Satellite-based inversion of global methane fluxes: capabilities and implications of GOSAT-2 measurements

Methane (CH 4 ) is a key greenhouse gas with a strong climate impact and a relatively short atmospheric lifetime, making accurate monitoring essential for mitigation strategies. Satellite observations provide global coverage and independent constraints on CH 4 emission estimates, and GOSAT-2, launched in 2018 as the successor to GOSAT, was designed to improve retrieval accuracy and enhance flux estimation. This study presents an evaluation of the GOSAT-2 Level 4 (G2L4) CH 4 flux product, supported by analysis of the underlying Level 2 (L2) XCH 4 retrievals, and summarizes key findings on global and regional CH 4 budgets. Using an atmospheric inversion framework, we generated G2L4 posterior CH 4 fluxes and assessed their consistency by comparing them with inversions constrained by alternative observational datasets, including GOSAT L2 retrievals and ground-based and aircraft measurements. GOSAT-2 achieved substantial improvements in observational coverage and data density compared to its predecessor, particularly in tropical and high-latitude regions. Posterior flux estimates derived from G2L4 are broadly consistent with global CH 4 budgets reported in synthesis studies, while prior-to-posterior differences reveal positive corrections in tropical regions and negative adjustments in several mid-latitude industrial areas. A preliminary sector-focused assessment further demonstrates the potential of GOSAT-2 to inform anthropogenic CH 4 emission evaluations in regions where such sources dominate. These findings highlight the value of GOSAT-2 observations for improving regional and global CH 4 emission estimates and underscore priorities for future improvements in retrieval algorithms, observation strategies, and integration with complementary datasets. The analysis-ready subsets of the GOSAT and GOSAT-2 data used in this study are available from Zenodo (https://doi.org/10.5281/zenodo.18883060, Saito, 2026).