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2009
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February
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- NSIDC Arctic Sea Ice Extent Graph February 26, 2009
- Chris Field of IPCC, interviewed by Democracy Now,...
- James Hansen talks with Charlie Rose about Coal, S...
- Capitol Hill coal power plant targeted by environm...
- Chris Field: Decisive Action Needed as Warming Pre...
- Mark Serreze (NSIDC) weighs in on George F. Will '...
- James Hansen: "Ways and Means" and peaceful protes...
- Climate researchers Stephen Schneider & Ken Caldei...
- J.B. Smith, Stephen H. Schneider, M. Oppenheimer e...
- James Hansen, NASA's Chief Climate Scientist Stirs...
- Samuli Helama et al., Multicentennial megadrought ...
- Ted Scambos: East Antarctica is warming slightly
- S. H. Schneider & M. D. Mastrandrea: Probabilisti...
- Profile of Stephen H. Schneider by Regina Nuzzo of...
- 4th International Polar Year (IPY) finds accelerat...
- Peter M. Sandman and George Marshall -- two takes ...
- Tamino's "What if ...?" post on NASA-GISS temps, L...
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- The Orbiting Carbon Observatory NASA Satellite Fai...
- Marco Tedesco: Graph of above-average melt days on...
- Andrew Revkin's Dot Earth blog on the NYT: Ike Sol...
- NSIDC experts present new research on Arctic ampli...
- Y. Luo et al., Response of Pacific subtropical-tro...
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- Purdue's Project Vulcan led by Dr. Kevin Gurney to...
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- Oleg A. Saenko: Sensitivity of the subpolar Atlant...
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- James Hansen: It is time to take a stand -- call ...
- George F. Will's Flagrant Dishonesty with regard t...
- Guido Grosse: Monitoring thaw lake dynamics using ...
- NASA studying thermokarst lakes - G. Grosse, K. Wa...
- Tsonis, Swanson & Kravtsov, GRL, 2007, A new dynam...
- Fred Pearce: North Atlantic is world's 'climate s...
- M. C. Serreze et al., The Cryosphere, 2009, The em...
- R. G. Graversen & M. Wang, Climate Dynamics, Polar...
- Graversen & Wang: Arctic's personal greenhouse tu...
- NOAA's NSIDC, Feb. 18, 2009: Satellite (SSM/I) sen...
- Christina Pedersen: Melt-pools 'accelerating Arcti...
- M. Montoya & A. Levermann, GRL, Surface wind-stres...
- Montoya & Levermann: Small variations in surface w...
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- NOAA's NCDC Global Climate Report for January 2009
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- Chris Field, 2009 AAAS Meeting: "What is New and ...
- K. M. Walter et al., Thermokarst Lakes as a Source...
- Katey Walter: Thermokarst lake formation is a sour...
- Peter A. Stott et al., Present-day aerosol cooling...
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- Maija E. Repo et al., Nature Geoscience, Large N2O...
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- Andrew Glikson: Antarctic blues and the Australian...
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- Dan McDougall, Observer: "Welcome to my world" (Do...
- NSIDC Arctic Sea Ice Extent Graph from February 15...
- Michael Coe, Anny Cazenave, Holly Gibbs, Christoph...
- James Hansen: Coal-fired power stations are death...
- K. M. Norgaard: Understanding the climate ostrich...
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- Chris Field at the 2009 AAAS: "What Is New and Su...
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- M. Hofmann & H.-J. Schellnhuber, PNAS, Oceanic aci...
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- Arctic Sea Ice Conditions, February 13, 2009 -- de...
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February
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Tuesday, February 3, 2009
Stephen McIntyre & Ross McKitrick, Proxy inconsistency and other problems in millennial paleoclimate reconstructions
Letter
Proxy inconsistency and other problems in millennial paleoclimate reconstructions
Stephen McIntyre* (ClimateAudit.org, 25 Playter Boulevard, Toronto, ON, Canada M4K 2W1) and Ross McKitrick (Department of Economics, University of Guelph, Guelph, ON, Canada N1G 2W1)
Mann et al. (1) present two paleoclimate reconstruction methods [‘‘error-in-variables’’ (EIV) and ‘‘composite plus scale’’ (CPS)], claiming statistically significant skill for both. Their figure 3 reveals that from approximately 750 to 1100, the CPS 95% confidence interval excludes the EIV 95% confidence interval and vice versa. This is evidence not of skill, but of inconsistency.
Contrary to assurances (1), archived Mann et al. source code did not show how they calculated their figure 3 confidence intervals, which are unjustifiably narrow. Paleoclimate reconstructions are an application of multivariate calibration, which provides a theoretical basis for confidence interval calculation (e.g., refs. 2 and 3). Inconsistency among proxies sharply inflates confidence intervals (3). Applying the inconsistency test of ref. 3 to Mann et al. A.D. 1000 proxy data shows that finite confidence intervals cannot be defined before 1800.
Numerous other problems undermine their conclusions. Their CPS reconstruction screens proxies by calibration-period correlation, a procedure known to generate ‘‘hockey sticks’’ from red noise (4). The proportion of proxies with ‘‘significant’’ correlation to gridcell temperature is overestimated by comparison to two (not one) gridcells, inclusion of ‘‘proxies’’ incorporating instrumental temperatures, and underadjustment for autocorrelation.
Their non-dendro network uses some data with the axes upside down, e.g., Korttajarvi sediments, which are also compromised by agricultural impact (M. Tiljander, personal communication), and uses data not qualified as temperature proxies (e.g., speleothem 13C).
Although Mann et al. purport to ‘‘follow the suggestions’’ of ref. 5, they employed ‘‘strip-bark’’ dendrochronologies despite the recommendation of ref. 5 that these chronologies be ‘‘avoided’’ and fail to observe the caveats of ref. 5 that negative CE statistics indicate unreliable results.
1. Mann, M.E., et al. (2008). Proxy-based reconstructions of hemispheric and global surface
temperature variations over the past two millennia. Proc Natl Acad Sci USA 105:13252–
13257.
2. Osborne, C. (1991). Statistical calibration: A review. Int Stat Rev 59:309–336.
3. Brown, P.J., Sundberg, R. (1987). Confidence and conflict in multivariate calibration. J R
Stat Soc Ser B 49:46–57.
4. Stockwell, D. (2006). Reconstruction of past climate using series with red noise. AIG News 8:314.
5. National Research Council (2006). Surface Temperature Reconstructions for the Last
2,000 Years (Natl Acad Press, Washington, DC).
Author contributions: S.M. and R.M. wrote the paper. The authors declare no conflict of interest.
*To whom correspondence should be addressed. e-mail: stephen.mcintyre@utoronto.ca
© 2009 by The National Academy of Sciences of the U.S.A.
Link to letter: http://www.pnas.org/content/early/2009/02/02/0812509106.full.pdf+html?etoc
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