The study presents a high-resolution record of atmospheric carbon dioxide (CO2) concentrations from the Dome C ice core in Antarctica, extending the record back to 800,000 years before the present (BP). This extension includes two complete glacial cycles, providing insights into CO2 variations during the late Quaternary. The data show a strong correlation between CO2 and Antarctic temperature throughout eight glacial cycles, with significant deviations during Marine Isotope Stage 16 (MIS 16) when CO2 levels were below 180 parts per million by volume (p.p.m.v.) for 3,000 years. The lowest CO2 concentration measured in the ice core is 172 p.p.m.v., redefining the natural range of pre-industrial CO2 concentrations to 170–300 p.p.m.v. The record also reveals millennial-scale variations in CO2, methane, and temperature during MIS 18, supporting the bipolar seesaw hypothesis. These findings highlight long-term slow fluctuations in atmospheric CO2 influenced by changes in weathering or global oceanic carbon reservoirs.The study presents a high-resolution record of atmospheric carbon dioxide (CO2) concentrations from the Dome C ice core in Antarctica, extending the record back to 800,000 years before the present (BP). This extension includes two complete glacial cycles, providing insights into CO2 variations during the late Quaternary. The data show a strong correlation between CO2 and Antarctic temperature throughout eight glacial cycles, with significant deviations during Marine Isotope Stage 16 (MIS 16) when CO2 levels were below 180 parts per million by volume (p.p.m.v.) for 3,000 years. The lowest CO2 concentration measured in the ice core is 172 p.p.m.v., redefining the natural range of pre-industrial CO2 concentrations to 170–300 p.p.m.v. The record also reveals millennial-scale variations in CO2, methane, and temperature during MIS 18, supporting the bipolar seesaw hypothesis. These findings highlight long-term slow fluctuations in atmospheric CO2 influenced by changes in weathering or global oceanic carbon reservoirs.