In order to forecast future long-term climate change accurately, scientists must first understand fluctuations that have already occurred. At the end of the last ice age, between 18,000 and 10,000 years ago, a succession of abrupt climate shifts occurred that had consequences around the globe. Earlier studies had suggested that a "see-saw" effect tied warming episodes in the Northern Hemisphere to opposing fluctuations in the Southern Hemisphere. But according to the results of a study published in the current issue of the journal Science, cooling in the south may actually have happened first.

Vin Morgan of the Antarctic Cooperative Research Center and his colleagues studied an ice core collected from the Law Dome site in Antarctica (see image). By comparing the Antarctic core to ones collected in Greenland, the team determined that the Southern Hemisphere began cooling prior to the warming recorded 14,500 years ago in Greenland. As a result, the scientists conclude that the southern changes were not a direct consequence of alterations in oceanic heat transfer brought on by changes in the Northern Hemisphere. Due to uncertainties surrounding the ages of the ice cores, the scientists could not dismiss the possibility that the changes occurred at the same time. According to an accompanying commentary by Thomas F. Stocker of the University of Bern in Switzerland, only further study of more high-resolution Antarctic ice cores will "provide a more spatially complete picture of abrupt climate changes and glacial-interglacial transitions."