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Climategate: McIntyre and the ‘Divergence Problem’
It’s been less than a month since the Climategate files were first disclosed, but they’ve already had a dramatic impact on the debate over climate change.

On the one hand is the dominant so-called consensus — that human emission of greenhouse gases has been the primary cause of an unprecedented warming of Earth’s climate. On the other hand, there has been an underground opposition trying to make itself heard. What the disclosure of the files did was demonstrate that these opposition voices had been suppressed unfairly and unscientifically.

As a result, the raw data that had been withheld is becoming available to outside researchers. This new openness is already having results.

Steve McIntyre of Climate Audit has done a careful analysis of the Climategate emails that affect one particular issue — the “tricks” that were applied to the data in composing the various reports. The particular issue McIntyre is considering is called “the divergence problem.” When we measure temperatures now, of course, we use a thermometer. For historical temperatures, however, reliable thermometers weren’t available until about 1724, with Fahrenheit’s mercury thermometer. And regular records of temperature weren’t done until some years later. (Thomas Jefferson was one of the first people to make regular temperature records.)...

...The green line is the version we saw above as part of the IPCC report, and the red line is the full series — which goes down rather dramatically, instead of up as the story suggested. If the full Briffa series had been included, the figure would look rather different. The hook upward, the blade of the hockey stick, would have been much less dramatic, the implied global warming much less significant. By truncating the data as they did, the global warming looks much worse....