Carbon dioxide concentrations have shown several cycles of variation from about 180 parts per million during the deep glaciations of the Holocene and Pleistocene to 280 parts per million during the interglacial periods. Carbon dioxide concentrations have varied widely over the Earth's 4.54 billion year history.
Carbon dioxide levels have demonstrated several fluctuations in concentration from approximately 180 parts per million during the most severe ice ages of the Holocene and Pleistocene epochs to 280 parts per million during the warmer interglacial periods. Carbon dioxide concentrations have undergone significant changes throughout the Earth's 4.54 billion-year history.