In this chapter, we review the respective influences of land-use change and climate change on the global balance of soil organic carbon (SOC) stocks. Based upon the results of a global biogeochemical model, past-century global land cover change caused a loss of SOC as atmospheric CO₂. This human induced SOC decrease was nearly balanced by the net SOC increase elsewhere due to rising CO₂ and wetter climate augmenting ecosystem primary productivity. In the future, both climate and land cover changes could cause a net source of atmospheric CO₂. Increased litter production may no longer compensate for increased decomposition from warming, particularly in tropical regions, but future SOC changes are highly uncertain. Reduction of the uncertainty requires improvement of future climate projections and land-use scenarios and better understanding of biogeochemical processes controlling SOC turnover.