According to a groundbreaking study conducted by Northwestern University, underground climate change, driven by global warming, has been steadily deforming the ground beneath urban areas. The researchers find this as a potential threat to civil infrastructure while presenting an untapped energy opportunity.
Assistant Professor Alessandro Rotta Loria of civil and environmental engineering at Northwestern University spearheaded the research to determine the extent of underground heat within Chicago’s Loop. Rotta Loria and his team installed over 150 temperature sensors in various underground locations across downtown Chicago.
Rotta Loria found startling discrepancies in ground temperatures. “The undisturbed ground temperature in the Chicago area is about 52 degrees Fahrenheit,” Rotta Loria said. “In the heart of the Loop, we measured a ground temperature exceeding 70 degrees. In some underground structures, we measured more than 97 degrees.” These findings led to the conclusion that underground climate change is a silent, significant driver affecting the operational performance of civil infrastructure.
The heat that permeates from the Loop’s building basements, subway systems, parking garages, and other underground spaces, combined with the warm air on the surface, results in a much hotter underground climate. This phenomenon is common in older cities globally.
Impact on Infrastructure
Excessive heat instigates soil layers to expand or contract, resulting in the swelling of the ground. Consequently, this causes building foundations to sink slowly over time. Rotta Loria underscored that no existing civil structure or infrastructure is designed to withstand these variations.
Moreover, he conducted computer simulations to predict the effects on buildings and other structures over the next 30 years. He stated, “The ground is deforming… It will affect the normal day-to-day operations of foundation systems and civil infrastructure at large.”
Turning a Challenge into an Opportunity
While this new research raises potential concerns, it also presents promising opportunities. Heat escaping from big building boiler systems and inefficient designs of the city’s earliest skyscrapers can be captured and reused as thermal energy. This energy can be utilized to warm spaces and water in downtown buildings.
Furthermore, Rotta Loria indicated that such an approach could potentially provide thermal energy to entire neighborhoods, adding that “we are in a position to transform this unwanted phenomenon into a significant opportunity for all cities worldwide.”
A Plan of Action
Firstly, officials need to identify which buildings or groups of buildings contribute the most to the underground heat. Secondly, energy efficiency measures should be implemented to prevent heat escape. Lastly, an assessment of building foundations and other structural issues surrounding the impact of the heat needs to be carried out.
Amy Masters, director of government and external affairs for the Building Owners and Managers Association Chicago, expressed that the research “presents promising opportunities” for downtown.
One striking example of an old building contributing to the heat problem is the nearly 100-year-old Union League Club building at 65 West Jackson Blvd. It has a massive boiler system that extends deep underneath the street and releases copious amounts of heat into the surrounding area.
The study also emphasizes the need for more research to be conducted, suggesting that these findings can be applied to other cities worldwide.
The research also hints at the prevalence of underground climate change globally. Researchers have found that in many urban areas, the shallow subsurface beneath cities warms by 0.1 to 2.5 degrees Celsius per decade. This phenomenon, known as “subsurface heat islands,” has been known to cause ecological issues and health issues.
“In general, cities are warmer than rural areas because construction materials periodically trap heat derived from human activity and solar radiation and then release it into the atmosphere. Now, we are looking at its subsurface counterpart, which is mostly driven by anthropogenic activity,” added Rotta Loria.
The findings of the research have been published in the journal Communications Engineering, affiliated with the London-based scientific journal Nature.