Simulated mean climate response to expanded Greenland Ice Sheet in the Kiel Climate Model

Proxy data suggest that the Plio-Pleistocene transition from ~3.2 - 3.0 to 2.5 Ma featured the onset of Northern Hemisphere glaciation and enhanced climate variability on obliquity timescale. Here, we investigate the influence of the expanding Greenland ice sheet (GrIS) on the mean climate and obliquity-related variability. Special attention is given to the Atlantic Meridional Overturning Circulation (AMOC). A series of climate model simulations suggest that the expanding GrIS weakens the AMOC by ~1 Sv, which is mainly due to reduced heat loss of the Greenland-Iceland-Norwegian Sea. Moreover, the expanded GrIS amplifies the Hadley circulation response to obliquity forcing. This drives enhanced obliquity-forced variations in freshwater export from the tropical Atlantic and in turn variations of the AMOC that increase by about a factor. The stronger AMOC response to obliquity forcing in turn drives a stronger global-mean near-surface temperature response. We conclude that the AMOC response to obliquity forcing is important to understand the enhanced climate variability on obliquity timescale during the Plio-Pleistocene transition.