Top-down estimate of regional carbon sinks over East Asia for 2010–2019 using satellite observations

Abstract. East Asia is a major source of fossil fuel emissions and strongly influences regional and global CO2 concentrations. Quantifying natural carbon sinks in this region is therefore essential for improving climate projections and informing mitigation strategies. We estimated the Net Ecosystem Exchange (NEE) and ocean carbon fluxes over East Asia (18.5–54° N, 73–146° E) during 2010–2019 using a Bayesian inversion framework. The GEOS-Chem chemical transport model was combined with GOSAT ACOS v9 XCO2 retrievals, and region-specific prior uncertainties were assigned using standard deviations from land and ocean models. Posterior estimates show enhanced carbon uptake relative to the prior, with NEE increasing from −0.17 ± 0.08 to −0.31 ± 0.06 PgC yr−1 and ocean uptake changing slightly from −0.20 ± 0.03 to −0.21 ± 0.03 PgC yr−1. Simulated CO2 concentrations based on posterior fluxes agreed better with independent observations than those from prior fluxes. East Asia's terrestrial ecosystems exhibited net carbon uptake during 2010–2019, consistent with increasing Enhanced Vegetation Index (EVI) trends. However, several regions showed temporary positive NEE during 2015–2016, likely linked to the strong 2015/2016 El Niño. When fossil fuel and biomass burning are included, East Asia released a net flux of +3.45 PgC yr−1 to the atmosphere during 2010–2019. Natural sinks offset only ∼ 13.6 % of fossil fuel emissions, leaving a substantial residual source. Despite increased posterior sinks, they remain insufficient to counter regional emissions, sustaining elevated CO2 levels and continued outflow from East Asia.