05/03/2010
A Potential Positive Feedback to Global Warming still up in the Air
Summary
It is commonly assumed that global warming will positively reinforce itself through accelerated decomposition of soil organic matter resulting in the release of ever more carbon dioxide into the atmosphere. In some field experiments, however, an instantaneous (step-change) increase in temperature (typically of several degrees Celsius) causes only a transient increase in carbon dioxide release from soil. Recently published results of DOE-sponsored modeling research proposes an explanation. With warming, the soil micro-organisms that decompose organic matter might become less metabolically efficient, and the amount of those decomposers (their biomass) therefore declines. If, and this is a critical if, the ongoing and gradual (rather than step-change) global warming being driven by increased atmospheric greenhouse gas concentrations does cause reduced efficiency of microbial metabolism and therefore microbial biomass, future increases in carbon dioxide emission from soils may be less than generally projected by present climate change models.
References
Allison SD, Wallenstein MD, Bradford MA (2010) Soil-carbon response to warming dependent on microbial physiology. Nature Geoscience doi:10.1038/ngeo846.