A: Plants photosynthesize carbon, which then enters the soil via fallen leaves or root material. The fluxes between soil carbon in the form of organic matter and carbon in the atmosphere as CO2 are very large. A small change in carbon cycling can have a huge affect on atmospheric CO2 concentrations, and therefore a huge feedback to climate change. As an example, a ten percent change in the soil carbon flux to the atmosphere would roughly double the net CO2 input. And if soils released only 0.3 percent of their carbon stores, it would equal year 2010 fossil fuel emissions.
What will happen to soil carbon as the climate changes? A team of scientists seeks answers
Where is the tipping point? We don't know.