TESTING THE EXCLUSION CRITERIA OF THE CORRIGENDUM 

The MBH98 Corrigendum purported to explain the discrepancy of 35 series between the series listed in the original SI and the series actually used as follows:

These series, all of which come from the International Tree Ring Data Bank (ITRDB), met all the tests used for screening of the ITRDB data used in Mann et al. [1998] (see Mann et al. (2000)), except one—namely, that in 1997, either it could not be ascertained by the authors how these series had been standardized by the original contributors, or it was known that the series had been aggressively standardized, removing multidecadal to century-scale fluctuations.

In this note, I show that these criteria do not explain either the exclusion of many of the 35 series or the seemingly inconsistent inclusion of series, which have been "aggressively standardized"..

Identification Information on Excluded Sites

First, the table shown here provides a listing of the 35 sites, sorted by originating author as shown in WDCP/ITRDB records.

Information on Authors of Excluded Sites

6 of the originating authors of excluded series had sites used directly or through a temperature reconstruction in MBH98. The exclusion of 6 Schweingruber series is particularly puzzling on this count as 38 Schweingruber series were used in MBH98; indeed series from the same time were both used and not used.

All of the excluded authors had been cited in the LTRR, Arizona bibliography here and it is difficult to surmise why methods of these authors were unknown to MBH authors or could not have been readily determined. The connections shown here do not represent an exhaustive search, but merely indicate that the exclusions were sites by well-known and well-published authors.

Table 1. Information on Exclusions and Inclusions in MBH98 by Author

Exclusion of Series which are "Aggessively Standardized"

The MBH98 authors do not define "aggressively standardized", but, in tree ring standardization methods, this would appear to be series that are standardized with short splines or that have been pre-whitened.

In the absence of an explicit definition of "aggressive standardization" - which should be provided, it is impossible to test the application of this criterion. However, this criterion makes it hard to understand the inclusion of many series.

• Stahle’s standardization procedures involve a prewhitening step that pretty much eliminates all variance exceeding 50 years. This would appear to be "aggressive standardization" under MBH criteria. Nonetheless, MBH98 uses 3 Stahle precipitation reconstructions (using 6 sites), 16 series in the Stahle/OK network, 22 series in the Stahle/SWM network and 17 series in the NOAMER network (including some series used twice). 

• Vaganov’s procedures are not described, but the Durbin-Watson statistics strongly indicate that some form of prewhitening as removed long-term variance. Other examples of “aggressive” standardization: 

• Serre (-Bachet) (fran009, fran010) smoothed with a 60-year lowpass filter.  Perhaps Morocco is standardized this way.

REFERENCES 

Archambault, Sylvain  and Bergeron, Yves, 1992. Canadian Journal of Forest Research, 22:674-682. This is a cedar site – also in controversial Gaspé series.

Briffa et al., 1992.  Journal of Climate 5: 735-754. This is ALSO used for Briffa WUSA temperature reconstruction applied as a proxy.

Dobry  et al. 1996. in Dean, J.S., D.M. Meko and T.W. Swetnam (eds.)Tree Rings, Environment and Humanity

Holmes et al.,  Tree-Ring Bulletin 45: 37-42.

Richter, K, D. Eckstein and R.L. Holmes, 1991.  Tree-Ring Bulletin 51: 1-13.

Serre-Bachet,1994.  Climatic Change 1994, 215

Smith, D.J. and Laroque, C.P., 1996. Géographie physique et Quaternaire 50(1): 47-55