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

Abstract. Given East Asia's highest CO₂ emissions, quantifying natural carbon sinks in this region is 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° N–54° N, 73° E–146° E) during 2010–2019 using a Bayesian inversion framework. The GEOS-Chem chemical transport model was combined with GOSAT ACOS v9.0 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. Most subregions in East Asia acted as net carbon sinks over the past decade. Enhanced Vegetation Index (EVI) trends also support strengthened carbon uptake. However, several regions showed temporary net carbon releases in 2015–2016, likely linked to the strong 2015/16 El Niño. 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 strengthened posterior sinks, they remain insufficient to counter regional emissions, sustaining elevated CO₂ levels and continued outflow from East Asia.