Volume 17, Number 9: 26 February 2014
In an intriguing paper published a few months ago, Shevliakova et al. (2013) wrote that "according to previous studies, [Earth's] land was a carbon source to the atmosphere from the pre-industrial period to the 1940s (Tans, 2009) and then became a carbon sink, which has steadily increased over the last 50 years (Pan et al., 2011; Ballantyne et al., 2012.)." And in doing so, they made particular mention of the fact that "one of the leading causes of the increasing residual terrestrial [carbon] sink is believed to be enhanced vegetation growth under elevated levels of atmospheric CO2 (i.e., CO2 fertilization)," citing the studies of Kramer (1981), Lewis et al. (2004), Denman et al. (2007), Pan et al. (2011) and Prentice et al. (2011).
In light of these facts, the question Shevliakova et al. addressed in their study of the subject was how much higher the CO2 concentration of the atmosphere would now be without the help of the vegetation-promoting fertilization effect of the historical increase in the air's CO2 content having helped earth's plants remove an ever-increasing amount of CO2 from the atmosphere with each passing year, plus how much higher the current mean temperature of the globe might otherwise have been at the time of their writing.
The six scientists addressed this question by using the Geophysical Fluid Dynamics Laboratory's comprehensive Earth System Model ESM2G and a reconstruction of historical land-use change to deduce that historical CO2-enhanced vegetation growth "lowered the historical atmospheric CO2 concentration by fully 85 ppm," thereby avoiding what they calculated to be "an additional 0.31 ± 0.06°C warming," which is a rather impressive feat for the biosphere.
Sherwood, Keith and Craig Idso
References
Ballantyne, A.P., Alden, C.B., Miller, J.B., Tans, P.P. and White, J.W.C. 2012. Increase in observed net carbon dioxide uptake by land and oceans during the past 50 years. Nature 488: 70-72.
Denman, K.L., Brasseur, G., Chidthaisong, A., Ciais, P., Cox, P.M., Dickinson, R.E., Hauglustaine, D., Heinze, C., Holland, E., Jacob, D., Lohmann, U., Ramachandran, S., da Silva Dias,, P.L., Wofsy, S.C. and Zhang, X. 2007: Couplings Between Changes in the Climate System and Biogeochemistry. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K.B., Tignor, M. and Miller, H.L. (Eds.). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
Kramer, P. 1981. Carbon dioxide concentration, photosynthesis and dry matter production. BioScience 31: 29-33.
Lewis, S.L., Phillips, O.L., Baker, T.R., Lloyd, J., Malhi, Y., Almeida, S., Higuchi, N., Laurance, W.F., Neill, D.A., Silva, J.N.M., Terborgh, J., Lezama, A.T., Vásquez Martinez, R., Brown, S., Chave, J., Kuebler, C., Núñez Vargas, P. and Vinceti, B. 2004. Concerted changes in tropical forest structure and dynamics: evidence from 50 South American long-term plots. Philosophical Transactions of the Royal Society of London Series B - Biological Sciences 359: 421-436.
Pan, Y., Birdsey, R.A., Fang, J., Houghton, R., Kauppi, P.E., Kurz, W.A., Phillips, O.L., Shvidenko, A., Lewis, S.L., Canadell, J.G., Ciais, P., Jackson, R.B., Pacala, S.W., McGuire, A.D., Piao, S., Rautiainen, A., Sitch, S. and Hayes, D. 2011. A large and persistent carbon sink in the world's forests. Science 333: 988-993.
Prentice, I.C., Harrison, S.P. and Bartlein, P.J. 2011. Global vegetation and terrestrial carbon cycle changes after the last ice age. New Phytologist 189: 988-998.
Shevliakova, E., Stouffer, R.J., Malyshev, S., Krasting, J.P., Hurtt, G.C. and Pacala, S.W. 2013. Historical warming reduced due to enhanced land carbon uptake. Proceedings of the National Academy of Sciences USA 110: 16,730-16,735.
Tans, P. 2009. An accounting of the observed increase in oceanic and atmospheric CO2 and an outlook for the future. Oceanography 22: 26-35.