Models Methods Software

Dan Hughes

Ensemble of Models

There’s a fundamental problem with the ensemble of GCM models approach used in climate science.

Updated 15 August 2010. See below.

Apparently there was not any, none whatsoever, a prior attempts to determine if any models, application procedures, and users were qualified for the calculations. No technical evaluation criteria, and corresponding objective success metrics, were developed and applied in an effort to arrive at a qualified members of the models, codes, application procedures, and users.

It seems that, If you can generate numbers you get included in the members of the ensemble, was everything needed.

At this point, after results using these members have been published and promoted all over the place, how can any consideration be given to filtering the members for future results. Elimination of some members now introduces the question of how does this new and improved ensemble perform relative to the results presented in past publications and promotions. Changes in the members of the ensemble are certain to change the past results.

As has been noted in several places, inclusion of members having arbitrary characteristics is sure to have led to wide variations in the calculated results. And sufficiently wide ranges will always increase the probability that observations will fall within the calculated ranges.

Due to the lack of initial investigations of the qualifications to be included in the ensemble, a fundamental error, I’ll say that eventually this whole approach will crumble. Any artifact built on an insecure foundation will eventually fail.

15 August 2010 Update..

I don’t understand why it has taken so long for Climate Science to simply state a blindingly obvious fact.

Once more into the breach

To put it in a nutshell, there is simply no theoretical, philosophical, or practical basis for the hope that the ensemble mean may coincide with the truth. I have demonstrated that the mean is always a better estimate – in terms of having a lower RMS error – than most of the constituent models, and explained why it is often better than all of the models – but that doesn’t make it the truth. In fact irrespective of how good the models are, the mean of the models is not a plausible climate simulation at all in many respects. The mean is a mathematical object that doesn’t even look like a model – it has far too little variability in both time and space, and numerous other completely unrealistic properties.

To repeat:

To put it in a nutshell, there is simply no theoretical, philosophical, or practical basis for the hope that the ensemble mean may coincide with the truth.

What we determinists have been saying for years.


August 10, 2010 - Posted by | Uncategorized |

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