Christian Science Monitor: We drive our cars on it, we build skyscrapers with it. But concrete, one of the most common building materials in the world, has an ugly secret: It’s a major source of carbon dioxide (CO2) emissions, which contribute to global warming. Roughly 5 to 10 percent of global CO2 emissions are related to the manufacture and transportation of cement, a major ingredient of concrete. With cement production expected to grow exponentially in coming decades, the industry is trying …