Atmospheric CO2 decrease led to Greenland glaciation in the Late Pliocene D.J. Lunt, G.L. Foster, A.M. Haywood, E.J. Stone Motivation Experimental Design Results Conclusions Future Work / Implications Lunt et al., EGU 2008

The Causes of Northern Hemisphere Glaciation? Lunt et al., EGU 2008 Zachos et al, Nature, 2001

The Causes of Northern Hemisphere Glaciation? 5 main hypotheses Closure of Panama Seaway Tectonic Uplift Termination of ‘Permanent El Nino’ Decrease in CO2 Oribital variations Lunt et al., EGU 2008

The Causes of Northern Hemisphere Glaciation? 5 main hypotheses Bartoli et al, 2005 Closure of Panama Seaway Tectonic Uplift Termination of ‘Permanent El Nino’ Decrease in CO2 Oribital variations Ruddiman, p163 Lunt et al., EGU 2008

The Causes of Northern Hemisphere Glaciation? 5 main hypotheses Japsen and Chalmers, 2000 Parrish et al, 2007 Closure of Panama Seaway Tectonic Uplift Termination of ‘Permanent El Nino’ Decrease in CO2 Oribital variations Ruddiman and Kutzbach, 1989 Lunt et al., EGU 2008

The Causes of Northern Hemisphere Glaciation? 5 main hypotheses e.g. Wara et al, 2005 Molnar and Cane, 2002 Closure of Panama Seaway Uplift of Rockies Termination of ‘Permanent El Nino’ Decrease in CO2 Oribital variations Lunt et al., EGU 2008

The Causes of Northern Hemisphere Glaciation? 5 main hypotheses 380ppmv mean, 425ppmv max 400ppmv to 280ppmv Raymo et al, 1996 Closure of Panama Seaway Uplift of Rockies Termination of ‘Permanent El Nino’ Decrease in CO2 Oribital variations Lunt et al., EGU 2008

Spinup of GCM simulations… Lunt et al., EGU 2008

GCM results… Panama ENSO Rockies CO2 Temp Precip Lunt et al., EGU 2008

Ice sheet model results… Lunt et al., EGU 2008

The Causes of Northern Hemisphere Glaciation? 5 main hypotheses From Berger and Loutre, 1991 Maslin et al, 1998 Closure of Panama Seaway Uplift of Rockies Termination of ‘Permanent El Nino’ Decrease in CO2 Oribital variations Lunt et al., EGU 2008

Ice sheet model results…(2) Extent of ‘cold orbit’ ice sheet Lunt et al., EGU 2008

Future Work / Implications Conclusions Enhancement of Greenland glaciation in the late Pliocene driven by decrease in atmospheric CO2 Greenland ice sheet waxed and waned on orbital timescales prior to 3 Ma. ENSO and tectonic forcing factors, with or without orbital trigger, did not play an important role in Greenland glaciation. Future Work / Implications Improvement of CO2 records of the pre-ice core era. Improvement of IRD records in North Atlantic (including provenance). Need for transient model simulations (using fully coupled Earth System Models). Strong dependence on CO2 has obvious implications for future ice sheet stability. Lunt et al., EGU 2008