Background
The authors write that "aside from sulfur dioxide, carbonyl sulfide (COS) is the most abundant sulfur gas in the atmosphere with relative constant mixing ratios of 450-500 ppt and a lifetime of more than two years." And due to this long lifetime, they say that "COS can be transported up into the stratosphere," where it "may serve as a source of sulfur to the stratospheric aerosol layer by conversion to sulfuric acid (Junge et al., 1961; Crutzen, 1976)," thereby contributing to the scattering of incoming solar radiation back to space and exerting a cooling influence on the earth. In addition, they note that terrestrial vegetation "acts as the main sink for this trace gas," further adding that it is "heavily underestimated" in this regard, citing the work of Notholt et al. (2003), Mu et al. (2004), Sandoval-Soto et al. (2005), Campbell et al. (2008), Suntharalingam et al. (2008) and Van Diest and Kesselmeier (2008).

What was done
To explore what effect the ongoing rise in the air's CO2 content might be having on this anti-warming phenomenon, Sandoval-Soto et al. grew three- to four-year-old holm oak (Quercus ilex L.) and European beech (Fagus sylvatica L.) trees in greenhouse chambers from March 1998 to February 2000 at atmospheric CO2 concentrations of either 350 or 800 ppm, while measuring a number of plant physiological properties and processes that are pertinent to this oft-ignored subject.

What was learned
In the case of holm oak, the five researchers report there was "a decrease of the COS uptake capacity induced by high CO2 levels under long-term conditions," and they say that their data for beech support "a similar interpretation."

What it means
As for the implications of the findings of Sandoval-Soto et al., they clearly suggest that (1) the historical increase in the atmosphere's CO2 concentration may have had a tempering effect on earth's rate of warming during the development of the planet's Current Warm Period, and that (2) that cooling influence could well increase in the years and decades ahead. For more on this subject, we direct you to the Summary Report on Carbonyl Sulfide in our Subject Index.

References
Campbell, J.E., Carmichael, G.R., Chai, T., Mena-Carrasco, M., Tang, Y., Blake, D.R., Blake, N.J., Vay, S.A., Collatz, G.J., Baker, I., Berry, J.A., Montzka, S.A., Sweeney, C., Schnoor, J.L. and Stanier, C.O. 2008. Photosynthetic control of atmospheric carbonyl sulfide during the growing season. Science 322: 1085-1088.

Crutzen, P.J. 1976. The possible importance of CSO for the sulfate layer of the stratosphere. Geophysical Research Letters 3: 73-76.

Junge, C.E., Chagnon, C.W. and Manson, J.E. 1961. Stratospheric aerosols. Journal of Meteorology 18: 81-108.

Mu, Y., Geng, C., Wang, M., Wu, H., Zhang, X. and Jiang, G. 2004. Photochemical production of carbonyl sulphide in precipitation. Journal of Geophysical Research 109: 10.1029/2003JD004206.

Notholt, J., Kuang, Z., Rinsland, C.P., Toon, G.C., Rex, M., Jones, N., Albrecht, T., Deckelmann, H., Krieg, J., Weinzierl, C., Bingemer, H., Weller, R. and Schrems, O. 2003. Enhanced upper tropical tropospheric COS: Impact on the stratospheric aerosol layer. Science 300: 307-310.

Sandoval-Soto, L., Stanimirov, M., von Hobe, M., Schmitt, V., Valdes, J., Wild, A. and Kesselmeier, J. 2005. Global uptake of carbonyl sulfide (COS) by terrestrial vegetation: Estimates corrected by deposition velocities normalized to the uptake of carbon dioxide (CO2). Biogeosciences 2: 125-132.

Suntharalingam, P., Kettle, A.J., Montzka, S.M. and Jacob, D.J. 2008. Global 3-D model analysis of the seasonal cycle of atmospheric carbonyl sulfide: Implications for terrestrial vegetation uptake. Geophysical Research Letters 35: 10.1029/2008GL034332.

Van Diest, H. and Kesselmeier, J. 2008. Soil atmosphere exchange of carbonyl sulfide (COS) regulated by diffusivity depending on water-filled pore space. Biogeosciences 5: 475-483.