## Thursday, October 27, 2005

### Hockey sticks: round 29

When some people claim that the human activity has warmed up the climate much more drastically than Nature could do Herself, their most convincing argument for their statement is the reconstruction of global temperatures in the last 1000 years. Although people used to think that the variations were large and there was a strong Medieval Warm Period as well as Little Ice Age afterwards, things suddenly changed in 1998 and 1999. Mann, Bradley, and Hughes published papers that argued that the temperature was essentially constant between 1000 and 1900 (the shaft of the hockey stick) and then it abruptly grew since 1900 (the blade).

Even though the hockey stick contradicted most of the folklore people used to believe, it was instantly accepted by most of the climate community. In 2001, it became the key graph on the final page of the climate report made by the United Nations (IPCC). For five years or so, no one tried to reproduce the graph. Ross McKitrick and Steve McIntyre became the pioneers. They attempted to reproduce the graph but nothing worked. After intense research, they discovered that Mann et al. used a mathematical step that essentially generated hockey sticks out of random input.

...This is probably an old unfinished posting. ...