Carbon-Emitting Soil Could Speed Global Warming, Warns 26-Year Study

An anonymous reader quote the Guardian:
Warming soil releases more carbon into the atmosphere than previously thought, suggesting a potentially disastrous feedback mechanism whereby increases in global temperatures will trigger massive new carbon releases in a cycle that may be impossible to break... The 26-year study is one of the biggest of its kind, and is a groundbreaking addition to our scant knowledge of exactly how warming will affect natural systems. Potential feedback loops, or tipping points, have long been suspected to exist by scientists, and there is some evidence for them in the geological record. What appears to happen is that once warming reaches a certain point, these natural biological factors kick in and can lead to a runaway, and potentially unstoppable, increase in warming...
In the Science study, researchers examined plots of soil in the Harvard Forest in Massachusetts, a mixed hardwood forest in the U.S. They experimented by heating some of the plots with underground cables to 5C above normal levels, leaving others as a control. The long-term study revealed that in the first 10 years there was a strong increase in the carbon released from the heated plots, then a period of about seven years when the carbon release abated. But after this second calmer period, which the scientists attribute to the adjustment of the soil microbes to the warmer conditions, the release of carbon resumed its upward path. From 1991, when the experiment began, the plots subjected to 5C warming lost about 17% of the carbon that had been stored in the top 60cm of the soil, where the greatest concentration of organic matter is to be found...

Lead scientist Jerry Melillo, points out that currently 10 billion metric tons of carbon gets released into the atmosphere every year, but "The world's soils contain about 3,500 billion tons of carbon. If a significant amount of that is added to the atmosphere, due to microbial activity, that will accelerate the global warming process. Once this self-reinforcing feedback begins, there is no easy way to turn it off. There is no switch to flip."