Transient Paleoclimate Simulations

with LOVECLIMOliver Elison Timm,

International Pacific Research Center, University of Hawai`i at Mānoa

Laurie Menviel,now at Climate and Environmental Physics,

University of Bern

Tobias Friedrich,International Pacific Research Center,

University of Hawai`i at Mānoa

Axel Timmermann, International Pacific Research Center,

University of Hawai`i at Mānoa

Ayako Abe-Ouchi,CCSR, University of

Tokyoand JAMSTEC,

Yokohama

Fuyuki Saito,JAMSTEC, Yokohama

Presented at the Synthesis of Transient Climate Evolution of the last 21-kyr(SynTraCE-21) PAGES Working Group Meeting,

 Timberline Lodge on Mt. Hood, Oregon, October 10-13, 2010

Pioneers in the field of transient paleoclimate modeling with EMICs and

GCMs:Hubert Gallee, J.P. van Persele, Th. Fichefet, Ch. Tricot, and A. Berger, Simulation of the Last Glacial Cycle by a Coupled, sectorially averaged climate-ice sheet model, JGR, 1992

John Kutzbach and P.J. Guetter: The influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18,000 years. J. Atmos. Sci., 1986.

Transient Paleoclimate Simulations with EMICs

o Holocene Climate (Examples)o only one major forcing factor: orbital changes

o Claussen et al. GRL 1999: Simulation of an abrupt change in Saharan

Vegetation in the mid-Holocene.

o Crucifix et al. Clim. Dyn., 2002: Climate Evolution during the Holocene:

A study with and earth system model of intermediate complexity

o Renssen et al., Clim. Past, 2007: On the importance of initial

conditions for simulations of the mid-Holocene climate

(Earth System Model of Intermediate Complexity)

Transient Paleoclimate Simulations with EMICso Last deglaciation

o Charbit et al., Glob. Planet. Change, 2005: Investigating the

mechanisms leading to the deglacitiation of past continental

Northern Hemisphere ice sheets with the CLIMBER-GREMLINS

model

o Lunt et al., Clim. Past, 2006: Comparing transient, accelerated

and equilibrium simulations of the last 30000 years with the GENIE-

1 model.

o Timm and Timmermann, J. Clim., 2007: Simulation of the last

21000 years using accelerated transient boundary conditions.

o Timm et al., Paleoceanography, 2008: On the definition on Paleo-

seasons in transient climate simulations

Overview:We use LOVECLIM in

transient paleoclimate simulations to :

Elucidate the mechanisms of orbitally forced Southern Hemispheric climate change during the last 130,000 years.

Study the ‘anatomy’ of the last glacial termination inclusive Heinrich 1, Antarctic

Cold Reversal, Younger Dryas

LOVECLIM

Ice-sheet forcingfrom ICIES(GLIMMER)

ECBilt – atmosphereT21, L3

Albedo + orographyAlbedo +

orography

In progressIn progress

CLIO – ocean sea-ice

3x3, L20

aia

aia

Air-sea fluxes

VECODE –vegetation

LOCH – Marine carbon cycle

aia

aia

CO2 fluxes

Transientexternal forcing

Antarctic Temperature evolution, last 130 ka

Simulation agrees well with

ice-core reconstructions

Timing of the deglaciation correct even

without Heinrich event 1

Simulation agrees well with

ice-core reconstructions

Timing of the deglaciation correct even

without Heinrich event 1

Timmermann, 2010, unpublished

Orbitally driven net shortwave irradiance changes at surface 80S-50S

Southern Hemisphere polar warming driven

by austral spring insolation and sea-ice feedback Net downward SW flux anomaly due to

Orbital forcing only Net downward SW flux due to sea-ice

related albedo changes

dQdQ

Q

A

Q

A dA

Orbitally driven net shortwave irradiance changes at surface 80S-50S

Southern Hemisphere polar warming driven

by austral spring insolation and sea-ice feedback Net downward SW flux anomaly due to

Orbital forcing only Net downward SW flux due to sea-ice

related albedo changes

Timmermann et al., 2009

Orbitally driven net shortwave irradiance changes at surface 80S-50S

Southern Hemisphere polar warming driven

by austral spring insolation and sea-ice feedback Combined effect on net downward SW flux

Timmermann et al., 2009

Southern Hemisphere polar warming driven

by austral spring insolation and sea-ice feedback

Timmermann et al., 2009

Observational evidence for strong austral spring forcing of Southern

Ocean climate change

Timmermann et al., 2010, in preparation

Quantifying the role of external forcings in driving seasonal and annual mean

deglacial climate changeGreenland Antarctica

Timmermann et al., 2009

Summary 1

Numerical simulation of of the last deglaciation show that polar SH warming and sea-ice retreat started around 18ka BP, consistent with paleo-evidence.

