Geoscience Reference
In-Depth Information
Chapter 5
A Closer Look at Regional Curve
Standardization of Tree-Ring Records:
Justification of the Need, a Warning of Some
Pitfalls, and Suggested Improvements
in Its Application
A Closer Look at Regional Curve Standardization
Keith R. Briffa and Thomas M. Melvin
Abstract
Some background describing the rationale and early development of
regional curve standardization (RCS) is provided. It is shown how, in the applica-
tion of RCS, low-frequency variance is preserved in the mean values of individual
series of tree indices, while medium-frequency variance is also preserved in the
slopes. Various problems in the use of the RCS approach are highlighted. The first
problem arises because RCS detrending removes the average slope (derived from
the data for all trees) from each individual tree measurement series. This opera-
tion results in a pervasive 'trend-in-signal' bias, which occurs when the underlying
growth-forcing signal has variance on timescales that approach or exceed the length
of the chronology. Even in a long chronology (i.e., including subfossil data), this
effect will bias the start and end of the RCS chronology. Two particular problems
associated with the use of RCS on contemporaneously growing trees, which might
represent a typical (i.e., modern) sample, are also discussed. The first is the bias-
ing of the RCS curve by the residual climate signal in age-aligned samples and the
undesirable subsequent removal of this signal variance in RCS application. The sec-
ond is the 'differing-contemporaneous-growth-rate' bias that effectively imparts a
spurious trend over the span of a modern chronology. The first of these two can
be mitigated by the application of 'signal-free' RCS. The second problem is more
insidious and can only be overcome by the use of multiple sub-RCS curves, with
a concomitant potential loss of some longer-timescale climate variance. Examples
