In this case, its perfectly clear that the IPCC don't agree with him, and given the recent academies statement (signed by the RAS) its clear he's not speaking for the RAS either.
Its puzzling that he is an IPCC vice-chair, given his apparent lack of any scientific interest in the issue. He appears (page 2) to be one of 3 vice-chairs of the IPCC bureau (none of whom I've heard of... this may not be their fault, it may be our interests don't overlap; or it may well be because the vice-chairship is a political sop to be given to placate certain interests). But then again, I'm not clear what the IPCC Bureau actually does... it doesn't look like he is connected to the IPCC WG's.
OTOH, although he is doing his best to make skeptic-like statements, he's still with the IPCC consensus:
Global temperatures will likely rise by 1.4-5.8 degrees during the next 100 years. The average increase will be three degrees. I do not think that this threatens mankind. Sea levels, due to rise by 47 cm in the 21st century, will not threaten port cities.
So for T change and SRL, he's straight down the IPCC line - no room for James's bets, sadly. This seems to becoming the way: skeptics are now accepting the IPCC views (YI isn't even trying to argue for the low end of the range) but embedding it in dodgy language. Progress, perhaps. Incidentally, whilst I wouldn't agree with "I do not think that this threatens mankind" (too definitively dismissive) I have some sympathy for that view, as I've written elsewhere. If skeptics like YI could just rephrase their language a bit, things could be so much better. All he is really saying is "We accept the WGI consensus but don't agree on the future damage". But perhaps thats too boring an opinion to print.