CMIP6 GCM validation based on ECS and TCR ranking for 21st century temperature projections and risk assessment.

Global climate models (GCMs) from the sixth Coupled Model Intercomparison Project Phases (CMIP6) have been employed to simulate the twenty-first century temperatures for the risk assessment of future climate change. Here, I rank 41 CMIP6 GCMs according to how successfully they hindcast the reported 0.5--0.6 $^\circC$ global surface warming from 1980 to 2021 using both their published ECS and TCR estimates. The sub-ensemble of GCMs with the best performance appears to be composed of the models with ECS ranging between 1.8 and 3 and TCR ranging between 1.2 and 1.8 ${}^\circ$C, which would imply that only the low-sensitivity models might be realistic. However, alternative climatic records ($e.g.$, the low troposphere ones, comparison between land and ocean regions, and temperature proxy models) appear to suggest that the actual surface global warming from 1980 to date could have been 30% less, which would imply that surface records are too contaminated by urban heats and other local non-climatic biases. As a result, the real global aggregated impact and risk estimates seem to be moderate, which implies that any negative effects of future climate change may be adequately addressed by adaptation programs.