Periodically, the planting of forests with the objective of removing CO2 from the atmosphere and sequestering its carbon in soil organic matter - which process tends to slow the rate-of-rise of the air's CO2 content - has come under fire as being only a stopgap measure in the quest to moderate global warming. Pearce (1999) has even referred to the concept as a dangerous delusion, saying that "planned new forests, called 'carbon sinks,' will swiftly become saturated with carbon and begin returning most of their carbon to the atmosphere."
The rationale for this twisted thinking is that rising temperatures will dramatically increase rates of soil respiration, thereby causing forest ecosystems to return CO2 to the air at a faster rate than they remove it from the atmosphere via photosynthesis. The way proponents of the theory describe it, future rates of photosynthesis would "flatten out," according to Pearce, while respiration rates would "soar." However, a number of studies have shown quite conclusively that much like the theory of CO2-induced global warming, this theory too is not supported by real-world observations. In fact, it's flat-out contradicted by them.
One of the first signs of nature's rebellion against the faulty carbon "unsequestration" concept came in the form of a study conducted in Finland. There, Liski et al. (1999) determined that carbon storage in the soils of both high- and low-productivity boreal forests actually increased with temperature along a natural temperature gradient. This finding, we hasten to point out, is just the opposite of what is predicted by those who are trying to downplay the value of forests in fighting predicted global warming.
Expanding the scope of the Finnish work just a bit, Giardina and Ryan (2000) analyzed organic carbon decomposition data derived from the forest soils of 82 different sites on five continents. Based on this worldwide assemblage of real-world data, they found 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 report the astounding fact that "despite a 20°C gradient in mean annual temperature, soil carbon mass loss ? was insensitive to temperature."
In the same issue of Nature in which Giardina and Ryan's work was published, a group of thirty other scientists weighed in with another important contribution to the debate (Valentini et al., 2000). This group of researchers had collected data on net ecosystem carbon exchange in fifteen European forests; and they reported that their results "confirm that many European forest ecosystems act as carbon sinks." Their data also demonstrated that the warmer forests of southern Europe annually sequester far more carbon than the cooler forests of northern Europe, again in direct contradiction of the claims of those who tout warming as a sure-fire recipe for forest carbon loss.
In yet another discussion of the subject, Grace and Rayment (2000) presented still more evidence refuting the claim that new forests "will swiftly become saturated with carbon and begin returning most of their carbon to the atmosphere." Specifically, they cited a number of additional studies that "show quite clearly," as they put it, "that old undisturbed forests, as well as middle-aged forests, are net absorbers of CO2." They also noted that these real-world observations mean 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."
Commenting further on the work of Giardina and Ryan (2000) and Valentini et al. (2000), Grace and Rayment unequivocally state 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. Sherwood B. Idso | Dr. Keith E. Idso |
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.
Liski, J., Ilvesniemi, H., Makela, A. and Westman, C.J. 1999. CO2 emissions from soil in response to climatic warming are overestimated - The decomposition of old soil organic matter is tolerant of temperature. Ambio 28: 171-174.
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.