CDR (Carbon Dioxide Removal) Approaches: Friends or Foes?

The road towards the Paris Agreement was potholed, full of controversies and antagonizing positions of States. Ultimately, the normative value of some provisions of the Convention was left unclear (Rajamani, p. 337-344). However, one thing is undisputedly accepted: under Article 4(1), all Parties have a binding obligation to reduce their greenhouse gas emissions (GHGE) in accordance with the global warming goal set in Article 2(1)(a), updated in the Glasgow Pact to 1.5^oC above pre-industrial levels (the “Paris goal”). This was unanimously asserted in the climate advisory opinions of the International Tribunal for the Law of the Sea (ITLOS, §77), the International Court of Justice (ICJ, §224), and the Inter-American Court of Human Rights (IACtHR, §323), as well as by the European Court of Human Rights in the KlimaSeniorinnen case (§436). Whilst States struggle to comply with this obligation, an increasing wave of climate litigation is forcing courts to determine to what extent mitigation pathways can rely on carbon dioxide removal (CDR) under the Paris Agreement framework.

Notably, the general agreement of States regarding the need to set a global warming goal under the Paris Agreement is grounded on a ‘bottom-up’ approach, in which States are not granted specific GHGE mitigation pathways or quotas; thus, departing from the (arguably failed) ‘top-down’ approach of the Kyoto Protocol. Under Article 4(2) of the Paris Agreement, States are required to set their own domestic mitigation pathways, named ‘Nationally Determined Contributions’(NDCs).

Under Article 4, States possess reasonable leeway to determine their mitigation strategies. Nevertheless, they must ensure that their NDCs are in alignment with the 1.5^oC goal, and that they reflect progressive and increasing ambition. Given the existential threat posed by climate change, climate obligations were deemed stringent in all advisory opinions. Moreover, the different Courts underlined the prominent role of the ‘best available science’ in the design and implementation of NDCs (ITLOS, §212, 241; ICJ, §138, 224; IACtHR, §231-237, 336).

To achieve the Paris goal, States must not exhaust the available carbon budget, defined by the Intergovernmental Panel on Climate Change (IPCC, p. 34) as the ‘total net amount of carbon dioxide (CO₂) that can still be emitted by human activities while limiting global warming to a specified level’. As of 2020, the remaining carbon budget for limiting global warming to 1.5^oC with a 67% probability was of 400 GtCO₂ (IPCC, p. 29). Noticeably, the United Nations Environmental Program warned in its 2025 emissions gap report that, under the net mitigation efforts implied by current NDCs, warming would likely be kept below 2.8^oC by 2100, far from the Paris goal.

After the 2015-2016 first NDCs submissions, an incipient wave of climate litigation cases emerged questioning the ambition and overall adequacy of domestic mitigation pathways and carbon budget projections. One of the claims raised in this regard relates to their heavy reliance on the use of CDR to achieve ‘negative emissions’, questioned by some as having serious side effects and being unable to deliver the high-scale results States promise (see here and here). Conversely, some suggest CDR is a key component of climate mitigation under Article 4 of the Paris Agreement needed for carbon neutrality (on debates surrounding CDR see here and here).

As such, Courts have been faced with the question of to what extent can mitigation pathways rely on negative emissions approaches, particularly CDR, without putting into question their ambition under the Paris Agreement? This blogpost evaluates climate litigation cases that have dealt (tangentially) with this controversy and points towards some criteria that judges can adopt when assessing if the use of CDR by States aligns with climate law. In this task, science plays a significant role.

CDRs in Light of the ‘Best Available Science’

According to the different advisory opinions, the ‘best available science’ with regards to climate change mitigation is provided by the IPCC (ITLOS, §208; ICJ, §74; IACtHR, §33). The IPCC (p. 2901) has defined CDR as a series of ‘anthropogenic activities’ that remove and ‘durably store’ CO₂ in ‘geological, terrestrial, or ocean reservoirs’. The IPCC’s AR6 CDR factsheet states that these ‘technologies’ and ‘approaches’ are ‘required’ to achieve net zero emissions and are part of ‘all modelled scenarios’ to keep global warming to 2^oC or lower by 2100. Nonetheless, it warns that they should not ‘substitute’ immediate emission reductions.

CDR encompass a host of techniques, including bioenergy with carbon capture and storage (BECCS, FAQ.4.2) which consists of using plants and trees to absorb CO_2, and then turn the ‘plant material’ (biomass) into bioenergy by burning it. The IPCC (SPM.C.3) has observed that all 1.5^oC pathways rely on CDR, particularly BECCS and/or afforestation and reforestation, to draw down CO₂ emissions. Noteworthily, the IPCC (Chapter 4.3.7.1) has also acknowledged that BECCS deployment is constrained by many factors, including ‘limited public acceptance’ of both bioenergy and carbon capture, insufficient economic incentives, and overarching questions about its mitigation potential.

Thus, for the ‘best available science’, CDR is expected to become mainstream, and presumably necessary, to achieve the Paris goal with no or limited overshoot, but must not replace emission reduction. Its deployment might also face constraints due to its contested mitigation potential and side effects.

