Re-reading Richard Tol's post at Die Klimazweibel (can anglophone readers call it The Climate Onion?), I was struck by this:
The models assessed by the IPCC all have that abatement costs grow and accelerate as targets become more stringent. Typically, doubling the rate of emission reduction would lead to a quadrupling of costs. The cost curve in SPM.6 (and SPM.4) bends the wrong way: Incremental costs fall as policy become stricter.
This was not picked up by the referees of the SPM because neither Table SPM.4 nor Table SPM.6 appeared in the drafts circulated for comment.
What is pricking my interest in the idea that this part of the report was not actually reviewed at all, and the reason I'm intrigued is that it's not the first time I've come across this kind of thing.
In The Hockey Stick Illusion, I cover the various drafts of the paleoclimate chapter and explain how the report's explanation of the divergence problem was only inserted in the final report - it did not appear in the drafts and was therefore entirely unreviewed.
And just the other day, in the posting I did on the Asia chapter of Working Group II, I noted that some major changes had been made between the second order draft and the final report. There was, however, one interesting change in that chapter that I've been meaning to cover and this seems like a good opportunity to explain it.
In the second order draft, the following statement on crop yields appears in the Executive Summary:
In recent years, the potential crop yield in most countries of Asia has exhibited a declining trend, likely due to rising temperatures.
Note carefully: it's potential yield, in most countries, and likely due to rising temperatures. Now see what happened to that statement after the review process was complete.
The crop yield in many countries of Asia has declined, partly due to rising temperatures and extreme weather events.
So, we are now talking about actual crop yields, not potential ones and the attribution to rising temperature has had any trace of uncertainty removed. One can say in partial mitigation that at least "most" has changed to "many". I've noted in my earlier posting that there were no relevant reviewer comments on this section of the report.
One would expect changes after the second order draft to be minor tweaks, but it appears that in these sections of the report at least, chapter authors are quite happy to make major changes. One wonders just how prevalent this kind of thing is. Could it be that this is the way that the small cabal who run the IPCC sideline the 2500 reviewers we are told about so often; how they control the output in the assessment reports?
Could be.