In a recent article on the climate skeptic site Watts Up With That backed up with a published paper in Energy and Environment, Pat Frank argues that current climate simulation models are scientifically useless. In his words:
the huge uncertainty limits in projections of future global air temperatures make them predictively useless
His basic argument seems to be that the effect of varying the key inputs to Global Circulation Models over a reasonable range of plausible values gives such a large range of temperature outputs that we can no longer see the key signals that allow us to judge whether the models are physically correct. In other words the range of uncertainty dominates the signal.
The GCM models can reproduce the past climate because the inputs can be adjusted together to reproduce history but we can't validate whether the combination of inputs is just fortuitously right or represents a physically correct set of values.
I'm skeptical despite my usual doubts about the reliability of any large complex computer models because I find it incredible that we could have spent so much effort on GCMs without a fairly basic form of scientific validation.
So, are Pat Frank's claims remotely plausible? If not, why not? What validation has been done to make the inputs to GCMs physically plausible?
PS for those who are experts on climate science, try to avoid excessive jargon in your answers (or translate the jargon into language educated laypeople can understand.)