Carbon pricing and market schemes targeting emissions reductions in certain sectors of the economy can allow for the use of CDR through offsets. While we focus here on markets for CDR, it should be noted that the majority of carbon offsets traded in markets currently come from reduced or avoided emissions rather than removals (Shankleman and Rathi, 2021). The UKs Woodland Carbon Code (WCC), Spain's Registro de Huella de Carbono (RHC), and France's Label Bas-Carbone (LBC) operate as domestic carbon standards which participate in voluntary carbon markets. Requirements of issued certificates to be surrendered to buffer accounts range from 20% for the WCC, 10% for the RHC and 10–25% for the LBC depending on the projects reversal risk (Cevallos et al., 2019; WCC, 2019a,b). Each standard is administered directly or indirectly by a government ministry and forestry projects are expected to last 30 years in the RHC and LBC or up to 100 years in the WCC. The WCC and RHC use public registries to sell RUs whereas in the LBC RUs are negotiated and traded directly between the project owner and the buyer. LBC largely focuses on afforestation and reforestation projects but is expected to expand to other forms of sequestration including agroforestry soil carbon in agriculture and mangroves (Cevallos et al., 2019). WCC units cannot be used in the UK Emissions Trading Scheme (ETS) or outside the UK (including shipping and aviation) and reporting is required every 10 years after the first 5 years. Follow up reports are required every 5 years with Spain's RHC and third party verification of ex-post GHG emissions if a buyer retires RUs.

Both Colombia and Chile have a carbon tax of approximately US$5/tCO₂e. In Columbia companies can avoid paying the tax by purchasing carbon offsets from projects located in Colombia. Accepted offsets include afforestation, improved forest management and REDD+ projects as well as agricultural and grassland management projects. The Colombian Government is expected to trial an ETS (COETS) which will allow for removals to offset emissions as a complementary policy to the carbon tax between 2023 and 2024 (Cevallos et al., 2019). The Chilean government is currently working on developing offset regulation which could allow regulated entities to offset part or all of their emissions subject to the tax. Offsets, their threshold limits, and their transactions are expected to be operational in 2023 (ICAP, 2021b).

Some ETSs already have experience with the use of RUs, albeit primarily in the context of offsets from afforestation and reforestation projects. Generally, offset projects must be located within the same nation as the ETS or in regions where ETSs are linked. Examples include in California (C&T), Québec (QC), China (CETS) and the Korean ETS (KE)—all of which established quantitative limits and qualitative criteria for offset use. Compliance entities may use RUs to meet up to 4% of their emissions compliance in the C&T, 5% in the CETS and 8% in the QC (EDF, 2020; CARB, 2021; ICAP, 2021a). Each project that is issued offset credits contributes between 17 and 19% in the C&T and 3% in the QC of their total credits into a buffer account (ARB, 2021; ICAP, 2021a). Mexico's proposed national ETS (ME), currently in a pilot phase, is expected to allow proposed participants to meet up to 10% of their compliance obligations with offsets generated domestically. Kazakhstan's Emissions Trading Scheme (KZE) allows for the use of domestic offsets without quantitative limits but projects are expected to apply Clean Development Mechanism principles (EDF, 2015; ICAP, 2021c). In Japan, the Saitama's ETS is linked to Tokyo's Cap-and-Trade Program and allows for forest absorption credits to be used as offsets (ICAP, 2022a). New Zealand's ETS (NZE) awards allowances for removals from forestry, without a limit on the total number of units from those activities that can go into the ETS. Owners of forest land created after 1989 in New Zealand can voluntarily join its ETS and receive RUs as their forest grows. Owners of non-exempt pre-1990 forest land are required to participate in the system and are subject to its obligations if they deforest (ICAP, 2022b).

