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Lonnie Thompson (geologist, glaciologist, paleoclimatologist) delivered
a seminar about global climate change on Nov 1 to a full house in the
Reitz Union. To watch the one hour video see
http://waterinstitute.ufl.edu/events/seminars.html 

Abstract

Over the last 30 years ice core records have been systematically
recovered from eleven high-elevation ice fields, ten of which are
located in the low latitudes. Three lines of evidence for abrupt climate
change both past and present are presented. First, annually and
decadally averaged O_18 (temperature proxy) and net mass balance
histories (precipitation proxy) for the last 400 years and 2000 years,
respectively, demonstrate that the current warming at high elevations in
the mid- to lower latitudes is unprecedented for at least the last two
millennia. Second, the continuing retreat of most mid to low-latitude
glaciers, many having persisted for thousands of years, signals a recent
and abrupt change in the Earth's climate system. Finally, rooted,
soft-bodied wetland plants, now exposed along the margins as the
Quelccaya ice cap (Peru) retreats, have been radiocarbon dated and when
coupled with other widespread proxy evidence, provides strong evidence
for an abrupt mid-Holocene climate event that marked the transition from
early Holocene warmer conditions in Peru to cooler, late Holocene
conditions. This abrupt event, roughly 5200 years ago, was widespread
and spatially coherent through much of the world and was coincident with
structural changes in several civilizations. These three lines of
evidence argue that the present warming and associated glacier retreat
are unprecedented in some areas for at least 5200 years. The ongoing
global scale, rapid retreat of mountain glaciers is not only
contributing to global sea level rise, but threatening fresh water
supplies in many of the world's most populous regions. The current and
present danger posed by ongoing climate change and the human response
will be discussed.