No freshwater forcing was used in our simulation=> AMOC shutdown and seesaw effect not the sole cause of SH warming.

Our conjecture: local insolation “jump-started” the deglaciation in the SH.

Disentangling the effects of orbital Disentangling the effects of orbital forcing on climate and carbon forcing on climate and carbon

cyclecycleOrbital forcing FComplex spatio-

temporalsignature

G(F)

D(R)

Climate Response R: Seasonal

sensitivities (Sea ice, westerlies, MLD)

Proxy Response D:Seasonal

sensitivities (accum. etc)

Carbon cycle Response C

Proposed mechanisms: Orbital forcing Proposed mechanisms: Orbital forcing - Climate- Climate

Stott et al. 2007 Huybers and Denton 2008Timmermann et al. 2009

Kawamura et al. 2007Denton et al., 2010

What is the role of precession and obliquity forcing on winds, sea-ice and temperatures in the Southern Hemisphere?

Optimal orbital forcing to change the Optimal orbital forcing to change the winds?winds?

From Loutre et al. (2004)

Obliquity forcing modulates meridional

temperature gradient

sea ice albedo feedback leads to

further amplification

From Loutre et al., 2004

Obliquity effects on climateObliquity effects on climate

Temperature response:high-low obliquity

Surface wind response:high-low obliquity

High obliquity: weaker windsLow obliquity: stronger winds

LOVECLIM

Obliquity effects on SH climateObliquity effects on SH climate

TEMPERATURE SUBTROPICS MINUS ANTARCTICA

LOVECLIM, DEUTERIUM EXCESS (Vimeux)

LOVECLIM SIMULATEDSH WESTERLIES STRENGTH

PRECIPITATION 30S-90S

LOVECLIM SIMULATED“WIND x PRECIPITATION”

DUST FLUX EPICA

Timmermann et al., 2010, in preparation

Summary 2

Obliquity forcing dominates the annual mean meridional temperature gradient in the SH:

Low obliquity increases the temperature gradient and the strength of the westerly winds

Last obliquity minimum (westerly winds maximum) was 27,000 years ago

However, CO2 did not rise until 18,000 BP. Why ?

LOVECLIM

Ice-sheet forcingfrom ICIES(GLIMMER)

ECBilt – atmosphereT21, L3

Albedo + orographyAlbedo +

orography

In progressIn progress

CLIO – ocean sea-ice

3x3, L20

aia

aia

Air-sea fluxes

VECODE –vegetation

LOCH – Marine carbon cycle

aia

aia

CO2 fluxes

Transientexternal forcing

Freshwater Forcing

Last Glacial Terminationwith freshwater forcing

YD

Menviel et al., 2010, in preparation

RC11-83

OCE326-GGC5OCE326-GGC5

RC11-83

Menviel et al., 2010, in preparation

MD03-2707

ODP 1002

Menviel et al., 2010, in preparation

905

Hulu Cave

Menviel et al., 2010, in preparation

EPICA C

Vostok

H214MD97-2120

ODP1233RC11-83TN057-21TN057-13PC

Menviel et al., 2010, in preparation

opal fluxTN057-13PC

AlkenonecontentMD97-2120

Menviel et al., 2010, in preparation

Summary:

EMIC-type simulations: valuable tools for testing the individual forcing factors, and feedbacks.

Obliquity-cycles change the meridional temperature gradient and the strength of the SH westerly winds. Accordingly, atmospheric CO2 should have increased 26ka BP, but the observed increase lacks the forcing.

Last Glacial Termination: Southern Atmosphere-Ocean system warmed in response to orbital forcing and sea-ice albedo feedback.

Proxy-observed orbital and millennial-scale climate change signals can be reproduced with LOVECLIM by prescribing orbital forcing , ice-sheets, GHG and freshwater input