CDR in Climate Litigation: The Aurora and Urgenda Cases

The corollary of climate inaction, as warned by the IPCC (SPM.C.3.3.), is that mid- and long-term mitigation pathways will likely depend increasingly on CDR. This raises serious questions as to what extent and in which ways mitigation pathways (and, by implication, carbon budgets) can factor in these approaches. These aspects were raised in the Aurora and Urgenda cases.

In the Aurora case, the applicants argued (§111-115) that Sweden’s mitigation targets and carbon budget were over-reliant on CDR, particularly BECCS, and their capacity to neutralize emissions in an overshoot scenario. Moreover, they questioned the availability of these approaches in the time and scale pretended in the Swedish carbon budget, as well as its mitigation potential and side effects. Accordingly, they requested to rule that ‘realistic’ climate policies must be anchored on transformative measures based on existing conditions, and not ‘hopes for future technological developments’. This case was rejected in limine by the Supreme Court; hence, these claims were not addressed. However, in April 2025, the case was resubmitted and is pending judgement.

In the Urgenda case, the Dutch State claimed that a ‘high level’ of CO₂ removal could be expected from CDR in the future. The District Court of The Hague (§4.72-4.73) deemed that this viewpoint was ‘insufficiently supported’ and that it was not ‘plausible’ that techniques of this nature be applied ‘in the short term’ and hence ‘in time’. Finally, the Court stressed the importance of prioritizing GHGE reduction, and acknowledged that, according to the IPCC, later intervention increases the future need for new technologies, albeit with the ‘risks and options’ of these methods remaining ‘uncertain’. The Hague Court of Appeal (§49) upheld this position. The Supreme Court made no considerations on this subject when dealing with this case at a later stage.

CDR Approaches in Mitigation Pathways: Friends or Foes?

While climate litigators tend to frame CDR approaches as ‘foes’ in the fight against climate change, States portray them as ‘friends’. It’s true standing probably lies somewhere in between. Admittedly, CDR is (and will increasingly be) a key element of mitigation pathways and carbon budget projections aimed at achieving the Paris goal with as limited overshoot as possible.

In September 2025, the Paris Agreement parties submitted their third NDCs. Thus far, there is no comprehensive study of the use of CDR approaches in these submissions. However, an analysis of early submissions made in April 2025 (mostly of developed countries) showed that around 60% of them (12/20) contained references to CDR. This was the first NDC group to explicitly mention CDR (see here and here). Ostensibly, in 2026 and upcoming years, climate litigators will step up again to question the use of CDR within domestic mitigation pathways and carbon budget projections, as was done in the aforementioned cases. To assess when CDR deployment is consistent with ‘ambitious’ mitigation, domestic judges will have to make substantive and procedural considerations.

It has been suggested by Rajamani et.al. (p.10-12) that the stringent due-diligence mitigation obligations emanating from the recent ICJ advisory opinion, entail a series of ‘guardrails’ for the deployment of CDR. From a substantive perspective, States must ensure, among others, that: (i) emission reductions are ‘prioritized’ over CDR; (ii) removals are supported by attainable policies, and (iii) there are strategies to ameliorate any negative ramifications resulting from CDR deployment. From a procedural perspective, NDCs should, among others: (iv) establish distinct targets for emission reductions and removals; (v) provide information on the planned use of each type of removal, and (vi) disclose all methodological assumptions used to account for removals in NDCs and carbon budgets.

Theoretically, the respect of these ‘guardrails’, may serve as a ‘test’ for judges to assess in concreto if CDR deployment is consistent with international climate law. In practice, however, such evaluation may be tortuous. A major hurdle that will likely emerge in this respect pertains to the challenges many judges face when translating complex notions from climate science into the law. Incipient projects have risen to deal with these notorious barriers (see e.g. here and here). Any success in the application of the ‘guardrails test’ and the interpretation of some of its open-textured elements will depend principally on the capacity of courts to broaden their comprehension of climate science through transdisciplinary dialogue.

Conclusion

In sum, CDR has been included in the most recent NDCs (largely by developed countries) and will therefore be reflected in updated carbon budget projections. As a matter of practice, the question of whether these approaches should be included has been settled. Accordingly, attention should instead turn to developing criteria to assess when their use is compatible with the Paris Agreement framework.

While CDR approaches can lever-up global efforts to achieve climate mitigation, States should not be given a carte blanche to use them indiscreetly due to the scientific uncertainties behind their effectiveness and consequences. The above-mentioned substantive and procedural criteria suggested by doctrine can provide useful guidance for judges when evaluating whether the use of CDR in mitigation pathways and carbon budget models is consistent with States’ obligations under international climate law.

Strikingly, the successful application of the ‘guardrails test’ requires judges to expand their understanding of climate science through transdisciplinary dialogue, a challenge that is now the subject of some incipient research projects. Their success will have a ripple effect in advancing engagement between judges and complex climate science issues, like the use of CDR technologies in mitigation pathways.