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How the Hockey Stick Crumbled: A Post Mortem

Last month, a group of scientists headed by geologist Shaun Marcott launched the latest salvo in the global warming war. They announced that they had reconstructed the last 11,000 years of Earth climate history, based on various proxies, and had found that in the 20th century there was an unprecedented uptick in temperature. The Marcott paper was hailed by liberal media outlets; to cite just a few examples:

* “We’re screwed: 11,000 years’ worth of ­climate data prove it.” The Atlantic, March 10.
* “The modern rise that has recreated the temperatures of 5,000 years ago is occurring at an exceedingly rapid clip on a geological time scale, appearing in graphs in the new paper as a sharp vertical spike.” Justin Gillis, New York Times, March 7.
* “’Rapid’ head spike unlike anything in 11,000 years. Research released Thursday in the journal Science uses fossils of tiny marine organisms to reconstruct global temperatures…. It shows how the glode for several thousands of years was cooling until an unprecedented reversal in the 20th century.” The Associated Press, March 7.

But when real scientists–that is, those who apply a skeptical, scientific approach rather than a religious attitude of fervor–studied the Marcott paper, it quickly fell apart. We wrote about the Marcott fiasco here and here. It turned out that Marcott and his colleagues had created the 20th century warming spike–which was, in reality, the sole purpose of their exercise–by changing the dates on some of the samples they used as proxies.

In the Financial Post, Ross McKitrick reviews the entire sorry episode:

The new, and startling, feature of the Marcott graph was at the very end: Their data showed a remarkable uptick that implied that, during the 20th century, our climate swung from nearly the coldest conditions over the past 11,500 years to nearly the warmest. Specifically, their analysis showed that in under 100 years we’ve had more warming than previously took thousands of years to occur, in the process undoing 5,000 years’ worth of cooling.

This uptick became the focus of considerable excitement, as well as scrutiny. One of the first questions was how it was derived. Marcott had finished his PhD thesis at Oregon State University in 2011 and his dissertation is online. The Science paper is derived from the fourth chapter, which uses the same 73 proxy records and seemingly identical methods. But there is no uptick in that chart, nor does the abstract to his thesis mention such a ­finding.

Stephen McIntyre of climateaudit.org began examining the details of the Marcott et al. work, and by March 16 he had made a remarkable discovery. The 73 proxies were all collected by previous researchers, of which 31 are derived from alkenones, an organic compound produced by phytoplankton that settles in layers on ocean floors, and has chemical properties that correlate to temperature. …

According to the scientists who originally published the alkenone series, the core tops varied in age from nearly the present to over a thousand years ago. Fewer than 10 of the original proxies had values for the 20th century. Had Marcott et al. used the end dates as calculated by the specialists who compiled the original data, there would have been no 20th-century uptick in their graph, as indeed was the case in Marcott’s PhD thesis. But Marcott et al. redated a number of core tops, changing the mix of proxies that contribute to the closing value, and this created the uptick at the end of their graph. Far from being a feature of the proxy data, it was an artifact of arbitrarily redating the underlying cores.

Worse, the article did not disclose this step.

Having been caught, Marcott and his colleagues have now recanted. On Easter Sunday, they published online responses to “FAQs” that included this stunner:

[The] 20th-century portion of our paleotemperature stack is not statistically robust, cannot be considered representative of global temperature changes, and therefore is not the basis of any of our conclusions.

I don’t see how this admission can be squared with what Marcott told the Associated Press last month:

What we’ve found is that temperatures increased in the last hundred years as much as they had cooled in the lst six or seven thousand. In other words, the rate of change is much greater than anything we’ve seen in the whole Holocene.

This appears to be one more in a long series of frauds and hoaxes perpetrated by climate alarmists. This one unravelled faster than most; nevertheless, it served its purpose. Newspapers and magazines around the world trumpeted Marcott’s findings, and reproduced his hockey stick graph, as though it were solid evidence of catastrophic anthropogenic global warming. Now the question is, will they leave their readers with this false impression, or will they publicize the fact that they were had, once again, by climate alarmists?

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