A Summary of Richard Tol's look at the IPCC AR4 Report

By Richard Tol

The Fourth Assessment Report of Working Group 2 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 (in one case jointly with Chris Green) argue that Working Group 3 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. I also looked at the reviewer comments and the responses. The errors were identified during the review process, but made it into the final report nonetheless.
In the post about population projections, I show that the IPCC misquotes a paper that cast doubt on the IPCC SRES scenarios. In the post about exchange rates, I demonstrate that the IPCC misrepresents or omits papers that criticise the IPCC SRES scenarios. These two cases suggest that the IPCC has lost the ability to be self-critical.
In the post about double dividends, I show that the IPCC’s claims that climate policy would stimulate economic growth and create jobs are not based on peer-reviewed literature. Furthermore, the IPCC fails in its role as policy advisor. Ecological tax reform could promote growth and employment – but only under very narrow conditions. An honest broker would spell out those conditions. A stealth advocate would suggest that those conditions are rather easily met – as does the IPCC.
In the post about technological progress, I show that the IPCC emphasizes the results of studies that show that the costs of emission reduction are lower than previously thought, while suppressing or misquoting studies that show the opposite – despite credible evidence that the latter papers are closer to the truth. The IPCC assessment is certainly incomplete, but I would argue it is biased.
In the post about selection bias, I demonstrate that the IPCC summarises the results of multiple abatement studies in a misleading way, failing to alert the reader to the fact that the estimates of the costs of stringent emission reduction are unrepresentative of the literature and severely biased downwards. This is deception pure and simple.
In the post about double-counting, we show that the IPCC confuses carbon savings due to “market forces” with carbon savings by “climate policy”. This again would suggest to the unsuspecting reader that emission reduction is cheaper than it really is. The IPCC again did this in spite of protests by the referees. The IPCC deliberately puts the reader on the wrong foot.
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.
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. Read more.