RESOLVING THE LEDGER
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Unprecedented. Record-breaking. Baffling. Experts are running out of ways to describe this year’s tornado season in the Midwest, which has unleashed more twisters on Illinois than any other place on Earth.
So far, 207 cyclones and counting have touched down on the Prairie State, some of which have flipped homes , toppled powerlines , and even torn through solar arrays . That figure may rise as officials continue working through the remaining post-storm assessments, according to the National Weather Service. The season has yet to wrap, but 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,” said Ford.
The dramatic surge in Illinois and throughout the Corn Belt 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.
Regardless of the answer to that question, Illinois is today the epicenter of tornadoes in the U.S. 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 like Iowa, Missouri, Michigan, and Ohio are in the top 10. A pair of tornadoes even touched down in New York City and Long Island .
That said, overall it has been a slow year. “It has been below average nationally, with the Southern Plains and Southeast less active than normal,” Nesbit said.
Even with the unusual flurry of tornadoes, the Land of Lincoln remains well short of the all-time record. 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, Nesbit said that in terms of tornado density, or concentration of tornadoes touching down in 80 kilometer (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.
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, 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, Winkley said. Tornado Alley also seems to be shifting east, putting new communities in danger. “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. 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.
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 qu...
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