Abstract: The objective of this study was to analyze the effects of climate change and doubled atmospheric CO₂ concentrations, as well as the combined effects of climate change and doubling atmospheric CO₂ concentrations on soil organic carbon (SOC) in the alpine steppe of the northern Tibetan Plateau using the CENTURY model. The results indicate that SOC loss in climate change scenarios varied from 49.77– 52.36% in the top 20 cm. The simulation results obtained for a P1T0 scenario (increased precipitation and unchanged temperature), P0T1 scenario (unchanged precipitation and increased temperature), and P1T1 scenario (increased precipitation and increased temperature) were similar. The alpine steppe in the P1T1 scenarios lost the greatest amount of SOC (844.40 g C m^-2, representing the least amount of SOC) by the end of the simulation. The simulation for P0T1 scenarios resulted in a 49.77% loss of SOC. However, SOC increased 12.87% under the CO₂ doubling scenario, compared with the unchanged CO₂ scenario. CO₂ enhancement effects on SOC were greater than the climate change effects on SOC alone. The simulation of combined climate change and doubling atmospheric CO₂ led to a decrease in SOC. This result indicated a decrease of 52.39% in SOC for the P1T1 + 2 × CO₂ scenario, 49.81% for the P0T1 + 2 × CO₂ scenario, and 52.30% for the P1T0 + 2 × CO₂ scenario over the next 50 years. Therefore, SOC content in the alpine steppe will change because of changes in precipitation, temperature and atmospheric CO₂ concentrations.

Key words: soil organic carbon (SOC), modeling, CENTURY, climate change, CO₂ concentration