Kevin Trenberth is head of the large US National Centre for Atmospheric Research and one of the advisory high priests of the UN's Intergovernmental Panel on Climate Change (IPCC).
A New Zealander by birth, Trenberth has had a distinguished career as a climate scientist with interests in the use of computer General Circulation Models (GCMs), the basis for most of the public alarm about dangerous global warming. When such a person gives an opinion about the scientific value of GCMs as predictive tools, it is obviously wise to pay attention.
In a remarkable contribution to Nature magazine's Climate Feedback blog, Trenberth concedes GCMs cannot predict future climate and claims the IPCC is not in the business of climate prediction. This might be news to some people.
Among other things, Trenberth asserts "... there are no (climate) predictions by IPCC at all. And there never have been". Instead, there are only "what if" projections of future climate that correspond to certain emissions scenarios.
According to Trenberth, GCMs "... do not consider many things like the recovery of the ozone layer, for instance, or observed trends in forcing agents".
"None of the models used by IPCC is initialised to the observed state and none of the climate states in the models corresponds even remotely to the current observed climate.
"The state of the oceans, sea ice and soil moisture has no relationship to the observed state at any recent time in any of the IPCC models.
"There is neither an El Nino sequence nor any Pacific Decadal Oscillation that replicates the recent past; yet these are critical modes of variability that affect Pacific rim countries and beyond ... the starting climate state in several of the models may depart significantly from the real climate owing to model errors" and "regional climate change is impossible to deal with properly unless the models are initialised".
GCMs "assume linearity" which "works for global forced variations, but it cannot work for many aspects of climate, especially those related to the water cycle ... the science is not done because we do not have reliable or regional predictions of climate".
Strange that. I could have sworn that I heard somewhere that the science was supposed to be settled.
One wonders whether anyone has told CSIRO that their much-vaunted regional climate models are worthless predictive tools. Perhaps someone will ask the CSIRO to refund the swingeing amounts state governments and others have paid for useless regional "climate forecasts"?
Trenberth's statements are a direct admission of the validity of similar criticisms that have been made of GCMs and the IPCC by climate rationalists for many years.
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