Ah, but that's not at all the same as not addressing it, or as you state "I have never seen anyone talk about this alternative hypothesis." (of course I read it, and asked that question)
They are talking about it, and saying that it's a potential source of error that nobody knows how to account for yet, which is pretty common in science. If someone can demonstrate that the potential effect is dominant, it's a real problem. If someone can demonstrate that the potential effect is trivial it can safely be left alone. Otherwise you do the best modeling you can with the best data you can and talk about the possible confounding issues as so we proceed.
So I don't see any particularly damning issue here, have I missed something? It would be nice to resolve the differences between estimates. Is i the lack of analysis of radiative forcing that is bothering you? Do we have any reason to believe it can be a significant term? These sources of vapor are certainly not large (relative to total sources of water vapor in the atmosphere) so I'm not seeing the mechanism.
This really isn't my area, and as always I'm more than happy to be wrong (I learn more that way).
