Glacial-interglacial evolution of greenhouse gases as inferred from ice core analysis: A review of recent results

Abstract

Ice core analysis provides the most direct evidence of changes in some major greenhouse gases (CO 2, CH 4 and N 2O) over the climatic cycle covering approximately the last 150,000 years. A remarkable overall correlation is observed between the CO 2 or CH 4 record and the climatic changes in the high latitudes of the Southern Hemisphere, with lowest greenhouse gas concentrations found under full glacial conditions. In terms of phase relationship, CO 2 and CH 4 are roughly in phase with the climatic signal during the deglaciation periods; when entering the glaciation, CH 4 appears to decrease in phase with the Antarctic cooling but CO 2 lags strikingly behind. The CH 4 record exhibits a marked signal which is most likely associated with the abrupt cooling of the Younger Dryas. Existing differences between CO 2 and CH 4 records in comparison with climate reflect differences in sources which are mainly oceanic in the case of CO 2 and continetal in the case of CH 4. For N 2O only few data are available suggesting that the N 2O concentrations may also have been lower during the Last Glacial Maximum than during the Holocene. Greenhouse gases are likely to have played an important climatic role in amplifying, together with continental ice, the initial orbital forcing of the glacial-interglacial climatic changes.