A few days ago Andy Revkin put a tweet out asking for comments on an old blog post by Isaac Held. Held had been looking at transient climate response (TCR) which he estimated at 1.8, a number that he observed was on the low side.
I pointed the tweet and the post out to Nic Lewis, who has been examining it in detail and seems to have uncovered a few issues which are appended in a comment to Held's post. These issues might lead to still lower estimates of TCR.