3 CDR Controversies
Anderson
Who is responsible for cleaning up CO2 from the atmosphere?
Various methods of carbon dioxide removal (CDR) are being pursued in response to the climate crisis, but they are mostly not proven at scale. Climate experts are divided over whether CDR is a necessary requirement or a dangerous distraction from limiting emissions. In this Viewpoint, six experts offer their views on the CDR debate.
CDR started appearing in mainstream emission scenarios in the late 2000s and has become a dominant element of most mitigation scenarios consistent with the Paris Agreement’s temperature goals. Initially, CDR was dependent on the assumed success of CCS applied to bioenergy (termed BECCS). Although there was much promise for CCS in the 2000s, including an IPCC Special Report in 2005, the technology has not yet lived up to its hope, despite lofty policy ambitions. CCS and most CDR methods are a complex set of technologies that have proved difficult to deploy at scale in real-world contexts. The repeated failure of CCS and CDR to deliver as promised has led many to question their feasibility, particularly at scale.
CDR terminology can be confusing as it combines two very different methods: restoring natural carbon sinks, such as forests, soils or oceans, and investing in unproven technologies, like BECCS, DACCS or enhanced weathering.
CDR has long been identified as a potential ‘dangerous distraction’ owing to its widespread deployment in emission scenarios but not in reality.
Given that the entire mitigation agenda is predicated on CDR working at scale, and if CDR does not work at the scale intended, then the world will go more rapidly into carbon debt and be locked into a higher-temperature pathway. A more risk-averse approach that uses only a modest scale of CDR would require greater near-term emission reductions that avoid going into carbon debt.
Enormous volumes of CDR are built into implausible mitigation scenarios for the second half of the century, generating a false sense of optimism that we can still meet ambitious temperature goals, even though global emissions are still not declining.
CDR in scenarios are effectively masking insufficient political action.
The main (IAM) modelling groups might work quite objectively, but they do so within deeply subjective political boundaries. Their low carbon futures are locked into tech-dominated versions of the present with no changes to core political elements or values of society in relation to fairness, or distribution of resources or power.
Tight political criteria, combined with very small carbon budgets, force all mitigation scenarios assessed by the IPCC to include increasingly extreme levels of CDR.
Restoration of natural carbon sinks should certainly not be used to justify any additional industrial or fossil fuel emissions. Speculative and largely unavailable CDR technologies are very different because they would require setting up entirely new industrial infrastructures at a large scale.
There is already about 2 billion tonnes of CDR occurring on land.
Big polluters and fossil fuel companies are promoting technological CDR as a cover-up for expanding their business.
The IPCC’s Working Group III report highlights the dangers of overreliance of governments on these unproven technologies. Unfortunately, these warnings are downplayed in the heavily negotiated IPCC Summary for Policymakers. They are buried under an array of models and pathways that rely on precisely such technologies, that project continued use of fossil fuels for decades and that overwhelmingly assume that the world will go beyond 1.5 °C for decades or longer — with surprisingly little attention paid to the human and environmental consequences such assumptions entail.
The major IAM modelling groups have inadvertently done the bidding of both Big Oil and those deeply wedded to the obscene asymmetry in responsibility for emissions. Since the early 2000s, these models have increasingly normalized many hundreds of billions of tonnes of CDR as a means of maintaining the political status quo and seriously delaying the need to phase out fossil fuels.
0.3 trillion tonnes of CO2 since the Paris Agreement in 2015.
An alliance has arisen between failed (and failing) political leadership and complicit IAM modelling of the community’s escalating dependence on CDR to reconcile the irreconcilable of delivering on the Paris Agreement 1.5 °C to 2 °C commitments without rocking the political boat.
As the climate is heating up, extreme weather events are becoming more frequent and we are approaching various tipping points; we risk losing the sink capacity of various ecosystems.
Industrial-scale ‘carbon farming’ to produce carbon credits is a false and dangerous promise.
It is not possible to say which CDR methods are most promising because, so far, all have failed to deploy at any meaningful scale.
It is possible to postulate theoretical pros and cons of each CDR method, but without sufficient deployment, they remain theoretical. Even afforestation and reforestation have limits, not only in terms of land competition but also in resilience to a changing climate and verifying how much carbon dioxide is removed over extended periods.
BECCS has little to no worthwhile potential, for multiple reasons. DACCS and some carefully applied nature-based solutions could have a useful role in GHG mitigation but should in no way be assumed to compensate for any fossil fuel emissions.
Important to keep a strong focus on CDR methods with characteristic timescales of storage beyond 100 years, like biochar, enhanced mineral weathering or DACCS.
CDR methods range widely regarding their climate mitigation potential, technology readiness level (TRL) and expected price range. Conventional CDR methods like afforestation, reforestation, soil carbon sequestration and peatland restoration have the highest TRL levels but do not offer long-term durability for CO2 storage. DACCS, BECCS and biochar are much more novel methods that offer strong mitigation potential and high durability and are not too far behind in terms of TRL.
The main problem is that international policymakers are implicitly relying on remarkably high volumes of CDR to help fix trajectories that already indicate a 1.5 °C overshoot, without necessarily knowing much about CDR or taking responsibility for the expected overshoot
Incorporating CDR in global scenarios is not slowing down emission reduction efforts, but it is hiding the impact of increasing global emissions and sparing climate policymakers the embarrassment of admitting that always staying under 1.5 °C is no longer achievable. But with the advent of national net-zero emission targets, the level of political scrutiny becomes higher, and it is easier to keep expectations about future national CDR levels in check.
Once governments start splitting their net-zero emission targets into emission reductions and carbon removal components, we can expect healthy national debates on the assumed trajectories, not only regarding CDR but also regarding the types and volumes of residual emissions.
Scaling up CDR could delay reducing emissions. Policymakers can address this risk by establishing separate climate targets for emission reductions and CDR.
We should cut emissions from our energy system assuming CDR will not work at scale.
Scaling these novel CDR technologies will require dedicated innovation policies.
Durability of different CDR methods are ranging from a few decades to thousands of years.It is crucial to guarantee that any residual emissions of fossil carbon are balanced by storage on the same millennial timescale
Setting up biochar production is relatively fast, hence, the reason biochar carbon removal has become the leading novel CDR method to deliver tonnes of carbon removed today. Building DACCS and BECCS plants is a longer and more complex undertaking that takes several years. Therefore, very different policy mixes and sequences must emerge to scale the vast ecosystem of CDR methods.
For direct air capture, low-carbon energy and cost are the main limitations. For biomass with carbon removal and storage, biomass and land are limitations. Other techniques face limitations in terms of land or in terms of robust schemes for monitoring and verification. The most relevant limitations will probably be social rather than technological.
There is the naive assumption that a few pilot schemes with chequered technical histories can unproblematically be rolled out at a planetary scale.
Global rates of CCS deployment are far below those in modelled pathways.