The models aren't based on observations and are regularly contradicted by them. GCMs are based on, in theory, physical laws. In practice they don't compute the

The models aren't based on observations and are regularly contradicted by them. GCMs are based on, in theory, physical laws. In practice they don't compute the right temperatures even for today, or the past, so we know they are incorrect or incomplete. Unfortunately nobody really knows why and this fact is hidden by only showing their outputs as self-anomalies, amongst other tricks.