Climate change and soil carbon impacts.

Soils contain vast reserves (∼1500 Pg) of carbon (C), about twice that found as carbon dioxide in the atmosphere. Historically, soils in managed ecosystems have lost a portion of this C (40-90 Pg) through land-use change, some of which has remained in the atmosphere. In terms of climate change, most projections suggest soil C changes driven by future climate change will range from small losses to moderate gains, but these global trends show considerable regional variation. The response of soil C in future will be determined by a delicate balance between the impacts of increased temperature and decreased soil moisture on decomposition rates, and the balance between changes in C losses from decomposition and C gains through increased productivity. In terms of using soils to mitigate climate change, soil C sequestration globally has a large, cost-competitive mitigation potential. Nevertheless, limitations of soil C sequestration include time limitation, non-permanence, displacement and difficulties in verification. Despite these limitations, soil C sequestration can be useful to meet short- to medium-term targets, and confers a number of co-benefits on soils, making it a viable option for reducing the short-term atmospheric CO2 concentration, thus buying time to develop longer-term emission reduction solutions across all sectors of the economy.