Operators who perform CCS in Europe can retain allowances when emissions have been verified as captured and transported for permanent storage under the European ETS (EU ETS) (Council Directive 2018/410/EC). While there is no current provision for CDR in the EU ETS, several potential methods for inclusion have been proposed. Rickels et al. (2021) propose that a regulatory authority could procure removal units into the market as a method to incentivise geological CDR too, a prerequisite to the approach would be the creation of an unused allowance pool that could be designated as RUs (Rickels et al., 2021). The European Commission has proposed that a Carbon Removal Certification Scheme could be integrated into the EU ETS in 2030 (European Commission, 2021a). Hickey and Allen (2021) propose a “European Removals Fund”, funded by allowances from the ETS and other sources, which could use a reverse auction to procure removals required to offset hard-to-abate sectors in Europe. Applying a temporary multiplier value on allowances to match the cost of RUs from geological CDR is also considered in their analysis i.e., operators of removals receive a multiple of allowances which match their costs (Hickey and Allen, 2021). ETS allowances could also be limited to a specific global-warming goal, but allowances for further emissions in the form of carbon debt which needs to be removed in future could be issued. Emitters pay for temporary storage in the atmosphere through interest payments on their carbon debt (Bednar et al., 2021). Bednar et al. (2021) conclude that this would lead both to earlier reductions in carbon emissions and to earlier application of removal technologies.

Cabral et al. (2019) find repurposed coal to Bioenergy with Carbon Capture and Storage (BECCS) plants could reduce the levelized cost of BECCS plants to between $70/MWh and $100/MWh, achieved through auctioning RUs at between $90/tCO₂ and $135/tCO₂, with a sequestration potential of 9GtCO₂ (Cabral et al., 2019). Subsequent analysis has found that incentivising CDR through RUs could mean that lower levels of carbon taxation are needed to meet the Paris Agreement, which in turn lowers electricity costs (Daggash and Mac Dowell, 2019). Value pool analysis of business models for BECCS, DACs and Distributed Biomass supports these findings, concluding that access to carbon credit mechanisms, has by far the greatest near-term potential to drive negative emissions technologies (Platt et al., 2018).

Governments can place obligations or standards on companies to reduce their emissions directly or trade with other companies to offset their emissions, though this is less common. For example, the US Renewable Portfolio Standards require that a specified percentage of the electricity utilities sell comes from renewable resources. Under the Swiss CO₂ Act, importers of motor fuels are required to offset up to 90% of their emissions. In support of the obligation, the Foundation for Climate Protection and Carbon Offset (KliK) was founded as a sector-wide carbon offset grouping for motor fuel suppliers. The KliK Foundation funds projects that generate carbon offset credits based on a Swiss carbon standard, which could include forestry, through a levy placed on consumers (st1, 2021). California's Low-Carbon Fuel Standard (LCFS) sets annual carbon intensity benchmarks on the full lifecycle emissions of transport fuels sold, supplied or offered for sale in California. Projects that directly capture CO₂ from the air can generate LCFS credits and be sold to buyers who exceed their carbon intensity benchmark (Townsend and Havercroft, 2019). Operators must agree to monitor the project for 100 years after injection, demonstrate a low probability (< 10%) of leakage with 8–16.4% of credits allocated to a buffer account. Funds must also be ring fenced for maintenance, project closure, and potential accidents (CARB, 2018). Projects are not restricted to California and may be located anywhere.

In a Carbon Take Back Obligation (CTBO), currently at a conceptual stage, producers or importers of carbon compounds must sequester/store an increasing fraction of the CO₂ produced from their products by acquiring RUs in-house or externally (100% by 2050) (Allen et al., 2009; Kuijper et al., 2021). Jenkins et al. (2021) find a CTBO could be comparable in cost, including economic costs, to similar ambition scenarios dominated by demand-side measures simulated by a global carbon price. In the near term, demand-side policy is required to incentivise emissions reductions before the CTBO stored fraction increases significantly enough to disincentive fossil fuel use (Jenkins et al., 2021).

Governments can also use mechanisms to procure a fixed level of demand or price per tonne of CDR in an existing mechanism. Australia's Emissions Reduction Fund (ERF) provides incentives to businesses to cut the amount of greenhouse gases they create and to undertake activities that store carbon. RUs can be sold to the government through a carbon abatement contract or in the unregulated secondary market as an offset (Inoplex, 2018). RUs are secured through a competitive bidding process based on lowest cost per tCO₂ (Clean Energy Regulator, 2022). The UK's Woodland Carbon Guarantee (WCG) allows landowners, who can also participate in the WCC, to sell captured carbon from their forests to the government in the form of verified RUs for a guaranteed price every 5 or 10 years up to 2055/56 (Forestry Commission, 2020, 2021). At years 5 and 15 the UK Accreditation Service checks if the predicted or actual carbon sequestration is materially correct (WCC, 2019c).

