a “level of devastation unlike anything I have ever seen,” he said.
Global scientists made clear that weather events, no matter how severe, are occurring against the backdrop of human-caused climate change; nevertheless, it all comes down to discerning how a warming planet is altering weather patterns, including geographical location and frequency, as well as severity.
Scientists say the short-lived scale of tornadoes, coupled with an extremely inconsistent and unreliable historical record, makes connecting outbreaks to long-term, human-caused climate change extremely challenging.
Unlike large-scale and slow-trending weather events such as droughts, floods and hurricanes, scientific research about the link between climate change and tornadoes has not been as robust.
Victor Gensini, a professor at Northern Illinois University and one of the top tornado experts, said the weekend’s outbreak is one of the most remarkable tornado events in US history – and while climate change may have played a part in its violent behavior, it’s not yet clear what that role was.
Think of a pair of dice, he said. On one of the die, you altered the value of five to six, which means it now has two sixes – raising the chances of you rolling the pair of dice and getting the value 12. Although you can’t immediately attribute that value of 12 to the change you made, you just altered the probability of that event occurring.
Gensini said that’s similar to how the climate system now works – the more humans pump greenhouse gases into the atmosphere and change the system, the chances of extreme weather events occurring will amplify.
He points to different ingredients that primed the landscape for the outbreak to happen, such as a late spring, early summer air mass and a strong wind shear.
In pictures: Deadly tornadoes hit central and southern US
“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 CNN. “But these events are becoming perhaps stronger, more frequent and also more variable.”
Research by Gensini found that over the past four decades, tornado frequency has increased in vast swaths of the Midwest and Southeast, while decreasing in parts of the central and southern Great Plains, a region traditionally known as Tornado Alley.
Some studies also indicate climate change could be contributing to an eastward shift in tornado alley, for instance, resulting in more tornadoes occurring in the more heavily populated states east of the Mississippi River, such as this tornado outbreak.
“It’s also very common when you have La Niña in place to see this eastward shift in highest tornado frequency,” Gensini 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.”
Tornadoes take shape under particularly specific atmospheric conditions, but are primarily fueled by warm, moist air from strong winds that shift direction with altitude.
Scientists have warned that the rise in greenhouse gas emissions in the atmosphere is drastically changing the climate system, even causing the jet stream – fast-flowing air currents in the upper atmosphere that influence day-to-day weather that could trigger a tornado event – to behave oddly.
Jennifer Marlon, a climate scientist at the Yale School of Environment, told CNN it’s too early to say what caused the outbreak – whether natural variability or climate change – but there are “some really important signatures that suggest that this very well may be linked to climate change,” and that scientists are “observing changes in the outbreaks, not just the severity of individual outbreaks and tornadoes, but also quiet periods.”
For example, if any of the tornadoes are rated EF-5 (estimated winds of 260 mph or greater), it would end a streak of 3,126 days since the last EF-5, which is the longest stretch without since records began in 1950. The last EF-5 tornado was the Moore, Oklahoma, tornado on May 20, 2013.
It’s likely that it was simply natural forces at play, against the background of climate change.
The World Weather Attribution, a group of the world’s leading scientists that establishes the link between climate and weather, for instance, has recently unveiled findings that the warming climate neither intensified the flooding in Vietnam that killed 138 people this summer nor the Madagascar drought that led to the country’s food scarcity.
Still, a recent report by the World Meteorological Organization found that an extreme weather event or climate disaster has occurred every day, on average, somewhere in the world over the last 50 years, marking a five-fold increase over that period and exacting an economic toll that has climbed seven-fold since the 1970s.
As such climate disasters worsen and expand in scope, Marlon points to significant factors that increase disaster risks across society during these times including worsening weather disasters, increasing exposure due to growing populations, and more vulnerable infrastructure assets.
That’s already taking shape in Mayfield, Kentucky, where officials say the city’s main fire station and some of its police assets have become inoperable as a result of the devastating tornado system. Now, authorities are looking for alternative ways to address emergency calls.
“All these things are feeding into increase disaster risk, with many more consequences, including the fatalities, of course, but also enormous economic damages,” she said.
As the climate crisis accelerates, more people will be vulnerable to the most severe consequences of extreme weather events. Experts say cities shouldn’t put off adaptation plans any longer, and instead treat them as a larger emergency response system.
But Gensini said one thing is certain: regardless of climate change, these types of tornado disasters will continue to worsen as humans alter the landscape and build larger, more sprawling cities.
“We have more assets and more targets for the severe storms to hit,” he said. “So even if you take climate change out of the equation, which is very likely to make the problem worse, we still have this issue of human and societal vulnerability.”
CNN Meteorologist Brandon Miller contributed to this report.