Warm temperatures may have helped set the stage for the deadly tornadoes that devastated several states and left at least 74 dead in Kentucky, but experts say they can’t directly attribute climate change as the source of the storms.
Experts on climate change who spoke to The Hill said that rising global temperatures that have led to a number of examples of extreme weather contributed to some of the “ingredients” that make tornadoes more likely to occur.
“It’s not that climate change caused the tornado,” said Walker Ashley, a professor and atmospheric scientist at Northern Illinois University. “It’s how it might have influenced what we call the ingredients necessary to produce the storm that of course went on to produce the tornado.”
Tornadoes ripped through Arkansas, Illinois, Kentucky, Mississippi, Missouri and Tennessee on Friday night, killing dozens of people and devastating communities.
The storms were unusual occurrences in December, and some quickly looked to climate change as an explanation. President Biden said he’d ask agencies like the Environmental Protection Agency (EPA) to assess whether climate played a role.
“The specific impact on these specific storms, I can’t say at this point. I’m going to be asking the EPA and others to take a look at that,” Biden said on Saturday.
Experts who spoke to The Hill said that the relationship between climate and tornadoes isn’t a direct cause and effect.
James Elsner, a professor at Florida State University who studies the changing nature of hurricane and tornado risks, compared the situation to blaming fog for car accidents.
“You might see that for example, when it’s foggy, there’s more crashes, but you don’t say the fog caused the crashes,” Elsner told The Hill.
“If you think about climate change as the fog, we can’t really say it caused the accident, but it contributes,” he said. “It’s increasingly warm and moist, but that’s not sufficient to produce tornadoes. It’s a necessary but not sufficient condition.”
He added that in the years ahead, people should expect to see an increase in things that contribute to tornadoes but not necessarily an increase in tornadoes themselves.
Experts told The Hill that factors that form tornadoes include warm moist air at low levels, cool dry air higher up, and changes in wind speed and direction known as wind shear.
Harold Brooks, an official at the National Oceanic and Atmospheric Administration’s National Severe Storms Lab, said that while climate change is connected to the warm, moist air, its effects on wind shear are less clear.
“It’s not obvious the wind shear’s going to become more, so we end up possibly with these two different effects that may not even be on the same side, so tornadoes are a lot harder to do than many other things,” Brooks said in describing connections between climate change and different types of severe weather.
Ashley said that the storms had the “hallmark of a potential climate change signal.” He cited the unseasonably warm December and warmer surface temperatures in the Gulf of Mexico as likely contributing factors.
“You have to think of these ingredients like a Venn Diagram and where they overlap, boom. That’s where you can get the potential for tornadoes,” he said, noting that the overlap appears to be growing.
Elsner and Brooks noted that the nation is seeing more days with a greater number of tornadoes, but fewer total tornado days. Brooks described the storms as becoming “clumpier” since more are happening at once.
Elsner said that this can happen because as air that’s higher in the atmosphere is warmer, it can create a “cap” that requires more energy to break.
“But when it breaks, then it’s like the popcorn popping, it just goes crazy,” he said.
He said it’s problematic because the strongest tornadoes usually happen “in an outbreak of tornadoes.”
Brooks said that more tornadoes happening at once can lead to a scarcity of disaster resources as communities look to rebuild in the aftermath.
“Recovery takes a lot of resources and so now, in a sense, places are competing for the available resources,” he said.