- Emissions must be reduced rapidly and deeply; CDR can only complement this effort, not replace it.
- Both new (often engineered) and more traditional (often forest-based) types of CDR need to be scaled up.
- Robust monitoring, reporting and verifying is critical for the success of further CDR deployment.
- The different time frames and types of CDR must be aligned with the specific type of emissions they are supposed to neutralise (a “like-for-like” approach).
- New, multi-level governance and policy instruments are required to support CDR innovation.
Meeting the Paris Agreement’s targets will require scaling up CDR from a current level of about 2 billion tonnes of CO2 to at least 5 billion tonnes or more by 2050. Today, virtually all CDR consists of afforestation, reforestation and management of existing forests. Only 0.1% of current removals come from the rest of deployed methods, such as direct air capture and storage, bioenergy with carbon capture and storage, biochar, enhanced weathering, and ocean-based methods. However, almost all scenarios that limit warming to 1.5°C or 2°C rely on large-scale deployment of these CDR methods.
While many of these CDR methods have great potential, current estimates predict a substantial shortfall compared with what is necessary to cover the hard-to-abate emissions to achieve net zero. That shortfall also means that these methods would be unlikely to compensate for initial exceedance of the carbon budget for a 1.5°C warming limit. The extent of efforts to develop what are currently small-scale (or even untested) CDR methods over the next decade will determine whether sufficient carbon removal capacity will be available at the scale necessary and in time to reach net-zero CO2 emissions by the early 2050s, and for achieving net-negative CO2 emissions afterwards.
A wide variety of CDR options exists, with different levels of technological readiness and sequestration or storage duration (Figure 3). All of these methods have uncertainties regarding their feasibility, life-cycle assessment, and monitoring, reporting and verification (MRV) (see In Focus box). For example, estimates of CO2 removal by forests are hampered by indeterminate effects from environmental changes (see Insight 4) and inconsistent definitions. Large uncertainties exist in the carbon storage rates for enhanced rock weathering, as well as the evolution of the air-sea gas exchange for direct ocean removal or ocean alkalinity enhancement. Direct air carbon capture and storage, on the one hand, has enormous potential to scale with relatively small land-use impacts, yet the viability of doing it at a feasible energy intensity is still unknown. The use of carbon capture and storage to enhance fossil fuel recovery presents a particular dilemma (see Insight 2, In Focus box).
Increasingly, the scientific community and standard-setting bodies are emphasising a “like-for-like” approach to CDR neutralisation claims. This means that fossil CO2 emissions should be neutralised through CDR that durably sequesters CO2, while forestry (and other land-use-based) CDR should only neutralise land-use-related CO2 emissions. This would address the concern about CO2 sequestered in vegetation and soils being at risk due to increased prevalence of wildfires, droughts and pests (see Insight 4).
The level of CDR deployment needed will require significant multi-level policy and governance. In some cases, policies can be built on experience from existing CDR methods, emissions reduction measures and, to a limited degree, from carbon capture and storage deployment. But many aspects of CDR policy instruments will require governance innovation. Political commitment and robust MRV systems are necessary.
The CDR mix will evolve
Currently, the vast majority of CDR happens through “conventional” methods, such as afforestation/reforestation. But forests in many regions are threatened by climate-driven disturbances such as droughts, heatwaves, fires, storms and pests (see Insight 4). Less-established CDR options, such as bioenergy with carbon capture and storage, direct air carbon capture and storage, enhanced weathering, biochar and ocean alkalinisation, play only a minor role, so far. The Intergovernmental Panel on Climate Change (IPCC) scenarios (AR6-WG3:Ch3) that stay below a 2°C warming assign a very large role to land-use and forestry-related CDR, as well as to bioenergy with carbon capture and storage, and partly also to direct air capture with storage. But the weight of these CDR options in the IPCC scenarios (and others) does not actually reflect a judgement of their feasibility. Many research and demonstration programmes, as well as policy strategies, consider a broader range of CDR options.
Implications & Recommendations
- CDR is not a substitute for deep and sustained emissions reductions.
- For CDR to become available on time and at the scale required to meet national net-zero targets, policies must be put in place in the near term to support deployment of new forms of CDR. These policies should responsibly incentivise research, development and demonstration, and targeted deployment.
- Relying on forest-based CDR, the main method of carbon removal today, is risky given major uncertainties due to the impacts of climate change (see Insight 4).
- Given the limited potential of each CDR method and the associated risks at scale (see In Focus box), a portfolio of CDR options should be planned for, the composition of which will adjust over time to account for technological progress, risk assessment and changing environmental, societal, economic and political requirements.
Specific proposals for policy action include:
- Set clear and separate targets for emission reductions and for carbon removal. For example, mandatory separation of reductions and removals in NDCs, specifically the Information to facilitate Clarity, Transparency and Understanding (ICTU) tables.
- Set separate targets based on removal processes that match the timescales of carbon removal permanence with the timescales of emissions permanence (like-for-like approach). For example, the separate setting of targets should be part of frameworks for CDR credits (as has currently been proposed by the European Commission).
- Develop common, robust and transparent MRV frameworks for CDR. For example, by improving existing and developing new inventory guidance through the IPCC’s Task Force for National GHG Inventories and ensuring consistency between project-level and country-level reporting.
- Create structured exchanges for mutual learning. This would be relevant not only for knowledge exchange and capacity building, but also in the context of establishing international carbon trading under the Paris Agreement’s Article 6.4 mechanism.