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?