With increasing greenhouse gas (GHG) emissions and increasingly severe climate impacts across the world in the form of droughts, floods, forest fires, desertification and more; the urgency to address climate change has never been greater. This is confirmed by findings from the UN Intergovernmental Panel on Climate Change’s (IPCC) Sixth Assessment Report (AR6) that human activity has unequivocally driven changes to the climate that are unprecedented in scale.
Whilst climate change mitigation solutions are critically important – including reducing emissions by transitioning to renewable energy, deploying energy efficiency and halting deforestation; science has shown that mitigation alone will not be enough to meet the goals of the Paris climate agreement under the United Nations Framework Convention on Climate Change (UNFCCC).
In the IPCC’s Special Report on Global Warming of 1.5°C, almost all pathways analysed relied to some extent on greenhouse gas removal (GGR) approaches to achieve net negative emissions after 2050.
It is important to note that GGR is not an alternative to reducing emissions, nor an excuse for delayed action. It is an additional solution in the transition to a net-zero future. Both emissions reduction and emissions removal need to be part of the portfolio of measures to ensure a comprehensive response to climate change.
What is greenhouse gas removal?
It is possible to capture greenhouse gases from the atmosphere and store them in various natural or artificial reservoirs. This process is best established for carbon dioxide (CO2) removal. There are many ways to remove carbon, some involving innovative technologies and others harnessing natural processes.
It is important to distinguish between emissions removal and emissions reduction. An activity can only be classified as GGR if it is removing existing greenhouse gases from the atmosphere and then storing them. For example, preventing emissions from a gas-fired power station from entering the atmosphere through their capture and storage would be considered emissions reduction (resulting in reduced, or at best, zero emissions). Similarly, a process that removes carbon dioxide from the atmosphere and uses this as an ingredient for a synthetic fuel, which when burned results in the return of the carbon dioxide to the atmosphere, is not greenhouse gas removal. In contrast, nature-based or technical approaches that remove greenhouse gases already present in the atmosphere and which store them constitute GGR (resulting in a net negative contribution).
Why do we need GGR?
Simply put, reaching global net zero emissions by 2050 is not possible without carbon removal. In fact, the term ‘net’ on a global basis implies use of greenhouse gas removal to compensate for those emissions which cannot be avoided.
- Reaching absolute zero emissions is not currently feasible, particularly for ‘harder to abate’ sectors including heavy industry (cement, steel, chemicals and aluminium) and heavy-duty transport (shipping, trucking and aviation).
- IPCC projections show that all pathways to limit global warming to 1.5°C will require 100-1000 GtCO2 of carbon dioxide removal over the 21st century.
For governments that have set net zero targets, including the UK, deploying carbon removal methods will be an important climate mitigation solution, alongside emission reduction practices. For businesses, carbon removal can play a role in reaching net zero targets, alongside action to reduce absolute carbon emissions.
Greenhouse gas removal solutions
GGR can take numerous forms from new technologies to land management practices. The various removal options can be divided into nature-based or enhanced natural processes; and those which require engineering and technology. The list of natural and technological solutions in this section is not exhaustive but covers the majority of the most widely considered GGR approaches.
Image 2: Negative emission technologies
Nature-based and enhanced natural solutions
Nature-based solutions for removing carbon from the atmosphere include afforestation, reforestation, and restoration of coastal and marine habitats.
Photosynthesis removes carbon dioxide naturally, and trees are an effective way of storing carbon removed from the atmosphere by photosynthesis. Expanding, restoring and managing forests to encourage more carbon uptake can leverage the power of photosynthesis, converting carbon dioxide in the air into stored carbon.
Enhanced natural processes include land management approaches to increase the carbon content in soil through modern farming methods.
While natural biological and chemical processes draw CO2 and other greenhouse gases out of the atmosphere, there are also engineering-based GGR solutions. These approaches are only beginning to become feasible but offer promising additional removals potential when combined with renewable electricity and/or sustainable biomass (e.g. from Afforestation).
