Assessing drivers of uncertainty in simulating δ¹³C-CH4 at global scale

Methane (CH₄), the second-largest contributor to global warming, necessitates a detailed examination of its sources and sinks to understand the recent rise in atmospheric CH₄ mole fractions. Atmospheric isotopic signals, especially δ¹³C-CH₄, offer critical insights for disentangling sectoral contributions and addressing these uncertainties.

This study focuses on enhancing our understanding of CH₄ sources and sinks by incorporating updated δ¹³C-CH₄ source signature datasets into atmospheric modeling. First, we updated these datasets to reflect the latest knowledge of methane emission processes. Next, we assessed the sensitivity of key modeling parameters such as atmospheric chemistry, the aggregation of δ¹³C-CH₄ source signatures, and prior flux estimates on simulated CH₄ signals and mole fractions. This analysis aims to validate the updated datasets and identify primary drivers of uncertainty in the simulations. We conducted forward modeling using the Global Circulation Model LMDZ coupled with the Community Inversion Framework (CIF), based on surface observations of methane and its isotopic signal from 1998 to 2022. These efforts lay the groundwork for improving the robustness of future isotopic inversions.

Building on these findings, our future work will focus on transitioning from forward simulations to atmospheric inversions to analyze global methane concentration trends. Initially, we will perform inversions using in-situ data from 1998 to 2022, leveraging the updated δ¹³C-CH₄ source signature datasets and setups. Subsequently, we will analyze trends from 2018 to 2022 by integrating satellite observations of total methane columns with surface isotopic measurements. This approach utilizes the high-resolution, global coverage of TROPOMI (TROPOspheric Monitoring Instrument) onboard the Sentinel-5P platform, which measures column-averaged methane dry-air mole fractions X(CH₄). By combining satellite and surface observations, we aim to enhance our ability to monitor methane dynamics and deepen our understanding of CH₄ source and sink interactions. These advancements will provide critical insights for designing more effective climate mitigation strategies.