This debate continues to generate more heat than light. I think it's time to attempt to bring some clarity into the proceedings.
One of the main problems (IMO) is the Rorschach-test nature of the original article. "Climate scientists must not advocate". There's a lot of room for people to read their own meanings into this. I'm not blaming Tamsin for this - the original article was necessarily brief and she can't be criticised for not anticipating every possible interpretation and misunderstanding. But I don't think I'm alone in having been repeatedly accused of misinterpreting what she wrote (though she herself has not commented one way or the other), and I don't think it is reasonable for people to throw out quite serious criticisms without being prepared to explain what they actually mean. One obvious way of moving forward is to ask for examples of this advocacy that has apparently cause so much trouble. What does this actually mean in practice?
So here's a test case for you - the recently updated AGU Position Statement on Climate Change (full statement here). Is this an example of climate scientists advocating on policy, outside of their areas of professional expertise? Does it reduce trust in climate science and/or climate scientists? Or are they just stating some fairly obvious and well-established truths?
I think it's obvious enough that (self-identified) climate sceptics will say that yes, the AGU is inappropriately dabbling in politics. Indeed a few of the usual suspects have already indicated as much (h/t Stoat) and I presume their followers will agree. I'm really more interested in the views of those who regard themselves lying in the mainstream in their scientific view - which we can probably take to mean, broadly in agreement with the content of the IPCC report (WG1 of AR4). The AGU is a huge and influential organisation, and probably a large proportion of climate scientists are AGU members at least on an occasional basis - you have to join to submit an abstract to one of the meetings, and it's only $20 anyway. (FWIW, I think my membership has just lapsed, at least my EOS subscription appears to not be working, and I'm not going to San Francisco this time round). So this is rather more than just a theoretical question about some inconsequential bit of fluff on the internet. I'm asking if one of the biggest voices in climate science is behaving appropriately in the opinion of its (real or potential) members.