Market readiness, cost and removal potential
Analysis from Vivid Economics shows the UK will require circa 100 MtCO2 of GGR to reach net zero by 2050, with Scotland playing a pivotal role. Even in a conservative scenario, net zero is achievable with GGR in Scotland representing a third of UK GGR by 2050.
The technology immaturity, uncertainty related to negative emissions potential and the feasible scale of different GGR methods (in terms of tonnes of emissions removed per year), are the subject of ongoing debate. However, it is possible to get a sense of the potential role of different GGR options in reducing greenhouse gases. As the GGR process is best established for carbon dioxide (CO2) removal, this section will focus on carbon removal.
The following graphic illustrates the technology readiness level (TRL), projected cost (in US$ per tonne of CO2 removed) and global CO2 removal potential (in GtCO2) for different carbon removal solutions based on data provided in the Royal Society’s Greenhouse Gas Removal report, 2018. The TRLs indicate the technology maturity on a scale from 1 to 9, with 9 being the most mature.
Note: Agroforestry, macroalgae farming and methane capture are not included as research has yet to identify removal potential and cost for these solutions.
Greenhouse gas removal mechanisms
It is important to consider the different ways in which GGR can be deployed in the net zero transition. From a business perspective, in some cases or sectors, GGR may be achieved via direct application within a business’s own operations. Businesses can also look within their own supply (or value) chain for GGR opportunities, or they may need to consider indirect GGR mechanisms where emissions are offset by funding GGR activity in another location.
Directly deploying GGR techniques is an option for businesses that have the capacity to start removing GHGs using their existing assets.
- Farmers can use nature-based solutions including agroforestry or soil carbon sequestration.
- Any landowner might reforest areas of land (recognising the need to take careful consideration of the type of species to gain the additional biodiversity benefits).
- Factories may be able to capture carbon at the source of the emissions – noting that this would be an emissions reduction, rather than greenhouse gas removal (from the atmosphere).
As opposed to carbon offsetting where an organisation pays for projects to capture atmospheric carbon dioxide in an external location, carbon insetting refers to an organisation investing in sustainable practices within its own value chain. Carbon insets support the implementation of practices, often through agroforestry and tree-planting projects, that sequester carbon, promote climate resilience, protect biodiversity and restore ecosystems.
Carbon offsetting is a process that involves either a reduction in emissions to, or removal from, the atmosphere of carbon dioxide or other greenhouse gases in order to compensate for emissions made elsewhere. Any activity that reduces emissions or involves removal of greenhouse gases from the atmosphere could constitute a carbon offset.
In the context of GGR, a company can pay for emissions reduction or greenhouse gas removal in another location and then count the associated reduction in emissions or removal of CO2 towards its own climate targets.
Whilst offsetting does not remove GHGs from the atmosphere which an organisation has directly released, it is an effective means of getting finance to flow to projects which can reduce, and remove, emissions.
Emissions reductions from offsetting projects should first be verified for accuracy by a third party. After verification, they are sold as a carbon credit or unit which represents a certain volume of emissions reductions.
Carbon credits allow companies to meet climate targets by purchasing credits for their emissions from an external source where emissions are either reduced, removed or avoided. This may then be counted towards a company’s own emissions targets.
A number of carbon offset standards and markets exist, including under mandatory (compliance) schemes and voluntary programs. Compliance markets are created and regulated by mandatory national, regional, or international carbon reduction regimes – namely those linked to national climate commitments under the UNFCCC. Voluntary markets function outside of compliance markets and enable companies and individuals to purchase carbon offsets on a voluntary basis with no intended use for compliance purposes.
For further information, read Chapter Zero’s explainer on carbon offsetting.
When should a business be thinking about GGR?
For heavy emitting industries and harder-to-abate sectors that, due to technical barriers, cannot reduce their emissions quickly enough to meet net zero targets, GGR provides an additional option to accelerate the transition to net zero emissions. Such sectors include heavy industry (cement, steel, chemicals and aluminium) and heavy-duty transport (shipping, trucking and aviation).
