From Section 1, "Inside the Email Trail" (pages 15 to 18):
Perhaps the most infamous example of this comes from the "hide the decline" email. This email initially garnered widespread media attention, as well as significant disagreement over its implications. In our view, the email, as well as the contextual history behind it, appears to show several scientists eager to present a particular viewpoint-that anthropogenic emissions are largely responsible for global warming-even when the data showed something different. Here is the email as written in 1999 by the CRU's Jones:
"I've just completed Mike [Mann]'s Nature trick of adding in the real temps to each series for the last 20 years (ie from 1981 onwards) and from 1961 for Keith's to hide the decline."
Jones's "trick" arose because of disagreement over the "hockey stick" temperature graph, authored by, among others, Dr. Michael Mann. As is noted elsewhere in this report, the hockey stick showed a relatively straight shaft extending from 1000 AD to 1900, when a blade turns sharply upward, suggesting that warming in the 20th century was unprecedented and caused by anthropogenic sources. The IPCC imputed great significance to the graph as it was featured on page 1 of the "Summary for Policymakers" in its Third Assessment Report.
The Jones email has been the subject of competing interpretations. In defending himself, Jones said, "The word 'trick' was used here colloquially as in a clever thing to do. It is ludicrous to suggest that it refers to anything untoward." Similarly, echoing Jones, Dr. John Holdren, President Obama's Science Adviser, asserted that "trick" merely means "a clever way to tackle a problem." Both Holdren's and Jones's explanation of "trick" used in this context has evidentiary support. Unfortunately, neither Jones nor Holdren addressed the "problem" that confronted Jones and his colleagues. The problem in this case is the so called "divergence problem."
The divergence problem is the fact that after 1960, tree ring reconstructions show a marked decline in temperatures, while the land-based, instrumental temperature record shows just the opposite (more on this below).
For some scientists, the divergence of data was a cause of great concern, but not necessarily for reasons scientific. For instance, IPCC author Chris Folland warned in an email that such evidence "dilutes the message rather significantly" that warming in the late 20th century relative to the last 1,000 years is "unprecedented":
"
A proxy diagram of temperature change is a clear favourite for the Policy Makers summary. But the current diagram with the tree ring only data somewhat contradicts the multiproxy curve and dilutes the message rather significantly. We want the truth. Mike thinks it lies nearer his result (which seems in accord with what we know about worldwide mountain glaciers and, less clearly, suspect about solar variations). The tree ring results may still suffer from lack of multicentury time scale variance. This is probably the most important issue to resolve in Chapter 2 at present."
Specifically, Jones et al. expressed concern about a temperature reconstruction authored by Keith Briffa, a senior researcher with CRU. Because reliable thermometer data go back only to the 1850s, scientists use proxy data such as tree rings to reconstruct annual temperatures over long periods (e.g., 1000 years) (it must be noted that proxy reconstructions are rife with uncertainties). Unfortunately for those in the email chain, Briffa's reconstruction relied on tree ring proxies that produced a sharp and steady decline in temperature after 1960.
This conflicted with the instrumental temperature readings that showed a steep rise. Briffa's graph was, according to Dr. Michael Mann, a "problem":
"Keith's series...differs in large part in exactly the opposite direction that Phil's does from ours. This is the problem we all picked up on (everyone in the room at IPCC was in agreement
that this was a problem and a potential distraction/detraction from the reasonably consensus viewpoint we'd like to show w/ the Jones et al. and Mann et al. series."
Briffa later addressed the "pressure to present a nice tidy story" about the "unprecedented warming in the late 20th century." In his view, "the recent warmth was matched about 1,000 years ago." Here is the email from Briffa in full:
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I know there is pressure to present a nice tidy story as regards 'apparent unprecedented warming in a thousand years or more in the proxy data but in reality the situation is not quite so simple. We don't have a lot of proxies that come right up to date and those that do (at least a significant number of tree proxies) some unexpected changes in response that do not match the recent warming.
I do not think it wise that this issue be ignored in the chapter. For the record, I do believe that the proxy data do show unusually warm conditions in recent decades.
I am not sure that this unusual warming is so clear in the summer responsive data. I believe that the recent warmth was probably matched about 1000 years ago. I do not believe that global mean annual temperatures have simply cooled progressively over thousands of years as Mike appears to and I contend that that there is strong evidence for major changes in climate over the Holocene (not Milankovich) that require explanation and that could represent part of the current or future background variability of our climate."
Mann was nervous that "skeptics" would have a "field day" if Briffa's decline was featured in the IPCC's Third Assessment Report. He said, "he'd hate to be the one" to give them "fodder." On September 22, 1999, Mann wrote:
"
We would need to put in a few words in this regard. Otherwise, the skeptics have a field day casting doubt on our ability to understand the factors that influence these estimates and, thus, can undermine faith in the paleoestimates. The best approach here is for us to circulate a paper addressing all the above points.
I'll do this as soon as possible. I don't think that doubt is scientifically justified, and I'd hate to be the one to have to give it fodder!"
Jones proceeded, then, to "hide the decline" with his ready-made "trick." Below is the graph that was eventually included in the IPCC's Third Assessment Report in 2001. It appears that Jones's trick was successful: Briffa's line in green is cutoff and "hidden" by the other lines. As UK's Daily Mail reported, "All [Jones] had to do was cut off Briffa's inconvenient data at the point where the decline started, in 1961, and replace it with actual temperature readings, which showed an increase."
So, it seems that, rather than employing a "clever way"-or "trick"-to honestly solve the post-1960 decline, Jones was trying to manipulate data to reach a preconceived conclusion. His method has been criticized by fellow scientists. Philip Stott, emeritus professor of biogeography at London's School of Oriental and African Studies, suggested the trick was deceitful. "Any scientist ought to know that you just can't mix and match proxy and actual data. They're apples and oranges. Yet that's exactly what [Jones] did."
As one can see, the "hide the decline" story is not an innocent one. Rather, it provides convincing evidence for the view that Jones and his colleagues didn't like the facts as depicted by the data, so they changed them. In short, Briffa, Mann, Jones, and others were aware of data that suggested that the world was warmer 1000 years ago, and rather than admit that openly, they intentionally hid it from public view. Moreover, they hid it by including temperature records in a dataset composed of tree ring data, which, by itself, is exceedingly questionable.
