2.) Surface temperature through the last 850,000 years, derived w from measurements of the ratio of 160 to 180 in fossil plankton which had settled to the sea floor and were recovered in a deepsea core from the equatorial Pacific Ocean (from N.J. Shackleton and N. Opdyke, Quaternary Research 3, 3'3-55, 1973). The changes mainly reflect variations in global ice volume; the scale used here was added to show schematicaly the probable associated changes in global average surface temperature, based on a model-derived difference of 4-6degreeC between full glacial and full interglacial conditions (from W.C. Clark, Carbon Dioxide Review, Oxford University Press, New York, 1982). The reference line at 15degree C corresponds to surface temperatures of the modern era. The glacial/interglacial oscillations, characteristic of the Pleistocene epoch, are now thought to be induced by periodic variations in the orbit of the earth and in its axis of inclination (the Milankovitch effect), which act together to bring about systematic changes in the seasonal distribution of sunlight over the surface of the planet.

3.) Air temperature over Antarctica, expressed as a difference from the modern surface temperature value. These estimates are derived from hydrogen/deuterium ratios measured in an ice core from the Vostok station in Antarctica (from J. Jouzel et al., Nature 329, 403 408, 1987). Of note are the present (Holocene) and the preceding, somewhat warmer "Eemian" interglacial periods, each characterized by a rapid onset to an Early interglacial maximum temperature, and a subsequent slower decline. The glacial period between, called the Wiscons in glaciation in the Americas, is itself characterized by signific ant variations in temperature that fall systematically to a co dest extreme (maximum glaciation) about 20,000 years before the present (B.P.).