SDE++ in the Netherlands covers the cost of CCS operation above the EU ETS price and exempts industrial facilities from the Dutch carbon tax for CO₂ captured and stored. Projects are ranked based on their subsidy intensity and only projects below the cost threshold for CCS could participate in the auction. Calculating the subsidy intensity is done by taking the base rate from the application and subtracting the long-term price divided by the emission factor (Andreas, 2021). Between 2026 and 2040, the Swedish government will use a reverse auction (SRA) to distribute SEK 400 million per year to BECCS operators who submit the lowest cost bids (Regeringen, 2021). Zetterberg et al. (2021) proposes a similar auction approach focused on guarantees, followed by a larger quota obligation scheme or integration of BECCS into the EU ETS to scale up BECCS in Sweden. They also considered a voluntary compensation scheme or international transfers of BECCS outcomes, but conclude these two approaches were too uncertain for the short term (Zetterberg et al., 2021). Honegger and Reiner (2018) also consider international transfers of outcomes through the Sustainable Development Mechanisms (SDM), which allow for voluntary transfers of mitigation units in exchange for payment of a price per tonne of CO₂ avoided emissions or removal by the receiving country. The received units might then be counted towards the buyer country's mitigation target or its climate finance pledges (Honegger and Reiner, 2018).

A CfD is a contract that pays the differences in the market price and an agreed price or cost for CDR. Conceptual policy analysis suggests funding for BECCS in the UK from CfD mechanisms on electricity pricing (CfDe), with a Negative Emissions Payment (NEP) and a standalone carbon CfD (CfDc) on the ETS price, with NEPs set at £92/tCO₂ and CfDc set at £107/tCO₂ (Element Energy and Vivid Economics, 2021). The state could recoup NEP costs by selling a NEP on the voluntary market, or the plant operator could sell a NEP at a discount (£40/tCO₂) on the voluntary market, with the state covering the difference. Europe's Innovation Fund, funded through allowances it sells in the EU ETS, could hypothetically provide support to projects through competitive tendering mechanisms such as CfDcs, but may be limited to second, or third of a kind projects (European Commission, 2021b). CfDcs may raise problems for an ETS forward market, effectively reducing the need for market participants to hedge their risks leading to reduced overall liquidity and thus less efficient price-formation (Europex, 2021).

Subsidies can involve the direct payment by governments to CDR project operators for the costs they incur. The UK's Countryside Stewardship Scheme (CSS) and Woodland Carbon Fund (WCF), New Zealand's One Billion Trees Fund (1BTF) and Ireland's Afforestation Scheme (IAS) offer direct grants paid per hectare (DEFRA, 2021b; MPI, 2021; Rural Payments Agency, 2021; Department of Agriculture Food and the Marine, 2022). IAS also covers the cost of afforestation. Mexico's Sowing Life (SL), intended to help meet climate goals with synergistic aims to support the country's efforts to reduce poverty and inequality, provides direct grants paid per farmer rather than per hectare. The US Conservation Reserve Program (CRP) operates on both a cost-share assistance basis (up to 50%) and financial incentives (additional 20% of soil rental rate) (Newton, 2020). Each mechanism can fund forestry, CSS and CRP consider soil restoration too, but only the WCF and 1BTF focus on carbon sequestration. Participants in the 1BTF can register their forests for carbon credits in the NZ ETS and therefore must adhere to its liability mechanism (Menzies, 2020). The proposed Environmental Land Management Scheme (ELMS) in the UK could fund some forms of soil carbon sequestration, biochar, and enhanced weathering (DEFRA, 2021a). The Climate-Smart Practice Incentive aims to increase sequestration through trees, permanent grasses and wetland restoration under the CRP although a funding mechanism is not yet established (USDA, 2021). California's Healthy Soils Program (HSP) is funded from the State's cap and trade proceeds. The HSP distributes funds through grants for: cover cropping, no-till, reduced-till, mulching, compost application, and conservation plantings (CDFA, 2022). The Regional Direct Air Capture Hubs (RDH) program in the USA will support four large-scale, regional direct air capture hubs that each comprise a network of CDR projects worth $3.5 billion (USDOE, 2022). Costa Rica's Payments for Environmental Services Program (PES) provides landowners with direct payments for the environmental services that their lands produce when adopting sustainable land-use and forest-management techniques. Funding comes from a variety of sources including fuel tax and water charge, Certificates of Conservation of Biodiversity, carbon credits, and strategic alliances with the public and private sector (UN Climate Change, 2020). Through its international climate and forest initiative (NICFI), the Norwegian government seeks to promote efforts to slow, halt, and ultimately reduce greenhouse gas emissions caused by deforestation and forest degradation in developing countries (REDD+) (Norad, 2020).

