One of the curious aspects of IPCC peer review procedure is that the ultimate authority for accepting or rejecting comments by peer reviewers rests with the IPCC authors, as opposed to the Review Editors. Review Editors are supposed to see that authors respond to Review Comments, but don’t follow up to see that it’s actually done.

Here’s a strange example in the AR4 Medieval Warm Period Box – the one which Overpeck (483. 1105978592.txt) described in January 2005 as follows:

Hi all – attached is Keith’s MWP box w/ my edits. It reads just great – much like a big hammer. Nice job.

Overpeck liked the metaphor and in a June email (537. 1119924849.txt) talked of using the MWP Box “to hammer in one more nail” and again in July (550. 1121686753.txt) talked of “hammering home” their MWP message – language that caused even Briffa (551. 1121721126.txt) to worry about Overpeck’s intonations.

One of the blocks in Overpeck’s beloved MWP Box was Hughes and Diaz (1994), who had challenged the concept of a MWP early on. The MWP Box cited Hughes and Diaz 1994 favorably as follows:

A later study, based on examination of more quantitative evidence, in which efforts were made to control for accurate dating and specific temperature response, concluded that it was not possible to say anything other than “… in some areas of the Globe, for some part of the year, relatively warm conditions may have prevailed” (Hughes and Diaz, 1994).

However, there were some important issues about whether Hughes and Diaz 1994 actually proved their point – in particular, whether their tree ring chronologies preserved any centennial variance. Remarkably, Jan Esper and I, in our capacity as AR4 reviewers were in complete agreement on this point.

Esper commented on this language in the AR4 First Draft as follows:

6-1281 A 28:21 28:24 I guess, I am a bit skeptical about the Hughes and Diaz (1994) paper, since it is conceptually similar to the Soon and Baliunas study, and even more importantly, the paper was published before the whole discussion on the preservation of low frequency trends in long tree-ring records really started. An evaluation of detrending techniques applied to tree-ring data and the consequences on retained low frequency variations would likely alter the main conclusions of the Hughes and Diaz paper. So, I think that the paper is in some sense outdated. [Jan Esper]

IPCC (i.e. Briffa) stated that they “in large part accepted” the observation:

Noted – and in large part accepted. Will considered amending text to reflect this.

I made essentially the same point as follows:

6-1282 A 28:21 28:23 Hughes and Diaz [1994] uses proxy series which do not capture centennial trends. It is not usable. [Stephen McIntyre]

While they “in large part accepted” the point as made by Esper, with me that merely said that the point was “taken into account”:

Taken into account – will elaborate

Despite these undertakings, the language in the Second Draft was word-for-word identical to the language in the First Draft, reading as follows:

A later study, based on examination of more quantitative evidence, in which efforts were made to control for accurate dating and specific temperature response, concluded that it was not possible to say anything other than “… in some areas of the Globe, for some part of the year, relatively warm conditions may have prevailed” (Hughes and Diaz, 1994).

Esper didn’t submit comments on the Second Draft. I re-iterated the comment from the First Draft, this time citing Esper’s First Draft comment as additional authority:

6-1139 B 28:56 28:56 Nearly all of the Hughes and Diaz [1994] proxy series have been processed in a way which do not capture centennial trends e.g. the Guiot series and the Serre-Bachet series, the Polar Urals version of Graybill and Shiyatov. In his comment on the FOD, Esper also pointed out that he was “skeptical” about the Hughes-Diaz paper for the same reason. It is irrelevant and should not be used as supposedly refuting Lamb. [Stephen McIntyre (Reviewer’s comment ID #: 309-35)]

This time the comment was rejected out of hand.

Rejected – the citation is a correct one and uses considerably more (and more recent) data than the reviewer refers to. It is not irrelevant.

The issue was whether the Hughes-Diaz chronologies had any centennial variance: they don’t. IPCC’s answer is unresponsive to the criticism – which remains valid.

In the final AR4 report, the language was word for word identical to the First Draft:

A later study, based on examination of more quantitative evidence, in which efforts were made to control for accurate dating and specific temperature response, concluded that it was not possible to say anything other than ‘… in some areas of the Globe, for some part of the year, relatively warm conditions may have prevailed’ (Hughes and Diaz, 1994).



