Geoscience Reference
In-Depth Information
tree growth in most extratropical temperature-sensitive chronologies in the Western
Cordilleras of both Hemispheres. Common patterns of interannual variations in
tree-ring chronologies from the relatively-dry subtropics in western North and
South America are largely modulated by ENSO. We used an independent recon-
struction of Niño-3 sea surface temperature (SST) to document relationships to
tree growth in the southwestern US, the Bolivian Altiplano and Central Chile and
also to show strong correlations between these regions. These results further doc-
ument the strong influence of SSTs in the tropical Pacific as a common forcing
of precipitation variations in the subtropical Western America during the past 3-4
centuries. Common patterns of interdecadal or longer-scale variability in tree-ring
chronologies from the subarctic and subantarctic regions also suggest common forc-
ings for the annular modes of high-latitude climate variability. A clear separation
of the relative influence of tropical versus high-latitude modes of variability is
currently difficult to establish: discriminating between tropical and extra-tropical
influences on tree growth still remains elusive, particularly in subtropical and tem-
perate regions along our transect. We still need independent reconstructions of
tropical and polar modes of climate variability to gain insight into past forcing inter-
actions and the combined effect on climates of the Western Americas. Finally, we
also include a series of brief examples (as 'boxes') illustrating some of the major
regional developments in dendrochronology over this global transect in the last
10 years.
Keywords
Dendrochronology
·
Regional scale
·
Continental scale
·
Climate
variations
·
Americas
7.1 Introduction
Instrumental records show that the climate system is characterized by low- and high-
latitude patterns or modes of variability such as the El Niño/Southern Oscillation
(ENSO) in the equatorial Pacific and the Arctic (AO) and Antarctic (AAO)
Oscillations in the extratropics. The Pacific and high-latitude atmospheric circu-
lation features associated with interannual to decadal variability of climate over
the Americas exhibit large spatial and temporal variance that remains poorly doc-
umented. The resulting regional climate variability has enormous socioeconomic
impacts, as was vividly demonstrated by the disastrous flooding in Paraguay and
eastern Argentina, and the extended drought and massive wildfires in the south-
western United States and Mexico during the 1997-1998 El Niño event. At decadal
scales, the prolonged shift in sea surface temperature (SST) patterns over the north
spheric changes that have caused costly changes in commercial fish populations
