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Pliocene Climate Modelling, and the onset of Northern Hemisphere Glaciation

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

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Pliocene Climate Modelling, and the onset of Northern Hemisphere Glaciation

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

  2. Orientation… Zachos et al, Nature, 2001

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

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

  5. The “mid-Pliocene” ~3.3 – 3.0 Ma Reconstructions of: e.g. vegetation, ice, SST Haywood et al, Geoscientific Model Development, 2010 • Enhanced CO2: • ‘Best’ estimate 360 – 400ppmv

  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. 4 main hypotheses • Closure of Panama Seaway • Tectonic Uplift • Termination of ‘Permanent El Nino’ • Decrease in CO2

  9. Ruddiman, p163 Bartoli et al, 2005 • Closure of Panama Seaway

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

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

  12. Changes in weathering/uplift: Raymo et al, Geology, 1988 Seki et al, EPSL, 2010 • (4) Decrease in CO2

  13. Pliocene Control: Modern continental configuration and bathymetry. Orbital parameters as modern CO2 = 400ppmv. PRISM orography, ice-sheets, and vegetation: ΔTglobal= 3.1oC

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

  15. GCM results… Panama ENSO Rockies CO2 Temp Precip

  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

  18. So, what is robust? 21% of simulations show ‘large’ (>3 m) change due to CO2 18% of simulations show ‘small’ (<0.2 m) change due to CO2 100% of simulations show a greater change due to CO2 than any other mechanism.

  19. DeConto et al, Nature, 2008

  20. Vizcaino et al, Palaeoceanography, 2010

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

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

  23. Summary • Enhancement of Greenland glaciation around 2.75 Ma • Many hypotheses including CO2, Panama, Rockies, ENSO … • Modelling work indicates CO2 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 CO2 time periods

  24. Problems / Challenges for pre-Quaternary ice sheets and climate… • pre ice-core multiproxy CO2 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?

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