Change in soil organic carbon and its climate drivers over the Tibetan Plateau in CMIP5 earth system models.

Soil organic carbon (SOC) is the largest carbon pool in the terrestrial carbon cycle, which is closely linked to climate change and global warming feedbacks. Based on proxy observation data and outputs from the fifth phase of the Coupled Model Inter-comparison Project (CMIP5), we analyzed quantitatively the spatial distribution and temporal change for SOC using boosted regression trees (BRT) over the Tibetan Plateau (TP). The ensemble proxy observation SOC stock data indicated a decreasing spatial distribution from southeast to northwest over the TP. We used data from ten CMIP5 earth system models (ESMs) for SOC, which exhibited differences. However, the CMIP5 multi-model ensemble (MME) result presented a similar spatial distribution pattern to the ensemble proxy observation SOC, while SOC storage and turnover times from the CMIP5 MME model were less than the ensemble proxy observation. The BRT results indicated that air temperature (Ta) accounted for 44.81% of the relative contribution and was the most influential variable on MME SOC. This was followed by net primary production (NPP), with a 19.09% relative contribution. The relative influence of the top 10 cm soil temperature, total soil water, and precipitation on MME SOC was 13.55%, 12.68%, and 9.87%, respectively. Using the BRT method to determine the spatial distribution of relative contribution of SOC for these five variables demonstrated that Ta was mainly higher over the central and northwestern regions of the TP, and NPP was higher over the western central regions and along the plateau's eastern edge. The statistical frequency of maximum relative contribution to SOC for the five variables indicated that the relative contribution of NPP covered the largest area, with 32% of the total grid numbers, followed by Ta, with 25%. [ABSTRACT FROM AUTHOR]