Towards robust regional estimates of CO2 sources and sinks using atmospheric transport models


Information about regional carbon sources and sinks can be derived from variations in observed atmospheric CO2 concentrations via inverse modelling with atmospheric tracer transport models. A consensus has not yet been reached regarding the size and distribution of regional carbon fluxes obtained using this approach, partly owing to the use of several different atmospheric transport models1,2,3,4,5,6,7,8,9. Here we report estimates of surface–atmosphere CO2 fluxes from an intercomparison of atmospheric CO2 inversion models (the TransCom 3 project), which includes 16 transport models and model variants. We find an uptake of CO2 in the southern extratropical ocean less than that estimated from ocean measurements, a result that is not sensitive to transport models or methodological approaches. We also find a northern land carbon sink that is distributed relatively evenly among the continents of the Northern Hemisphere, but these results show some sensitivity to transport differences among models, especially in how they respond to seasonal terrestrial exchange of CO2. Overall, carbon fluxes integrated over latitudinal zones are strongly constrained by observations in the middle to high latitudes. Further significant constraints to our understanding of regional carbon fluxes will therefore require improvements in transport models and expansion of the CO2 observation network within the tropics.

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Figure 1: Mean estimated sources and uncertainties for two inversions.
Figure 2: CO2concentrations input to, and as fitted by, the inversion.
Figure 3: Mean sources and uncertainties for six aggregated regions and global land and ocean.


  1. 1

    Enting, I. G., Trudinger, C. M. & Francey, R. J. A synthesis inversion of the concentration and δ13C of atmospheric CO2. Tellus B 47, 35–52 (1995).

  2. 2

    Fan, S. et al. A large terrestrial carbon sink in North America implied by atmospheric and oceanic carbon dioxide data and models. Science 282, 442–446 (1998).

  3. 3

    Kaminski, T., Heimann, M. & Giering, R. A coarse grid three-dimensional global inverse model of the atmospheric transport, 2, inversion of the transport of CO2 in the 1980s. J. Geophys. Res. 104, 18555–18581 (1999).

  4. 4

    Bousquet, P., Ciais, P., Peylin, P., Ramonet, M. & Monfrey, P. Inverse modelling of annual atmospheric CO2 sources and sinks. Part 1: method and control inversion. J. Geophys. Res. 104, 26161–26193 (1999).

  5. 5

    Baker, D. F. Sources and Sinks of Atmospheric CO2 Estimated from Batch Least-Squares Inversions of CO2 Concentration Measurements. Thesis, Princeton Univ. (2001).

  6. 6

    Taguchi, S. Synthesis inversion of atmospheric CO2 using the NIRE chemical transport model. Geophys. Monogr. 114, 239–254 (2000).

  7. 7

    Peylin, P., Baker, D., Sarmiento, J., Ciais, P. & Bousquet, P. Influence of transport uncertainty on annual mean and seasonal inversions of atmospheric CO2 data. J. Geophys. Res. (submitted).

  8. 8

    Rayner, P. J., Enting, I. G., Francey, R. J. & Langenfelds, R. Reconstructing the recent carbon cycle from atmospheric CO2, δ13C and O2/N2 observations. Tellus B 51, 213–232 (1999).

  9. 9

    Bousquet, P. et al. Regional changes in carbon dioxide fluxes of land and ocean since 1980. Science 290, 1342–1346 (2000).

  10. 10

    Takahashi, T. et al. Global sea-air CO2 flux based on climatological surface ocean pCO2, and seasonal biological end temperature effects. Deep-Sea Res. I. (submitted).

  11. 11

    Tans, P., Fung, I. & Takahashi, T. Observational constraints on the global atmospheric CO2 budget. Science 247, 1431–1438 (1990)

  12. 12

    Denning, S. et al. Three-dimensional transport and concentration of SF6: A model intercomparison study (Transcom 2). Tellus B 51, 266–297 (1999).

  13. 13

    Metzl, N., Brunet, C., Jabaud-Jan, A., Poisson, A. & Schauer, B. in Extended Abstr. 6th Int. Carbon Dioxide Conf. 685–688 (Organizing Committee of Sixth Carbon Dioxide Conference, Sendai, 2001).

