It’s an assertion repeated by politicians and climate campaigners the world over: “2,500 scientists of the United Nation’s Intergovernmental Panel on Climate Change (IPCC) agree that humans are causing a climate crisis.”
But it’s not true. And, for the first time ever, the public can now see the extent to which they have been misled. As lies go, it’s a whopper. Here’s the real situation.
Like the three IPCC “assessment reports” before it, the Fourth Assessment Report (AR4) released during 2007 (upon which the UN climate conference in Bali was based) includes the reports of the IPCC’s three working groups.
Working Group I (WG I) is assigned to report on the extent and possible causes of past climate change as well as future “projections”. Its report is titled “The Physical Science Basis”.
The reports from working groups II and III are titled “Impacts, Adaptation and Vulnerability” and “Mitigation of Climate Change” respectively, and since these are based on the results of WG I, it is crucially important that the WG I report stands up to close scrutiny.
There is, of course serious debate among scientists about the actual technical content of the roughly 1,000-page WG I report, especially its politically motivated Summary for Policymakers which is often the only part read by politicians and non-scientists. The technical content can be difficult for non-scientists to follow and so most people simply assume that if large numbers of scientists agree, they must be right.
Consensus never proves the truth of a scientific claim, but is somehow widely believed to do so for the IPCC reports, so we need to ask how many scientists really did agree with the most important IPCC conclusion, namely that humans are causing significant climate change - in other words the key parts of WG I?
The numbers of scientist reviewers involved in WG I is actually less than a quarter of the whole, a little more than 600 in total. The other 1,900 reviewers assessed the other working group reports. They had nothing to say about the causes of climate change or its future trajectory. Still, 600 “scientific expert reviewers” sounds pretty impressive. After all, they submitted their comments to the IPCC editors who assure us that “all substantive government and expert review comments received appropriate consideration”. And since these experts reviewers are all listed in Annex III of the report, they must have endorsed it, right?
For the first time ever, the UN has released on the Web the comments of reviewers who assessed the drafts of the WG I report and the IPCC editors’ responses. This release was almost certainly a result of intense pressure applied by “hockey-stick” co-debunker Steve McIntyre of Toronto and his allies. Unlike the other IPCC working groups, WG I is based in the US and McIntyre had used the robust Freedom of Information legislation to request certain details when the full comments were released.
An examination of reviewers’ comments on the last draft of the WG I report before final report assembly (i.e. the “Second Order Revision” or SOR) completely debunks the illusion of hundreds of experts diligently poring over all the chapters of the report and providing extensive feedback to the editing teams. Here’s the reality.
A total of 308 reviewers commented on the SOR, but only 32 reviewers commented on more than three chapters and only five reviewers commented on all 11 chapters of the report. Only about half the reviewers commented on more than one chapter. It is logical that reviewers would generally limit their comments to their areas of expertise but it’s a far cry from the idea of thousands of scientists agreeing to anything.