Development and application of regional inversion systems for China’s methane emission tracking and mitigation

Methane (CH₄) emission mitigation has become the critical and urgent strategy for controlling near-term climate change. Identifying key emitting regions, quantifying their contributions, and elucidating the underlying drivers have become pressing needs. However, regional CH₄ emissions remain constrained by diffuse emission sources, limited monitoring capacity, and complex inversion frameworks. To address these challenges, we developed two independent regional inversion systems and applied them to deliver multi-year CH₄ emissions estimates for China, the world’s largest anthropogenic CH₄ emitter.

Given the difficulty in attributing observations to specific source regions and the scarcity of surface monitoring stations, we presented an innovative regional CH₄ inversion system integrating satellite-based carbon monoxide (CO) observations with ground-based CH₄-to-CO flux ratios. Our study estimates China’s CH₄ fluxes between 2000 and 2021, revealing an average of 48.4 ± 13.8 Tg yr⁻¹ and a significant increasing trend of 1.1 ± 0.2 Tg yr⁻². Socioeconomic development drove a 92.1 Tg cumulative increase over this period, partially offset by a 78.1 Tg reduction due to declining emission intensity; however, this mitigating effect weakened after 2015. The approach is validated against independent estimates and supported by comprehensive sensitivity and uncertainty analyses. It demonstrates the feasibility of deriving reliable emission estimates for large-scale regions from single‑site measurements, offering an affordable and practical tool that integrates air-pollution data into regional greenhouse-gas quantification and mitigation.

To obtain higher temporal resolution and enable spatial and sectoral attribution of emissions, we further built a regional atmospheric inversion framework based on the Local Ensemble Transform Kalman Filter (LETKF) algorithm and constrained by TROPOMI satellite data. Built on the global GEOS-Chem CHEmistry and Emissions REanalysis Interface with Observations (CHEEREIO) tool, our study supports high-resolution regional inversion. Applied to East Asia at 0.5° × 0.625° resolution, this system produces weekly CH₄ fluxes for China during 2019–2024. We show that China’s CH₄ emissions increased from 61.1 (56.2–66.7) Tg in 2019 to 66.8 (61.5–73.0) Tg in 2024. The livestock sector contributed nearly half of the growth, while rising waste and oil-gas emissions and northward expansion of rice cultivation shifted China’s emissions growth to previously low-emitting Northwest and Northeast regions. This framework demonstrates the feasibility of near-real-time, regional-scale emissions monitoring, offering a transferable tool for other high-emitting countries for long-term emission monitoring. In summary, these two inversion systems advance the capability to track and attribute regional CH₄ emissions, provide scalable, cost‑effective, and policy‑relevant tools for clarifying emission patterns, tracking mitigation progress, and supporting national and global climate action.