The blue planet is becoming grayer by the day, as Earth is paved over with concrete. The world churns out about 4 billion tons of cement, the glue that holds concrete together, every year, and the appetite for concrete is expected to balloon as humanity continues to move from rural areas into cities. By one estimate, the world will add 2 trillion square feet of buildings by 2060 — the equivalent of building another New York City every month for the next 40 years.

All of that building comes at a steep cost for the environment. Producing concrete requires heating limestone with other aggregates in a kiln at 1,450 degrees Celsius, fired by burning coal or other fossil fuels that produce carbon dioxide. (The amount of energy used to bake one ton of cement could power the average U.S. home for more than a month.) What’s more, the heated limestone vents CO2 into the atmosphere. If the concrete industry were a country, it would be the third-largest CO2 emitter, according to one estimate, responsible for 8 percent of annual global emissions, behind only China and the United States. On the current trajectory, global cement production is set to increase to over 5 billion tonnes a year over the next 30 years, according to the International Energy Agency, spewing more CO2 into the air with it.

The current Intergovernmental Panel on Climate Change models on how to avoid the worst-case scenarios of global warming rely on the deployment of significant amounts of carbon capture and sequestration in the latter part of the century, which is where new concrete technologies that trap and reuse C02 emissions may be key.

read more at nymag.com