Carbon capture and storage (CCS) or carbon capture and sequestration is the process of capturing carbon dioxide before it enters the atmosphere, transporting it, and storing it (carbon sequestration) for centuries or millennia. Usually the CO₂ is captured from large point sources, such as a chemical plant or biomass power plant, and then stored in an underground geological formation. The aim is to prevent the release of CO₂ from heavy industry with the intent of mitigating the effects of climate change. CO₂ has been injected into geological formations for several decades for enhanced oil recovery and after separation from natural gas, but this has been criticised for producing more emissions when the gas or oil is burned. There are number of initiatives around the globe driven by the oil and gas industry. It is expensive and controversial and not fully proven.