Global and regional methane emissions for 2000-2017 estimated from CTE-CH4 - contribution to GCP methane

Methane (CH₄) is an important greenhouse gas that contributes to human-induced climate change. CH₄ is emitted from both human activities and natural sources, where the global total emissions in the 21st century are estimated to be around 526-569 Tg CH₄ per year (GCP2017). Although the global total emissions estimated by various models agree fairly well, the regional budgets and source attributions vary between the models. In this study, we estimate global and regional CH₄ emissions from a CTE-CH₄ inverse model, to better quantify the range of the estimates and emission attributions as a part of Global Carbon Project methane budget. The prior emission from anthropogenic, wetlands and peatlands, biofuels and biomass burning, termites, ocean and geological sources are taken into account, and among those, the emissions from anthropogenic and wetlands and peatlands are optimized simultaneously based on ensemble Kalman filter. The spatial resolution of the optimization is 1°x1° over Europe, and region-wise elsewhere, and on weekly temporal resolution. CTE-CH₄ employs off-line TM5 chemistry transport model, with 1°x1° zoom over Europe, constrained by ECMWF ERA-Interim meteorological data. We performed two inversions that assimilate 1) the global network of ground-based atmospheric CH₄ observations, and 2) column averaged dry-air mole fraction of CH₄ (XCH₄) retrieved from GOSAT TANSO-FTS. The estimated atmospheric CH₄ is compared with the assimilated and non-assimilated observations, and the estimated emissions are compared with other inverse models and process-based models for evaluation.