Transient Paleoclimate Simulations with LOVECLIM Oliver 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 Tokyo and 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 EMICs o 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 years with the GENIE-1 model. o Timm and Timmermann, J. Clim., 2007: Simulation of the last 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 forcing from ICIES (GLIMMER) ECBilt – atmosphere T21, L3 Albedo + orography In progress CLIO – ocean sea-ice 3x3, L20 aiaaia aiaaia Air-sea fluxes VECODE – vegetation LOCH – Marine carbon cycle aiaaia aiaaia CO 2 fluxes Transient external 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 dQ 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 change Greenland 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 forcing on climate and carbon cycle Orbital forcing F Complex spatio- temporal signature Orbital forcing F Complex spatio- temporal signature G(F) D(R) Climate Response R: Seasonal sensitivities (Sea ice, westerlies, MLD) Proxy Response D: Seasonal sensitivities (accum. etc) Proxy Response D: Seasonal sensitivities (accum. etc) Carbon cycle Response C

Proposed mechanisms: Orbital forcing - Climate Stott et al Huybers and Denton 2008 Timmermann et al Stott et al Huybers and Denton 2008 Timmermann et al Kawamura et al Denton et al., 2010 Kawamura et al Denton et al., 2010 What is the role of precession and obliquity forcing on winds, sea-ice and temperatures in the Southern Hemisphere? 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 winds? From Loutre et al. (2004) Obliquity forcing modulates meridional temperature gradient  sea ice albedo feedback leads to further amplification Obliquity forcing modulates meridional temperature gradient  sea ice albedo feedback leads to further amplification From Loutre et al., 2004

Obliquity effects on climate Temperature response: high-low obliquity Surface wind response: high-low obliquity High obliquity: weaker winds Low obliquity: stronger winds High obliquity: weaker winds Low obliquity: stronger winds LOVECLIM

Obliquity effects on SH climate TEMPERATURE SUBTROPICS MINUS ANTARCTICA LOVECLIM, DEUTERIUM EXCESS (Vimeux) LOVECLIM SIMULATED SH 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, CO 2 did not rise until 18,000 BP. Why ?

LOVECLIM Ice-sheet forcing from ICIES (GLIMMER) ECBilt – atmosphere T21, L3 Albedo + orography In progress CLIO – ocean sea-ice 3x3, L20 aiaaia aiaaia Air-sea fluxes VECODE – vegetation LOCH – Marine carbon cycle aiaaia aiaaia CO 2 fluxes Transient external forcing Freshwater Forcing

Last Glacial Termination with freshwater forcing YD NOTE: read literature about routing of meltwater Timing and amplitude Of H1 MWP1 Odryas Ydryas Natl vs Arctic vs Gulf of Mexico Menviel et al., 2010, in preparation

RC11-83 OCE326-GGC5 RC11-83 Menviel et al., 2010, in preparation

MD ODP 1002 Menviel et al., 2010, in preparation

905 Hulu Cave Menviel et al., 2010, in preparation

EPICA C Vostok H214 MD ODP1233 RC11-83 TN TN057-13PC Menviel et al., 2010, in preparation

opal flux TN057-13PC Alkenone content MD 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 CO 2 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