Willis Eschenbach sent in the following information about the Coupled Model Intercomparison Project (CMIP) project. I’ve not checked the analysis myself, but it is an interesting topic and well worth a separate thread. There are some other pretty good posts like this. If people want to suggest some back posts for individual threads, it just takes a couple of minutes for me to transpose them and I’m happy to do so.
Dana provided a very relevant link to the Coupled Model Intercomparison Project (CMIP) project. Here’s Figure 1 from the project, showing the “control run” for each computer. (Before they try to hindcast the past or forecast the future, they do a “control run”. This is described by the CMIP as a run with constant forcing, rather than a run where the CO2 is changing over time.) Here are the results from that control run:
Now, before we start talking about subtle changes in temperatures from subtle changes in atmospheric gases, you’d imagine that all of the GCMs would at least be able to give an accurate figure for the current global temperature … but noooooo …
Instead, we find that when presented with identical forcings, the various GCMs give results for the current global temperature that vary from 11.5° to 16.5°C.
Why does this matter? Well, we’ve been discussing the fact that the change in forcing is expected (according to DanàÆàs reference, which agrees with my own forecast) to be on the order of 1 watt per square meter over the next fifty years. So we’re asking the computers to be accurate to this size of forcing, accurate to within 1 w/m2.
The difference in the radiation temperatures from the highest to the lowest GCMs global control runs (from 16.5°C to 11.5°C), on the other hand, is 27 watts per square meter … clearly, some of them are very, very wrong. Heck, look at the top red line. It changes by 1°C, that’s 5.5 w/m2, when the forcings haven’t changed at all. Can this GCM tell us anything about a 1 watt/m2 change over 50 years? I don’t think so …
What is the IPCC response to this? You’ld think that with the Fourth Annual Report coming up, that by now they would have created some standards and would only consider models that met those standards … but nooooo … that might offend somebody, I guess. So they just average them all together, the good, the bad, and the ugly, and call it an “ensemble” to make it sound scientific. Their only standard seems to be that the computer program be a) really complex, and b) have lots of people working on it. Other than that, anything goes.
To me, that’s not science, that’s intellectual dishonesty.
Perhaps the biggest scam in all of this is that they tune their models to reproduce the past temperature trends, and then claim that they are ready for prime time because they can reproduce the past … folks, the fact that they can reproduce the past means absolutely nothing. They have tuned their models to reproduce the past, it would be embarrassing if they couldn’t, but it doesn’t prove a thing.
The real way to test GCMs against the past is to compare other metrics than temperature trends, to compare such things as the standard deviation, interquartile range, derivatives, skewness, kurtosis, outliers, and other statistical measures, for their hindcasts with the actual reality. When we do this, we find that although they may be able to roughly reproduce the temperature trends, they do it by predicting patterns of temperature that are widely different from reality “¢’¬? temperatures that wander all over the place, or temperatures that hardly change at all month to month, or temperatures that change monthly more than has ever been seen in the historical record. Yes, they reproduce the trends … but that is by no means enough.
In fact, even if they could reproduce all of the above, that may not be enough. As the performance of computer models in related fields such as the stock market has proved over and over again, enough so that it is a required disclaimer in US brokers advertisements, “Past performance is no guarantee of future results, and there can be no assurance that any investment vehicle will perform as well as the prior performance results illustrated herein.”
… and the same disclaimer should be required on all GCMs … but I digress …
I am always amazed by the unbelievable credulity of people who, knowing full well that computers cannot forecast next week’s weather, nonetheless believe that they can forecast next century’s climate. Folks, they can’t even get today’s global temperature right, they’re all over the map, temperatures from 11.5°C to 16.5°C … do you really think they can forecast next century’s climate?