  14. 14

    Kaminski, T., Rayner, P. J., Heimann, M. & Enting, I. G. On aggregation errors in atmospheric transport inversions. J. Geophys. Res. 106, 4703–4715 (2001).

  15. 15

    Denning, A. S., Fung, I. Y. & Randall, D. A. Latitudinal gradient of atmospheric CO2 due to seasonal exchange with land biota. Nature 376, 240–243 (1995).

  16. 16

    Tarantola, A. Inverse Problem Theory: Methods for Data Fitting and Model Parameter Estimation 3rd impr. (Elsevier, Amsterdam, 1998).

  17. 17

    Andres, R. J., Marland, G., Fung, I. & Matthews, E. Distribution of carbon dioxide emissions from fossil fuel consumption and cement manufacture, 1950-1990. Glob. Biogeochem. Cycles 10, 419–429 (1996).

  18. 18

    Brenkert, A. L. Carbon dioxide emission estimates from fossil-fuel burning, hydraulic cement production, and gas flaring for 1995 on a one degree grid cell basis. 〈〉 (1998; accessed Oct. 1998).

  19. 19

    Randerson, J. et al. The contribution of terrestrial sources and sinks to trends in the seasonal cycle of atmospheric carbon dioxide. Glob. Biogeochem. Cycles 11, 535–560 (1997).

  20. 20

    GLOBALVIEW-CO2: Cooperative Atmospheric Data Integration Project - Carbon Dioxide CD-ROM (NOAA CMDL, Boulder, Colorado, 2000); also available at 〈〉 (2000).

  21. 21

    De Fries, R. S. & Townshend, J. R. G. NDVI-derived land cover classifications at a global scale. Int. J. Remote Sensing 15, 3567–3586 (1994).

  22. 22

    Taylor, K. E., Williamson, D. & Zwiers, F. AMIP II sea surface temperature and sea ice concentration boundary conditions. 〈http://www–〉 (1997).

  23. 23

    Apps, M. J. & Kurz, W. A. in Carbon Balance on World's Forested Ecosystems: Towards a Global Assessment (ed. Kanninen, M.) 14–39 (Publications of the Academy of Finland, Helsinki, 1994).

  24. 24

    Kurz, W. A. & Apps, M. J. A 70 year retrospective analysis of carbon fluxes in the Canadian forest sector. Ecol. Applicat. 9, 526–547 (1999).

  25. 25

    Greenhouse Gas Inventory Data from 1990 to 1998 (Secretariat of the United Nations Framework Convention on Climate Change, National Communications from Parties Included in Annex 1 to the Convention, FCCC/SBI/2000/11, Bonn, 2000).

  26. 26

    Pacala, S. et al. Convergence of land- and atmosphere-based U.S. carbon sink estimates. Science 292, 2316–2320 (2001).

  27. 27

    Houghton, R. A. The annual net flux of carbon to the atmosphere from changes in land use 1850-1990. Tellus B 51, 298–313 (1999).

  28. 28

    Dixon, R. K. et al. Carbon pools and flux of global forest ecosystems. Science 263, 185–190 (1990).

  29. 29

    Houghton, R. A. & Hackler, J. L. Emissions of carbon from forestry and land-use change in tropical Asia. Glob. Change Biol. 5, 481–492 (1999).

  30. 30

    Kauppi, P. E., Mielikainen, K. & Kuusela, K. Biomass and carbon budget of European forests, 1971 to 1990. Science 256, 70–74 (1992).

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We thank B. Stephens for comments and suggestions on earlier versions of the manuscript. This work was supported by the NSF, NOAA and the International Geosphere Biosphere Program/Global Analysis, Interpretation, and Modeling Project. S.F. and J.S. were supported by NOAA's Office of Global Programs for the Carbon Modeling Consortium.

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Correspondence to A. Scott Denning.

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Supplementary figures 1 - 3; supplementary tables (DOC 678 kb)

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