The work of M.D.Z. and S.A.K. is supported by the Regional and Global Climate Modeling Program of the Office of Science of the US Department of Energy (DOE) and was performed under the auspices of the US DOE by LLNL under contract DE-AC52-07NA27344. D.A.R. was supported by the National Science Foundation under Grant AGS-1538532 to Colorado State University. M.J.W. is supported by the Joint UK BEIS/Defra Met Office Hadley Centre Climate Programme (GA01101). We acknowledge the World Climate Research Programme's Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modelling groups for producing and making available their model output. For CMIP, the US DOE's Program for Climate Model Diagnosis and Intercomparison provided coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. We thank D. S. Linehan, S. Po-Chedley, B. D. Santer, and K. E. Taylor for stimulating discussions and comments on an earlier version of this Commentary.