Our friend Illusory Tenant says "that is not at all what was done."
It is precisely what was done.. Directly mixing apples and oranges was the recently cashiered Phil Jones' "trick." He grafted measured temperature date onto a graph of "reconstructions" of temperature based on "proxy" data (i.e., data other than measured temperature)for the period in which the proxy data doesn't correlate with the measured temperature. This graph, combining two different things and presenting them as the same, was then published in a World Meterological Organization report designed to influence policymakers. The graph was placed on the cover of the report and shows a version of the 1000 year "hockey stick" used to demonstrate that the measured warming trend (which covers only the past 150 years or so) is historically unique.
Tom apparently thinks that the report disclosed what was done by a vague reference to using both "historical and long instrumental" records as well as a reference to another publication that may have provided a better explanation.
Hardly. The report showed several different reconstructions. While the caption may have disclosed the both proxy and instrumental records were used, it did not say that they were combined together.
What one would have needed to do was to admit that the proxy data used in one of the reconstructions only seems to reflect actual temperature for the first portion of the measured period and either stop there or clearly indicate where the reconstruction ends or the actual temperatures have been inserted.
Keep in mind, that this is a critical issue. As noted in my earlier post, these reconstructions are the evidence for historically unique global warming since we do not have a long enough history of temperature data to know whether measured temperature increases are unprecedented or unusual.
Well, Tom says, all this was the cover of one report. But there is more. As Steve McIntyre relates, the IPCC also attempted to "hide the decline" in the tree ring reconstruction and seems to have done so intentionally, fearing that showing policymakers contradictory date would dilute the message if historically unprecedented AGW.
The IPCC "trick" was a little different. It did not involve grafting temperature data onto a line charting proxy data. It simply omitted the inconvenient data like this, The tree ring construction is the green line and was plotted on a chart showing graphs of other reconstructions and actual temperature data:
The tree ring reconstruction had recently been altered (more on that later)and now showed that tree ring data would indicate a very substantial decline in temperatures in years following 1960. That didn't happen, calling into question the accuracy of the reconstruction. So they just omitted the inconvenient data like this:
This contradicts the view that the controvesry was hidden in plain sight. The questions raised by the discrepancies between reconstructive models are precisely the things that the scientists did not want to address because, in their own words, it would be distracting and interfere with a tidy picture. Hiding complications was precisely what they wanted to do.
In fact, the IPCC report in which this was originally done offered no explanation that the reconstruction had been truncated. Steve McIntyre explains:
Contrary to claims by various climate scientists, the IPCC Third Assessment Report did not disclose the deletion of the post-1960 values. Nor did it discuss the “divergence problem”. Yes, there had been previous discussion of the problem in the peer-reviewed literature (Briffa et al 1998) – a point made over and over by Gavin Schmidt and others. But not in the IPCC Third Assessment Report. Nor was the deletion of the declining values reported or disclosed in the IPCC Third Assessment Report. [Dec 11.- IPCC TAR does contain a sly allusion to the problem; it mentions "evidence" that tree ring density variations had "changed in their response in recent decades". Contrary to claims of realclimate commenters, this does not constitute disclosure of the deletion of the post-1960 values in the controversial figure or even of the decline itself.] The hiding of the decline was made particularly artful because the potentially dangling 1960 endpoint of the Briffa reconstruction was hidden under other lines in the spaghetti graph as shown in the following blow-up:
Figure. Blow-up of IPCC Third Assessment Report Fig 2-21.
To my knowledge, no one noticed or reported this truncation until my Climate Audit post in 2005 here. The deletion of the decline was repeated in the 2007 Assessment Report First Order and Second Order Drafts, once again without any disclosure. No dendrochronologist recorded any objection in the Review Comments to either draft. As a reviewer of the Second Order Draft, I asked the IPCC in the strongest possible terms to show the decline reported at CA here:
"Show the Briffa et al reconstruction through to its end; don’t stop in 1960. Then comment and deal with the “divergence problem” if you need to. Don’t cover up the divergence by truncating this graphic. This was done in IPCC TAR; this was misleading. (Reviewer’s comment ID #: 309-18)]"
They refused, stating that this would be “inappropriate”, though a short discussion on the divergence was added – a discussion that was itself never presented to external peer reviewers.
This after a series of e-mails expressing the desire to present a "tidy picture" and to avoid providing "fodder" to skeptics. This sounds like advocacy, not science.
To be sure, one can argue that the claims of historically unique warming are right anyway, relying on other forms of reconstruction or by arguing that the "divergence" is caused by some factor other than a flaw in the reconstruction model. Maybe you can use ice core data (or maybe you can't).
But the thing gets worse and that's where I'll go next.