Carbon removal: a crucial yet confusing element of climate mitigation

In our latest 'Hot Topics' discussion piece, Mark Preston Aragonès, policy advisor at Bellona Europa, explores rising interest in carbon dioxide removal and the opportunities and dangers this presents.

Carbon Dioxide Removal (CDR) has hit the climate agenda with a bang. The overall idea of carbon removal is straightforward but not widely understood: we must physically remove carbon dioxide from the atmosphere, put it someplace else where it will not cause harm for a very long time and, in the process, make sure we do not emit more greenhouse gases than are being removed. Storing atmospheric or biogenic CO2 with carbon capture and storage (CCS) is a leading contender to achieve this.

In the space of just 18 months, what was previously a largely niche and academic subject has become urgently and widely debated - from Microsoft aiming to remove all its historical emissions[1], to the governments of India[2] and the US[3] acknowledging that rich countries must go ‘net negative’.

Necessity, opportunity and dangers of the CDR debate

On the one hand, the rising interest in carbon removal is to be celebrated. CDR has huge potential to make our mitigation efforts more comprehensive and more cost-effective. It can cancel out the climate effect of emissions which are impossible, or prohibitively expensive, to abate and help reduce the quantity of CO2 present in the atmosphere. And a more serious discussion of CDR’s role beyond academia was long overdue. As long ago as 2007, the IPCC’s Fourth Assessment Report highlighted the need for carbon removal[4]. Bellona, meanwhile, modelled the role of biomass combustion with carbon capture and storage (Bio-CCS or BECCS) back in 2008[5], possibly making it the first NGO to do so. While inaction on climate mitigation continued, the importance of CDR became clearer and more urgent. The IPCC’s 2014 Fifth Assessment Report and 2018 Special Report on 1.5°C expanded on the need to remove more carbon.

As long as we continue to dump vast quantities of greenhouse gases into the atmosphere, the need for CDR will become greater and more urgent. The growing calls for CDR are a direct result of decades of inaction and failure to reduce emissions at a pace commensurate with the climate crisis. It is clear that, if we are to prevent the worst impacts of climate change, we need real and robust carbon removals, hand in hand with enormous emission cuts.

On the other hand, the explosion of hype surrounding carbon removal must be managed. The framing of ‘net zero’ and the Paris Agreement’s aim of achieving a balance between emissions and removals, risk creating complacency, if accompanied by an erroneous expectation that large amounts of continuing emissions can be offset. While it is increasingly clear that not all greenhouse gas emissions can be fully eliminated within the next few decades, the ambition should still be to reduce emissions as much as possible, rather than using removals to supposedly neutralise their impact.

A major concern is that emissions and removals are not necessarily equivalent. Usually, ‘emissions’ take carbon from a geological store and place it in the atmosphere. ‘Removals’ are an attempt to reverse this process, with varying degrees of difficulty and equivalence. Many types of removals store carbon in the biosphere, such as trees and soils, thereby taking it out of the atmosphere but keeping it within the natural cycle. Carbon retained in this way runs a high risk of being re-emitted in a warmer future through increasingly likely extreme weather events, such as droughts or forest fires. Despite this, it is abundantly clear that significant efforts must be taken to not only preserve, but also enhance, natural land sinks which already act as a huge ‘carbon sponge’. Ensuring we do this without forgetting other equally important criteria, such as biodiversity and water consumption, will show that deploying ‘nature-based solutions’ are inherently worth the effort. However, it is wrong to assume that these natural carbon removals can be used to offset fossil carbon emissions; these removals are not as ‘permanent’ as the emissions they aim to balance out. We must both increase natural sinks and also reduce fossil carbon emissions - not play one off against the other.

In the few cases where reducing emissions may not be an option, offsetting them could be done with carbon removal solutions that are more long term. Direct Air Capture and Bio-CCS take carbon from the atmosphere and store it in geological formations, effectively removing it from the carbon cycle. These types of carbon removal might be seen as the reverse of fossil emissions; using them as offsets could be justifiable as long as the process does not emit more carbon than it removes. These longer-term removals are noticeably more expensive than their nature-based counterparts, but are likely to be just as necessary to reach net-zero emissions. From a climatic perspective, if offsets are to be used, only carbon removal with reliable long-term storage such as Bio-CCS and DACCS, can be justified.

The sheer effort required to meet the aims of the Paris Agreement combined with these varying degrees of equivalence, means we must not fall into the trap of offsetting emissions which are possible to abate. However, this logic permeates climate modelling and policy, and has filtered through to society-at-large.

