Yes, I know that alternative theories have been proposed. However, none of them so far has outperformed the AGW hypothesis in explaining observed data on global temperature.
Nonsense. Provisionally accepting a hypothesis because it is currently the best explanation we have for the observed data is not the same thing as “taking it on faith”.
Nor is the AGW hypothesis “untestable”, any more than theories about galaxy formation in the early universe, or continental drift, or the evolution of early hominids on earth are “untestable”.
Sure, we can’t test them by running repeated controlled experiments the way we do in many lab sciences, but we can still test their predictions against the data that we collect.
I’m not trying to downplay any of the uncertainties or unanswered questions in the AGW hypothesis; it’s still a very incomplete theory and may yet have to be drastically modified or even (less probably, but not inconceivably) rejected altogether in favor of a substantially different hypothesis.
In the meantime, though, it amounts to willful ignorance to call the AGW hypothesis “not good science”. On the contrary, AGW is not only a perfectly legitimate scientific hypothesis but currently the best scientific hypothesis available to describe current climate trends. It would be silly to try to pretend that it’s thoroughly established or infallible, but it’s even sillier to try to pretend that it somehow shouldn’t be accepted by researchers as a reasonable working hypothesis.