Expanding Greenland Ice Sheet Enhances Sensitivity of Plio‐Pleistocene Climate to Obliquity Forcing in the Kiel Climate Model

Abstract

Proxy data suggest the onset of Northern Hemisphere glaciation during the Plio‐Pleistocene transition from 3.2 to 2.5 Ma before present resulted in enhanced climate variability at the obliquity (41 kyr) frequency. Here we investigate the influence of the expanding Greenland ice sheet on the mean climate and obliquity‐related variability in a series of climate model simulations. These suggest that an expanding GrIS weakens the Atlantic Meridional Overturning Circulation (AMOC) by ~1 Sverdrup, mainly due to reduced heat loss in the Greenland‐Iceland‐Norwegian Sea. Moreover, the growing GrIS amplifies the Hadley circulation response to obliquity forcing driving variations in freshwater export from the tropical Atlantic and in turn variations of the AMOC. The stronger AMOC response to obliquity forcing, by about a factor of 2, results in 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 at the obliquity frequency during the Plio‐Pleistocene transition.