Our built environment—from houses to offices, schools and shops—is not environmentally benign. Buildings and the construction industry are, in fact, the world’s biggest consumer of raw materials and contribute 25–40% of global carbon dioxide emissions (F. Pomponi & A. J. Moncaster Clean. Prod. 143, 710–718; 2017). Making buildings part of a circular economy that minimizes the waste of materials could therefore yield huge environmental rewards. Conversely, failure on this front could have dire consequences.

“Buildings can, and must , work in a circular way,” says Francesco Pomponi, who studies the built environment at Edinburgh Napier University, UK. “Otherwise, there’s no way out of the climate crisis.”

Take concrete, made by mixing gravel, cement and water. It is the world’s most widely used building material, yet it is also a huge carbon source, accounting for up to 8% of global human-made carbon emissions. Cement, more than four billion tonnes of which are made each year, is the biggest contributor. Its production requires limestone (primarily composed of calcium carbonate) to be heated to yield lime (calcium oxide). The reaction releases CO2, and yet more CO2 is produced by fuel combustion to generate the heat.

Across the globe, engineers, construction companies and architects are beginning to embrace and apply the circular model. There are ample opportunities to improve the materials that are used in construction, to introduce circular design principles so that those materials can be properly repurposed, and—even more ambitiously—to create buildings that make a positive contribution to climate and biodiversity. But much work needs to be done if those huge contributions to emissions are going to come down. And come down they must—fast.

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