Human-made systems
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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. We recommend using a unified unit of MJ energy/t 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.
The energy footprint should include all relevant energy consumption and production processes, e.g.
- BECCS: energy consumption in farming and forestry activities, biomass feedstock preparation (e.g., pelleting and drying) and transport; CO2 capture, compression, and transport to storage + energy production;
- Enhanced Rock Weathering: energy consumption for rock crushing and transport, spreading on soil.
- DACCS: energy consumption for CO2 capture, compression, and transport to storage.
A low CDR energy footprint means less dependency on the wider energy system, which makes the CDR easier to scale.
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.
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. We recommend using a unified unit of kg critical material/t 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.
To enable faster CDR scale-up we recommend a statement on infrastructure requirements and expectations that indicates how contingent the CDR is on certain infrastructure assumptions. It is important to state whether new infrastructure needs include processes or materials considered hard-to-decarbonise, to avoid making climate mitigation harder.
Economic costs
The cost of CDR removal can be estimated by considering costs associated with the full life cycle of delivering that removal, as described in the Removal dimension. The economic costs of removal should be sustainable over time, e.g. the CDR supply chain should become self-sustaining in economic terms, lessening the costs on the wider system. The economic costs of the CDR include expenditures on e.g. energy, infrastructure, labour- costs.
A good indicator of the removal cost is the annual capital and operating expenses. To allow for a consistent comparison across different CDR projects, these costs should be normalised on the net amount of CO₂ removed, estimated as described in the ‘Net GHG flux’ indicator in the GHG Removal dimension.