1- In 1998 a paper is published by Dr. Michael Mann. Then at the University of Virginia, now a Penn State climatologist, and co-authors Bradley and Hughes. The paper is named: Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations. The paper becomes known as MBH98.
The conclusion of tree ring reconstruction of climate for the past 1000 years is that we are now in the hottest period in modern history, ever.
See the graph http://www.ncdc.noaa.gov/
Steve McIntyre, a Canadian mathematician in Toronto, suspects tree rings aren’t telling a valid story with that giant uptick at the right side of the graph, implicating the 20th century as the “hottest period in 1000 years", which alarmists latch onto as proof of AGW. The graph is dubbed as the "Hockey Stick" and becomes famous worldwide. Al Gore uses it in his movie An Inconvenient Truth in the famous "elevator scene".
2- Steve attempts to replicate Michael Mann’s tree ring work in the paper MBH98, but is stymied by lack of data archiving. He sends dozens of letters over the years trying to get access to data but access is denied. McIntyre and Ross McKitrick, of the University of Guelph publish a paper in 2004 criticizing the work. A new website is formed in 2004 called Real Climate, by the people who put together the tree ring data and they denounce the scientific criticism:
3- Years go by. McIntyre is still stymied trying to get access to the original source data so that he can replicate the Mann 1998 conclusion. In 2008 Mann publishes another paper in bolstering his tree ring claim due to all of the controversy surrounding it. A Mann co-author and source of tree ring data (Professor Keith Briffa of the Hadley UK Climate Research Unit) used one of the tree ring data series (Yamal in Russia) in a paper published in the Philosophical Transactions of the Royal Society in 2008, which has a strict data archiving policy. Thanks to that policy, Steve McIntyre fought and won access to that data just last week.
4- Having the Yamal data in complete form, McIntyre replicates it, and discovers that one of Mann’s co-authors, Briffa, had cherry picked 10 trees data sets out of a much larger set of trees sampled in Yamal.
5- When all of the tree ring data from Yamal is plotted, the famous hockey stick disappears. Not only does it disappear, but goes negative. The conclusion is inescapable. The tree ring data was hand picked to get the desired result.