Read here. Richard Tol is a world expert who has been involved with the IPCC's previous reports. In a series of posts at Roger Pielke Jr's blog he has been examining bias within the IPCC report, specifically the "Working Group III" report and has found it wanting (see below).
His last sentence is the one that begat the headline for this C3 post: "Dr Ottmar Edenhofer of the Potsdam Institute for Climate Impact Research was one of the lead authors of Chapter 11 where most of the “errors” originate. He has since been appointed as the co-chairperson of WG3 for the Fifth Assessment Report of 2014."
Other gems:
"The Fourth Assessment Report of Working Group 2 (II) of the Intergovernmental Panel on Climate Change has been widely criticised for being overly pessimistic about the impacts of climate change. The IPCC has admitted that errors were made, but argues that the mistakes were just that. However, all errors point in one direction: alarmism about climate change. This suggests, at least, an inadvertent bias....In the previous guest posts, I argue that Working Group 3 (III) also contains mistakes, and that most errors point in one direction: optimism about the impacts of climate policy. The other mistakes reveal the inability of the IPCC to constructively engage with valid criticism."
"In sum, the review process of the IPCC failed miserably. AR4 of WG3 substantially and knowingly misrepresents the state of the art in our understanding of the costs of emission reduction. It leads the reader to the conclusion that emission reduction is much cheaper and easier than it will be in real life."
Tol's previous postings: One, Two, Three, Four, Five, Six