Beneath Chicago’s towering Art Deco towers, its myriad streets and busy subways and railroads, the ground is sinking, and not for the reasons you might expect.
Since the mid-1900s, the ground between the city and the reef has warmed by 5.6 degrees Fahrenheit on average, according to a new study from Northwestern University. All that heat, which comes mainly from basements and other underground materials, has caused the sand, clay and stone under some buildings to shrink or swell by several millimeters over decades, which can cause cracks and defects in walls and foundations. .
“All around you, you have heat,” said the study’s author, Alessandro F. Rotta Loria, as he walked with a backpack through Millennium Station, a commuter train under the city’s Loop district. “These are things that people don’t see, so it’s like they don’t exist.”
It’s not just Chicago. In major cities around the world, people burn fossil fuels it raises the mercury to the surface. But heat is also escaping from basements, parking garages, train tunnels, pipes, sewers and power lines and the surrounding earth, a phenomenon scientists call “underground climate change.”
“Today, you don’t see that problem,” said Asal Bidarmaghz, senior lecturer in geotechnical engineering at the University of New South Wales in Australia. But in the next 100 years, there is a problem. And if we just sit for the next 100 years and wait 100 years to solve it, then it would be a big problem. “
Dr. Bidarmaghz studied underground heating in London but did not participate in the study in Chicago.
To see climate change underground in Chicago, Dr. Rotta Loria, an assistant professor of civil engineering and environmental engineering at Northwestern, has installed more than 150 sensors above and below the Loop. They combined three years of readings from these sensors with detailed computer models of the region’s basements, tunnels and other structures to estimate how the deep earth has warmed between 1951 and now, and how it will warm between now and 2051.
Near the hot spot, the ground beneath Chicagoans’ feet has warmed 27 degrees Fahrenheit over the past seventy years, they found. This has caused soil layers to rise or fall as much as half an inch under some buildings.
The warming and evolution of the land is happening more slowly than in the 20th century, they found, because the earth is about as warm as the basements and tunnels buried inside it. Increasingly, the buildings are heated instead of losing heat to the ground around them.
What Dr. Rotta Loria’s findings were published Tuesday in the journal Communications Engineering.
He said that the best way for the owners and workers of the canal to deal with the problem, would be to improve the temperature of the air in the world. They can also cause fever. Dr. Rotta Loria is the chief technology officer of Enerdrape, a Swiss start-up company that makes panels that absorb ambient heat in tunnels and parking garages and use it to drive. electric heat pumps, to reduce aid costs. The company has installed 200 of its panels in a supermarket parking garage near Lausanne as a pilot project.
Dr. Rotta Loria deliberately left out one factor in his estimate of Chicago’s global warming: climate change at the city’s surface.
Hot weather warms the topsoil. But the calculations of Dr. Rotta Loria predicts that Chicago’s air temperatures will remain at their current levels until 2051 — that is, his estimate does not include what scientists have found about future climate change. Nor does it account for the fact that, as we continue to warm the planet, large buildings will likely use air conditioners and pump more waste heat into the ground.
The reason for this omission, Dr. Rotta Loria said, is that they are trying to find a way to reduce the temperature of the ground, not the worst case scenario. “It is already showing that there is a problem,” he said.
The office of Chicago mayor Brandon Johnson did not respond to a request for comment.
On a recent morning, Dr. Rotta Loria and Anjali Thota, a Northwestern doctorate in civil engineering, took a reporter and photographer on a tour of their thermal imaging equipment, which looks at the invisible city beneath the city.
Dr. Rotta Loria said the Chicago Transit Authority did not allow him to install sensors in subway stations because of concerns that people would mistake them for bombers. But he and his team have managed to find sensors in many other well-known and unknown places: on railway platforms and on security gates behind high mountains, in the leafy Millennium Park and under Wacker Drive, the concrete factory famous for car chases in the “Blues” movies Brothers” and “Dark Knight”.
The sensors themselves are nondescript: a white plastic box with a button and two indicator lights. He destroys Dr. Rotta Loria $55 each. The temperature information they collect — one reading every minute or every 10 minutes, depending on location — is downloaded to a phone via Bluetooth, which means Dr. Rotta Loria and his students must visit them periodically to harvest their data of 20,000 records each day.
Most of the sensors were replaced or lost over the years, leaving 100 in operation. At the Millennium Garages, an underground parking lot, one of them is built with a pipe behind the monument.
“That’s all, isn’t it?” Said Admir Sefo, the head of the garage, looking at the widget. “And no one found them?”
“It is difficult for even us to find them,” said Mrs. Thota. He has their location saved on Google Maps, but underground, there are often no cell phones, forcing him to search around.
Another sensor, at the Blackstone Hotel, is in a basement filled with chairs and bags of ice-melting paper. There is one in the furnace room of the Union League Club in Chicago that has been heated to 96 Fahrenheit. The sensor in the Grant Park South garage recorded 97 degrees in September 2021.
Beyond the walls in each of these places, unseen and unthought of, this heat is quietly doing what heat does: spreading.