RE: "it isn't the real world's fault. Show me the the model that accurately reflects the decrease in measured global temperature over a 50 year period during the 20th century even as the CO2 levels rose."

A hugely false pretext. Who uses relativity and quantum mechanics in everyday engineering calculations? We Know Newtonian physics are not absolutely accurate but we use them anyway because the error in them is not significant. Your premise artificially ignores the fact that there is a lot of annual variation in average temperatures. Most natural processes have variation. That doesn't mean comparing averages between populations has no value or that a model predicting such averages would have no value because it didn't predict the range as well. As has been mentioned numerous times and the raange of model predictions do fall within the actual data. A model predicting no global warming due to CO2 does not yet this is the model you prefer. Why is it the real world doesn't intrude on your support of this model?

RE: "Show me the model that can take a set of known climate values from a given starting point and accurately model what happened over that time period. Until you can do that, you'll never convince me that the models are worth a damn. If the models can't reflect what actually happened, then the models are fatally flawed and useless for predicting the future."

This is an even bigger false pretest. It does not matter all that much if the global temperature will rise x degrees in y or z years if they are on similar time scales. The important prediction is how much impact an X degree rise will have and whether or not the risk from such a rise is worth spending money to prevent over the range of time periods suggested by the models.

No one in there right mind makes risk decisions based on waiting until they know exactly the when and magnitude of a negative consequence. I would think you have done many risk assessments in your field as I have in mine. Do you demand to know the date and magnitude of a failure before impelmenting preventive measures?

RE: "Too bad you seen too blinded by the models themselves to seperate predicted values from historical evidence.

The evidence is that the Earth has warmed significantly as CO2 levels have risen. Models are merely an attempt to extrapolate this trend to assess our risk. They are an imperfect tool still in development, but a far more rational a basis for making risk assessments that greenhouse gases won't cause global warming.

RE: "Without validation, a model is nothing more than a hypothesis that runs on a computer. Depending on unvalidated models to make policy decisions is foolish, to put it mildly."

Major parts of the model have been validated. It is clear that all minor variables of importance have not been included in any single model. In the face of what has been validated your statement is like demanding that the ideal gas law be stricken from text books because it is not accurate. The fact that under many circumstances it points out how a gas will behave and gives you at least an approximation of what will happen gives it utility. This is how I view current climate models. They are not accurate, but they do give an order of magnitude sense of the risks involved. You also keep ignoring that the underlying basics of the model have been validated by laboratory experiment and comparitive planetology. There is plenty of reason to believe not all variables are accounted for, but there is none to believe that the prime driving forces are wrong.

What is foolish is to expect to wait until mounting fatalities and property damage prove global warming is an issue before acting. It is also foolish to assume proven greenhouse gas emmisions will not cause global warming in the absence of ANY supporting evidence. It would be foolish to bankrupt the worlds economy in an atempt to stop global warming, but it is just as foolish to ignore the problem and spend no money on trying to find potential solutions.

You also continue ignore the fact that most real life and political decisions are based on best assessments of risk and benefits not absolute certainty. Until you can admit this, my opinion of you will remain that on this issue and this issue alone personal prejudice outweighs your ability to be objective.

Regards,
Mark