Soil carbon (C) is a dynamic and integral part of the global C cycle. It has been a source of atmospheric carbon dioxide (CO2) since the dawn of settled agriculture, depleting more than 320 billion metric tons (Pg) from the terrestrial pool, 78±12 Pg of which comes from soil. In comparison, approximately 292 Pg C have been emitted through fossil-fuel combustion since about 1750. However, terrestrial pools can act as a sink for as much as 50 parts per million of atmospheric CO2 for 100 to 150 years. The technical sink capacity of US soils is 0.288 Pg C per year; Earths terrestrial biosphere can act as a sink for up to 3.8 Pg C per year. The economic potential of C storage depends on its costs and cobenefits, such as global food security, water quality, and soil biodive'rsity. Therefore, optimally managing the soil C pool must be the basis of any strategy to improve and sustain agronomic production, especially in developing countries. Recarbonization of the terrestrial biosphere by restoring C pools in Earth's soils, trees, and wetlands is an important step toward both mitigation and adaptation to ACC. In comparison with the engineering techniques of geologic and oceanic sequestration, C sequestration in terrestrial ecosystems has numerous cobenefits, such as increasing NPP, advancing food security, improving the quality and quantity of water resources, enhancing biodiversity, and others.
Payment for ecosystem services can promote the adoption of recommended management practices and conversion to restorative land use. In order to realize the potential for C sequestration in the terrestrial biosphere we need a better understanding of basic processes at a range of scales, from molecular to watershed, and through life-cycle analyses of the managed ecosystems. In addition to the technical and maximum potential, the economic and realizable potential must be computed through assessment of the marginal abatement cost. There is therefore a strong need for multidisciplinary approaches to addressing this important global issue. Measurement, monitoring, modeling, and verification of the C pool and fluxes at soilscape, landscape, watershed, regional, and national scales are essential for terrestrial C sequestration to be adopted by the UN Framework Convention on Climate Change as an offset for anthropogenic emissions. Regardless of climate change, it is important to realize that the basic needs (e.g., food, feed, fiber, fuel) of Earth's 10 billion inhabitants by 2100 cannot be met without restoring the services of the terrestrial ecosystems, especially soil quality, for which recarbonization of the biosphere and enhancement of the SOC pool are essential prerequisites.