CHICAGO — Underneath downtown Chicago’s soaring art deco towers, its multilevel roadways and its busy subway and rail lines, the land is sinking, and not only for the reasons you might expect.
Rising underground temperatures lead to warmer subway tunnels, which can cause overheated tracks and steam-bath conditions for commuters. And, over time, they cause tiny shifts in the ground beneath buildings, which can induce structural strain, whose effects aren’t noticeable for a long time until suddenly they are.
Near some heat sources, the ground beneath Chicagoans’ feet has warmed by 27 degrees Fahrenheit over the past seven decades, he found. This has caused the earthen layers to expand or contract by as much as half an inch under some buildings. Hot weather warms the upper layers of soil. But Rotta Loria’s calculations assume that air temperatures in Chicago remain at their average recent levels all the way through 2051 — that is, his estimates don’t incorporate climate scientists’ projections for future global warming. Nor do they account for the fact that, as we continue warming the planet, large buildings will most likely use more air conditioning and pump even more waste heat into the ground.
The sensors themselves are nondescript: a white plastic box with a button and two indicator lights. They cost Rotta Loria $55 each. The temperature information they collect — one reading every minute or one every 10 minutes, depending on the location — is downloaded onto a phone via Bluetooth, which means Rotta Loria and his students must periodically visit them in person to harvest their data, around 20,000 records per day in all.