Carbon Capture and Storage

Carbon capture and storage, usually abbreviated CCS, describes a chain of steps: separating carbon dioxide (CO₂) from a gas stream, transporting it to a suitable location, and injecting it into a deep geological formation for long-term storage. Sources can include industrial processes and power generation; some systems instead capture CO₂ directly from the atmosphere. The term is sometimes used alongside carbon capture, utilisation and storage (CCUS), which also covers uses for captured CO₂. Use is not automatically permanent storage: the climate outcome depends on what the CO₂ is used for and whether it is subsequently released.

Capture systems separate CO₂ from other gases at facilities or draw it from ambient air. After capture, the gas is compressed and can be moved by pipeline, ship, rail or truck to a storage site. Suitable deep geological formations include saline formations and some depleted oil and gas reservoirs. In the subsurface, CO₂ occupies pore spaces in rock, can dissolve into fluids in the formation and, over longer periods, may react to form stable minerals. These processes are part of the geological trapping of injected carbon.

The source of the CO₂ matters. Capturing some emissions from a fossil-fuel power station or industrial plant can prevent that portion from reaching the atmosphere, but it does not by itself take previously emitted CO₂ out of the air. Capture directly from ambient air followed by durable storage is a carbon-dioxide-removal pathway; capturing CO₂ from sustainable biomass and storing it can also remove atmospheric carbon over the full carbon cycle. These approaches have different energy needs, accounting questions and environmental effects, so their benefits should not be treated as interchangeable. CCS is a possible climate-mitigation tool, not a substitute for reducing emissions at their source.

Geological storage requires suitable geology, engineered wells and monitoring. In the United States, the Environmental Protection Agency's Class VI rules for wells used in geologic sequestration include site-characterisation, construction, operating, testing and monitoring requirements intended to protect underground sources of drinking water. Monitoring continues after injection until the permitting authority determines that no additional monitoring is needed.

The technology also depends on capture equipment, energy, transport links and accessible storage sites. Project assessments therefore consider emissions across the full chain, the suitability of the reservoir, possible leakage pathways, monitoring and long-term responsibility. A captured ton is not automatically a permanently stored ton, and reported capture capacity alone does not establish a project's net climate benefit.