The Global Land Carbon Sink

According to Gurney and Eckels (2011), "projections of atmospheric CO₂ concentrations and the resulting climate change rely to a significant degree on projections about future land and ocean uptake," and citing the work of Friedlingstein et al. (2006) and Sitch et al. (2008), the two authors proceeded to investigate how CO₂ uptake by earth's terrestrial surfaces has varied over the past three decades. In doing so, the 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. So what did they learn?

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).

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.

Additional References
Cao, M.K., Prince, S.D. and Shugart, H.H. 2002. Effects of interannual climate variability on global terrestrial biospheric CO₂ fluxes. Global Biogeochemical Cycles 16: 10.1029/2001GB001553.

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.

Gurney, K.R., Law, R.M., Denning, A.S., Rayner, P.J., Baker, D., Bousquet, P., Bruhwiler, L., Chen, Y.-H., Ciais, P., Fan, S., Fung, I.Y., Gloor, M., Heimann, M., Higuchi, K., John, J., Maki, T., Maksyutov, S., Masarie, K., Peylin, P., Prather, M., Pak, B.C., Randerson, J., Sarmiento, J., Taguchi, S., Takahashi, T. and Yuen, C.-W. 2002. Towards robust regional estimates of CO₂ sources and sinks using atmospheric transport models. Nature 415: 626-630.

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.

Sitch, S., Huntingford, C., Gedney, N., Levy, P.E., Lomas, M., Piao, S.L., Betts, R., Ciais, P., Cox, P., Friedlingstein, P., Jones, C.D., Prentice, I.C. and Woodward, F.I. 2008. Evaluation of the terrestrial carbon cycle, future plant geography and climate-carbon cycle feedbacks using five Dynamic Global Vegetation Models (DGVMs). Global Change Biology 14: 2015-2039.

Tans, P.P., Fung, I.Y. and Takahashi, T. 1990. Observational constraints on the global atmospheric CO₂ budget. Science 247: 1431-1438.