(H/T the Talkmaster)
Take a look at the following graph and see if you can tell what it is and what it means:
If you couldn't tell the above graph, linked from Climate Audit, is the now famous "Hockey Stick" graph that depicts global temperatures over the last roughly 2,500 years. The data comes from tree-ring data, which is considered by climatologists to be among the more accurate methods of determining global mean temperatures before thermometric data (observed temperatures using thermometers) was available.
As you can see, there are two lines, one red and one black. The red line of the graph shows a tremendous spike toward the right hand side, depicting global temperatures rising precipitously during the last roughly 150 years. This is the Hockey Stick: Relatively stable rising and falling of temperatures over 2,300 years, then sudden rise over the final 200. This chart was depicted in 1998 by Dr. Michael Mann, a US-based climatologist. The IPCC, various governments and evironmentalists use Mann's report, among others, and his graph to back up their claims that human beings are causing global warming an CO2 emissions are the culprit.
After its release, Steve McIntyre, a Canadian statistician, saw the graph and believed it to be flawed. It seemed to eliminate the so-called "Medieval Warm Period," the period from 900 CE to 1300 CE, when temperatures were much warmer than they were during the preceding 400-year-long "Dark Ages" or the following 450 years, a period known as the "Little Ice Age."
Curious, McIntyre tried to replicate Mann's data (a common practice in science and a cornerstone of any scientific "proof"). He asked for the source data from the Climate Research Unit at the University of East Anglia (which held the records). Amazingly, instead of being happy to provide the data, McIntyre was told that giving him access would upset the nations that provided it. When he pressed further, he had been told the data was lost.
Fast forward a few years. In 2008, Mann published another paper to back up his claims about the Hockey Stick. McIntyre was finally able to get the data used by Mann for his new paper. He used a much broader range of data (the more data, the better the statistical certainty), but all the regions used matched Mann's selections. Using this data, he developed the black line.
Below you can see a linked image from the Examiner showing the "smoothed" data for the last 150 years, or the overall trends (which may be easier to read than the raw datapoints).
A cursory inspection shows that the two lines match each other closely--although Mann's Hockey Stick data shows a perceptibly warmer planet--until the middle of the 20th century. At this point, the two lines' data series diverge greatly: Mann's "Hockey Stick" is perilously evident in red, but McIntyre's black line (the one with more complete data) begins to trend downward at the end, showing a relative cooling of the planet's surface during the last century until the 1980s, rising again and finally stabilizing at roughly the turn of the millenium.
In this third image, also linked from Climate Audit, we can see the merged dataset, in green. Charactaristic of this type of analysis, the two datasets merge:
Instead of the climatalogical catastrophe depicted by the Hockey Stick, McIntyre's data shows a system in its normal up-and-down cycle. If anything, McIntyre's more complete data set seems to show that rather than being on the hot, high precipice of disaster, we are in a cooler valley of the planet's normal warm-period routine.
Not that any of this is much "proof" of anything. All Mann and McIntyre have "proved" is the need for double-blind research. You see, both researchers were biased: Mann is a climatologist. He knows that the only reason climate research gets funded is because of the fear of escalating temperatures. McIntyre is also biased: He came to the project with the intent of disproving Mann's research and comes with a skeptic's background.
Until and unless real research from double-blind studies with repeatable results are available, everything we do with respect to Anthropogenic Global Warming is literaly stabbing in the dark. Indeed, the human race seems Hell-bent on charging off into battle while wearing a blind-fold. Just as a soldier cannot fight his enemies if he cannot see them, the people of this planet cannot fight real threats to the Earth if we blind ourselves to the real problems.
Cross-posted at Seeking Liberty.
Update: Oh, and why is tree-ring data considered more reliable today, even with thermometers? To answer that, check out Citizen Link's Stoplight.