[A-CG35] Global Carbon Cycle Observation and Analysis

[ACG35-04] Majority of atmospheric CO2 inversion models overestimate northern extratropical carbon uptake (compared to MIROC4-ACTM?)

*Suman Maity¹, Prabir K. Patra^1,2, Naveen Chandra¹, OCO2-MIP flux Team - (1.Japan Agency for Marine-Earth Science and Technology, 2.Center for Environmental Remote Sensing, Chiba University)

Keywords:OCO2-MIP flux, Atmospheric inversion, MIROC4

Carbon dioxide (CO₂) is the major anthropogenically produced greenhouse gas since the preindustrial era. Estimation of CO₂ emissions by sources and removals by sink at semi-hemispheric scale by the top-down inverse modelling approach remained inconclusive due to the lack of adequate high-quality observations and the uncertainty in atmospheric transport. We use CO₂ fluxes from a Model Intercomparison Project (OCO2-MIP, 3rd iteration or ACOS v10 OCO-2 MIP) that were conducted for situ CO₂ and Orbiting Carbon Observatory 2 (OCO-2) observations of the total-column CO₂ mixing ratio (XCO₂) for the period 2015-2020. All the OCO2-MIP and MIROC4-ACTM inversion fluxes are run forward by MIROC4-ACTM to derive flux evaluation metric (ACTM: atmospheric chemistry-transport model). The use of MIROC4-ACTM is “circular” and should be treated as a reference. Our analysis of meridionally cumulative total flux and mean concentration difference between model and observation, for the first time, shows clear dependency in the case of both in-situ (IS) CO2 and land nadir + landglint (LNLG) XCO2 data. Our best estimated non-fossil CO2 fluxes (IS) are -2.17, -0.85 and -1.18 PgC yr^-1 for the land and ocean located in the northern extratropics (north of 30N), tropics and southern extratropics (south of 30S), respectively, for the period 2015-2020.