There are different terms to describe capturing CO2. The Intergovernmental Panel on Climate Change (IPCC) makes a distinction between CO2 capture and storage (CCS) and CO2 capture and utilisation (CCU), though often they are spoken about together:
- In CCS, CO2 from industrial and energy-related sources is separated (or captured), conditioned, compressed and transported for long-term storage where it cannot enter the atmosphere.
- In CCU, the captured CO2 is used in making a new product which also prevents it entering the atmosphere.
The IPCC states that where the product locks up the CO2 for “a climate-relevant time horizon” it can be described as CO2 utilisation and storage (CCUS). In general terms, CCUS is the process of capturing CO2 emissions from fossil fuel-based power generation and industrial processes for storage deep underground or for reuse.
CCUS is related to, but distinct from, other concepts such as carbon dioxide removal (CDR), which is the removal of CO2 from the atmosphere (as opposed to capturing it at the point of emission or generation). CDR may also involve long-term storage but can also include natural processes such as sequestering carbon through reforestation and afforestation.
The International Energy Agency (IEA) has explained how the storage process in CCUS works in more detail:
Storing CO2 involves the injection of captured CO2 into a deep underground geological reservoir of porous rock overlaid by an impermeable layer of rocks, which seals the reservoir and prevents the upward migration or “leakage” of CO2 to the atmosphere. There are several types of reservoir suitable for CO2 storage, with deep saline formations and depleted oil and gas reservoirs having the largest capacity. Deep saline formations are layers of porous and permeable rocks saturated with salty water (brine), which are widespread in both onshore and offshore sedimentary basins. Depleted oil and gas reservoirs are porous rock formations that have trapped crude oil or gas for millions of years before being extracted and which can similarly trap injected CO2.
The IPCC has suggested that there is sufficient theoretical geological storage for captured CO2:
The technical geological CO2 storage capacity is estimated to be on the order of 1,000 gigatonnes of CO2, which is more than the CO2 storage requirements through 2100 to limit global warming to 1.5°C, although the regional availability of geological storage could be a limiting factor.
However, the availability and location of suitable storage is not the only issue associated with CCS. The IPCC also stated that “implementation of CCS currently faces technological, economic, institutional, ecological-environmental and sociocultural barriers”. The IEA has also argued that storage, rather than reuse, should be the primary focus of carbon capture:
While some CO2 use could bring substantial climate benefits, the relatively limited market size for these applications means dedicated storage should remain the primary focus of carbon capture, utilisation and storage deployment. In the net zero scenario, over 95% of the CO2 captured in 2030 is geologically stored, and less than 5% is used. With a retention time in the order of millions of years, building aggregates are the only CO2 use application that could qualify as permanent sequestration, in contrast with fuels and chemicals, which typically retain the CO2 for one year and up to ten years respectively.
Some campaign organisations, such as Climate Action Network, have argued that CCS “risks distracting from the need to take concerted action across multiple sectors in the near-term to dramatically reduce emissions”.
However, capturing carbon has been described by the Committee on Climate Change (the statutory body established under the Climate Change Act 2008) as “a necessity not an option” if the UK is to reach net zero greenhouse gas emissions. The committee also said that CCUS processes needed to be operating by 2026:
Carbon capture and storage is essential. We previously recommended that the first CCS cluster should be operational by 2026, with two clusters, capturing at least 10 Mt CO2, operating by 2030. For a net zero target it is very likely that more will be needed. At least one of the clusters should involve substantial production of low-carbon hydrogen. The government will need to take a lead on infrastructure development, with long-term contracts to reward carbon capture plants and encourage investment.
A cluster is a regional group where several CCUS facilities share infrastructure. The government has committed to supporting the development of two CCUS clusters by the mid-2020s and a further two by the end of the 2020s.
The IEA has said that CCUS facilities currently capture nearly 45 Mt of CO2 globally. According to the IEA, there are about 35 commercial facilities operating worldwide that apply CCUS to industrial processes, fuel transformation and power generation. The IEA has also stated that the speed of deployment has not met expectations in the past but “momentum has grown substantially in recent years”. The agency has said that over 200 capture facilities have been announced by project developers to be operational by 2030, which would capture more than 220 Mt CO2 per year. However, the IEA has said that, as of June 2022, only around 10 commercial capture projects that were under development had taken final investment decisions. It has argued that “to translate momentum into action”, policy makers “should roll out additional policy support, while also ensuring that appropriate legal and regulatory frameworks are in place”. Writing in October 2022, the consultancy firm McKinsey expressed concern that the deployment of CCUS needed to be sped up:
According to McKinsey analysis, CCUS uptake needs to grow 120 times by 2050 for countries to achieve their net zero commitments, reaching at least 4.2 gigatons per annum (GTPA) of CO2 captured, with some estimates ranging from 6.0 to 10.0 GTPA. This could lead to CCUS decarbonizing 45 percent of remaining emissions in the industry sector. Even in conservative scenarios, CCUS demand would reach approximately two GTPA by 2050—a 60-fold increase over today’s pipeline of projects.
The UK government has said that CCUS would likely play “an essential role” in meeting its statutory carbon emissions targets. The government’s Energy Bill was introduced in the Lords in July 2022 and contains measures aimed at accelerating the growth of low carbon technologies, including CCUS. The bill would establish Ofgem as the economic regulator of CO2 transport and storage. It would also provide for a framework for the economic licensing of CO2 transport and storage activities and make provision for “spending powers to provide financial assistance to support the establishment of CCUS”. At the time of writing, the bill is completing its committee stage in the House of Lords.