Climate change means temperatures are slowly rising in the air—and also underground. Different materials in the earth expand or contract in response to underground climate change, affecting the buildings constructed above them.
By Paige Castle
When hearing about global warming and climate change, what usually comes to mind is increasing temperatures in the atmosphere, or maybe even melting ice caps or rising ocean levels. What isn’t usually thought about is the increase in temperatures underground, and little is known about the impact this could have.
But new research in civil and environmental engineering by Dr. Alessandro Rotta Loria from Northwestern University in Illinois has found that temperature rises underground in Chicago is causing the ground to deform and warp significantly, and this underground climate change is likely to impact already existing buildings.
What is causing warming underground?
Most of the underground climate change is caused by human activity. Buildings inject heat into the ground when heat escapes from basements and parking garages. Underground transportation within cities is another major cause of underground heating—trains, cars, and people travelling underground generate extra heat. The many cables, pipelines, sewers, and heating systems underground also produce heat. Underground temperature sensors used in the recent Chicago study recorded more significant variations in ground temperature in more densely built underground environments than in less dense areas.
Air temperature also has an effect. The ground temperature 4 to 6 meters (13 to 20 feet) below the surface is usually the same temperature as the air above. Rising air temperatures cause this shallow ground temperature to rise, which then warms the ground below it too.
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For the recent study carried out in Chicago, Dr. Rotta Loria placed 150 sensors above and below ground around Chicago, and measured the temperature changes. He found that underground global warming varied by soil type but was currently warming at an average of 0.14°C per year within the Chicago Loop, which is the city’s downtown area.
How is the ground deforming?
The soil and clay types underneath cities are usually not consistent. The different types of soils and clays underground react differently under different conditions. The study in Chicago found that soft and stiff clay layers contract with increased heat, but harder clays, as well as shallower sand and limestone layers, expand with increased heat. These soil and clay layers expanding and contracting differently from each other can cause the ground to deform and change shape.
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The effect on our buildings
When putting the findings into a 3D computer simulation model, Dr. Rotta Loria found that the ground can expand up to 12 mm (about 0.5 inch) and contract (particularly under buildings) by as much as 8 mm (about 0.3 inch).
While this doesn’t sound like a lot, it does mean that the buildings within the city are sinking very slowly. The vertical changes within the ground are also causing structures such as walls and slabs to rotate and tilt. The study found that at the current rate, it is unlikely that underground climate change would cause buildings to collapse, but it could impact their durability, aesthetic, and ability to operate effectively, and it is likely to have already caused some foundations of buildings to crack and move.
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Future impacts from underground climate change
So, while the underground climate change does not currently pose a risk to the safety of people living within cities, the findings from this research suggests that the movement and deformation of the ground below should be considered within the design of new buildings to help prevent or reduce the impact on the building’s durability.
With the increased knowledge of underground heating, further planning could be done in order to reduce the release of heat from man-made structures into the ground. Alternatively, geothermal technologies could be incorporated within cities to collect waste heat in the ground and reuse it as heating within buildings.
This study was published in the peer-reviewed journal Communications Engineering.
Rotta Loria, A. F. (2023). The silent impact of underground climate change on civil infrastructure. Communications Engineering 2, 44. https://doi.org/10.1038/s44172-023-00092-1
About the Author
Paige Castle has a passion for conservation and the environment but likes to dabble in all aspects of science. Paige is a keen traveller, and loves discovering new places, cultures, wildlife, and natural landscapes.