Metrics for Emissions Removal Limits for Nature

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Geosciences

Abstract

MERLiN is series of modelling studies designed to assess the limits of Greenhouse Gas Removal (GGR) effectiveness for prevention of climate change impacts, climate change reversibility, and the accounting of GGR.

Global temperature rise is determined by cumulative emissions of CO2, with climate policy temperature targets corresponding to emissions budgets e.g. 2K = around 1000 Gt C emitted. GGR is suggested as a way of recapturing CO2 some time after it has been emitted such that the eventual net quantity emitted meets a temperature target budget. Current climate mitigation action appears reliant on future application of GGR in this role to meet the international climate warming targets of the UNFCCC Paris Agreement of less than 2K and ideally 1.5K warming.

However, even if the same eventual budget is attained, it is expected that climate change impacts resulting from an emissions overshoot and later recapture pathway will be different to impacts associated with pathways in which no recapture is required. This difference in impacts sets limits to the contribution of GGR to avoiding dangerous climate change impacts. MERLiN is designed to determine these limits, and develop simple metrics relating the difference in committed climate change impacts to the amount and duration of emissions budget excess.

MERLiN will also, with international collaborators, investigate climate change reversibility, and how the Earth system (in particular the carbon cycle) respond to GGR recapture of CO2. Here, different timescales in carbon cycle components create inertia whereby emission and later recapture of CO2 do not have equal (cancelling) temperature effect. This creates an accounting challenge for GGR which MERLiN will investigate and quantify.

These results are crucial to informing policy choices and actions on GGR. Using MERLiN researcher's strong policy experience, MERLiN will translate and communicate its findings on climate change impact GGR limits, climate change reversibility, and GGR accounting to inform policy-makers on the implications for climate mitigation action, policies and mechanisms.

Planned Impact

Improved understanding of the potentials and implications of Greenhouse Gas Removal (GGR) as an approach to climate mitigation is crucial to inform climate policy developent and climate mitigation action. MERLiN is designed to assess the effectiveness and limitations of GGR to prevent climate change impacts following an overshoot of the emissions budget corresponding to climate mitigation policy targets.
MERLiN will benefit both the technical climate sceinec and climate policy communities. MERLiN advances initial studies of Earth system responses to GGR through detailed investigation of the reversibility of climate change, Earth system components and resulting climate change impacts, and how these relate to emissions budget and GGR quantities and timing. From these, MERLiN will establish limits and metrics for GGR contribution to climate mitigation, producing new understanding of Earth system behaviour, creating metrics relating GGR pathways to impacts, and assessing and defining approaches to GGR accounting. This work and its results will be of considerable benefit to climate modelling, climate change impacts and mitigation, and climate policy researchers.
MERLiN's collaboration in the Carbon Dioxide Removal Model Inter-comparison project (co-lead by MERLiN researcher Dr Scott) will strengthen this international multi-model analysis and enable greater interpretation of climate reversibility and GGR rebound experiment results.
These science advances will be published and presented at international conferences, and MERLiN researchers will undertake research collaboration visits to project partners and their respective GGR research programmes.
For the climate policy community, MERLiN will inform on the role of GGR in climate change mitigation pathway choices. International climate warming limit targets in the Paris Agreement of less than 2K and ideally 1.5K appear reliant on large scale future application of GGR including to deliver global net-GGR. Here, it is crucial to improve understanding of the ability of GGR to recapture excess emissions and any associated consequences for climate change impacts. MERLiN will assess and develop simple and communicable metrics that relate these net-GGR pathways and impacts. MERLiN will also analyse the accounting of GGR and suggest how it might be incorporated into climate policy mechanisms. These findings will be valuable to assessments of climate change for policy (e.g. IPCC), for UK and EU government officials and elected representatives. The MERLiN team has strong experience in policy communication and will prepare an accessible policy-focussed final report and host a workshop to discuss MERLiN's conclusions.

