Concrete, the most widely used human-made material, shapes much of our built world. The manufacture of one of its key components, cement, creates a substantial yet underappreciated amount of human-produced carbon dioxide: up to 8 percent of the global total, according to London-based think tank Chatham House. It has been said that if cement production were a country, it would be the third-largest emitter after China and the U.S. Currently four billion tons of cement are produced every year, but because of increasing urbanization, that figure is expected to rise to five billion tons in the next 30 years, Chatham House reports. The emissions from cement production result from the fossil fuels used to generate heat for cement formation, as well as from the chemical process in a kiln that transforms limestone into clinker, which is then ground and combined with other materials to make cement.
Although the construction industry