Response of terrestrial carbon cycle: Climate variability in CarbonTracker and CMIP5 Earth System Models

Terrestrial carbon sink in the coupled carbon-climate models of CMIP5 (the fifth phase of the Coupled Model Intercomparison Project) is affected by various climatic factors. However, the spatio-temporal carbon exchange between land and atmosphere still has a lot of uncertainty in these models. This study focuses on the variability in terrestrial carbon flux in response to climatic variation. The relationship between climate factors and land carbon flux is analyzed by comparisons between ten CMIP5 models and CT (CarbonTracker). From 2001 to 2012, the CMIP5 multi-model ensemble mean overestimated the NEP (Net Ecosystem Production) compares to CT. Several CMIP5 models strongly simulate carbon sink in the Africa, Southeast Asia, South America, and some areas of the United States. Results of partial correlation between temperature and NEP show positive correlation with temperature at higher than mid-latitudes in the Northern Hemisphere but negative correlation represent at other latitudes in CT and most CMIP5 models. The CMIP5 models except for few models indicate that the precipitation is affecting NEP positively at 30°N-90°N, but higher percentage of negative correlation shows at 60°S-30°N compare to CT. NEP has positive correlation with solar radiation at most latitudes in CT and most CMIP5 models. For each season, the correlation between temperature (solar radiation) and NEP in the CMIP5 ensemble mean is similar to that of CT, but overestimated. Climate variability of NEP is strongly affected by temperature and solar radiation. There is a direct correlation between NEP and precipitation especially in the tropics. The variability of terrestrial carbon flux with respect to temperature and solar radiation in CMIP5 model is similar to CT, but relationship between precipitation and terrestrial carbon flux is different from CT due to the differences in the simulation performance of each parameter in CMIP5 models.