Cooperative Institute for Research in Environmental Sciences

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

Lonnie G. Thompson

Distinguished University Professor
Department of Geological Sciences
Research Scientist
Byrd Polar Research Center
The Ohio State University

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 d¹⁸O 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.

About the Lecturer

Lonnie G. Thompson is a Distinguished University Professor in the Department of Geological Sciences and a Research Scientist Byrd Polar Research Center at The Ohio State University. Probably the most important contribution of his research efforts has been to propel the field of ice core paleoclimalology out of the Polar Regions to the highest tropical and subtropical ice fields. To do this he and his team have developed light-weight solar-powered drilling equipment for acquisition of histories from ice fields in the tropical South American Andes and on Kilimanjaro. These paleoclimate histories, published in more than 180 articles, including 14 in Science and Nature, have helped advance our understanding of the coupled nature of the Earth's climate system. Special emphasis has been placed on the El Niño and monsoon systems that dominate the climate of the tropical Pacific and affect global-scale oceanic and atmospheric circulation patterns. In 2000, his team drilled the ice fields of Kilimanjaro, recovering six ice cores to bedrock and then went on to recover three ice cores, two to bedrock from the Puruogangri ice cap in the center of the Tibetan Plateau. In 2002 the team successfully recovered a 460-meter core to bedrock on the col on Bona-Churchill in Southeast Alaska. This was the longest core ever recovered from a mountain range. In 2003, the OSU team successfully recovered 550 meters of core from Quelccaya and Coropuna ice caps in the high Andes of Peru. The later expedition represented the successful completion of Lonnie’s 47th expedition to polar and high-altitude regions. Over the years that he has been conducting these ice core drilling programs, he and his team have been mapping the total area and volume of the ice cover at many of these sites. The results of more than 20 years of measurements were presented at the annual meeting of the American Association for the Advancement of Science in San Francisco in February of 2001. Those results show that many of the glaciers and ice caps atop mountains in Africa and South America will disappear in the next 10 to 20 years. For example, since 1912 when the first map of the ice fields of Kilimanjaro was made and 2000, when he had aerial photos taken and a map produced, roughly 82% of the total area of ice cover on the mountain had disappeared.

Thompson recovered the first tropical ice core in 1983 from the Quelccaya ice cap, in Peru, and then went on in 1987 to recover the first long ice core from Tibetan Plateau from the Dunde Ice Cap. In 1992 his team recovered cores from the Guliya Ice Cap (northwestern Tibet) that contain both the entire sequence of the Last Glacial Stage (~120 kyr) and the oldest ice on Earth that dates more than 700,000 years in age. Other tropical cores recovered include those from Huascarán, Peru (1993) and from the summit of Sajama, the highest mountain in Bolivia (1997). Moreover, insects and plant fragments found in the Sajama ice core allowed the first systematic AMS ¹⁴C dating of an ice core.

Professor Thompson has served on a number of National Academy of Sciences Committees and planning panels for NSF and NOAA, as well as planning activities for IGBP, PAGES and the International Atomic Energy Agency study of Environmental Change Using Isotope Techniques. His research has resulted in major revisions in the field of paleoclimatology, in particular showing that the tropical regions have undergone significant climate changes, countering the earlier view that the higher latitudes dominate climate change.

Unprecedented global changes of the 20th Century have heightened awareness of human vulnerability to potential climate changes in the next millennium. Half of the Earth's surface area lies between 30°N and 30°S and this region supports 70% of the population. Thus, variations in the occurrence and intensity of the El Niño-Southern Oscillation and monsoons are of significance to humanity. Here meteorological records are short and scarce, but the ice core records collected by Thompson and his team have helped fill that gap. Unfortunately, as a result of the recent warming, all known tropical glaciers and ice caps are retreating and soon they will no longer continue to preserve viable paleoclimatic records. Fortunately, the OSU Ice Core Paleoclimate Group has created an archive of some of these records for use by future generations. These cores are stored in the cold room facilities at the Byrd Polar Research Center, at The Ohio State University.

In 2001 Prof. Lonnie G. Thompson was elected a Fellow of the American Geophysical Union and was selected by The Ohio State University as a Distinguished Scholar. In 2002 he was awarded Ohio State’s highest honor, the permanent title of Distinguished University Professor. He was selected by Time Magazine and CNN as one of America's Best in Science and Medicine and his research was highlighted in a portion of CNN Presents AAmerica’s Best in Science and Medicine@ on August 12 and in a special section of the August 13th, 2001 Time Magazine. In 2002, he was honored with the Vega Medal by the Swedish Society for Anthropology and Geography, the Commonwealth Award for Science and Invention, and the Heineken Prize for Environmental Sciences by the Royal Netherlands Academy of Arts and Sciences. A science profile appears in Science, Volume 298, 2002. His research is highlighted in the August, 2004 issue of National Geographic Adventure Magazine as well as in the September, 2004 issue of the National Geographic Magazine. In April, Prof. Thompson was awarded the 2005 Tyler Prize for Environmental Achievement for outstanding contributions in the field of global environmental science on April 8, 2005 and in October he was elected a fellow of AAAS.

Lonnie G. Thompson