:::::::And? Evidence != proof! And of course I can prove a computer model false (i.e. falsify it). It is false if the theory it is based on is false, or it is false if it does not faithfully implement the theory. Both cases are possible, and both are, in principle, detectable. But the fact is that our current GCM models are rather good at explaining past and current climate variations, both temporarily and spatially. That's why we put some trust into them. That is the scientific method. You create a theory, and you test it. If the test succeeds, you gain confidence. Do it often enough, and you gain a lot of confidence.