Underground climate change: Silent hazard is destroying our buildings from beneath

Our cities are facing a hidden peril – a danger that has gone unnoticed and unstudied until now. It’s called underground climate change. This phenomenon is literally causing the ground beneath our urban areas to shift and deform, leading to significant damage in our infrastructure.

An unsettling study from Northwestern University reveals the existence of this lurking, silent hazard. As the earth beneath our cities heats up, it morphs and transforms.

This leads to unexpected and excessive movements in building foundations and the surrounding ground. It can even result in cracking.

The implications of this are profound, affecting the long-term operational performance and durability of our structures. It’s becoming increasingly clear that previous building damages may have been caused by such rising temperatures.

Worryingly, this is not a problem that’s going away. These issues are expected to persist and possibly even worsen in the coming years.

But, the study suggests, there could be a silver lining. While these underground temperature changes pose a threat to our urban infrastructure, they also present a potential opportunity.

Waste heat from below ground level, given off by transportation systems, parking garages, and basement facilities, could be harnessed. This could help mitigate the impacts of underground climate change and simultaneously provide an untapped resource of thermal energy.

This groundbreaking study will be published on July 11, in the Nature Portfolio journal Communications Engineering. This is the first-ever research to quantify the ground deformations caused by subsurface heat islands and their effect on civil infrastructure.

Leading the study is Alessandro Rotta Loria. He is an assistant professor of civil and environmental engineering at Northwestern’s McCormick School of Engineering.

What is underground climate change?

Loria explains the significance of this discovery, saying, “Underground climate change is a silent hazard. The ground is deforming as a result of temperature variations, and no existing civil structure or infrastructure is designed to withstand these variations.”

He further notes that many cities, including Chicago, are facing an unseen threat due to this phenomenon.

“As a result of temperature increases underground, many foundations downtown are undergoing unwanted settlement, slowly but continuously,” says Loria. “In other words, you don’t need to live in Venice to live in a city that is sinking — even if the causes for such phenomena are completely different.”

Urban areas worldwide are facing a heating issue. Heat diffuses from buildings and underground transportation, warming the ground at an increasingly fast rate. Previous researchers have found that the shallow subsurface beneath cities warms by 0.1 to 2.5 degrees Celsius per decade.

This phenomenon, known as “underground climate change” or “subsurface heat islands,” is not only an ecological issue but also a health concern. However, the impact of this underground heating on our civil infrastructure has, until now, been largely overlooked.

Using Chicago to study underground climate change

Over the past few years, Rotta Loria and his team have been collecting temperature data using a wireless network of more than 150 temperature sensors across Chicago’s Loop. They compared these findings to the temperatures beneath Grant Park, a green space located away from buildings and transportation systems.

The results were startling, with temperatures beneath the Loop often being 10 degrees warmer. This heat diffusion places enormous stress on materials, causing them to expand and contract with the changing temperatures.

Based on their data, the researchers built a 3D computer model to simulate how ground temperatures have evolved since 1951. The findings were consistent with the field measurements.

The simulation was also used to predict how temperatures might change by the year 2051. Ground deformations in response to increasing temperatures were also modelled. The results showed that while some materials contract when heated, others expand.

Our buildings are slowly sinking

The simulation revealed that warmer temperatures could cause the ground to swell upward by as much as 12 millimeters or sink downward by as much as 8 millimeters.

Rotta Loria warned of the implications of these changes: “It’s very likely that underground climate change has already caused cracks and excessive foundation settlements that we didn’t associate with this phenomenon because we weren’t aware of it.”

He also suggested potential strategies to combat this issue. “The most effective and rational approach is to isolate underground structures in a way that the amount of wasted heat is minimal,” Rotta Loria said.

“If this cannot be done, then geothermal technologies offer the opportunity to efficiently absorb and reuse heat in buildings.”

The researchers’ work shines a light on an issue that’s been literally underground, but the impact on our infrastructure could be profound. This “silent hazard” is one we need to acknowledge and address as we continue to build and evolve our cities.

With careful planning and innovative strategies, the threats posed by underground climate change can be mitigated, potentially offering new opportunities for energy efficiency.

More about underground climate change

Underground climate change is also known as “subsurface heat islands.” It is a relatively new field of study that focuses on the impact of human activities on the temperature of the ground beneath urban areas.

This term is an extension of the more commonly known phenomenon of urban heat islands, where urban regions are significantly warmer than their rural surroundings due to human activities.

The ground underneath cities absorbs and retains heat from various sources, including buildings, transport systems, industrial processes.

It also includes waste heat from basements and other subterranean facilities. Over time, the accumulation of this heat can lead to an increase in subsurface temperatures.

Here’s what we know so far about underground climate change:

Causes

Urbanization and industrialization have increased the amount of heat that is introduced into the subsurface environment.

Heat is generated by human activities such as transportation, manufacturing, heating, and cooling systems, and even simple daily tasks like cooking. It’s also a result of the thermal properties of common construction materials which can absorb, store, and gradually release heat into the ground.

Effects on the environment and infrastructure

As the ground heats up, it expands, causing ground deformations. This can lead to instability in building foundations, causing them to crack or move. Over time, these changes can significantly affect the durability and operational performance of buildings and infrastructure.

In addition, the heating can change the characteristics of the soil and rock. These can affect underground water resources and lead to other environmental issues.

Health and ecological impacts

Subsurface heat islands can contribute to the overall urban heat island effect, exacerbating heatwaves in cities which can have serious health implications, such as heat stroke and respiratory problems.

The increase in temperature can also lead to ecological issues. These include changing the conditions for subterranean ecosystems and possibly contaminating groundwater sources.

Potential for energy harnessing

Despite its threats, underground climate change also presents an opportunity. The heat generated can be captured and used as a source of geothermal energy. By harnessing this waste heat, it’s possible to reduce the impact of underground climate change while providing a sustainable source of energy.

Solutions

Strategies to mitigate the impact of underground climate change can include urban planning measures to minimize heat generation, using materials with lower thermal conductivity in urban construction, improving the insulation of buildings, and capturing and using the waste heat.

Research into underground climate change is still relatively new, and much is still being discovered about its full impacts and potential mitigation strategies.