A Summary of Glaciation

Abstract

CLIMATE SCIENCE The EPILOG (Environmental Processes of the Ice Age: Land, Oceans, Glaciers) program originated in 1998, under the aegis of the IMAGES (International Marine Global Change Study) program of IGBP/PAGES (International Geosphere-Biosphere Programme/Past Global Changes). It was charged with developing a comprehensive description of Earth during the last glacial maximum (LGM) 21,000 years ago. A primary goal was to explore the transitions into and out of a full glacial state by updating the pictures of sea surface temperature, glacial ice distribution, and albedo provided in 1981 by the landmark study CLIMAP. The EPILOG 2000 workshop summarized the current knowledge about continental ice sheets and sea level immediately before, during, and after the LGM. A collection of papers drawn from the workshop addresses four main issues: (i) the extent, volume, and evolution of glaciers and ice sheets; (ii) the magnitude of global sea level change caused by the growth and decay of ice sheets; (iii) the isostatic response to the global redistribution of ice and water; and (iv) the relation between ice sheets and global climate change. These papers discuss geological reconstructions of ice sheet extent, records of sea level change, ice sheet modeling, geophysical models of glacial isostatic adjustment, and geochemical proxies of ice volume. From this body of work, several important conclusions emerge. First, sea level at the LGM was 118 to 135 meters below the modern value, bracketing the lower bound for sea level drop of 127 meters and much less than the maximum value of 163 meters estimated by CLIMAP. Second, although new estimates of the margins of ice sheets agree in most cases with the boundaries drawn by CLIMAP, the amount and distribution of ice were substantially less than the CLIMAP estimates. Finally, some or all of the ice sheets must have been thinner than the minimum value given by CLIMAP. — HJS Quat. Sci. Rev. 21 , 1 (2002).