Of what importance are records of past changes in climate, today and in the future? What are the most significant implications of the ice core records of past climate changes?

SPEAKERS: Dr. Lonnie G. Thompson, Ohio State Univ. & Dr. Michael Bender, Univ. of Rhode Island

INTRODUCTION: Dr. C. Mark Eakin, Program Officer, NOAA Paleoclimatology Program

LOCATION & TIME: Mon., Sept. 18, 1995, 3:15pm - 4:45pm, Rayburn House Office Bldg., Room B369 - RECEPTION FOLLOWING

Because climate processes that have operated in the past continue to operate today, ice core records are providing very valuable insights. Within the last two decades, long cores of glacial ice have been used to establish and improve the record of past changes in climate. Analyses of ice cores from Antarctica, Greenland and tropical and subtropical areas have provided a wealth of detailed information on past climate changes. As the ice in these glaciers and ice sheets grew over time, layer by layer, tiny pockets of air were trapped within each layer, preserving a continuous record of the natural changes in the concentrations of greenhouse and other gases. In addition, these ice cores have preserved indirect/proxy records of changes in temperature (which can be closely estimated from the isotopic record of oxygen trapped in the ice), in the concentration of windblown dust, and in volcanic activity. By combining this information, these ice cores have preserved a 200,000-year history of climate changes and factors contributing to these changes.

Recent efforts by Drs. Thompson and Bender, and others, to establish a more precise chronology within ice cores has resulted in the ability to determine the sequence of events as the global climate changed. They are exploring questions such as : Did greenhouse gases such as CO2 increase before, after, or along with the rise in temperature? Was the sequence and timing of changes the same at all places around the world?

Dr. Bender will describe dramatic shifts in the concentrations of greenhouse gases such as CO2 and methane. These changes took place on a variety of timescales (from decades to many millennia). Some climate changes and processes appear to be periodic or cyclic, while others do not. In general, when the Earth was in an ice age, the concentrations of atmospheric greenhouse gases CO2 and methane were substantially lower, while the concentration of wind blown dust was substantially increased (due to the cold, dry conditions), and vice-versa. Ice core records also reveal a number of abrupt climate changes and abrupt changes in the concentration of greenhouse gases.

Information on the rates of climate change can also be derived. Climate warming and the melting of ice sheets appear to have proceeded much more rapidly than climate cooling and the buildup of ice sheets. Polar ice core records reveal that atmospheric CO2 and methane concentrations began to rise 2000 to 3000 years before the warming began in Greenland and apparently contributed to the ultimate warming and the melting of ice sheets.

Dr. Thompsonıs work focuses on the climate record from tropical and subtropical glaciers. He and his colleagues have drilled and analyzed ice cores from the high mountains of Huascaran, Peru. These cores provide the very first tropical record of global and tropical climate change extending back 20,000 years. Their results show that glacial temperatures at high elevations in the tropics during the peak of the Earthıs last ice age were 8o to 12o C. cooler than today. Previously, scientific results, based upon the record of climate change from tropical marine sediment cores, that suggested temperatures in the tropics varied little between an ice age and a period of global warming. However, these new data indicate that the tropical Atlantic was probably 5o to 6o C. cooler during the last ice age.

The Huascaran ice cores also show that a very strong warming has dominated the last two centuries and that the last two decades have been the warmest in the last 3000 years. Dr. Thompson's new findings also point to the water vapor pumping capacity of tropical convection systems as a mechanism capable of re-organizing the ocean's conveyor belt (thermohaline circulation). Associated evidence indicates that all of the Earthıs tropical mountain glaciers have been melting for at least 2 decades. The rate of melting has been increasing over time. This evidence is also consistent with climate model projections that high tropical elevations as well as the interiors of continents will experience greater and more rapid warming in a greenhouse warmed Earth than the globe as a whole.

Dr. Thompson is a professor of geosciences at Ohio State University (OSU), as well as a research scientist at OSUıs Byrd Polar Research Center. He has been investigating the patterns and sources of interannual, decadal, and centennial-scale climate variability for over thirty years. Dr. Thompsonıs research interests also focus on reconstructing the Earthıs record of global changes, monsoonal variability, El Nino/Southern Oscillation variations, evidence of past volcanic activity, and on ice processes. Dr. Thompson has led over 80 expeditions to recover ice cores from the Peruvian Andes, China, Pamir and Tien Shan of the former USSR, Mt. Kenya, Africa, Franz Josef Land, Russia, Bolivia, Greenland, and Antarctica. He also serves as a member of the National Research Councilıs US National Committee for the International Union for Quaternary Research, NOAAıs Scientific Advisory Panel for the Climate and Global Change Program, and the National Academy of Sciences Panel on Climate Variability on Decade-to-Century Time Scales He is also on the Editorial Board of Geology, and on the Editorial Advisory Board of a major international journal, The Holocene. Dr. Thompson received a B.S. degree in Geology from Marshall University in 1970, and M.S. and Ph.D. degrees in Geology from Ohio State University between 1971 and 1976.

Dr. Bender has been a professor of oceanography at the University of Rhode Island since 1982. He received a B.S. in Chemistry from The Carnegie-Mellon University in 1965. After spending a year at the Weizman Institute of Science in Rehovoth, Israel, he was awarded a Ph.D. in Geology from Columbia University in 1970. Much of his research has centered around geochemical processes on the ocean floor, reconstructions of the chemistry of oceans in the past, reactions between seawater and volcanic rocks on the sea floor, the use of oxygen isotopes to study photosynthesis and respiration in the oceans, the fate of anthropogenic CO2 in the oceans, and the stratigraphy and paleoclimatic records in ice cores. Dr. Bender has been a member of the Deep Sea Drilling Project, and has served on the National Science Foundationıs Oceanography Advisory Panel. He has also been a member and Director of the Manganese Nodule Program Scientific Advisory Committee, and director and member of the Joint Global Ocean Flux Study (JGOFS) Steering Committee. He is also the Associate Editor of Global Biogeochemical Cycles, and is a member of the National Science Foundationıs Ice Core Working Group.