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I have actual experience with modeling complex physical systems. In my case, all the physical parameters of note are known to at least three significant digits of precision. We have no “free variables” to really “tune” the system. It is a nonlinear, chaotic system, a similar situation as Earth’s climate, though much simpler.

Finally, after many many years of working on the model, we manage to get it to match the result of our experiment, well, at least in substantial manners! Mind: we had a real opportunity to vary single parameters in the experiment which greatly helped our ability to eliminate faulty program assumptions.

Based on the model, we changed the size and shape of the physical structure in a rather minor way. The parameters we had to change were all known to at least FOUR significant digits of precision, and most were FIVE or more. Spent a lot of time and money building the new chamber based on the model. UTTER FAILURE! Years later- we still don’t know why. We will have to rebuilt the whole model.

This system is probably only one percent of the complexity of Earth’s climate system. The important parameters in the climate are CERTAINLY not all known. Many of those known are only vaguely understood, and the precision with which we can measure them is often not known with even two digits of precision. There are literally thousands of parameters that are adjusted by the modelers to get the results that even vaguely represent Earth’s system.

I tell alarmist females that I could use the climate models to design the dress they are wearing now, including all the folds when they are standing up or sitting, by adjusting the free parameters in the GCM’s. I’m not joking about that, either.