Quantifying progress across different CMIP phases with the ESMValTool

Abstract

More than 40 model groups worldwide are participating in the Coupled Model IntercomparisonProject Phase 6 (CMIP6), providing a new and rich source of information to better understand past,present, and future climate change. Here, we use the Earth System Model Evaluation Tool (ESMValTool) toassess the performance of the CMIP6 ensemble compared to the previous generations CMIP3 and CMIP5.While CMIP5 models did not capture the observed pause in the increase in global mean surface temperaturebetween 1998 and 2013, the historical CMIP6 simulations agree well with the observed recent temperatureincrease, but some models have difficulties in reproducing the observed global mean surface temperaturerecord of the second half of the twentieth century. While systematic biases in annual mean surfacetemperature and precipitation remain in the CMIP6 multimodel mean, individual models andhigh‐resolution versions of the models show significant reductions in many long‐standing biases. Someimprovements are also found in the vertical temperature, water vapor, and zonal wind speed distributions,and root‐mean‐square errors for selectedfields are generally smaller with reduced intermodel spread andhigher average skill in the correlation patterns relative to observations. An emerging property of the CMIP6ensemble is a higher effective climate sensitivity with an increased range between 2.3 and 5.6 K. A possiblereason for this increase in some models is improvements in cloud representation resulting in strongershortwave cloud feedbacks than in their predecessor versions.