Ice cores have yielded a long and detailed proxy record of Earth's past climate. Oxygen isotope analysis, trapped air bubbles, and atmospheric aerosol deposits within the layers of ice have offered information about past temperature and greenhouse gas concentrations, as well as cataclysmic events such as major volcanic eruptions. Of all the locations where ice cores have been extracted from glaciers, the most significant is probably Dome C in Antarctica.

The Dome C climate record shows that the present concentration of CO₂ in the atmosphere is greater than at any time in the last 800,000 years, and that increases and decreases in global temperature are closely correlated with changes in CO₂ concentration-with temperatures high when CO₂ concentrations are high, and vice versa. Further, the findings at Dome C closely match the proxy climate record derived from the nearby Vostok, Antarctica, ice core, as well as oxygen isotope analysis o foraminifera (tiny marine creatures) found in oceanic sediments, adding to the Scientists' confidence in the soundness of the Dome C data.

Among the most interesting findings of the ice core analysis are from a period between about 400,000 and 650,000 years ago. Two of the warm interglacial periods that occurred during this time span were relatively mild compared to the interglacial periods of the last 400,000 years. Further, carbon dioxide and methane concentrations were lower during those two earlier interglacial periods than during more recent interglacials.