Lies, damned lies and hockey sticks
...The real inconvenient truth - for Mann, Gore and the IPCC - is that the ‘hockey stick’ was a mirage. A Canadian geologist, Stephen McIntyre, received one of those government leaflets. Sceptical, he decided to investigate the methods and data behind the paper. He found that the data used relied heavily on tree-ring measurements from one particular kind of tree - American bristlecone pines - which showed a spurt in growth in the twentieth century that had nothing to do with climate change. Furthermore, there were errors in Mann’s methods such that even random data processed in this way could produce hockey-stick graphs. This was hardly the damning evidence of manmade influence on the climate it had been made out to be.
So no wonder alarm bells rang out when last month’s new hockey-stick graph emerged. Not only did it seem to confirm Mann’s original, but it was used in exactly the same way - as a STFU to climate sceptics who suggest that current, comparatively mild temperatures could be partly or wholly explained by natural trends that have nothing to do with human greenhouse gas emissions....
...The Science paper was soon getting torn apart. One academic at the University of Nottingham, Paul Matthews, noted in a comment on Montford’s blog that the data relied upon ‘show no dramatic increase in the twentieth century’. Oddly, he pointed out, Marcott’s own PhD thesis on the same subject ‘uses the same data sets and plots similar graphs, but with no trace of any sharp increase’. Of course, the change in Marcott’s results could easily be the product of further work, but this disparity seems strange nonetheless....
...On Easter Sunday, Marcott and his colleagues published a response on the Real Climate blog. Most notable was this comment: ‘Our global paleotemperature reconstruction includes a so-called “uptick” in temperatures during the twentieth century. However, in the paper we make the point that this particular feature is of shorter duration than the inherent smoothing in our statistical averaging procedure, and that it is based on only a few available paleo-reconstructions of the type we used. Thus, the twentieth-century portion of our paleotemperature stack is not statistically robust, cannot be considered representative of global temperature changes, and therefore is not the basis of any of our conclusions.’...
