Geoscience Reference
In-Depth Information
The major contributions that dendroclimatology has made, and continues to
make, to the reconstruction of global and hemispheric temperatures during recent
centuries and millennia depend on the same approaches and have been covered else-
While the visibility of large-scale (average and spatially detailed) reconstructions stems
from their ability to contextualize 'unprecedented' climate change in the twentieth century
against a multicentury backdrop, such multiproxy reconstructions are critical to a variety of
climate science studies. They provide a large-scale context with which to compare regional
climate variability as reconstructed by single proxy records, which may ultimately help
resolve the large-scale mechanisms of past low-frequency climate change. They also pro-
vide much-needed tests of the response of large-scale climate to a variety of climate forcings
which occurred during the last millennium (most notably solar and volcanic forcing).
Its capacity to identify patterns of climate variability on various spatial scales per-
mits the application of dendroclimatology to a remarkable range of fields of direct
relevance to human concerns, in addition to their relevance to the pressing questions
of current and impending climate change. As is described in this topic, these include
but are not limited to hydrology and the management of water resources (Meko and
Woodhouse,
Chapter 8
, this volume), interactions of climate and ecological systems
(Swetnam and Brown,
Chapter 9
, this volume), and the study of the relationships
between climate extremes and social disasters (Stahle and Dean,
Chapter 10
,this
volume).
In each case, the usefulness of dendroclimatology rests on:
•
appropriate sample design
•
precise and accurate annual chronology
•
removal of non-climatic variability
•
distillation of a common climate signal by sample replication and combination
into site chronologies
•
understanding of the mechanisms producing the tree-ring record, especially the
role of climate
•
the demonstration of climatically credible spatiotemporal behavior in geographic
networks of site chronologies
This cascade of requirements flows directly from the peculiar nature of the poten-
tial proxy records of past climate embedded in tree rings, whether structural (for
example, total ring width and maximum latewood density) or compositional (for
example, stable isotopic ratios in cellulose) (see Gagen et al.
Chapter 6
, this vol-
ume). In spite of the presence of multiple confounding influences on all of these
proxy records, the presence of common patterns of variation repeatedly emerges
when the above requirements are met. This trend is seen in the time series from tens
or more of trees sampled at one location, and across regions represented by tens
or even hundreds of site chronologies, each 'distilled' from each location's set of
multiple individual samples. Thus, although climate signals in tree rings are emer-
gent from a complex and varying set of influences (Cook and Pederson,
Chapter 4
,
