Cement is the glue of modern construction, and about 7% of global CO2 emissions, much of it released by the chemistry of limestone itself.
Making new aluminium from bauxite takes huge amounts of electricity, and where that power comes from coal, each tonne can carry 15 tonnes of CO2 or more.
Every window, glass facade and balcony panel starts in a furnace burning natural gas at around 1,500°C, melting sand, soda ash and limestone.
Making a tonne of steel in a blast furnace releases around two tonnes of carbon dioxide, because coal is used to strip oxygen from iron ore.
India is the world's second-largest aluminium producer, and almost all of its smelters run on captive coal power, giving its metal one of the highest carbon footprints anywhere.
