Hardcore greenhouse gas (GHG) geeks will recall that cement is a huge source of greenhouse gas emissions, with approximately 1 ton of CO2 equivalent emitted into the atmosphere for every 1 ton of cement produced. Damn. Forget your carbon guilt from flying, people! Cement is responsible for 5% of the Earth’s CO2 emissions, and it’s the third largest source of greenhouse gas pollution in the US according to the EPA.