Tax credits reduce the amount of income tax companies operating CDR owe to governments. Section 45Q of the US tax code offers a tax credit for geologic CO₂ storage in general, and so both BECCS and Direct Air Carbon Capture and Storage (DACCS) are eligible (Bright, 2021). The credit is based on the amount of CO₂ captured and is provided to the company that captures it. CO₂ must either be placed in permanent geological storage or utilised in products (e.g., plastics and cement), as well as enhanced oil recovery (EOR). CDR projects are likely to require higher financial incentives than CCS projects involving high-purity CO₂ capture or EOR. The taxpayer has to repay the tax credit (credit recapture) to the Treasury if the carbon dioxide ceases to be captured, disposed of, or used in a qualifying manner (CRS, 2021). The Inflation Reduction Act of 2022 increased the 45Q tax credit to between $85/tCO₂ and $180/tCO₂ for geological CDR (Clean Air Task Force, 2022). For DAC facilities, the CO₂ capture threshold decreased from 100,000 tonnes captured per year to 1,000 tonnes per year. Sanchez et al. (2018) estimate that a $60/tCO2 sequestration credit (e.g., the 45Q) may result in the sequestration of 30 MtCO₂, while a $90/tCO₂ carbon abatement credit (e.g., LCFS in Section 2.1) might incentivise the reduction of 38 MtCO₂ (Sanchez et al., 2018). Edwards and Celia (2018) estimate that the use of direct government financing in addition to the 45Q tax credit could lead to capturing an additional 19–30 MtCO₂ profitably each year (Edwards and Celia, 2018).

Vivid Economics (2019) propose a similar tax credit for the UK, potentially funded by a carbon levy. They also suggest the tax credit could apply to the initial capital investment (similar to the US 48 a/b tax code) and be tradeable between companies (Vivid Economics, 2019). Canada recently proposed a CCUS tax credit offered on the cost of purchasing or installing eligible equipment used in a CCUS project. The credit works on an initial sliding scale of 60% for equipment on a direct air capture project, 50% for other eligible capture equipment and 37.5% for transport, storage and use equipment (Johnson et al., 2022). Liability for released CO₂ is expected to be managed through a recovery of tax credit mechanism (EY, 2022).

This section illustrates the price and potential scale for each mechanism described in Sections 2.1–2.5 where possible. For some market-based mechanisms the level of CDR is not reported and the theoretical potential is used i.e., the maximum amount of CDR that could receive a payment in that market.

Figure 2 shows the range of average prices per tonne of CO₂ available in each mechanism by CDR type, as well as the potential scale for each mechanism. Supplementary Table A1 presents the prices and scale for each of the mechanisms assessed. Mechanisms without either a price or scale reported which could not be plotted are available in the Appendix.

