In my first post, I criticised Peter Stott for muddling the IPCC’s definition of climate change. It seems that I owe Stott an apology: it’s not he who got the definitions confused, it’s the IPCC itself.
I gave a link to the IPCC’s definition of climate change, from the 2007 AR4 synthesis report. This states that
Climate change in IPCC usage refers to a change in the state of the climate that can be identified (e.g. using statistical tests) by changes in the mean and/or the variability of its properties, and that persists for an extended period, typically decades or longer. It refers to any change in climate over time, whether due to natural variability or as a result of human activity.
So it’s quite clear that when the IPCC says climate change, it means either man-made or natural change. And this is what the IPCC studies, since of course CC = “climate change”. The closest thing I can find to a definition in AR5 is Chapter 1 page 5, which again refers to any change, regardless of cause.
But hang on. There’s another document called “Principles Governing IPCC Work”. This says
The role of the IPCC is to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation.
So now it appears that the IPCC is only concerned with man-made climate change! This was probably the statement Peter Stott was referring to.
Related confusion arose in a twitter conversation between Richard Tol, Andy Revkin and Roger Pielke Jr:
@RichardTol That note stressing that “climate change” ≠ “anthropogenic climate change” really muddles significance of many WGII findings.
— Andy Revkin (@Revkin) November 2, 2013
— Roger Pielke Jr. (@RogerPielkeJr) November 2, 2013
The link leads to a 2005 paper by Pielke, Misdeﬁning ‘‘climate change’’: consequences for science and action, which draws attention to the confusion between the narrow definition used by the UNFCC and the broader one used by the IPCC, and also notes the “schizophrenic” internal inconsistency of definitions within the IPCC.
The reference here to WGII and a note refers to the recently leaked WGII report, see this Bishop Hill thread, where Hilary Ostrov comments on a footnote,
 Attribution of observed impacts in the WGII AR5 links responses of natural and human systems to climate change, not to anthropogenic climate change, unless explicitly indicated.
This of course is in contradiction with the second blockquote above, that says the IPCC’s role is to assess the impacts of human-induced climate change.
What a shambles.