Have you heard the phrase “it’s warmer by the lake”? If you live in Chicago, you probably have. And although it’s nice in winter, the warmth has a problematic underlying cause, called meteorological heat islands (or surface heat islands) thanks to city density — and it’s only getting more complicated thanks to climate change.
Surface heat islands occur when buildings release heat from solar radiation, car traffic, and other structural facilities. The heat is released mostly at night, and heats up the surface level of the city. It occurs in every major city and is exacerbated by climate-change-induced heat waves. And because Chicago has an older infrastructure, some of the heat is leaching into the ground as well, contributing to something called a subsurface urban heat island, or underground climate change.
Alessandro F. Rotta Loria, Ph.D., a professor at Northwestern University who conducted a large-scale investigation of Chicago’s subsurface heat islands, notes that global warming is responsible for about 20 percent of underground climate change. The rest, he says, is from “the heat coming from building basements, underground parking garages, tunnels, and underground facilities,” where the older constructions are less thermally insulated than newer structures, allowing heat from inside to escape into the ground around it.
But no matter how the temperature is rising underground, it can cause significant issues with Chicago’s infrastructure. The temperature variation can lead to ground deformities which can affect city structures.
“[It] can lead to phenomena such as excessive settlement or excessive distortion of structure or even cracking,” Rotta Loria said. “If you have excessive cracking that happens in a reinforced concrete structure, very likely water will penetrate more easily toward the reinforcement and that will lead to corrosion and can affect in the long term the durability.”
That doesn’t necessarily mean a building will collapse, but it could cause some costly structural and aesthetic issues, he said.
Rotta Loria notes that it is possible to mitigate the issues surrounding underground climate change. We can either attack the problem at the source by adding thermal insulation to all underground structures that need it, or we can use geothermal technologies to absorb and repurpose some of the heat, like using it for hot water production. But no matter what, we won’t be able to resolve the effects caused by global warming on underground climate change until we can slow down the heating process worldwide.