This 'Silent Hazard' Is Putting Big Cities at Risk

The climate issue that's probably not on your radar? Rising underground temperatures. NBC News has the scoop on a recent paper published in Nature that examines how this trapped heat can affect cities if not mitigated properly. This phenomenon, dubbed "underground climate change," is unrelated to atmospheric climate change that's caused by an imbalance of greenhouse gases in the atmosphere. Instead, increased temperatures come from heat generated from subways and buildings that's directly released into the ground, causing deformation and potential damage to city structures. The paper's author, Alessandro Rotta Loria of Northwestern University, calls it a "silent hazard." "There's already a significant amount of heat beneath our feet," he tells NBC. "And this heat has caused the ground to deform already."

Major cities like Chicago, New York, and London are at risk of sinking due to this underground climate change. Rotta Loria's data, which examines Chicago specifically, shows that underground heat associated with buildings and parking garages has been spreading and increasing faster than surface temperatures, with one exception being Millennium Park in Chicago. "If we compare it with global warming and how surface temperatures have risen, it's actually faster," he said. "The temperatures underground are rising faster in cities than at the surface." To track temperatures, Rotta Loria and his team installed more than 150 credit-card-size sensors across Chicago over a three-year period, per Scientific American.

He says that temperatures under human-made structures can be as much as 77 degrees Fahrenheit warmer than undisturbed underground locations. Mitigation solutions include installing thermal insulation, as well as capturing excess heat for geothermal energy. Transportation Secretary Pete Buttigieg acknowledged the importance of addressing this issue as part of the administration's climate agenda. "We're partnering with states on this, because it may be that something down to the kind of cement or steel or asphalt that you're using for the 21st century needs to look a little different than what we learned to build with 100 years ago," he told NBC. (There are some hopeful tones in this new climate report).