Friday, September 23, 2011



Michael "Piltdown" Mann, part of the ACU study center, is famous for his "Hockey Stick" graph:

There are three basic problems with this graph, which bear repeating.

First, it totally ignores a major warming periods that took place in the flat part; the Medieval Warm Period which was actually warmer than it got in the last century, according to ice and tree ring data - what's used for most of that graph. If it was properly charted, the graph would have a big hump from 1400-1800 or so, which would ruin the whole "we're all doomed" image.

The Roman Warm Period, which took place around 250-450 BC, is before the graph and similarly was warmer than the recent warming trend.

Second, see that steeply rising area at the end? It describes the time period from roughly 1920-2000, claiming that the world just skyrocketed in temperature dramatically after a long period of calm unchanged weather (which we know is not true). The problem is that its based on scattered, often improperly placed temperature stations, mostly in urban areas. The ones outside urban areas were deliberately adjusted upward to be closer to those warmer spots.

Third, that tail there is actually not accurate. The graph was released in 1999 and predicted the temperature would skyrocket in the next few years, which it did not. The temperature from 1998 has trended downward, actually, with variations of warming and cooling. In other words, the end of the hockey stick is a lie. Here's what it actually should look like, superimposed on the Mann graph:

Corrected Graph
Not quite as scary looking, is it? That's what happens when you use all the tree ring data available, not just the ones Mann chose, and when you include all the warming periods, not ignore them as troublesome for your pet theory. As the Warmaquiddick emails show, Mann and his colleagues deliberately shunned some data as problematic for their conclusions, "hid the decline" and doctored the data to show what they wanted instead of what really happened.

Still, people cling to the graph tenaciously. Sites like Real Climate desperately try to spin the graph as accurate, claiming the Warm Period was just localized in Europe (it was worldwide, according to data from all over, and the Hockey Stick only shows northern hemisphere data in any case). And Yale University's science department clings to the hockey stick graph, calling it "particularly effective." It was, too - effective at fooling people.

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