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Heated and control plots in a long-term soil warming study at Harvard Forest, Petersham, Mass. Jerry Melillo of the Marine Biological Laboratory and colleagues began the study in 1991. (Credit: Audrey Barker-Plotkin)

Heated and control plots in a long-term soil warming study at Harvard Forest, Petersham, Mass. Jerry Melillo of the Marine Biological Laboratory and colleagues began the study in 1991. (Credit: Audrey Barker-Plotkin)

Warming Soils Could Trigger Potentially Unstoppable Climate Feedback Loop: Study

Increased temperatures led to microbial activity that led to surges of carbon emissions

Andrea Germanos

New results from a long-term study point towards a potentially unstoppable feedback loop as earth's rising temperatures drive soils to release more carbon emissions.

As Bloomberg put it, "There's a carbon bomb right under your feet."

Researchers behind the 26-year, ongoing experiment buried cables in a set of plots in a Massachusetts forest and warmed the soil to 5 degrees C (9 degrees F) above the ambient temperature to see how their carbon emissions varied with those of control plots. The researchers found four phases of alternating soil carbon loss and carbon stability. Newsweek explains that "the team believes that during the peak periods, microbes [in the soil] are using up a plentiful supply of food. But when that runs out, the community has to find a new source of food, leading to the lulls in carbon release."

Over the course of the whole experiment, they found the warmed plots had lost 17 percent of the carbon that had been stored in organic matter in the top 60 centimeters (24 inches) of soil.

"To put this in context," stated lead author Jerry Melillo, distinguished scientist at the Marine Biological Laboratory in Woods Hole, Mass., "each year, mostly from fossil fuel burning, we are releasing about 10 billion metric tons of carbon into the atmosphere. That's what's causing the increase in atmospheric carbon dioxide concentration and global warming."

"The world's soils contain about 3,500 billion metric tons of carbon," he continued. "If a significant amount of that soil carbon is added to the atmosphere due to microbial activity in warmer soils, that will accelerate the global warming process. And once this self-reinforcing feedback begins, there is no easy way to turn it off. There is no switch to flip."

If the same kind of carbon release measured at the New England site occurred across the globe, over the course of the century it would be the "equivalent to the past two decades of carbon emissions from fossil fuel burning," the researchers extrapolate.

"The future is a warmer future. How much warmer is the issue," Melillo said, noting that actions like shutting down coal plants can help reign in carbon emissions from fossil fuels. "But if the microbes in all landscapes respond to warming in the same way as we've observed in mid-latitude forest soils, this self-reinforcing feedback phenomenon will go on for a while and we are not going to be able to turn those microbes off.  Of special concern is the big pool of easily decomposed carbon that is frozen in Artic soils. As those soils thaw out," he continued, "this feedback phenomenon would be an important component of the climate system, with climate change feeding itself in a warming world."

As Melillo's study, published Friday in the journal Science, adds to research finding warming leads to soils releasing, rather than sequestering, carbon, separate research is also showing how soil, with better land management practices, can help mitigate climate change.

"Dirt," said Rob Jackson, who lead the research published in the Annual Review of Ecology, Evolution and Systematics, "is a no-risk climate solution with big co-benefits. Fostering soil health protects food security and builds resilience to droughts, floods, and urbanization."


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