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SPECIAL INVESTIGATION: Climate change emails row deepens as Russians admit they DID come from their Siberian server
...However, Warmergate strikes at something more fundamental - the science that justifies the basic assumption that the present warming really is unprecedented, at least in the past few thousand years.

Take the now-notorious email that the CRU’s currently suspended director, Dr Phil Jones, sent to his IPCC colleagues on November 16, 1999, when he wrote he had ‘just completed Mike’s Nature trick’ and had so managed to ‘hide the decline’. ..

...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.’

Another British scientist - Chris Folland of the Met Office’s Hadley Centre - wrote the same day that using Briffa’s data might be awkward, because it suggested the past was too warm. This, he lamented, ‘dilutes the message rather significantly’.

Over the next few days, Briffa, Jones, Folland and Mann emailed each other furiously. Mann was fearful that if Briffa’s trees made the IPCC diagram, ‘the sceptics [would] have a field day casting doubt on our ability to understand the factors that influence these estimates and, thus, can undermine faith [in them] - I don’t think that doubt is scientifically justified, and I’d hate to be the one to have to give it fodder!’

Finally, Briffa changed the way he computed his data and submitted a revised version. This brought his work into line for earlier centuries, and ‘cooled’ them significantly. But alas, it created another, potentially even more serious, problem.

According to his tree rings, the period since 1960 had not seen a steep rise in temperature, as actual temperature readings showed - but a large and steady decline, so calling into question the accuracy of the earlier data derived from tree rings.

This is the context in which, seven weeks later, Jones presented his ‘trick’ - as simple as it was deceptive.

All he 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.

On the hockey stick graph, his line is abruptly terminated - but the end of the line is obscured by the other lines. ...

...In 2007, McIntyre examined records across America. He found that between 1999 and 2007, the US equivalent of the Met Office had changed the way it adjusted old data.

The result was to make the Thirties seem cooler, and the years since 1990 much warmer. Previously, the warmest year since records began in America had been 1934.

Now, in line with CRU and IPCC orthodoxy, it was 1998. ...

...For example, last year the BBC environment reporter Roger Harrabin made substantial changes to an article on the corporation website that asked why global warming seemed to have stalled since 1998 - caving in to direct pressure from a climate change activist, Jo Abbess.

‘Personally, I think it is highly irresponsible to play into the hands of the sceptics who continually promote the idea that “global warming finished in 1998” when that is so patently not true,’ she told him in an email.

After a brief exchange, he complied and sent a final note: ‘Have a look in ten minutes and tell me you are happier. We have changed headline and more.’

Afterwards, Abbess boasted on her website: ‘Climate Changers, Remember to challenge any piece of media that seems like it’s been subject to spin or scepticism. Here’s my go for today. The BBC actually changed an article I requested a correction for.’

Last week, Michael Schlesinger, Professor of Atmospheric Studies at the University of Illinois, sent a still cruder threat to Andrew Revkin of the New York Times, accusing him of ‘gutter reportage’, and warning: ‘The vibe that I am getting from here, there and everywhere is that your reportage is very worrisome to most climate scientists ... I sense that you are about to experience the “Big Cutoff” from those of us who believe we can no longer trust you, me included.’ ...