Safe scale-up of CO₂ removal is needed to tackle hard-to-abate emissions and climate risks

Key messages

• Carbon Dioxide Removal (CDR) is essential for meeting Paris Agreement goals and is a necessary complement to deep and sustained GHG emissions reductions. Yet, current national plans fall far short, creating an emerging ‘CDR gap’.
• Large-scale CDR deployment entails significant sustainability risks, competing for land, energy, and materials, and should be limited to compensating for hard-to-abate residual emissions and, eventually, to achieving net-negative removals, rather than being used to offset additional emissions from sources in which abatement options are readily available.
• Novel CDR methods are technically feasible and are beginning to be deployed at scales of tens of millions of tons. Dedicated support for research, development, and deployment is needed to accelerate progress to close the CDR gap.
• Additionally, significant ‘preventive CDR’ capacity is needed to stabilise temperatures in the longer term through net-negative removals, especially to hedge against climate system uncertainties.

To achieve the Paris Agreement’s climate objectives, we must scale up CO₂ removal (CDR) alongside deep and sustained emissions reductions. Yet there are risks and uncertainties. Recent evidence shows that scale-up is limited by sustainability constraints, and using it to compensate for otherwise unavoidable emissions risks falling far short of climate goals. A “preventive CDR capacity” is also needed for overshoot (see Box 3 for definitions, henceforth indicated with *) and to hedge against physical climate uncertainties, but countries are failing to plan and implement an adequate scale-up (Figure 8).

CDR involves extracting CO₂ from the atmosphere and storing it in geological sinks, the biosphere, or products (e.g., harvested wood). “Conventional” methods* include afforestation/reforestation and forest management practices, while “novel” methods* such as Bioenergy with Carbon Capture and Storage (BECCS), Direct Air Carbon Capture and Storage (DACCS), enhanced weathering, carbon mineralisation, and biochar, are technically feasible but not yet scaled up. Current deployment is primarily conventional and low, at 2 Gt CO₂/yr, while overall net emissions from land use and forestry are about 4.4 Gt CO₂/yr, so emissions from deforestation and peat fires still significantly outweigh CDR in the land sector.

A key purpose of CDR is to compensate for future “residual emissions”*, and allow countries, cities, or companies to achieve net-zero emissions targets by a given date (Figure 8A). Residual emissions will remain because it may not be possible to eliminate all emissions sources, especially those that are “hard-to-abate”* due to high mitigation costs and limited substitution options, such as emissions from livestock, international aviation, and some heavy industry. These sectors could still reduce emissions via demand-side measures.

The interplay between CDR and residual emissions can be observed in integrated assessment modelling (IAM) scenarios. For example, CDR deployment across 81 scenarios (type C2 scenarios, i.e., 1.5°C with high overshoot*) averaged over 2050–2100 balances residual emissions of CO₂, N₂O and F-gases* over the same period. Though later in the century, CDR often reaches higher levels, becoming substantially larger than the residual long-lived greenhouse gas emissions. In C1 or C3 scenarios (i.e., 1.5°C or 2°C scenarios with no/limited overshoot, respectively), modelling suggests a slightly smaller average over 2050–2100, so residual emissions remain higher.

The risks to sustainability implied in the deployment of CDR at the levels envisioned in these models are great. Conventional CDR will compete with both food production and biodiversity protection for land, while novel CDR at scale could require significant energy and materials (Figure 8B). More sustainable C1–C3 scenarios which take into account these considerations have lower overall CDR deployment levels and more stringent and deep emissions reductions in the near term.

Given sustainability constraints, it is important to minimise emissions such that achievable CDR capacity is available to compensate for the residual emissions from truly hard-to-abate sectors that serve critical needs (Figure 8C). Yet many IAM scenarios deploy CDR to compensate for emissions that are relatively easier to abate, such as the power sector, where cost-effective alternatives are readily available. Similarly, voluntary carbon markets and company net-zero targets will need to adjust for a limited supply of CDR.

Another purpose of CDR is achieving long-term global temperature decline after overshoot. Most studies focus on median warming scenarios, like a 50% chance to limit warming to 1.5°C by 2100. However, assessing overshoot risks and CDR requirements for warming reversal requires accounting for uncertainties in Earth system feedbacks. If these are stronger than expected, it could require hundreds of gigatonnes of additional CDR, beyond current pathway estimates. In a 1.5°C no-overshoot pathway, it is estimated that high-warming outcomes (which have a 1-in-4 probability of occurring) would need CDR deployment up to 400 Gt CO₂ (cumulative) by 2100, approximately double the amount in IPCC AR6 WGIII scenarios.

It is increasingly important to evaluate national plans for implementing and scaling CDR activities. In their Nationally Determined Contributions (NDCs) and Long-Term Low-Emission Development Strategies (LT-LEDS) under the Paris Agreement, countries currently plan only minimal additions of 0.05–0.53 Gt CO₂/yr by 2030, primarily through conventional CDR methods. By 2050, additions of 1.5–1.9 Gt CO₂/yr are suggested in the LT-LEDS, potentially including novel CDR methods (Figure 8C). These plans fall short of the scenario levels needed to limit warming to 1.5°C, even in scenarios focused on reducing demand and limiting CDR dependence. This indicates an emerging “CDR gap” between country plans and needed future deployment levels. More ambitious commitments, early policy support for CDR, and strengthened emissions reductions, especially with a view to minimising residual emissions, are necessary to close the gap.

Despite the critical role of CDR, dedicated deployments, finance, and policies to support large-scale implementation are limited. Without robust and comprehensive policy action in the near term, achieving the CO₂ removal required by mid-century will be a challenge. Funding for research, development, and demonstration projects across multiple CDR pathways is required to foster a diverse portfolio of solutions, which will be necessary to address sustainability constraints. Policies should also include incentives for commercial-scale deployment, as well as regulatory support for high-quality monitoring, reporting, and verification. Policymakers must implement ambitious emissions-reduction policies, alongside measures to scale up CDR and minimise residual emissions from hard-to-abate sectors and reduce energy demand. Importantly, policies will be most effective if they consider regional constraints, equity, fairness and procedural justice. Responsibilities for sharing the burden of preventative CDR can be based on equity and fairness principles.

At COP28, discussions emphasised the need for global commitments to scale CDR technologies alongside emission reductions. An important first step is to strengthen net emission reduction pledges in the NDCs while increasing transparency and clarity on the role of CDR in meeting these targets. While associated sustainability risks exist and must be accounted for in policies and pledges going forward, they must also be balanced against the risks of inaction – risks that will disproportionately affect vulnerable populations. The urgency of scaling up CDR and achieving net-negative emissions cannot be overstated. They are critical to mitigating the severe impacts of climate change.