Carbon Flux Estimation By Using AGCM-Based Chemistry Transport Model for the Period 1990−2011

Carbon fluxes were estimated for 84 regions (54 lands + 30 oceans) over the globe during the period of 1990−2011. We used (1) the CCSR/NIES/FRCGC AGCM-based Chemistry Transport Model (ACTM), (2) atmospheric CO₂ concentrations at 74 sites from GLOBALVIEW-CO2 (2013) data product, (3) Seasonally varying a presubtracted fluxes for atmosphere-ocean exchange (Takahashi et al., 2009), (4) interannually varying a priori fossil fuel fluxes (incl. cement production) from CDIAC global totals and EDGAR4.2 spatial distributions, and (5) 3-hourly terrestrial biosphere fluxes are constructed from the annually balanced CASA and JRA-25 reanalysis meteorology (Y. Niwa, Pers. Comm., 2013).

As a result of time-dependent inversions, mean total flux (excluding fossil fuel) for the period 1990−2011 is estimated to be −3.33 GtC/yr, where land (incl. biomass burning and land use change) and ocean absorb an average rate of −1.98 and −1.35 GtC/yr, respectively. The land uptake is mainly due to northern land (−1.57 GtC/yr), while the tropical and southern lands contribute −0.03 and −0.38 GtC/yr, respectively. It is also found that Boreal North America and Boreal Eurasia show negative trends in the estimated fluxes during the analysis period. The global ocean sink has no clear long-term trend in the period. Results with different inversion settings and for other regions will be discussed. Our analysis suggests that no known transport bias in ACTM forward simulation allow us to estimate CO₂ fluxes at good accuracy at hemispheric and regional scale.

Acknowledgements. This study is supported by the JSPS KANEHI Kiban-A and Global Environment Research Fund (2-1401) of the Ministry of the Environment, Japan.