Oh Yeah We Found a Trend…!

AD HOC COMMITTEE REPORT ON THE ‘HOCKEY STICK’ GLOBAL CLIMATE RECONSTRUCTION

(Report authored by Edward J. Wegman, et al.)

EXECUTIVE SUMMARY
(Excerpts)

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While the work of Michael Mann and colleagues presents what appears to be compelling evidence of global temperature change, the criticisms of McIntyre and McKitrick, as well as those of other authors mentioned are indeed valid.

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The papers of Mann et al. in themselves are written in a confusing manner, making it difficult for the reader to discern the actual methodology and what uncertainty is actually associated with these reconstructions. Vague terms such as “moderate certainty” (Mann et al. 1999) give no guidance to the reader as to how such conclusions should be weighed.

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Centering the mean is a critical factor in using the principal component methodology properly. It is not clear that Mann and associates realized the error in their methodology at the time of publication. Because of the lack of full documentation of their data and computer code, we have not been able to reproduce their research.

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In general, we found MBH98 and MBH99 to be somewhat obscure and incomplete and the criticisms of [McIntyre and McKitrick] to be valid and compelling.

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Our committee believes that the assessments that the decade of the 1990s was the hottest decade in a millennium and that 1998 was the hottest year in a millennium cannot be supported by [Mann’s] analysis.

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… the fact that their paper fit some policy agendas has greatly enhanced their paper’s visibility. Specifically, global warming and its potentially negative consequences have been central concerns of both governments and individuals. The ‘hockey stick’ reconstruction of temperature graphic dramatically illustrated the global warming issue and was adopted by the IPCC and many governments as the poster graphic. The graphics’ prominence together with the fact that it is based on incorrect use of PCA puts Dr. Mann and his co-authors in a difficult face-saving position. We have been to Michael Mann’s University of Virginia website and downloaded the materials there. Unfortunately, we did not find adequate material to reproduce the MBH98 materials. We have been able to reproduce the results of McIntyre and McKitrick.

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As analyzed in our social network, there is a tightly knit group of individuals who passionately believe in their thesis. However, our perception is that this group has a self-reinforcing feedback mechanism and, moreover, the work has been sufficiently politicized that they can hardly reassess their public positions without losing credibility.

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Our perception is that principal components (statistical) analysis was used incorrectly and, based on this, unsupportable inferences were drawn about the current magnitude of global warming relative to the historical past.

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Source: http://energycommerce.house.gov/108/home/07142006_Wegman_Report.pdf

Update (2January2013) active link for some or all of the above source:

http://www.uoguelph.ca/~rmckitri/research/WegmanReport.pdf

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