Circular Economy

Concrete Is Causing the Downfall of Cities. Literally.

In addition to generating 8% of global carbon emissions, recent studies have highlighted another negative impact of the world’s most popular building material — its weight, which is causing a host of coastal cities to sink faster than sea levels are rising.

By Christian Yonkers | Published 7 months ago | About a 5 minute read

Image: Michael Pewny

Concrete is the second most widely used substance on earth, next to water. It’s well understood that concrete has an emissions problem — the concrete industry is responsible for 8 percent of all global carbon emissions — however, the impact of its weight in sustainable development is less discussed. Concrete demand is expected to increase 48 percent by 2050, but humanity’s favorite building material is literally causing the downfall of cities around the world.

Subsidence — the sinking or lowering of the earth’s surface — could significantly impact nearly 20 percent of the global population, especially as sea levels continue to rise. Subsidence is caused by multiple factors, both natural- and human-caused. 2022 research by the University of Rhode Island used five years of satellite data to measure the subsidence rate of 99 coastal cities across the globe. The results: Coastal cities are sinking under their weight faster than sea levels are rising.

“If subsidence continues at present rates, these cities will be challenged by flooding much sooner than projected by sea-level-rise models,” the report reads. “Expanded monitoring and policy interventions are required to reduce subsidence rates and minimize their consequences.”

In most of the coastal cities evaluated, areas are subsiding at roughly 2mm per year — faster than the normal subsidence of more stable regions. But in 33 cities, parts are sinking 10mm or more each year — five times faster than global sea-level rise. The worst sinking is occurring in cities located in South, Southeast and East Asia: In several Asian cities, subsidence rates exceed 30mm per year — overshooting sea-level rise nearly fifteen-fold.

Many geological phenomena outside of human control play a pivotal role in subsidence rates. But groundwater extraction, oil and gas production, and the weight of the built environment are dominant factors causing many of the worst subsidence rates in the world. While groundwater withdrawal for manufacturing and urban centers is usually the biggest anthropogenic contributor to subsidence, the weight of the built environment is undeniably making it worse in some of the world’s biggest cities.

China’s record-breaking urban expansion over the past several decades created an unprecedented demand for concrete, where the unimaginable weight of the country’s rapidly growing cities is causing major population centers to sink rapidly: Some portions of Beijing are sinking over 40mm each year.

But Beijing is not alone: A Chinese study published last month in the journal, Science, found that 40 percent of the landmass in 82 large Chinese cities exhibits moderate to severe sinking — exacerbating the effects of sea-level rise and flooding events for millions of people.

“By 2120, 22 to 26 percent of China’s coastal lands will have a relative elevation lower than sea level, hosting 9 to 11 percent of the coastal population, because of the combined effect of city subsidence and sea-level rise,” the report reads. “Our results underscore the necessity of enhancing protective measures to mitigate potential damages from subsidence.”

A 2023 study published in the journal, Earth’s Future, found a similar thing happening in New York City. Like many cities across the world, New York’s broader subsidence rate is thought to be hastened by factors including glacial retreat and groundwater extraction. While building load alone isn’t the only factor causing the world’s cities to sink, heavy buildings and infrastructure can greatly exacerbate the natural subsidence rate of an area — especially when constructed on soft or previously excavated ground like that beneath parts of Manhattan.

“[E]very additional high-rise building constructed at coastal, river or lakefront settings could contribute to future flood risk, and mitigation strategies may need to be included,” wrote the authors of the New York study. “Major cities on every continent except Antarctica are observed to be subsiding … and the issue may be worsened as populations grow. Increasing urbanization will likely exacerbate subsidence by groundwater extraction and/or construction density — which, combined with accelerating sea-level rise, implies a growing flood hazard in coastal cities. As these trends continue, it will be important to be mindful of accompanying mitigation strategies against inundation in growing coastal cities.”

As the Rhode Island authors warn: “Even in developed countries of North America, Europe and Australia, parts of many cities appear to be sinking faster than sea level is rising. [C]ities and nations that fail to address the cause(s) of their subsidence will be challenged by flooding much sooner than projected by sea-level rise models. … Continuous monitoring and policy intervention are required to reduce subsidence rates and minimize their consequences.”

Many low-carbon material-science startups are creating ways to reduce concrete’s climate impacts — finding solutions in biomimicry and alternative materials such as captured carbon. One company, Eco Material Technologies, utilizes waste fly ash to produce low-carbon alternatives for the Portland cement found in concrete. But low-carbon concrete doesn’t necessarily mean less weight.

"Eco Material’s products greatly improve the durability and sustainability of concrete, but they do nothing for reducing its weight,” the company told Sustainable Brands® in an email.

Potentially, a combination of low-carbon concrete that’s more durable than legacy concrete — coupled with smarter design to utilize less of the material — could mitigate some of the adverse global effects of concrete production and use. But weight is still a looming issue that will need to be addressed for coastal cities to adapt to the effects of climate change.

Christian Yonkers

Christian is a writer, photographer, filmmaker, and outdoor junkie obsessed with the intersectionality between people and planet. He partners with brands and organizations with social and environmental impact at their core, assisting them in telling stories that change the world.

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