New study challenges traditional notions of global climate change

May 30, 2002

A study of past climate changes in the South American tropics has challenged traditional understanding of the mechanisms that triggered the advance and retreat of glaciers across the earth during the last ice age. The National Science Foundation-funded study was published in the May 31 issue of Science.

A team of researchers from Syracuse University, Duke University, Union College, the University of Nebraska and Stanford University have found that glaciers in the tropical Andes Mountains retreated several thousand years earlier than North American glaciers during a period of wet climate conditions, indicating that temperature change was probably the ultimate cause of glacial retreat in the Andes.

"Our findings challenge the traditional thinking that climate conditions in the high northern latitudes generate the advance and retreat of glaciers globally," says Geoffrey Seltzer, Syracuse University professor and lead researcher for the study. "If the tropics warmed earlier than the northern latitudes during the last glacial to interglacial transition, that means there is something else influencing climate change that we don't yet understand."

"We know from our experiences with El Niño, that the tropics are an important source of energy and water vapor that can drive changes in the global climate system," Seltzer says. "Our research provides a hint that something happened in the tropics that could have been an important trigger for the end the last global ice age."

"The results of this study really fly in the face of conventional wisdom about climate change on glacial-interglacial time scales," says Donald Rodbell, professor of geology at Union College. "For years we have been led to believe that the high latitudes, particularly the Northern Hemisphere, hold the key to globally synchronous climate change. In fact, this study suggests it may well be that the tropics drive the global climate system."

The researchers compared climate data derived from sediment cores they collected from Lake Titicaca, located on the boarder of Peru and Bolivia; and Lake Junin, located in Peru, in 1996 and 1998 with published data from ice cores collected in Greenland and Antarctica. A key component of the research was an analysis of inorganic sediment accumulation in the lakes. The researchers found that during periods of maximum glaciation, the tropical lakes overflowed and the sediment that was deposited in the lakes from the surrounding region contained a high concentration of fine-grained magnetic minerals. During periods of glacial retreat, the sediment was trapped behind moraines (mounds of rock and debris left by glaciers), which resulted in a lower concentration of magnetic minerals flowing into lakes Titicaca and Junin.

"From the analysis, it is clear that the tropical Andes deglaciated several thousand years earlier than higher latitude warming," the authors wrote. "If early warming occurred throughout the tropics, this climate change could have been transmitted both atmospherically and by ocean circulation processes to produce deglaciation of alpine and continental ice sheets in the Northern Hemisphere."

"Seltzer and his colleagues offer remarkable insights into the intricate movements of a climatic tango of sorts between the low and high latitudes as one hemisphere alternately leads or follows in influencing long-term weather," says David Verardo, director of the NSF Paleoclimate Program, which funded the project. "Getting the moves of this tango down is important for understanding climate."

The study is part of a larger, ongoing research project on climate change in the tropics the scientists are involved with that includes a $2 million expedition to Lake Titicaca a year ago funded by the Earth System History (ESH) program of the National Science Foundation and the International Continental Drilling Program (ICDP). The ESH program supports projects that focus on the past behavior of the Earth-Ocean-Atmosphere-Biosphere system to provide insight into the factors that govern environmental variability, rates of climate change and large-scale responses to climate forcing.

Syracuse University

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