A study conducted in Chicago discovered that a phenomena known as "underground climate change" is deforming the earth beneath cities.

According to Alessandro Rotta Loria, an engineer at Northwestern University and the study's principal investigator, "Underground climate change is a silent hazard. The ground is deforming as a result of temperature variations, and no existing civil infrastructure or structure is designed to withstand these variations."

Underground climate change, also known as "subsurface heat islands," is generated by heat radiating into the earth from man-made structures such as buildings and subways. It is not the same as climate change in the atmosphere, which is caused by greenhouse gases emitted by the combustion of fossil fuels.

Rotta Loria and his colleagues erected a network of 150 temperature sensors above and below ground in the Chicago Loop – the metropolitan area's heart – to discover exactly how warming impacts the land beneath Chicago. They also installed sensors in Grant Park, a downtown green space, for comparison. The scientists collected temperature data for three years before developing a model to mimic how temperatures have changed since 1951, when the Loop subway tunnels were completed. Rotta Loria and his colleagues also used the model to forecast future temperatures and how the ground moves in reaction to heat until 2051.

Chicago's clay soil shrinks when the temperature rises, which may cause cracks in building foundations and even deformation or tilting of the structures. Studies have shown that the ground beneath cities warms by 0.18 to 4.5 degrees Fahrenheit every 10 years.

"It's critical to emphasize that underground climate change does not endanger people's safety or threaten the collapse of structures and buildings," Rotta Loria stated. "It does pose a potential challenge to the functionality and durability of structures, because excessive ground deformations can lead to distortion, tilting, and potentially cracking."

As a result, water could enter fractured structures more easily, potentially causing corrosion in materials such as reinforced concrete.

To reduce the amount of waste heat that escapes into the ground, Rotta Loria suggested adding thermal insulation to underground building enclosures, the city could mitigate the issue of waste heat escaping into the earth. But if for some reason we are unable to thermally insulate the buildings to improve their energy efficiency, we could at least use geothermal technology to absorb waste heat produced and use it for heating and cooling underneath or adjacent to them. The scientists also propose that this extra heat from the Earth's crust might be trapped and used as geothermal energy to heat and cool buildings.

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