The week's big global warming news continues to be "hackergate" - emails stolen from a few climate scientists that purport to reveal a global science conspiracy. The most talked-about email continues to be Dr. Phil Jones's (of the UK's Met Office) containing this sentence:
I’ve just completed Mike’s Nature trick of adding in the real temps to each series for the last 20 years (ie from 1981 onwards) amd [sic] from1961 for Keith’s to hide the decline.
Skeptics jumped on the quote as the "smoking gun" - proof scientists were altering data to show warming. But as always, their rush to judgment was premature, and as more evidence came to light, it quickly became apparent that the "trick" was completely innoucuous: Dr. Jones had simply tacked the instrumental temperature record onto the end of a reconstruction based on tree rings. Skeptical Science has the best explanation of why this trick is necessary:
"Mike's Nature trick" refers to the paper Global-scale temperature patterns and climate forcing over the past six centuries (Mann 1998), published in Nature by lead author Michael Mann. The "trick" is the technique of plotting recent instrumental data along with the reconstructed data. This places recent global warming trends in the context of temperature changes over longer time scales.
The "decline" refers to the "divergence problem". This is where tree ring proxies diverge from modern instrumental temperature records after 1960. The divergence problem is discussed as early as 1998, suggesting a change in the sensitivity of tree growth to temperature in recent decades (Briffa 1998). It is also examined more recently in Wilmking 2008 which explores techniques in eliminating the divergence problem. So when you look at Phil Jone's email in the context of the science discussed, it is not the schemings of a climate conspiracy but technical discussions of data handling techniques available in the peer reviewed literature.
But let's give skeptics the benefit of the doubt, and assume Dr. Jones was nefariously altering data. We'll throw out his dataset and use NASA's (which is more accurate anyway), starting in 2000 (2 months after Dr. Jones wrote his email). Here's what the "decline" looks like:
Here's another way of looking at it, showing that global temperatures were 0.23 degrees warmer over the 10 years after Jones wrote the email than the 10 years before:
So even if you grant skeptics' most wild-eyed accusations, the datasets Dr. Jones had nothing to do with confirm that temperatures continue to rise - most of all in the Arctic.
In fact, what's interesting is that the British data which were hacked show LESS warming over recent years than NASA's. If British scientists are altering data to "hide the decline," they aren't doing a very good job.
And yet this is unlikely to make skeptics more skeptical of their climate conspiracies. What is it about global warming that inspires such passion among the conspiracy theorists? More on that to come.
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