Reducing greenhouse gas emissions is not enough to reverse global warming: we must also reduce the concentration of carbon dioxide in the atmosphere. The Marin Carbon Project is investigating the potential for specific land management practices to enhance sequestration of atmospheric carbon dioxide as organic matter in rangeland and agricultural soils in California.
Soil carbon sequestration is the process of moving carbon dioxide from the atmosphere into the soil. Through the process of photosynthesis, plants pull carbon dioxide out of the atmosphere and transfer that carbon below ground via root exudates and sloughing of roots; and to the soil surface when they drop leaves or other plant parts, and when they die. In this way, atmospheric carbon dioxide becomes soil organic matter.
Soil organic matter is approximately fifty percent carbon. Over the past 150 years we may have lost fifty to eighty percent of our topsoil worldwide. It is estimated that more than a third of the carbon dioxide we have added to the atmosphere during that time has come from changes in land use and poor land management. This soil-derived change in atmospheric carbon dioxide concentration suggests the potential for improved land management practices to result in sequestration of significant amounts of atmospheric carbon dioxide in the soil as organic matter.
Increasing soil organic matter has innumerable benefits in addition to helping to slow or reverse global warming. Improved soil water holding capacity, improved soil fertility, improved soil tilth, improved water quality, decreased need for petroleum-based pesticides and fertilizers, decreased erosion and increased production are all well-documented effects of increasing soil organic matter.
As climate change worsens, and climate change legislation, including California's AB32, comes into effect, more and better solutions will be needed for reaching targeted atmospheric carbon dioxide reductions. In this dynamic context, soil carbon sequestration provides numerous ecological and economic opportunities.