Underground warming is a 'silent hazard' for densely built cities

Climate change isn't just limited to above the planet's surface. The temperature is rising underground as well, putting densely built cities at risk, according to a study published in the journal Communications Engineering. The study found that urban areas struggle with subsurface heat islands, which are "an underground climate change responsible for environmental, public health, and transportation issues." The phenomenon leads to "ground deformations and displacements" that can impact the "operational performance of structures and infrastructures with time."

"All around you, you have heat sources," the study's author, Alessandro F. Rotta Loria, told The New York Times. "These are things that people don't see, so it's like they don't exist." The study analyzed Chicago, specifically finding that much of the heat came from underground infrastructure like basements, as well as pipes, train tunnels, parking garages, and electrical wires. The phenomenon was deemed "underground climate change."

The underground changes can be attributed to natural and human changes to the environment, but it's tough to say what's coming from the "climate itself changing and what is coming from the actual activities of the city," climate scientist Hugo Beltrami told The Washington Post. Over time, the heat can cause strain and structural shifts that can gradually worsen. "Today, you're not seeing that problem," said Asal Bidarmaghz, a senior lecturer in geotechnical engineering at the University of New South Wales, to the Times. "But in the next 100 years, there is a problem."

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The other concern is the warming's impact on the underground ecosystem. Below the surface is "home to animals that ... such as worms, snails, insects, crustaceans and salamanders," that are used to "very static conditions," Grant Ferguson, an engineering geologist at the University of Saskatchewan, told Scientific American.

Per the study, underground climate change poses a "silent hazard" to cities, "but also an opportunity to reutilize or minimize waste heat in the ground."