Carbon capture use and storage (CCUS) and carbon dioxide removal (CDR) techniques are often discussed together differ significantly. CCUS involves 3 steps; firstly, capturing CO2 emissions from industrial processes, such as power generation, cement and steel production, or hydrogen production; secondly, transporting CO2 or using some of it in the manufacturing process (e.g. enhanced oil recovery, chemicals, plastics, food and drink); and thirdly, storing CO2 permanently underground. The amount of CO2 that is eventually stored will mainly be a function of the capture rate, the percentage of CO2 emissions captured, typically estimated to be in the region of 85-90% (although this will differ depending on the process). Therefore, CCUS does not mitigate all emissions from an industrial process. 

CDR techniques capture CO2 from the air and store it permanently. This can happen through different processes - biological, industrial chemical, or rock weathering. Storage can also differ, in trees, plant matter, in the soil, deep underground, in the oceans, or in long-lived products. Some of the most prominent techniques include afforestation/reforestation, peatland restoration, enhanced rock weathering, bioenergy with Carbon Capture and Storage (BECCS), and Direct Air Carbon Capture and Storage (DACCS). See here for a useful overview of CDR. 

As CO2 is removed from the atmosphere, these techniques generate what are known as negative emissions, which can offset emissions from other emission sources. BECCS and DACCS overlap with CCUS; BECCS is a form of CCUS but not only sequesters CO2 from combustion of fuels (in this case bioenergy) but also removes it based on the assumption that sequestration will also happen when the bioenergy regrows. DACCS removes CO2 directly from the atmosphere and then uses similar processes to CCUS in terms of transport, use and storage.  

Some of the above approaches are either at the early stage of development, or are more mature technologies that have yet to scale e.g. CCUS. In view of this, their deployment as mitigation levers are highly uncertain. However, for ambitious global mitigation pathways, they often form a critical lever to achieve emission reduction goals. They also have an important impact on the role of fossil fuels in the energy system, allowing increased levels in mitigation pathways that achieve global goals (see Achakulwisut et al., 2023). This section focuses on two papers by Grant et al. that highlight the uncertainty of CCUS/CDR in modelling approaches, and Achakulwisut et al. who identify the implications of CCUS/CDR on the role of fossil fuels. 

Grant et al. (2021a) recognise that there is still large uncertainty regarding the future potentials of these technologies to deliver the promised effects. As a result of these uncertainties, near-term policies should not rely on removing greenhouse gases in the future but focus on reducing fossil fuel production and consumption right now. The risk that anticipated future CDR could dilute incentives to reduce emissions now is also known as mitigation deterrence. Grant et al. (2021b) warn against this phenomenon. They challenge the common assumptions that emissions reduction and removals are perfect substitutes and that future CDR availability is known with certainty. These studies caution against optimism about future emission-removal technologies and advocate for stronger efforts to reduce emissions now.