Tree ring history spurs actual climate science debate

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Climate reconstructions based on tree rings have become a major point of contention. In 1998, a climate scientist by the name of Michael Mann had the misfortune of publishing a Northern Hemisphere temperature reconstruction dubbed “the hockey stick,” due to the appearance of the abrupt warming of the last century. He quickly became a favorite target for several high-profile contrarians, which has brought him a great deal of harassment.

Lost in the noise of this blogosphere-generated public controversy is the fact that real debates do go on between climate scientists. Recently, Michael Mann has gotten himself into one of those, as well.

It started with a paper published last year by Mann, Jose Fuentes, and Scott Rutherford, one that focused on a curious feature of some reconstructions of temperature based on the width of annual tree rings. When you look at the tree rings that were laid down at times of large volcanic eruptions, the cooling in the reconstruction is much smaller than the dip in temperatures predicted by climate models.