High-latitude polar regions of the Earth have experienced cold, cool, and temperature paleoclimates in the course of their geologic history, but they have probably always been colder than low-latitude continents and oceans. Extreme climates leading to development of extensive frozen and ice-covered regions at high latitudes can, however, only be documented for a few, relatively short intervals of the Earth’s history, separated by long time spans with little or no ice (Frakes, 1979). The Cenozoic evolution of glacial-type climates during the past 30 to 40 m.y. is the most recent period of extreme climate, and differs from the preceding ones. During the Cenozoic, plate-tectonic processes generated climatically isolated land areas and ocean basins in both the Southern and Northern Hemispheres, which were repeatedly affected by glaciations. For glacial-type paleoclimates older than the Cenozoic, we have only been able to document unipolar glaciation because the opposite high-latitude area was situated in wide and deep ocean basins and was probably relatively ice free due to advection of warmer surface water from lower latitudes.

Despite the apparent similarity of Quaternary high-latitude paleoclimates, the development of glacial-type paleoceanographies of the northern and southern polar oceans have revealed important differences, and they are not easily compared with each other. Our understanding of Cenozoic Southern Hemisphere paleoclimates is much more advanced than it is for the Northern Hemisphere. It is particularly intriguing that the available data appear to indicate that the Southern Hemisphere may have become cold more than 20 m.y. earlier than its northern counterpart.