What Is Carbon Sequestration?

Carbon sequestration is the process of capturing carbon dioxide from the atmosphere or from industrial emission streams and storing it in a stable form over geologically or biologically meaningful timescales. It is a central element of strategies to reduce atmospheric greenhouse gas concentrations and limit global warming. The practice encompasses both natural pathways, which rely on the carbon-storing capacity of ecosystems, and engineered pathways, which inject CO2 into geological formations or convert it into solid or liquid products.

The field draws on atmospheric chemistry, geology, ecological science, and chemical engineering. As described by the U.S. Department of Energy's Office of Science, carbon sequestration research spans the foundational sciences of capture chemistry and geological storage as well as biological and environmental processes at ecosystem scale.

Geological Carbon Sequestration

Geological carbon sequestration involves compressing CO2 to a supercritical state and injecting it deep underground into porous rock formations, typically saline aquifers, depleted oil and gas reservoirs, or basalt. At depths greater than 800 meters, the ambient pressure and temperature keep CO2 in a dense, liquid-like phase that occupies far less volume than the gas. Over time, several trapping mechanisms immobilize the CO2: it dissolves into formation brines, reacts with silicate minerals to form stable carbonate precipitates, or is physically trapped beneath an impermeable caprock layer. The U.S. Geological Survey characterizes geologic storage as a multi-mechanism process involving these physical and geochemical containment pathways.

Carbon capture and storage (CCS) systems combine a capture step, typically post-combustion amine scrubbing or pre-combustion gasification, with a compression, transport, and injection system. Large-scale demonstration projects, including the Sleipner project in the North Sea operating since 1996, have validated long-term geological containment at megatonne-per-year scale.

Biological Carbon Sequestration

Biological carbon sequestration refers to the storage of atmospheric carbon in living biomass, dead organic matter, soils, and aquatic systems. Forests, wetlands, grasslands, and ocean phytoplankton all function as natural carbon sinks. Managed afforestation, improved soil carbon practices such as no-till agriculture and biochar application, and the restoration of coastal blue-carbon ecosystems like mangroves and seagrass beds can measurably increase biological storage rates. The distinction between geological and biological sequestration, as explained by the U.S. Geological Survey's FAQ on geologic vs. biologic sequestration, centers on the permanence and monitoring requirements of each approach: geological storage is generally considered more permanent but more technically complex, while biological storage is more reversible due to disturbance, fire, and land-use change.

Carbon Capture, Utilization, and Storage

An extension of pure storage is carbon capture and utilization (CCU), in which captured CO2 is converted into useful products rather than simply buried. CO2 can serve as a feedstock for synthetic fuels, urea fertilizer, concrete curing, and polymer production. Combining CCU with geological storage in so-called carbon capture, utilization, and storage (CCUS) systems creates flexibility in how captured carbon is managed. The trade-off is that many utilization pathways re-release CO2 relatively quickly through combustion or decomposition, so the net climate benefit depends on the product lifecycle.

Applications

Carbon sequestration has applications in a wide range of contexts, including:

• Mitigation of CO2 emissions from power generation and heavy industry
• Enhanced oil recovery using injected CO2 to improve well yields
• Restoration of degraded forests and peatlands as managed carbon sinks
• Agricultural soil carbon programs linked to carbon credit markets
• Environmental remediation of sites affected by greenhouse gas pollution
• Policy frameworks addressing global warming and the greenhouse effect