IPCC Errors: Fact and Spin

By RealClimate

Currently, a few errors — and supposed errors — in the last IPCC report (AR4) are making the media rounds, together with a lot of distortion and professional spin by parties interested in discrediting climate science.

Time for us to sort the wheat from the chaff: Which of these putative errors are real, and which are not? And what does it all mean, for the IPCC in particular, and for climate science more broadly?

Let’s start with a few basic facts about the IPCC. The IPCC is not, as many people seem to think, a large organization. In fact, it has only 10 full-time staff in its secretariat at the World Meteorological Organization in Geneva, plus a few staff in four technical support units that help the chairs of the three IPCC working groups and the national greenhouse gas inventories group. The actual work of the IPCC is done by unpaid volunteers — thousands of scientists at universities and research institutes around the world who contribute as authors or reviewers to the completion of the IPCC reports. A large fraction of the relevant scientific community is thus involved in the effort. The three working groups are:

Working Group 1 (WG1), which deals with the physical climate science basis, as assessed by the climatologists, including several of the RealClimate authors.

Working Group 2 (WG2), which deals with impacts of climate change on society and ecosystems, as assessed by social scientists, ecologists, etc.

Working Group 3 (WG3), which deals with mitigation options for limiting global warming, as assessed by energy experts, economists, etc.

Assessment reports are published every six or seven years and writing them takes about three years. Each working group publishes one of the three volumes of each assessment. The focus of the recent allegations is the Fourth Assessment Report (AR4), which was published in 2007. Its three volumes are almost a thousand pages each, in small print. They were written by over 450 lead authors and 800 contributing authors; most were not previous IPCC authors. There are three stages of review involving more than 2,500 expert reviewers who collectively submitted 90,000 review comments on the drafts. These, together with the authors’ responses to them, are all in the public record.

Errors in the IPCC Fourth Assessment Report (AR4)

As far as we’re aware, so far only one — or at most two — legitimate errors have been found in the AR4:

Himalayan glaciers: In a regional chapter on Asia in Volume 2, written by authors from the region, it was erroneously stated that 80% of Himalayan glacier area would very likely be gone by 2035. This is of course not the proper IPCC projection of future glacier decline, which is found in Volume 1 of the report. There, we find a 45-page, perfectly valid chapter on glaciers, snow and ice (Chapter 4), with the authors, including leading glacier experts (such as our colleague Georg Kaser from Austria, who first discovered the Himalaya error in the WG2 report). There are also several pages on future glacier decline in Chapter 10 (“Global Climate Projections”), where the proper projections are used, e.g. to estimate future sea level rise. So the problem here is not that the IPCC’s glacier experts made an incorrect prediction. The problem is that a WG2 chapter, instead of relying on the proper IPCC projections from their WG1 colleagues, cited an unreliable outside source in one place. Fixing this error involves deleting two sentences on page 493 of the WG2 report.