Human-made systems
CDR methods require different amounts of material, energy and financial resources in various steps of their supply chain. For instance, DACCS captures CO₂ from ambient air, compresses it and sends it to geological storage, requiring (human-made) energy and chemical solvents. These demands may impose additional pressure on material and energy supplies, as well as on waste disposal management. In contrast, CDRs such as BECCS could produce excess energy to be fed into the energy system. However, this could come at the expense of increased natural resource demand, such as land and water, which could inhibit their scale up.
As shown in these examples, CDRs can both require inputs from and/or provide useful output for the wider socio-techno-economic systems. To monitor these interactions, we recommend assessing several indicators, i.e. energy and material footprints, infrastructure requirements, and total costs. Whilst this set of indicators is not comprehensive, it enables comparing the relative ease by which different CDRs can be integrated into existing human-made systems and the key enabling factors for their scale up over time.
Energy footprint
The energy footprint is defined as the sum of the net¹ amount of energy consumed in each stage of the CDR supply chain. This includes, for example, energy used in biomass management, in transport processes and in CO2 capture processes. The energy footprint can be defined as megajoules of energy per tonne CO₂ removed to enable cross-CDR comparison. As we measure this footprint per tonne CO₂ removed, is important that CDRs prioritise phasing out fossil fuels from their supply chains, as the higher the fossil content of the CDR energy supply, the lower the net removal. A low CDR energy footprint means less dependency on the wider energy system, which makes the CDR easier to scale.
Critical materials footprint
The critical material footprint is defined as the total amount of critical materials consumed across the full life cycle of the CDR. This can be defined using a unified unit of kilogrammes of critical material per tonne of CO₂ removed to enable cross-CDR comparison.
A low CDR critical materials footprint means less dependency on critical materials availability. This reduces the reliance on an already scarce resource, therefore making the CDR easier to scale.
Infrastructure requirements
The establishment of adequate infrastructure is critical to the scaling up of any CDR. While some CDRs benefit from established infrastructure, e.g. afforestation, other CDRs, e.g. BECCS and DACCS, require new infrastructure to transport CO₂ to the geological storage. The type of new infrastructure also matters, especially if it includes processes or materials considered hard-to-decarbonise, to avoid making climate mitigation harder.
Economic costs
The economic cost indicator captures the full cost of delivering carbon removal, across the entire life cycle of a CDR project. Beyond the immediate expenditure involved, this indicator also considers a project’s longer-term economic sustainability. A viable CDR method should ideally become self-sustaining over time, rather than relying indefinitely on external support to cover its costs.
Since CDR projects vary enormously in scale and structure, comparing costs meaningfully means looking at cost per tonne of CO₂ removed, rather than total project cost alone. This allows for a fair, like-for-like comparison of economic viability across otherwise very different CDR methods.
1 This is defined as total energy use – energy consumed in each stage, to account for the co-production of energy (e.g. electricity, heat) in BECCS and biochar projects.