Geoscience Reference
In-Depth Information
additive effects of low- and high-latitude forcings on climates along the American
Cordilleras hamper a current estimation of past interactions between tropical and
high-latitude forcings. Independent reconstructions of tropical and polar modes of
variability are needed to gain insight on past forcing interactions and the combined
effect on climates of the western Americas.
Teleconnections between precipitation estimates and climatic forcings evolve
over time, suggesting a changing global signature of ENSO and other forcings.
Our results indicate that the timing of interdecadal transitions in temperature- and
precipitation-sensitive records has not always been consistent across the region. In
addition, the degree of correlation between records has varied over time. Over the
last 400 years, interdecadal climate variations in the Pacific alternated between times
of larger amplitude and more geographically widespread interdecadal changes and
times of lower amplitude and less geographically organized interdecadal changes.
Most tree-ring records suggest that the interdecadal variability in the Pacific
region was particularly more organized before the mid-1800s, whereas interannual
variability increased after that period. These observations point to a major reorgani-
zation of the climate modes of variability in the Pacific around 1850, the generally
accepted time of the end of a particularly cool period in the 1800s, identified in some
Detailed analysis of the influences of tropical and high-latitude modes of cli-
mate variability across the American Cordilleras is somewhat constrained by the
current length of the proxy records. Additional insight can be gained by extend-
ing the records to cover different climatic intervals, such as the 'warmer' medieval
stressed the critical need for developing longer proxy records of both regional cli-
mate variations and hemispheric climatic forcings. Longer proxy series can be used
to evaluate the long-term natural behavior of these modes of variation and their
regional impacts more comprehensively. In so doing, these extended series can pro-
vide a long-term context for variability during the period of increasing trace gases,
and for testing climate prediction models. Proxy climate records stand as our only
means of assessing the long-term variability associated with large-scale modes of
climate variability and their global influences.
Acknowledgements
We gratefully acknowledge the support of the Inter-American Institute for
Global Change Research through its Collaborative Research Network Program for the past 6 years.
Parts of this project have also been funded by a range of national, international, and nonprofit
organizations.
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