Community Integrated Earth System Model (CIESM): Description and Evaluation

A team effort to develop a Community Integrated Earth System Model (CIESM) was initiated in China in 2012. The model was based on NCAR Community Earth System Model (Version 1.2.1) with several novel developments and modifications aimed to overcome some persistent systematic biases, such as the double Intertropical Convergence Zone problem and underestimated marine boundary layer clouds. Aerosols' direct and indirect effects are prescribed using the MACv2‐SP approach and data sets. The spin‐up of a 500‐year preindustrial simulation and three historical simulations are described and evaluated. Prominent improvements include alleviated double Intertropical Convergence Zone problem, increased marine boundary layer clouds, and better El Niño Southern Oscillation amplitude and periods. One deficiency of the model is the significantly underestimated Arctic and Antarctic sea ice in warm seasons. The historical warming is about 0.55 °C greater than observations toward 2014. CIESM has an equilibrium climate sensitivity of 5.67 K, mainly resulted from increased positive shortwave cloud feedback. Our efforts on porting and redesigning CIESM for the heterogeneous Sunway TaihuLight supercomputer are also introduced, including some ongoing developments toward a future version of the model. Plain Language Summary Based on NCAR Community Earth System Model (Version 1.2.1), a Community Integrated Earth System Model was introduced. It has over 10 major modifications and developments aimed to reduce some persistent biases in Community Earth System Model Version 1.2.1. Evaluation of simulations for Coupled Model Intercomparison Project Phase 6 indicated that the model produced reasonable mean climate states with improvement in rainfall, cloud, and El Niño Southern Oscillation. Community Integrated Earth System Model has an equilibrium climate sensitivity of 5.67 K, much higher than all CMIP5 models. Some of the deficiencies of the model, such as the underestimated Arctic and Antarctic sea ice in warm seasons and the greater warming in the early 21st century, will be investigated in the future. Key Points Community Integrated Earth System Model (CIESM) includes many new developments and modifications Preindustrial control and historical simulations were performed and evaluated Some persistent climate model biases are alleviated, but sea ice is significantly underestimated in the warm season