Flattening the Mann hockey stick

The shape of Mann’ s hockey stick is morphing. The long horizontal handle (obtained by eliminating the MWP)  actually turns out to be sloping and the sharp upturn gets flattened.

WUWT reports a new and important study on temperature proxy reconstructions (McShane and Wyner 2010) submitted into the Annals of Applied Statistics and is listed to be published in the next issue.

A Statistical Analysis of Multiple Temperature Proxies: Are Reconstructions of Surface Temperatures Over the Last 1000 Years Reliable?

BY BLAKELEY B. MCSHANE∗ AND ABRAHAM J. WYNER†
Northwestern University∗ and the University of Pennsylvania†
This paper is a direct and serious rebuttal to the proxy reconstructions of Mann. It seems watertight on the surface, because instead of trying to attack the proxy data quality issues, they assumed the proxy data was accurate for their purpose, then created a bayesian backcast method. Then, using the proxy data, they demonstrate it fails to reproduce the sharp 20th century uptick

FIG 16. Backcast from Bayesian Model of Section 5. CRU Northern Hemisphere annual mean land temperature is given by the thin black line and a smoothed version is given by the thick black line. The forecast is given by the thin red line and a smoothed version is given by the thick red line. The model is fit on 1850-1998 AD and backcasts 998-1849 AD. The cyan region indicates uncertainty due to t, the green region indicates uncertainty due to β, and the gray region indicates total uncertainty.

The Mann Hockey Stick
Multiproxy reconstruction of Northern Hemisphere surface temperature variations over the past millennium (blue), along with 50-year average (black), a measure of the statistical uncertainty associated with the reconstruction (gray), and instrumental surface temperature data for the last 150 years (red), based on the work by Mann et al. (1999). This figure has sometimes been referred to as the hockey stick. Source: IPCC (2001).

The authors conclude that:

“…..we conclude unequivocally that the evidence for a ”long-handled” hockey stick (where the shaft of the hockey stick extends to the year 1000 AD) is lacking in the data.…..Climate scientists have greatly underestimated the uncertainty of proxy based reconstructions and hence have been overconfident in their models.”


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One Response to “Flattening the Mann hockey stick”

  1. Termites predict climate change! « The k2p blog Says:

    […] They rely on instinct rather than mathematical models but they surely couldn’t do worse than Michael Mann & The Hockey Stick Gang […]

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