22 Dec 2021

22 Dec 2021

Review status: this preprint is currently under review for the journal ACP.

Estimated regional CO2 flux and uncertainty based on an ensemble of atmospheric CO2 inversions

Naveen Chandra1, Prabir K. Patra1,2,3, Yousuke Niwa4, Akihiko Ito4, Yosuke Iida5, Daisuke Goto6, Shinji Morimoto3, Masayuki Kondo7, Masayuki Takigawa1, Tomohiro Hajima1, and Michio Watanabe1 Naveen Chandra et al.
  • 1Research Institute for Global Change, JAMSTEC, 3173-25 Showa-machi, Kanazawa, Yokohama, 236-0001, Japan
  • 2Center for Environmental Remote Sensing, Chiba University, Chiba, 263-8522, Japan
  • 3Graduate School of Science, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan
  • 4Earth System Division, National Institute for Environmental Studies, Tsukuba 305-8506, Japan
  • 5Atmosphere and Ocean Department, Japan Meteorological Agency, Tokyo 105-8431, Japan
  • 6National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo, 190-8518, Japan
  • 7Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Aichi 464-8601 Japan

Abstract. Global and regional sources and sinks of carbon across the earth’s surface have been studied extensively using atmospheric carbon dioxide (CO2) observations and chemistry-transport model (ACTM) simulations (top-down/inversion method). However, the uncertainties in the regional flux (+ve: source to the atmosphere; −ve: sink on land/ocean) distributions remain unconstrained mainly due to the lack of sufficient high-quality measurements covering the globe in all seasons and the uncertainties in model simulations. Here, we use 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 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 (without riverine export correction), offsetting about 22–33 % and 16–18 % of global fossil-fuel CO2 emissions. Aggregated fluxes for 15 land regions compare reasonably well with the best estimations for (approx. 2000–2009) given by the REgional Carbon Cycle Assessment and Processes (RECCAP), and all regions appeared as a carbon sink over 2011–2020. 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). We have evaluated the inversion fluxes using 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.

Naveen Chandra et al.

Status: open (until 10 Feb 2022)

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Naveen Chandra et al.

Naveen Chandra et al.


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Short summary
This paper is intended to accomplish two goals: 1) quantify mean and uncertainty in non-fossil fuel CO2 fluxes estimated by the inverse modeling, and 2) provide in-depth analyses of regional CO2 fluxes in support of the emission mitigation policymaking. CO2 flux variability and trends are discussed concerning natural climate variability and human disturbances using multiple lines of evidence. Finally, some recommendations are given for inversion flux comparison from multiple transport models.