Some companies are well placed to directly deploy GGR techniques using existing resources, for example in certain industrial processes or in the agricultural sector.
A company may also apply carbon insetting along their value chain, as explained above. Insetting can generate GHG emissions reductions and carbon storage/removal helping an organisation to meet net zero targets, whilst simultaneously generating positive impacts for communities, landscapes and ecosystems.
For some companies, the ability to capture and value carbon may present an opportunity to become carbon negative, removing more CO2 from the atmosphere than they emit.
GGR may also present new revenue and growth opportunities for businesses by tapping into future trillion-dollar markets for products which use GHGs as an input.
As business leaders realign company strategies towards value-led approaches with long-term sustainability a core objective, they should consider:
- Innovation, supply chain and customer opportunities and risks presented by GGR approaches.
- How competitive advantage could be enhanced by engaging with GGR innovators to help them scale-up.
- What GGR approaches could be adopted to accelerate achievement of corporate climate commitments, and expand them.
- How GGR investment can align with community sustainability objectives.
UK policy outlook for GGR
Recent calls for evidence from the UK’s Department for Business Energy and Industrial Strategy (BEIS) and National Infrastructure Commission (NIC) indicate that the UK is seriously considering carbon removals as part of its wider portfolio of solutions to meet its legally binding commitment to net zero emissions by 2050, and plans set out in its Net Zero Strategy.
The scale-up of greenhouse gas removals to the level necessary to achieve net zero will require funding, public support, and a stable long-term policy framework.
Public acceptability must be considered for any potential deployment of GGR at scale. The proposed GGR solutions have a variety of risk profiles and externalities, and the publics’ acceptance of these factors will be critical for the long-term success and continued deployment of the solutions. There is a need to ensure innovation is undertaken responsibly whilst also acting with haste.
A programme of public engagement surrounding GGRs should be considered. Carbon credits for offsetting and CCS have suffered from poor public perception, branded as ‘ways to let ourselves off the hook of reducing carbon emissions’ or even as ‘geoengineering’. As highlighted in this paper, GGRs are not an alternative to emissions reduction solutions, and it is important that their role is framed appropriately.
Risks to other sectors
Deploying GGR at scale could pose a number of risks to other sectors. Direct air capture will require a large amount of energy when deployed at scale, whilst BECCS and biochar would have impact on land and water in terms of requirements for forestation. Some nature-based solutions also pose risks to biodiversity and ecosystem services.
A policy framework should recognise the key benefits and risks of different methods and use the full range of different technologies needed to tackle an issue of this scale. Doing so will allow government to make the most efficient use of land and resources, and avoid potential acute negative impacts caused by deploying technologies in isolation at a large scale.
Knowledge and skills gaps
A sufficiently experienced base of GGR practitioners has not yet been developed.
Many of the skills in sectors that will need to be phased out, such as coal and oil, could be transferred into the emerging GGR industry and therefore the risk of job losses could be mitigated with new, ‘green’ jobs.
Summary and next steps
Greenhouse Gas Removal activities will form an essential component of the global transition to net zero by 2050, as well as longer-term mitigation of climate change. Despite this, there are significant technological and research challenges yet to be addressed, and the current readiness levels of most GGR solutions are insufficient. A rapid programme of research and development to address remaining knowledge gaps, accelerate new GGR technologies and to fund, construct and evaluate pilot projects is urgently required in order to meet net zero targets.
Published November 2021
Authors and contributors:
- Harriet Harthan, Nick Scott and Emily Farnworth, Centre for Climate Engagement, Hughes Hall, University of Cambridge
- Anthony Lindley, Policy Intern, Centre for Science and Policy, University of Cambridge
- Dr Shaun Fitzgerald and Katie Parker, Centre for Climate Repair, University of Cambridge
- Ana Patricia Santana, PhD Candidate, University of Cambridge