Fine, now let them start with the known conditions...
from 1000 years ago and see how well it reflects what actually happened. Without that step, no one can say if the model is in any way accurate for predicting what will happen in the next 1000 years. It's really as simple as that.
Too bad you seem to put blind faith in the computers and the programmers without expecting them to prove their model is accurate. Stability over a long run is fine, but validation is essential. That's all I ask before accepting predictions from their models as being conclusive proof of anything. This has nothing to do with politics (at least not to me) but with scientific rigor. "It must be accurate because the computer said so" is the mark of fools who know nothing about computers.