Today's New York Times contains an article noting that new research undermines the claim that historical climate trends are shaped like a "hockey stick" -- that is a long period of relative climate stability followed by an large upswing in temperature in the 20th century. The story, "New Research Questions Uniqueness of Recent Warming" by Andrew Revkin, is here. Some excerpts:

A new analysis has challenged the accuracy of a climate timeline showing that recent global warming is unmatched for a thousand years.

That timeline, generated by stitching together hints of past temperatures embedded in tree rings, corals, ice layers and other sources, is one strut supporting the widely accepted view that the current warm spell is being caused mainly by accumulating heat-trapping smokestack and tailpipe emissions.

The authors of the study, published in the current issue of the online journal ScienceExpress, said they did not dispute that a sharp warming was under way and that its pace could signal a human influence. But they said their test of the methods used to mesh recent temperature records with centuries-old evidence showed that past natural climate shifts were most likely sharply underestimated.

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The significance of the new analysis comes partly because the record it challenges is a central icon in the debate over whether heat-trapping emissions should be curbed. The hallmark of the original method is a graph widely called the "hockey stick" because of its shape: a long, relatively unwavering line crossing the last millennium and then a sharp, upward-turning "blade" of warming over the last century.

The new study essentially says the shaft of the stick could well be profoundly warped and the old statistical method would not notice.