Differences between the glacial cycles of Antarctic temperature and greenhouse gases

Abstract. Ice-core measurements have indicated that the atmospheric concentrations of the greenhouse gases CO₂ and CH₄ show glacial-interglacial variations in step with Antarctic temperature. To obtain more insight into the nature of this relationship for cycles of different frequencies, measured time series of temperature, CO₂, and CH₄ are reanalysed. The results indicate that the temperature signal consists of a linear superposition of a component related to CO₂ with a period of ~100 000 yr and a component related to variations in the obliquity of the Earth's orbital plane with a period of ~41 000 yr. This suggests that either there operate very different feedback mechanisms at the different time scales or that CO₂ is not merely a~passive follower and amplifier of the glacial-interglacial variations in Antarctic temperature.