Stratocumulus Clouds of the Subtropical North and South Atlantic
Evan, A.T., Allen, R.J., Bennartz, R. and Vimont, D.J. 2013. The modification of sea surface temperature anomaly linear damping time scales by stratocumulus clouds. Journal of Climate 26: 3619-3630.
In discussing their findings the four researchers report that "most models have negative biases in the mean state of Sc cloud cover and do not reproduce the observed spatial structure of Atlantic Sc clouds." In addition, they indicate that "while the majority of models exhibit some agreement with observations in the meridional structure of the Sc feedback, the vast majority of models underestimate the dependence of Sc cloud cover on the underlying sea surface temperature."
Once again, we have a situation where important aspects of both cloud type and cloud cover are simply not portrayed to an acceptable degree of real-world faithfulness in the "majority" - or better make that the "vast" majority - of CMIP3 models.