The planet's soil releases about 60 billion tons of carbon into the atmosphere each year, which is far more than that released by burning fossil fuels.
This soil respiration and the enormous release of carbon is balanced by carbon coming into the soil system from falling leaves and other plant matter, as well as by the underground activities of plant roots.
Short-term warming studies have documented that rising temperatures increase the rate of soil respiration. As a result, scientists have worried that global warming would accelerate the decomposition of carbon in the soil, and decrease the amount of carbon stored there. If true, this would release even more carbon dioxide into the atmosphere, where it would accelerate global warming.