The CRU’s supporters have protested bitterly about the attention paid to this message. In the course of an extraordinary BBC interview in which he called an American critic an ‘****hole’ live on air, Jones’s colleague Professor Andrew Watson insisted that the fuss was completely unjustified, because all Jones had been talking about was ‘tweaking a diagram’.This is a must read on the matter.
Davies told me that the email had been ‘taken out of context’ adding: ‘One definition of the word “trick” is “the best way of doing something”. What Phil did was standard practice and the facts are out there in the peer-reviewed literature.’
However, the full context of that ‘trick’ email, as shown by a new and until now unreported analysis by the Canadian climate statistician Steve McIntyre, is extremely troubling.
Derived from close examination of some of the thousands of other leaked emails, he says it suggests the ‘trick’ undermines not only the CRU but the IPCC.
There is a widespread misconception that the ‘decline’ Jones was referring to is the fall in global temperatures from their peak in 1998, which probably was the hottest year for a long time. In fact, its subject was more technical - and much more significant.
It is true that, in Watson’s phrase, in the autumn of 1999 Jones and his colleagues were trying to ‘tweak’ a diagram. But it wasn’t just any old diagram.
It was the chart displayed on the first page of the ‘Summary for Policymakers’ of the 2001 IPCC report - the famous ‘hockey stick’ graph that has been endlessly reproduced in everything from newspapers to primary-school textbooks ever since, showing centuries of level or declining temperatures until a dizzying, almost vertical rise in the late 20th Century.
There could be no simpler or more dramatic representation of global warming, and if the origin of worldwide concern over climate change could be traced to a single image, it would be the hockey stick.
Drawing a diagram such as this is far from straightforward.
Gabriel Fahrenheit did not invent the mercury thermometer until 1724, so scientists who want to reconstruct earlier climate history have to use ‘proxy data’ - measurements derived from records such as ice cores, tree-rings and growing season dates.
However, different proxies give very different results.
For example, some suggest that the ‘medieval warm period’, the 350-year era that started around 1000, when red wine grapes flourished in southern England and the Vikings tilled now-frozen farms in Greenland, was considerably warmer than even 1998.
Of course, this is inconvenient to climate change believers because there were no cars or factories pumping out greenhouse gases in 1000AD - yet the Earth still warmed.
Some tree-ring data eliminates the medieval warmth altogether, while others reflect it. In September 1999, Jones’s IPCC colleague Michael Mann of Penn State University in America - who is now also the subject of an official investigation --was working with Jones on the hockey stick. As they debated which data to use, they discussed a long tree-ring analysis carried out by Keith Briffa.
Briffa knew exactly why they wanted it, writing in an email on September 22: ‘I know there is pressure to present a nice tidy story as regards “apparent unprecedented warming in a thousand years or more”.’ But his conscience was troubled. ‘In reality the situation is not quite so simple - I believe that the recent warmth was probably matched about 1,000 years ago.’