Physics Colloquium, February 21, 2006

Glaciological Evidence of Abrupt Tropical Climate Change: Past, Present and Future

Lonnie G. Thompson

Department of Geological Sciences, OSU

Over the last 28 years ice core records have been systematically recovered from ten high-elevation ice fields, nine of which are located in the low latitudes. The records provide compelling evidence for asynchronous glaciation on Milankovitch timescales and hence challenge existing paradigms about the Earth's climate system. In addition, three lines of evidence for abrupt climate change both past and present in the tropics are presented. First, annually and decadally averaged δ ¹⁸O and next mass balance histories 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 'Hypsithermal' conditions to cooler, late Holocene 'Neoglacial' conditions. This abrupt event, roughly 5200 years ago, was widespread and spatially coherent through much of the tropics 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. Some thoughts on the human response to global climate change will be discussed.

An OSU Today article about Professor Thompson's recent expedition.

4:00 p.m., Physics Research Building (PRB), Room 1080

Reception at 3:45 p.m., Atrium, PRB