Recent global CO<sub>2</sub> flux inferred from atmospheric CO<sub>2</sub> observations and its regional analyses

Abstract

Abstract. The net surface exchange of CO 2 for the years 2002-2007 is inferred from 12 181 atmospheric CO 2 concentration data with a time-dependent Bayesian synthesis inversion scheme. Monthly CO 2 fluxes are optimized for 30 regions of the North America and 20 regions for the rest of the globe. Although there have been many previous multiyear inversion studies, the reliability of atmospheric inversion techniques has not yet been systematically evaluated for quantifying regional interannual variability in the carbon cycle. In this study, the global interannual variability of the CO 2 flux is found to be dominated by terrestrial ecosystems, particularly by tropical land, and the variations of regional terrestrial carbon fluxes are closely related to climate variations. These interannual variations are mostly caused by abnormal meteorological conditions in a few months in the year or part of a growing season and cannot be well represented using annual means, suggesting that we should pay attention to finer temporal climate variations in ecosystem modeling. We find that, excluding fossil fuel and biomass burning emissions, terrestrial ecosystems and oceans absorb an average of 3.63 ± 0.49 and 1.94 ± 0.41 Pg C yr −1 , respectively. The terrestrial uptake is mainly in northern land while the tropical and southern lands contribute 0.62 ± 0.47, and 0.67 ± 0.34 Pg C yr −1 to the sink, respectively. In North America, terrestrial ecosystems absorb 0.89 ± 0.18 Pg C yr −1 on average with a strong flux density found in the south-east of the continent.

Inferring regional sources and sinks of atmospheric CO<sub>2</sub> from GOSAT XCO<sub>2</sub> data

“…The sensitivity of the inferred flux estimates for boreal North America is not surprising since the GOSAT observational coverage is limited at high latitudes over North America. The temperate North America region has been described as a sink in previous inversions using flask observations of atmosphere CO 2 (Deng and Chen, 2011;Gurney et al, 2004;Peters et al, 2007;Rayner et al, 2008;Deng et al, 2007). Here we estimated the region to be a significant source in RUN_A, but a weak sink in RUN_B and a strong sink in RUN_C.…”

“…We also assigned 22 % of the prior estimates in each 3 h time step and in each model grid as the prior TER uncertainty. For the ocean flux we assumed an a priori uncertainty of 44 %, to keep the relative proportions for land and ocean in the range of those used in previous studies (Deng and Chen, 2011).…”

“…Specifically, these include (i) monthly national fossil fuel and cement manufacture CO 2 emission from the Carbon Dioxide Information Analysis Center (CDIAC) ; (ii) monthly shipping emissions of CO 2 from the International Comprehensive Ocean-Atmosphere Data Set (ICOADS) (Corbett and Koehler, 2003;Corbett, 2004;Endresen et al, 2004Endresen et al, , 2007; (iii) 3-D aviation CO 2 emissions (Kim et al, 2007;Wilkerson et al, 2010;Friedl 1997); (iv) monthly mean biomass burning CO 2 emissions from the Global Fire Emissions Database version 3 (GFEDv3) (van der Werf et al, 2010); (v) biofuel (heating/cooking) CO 2 emission estimated by Yevich and Logan (2003); (vi) the flux of CO 2 across the air-water interface based on the climatology of monthly ocean-atmosphere CO 2 flux by Takahashi et al (2009);and (vii) 3-hourly terrestrial ecosystem exchange produced by the Boreal Ecosystem Productivity Simulator (BEPS) (Chen et al, 1999), which was driven by NCEP reanalysis data (Kalnay et al, 1996) and remotely sensed leaf area index (LAI) (Deng et al, 2006). The annual terrestrial ecosystem exchange imposed in each grid box is neutral (Deng and Chen, 2011). The emission inventories for 2010 used in our GEOS-Chem simulation are summarized in Table 1.…”

“…In this study, we used the annual balanced, 3-hourly terrestrial ecosystem fluxes as described by Deng and Chen (2011), which also produced a weak seasonal cycle in the a priori CO 2 fields. However, as shown in Figs.…”

“…These data have been intensively used in estimating global and regional carbon sinks and sources via various kinds of atmospheric inversions (e.g., Enting et al, 1995;Fan et al, 1998;Rayner et al, 1999;Gurney et al, 2002;Peylin et al, 2002;Rödenbeck et al, 2003;Law et al, 2003;Patra et al, 2005;Michalak et al, 2005;Baker et al, 2006b;Peters et al, 2007;Deng and Chen, 2011;Bruhwiler et al, 2011). Though there is general agreement in the estimates of hemispheric-scale fluxes, large uncertainties still remain in the estimates of the fluxes on smaller, regional scales, due partly to the limited spatial scale of the observations, errors in the atmospheric models (e.g., Stephens et al, 2007), and to the different configurations of the atmospheric inversions.…”