On that return trip, “I measured the temperature of seeps all over, wherever I could,” he says. The closer to the surface he measured, the warmer the water was. In 2008, a separate team from the University of Minnesota had [predicted](https://conservancy.umn.edu/items/a9ae3228-1d09-4dd9-8bd2-8f63e23e000c) that heat from Minneapolis’s urban surface was conducting itself deep underground, heating the groundwater there like a metropolitan microwave. Brick’s subsequent research proved them right—but also showed that they had significantly underestimated the extent of the warming.
Brick published his results in 2022, as a chapter in [_Threats to Springs in a Changing World_](https://agupubs.onlinelibrary.wiley.com/doi/book/10.1002/9781119818625), published by the American Geophysical Union. His findings aren’t unique to Minneapolis. From Japan to Italy, Canada to Switzerland, scientists have found other “subsurface urban heat islands” where pavement and basements warm up what’s below them.
The Strange Heat Island Lurking Beneath Minneapolis by Sarah Scoles