[willyt]

The reason clouds are starting to be simulated now where they weren't before is probably because we have only recently had the computing power available to do this at the level of detail required. Switching the 'clouds' feature on and off is part of the model verification process. Listen to this podcast[0], it's a in depth technical discussion about weather forecasting models with the actual scientists that create them. They discuss model verification for weather models and they touch on how this also applies to climate modelling.

[0]http://omegataupodcast.net/326-weather-forecasting-at-the-ec...