If the cement industry were a country, it would be the third largest emitter of CO2 on Earth, behind only China and the United States. Cement is used to make concrete, an essential material in global housing, construction and infrastructure, but can it be made less damaging to the planet? As countries come together at the COP27 summit in Egypt's Sharm el-Sheikh, the UN’s chief has warned that nations must cooperate or face "collective suicide" in the fight against climate change, at a summit where developing countries reeling from global warming demanded more action from rich polluters. "Humanity has a choice: cooperate or perish," Antonio Guterres said.