How to Avoid a Climate Disaster: The Solutions We Have and the Breakthroughs We Need

by Bill Gates

As challenging as that may sound, concrete is even harder. (Sorry—no pun intended.) To make it, you mix together gravel, sand, water, and cement. The first three of these are relatively easy; it’s the cement that is a problem for the climate. To make cement, you need calcium. To get calcium, you start with limestone—which contains calcium plus carbon and oxygen—and burn it in a furnace along with some other materials. Given the presence of carbon and oxygen, you can probably see where this is going. After burning the limestone, you end up with the thing you want—calcium for your cement—plus something you don’t want: carbon dioxide. Nobody knows of a way to make cement without going through this process. It’s a chemical reaction—limestone plus heat equals calcium oxide plus carbon dioxide—and there’s no way around it. It’s a one-to-one relationship. Make a ton of cement, and you’ll get a ton of carbon dioxide.