1. Pliocene Climate Modelling, and the onset of Northern Hemisphere Glaciation 1)The Pliocene 2)Expansion of Greenland glaciation in the Late Pliocene – uncertainties. 3)Uplift and North American Pliocene glacial inception. 4)Impact of changing Cenozoic ice sheets on climate sensitivity.

2. Zachos et al, Nature, 2001 Orientation…

3. From Rainer Zahn Legacy of ODP. Climate evolution - the last 5 million years

4. Expansion in Greenland glaciation at ~2.75 Ma Bartoli et al, EPSL, 2005

5. The mid-Pliocene ~3.3 – 3.0 Ma Enhanced CO 2 : Best estimate 360 – 400ppmv Reconstructions of: e.g. vegetation, ice, SST Haywood et al, Geoscientific Model Development, 2010

6. The mid-Pliocene represents an accessible example of a world that is similar in many respects to what models estimate could be the Earth of the late 21st Century. Taken together, the average of the warmest times during the mid-Pliocene presents a view of the equilibrium state of a globally warmer world, in which atmospheric CO2 concentrations were likely higher than pre-industrial values. Jansen et al. 2007 chapter 6, pages 440 to 442.

7. A palaeoclimate modellers paradise

8. (1) Closure of Panama Seaway (2) Tectonic Uplift (3) Termination of Permanent El Nino (4) Decrease in CO 2 4 main hypotheses

9. (1) Closure of Panama Seaway Ruddiman, p163 Bartoli et al, 2005

10. (2) Tectonic Uplift Ruddiman and Kutzbach, 1989 Parrish et al, 2007

11. (3) Termination of Permanent El Nino e.g. Wara et al, 2005 Molnar and Cane, 2002 Fedorov et al, 2010

12. (4) Decrease in CO 2 Seki et al, EPSL, 2010 Raymo et al, Geology, 1988 Changes in weathering/uplift:

13. Pliocene Control: Modern continental configuration and bathymetry. Orbital parameters as modern CO 2 = 400ppmv. PRISM orography, ice-sheets, and vegetation: ΔT global = 3.1 o C

14. 400ppmv to 280ppmv… Changes to the model for each hypothesis tested…

15. PanamaENSORockiesCO 2 Temp Precip GCM results…

16. Ice sheet model results… Lunt et al, Nature, 2008

17. But… Never trust a single model simulation Stone et al, The Cryosphere, in press

19. So, what is robust? 21% of simulations show large (>3 m) change due to CO 2 18% of simulations show small (<0.2 m) change due to CO 2 100% of simulations show a greater change due to CO 2 than any other mechanism.

20. DeConto et al, Nature, 2008

21. Vizcaino et al, Palaeoceanography, 2010

22. Foster et al, Climate of the Past, in press Possible role for Canadian Rockies uplift?

23. Possible Priming mechanism for Cordilleran ice sheet. And possible explanation for non- glaciation in the low CO2 of the Miocene:

24. Summary Enhancement of Greenland glaciation around 2.75 Ma Many hypotheses including CO 2, Panama, Rockies, ENSO … Modelling work indicates CO 2 is primary driver, with orbital modulation. BUT, magnitude of effect is uncertain. Maybe role for Canadian Rockies uplift in determining timing of more general NH glaciation…..and non-glaciation during low CO 2 time periods

25. Problems / Challenges for pre-Quaternary ice sheets and climate… pre ice-core multiproxy CO 2 reconstructions Interpretation of records – proxy modelling Development and use of Earth System Models – especially with fully coupled ice sheets Proper treatment of uncertainties in modelling Can pre-quaternary data ever constrain ice sheet models?