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So far this year 207 tornadoes and counting have touched down in Illinois. That figure may rise as officials continue working through the remaining post-storm assessments, according to the National Weather Service. The tornado season also has yet to finish, but it has already handily topped the previous record of 142 funnel clouds set just two years ago, according to Trent Ford, the Illinois state climatologist. This is the third year in a row that Illinois has experienced a triple-digit tornado season; the state’s historical average is closer to 50.
“It’s just anything beyond what we would expect,” Ford said.
The dramatic surge in Illinois and throughout the Midwest contrasts with a decreasing trend of twisters in the Great Plains, the region traditionally billed as Tornado Alley. Experts are still working through the data, trying to understand whether it has been inching eastward, and if so whether climate change has anything to do with it.
A recent analysis by Steve Nesbitt, a meteorologist and professor of atmospheric sciences at the University of Illinois Urbana-Champaign, found that the region is getting a historic hammering. Illinois and Indiana have already recorded the highest level of tornado activity since the National Weather Service started keeping track in 1950. He added that nearby states including Iowa, Missouri, Michigan, and Ohio are in the top 10.
That said, overall it has been a slow year across the rest of the United States.
“It has been below average nationally, with the southern Plains and Southeast less active than normal,” Nesbitt said.
Even with the unusual flurry of tornadoes, Illinois remains well short of the all-time record in the U.S. That belongs to Texas, which experienced 255 in 2015. Some experts argue it’s not a fair comparison because Texas is about 4.7 times larger than Illinois. However, Nesbitt said that in terms of tornado density, or concentration of tornadoes touching down in 50-mile squares, Illinois is on top. He added that as of mid-August no region of the country has had a higher reported density of tornadoes than parts of central Illinois.
A climate change connection?
Tornadoes are the result of atmospheric contrasts and chaos. They develop when moist air near the ground lies beneath drier, hotter air aloft, creating a sandwich of sorts. In this unstable atmosphere, differences in wind speed and direction at different heights create rotation and thunderclouds.
“So just a difference between air masses,” said Shel Winkley, chief meteorologist at the research group Climate Central. “That’s also going to provide some spin in the atmosphere.”
Scientists measure this as “convective available potential energy,” or CAPE, which describes the available fuel for thunderstorm development. Look inside these towering thunderclouds and you’ll find warm air rising, but cool air falling, which creates spinning currents that can spawn a tornado. One trend scientists can parse, Winkley said, is the increase in the number of potential thunderstorm days. “That doesn’t necessarily mean a tornado will form,” Winkley added, “but we have these higher values of CAPE over the East and the Southeast during the spring than we used to have.”
The other component is that moisture. An abundantly clear climate signal is playing out in the Gulf of Mexico, which has been exceptionally warm of late. Since humans began pumping greenhouse gases into the atmosphere, the oceans have absorbed more than 90 percent of the additional heat. The hotter the Gulf gets, the more moisture it can pump into the atmosphere, and the more fuel it can provide for thunderstorms and tornadoes. (This is also how climate change is supercharging hurricanes, as those storms also love moisture.)
Even given all that, experts agree it doesn’t seem that climate change is in and of itself resulting in more tornadoes. However, on the days when we get the biggest tornado outbreaks, more twisters are touching down, including in Illinois, Winkley said. Tornado Alley also seems to be shifting east, putting new communities in danger, according to Winkley.
“At least the science that we have right now, we don’t see a connection between more tornadoes occurring because of climate change,” Winkley said. “It’s more about where they’re occurring, when they’re occurring, and then again the number that they’re happening on specific days versus others.”
Another wrinkle: It has never been easier to spot a tornado.
“Our radar data has increased in resolution multiple times over compared to even when I started at this office 20 years ago,” said Ginno Izzi, a senior meteorologist at the National Weather Service office covering Chicago and parts of Northwest Indiana. He adds that advancement in radar resolution, satellite data, and remote sensing has made it possible to count smaller tornadoes that might not have been previously detected.
Better detection has also translated to a better warning system. Izzi’s office, which monitors weather activity in 18 counties in northern and central Illinois and five counties in Northwest Indiana, has issued a record-breaking 330 severe thunderstorm and tornado warnings this year.
Izzi added that despite Illinois’ tornado-heavy year, it’s far too early for any kind of climate change attribution.
If that seems unsatisfyingly inconclusive, it’s not for lack of trying. Tornadoes are hyperlocal weather events, so they’re difficult to simulate in climate models. Massive hurricanes, on the other hand, are easier to model. So scientists are still working to figure out how much the change in tornado activity is due to natural variability — what you’d expect if humans hadn’t warmed the planet — versus what’s the consequence of runaway greenhouse gas emissions.
“That’s still one of those things that we just need faster computers and stronger computers in order to be able to do that sort of modeling with it,” Winkley said, “and we’re just not quite there yet.”