HR: 14:35h
AN: GC43B-04 INVITED    [Abstracts]
TI: The Fingerprint of Persistence: The Remarkable Character of Medieval Climate Change over the Western US
AU: * Graham, N E
EM: ngraham@hrc-lab.org
AF: Hydrologic Research Center, 12780 High Bluff Dr., Suite 250, San Diego, CA 93120, United States
AU: * Graham, N E
EM: ngraham@hrc-lab.org
AF: Scripps Institution of Oceanography, Mail Code 0224, La Jolla, CA 92093, United States
AU: Hughes, M K
EM: m.hughes@ltrr.arizona.edu
AF: University of Arizona, 105 West Stadium, Tucson, AZ 85721-0058, United States
AB: The body of evidence for persistent aridity and recurrent severe drought across the western US during Medieval times (more or less 800-1300 AD) has grown from suggestive tree-ring chronologies developed during 1970s to a variety of convincing proxy records available today. These records come from tree-rings (moisture availability), lake level reconstructions (precipitation), sediment charcoal and fire scar records (wild fire), pollen and diatom assemblages (moisture availability, river discharge), soil mobilization (rainfall, wind) and archeological studies. Two recurring themes that arise from this collected work are that a) the instrumental climate record for the West is not representative of the past millennium, and b) Medieval climate in the West was marked more by persistent precipitation deficits than by remarkably dry years. Such change requires persistently altered circulation patterns which, in turn, imply important and long-lasting changes in boundary conditions. Recent proxy-model statistical studies and dynamical model experiments have attempted to reconstruct circulation changes and mechanisms that may have produced these precipitation changes. Not surprisingly, the results are consistent with the idea that Medieval climate change over the western US resulted from persistently cool sea surface temperatures in the eastern tropical Pacific. Notably, such cooling is supported by proxy records from the tropical and mid-latitude Pacific. While this congruence of proxy and model results is not conclusive, alternative candidates for producing such circulation changes have not yet been put forward and tested. The presentation will review the much of evidence discussed above and frame a general picture of current hypotheses.
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1630 Impacts of global change (1225)
DE: 4522 ENSO (4922)
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting