A reader writes in:
I think Steve and the other CA readers will be interested in the new article by Matthew Salzer and Malcolm Hughes (of MBH fame) entitled “Bristlecone pine tree rings and volcanic eruptions over the last 5000 yr” in the latest issue of Quaternary Research, “> available for free.
I don’t have time to review this right now but look forward to it.
Here’s the reader’s summary:
The article begins quite straightforwardly with the observation that “Over the last millennium the agreement between the tree-ring data and volcano/ice-core data is high: years of ring-width minima can be matched with known volcanic eruptions or ice-core volcanic signals in 86% of cases’. It actually strikes me as quite plausible that cold snaps could immediately and rather unambiguously retard tree-ring growth, unlike warming which usually would happen slowly over many years and with many complicating factors.
The introduction is also clear: ” Two primary factors are thought to have forced much of late Holocene variation in climate prior to industrialization: solar output and volcanic eruptions (Free and Robock, 1999, Crowley, 2000 and Shindell et al., 2001). While there is some debate regarding which of these forcings has played the dominant role (Shindell et al., 2003), there is little doubt that volcanism affects climate. Large explosive eruptions inject great quantities of sulfur compounds into the stratosphere, which combine with water to produce sulfuric acid aerosol (Rampino and Self, 1982). This injection changes the radiative balance by increasing absorption and reflection of incoming short wave radiation by stratospheric aerosols, and generally has a cooling effect on climate (Lacis et al., 1992, Minnis et al., 1993 and McMormick et al., 1995)”.
However, I get nervous when I read
“Standardization is a basic procedure in dendrochronology that is designed to remove long-term non-climatic factors associated with increasing tree age and tree size from individual time series of ring-width measurements (Fritts, 1976 and Cook et al., 1990). The standardization procedure involved the fitting of a line or curve to the individual sample ring-width series using the program ARSTANL (Cook et al., 1985), (version 6.04P; also available at: http://www.ltrr.arizona.edu/software.html) and dividing the raw data by the fitted curve. Due to the open non-competitive nature of high elevation bristlecone pine stands, a modified negative exponential curve, a straight line of negative slope, or a horizontal line were used in the standardization. To create a mean site chronology, the annual standardized indices of tree growth were averaged. This process was repeated for each of the five upper forest border chronologies used in the study. Mean segment length was 492 yr, so that this standardization procedure should retain variability on time scales up to 164 yr (Cook et al., 1995), but as time scales lengthen beyond 164 yr the proportion of variability retained declines.
The variances of the chronologies were adjusted to remove variance bias as a result of sample size (Osborn et al., 1997; pp. 90–92, equations 4–6) and the chronologies normalized using the mean and standard deviation. The resulting normalized index chronologies consist of a variance-adjusted average of many individual samples from living trees and from dead remnant material. The average correlation between the five chronologies over their common intervals is 0.41 (n > 2230 yr, all significant at p < 0.0001) despite an average distance between sites of over 440 km. The five chronologies were then averaged to form a single time series. This series was also adjusted to remove variance bias (Osborn et al., 1997) and normalized. The resulting regional tree growth time-series is a high elevation chronology of upper forest border tree growth from 3000 BC to AD 2002 with a variance that does not depend on the size of the sample. The chronology minimizes any single site idiosyncrasies and maximizes the signal common to all five sites (Fig. 2), (hereafter referred to as the HI5 chronology). It should be noted that due to the nature of chronology building, particularly the use of overlapping series with a mean length of approximately 500 yr, millennial-scale variability would not be retained in the HI5 chronology".
And the picture on page 60 looks awfully familiar, even if it’s a tree-ring index rather than temperature. Anyway, I hope Steve and some of the CA readers will have a look. There are a few other articles in this free issue that are also interesting.
Ref: Bristlecone pine tree rings and volcanic eruptions over the last 5000 yr, Matthew W. Salzer and Malcolm K. Hughes, Quaternary Research Volume 67, Issue 1 , January 2007, Pages 57-68, doi:10.1016/j.yqres.2006.07.004