[A-CG37] Global Carbon Cycle Observation and Analysis

[ACG37-02] Estimated regional CO₂ flux and uncertainty based on an ensemble of atmospheric CO₂ inversions

*Naveen Chandra¹, Prabir Patra^1,2,3, Yosuke Niwa⁴, Akihiko Ito⁴, Yosuke Iida⁵, Daisuke Goto⁶, Shinji Morimoto³, Masayuki Kondo⁷, Masayuki Takigawa¹, Tomohiro Hajima¹, Michio Watanabe¹ (1.Research Institute for Global Change, JAMSTEC, 3173-25 Showa-machi, Kanazawa, Yokohama, 236-0001, Japan , 2.Center for Environmental Remote Sensing, Chiba University, Chiba, 263-8522, Japan, 3.Graduate School of Science, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan , 4.Earth System Division, National Institute for Environmental Studies, Tsukuba 305-8506, Japan , 5.Atmosphere and Ocean Department, Japan Meteorological Agency, Tokyo 105-8431, Japan, 6.National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo, 190-8518, Japan , 7.Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Aichi 464-8601 )

Keywords:Carbon Cycle, MIROC4-ACTM, Inverse Modelling

We estimate the uncertainties in the regional carbon flux using a suite of 16 inversion cases, derived from a single transport model (MIROC4-ACTM) but different sets of a priori (bottom-up) terrestrial biosphere and oceanic fluxes, as well as prior flux and observational data uncertainties (50 sites) to estimate CO₂ fluxes for 84 regions over the period 2000-2020. The ensemble inversions provide a mean flux (posterior fluxes) field that is consistent with the global CO₂ growth rate, land and ocean sink partitioning of -2.9±0.3 (±1σ uncertainty on mean) and -1.6±0.2 PgC yr^-1, respectively, for the period 2011-2020, offsetting about 22-33% and 16-18% of global fossil-fuel CO₂ emissions. Interannual variability and seasonal cycle in CO₂ fluxes are more consistently derived for different prior fluxes when a greater degree of freedom is given to the inversion system (greater prior flux uncertainty). The posterior fluxes are further evaluated using the independent aircraft and surface measurements (not used in the inversions), which raises our confidence in the ensemble mean flux rather than an individual inversion. Differences between 5-year mean fluxes show promises and capability to track flux changes under ongoing and future CO₂ emission mitigation policies.