I have put a comment in Wottsupwithatblog, http://wottsupwiththatblog.wordpress.com/2013/09/13/learning-from-my-mistakes/comment-page-1/#comment-4927
which I post here in case it gets lost. Most readers of this blog will be only too familiar with the argument and can pass on this post.
In debating with climate Pseudo-sceptics,
Q1 is - do you accept that doubling CO2 will increase global temps by ~1C?
If so, Q2 is - what do you accept as the figure for Equilibrium Climate Sensitivity?
In practice, it is very difficult to get a pseudo-sceptic to answer Q1. They have an infinite number of questions, but an aversion to answering even one single question put to them. With persistence, I have sometimes extracted an answer, only to have them go back on it later on. At which point it is valid to terminate the discussion on grounds of inconsistency.
If the answer to Q1 is "no", there is no point in pursuing the discussion, because the pseudo-sceptic is in denial of basic physics and the greenhouse effect, and is therefore beyond reason.
The response to Q2 is interesting. Many p-sceptics do not understand what is meant by ECS, but with those that do it is possible to have a useful discussion of the evidence for and against CS values of 2-4.5C.
The other positive outcome of a discussion framed in this way is that most reasonable Lukewarmers will accept 2C as a high bound of ECS, whereas climatology can accept 2C as a low bound. We can therefore discuss whether the agreed figure of 2C is something that can be viewed with equanimity or not.
So fruitful discussion is still theoretically possible with some kinds of climate sceptics. They are unlikely to change, but the discussion can have a positive influence on the lurkers and the uncommitted.