Soils could release much more CO2 than expected into the atmosphere as the climate warms, according to new research by scientists from the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). Their findings are based on a field experiment that, for the first time, explored what happens to organic carbon trapped in soil when all soil layers are warmed, which in this case extend to a depth of 39 in.
Soil organic carbon harbors three times as much carbon as Earth’s atmosphere. In addition, warming is expected to increase the rate at which microbes break down soil organic carbon, releasing more CO2 into the atmosphere and contributing to climate change.
Until now, the majority of field-based soil warming experiments only focused on the top 2 to 8 in. of soil, which leaves a lot of carbon unaccounted for. Experts estimate soils below 8 in. in depth contain more than 50% of the planet’s stock of soil organic carbon.
The need to better understand the response of all soil depths to warming is underscored by projections that, over the next century, deeper soils will warm at roughly the same rate as surface soils and the air. In addition, simulations of global average soil temperature by the Intergovernmental Panel on Climate Change, using a “business-as-usual” scenario in which carbon emissions rise in the decades ahead, predict that soil will warm 7 or 8 degrees F by 2100.
Researchers heated soil plots at California’s Blodgett Forest Research Station. They discovered that, of the 34 to 37% increase in CO2 released at the three warmed plots, 40% of this increase was due to CO2 that came from below 6 in. They also found the sensitivity of soil to warming was similar across the five tested depths.
The scientists say these findings suggest the degree to which soil organic carbon influences climate change may be currently underestimated.
“There’s an assumption that carbon in the subsoil is more stable, and not as responsive to warming as in the topsoil, but we’ve learned that’s not the case,” says co-author Margaret Torn. “Deeper soil layers contain a lot of carbon, and our work indicates it’s a key missing component in our understanding of the potential feedback of soils to the planet’s climate.”
The research was supported by the Department of Energy’s Office of Science.
NewTerrain March 15, 2017