Publications

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Title Carbon accounting for negative emissions technologies 
Description Negative emissions technologies (NETs) are an essential part of most scenarios for achieving the Paris Agreement goal of limiting warming to below 2°C and for all scenarios that limit warming to 1.5 °C. The deployment of these technologies requires carbon accounting methods for a range of different purposes, such as determining the effectiveness of specific technologies or incentivising NETs. Although the need for carbon accounting methods is discussed within the literature on NETs, there does not appear to be a clear understanding of the range of different accounting challenges. Based on a systematic literature review this study identifies five distinct accounting issues related to NETs: 1. estimating total system-wide change in emissions/removals; 2. non-permanence; 3. non-equivalence of 'no overshoot' and 'overshoot and removal'; 4. accounting for incentives for NETs; and 5. the temporal distribution of emissions/removals. Solutions to these accounting challenges are proposed, or alternatively, areas for further research and the development of solutions are highlighted. One key recommendation is that carbon accounting methods should follow a 'reality principle' to report emissions and removals when and where they actually occur, and an important overall conclusion is that it is essential to use the correct accounting method for its appropriate purpose. For example, consequential methods that take account of total system-wide changes in emissions/removals should be used if the purpose is to inform decisions on the deployment or incentivisation of NETs. Attributional methods, however, should be used if the purpose is to construct static descriptions of possible net zero worlds. Key policy insightsNegative emissions technologies (NETs) raise a number of distinct carbon accounting challenges, the importance of which varies across different NETs.Attributional life cycle assessment is not an appropriate method for estimating the system-wide changes caused by the deployment of NETs.Consequential greenhouse gas accounting methods should be used to estimate system-wide changes, and should be used as much as possible for guiding incentives for NETs.Greenhouse gas accounting methods should follow a 'reality principle' to report emissions and removals when and where they actually occur. Negative emissions technologies (NETs) raise a number of distinct carbon accounting challenges, the importance of which varies across different NETs. Attributional life cycle assessment is not an appropriate method for estimating the system-wide changes caused by the deployment of NETs. Consequential greenhouse gas accounting methods should be used to estimate system-wide changes, and should be used as much as possible for guiding incentives for NETs. Greenhouse gas accounting methods should follow a 'reality principle' to report emissions and removals when and where they actually occur. 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
URL https://tandf.figshare.com/articles/dataset/Carbon_accounting_for_negative_emissions_technologies/13...
 
Title Carbon accounting for negative emissions technologies 
Description Negative emissions technologies (NETs) are an essential part of most scenarios for achieving the Paris Agreement goal of limiting warming to below 2°C and for all scenarios that limit warming to 1.5 °C. The deployment of these technologies requires carbon accounting methods for a range of different purposes, such as determining the effectiveness of specific technologies or incentivising NETs. Although the need for carbon accounting methods is discussed within the literature on NETs, there does not appear to be a clear understanding of the range of different accounting challenges. Based on a systematic literature review this study identifies five distinct accounting issues related to NETs: 1. estimating total system-wide change in emissions/removals; 2. non-permanence; 3. non-equivalence of 'no overshoot' and 'overshoot and removal'; 4. accounting for incentives for NETs; and 5. the temporal distribution of emissions/removals. Solutions to these accounting challenges are proposed, or alternatively, areas for further research and the development of solutions are highlighted. One key recommendation is that carbon accounting methods should follow a 'reality principle' to report emissions and removals when and where they actually occur, and an important overall conclusion is that it is essential to use the correct accounting method for its appropriate purpose. For example, consequential methods that take account of total system-wide changes in emissions/removals should be used if the purpose is to inform decisions on the deployment or incentivisation of NETs. Attributional methods, however, should be used if the purpose is to construct static descriptions of possible net zero worlds. Key policy insightsNegative emissions technologies (NETs) raise a number of distinct carbon accounting challenges, the importance of which varies across different NETs.Attributional life cycle assessment is not an appropriate method for estimating the system-wide changes caused by the deployment of NETs.Consequential greenhouse gas accounting methods should be used to estimate system-wide changes, and should be used as much as possible for guiding incentives for NETs.Greenhouse gas accounting methods should follow a 'reality principle' to report emissions and removals when and where they actually occur. Negative emissions technologies (NETs) raise a number of distinct carbon accounting challenges, the importance of which varies across different NETs. Attributional life cycle assessment is not an appropriate method for estimating the system-wide changes caused by the deployment of NETs. Consequential greenhouse gas accounting methods should be used to estimate system-wide changes, and should be used as much as possible for guiding incentives for NETs. Greenhouse gas accounting methods should follow a 'reality principle' to report emissions and removals when and where they actually occur. 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
URL https://tandf.figshare.com/articles/dataset/Carbon_accounting_for_negative_emissions_technologies/13...