Lack of harmonisation of greenhouse gases reporting standards and the methane emissions gap.

Monitoring companies' contributions to climate dynamics and their exposure to transition risks requires accurate measurements of their non-carbon dioxide greenhouse gas emissions (non-CO2 GHG). However, carbon accounting standards are not harmonised and allow for some discretion when converting emissions of different GHGs into CO2 equivalent units, the currency in which carbon footprints are expressed. Focusing on methane, we build counterfactual harmonised standards using the latest IPCC Global Warming Potential (GWP) values over 100 years and estimate a cumulative gap in reported methane emissions of 170MtCO2e ( ~6Tg) over a sample of 2864 companies. Changing the counterfactual from GWP100to GWP20, as recently codified in certain jurisdictions and initiatives, increases the cumulative gap to 3300MtCO2e ( ~40Tg). The gap only covers direct emissions and hence understates the extent of potential under-reporting across value chains. Overall, our study underscores the importance of global harmonisation of CO2-equivalence standards to coherently track corporate GHG emissions and their exposure to transition risks.