When architecture becomes carbon accounting
Researchers calculated how much carbon is locked up in city buildings—and then started thinking about how to keep it there
By Sarah DeWeerdt October 28, 2025 in Anthropocene
Buildings across 12 U.S. cities have the potential to store a whopping 134,863 million metric tons of carbon dioxide for the long term, according to a new study.
“Existing urban buildings represent a substantial, yet largely untapped, long-term carbon storage potential that must be actively preserved and managed through targeted policy interventions,” says study team member Ming Hu, professor of architecture and environmental engineering at University of Notre Dame in Indiana.
Urban buildings can store carbon in their wooden components and through concrete carbonation, a naturally occurring process by which carbon dioxide reacts with cement-based materials, gradually accumulating more carbon over its lifetime in use.
concrete carbonation, a naturally occurring process by which carbon dioxide reacts with cement-based materials, gradually accumulating more carbon over its lifetime in use
The idea that wooden building materials can act as a carbon reservoir has received a fair bit of attention over the past few years, but research has been mostly theoretical: buildings could store so much carbon if they were all made of such-and-such material.
The carbon sequestration potential of concrete carbonation, meanwhile, is relatively under-appreciated. It’s thought that a kilogram of cement can reabsorb 0.05 kilograms of carbon dioxide over the course of 64 years. At the scale of a big city, that really adds up, Hu and her coauthor, Notre Dame graduate student Siavash Ghorbany discovered.
The researchers combined building stock data, satellite imagery, and AI-analyzed Google Street View images to investigate buildings constructed before 2000 in 12 large US cities. They categorized buildings in Baltimore, Boston, New York, San Francisco, Atlanta, Las Vegas, Houston, Chicago, Denver, Cincinnati, Miami, Indianapolis into 1,715 different types depending on the mix of materials used to construct them, then calculated the amount of carbon stored in each.
Chicago and Las Vegas can claim the largest stores of carbon in wood building materials, with 156.06 and 72.88 million metric tons respectively, the researchers found. Hu calls it “unexpected” that “two cities with vastly different climates and building practices” would come out on top in this measure, “suggesting that policy and material choices may outweigh geography in shaping carbon storage.”
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Chicago is also the champ at concrete carbon storage, with 56.64 million metric tons, followed by New York with 15.36 million metric tons. Overall, concrete carbonation is a bigger player in urban carbon sequestration than wood building materials, the researchers found – highlighting the surprising potential of a material that is usually thought of as a climate villain.
But keeping all that carbon sequestered in buildings for the long term is no given, considering how people like to rip out and remodel the guts of buildings or tear them down altogether to build new ones.
So cities need policies to make sure that carbon stays locked up in the built environment and out of the atmosphere – and those policies will vary from city to city, depending on the specifics of the built environment and the history of urban development.
Carbon stores in wood building materials could be maintained with the help of recycling, preservation, and adaptive reuse policies. To boost concrete carbon stores, construction methods to maximize carbonation potential, preservation of existing concrete structures until they have absorbed as much carbon as they can, and exposing salvaged concrete to carbon dioxide before disposal will all help, the researchers suggest.
Source: Hu M. and S. Ghorbany. “Carbon storing in United States cities through biogenic storage and concrete carbonation in the built environment.” Communications Earth & Environment 2025