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Soil Organic Carbon Decomposition
Reference
Ise, T. and Moorcroft, P.R. 2006. The global-scale temperature and moisture dependencies of soil organic carbon decomposition: an analysis using a mechanistic decomposition model. Biogeochemistry 80: 217-231.

Background
Warming-induced increases in soil organic carbon (SOC) decomposition (which releases CO2 to the atmosphere) have long been hypothesized to represent a significant positive feedback phenomenon that can accelerate global warming believed to be induced by anthropogenic CO2 emissions. Hence, it is important to determine just how sensitive to rising temperatures earth's store of SOC might be.

What was done
As the authors describe it, they estimated the global-scale temperature and moisture dependencies of SOC decomposition "by fitting a mechanistic decomposition model to a global dataset of SOC, optimizing the model's temperature and moisture dependencies to best match the observed global distribution of SOC," which was done for "a series of grid cells covering the terrestrial land surface."

What was learned
Ise and Moorcroft write that the results of their analysis indicate that "the temperature sensitivity of decomposition at global scales is significantly less than is assumed by many terrestrial ecosystem models that directly apply temperature sensitivity from small-scale studies, and that the maximal rate of decomposition occurs at higher moisture values than is assumed by many models," which values they describe as being "much higher than previously thought."

What it means
The two Harvard University (USA) researchers say their results suggest that "the magnitude of the soil decomposition feedback onto rate of global climate change will be less sensitive to increases in temperature" than had previously been believed, and that the "modeling of temperature and moisture dependencies of SOC decomposition in global-scale models" should consider the moderating "effects of scale" that their analysis has revealed.

Reviewed 8 October 2008