Professor Myles Allen CBE FRS

Abstract:

With the 1.5 °C target rapidly approaching, net-zero emissions plans routinely call for the rapid expansion of offsets based on carbon removals. This is particularly true in sectors such as aviation, where decarbonisation options are limited or progressing slowly. To comply with like-for-like offsetting requirements, such sectors will likely rely on durable CO₂ offsets, which may be delivered through bioenergy production or direct air capture combined with geological CO₂ storage. If geological CO2 removals are to ensure broad societal buy-in and market integration, they must be underpinned by robust Measurement, Reporting and Verification (MRV) and certification systems. These systems must also be recognised by a diverse set of policies, standards, and voluntary schemes.This study investigates what certificates for geological CO₂ removal would need to look like to play a meaningful role in the decarbonisation of the aviation sector. Aviation provides a relevant focus because it is a strong use-case for high-durability offsets since direct decarbonisation options such as sustainable and low-carbon aviation fuels have high energy demands and feedstock limitations. Moreover, these options partially overlap with components of geological CO2 removals and similarly rely on extensive certification under aviation climate policy frameworks.  To address this question, we conduct a comprehensive empirical assessment that: identifies the most common MRV and certification criteria embedded in leading policies and standards; and evaluates the certification requirements for geological CO₂ removal. Based on this mapping, we identify priority design features that geological CO₂ offsets would need to satisfy to achieve policy recognition and market uptake in aviation.To do so, we analyse a corpus of 10 policies and over 45 supporting documents, including carbon-crediting and voluntary carbon market (VCM) frameworks, as well as aviation-related policies and fuel mandates. These control the design of certification programmes and how geological CO2 removals may integrate in the aviation sector. We combine natural-language processing with an LLM-as-a-judge approach to assess the presence and strength of certification criteria across policies, followed by manual expert coding of a subset to identify differences in requirements. These 38 criteria span governance, adaptability, quantification, counterfactuals, MRV, permanence, accounting integrity, and sustainability safeguards.We find that criteria most consistently present across both policy families relate to MRV (reporting, verification, recordkeeping), quantification (system boundaries, demonstrable climate benefits), counterfactuals (baselines and leakage), and accounting (registries and tracking) and governance (compliance). Fuel policies place stronger emphasis on quantification, boundaries, reporting, and compliance, but tend to be less specific with respect to governance, permanence, long-term accounting, and social safeguards. When manually assessing certification requirements, we find recent certification standards (Paris Agreement 6.4, ICVCM, CRCF) to perform best as they have extensive and specific requirements. Fuel policies, on the other hand, are more explicit in their treatment of lifecycle quantification for narrowly defined pathways.

Abstract:

Net-zero targets are widely adopted by companies and countries worldwide. To achieve these goals, more companies are investing in diverse carbon removal portfolios. This study develops a new risk management framework that combines forestry, biochar, and geological storage offsets into portfolios that could stabilize global temperatures over multi-century time periods. We find that if a carbon storage portfolio reaches an equilibrium state of CO2 stored, it can be leveraged to stabilize global temperatures by increasing the size of the portfolio relative to the amount of removal claimed. For moderate-risk primarily forestry portfolios retaining 0.75–0.55 tCO2 of the 1 tCO2 stored, an additional 0.30–0.80 tCO2 removal is needed to offset re-releases over 1,000 years. High-risk portfolios retaining only 0.10 tCO2 require over 9 tCO2 additional removal. Portfolios that are predicted to re-release almost all CO2 cannot be leveraged and are ineffective at meeting temperature stabilization goals. These findings have implications for policy and corporate climate action.

Abstract:

<jats:title>Abstract</jats:title> <jats:p/>