Concrete's Climate Problem

Making Portland cement requires heating limestone to about 1,450°C in massive kilns. This process does two damaging things at once: it burns enormous amounts of fuel to reach that temperature, and the limestone itself releases CO2 as calcium carbonate breaks down into calcium oxide.

The cement industry produces approximately 8% of global CO2 emissions — more than aviation and shipping combined. If concrete were a country, it would be the third-largest emitter after China and the United States.