Six months ago I posted, “Sensational statements by Dr Kevin Trenberth, IPCC supporter”, June 23rd, 2007 by Warwick Hughes.
Pat Frank says:
December 18th, 2007 at 3:40 pm
The central point Trenberth makes about GCM predictive reliability is this one, “The current projection method works to the extent it does because it utilizes differences from one time to another and the main model bias and systematic errors are thereby subtracted out. This assumes linearity.”
What he’s saying is that one can reliably project future forced global temperature differences because in subtracting forced GCM runs from control GCM runs all the errors subtract away, leaving a reliable trend in anomalies.
But this is assuming much more than mere “linearity.” It assumes the GCMs procduce global climate projections with completely accurate slopes. Trenberth is claiming that GCM runs are only linearly offset by some standard vertical magnitude from being fully correct — and the same standard vertical magnitude is present in both control runs and forcing runs. Therefore, subtracting the latter from the former produces accurate anomalies.
But this is very different from assuming mere linearity. It supposes that the physical representation of the global climate itself — the physical theory in the GCMs — is complete and accurate. The errors are merely from imperfect measurements and a too-coarse resolution because of computer limitations. This assumption — assertion, really — is entirely unjustifiable.
For example, all GCMs include a hyperviscosity because the Navier-Stokes equations can’t be solved at all the necessary levels of resolution. The hyperviscosity, which is completely unphysical, is the only thing that makes the GCMs integrable — they would catastrophically diverge otherwise. Because there is an unphysical hyperviscosity, the parameterizations in GCMs must also be unphysical in order to compensate. Consequently, GCMs inherently cannot be physically correct. Trenberth’s claim includes an implicit but absolutely central assertion that cannot be true. The physical theory in GCMs is neither correct nor complete. Trenberth is wrong, the reliability of temperature predictions can not be claimed accurate through taking differences, and the whole of AGW so-called science is powered by this sort of tendentious delusionalism.