As the planet heats up due to global warming over much of the past century, so have spaces underneath the Loop. That’s a cause for concern around the impact on buildings, new research from Northwestern University finds — though it also presents an opportunity to reuse that heat. Building basements, the subway system, parking garages and other below-ground areas generate a lot of heat. That combined with warmer air on the surface has made for a significantly hotter underground, something old cities across the world experience. So Alessandro Rotta Loria, an assistant professor of civil and environmental engineering, decided to...