Back in 2003, Ross McKitrick and Stephen McIntyre ripped apart the famous "Mann hockey stick" graph (also known as MBH98), the foundation upon which many global warming proponents build their case to justify proposals to regulate greenhouse gas emissions.

McKitrick and McIntyre's critique corrected the faulty data (primarily bristlecone pine tree ring data) supplied by Michael Mann (the principle creator of the MBH98) and then recreated the graph, which showed that the earth has most certainly been both warmer and colder in the past. Here's the recreated graph superimposed on the original MBH98 graph:

This critique of MBH98 was endorsed by experts around the world. At the time though, another set of tree ring data was used to support the belief that the world is experiencing the warmest weather on record in many centuries.

Why is it important to global warming advocates to show that now is the warmest the earth has been in centuries, if not millennia? Well, the theory of global warming is that, for quite some time, the climate of the earth has been fairly stable. Temperatures did go up and down, but nothing like the spike in temperatures that we are seeing now. Global warming proponents believe that this spike in temperatures is directly attributed to the greenhouse gas emissions released by mass industrialization and automobile use since the late 1800s.  Therefore, to contain global warming, the world must rein in industrial activities, automobile use, and other sources of greenhouse gas emissions.

If it can be shown that current temperatures are, in fact, neither the hottest nor the coldest in earth's recent history, and that these temperature fluctuations occurred naturally prior to the industrial revolution, then the theory of global warming is blown to pieces. If that happens, one must look for other primary sources of climate change, like the sun, rather than man-made greenhouse gas emissions. One must also, then, reject any proposed "solutions" to global warming like cap-and-trade. Needless to say, global warming proponents are desperate to suppress any evidence that casts doubt on their theory.

While it's not being reported much in the MSM (no surprise there!), it turns out that McIntyre and McKitrick are once again casting doubt on the theory of global warming. And once again, they're doing it by taking a look at tree ring data, this time the "tree ring curve from the Yamal Peninsula in Siberia, compiled by UK scientist Keith Briffa." Over at the Financial Post, Ross McKitrick has more to say (Bold emphasis added by me.):

Briffa had published a paper in 1995 claiming that the medieval period actually contained the coldest year of the millennium. But this claim depended on just three tree ring records (called cores) from the Polar Urals. Later, a colleague of his named F. H. Schweingruber produced a much larger sample from the Polar Urals, but it told a very different story: The medieval era was actually quite warm and the late 20th century was unexceptional. Briffa and Schweingruber never published those data, instead they dropped the Polar Urals altogether from their climate reconstruction papers.

In its place they used a new series that Briffa had calculated from tree ring data from the nearby Yamal Peninsula that had a pronounced Hockey Stick shape: relatively flat for 900 years then sharply rising in the 20th century. This Yamal series was a composite of an undisclosed number of individual tree cores. In order to check the steps involved in producing the composite, it would be necessary to have the individual tree ring measurements themselves. But Briffa didn't release his raw data.

Over the next nine years, at least one paper per year appeared in prominent journals using Briffa's Yamal composite to support a hockey stick-like result. The IPCC relied on these studies to defend the Hockey Stick view, and since it had appointed Briffa himself to be the IPCC Lead Author for this topic, there was no chance it would question the Yamal data.

Despite the fact that these papers appeared in top journals like Nature and Science, none of the journal reviewers or editors ever required Briffa to release his Yamal data. Steve McIntyre's repeated requests for them to uphold their own data disclosure rules were ignored.

Then in 2008 Briffa, Schweingruber and some colleagues published a paper using the Yamal series (again) in a journal called the Philosophical Transactions of the Royal Society, which has very strict data-sharing rules. Steve sent in his customary request for the data, and this time an editor stepped up to the plate, ordering the authors to release their data. A short while ago the data appeared on the Internet. Steve could finally begin to unpack the Yamal composite.

It turns out that many of the samples were taken from dead (partially fossilized) trees and they have no particular trend. The sharp uptrend in the late 20th century came from cores of 10 living trees alive as of 1990, and five living trees alive as of 1995. Based on scientific standards, this is too small a sample on which to produce a publication-grade proxy composite. The 18th and 19th century portion of the sample, for instance, contains at least 30 trees per year. But that portion doesn't show a warming spike. The only segment that does is the late 20th century, where the sample size collapses. Once again a dramatic hockey stick shape turns out to depend on the least reliable portion of a dataset.

But an even more disquieting discovery soon came to light. Steve searched a paleoclimate data archive to see if there were other tree ring cores from at or near the Yamal site that could have been used to increase the sample size. He quickly found a large set of 34 up-to-date core samples, taken from living trees in Yamal by none other than Schweingruber himself! Had these been added to Briffa's small group the 20th century would simply be flat. It would appear completely unexceptional compared to the rest of the millennium.

After reading those allegations, honestly, how is anyone expected to trust many of the studies coming out with data to "prove" global warming? While we should hope that scientists are in the business of pursuing truth and presenting facts, the reality now is that many scientists are pursuing purely politicized interests. As we all know, once trust is lost, it is terribly difficult to recover. Thankfully, there are scientists and others, like McIntyre, McKitrick, and the Philosophical Transactions of the Royal Society, who seem to be pursuing truth and holding other scientists accountable.

Briffa and Schweingruber have served up a massive Fail for their cause. And a cause it is. In this era of the politicization of science, with so many reputations and so much government funding on the line, this case stands as prime evidence that it is important to always remain skeptical and to ask questions of everyone, particularly before we go rushing off to pass massive, new regulations like cap-and-trade.