Transient Paleoclimate Simulations with LOVECLIM Oliver Elison Timm

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 (Syn. Tra. CE-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. These image may be subject to copyright

Transient Paleoclimate Simulations with EMICs (Earth System Model of Intermediate Complexity) 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

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 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 Paleoseasons in transient climate simulations

Overview: We use LOVECLIM in transient paleoclimate simulations to : Additional freshwater forcing scenarios In the ocean Study the ‘anatomy’ of the last glacial termination inclusive Heinrich 1, Antarctic Cold Reversal, Younger Dryas Accelerated orbital, GHG and ice-sheet forcing Elucidate the mechanisms of orbitally forced Southern Hemispheric climate change during the last 130, 000 years.

LOVECLIM Transient external forcing Ice-sheet forcing from ICIES (GLIMMER) In progress Albedo + orography ECBilt – atmosphere T 21, L 3 a Air-sea i fluxes a CLIO – ocean sea-ice 3 x 3, L 20 These image may be subject to copyright VECODE – vegetation a CO 2 fluxes i a LOCH – Marine carbon cycle

Antarctic Temperature evolution, last 130 ka Simulation agrees well with ice-core reconstructions Timing of the deglaciation correct even without Heinrich event 1 Timmermann, 2010, unpublished

Southern Hemisphere polar warming driven by austral spring insolation and sea-ice feedback Orbitally driven net shortwave irradiance changes at surface 80 S-50 S Net downward SW flux anomaly due to Orbital forcing only Net downward SW flux due to sea-ice related albedo changes d. Q Q A d. A

Southern Hemisphere polar warming driven by austral spring insolation and sea-ice feedback Orbitally driven net shortwave irradiance changes at surface 80 S-50 S 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

Southern Hemisphere polar warming driven by austral spring insolation and sea-ice feedback Orbitally driven net shortwave irradiance changes at surface 80 S-50 S 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 Antarctica Greenland Timmermann et al. , 2009

Summary 1 u Numerical simulation of of the last deglaciation show that polar SH warming and sea-ice retreat started around 18 ka BP, consistent with paleoevidence. u No freshwater forcing was used in our simulation => AMOC shutdown and seesaw effect not the sole cause of SH warming. u 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 spatiotemporal signature G(F) Climate Response R: Seasonal sensitivities (Sea ice, westerlies, MLD) D(R) Carbon cycle Response C Proxy Response D: Seasonal sensitivities (accum. etc)

Kawamura et al. 2007 Denton et al. , 2010 “South forces South” Austral spring insolation or summer duration “North forces South” Boreal summer insolation at 65 N Proposed mechanisms: Orbital forcing Climate Stott et al. 2007 Huybers and Denton 2008 Timmermann et al. 2009 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? Obliquity forcing modulates meridional temperature gradient sea ice albedo feedback leads to further amplification From Loutre et al. (2004) From Loutre et al. , 2004

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

Obliquity effects on SH climate TEMPERATURE SUBTROPICS MINUS ANTARCTICA LOVECLIM, DEUTERIUM EXCESS (Vimeux) LOVECLIM SIMULATED SH WESTERLIES STRENGTH PRECIPITATION 30 S-90 S LOVECLIM SIMULATED “WIND x PRECIPITATION” DUST FLUX EPICA Timmermann et al. , 2010, in preparation

Summary 2 u Obliquity forcing dominates the annual mean meridional temperature gradient in the SH: u Low obliquity increases the temperature gradient and the strength of the westerly winds u Last obliquity minimum (westerly winds maximum) was 27, 000 years ago u. However, CO 2 did not rise until 18, 000 BP. Why ?

LOVECLIM Transient external forcing Ice-sheet forcing from ICIES (GLIMMER) In progress Albedo + orography ECBilt – atmosphere T 21, L 3 a Air-sea i fluxes a Freshwater Forcing CLIO – ocean sea-ice 3 x 3, L 20 This image may be subject to copyright VECODE – vegetation a CO 2 fluxes i a LOCH – Marine carbon cycle

Last Glacial Termination with freshwater forcing YD Menviel, et al. , Quaternary Science Reviews, accepted, 2011

OCE 326 -GGC 5 RC 11 -83 Menviel, et al. , Quaternary Science Reviews, accepted, 2011

ODP 1002 MD 03 -2707 Menviel, et al. , Quaternary Science Reviews, accepted, 2011

Hulu Cave 905 Menviel, et al. , Quaternary Science Reviews, accepted, 2011

ODP 1233 H 214 MD 97 -2120 EPICA C Vostok RC 11 -83 TN 057 -21 TN 057 -13 PC Menviel, et al. , Quaternary Science Reviews, accepted, 2011

Alkenone content MD 97 -2120 opal flux TN 057 -13 PC Menviel, et al. , Quaternary Science Reviews, accepted, 2011

Summary: Proxy-observed orbital and millennial-scale climate change signals can be reproduced with LOVECLIM by prescribing orbital forcing , ice-sheets, GHG and freshwater input EMIC-type simulations: valuable tools for testing the individual forcing factors, and feedbacks. Last Glacial Termination: Southern Atmosphere. Ocean system warmed in response to orbital forcing and sea-ice albedo feedback. Obliquity-cycles change the meridional temperature gradient and the strength of the SH westerly winds. Accordingly, atmospheric CO 2 should have increased 26 ka BP, but the observed increase lacks the forcing.

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