CO2 Lag as Glacial Cooling Initiates

Abstract

Joseph Higginbotham*

Antarctic ice core data reveal a consistent pattern across glacial cycles: atmospheric CO2 does not immediately track temperature decline as interglacial conditions give way to glaciation. The most dramatic example occurs during the Last Interglacial (Eemian, MIS 5e), where CO2 remained essentially constant at 275–280 ppm for approximately 13,000 years while temperature fell 7°C. This paper examines whether similar behavior can be detected during cooling from earlier interglacials. Using harmonic fits to temperature and CO2 data spanning 350,000 years, phase plots are constructed of CO2 versus temperature that isolate the warming and cooling branches of each glacial cycle. The analysis reveals that the Eemian is the clearest but not unique example: MIS 9 shows comparable behavior, while the MIS 7 complex presents an instructive exception that may reflect extreme orbital forcing conditions. The asymmetry between rapid CO2 release during warming and slow CO2 absorption during cooling suggests rate-limited processes govern the return of atmospheric carbon to oceanic and terrestrial reservoirs. These observations are inconsistent with CO2 acting as the primary driver of temperature change on glacial-interglacial timescales.

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