Mitigation of Climate Change is open for comment (at the bottom). Now, you would think that with all the fuss about the Working Group I, the Physical Basis report that this would have been noted somewhere, as the WGIII report is the one that puts some costs onto climate change. But the big blogs are silent.
Viewing the drafts does require that you have an institutional commitment, and that you acknowledge that
the purpose of receiving the draft is for review and comment; and do you agree that you will not quote, cite, or publish, through any medium, any of the contents of the draft report?The comment periods for WGI and WGII (Impacts, Adaptation, and Vulnerability ) have already passed, and these are no longer available for comment. You can get a good idea about what will be in the WGII report from the outline. However, for those with too much time on their hands, you can quibble with the guidance for Lead Authors on addressing uncertainties.
Still, without revealing any of the contents of these drafts, one can read them, and doing so can inform one's thinking.
Allow me to address another red herring that has been dragged across the discussion of anthropic climate change, the tension between adaptation and mitigation. It must be recognized that any response will be a balance between these two approaches. In business as usual of course, the entire response has to be adaptation, in which case, one can wonder at the cost of, for example, moving hundreds of millions of people out of low lying areas such as Bangladesh, or the loss of capital associated with the flooding of low lying areas on the East Coast of the US. Anyone who claims that the problem can be met with adaptation alone has about 60 cards in his deck.
The cost balance will be determined by the political decision of where greenhouse gas concentrations will be stabilized. Before you get into a discussion of what the cost of dealing with climate change is, you have to pick a stabilization point. Arresting the situation where it is, is simply not in the cards. Anyone claiming that this can be done is not playing with a full deck.
Even 450-500 ppm CO2 equivalent will be extremely difficult and expensive. 600-650 ppm (essentially doubling CO2 from pre-industrial) is doable. The questions that WGIII attempts to answer are what are the costs at different levels.
Clearly the balance of importance in AR4 is shifting to WGII and WGIII and away from WGI.