It’s an assertion repeated by politicians and climate campaigners the world over: “2500 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 1000-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 1900 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?

Wrong.

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.

Compounding this is the fact that IPCC editors could, and often did, ignore reviewers’ comments. Some editor responses were banal and others showed inconsistencies with other comments. Reviewers had to justify their requested changes but the responding editors appear to have been under no such obligation. Reviewers were sometimes flatly told they were wrong but no reasons or reliable references were provided.

In other cases reviewers tried to dilute the certainty being expressed and they often provided supporting evidence, but their comments were often flatly rejected. Some comments were rejected on the basis of a lack of space - an incredible assertion in such an important document.

The attitude of the editors seemed to be that simple corrections were accepted, requests for improved clarity tolerated but the assertions and interpretations that appear in the text were to be defended against any challenge.

An example of rampant misrepresentation of IPCC reports is the frequent assertion that “hundreds of IPCC scientists” are known to support the following statement, arguably the most important of the WG I report, namely “Greenhouse gas forcing has very likely caused most of the observed global warming over the last 50 years”.

In total, only 62 scientists reviewed the chapter in which this statement appears, the critical chapter 9, “Understanding and Attributing Climate Change”. Of the comments received from the 62 reviewers of this critical chapter, almost 60 per cent of them were rejected by IPCC editors. And of the 62 expert reviewers of this chapter, 55 had serious vested interest, leaving only seven expert reviewers who appear impartial.

Two of these seven were contacted by NRSP for the purposes of this article - Dr Vincent Gray of New Zealand and Dr Ross McKitrick of the University of Guelph, Canada. Concerning the “Greenhouse gas forcing …” statement above, Professor McKitrick explained “A categorical summary statement like this is not supported by the evidence in the IPCC WG I report. Evidence shown in the report suggests that other factors play a major role in climate change, and the specific effects expected from greenhouse gases have not been observed.”

Dr Gray labeled the WG I statement as “Typical IPCC doubletalk” asserting “The text of the IPCC report shows that this is decided by a guess from persons with a conflict of interest, not from a tested model”.

Determining the level of support expressed by reviewers’ comments is subjective but a slightly generous evaluation indicates that just five reviewers endorsed the crucial ninth chapter. Four had vested interests and the other made only a single comment for the entire 11-chapter report. The claim that 2500 independent scientist reviewers agreed with this, the most important statement of the UN climate reports released this year, or any other statement in the UN climate reports, is nonsense.

“The IPCC owe it to the world to explain who among their expert reviewers actually agree with their conclusions and who don’t,” says Natural Resources Stewardship Project Chair climatologist Dr Timothy Ball. “Otherwise, their credibility, and the public’s trust of science in general, will be even further eroded.”

That the IPCC have let this deception continue for so long is a disgrace. Secretary General Ban Kai-Moon must instruct the UN climate body to either completely revise their operating procedures, welcoming dissenting input from scientist reviewers and indicating if reviewers have vested interests, or close the agency down completely.

Until then, their conclusions, and any reached at the Bali conference based on IPCC conclusions, should be ignored entirely as politically skewed and dishonest. 

Tom Harris is an Ottawa-based mechanical engineer and Executive Director of the International Climate Science Coalition.

John McLean is climate data analyst based in Melbourne, Australia.