Current prices for forestry can come close to or exceed cost estimates of €40/tCO₂ in KF, WCG, and CRP, however upper estimates by the IPCC can rise to €240/tCO₂ (Fuss et al., 2018; IPCC, 2022). The remaining mechanisms, which comprise the majority of biological CDR's total scale, are estimated to pay below €20/tCO₂. IPCC cost estimates of DACCS and BECCS which can rise to €300/tCO₂ and €400/tCO₂ in cost, respectively are above current prices in all mechanisms. Policy documents for BECCS in the UK indicate a price of between €107/tCO₂ and €151/tCO₂ (Element Energy and Vivid Economics, 2021). Spot prices for DACCS today can rise to between €204/tCO₂ and €2,132/tCO₂ for voluntary purchases (cdr.fyi, 2022). However, voluntary markets have had an average price of €4/tCO₂ in 2021, which is also below the costs of these technologies (Ecosystem Marketplace, 2022). Contracts with better terms are possible outside of the voluntary market. In these instances, the purchaser of credits is typically a large corporation or consortia (e.g., Microsoft, Airbus and Frontier) placing a low volume prepurchase of CDR based on a maximum spend (Joppa et al., 2021; 1PointFive, 2022; Frontier Climate, 2022). Reforms to the 45Q result in prices for DAC and BECCS of €180/tCO₂ and €85/tCO₂, respectively. SDE++ may incentivise geological storage but could be too low to support removal. The LCFS maintained a price of ~€200/tCO₂ in 2019 and 2020 until recently declining to €68/tCO₂ in September 2022. The price decline arose from a sharp rise in new credits from renewable gas projects due to a combination of interlocking incentives (Blackburn, 2022). It is possible to combine mechanisms to achieve higher prices to cover CDR costs. For example, the LCFS and 45Q, NZE and 1BTF, the WCF and CSS with the WCC. Generally, subsidies can be combined with other mechanisms.

The theoretical potential scale of operational mechanisms which support geological storage of CO₂ in this survey is estimated at 0.95 GtCO₂ in total, the total scale of operational mechanisms supporting biological storage is estimated at 0.273 GtCO₂. These numbers represent the potential scale of mechanisms for which estimates could be established, not how much CO₂ is currently being removed and stored.

IPCC scenarios which keep temperatures at 1.5C with low overshoot indicate annual volumes in 2050 for geological storage total 2.77 GtCO₂ yr⁻¹, with 2.75 (0.52–9.45) GtCO₂ yr⁻¹ coming from BECCS and 0.02 (0–1.74) GtCO₂ yr⁻¹ from DACCS. Net CO₂ removal on managed land (including forestry) is estimated at 2.98 (0.23–6.38) GtCO₂ yr⁻¹ (IPCC, 2022). IEA estimates are lower for geological storage of 0.027 GtCO₂ yr⁻¹ by 2030 and 1.93 GtCO₂ yr⁻¹ by 2050, through 0.2 GtCO₂ yr⁻¹ of BECCS by 2030 and 1.3 GtCO₂ yr⁻¹ by 2050 and DACCS at 0.07 GtCO₂ yr⁻¹ and 0.63 GtCO₂ yr⁻¹, respectively (IEA, 2021). A significant proportion of biological CDR is not covered by mechanisms today, it is therefore difficult to compare it with future biological CDR requirements in scenarios. However, geological CDR is considerably underdeveloped relative to future requirements.

Figure 3 indicates that the majority of currently operational mechanisms are concentrated in carbon markets and subsidies which mostly support biological CDR. Average prices in carbon pricing and market mechanisms tend to be lower than other mechanisms. One reason for this is that prices are set independently of the cost of CDR and can reflect the cost of allowances targeting mitigation. Higher prices for CDR are generally offered in the remaining mechanism types as they can be tied towards the cost of CDR, excluding the LCFS and ERF.

With the exception of the WCC, NZE, ERF and KF, the estimates of scale for carbon pricing and markets and tradeable obligation mechanisms represent their potential scale. Potential scale represents the maximum amount of RUs that could theoretically be operating in the mechanism, reporting on the values of CDR in these mechanisms is limited. 45Q's scale includes several projects that will have received varying prices, but 45Q in Figure 3 indicates the greatest price that could be obtained through that mechanism. For all other mechanisms and mechanism types the values for scale are either reported or estimated levels of direct CDR activity. The approached used to generate estimates is outlined in the Appendix. One implication of overlapping mechanisms is that the mechanism scales in Figure 3 are not necessarily additive.