Found the initial pointer for this over at the Devils Kitchen (language warning). Followed it to Steve McIntyres post at Climate Audit, and gave this and the next 2 posts a read. It seems Steve has been trying to pry loose the dataused to produce the famous Hockey Stick graph shown below:
That would be the red line. It turns out that in spite of data being more avail;able for recent times, the authors decided to dump most of the available data, and use only 12 points to produce the dramatic uptick at the end. The black line is McIntyres effort to duplicate the results of the original study, and test the methodology. While the methods seem to be generally in agreement, when the remaining available data, 34 points, are substituted for the 12 points originally used, the result is the black line. Note that the Hockey Stick not only completely disappears, temperatures are shown to be declining, in agreement with globally collected data.
The temperature data are inferred from the relative widths of tree rings from trees in Russia. My experience with trees is that ring width is far more sensitive to moisture availability than temperature variations, but there may be methods to allow for this.
Visit the site, and check the post, as well as the 2 following ones. Warning: There is math, specifically statistical analysis, and lots of it. The stuff in between in interesting, though.
In any case, not to worry, it's nothing a massive tax increase won't quickly cure.