Global warming

Roy Spencer, of the University of Alabama, looks at the "hockey-stick" global warming curve featured in the Intergovernmental Panel on Climate Change.

According to an article in Geophysical Research Letters,

McIntyre & McKitrick found that the Mann et al. methodology included a data pre-processing step, one which was not reported in the original study, that essentially guaranteed that a hockey stick curve would result from their analysis. They demonstrated this by applying the same methodology to many synthetic temperature records that were constructed with random noise. In almost every case, a hockey stick curve resulted. The claim of unprecedented warmth and the hockey stick shape appear to hinge on the treatment of one species of tree, the bristlecone pine, from North America in the 1400's. Further statistical tests showed that this critical signal in the early 15th century lacked statistical significance. This suggests that the results of Mann et al. were simply a statistical fluke, which greatly exaggerated a characteristic of the bristlecone pines, which may or may not be related to global temperatures.

Science is considered a self-correcting enterprise, because any published results are subject to checking, rechecking, double-checking, cross-checking, and occasionally, check-mate. (Well, the last isn't used in scientific discourse, but...) The give-and-take in science is a filter that eventually screens out bad results and passes along good ones.

Sometimes, though, a particular result has a lot of political charge, and filtering it out creates a storm.

The new article, like so much published science, simply points out errors in previously published science, which is the way science should work. So why should there be so much fuss this time? Because the original Mann et al. article has had huge repercussions. The hockey stick, along with the "warmest in 1,000 years" argument, has become a central theme of debates over the Kyoto Protocol, a treaty to limit emissions of greenhouse gases, in governments around the world. The question begging to be answered is: Why did the IPCC so quickly and uncritically accept the Mann et al hockey stick analysis when it first appeared? I cannot help but conclude that it's because they wanted to believe it.

At the very least, the name of the panel biased it toward accepting a "hockey-stick" result. After all, when a panel is called the Intergovernmental Panel on Climate Change, it's already primed to find – well, change.