Equilibrium and transient simulations of the interglacial climate response to CO2 and astronomical forcing

Berger, André [UCL] Yin, Qiuzhen [UCL]

The climate of nine interglacials of the past 800,000 years has been simulated with both snapshot and transient experiments using the model LOVECLIM. These simulations allow to investigate the relative contributions of insolation and CO2 to the intensity and duration of each interglacial as well as the differences between the interglacials at global and regional scales. The transient simulations which cover a full range of precession, obliquity and eccentricity values allow to investigate the response of different climate variables at different latitudes to these three astronomical parameters. The results show that the relative contribution of insolation and CO2 on the warmth intensity varies from one interglacial to another. They also show that CO2 plays a dominant role on the variations of the global annual mean temperature and the southern high latitude temperature and sea ice, whereas, insolation plays a dominant role on the variations of monsoon precipitation, vegetation and of the northern high latitude temperature and sea ice. The results also show that, compared to today, the past interglacials are warmer during boreal summer and cooler during boreal winter leading to a warmer annual mean with varying length for different interglacials. The warm interval of MIS-11 is the longest, confirming its long duration as found in proxy records. The long duration of MIS-11 is related to a particular combination of eccentricity, obliquity and precession as well as to a high CO2 concentration. Through the comparison with other interglacials, unique features in precession and obliquity as well as in regional climate response are found in MIS-5e and MIS-11, which might help to understand why they appear as the two warmest interglacials during the past 800ka. The transient simulations allow also to look for past interglacial analogues for our present interglacial and its natural future. The differences between the simulated seasonal behaviour of the past interglacials highlight the importance of seasonal climate reconstruction and therefore the necessity to obtain seasonal proxies.