Quality of reporting
Greenhouse gas removal can be delivered through a multitude of options, each involving different material and energy requirements, different practices in different locations, resulting into quite different footprints on the environmental, social and economic environments in which the GGRs are deployed. Evaluating and comparing such different GGR systems needs to be done on a common base, so their climatic merits, co-benefits and impacts can be reported and compared in the same terms.
Three key factors underpin this common base, namely the definition of consistent boundaries around what constitutes a complete GGR life cycle, the definition of a counterfactual or what would have happened in the absence of specific GGR deployment, and a clear set of GGR specific Monitoring, Reporting and Verification (MRV) criteria and guidelines.
Our guidelines for the definition of GGR system boundaries and counterfactual scenarios follow the Life Cycle Assessment methodology. In particular, we adopt the GHG Protocol Policy and Action Standard guidelines for defining consistent system boundaries and counterfactual scenarios of what would have happened in the absence of GGR deployment.
Definition of GGR system boundaries
A coherent GGR evaluation needs to consider all changes caused by the deployment of the GGR within a relevant timeframe to climate change. These include all direct and indirect emissions and removals caused by the deployment of the GGR, including the stages in which CO2 emissions from the atmosphere are captured, the stages in which captured CO2 is stored, all processes connecting the capture and storage of CO2, and all the indirect effects, including market mediated, and material or energy displacement effects, e.g. displacement of renewable energy from heat decarbonisation to removals by DACS. Indirect effects also include effects induced by co-production of other useful products alongside GHG removal, e.g. energy generation by BECCS projects.
It is rare that one project or company controls the full supply chain of a GGR. Each GGR operation is location specific and may change over time, as technologies and processes along the supply chain evolve. However, for a comprehensive evaluation it is important to consider the full supply chain of each GGR, so co-benefits and impacts are measured consistently across all GGRs.
To evaluate the completeness of the boundary definition reported by each GGR project, we propose using a scale 1 to 5, with 1 representing incomplete or partial boundaries, and 5 representing complete representation of the GGR option, including its interactions with the wider system and specification of the assessment period:
5. Comprehensive causal and temporal boundary definition, including documentation of choices
4. Complete causal boundaries, partial description and justification of temporal boundaries
3. Partial causal chains and/or no justification of exclusions. Partial or no temporary boundaries set
2. Causal boundary defined for processes under control only, no temporal boundary
1. Absent definition of causal and temporal boundaries
The score indicates how confident we are with the evaluation of a GGR. The higher the score is, the more confident we feel with the evaluation.
Once a score is estimated, users should strive for improving it through re-drawing the system boundaries to cover as much as possible the complete GGR system, following the guidelines set by the GHG Protocol Policy and Action Standard.
Definition of the counterfactual
Assessing the removal provided by a GGR as a simple balance between emissions and sinks across its supply chain ofers a partial view of the contribution of the GGR to removing atmospheric GHG and may lead to decisions contributing to further increasing atmospheric GHG emissions. For instance, a BECCS supply chain using forestall residues from an intensively harvested forest may deliver removals overall. However, if leaving the forest unharvested would have fixed more CO2 over the timeframe of analysis, e.g. 100 years, then the BECCS supply chain would in effect contribute to increasing GHG emissions over that time. A scenario definining what would have happened in the absence of GGR deployment is called a counterfactual, reference, or baseline scenario.
The overall removal estimation in the counterfactual vs the GGR deployment scenario should be done based on the same system boundaries, with the same accounting rules, and considering all key emission and removal drivers over the assessment period. This means that every emission sink and source category is included in the two scenarios, albeit under different circumstances, i.e. with and without deployment of the GGR option. Note that if the GGR project delivers co-products, the delivery of these in the same amount should be also included in the counterfactual, although delivered by alternative processes. It also means that the same IPCC factors should be used for the global warming potential values. Finally, drivers should include both policy drivers, such as implemented or adopted policies, as well as non-policy drivers, such as economic conditions, energy prices, and technological development. If more than one set of drivers can be demonstrated as plausible, both should be considered, resulting into two or more counterfactuals.
The accuracy of counterfactual definition is assessed on a scale 1 to 5, with 1 representing incomplete/partial counterfactual and 5 representing a well evidenced counterfactual, covering the complete system boundaries, accounting methods, and key drivers:
5. Plausible and well documented baseline(s). Covers all sinks and sources of GHG considered in the GGR deployment scenario(s). Includes all key drivers
4. Complete baseline, partial drivers. Partial policies. Partial description of driver and parameter assumptions
3. Plausible and documented baseline. Unclear data sources. No description of driver assumptions
2. Partial baseline. Covers key sources and sinks, but incomplete boundary coverage. No policy and non-policy drivers
1. The project does not define a baseline
A high score in this case means that the counterfactual is robustly defined, hence the GGR case can be compared like-to-like against the counterfactual, to inform the real benefits and impacts from deploying the GGR option. For instance, the difference between the removals in the counterfactuals vs the GGR deployment scenarios will better characterise the uncertainty range around the size of removal delivered by a specific GGR option.
Once a score is estimated, users should strive for improving it as much as possible by using the guidelines set by the GHG Protocol Policy and Action Standard.
Dr Jo House, University of Bristol (CO2RE)
Dr Isabela Butnar, UCL (CO2RE)
Dr Sylvia Vetter, University of Aberdeen (Enhanced rock weathering)
Prof Astley Hastings, University of Aberdeen (Afforestation)
Dr Jon Mckechnie, University of Nottingham (Biochar)
Dr Mirjam Roeder, Aston University (Peatlands)
Dr Phil Renforth, Heriot Watt University (Enhanced rock weathering)
Prof Timothy Cockerill, University of Leeds (Biochar)
Dr John Lynch, University of Oxford (CO2RE)
Dr Eleni Michalopoulou, University of Bristol (CO2RE)