Hemispheric roles of climate forcings during glacial-interglacial transitions as deduced from the Vostok record and LLN-2D model experiments

The Vostok ice contains fingerprints of atmospheric greenhouse trace gases, Antarctic temperature, Northern Hemisphere temperature, and global ice volume/sea level changes during the last glacial‐interglacial cycles and thus allows us to investigate the sequences of these climatic events, in particular during the transitions from full glacial to interglacial conditions. The use of the updated CO2 record presented here and a reexamination of the sea level proxy confirm that the succession of changes has been similar through each of the four marked transitions found at Vostok. Antarctic air temperature and CO2 increase in parallel and almost synchronously, while the rapid warmings over Greenland take place during the last half of their change and coincide with the marked decay in continental ice volume. The Vostok results thus emphasize a fundamental difference between South and North in terms of climate dynamics. Our results confirm the role of CO2 as an important amplifier of the glacial‐interglacial warming in the South. It appears also that the marked warming observed at high northern latitudes (lagging behind the CO2 increase by several thousand years) is roughly synchronous with the decay of the northern ice sheets, suggesting a major role of climatic feedback due to this decay. Such a climatic scenario is supported by sensitivity experiments performed with the LLN 2‐D model forced by the Northern Hemisphere insolation and CO2. Model results indicate that the decay of the northern ice sheets and the Northern Hemisphere temperature depend primarily on the northern summer insolation. These results, nevertheless, could be affected if mechanisms specific to the Southern Hemisphere appear to play a major role in driving the Northern Hemisphere climate. The model also helps to constrain the time response of ice volume to insolation and CO2 changes.