The locations of various ice core drilling sites at Greenland and Antarctica are described. Temperature data from Greenland and Antarctica are given in detail. It is shown that data from several sites at Antarctica provide similar data, which indicates that the data represent regional climate data. A comparison of Greenland and Antarctica ice core records provides some interesting relationships that are not fully understood. The Greenland data show large numbers of sharp, relatively sudden changes in climate. A number of theories have evolved that partly explain these changes. High elevation ice sheets, particularly in Tibet, have also provided data on past climates. It was not until the processing of ice cores in the 1990s that it was discovered that the CO2 concentration dropped to extremely low levels (less than 200 ppm) during the latter phases of Ice Ages. With this discovery, many scientists have attempted to explain why this occurred, but only with limited success. There is ample evidence that the CO2 concentration reaches roughly 280 ppm during Interglacials, but drops off during the progress of an Ice Age, typically over 70,000–90,000 years. During the last 10,000 years of an Ice Age (“glacial maximum”) the CO2 concentration typically drops to about 190 ppm. Quite a number of studies have attempted to explain this CO2 cycle but none are entirely satisfactory. The ice cores have also generated quite a bit of data on dust entrained in the ice. Chapter 11 expands on this topic.