Andy Lacis sent me a follow up his guest post
which I have presented below with his permission.
Thanks for the post. It looks very good. No doubt you will be receiving a variety of comments on it.
I am pleased that both Roy Spencer’s and your initial comments were basically that “there is really nothing that is particularly new” in our Science paper, for that would be precisely Jim Hansen’s opinion. Of course Jim Hansen would go further and say that there is nothing that is particularly new about proclaiming CO2 to be control knob that governs the temperature of Earth, since he has been saying that for years.
Roy felt that we were engaged in “circular” reasoning by ASSUMING(?) that water vapor and clouds were feedbacks, hence no surprise about the greenhouse effect collapsing when the non-condensing greenhouse gases are zeroed out.
I am not personally involved with the GCM evaporation and condensation of water vapor treatment. (I think that is Tony Del Genio’s job.) But it is my impression that evaporation and condensation of water vapor in the GCM is all physics based, with perhaps some coefficients based on field campaign observations. Nothing that could be interpreted as an “assumption”.
One of my objectives in writing the Science paper was to make a clear distinction between global warming (which can be understood as a cause and effect problem) and global climate change, which includes the much less well understood natural (unforced) variability on inter-annual and decadal time scales, the well documented 11-year solar variability and sporadic volcanic activity.
Since the natural variability and solar cycle forcing produce fluctuations about the global equilibrium temperature, they make no long term trend contribution (except that for a short climate record, they make it difficult to extract the global warming trend due to GHG increases from the climate record by statistical means).
Accordingly, there is a clear demonstration that without the radiative forcing provided by the non-condensing GHGs, the terrestrial greenhouse effect collapses because there is no structural temperature support to restrain the current climate water vapor from condensing and precipitating. Since atmospheric CO2 accounts for about 80% of the non-condensing GHG forcing, we thus conclude that CO2 acts as a thermostat in controlling the equilibrium temperature of Earth.
I invited Roy Spencer to comment, and he referred me to his post
My comments on Andy’s guest posts will appear tomorrow.