pliocene climate modelling, and the onset of northern hemisphere glaciation 1)the pliocene...
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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.
Zachos et al, Nature, 2001
Orientation…
From Rainer ZahnFrom Rainer ZahnLegacy of ODP.Legacy of ODP.
Climate evolution - the last 5 million yearsClimate evolution - the last 5 million years
Expansion in Greenland glaciation at ~2.75 Ma
Bartoli et al, EPSL, 2005
The “mid-Pliocene” ~3.3 – 3.0 Ma
Enhanced CO2: ‘Best’ estimate 360 – 400ppmv
Reconstructions of: e.g. vegetation, ice, SST
Haywood et al, Geoscientific Model Development, 2010
“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.
A palaeoclimate modellers paradise
(1) Closure of Panama Seaway
(2) Tectonic Uplift
(3) Termination of ‘Permanent El Nino’
(4) Decrease in CO2
4 main hypotheses
(1) Closure of Panama Seaway
Ruddiman, p163
Bartoli et al, 2005
(2) Tectonic Uplift
Ruddiman and Kutzbach, 1989
Parrish et al, 2007
(3) Termination of ‘Permanent El Nino’
e.g. Wara et al, 2005
Molnar and Cane, 2002
Fedorov et al, 2010
(4) Decrease in CO2
Seki et al, EPSL, 2010
Raymo et al, Geology, 1988
Changes in weathering/uplift:
Pliocene Control:
Modern continental configuration and bathymetry.
Orbital parameters as modern
CO2 = 400ppmv.
PRISM orography, ice-sheets, and vegetation:
ΔTglobal = 3.1oC
400ppmv to 280ppmv…
Changes to the model for each hypothesis tested…
Panama ENSO Rockies CO2
Temp
Precip
GCM results…
Ice sheet model results…
Lunt et al, Nature, 2008
But…
”Never trust a single model simulation”
Stone et al, The Cryosphere, in press
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.
DeConto et al, Nature, 2008
Vizcaino et al, Palaeoceanography, 2010
Foster et al, Climate of the Past, in press
Possible role for Canadian Rockies uplift?
Possible “Priming” mechanism for Cordilleran ice sheet.
And possible explanation for non-glaciation in the low CO2 of the Miocene:
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
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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