Soil, Carbon, and Climate Change.

The earth’s soils are major depositories of carbon, in the forms of fresh organic residues, humus, peat, and mineral carbonates. The organic carbon in soils alone constitutes a reserve that is at least three times greater than the amount contained in the atmosphere. Moreover, soil organic matter is exceedingly labile: It may be augmented by judicious soil and vegetation management but may decompose and release greenhouse gases (CO₂, CH₄, N₂O) if mismanaged. 

            Appropriate management of organic matter in soils may enhance their fertility and thus may help to absorb carbon from the atmosphere via green plants and store, i.e., sequester, it in the soil. Carbon sequestration in soils can therefore contribute significantly to the global effort to mitigate the greenhouse effect, while enhancing soil structural stability and productivity. However, because soils of different regions vary greatly in their properties and in their existing and possible modes of management, no universal prescriptions can fit all circumstances. Rather, the soil of each region and type must be regarded in terms of its own characteristics and its contribution, and potential response, to anticipated climate change.

            Soil carbon sequestration provides a mechanism to ameliorate agricultural soils in developing countries, since when denuded and cultivated, soils are subjected to rapid organic-matter decomposition without replenishment. Particularly vulnerable are cultivated and overgrazed soils in the humid tropics, where decomposition tends to be very rapid and where bared topsoil tends to erode by intense downpours during rainy seasons and by winds during dry spells. Even more vulnerable are organic soils of bogs and marshes. A major goal is to reverse loss of vegetative cover and of organic matter from soils and the ensuing structural degradation, fertility depletion, and accelerated erosion.