To get CDR right, we need to understand what it is – and is not

It is now a regular occurrence to see companies and countries make pledges to be ‘net zero’, or ‘carbon neutral’ or even ‘climate positive’ without providing much detail on how they will achieve this or what they mean when they use these terms. There is nothing inherently wrong with setting long-term climate neutrality targets. However, failing to follow them up with concrete and transparent climate-compatible pathways has left the door open to all sorts of manipulations and misunderstandings

The confusion starts already with the concepts of net zero, net negative and carbon removals themselves, even in academic literature[6]. It is no surprise that it also extends to the wider public. Without basic principles to qualify carbon dioxide removal, the conversation can very quickly go off the rails. This is why the four principles below should always be the starting point for conversations about CDR[7]. Any project or process must respect all the principles to be able to qualify as ‘carbon removal’:

  1. Carbon dioxide is physically removed from the atmosphere.
  2. The removed carbon dioxide is stored out of the atmosphere in a manner intended to be permanent.
  3. Upstream and downstream greenhouse gas emissions, associated with the removal and storage process, are comprehensively estimated and included in the emission balance.
  4. The total quantity of atmospheric carbon dioxide removed and permanently stored is greater than the total quantity of carbon dioxide equivalent emitted to the atmosphere.

These principles state the obvious. Yet many alleged carbon removal solutions fail to meet these simple criteria. With these principles in mind, it is easy to spot the egregious mistakes which are peppered around climate discussions.

A few weeks ago, UN climate envoy Mark Carney, initiator of the Taskforce on Scaling Voluntary Carbon Markets, provoked an uproar when he declared that the financial firm he works for is ‘net zero’ because it finances renewable energy[8]. This error of judgement, which he subsequently corrected, points to the wider confusion around the concept of ‘net zero’. At the same time, consultancy EY recently pledged to be ‘carbon negative’ this year before reaching ‘net zero’ by 2025[9] exemplifying the confusion of what these two terms actually mean - since reaching ‘net zero’ is on the pathway towards going carbon negative. As a result, the use of ‘net zero’ is often questioned[10], partly because its constructive ambiguity is often confusing or used in confusing ways, as illustrated by Carney’s gaffe or EY’s pledge.

In the wild west of carbon removal, companies are exploiting the absence of standards to market products or rebrand emission reductions in different ways. Some ignore the need for storage, by selling ‘carbon-negative sunglasses’[11] or ‘climate-positive carpets’[12]. Others ignore the source of the CO2, seeking to rebrand conventional fossil CCS projects as carbon removal. Even worse, some ignore both, promoting ‘carbon-negative fuels’, where the CO2 is from fossil sources and the storage is non-existent. Perhaps worst of all, some simply go against baselines to claim ‘carbon negativity’, rebranding avoided emissions as CDR. These are just a few real examples which make CDR look more achievable than it really is.

In reality, CDR is challenging. Firstly, removing material amounts of CO2 from the atmosphere requires considerable resources, be they water or land or renewable electricity, among other things. The models used in the IPCC’s Special Report on 1.5°C require such a large amount of Bio-CCS that an area the size of India would be needed to grow the necessary biomass[13]. Powering DACS, meanwhile, requires renewable energy that may well be of better use for powering electric vehicles.

Secondly, storing CO2 for a very long time is not a given. Storage can be reversible (for example, because climate change can lead to forest dieback) and has different timelines (for example, because forests take a long time to grow or regrow). It is expensive, and is, in many ways, difficult to reliably prove. Carbon removal methods need significant advancements not only in their development, but also in how they can be verified and monitored. Progress has been quite slow, but until these accounting issues are resolved, carbon removal will be difficult to quantify (and credit). The European Commission is working on addressing these unknowns and will propose a certification mechanism by 2023.

In this sense, the hype on carbon removal is putting the cart before the horse. So much so, that its basic tenets – removal of atmospheric CO2 and permanent storage – are often discarded. Nevertheless, some carbon offset purchasers are starting to do their homework. Microsoft, for instance, last year issued a Call for Tender to remove 1 million tons of CO2. It then transparently listed all the applications it received and those subsequently funded. The selection criteria prioritised quality over quantity, a necessary approach in the early days of carbon removal. Projects had to be robust and quantifiable, with carbon stored for as long as possible. This first attempt at purchasing removals was not perfect, but headed in the right direction; it illustrated the current limitations with removals, such as scale, durability and reliability, and provided useful steps forward. Other companies, such as Stripe, Shopify and SwissRE, are attempting similar exercises.

A regular finding in these endeavours is that removing CO2 using technology and storing it in geological formations or minerals is more reliable and traceable than doing so through natural means. This is particularly the case if the ulterior motive is to use the carbon removal as a credit. Nature-based removals do not lend themselves to being creditable and tradeable; the more expensive engineered solutions involving CCS could be more robust for this purpose. Underlining the need for permanent storage of CO2 helps to shift the CDR conversation more broadly to solutions which can reliably meet this requirement


The growing interest in carbon removal is a positive development. However, expectations must be managed. Removing CO2 is not a simple endeavour, nor is it an excuse to delay emission reductions. In fact, growing dependence on carbon removal is a sign that we are not doing enough to cut emissions in the first place. We must be wary of outlandish claims and work on developing the right framework to deploy real and robust carbon removals. The first step is to acknowledge what CDR is and its purpose. Otherwise, we may well end up with a system which bears no link to reality. Setting out the principles which define CDR is the starting point to prevent this.




Image: © Bellona Foundation, 2021. All rights reserved.