Background
The authors write that "projections of atmospheric CO2 concentrations and the resulting climate change rely to a significant degree on projections about future land and ocean uptake," citing the work of Friedlingstein et al. (2006) and Sitch et al. (2008); and, therefore, they felt it important to attempt to learn how CO2 uptake by earth's terrestrial surfaces has varied over the past three decades.

What was done
Gurney and Eckles utilized the results of atmospheric CO2 inversions -- constrained by observed atmospheric CO2 concentrations (Tans et al., 1990) and simulated atmospheric transport -- to estimate trends in air-to-land carbon fluxes, as per Enting (2002). This they did, as they describe it, "at spatial scales down to the continents using the results of the TransCom 3 international atmospheric CO2 inversion inter-comparison (Gurney et al., 2002, 2008)," which effort involved 13 participating modeling groups.

What was learned
The two U.S. researchers report that the results of their analyses indicate that the global land carbon sink is intensifying, and that it is doing so at a rate of 0.057 PgC/year/year, resulting in 1.65 PgC of additional uptake over the period examined (1980-2008), which finding, in their words, "is consistent with related findings in recent years," citing in this regard the studies of Cao et al. (2002), Cao et al. (2005), Le Quere et al. (2009) and Piao et al. (2009).

What it means
As ever more anthropogenic CO2 is emitted into the atmosphere and the air's CO2 concentration rises ever higher, so too does the photosynthetic prowess of earth's terrestrial vegetation grow ever stronger, as the great global greening of the earth gains ever more momentum and sucks ever more CO2 out of the air and incorporates it into living biomass and soil organic matter, thereby muting the rate of global warming that would otherwise prevail in the absence of this important negative feedback phenomenon.

References
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Cao, M., Prince, S.D., Tao, B., Small, J. and Li, K. 2005. Regional pattern and interannual variations in global terrestrial carbon uptake in response to changes in climate and atmospheric CO2. Tellus B 57: 210-217.

Enting, I. 2002. Inverse Problems in Atmospheric Constituent Transport. Cambridge University Press, Cambridge, United Kingdom.

Friedlingstein, P., Cox, P., Betts, R., Bopp, L., von Bloh, W., Brovkin, V., Cadule, P., Doney, S., Eby, M., Fung, I., Bala, G., John, J., Jones, C., Joos, F., Kato, T., Kawamiya, M., Knorr, W., Lindsay, K., Matthews, H.D., Raddatz, T., Rayner, P., Reick, C., Roeckner, E., Schnitzler, K.-G., Schnur, R., Strassmann, K., Weaver, A.J., Yoshikawa, C. and Zeng, N. 2006. Climate-carbon cycle feedback analysis: Results from the (CMIP)-M-4 model intercomparison. Journal of Climate 19: 3337-3353.

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Gurney, K.R., Baker, D., Rayner, P., Denning, A.S. and TransCom 3 L2 modelers. 2008. Interannual variations in continental-scale net carbon exchange and sensitivity to observing networds estimated from atmospheric CO2 inversions for the period 1980 to 2005. Global Biogeochemical Cycles 22: 10.1029/2007GB003082.

Le Quere, C., Raupach, M.R., Canadell, J.G., Marland, G., Bopp, L., Ciais, P., Conway, T.J., Doney, S.C., Feely, R.A., Foster, P., Friedlingstein, P., Gurney, K., Houghton, R.A., House, J.I., Huntingford, C., Levy, P.E., Lomas, M.R., Majkut, J., Metzl, N., Ometto, J.P., Peters. G.P., Prentice, I.C., Randerson, J.T., Running, S.W., Sarmiento, J.L., Schuster, U., Sitch, S., Takahashi, T., Viovy, N., van der Werf, G.R. and Woodward, F.I. 2009. Trends in the sources and sinks of carbon dioxide. Nature Geoscience 2: 831-836.

Piao, S., Ciais, P., Friedlingstein, P., de Noblet-Ducoudre, N., Cadule, P., Viovy, N. and Wang, T. 2009. Spatiotemporal patterns of terrestrial carbon cycle during the 20th century. Global Biogeochemical Cycles 23: 10.1029/2008GB003339.

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