Carbon capture and storage (CCS) is a process in which carbon dioxide (CO2) from industrial installations is separated before it mixes with the atmosphere, then transported to a long-term storage location.[1]: 2221 In CCS, the CO2 is captured from a large point source, such as a natural gas processing plant and typically is stored in a deep geological formation. Around 80% of the CO2 captured annually is used for enhanced oil recovery (EOR), a process in which CO2 is injected into partially-depleted oil reservoirs in order to extract more oil and then is left underground.[2] Since EOR utilizes the CO2 in addition to storing it, CCS is also known as carbon capture, utilization, and storage (CCUS).[3]
Oil and gas companies first used the processes involved in CCS in the mid 20th century. Early versions of CCS technologies served to purify natural gas and to facilitate oil production. Subsequently, CCS was discussed as a strategy to reduce greenhouse gas emissions.[4][5] Around 70% of announced CCS projects have not materialized.[2] As of 2023, 40 commercial CCS facilities are operational[6] and collectively capture about one thousandth of anthropogenic CO2 emissions.[7] Plants with CCS require more energy to operate, thus they typically burn additional fossil fuel and increase the pollution from extracting and transporting fuel.
In strategies to mitigate climate change, CCS plays a small but critical role. Other ways to reduce emissions such as renewable energy, electrification, and public transit are less expensive than CCS and also much more effective at reducing air pollution. Given its cost and limitations, CCS is envisioned to be most useful in specific niches. These niches include heavy industry, plant retrofits, natural gas processing, and electrofuel production.[8]: 21–24 In electricity generation and hydrogen production, CCS is envisioned to complement a broader shift to renewable energy.[8]: 21–24 CCS is a component of bioenergy with carbon capture and storage, which can under some conditions remove carbon from the atmosphere.
The effectiveness of CCS in reducing carbon emissions depends on the plant's capture efficiency, the additional energy used for CCS itself, leakage, and business and technical issues that can keep facilities from operating as designed. Many large CCS implementations have sequestered far less CO2 than originally expected.[9] Additionally, there is controversy over whether CCS is beneficial for the climate if the CO2 is used to extract more oil.[10] Fossil fuel companies have heavily promoted CCS.[11] Many environmental groups regard CCS as an unproven, expensive technology that will perpetuate dependence on fossil fuels and distract from more effective ways to reduce emissions.[12] Other environmental groups support the use of CCS under certain circumstances.[13]
Some international climate agreements refer to the concept of fossil fuel abatement, which is not defined in these agreements but is generally understood to mean some use of CCS.[14] Almost all CCS projects operating today have benefited from government financial support, usually in the form of grants.[15]: 156–160 Countries that are developing programs to support or mandate CCS technologies include the US, Canada, Denmark, China, and the UK.[16][17]
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