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Biospheric Carbon Sequestration Revisited
Volume 3, Number 20: 30 August 2000

In our editorial of 1 December 1999 - Biospheric Carbon Sequestration: Does It Really Work? - we addressed what Pearce (1999) called the dangerous delusion that "planting trees means less atmospheric CO2." Claiming that "planned new forests, called 'carbon sinks,' will swiftly become saturated with carbon and begin returning most of their carbon to the atmosphere," Pearce painted an ominous picture of runaway global warming fueled by future forests acting as sources of CO2 and mockingly asked "How did researchers get it so wrong?"

In a treatise about three times longer than our normal editorial fare, we responded by demonstrating that it was Pearce who was blatantly wrong on this point, notwithstanding his quoting (or misquoting) of several IPCC experts to the contrary. And now, we are happy to report, a pair of important new studies firmly establishes the validity of the case we constructed against Pearce's fiction-as-fact piece half a year ago.

Pearce's confusion on the issue appears to have originated from the idea that global warming (hypothesized to result from rising atmospheric CO2 concentrations) would ultimately become a more powerful force in increasing ecosystem respiration rates than the rising atmospheric CO2 concentration would ultimately become in increasing ecosystem photosynthesis rates, the latter of which, according to one of the experts he cited, was destined to "flatten out while respiration rates soar." The new studies, however, clearly demonstrate that this latter idea is not supported by real-world data.

In the first study, Giardina and Ryan (2000) compiled decomposition data for organic carbon contained in forest mineral soils from 82 sites on five continents, finding that carbon decomposition rates "are not controlled by temperature limitations to microbial activity, and that increased temperature alone will not stimulate the decomposition of forest-derived carbon in mineral soil." In fact, they found that "despite a 20C gradient in mean annual temperature, soil carbon mass loss ? was insensitive to temperature."

In the second study, authored by 30 different scientists, Valentini et al. (2000) present data on net ecosystem carbon exchange in 15 European forests, which, in their words, "confirm that many European forest ecosystems act as carbon sinks." Their data also demonstrate that the more southerly, warmer forests annually sequester far more carbon than the more northerly, cooler forests. Hence, if anything, these real-world data suggest that global warming would likely promote just the opposite of what has long been believed to be the effect of rising temperatures on carbon sequestration.

In a companion "news and views" piece, Grace and Rayment (2000) cite additional studies that also "show quite clearly that old and undisturbed forests, as well as middle-aged forests, are net absorbers of CO2." This is good news, they say, for "it means that forests are serving as a carbon sink, providing a global environmental service by removing CO2 from the atmosphere and thus reducing the rate of CO2-induced warming," which is clearly in contrast to the once commonly held view - "now enshrined in models of global change" - that "the carbon sink provided by forests will weaken, and that in the long term the world's forests may eventually become a source of carbon to the atmosphere."

In view of the findings of Giardina and Ryan (2000) and Valentini et al. (2000), Grace and Rayment thus conclude that "the results from these two papers should send a powerful message to those working with models of global vegetation change," namely, "that the doomsday view of runaway global warming now seems unlikely."

We couldn't agree more.

Dr. Craig D. Idso
President
Dr. Keith E. Idso
Vice President

References
Giardina, C.P. and Ryan, M.G. 2000. Evidence that decomposition rates of organic carbon in mineral soil do not vary with temperature. Nature 404: 858-861.

Grace, J. and Rayment, M. 2000. Respiration in the balance. Nature 404: 819-820.

Pearce, F. 1999. That sinking feeling. New Scientist 164 (2209): 20-21.

Valentini, R., Matteucci, G., Dolman, A.J., Schulze, E.-D., Rebmann, C., Moors, E.J., Granier, A., Gross, P., Jensen, N.O., Pilegaard, K., Lindroth, A., Grelle, A., Bernhofer, C., Grunwald, T., Aubinet, M., Ceulemans, R., Kowalski, A.S., Vesala, T., Rannik, U., Berbigier, P., Loustau, D., Gudmundsson, J., Thorgeirsson, H., Ibrom, A., Morgenstern, K., Clement, R., Moncrieff, J., Montagnani, L., Minerbi, S. and Jarvis, P.G. 2000. Respiration as the main determinant of carbon balance in European forests. Nature 404: 861-865.