Transient Paleoclimate Simulations with LOVECLIM

1. 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

2. 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.

3. Transient Paleoclimate Simulations with EMICs (Earth System Model of Intermediate Complexity) • Holocene Climate (Examples) • only one major forcing factor: orbital changes • Claussen et al. GRL 1999: Simulation of an abrupt change in Saharan Vegetation in the mid-Holocene. • Crucifix et al. Clim. Dyn., 2002: Climate Evolution during the Holocene: A study with and earth system model of intermediate complexity • Renssen et al., Clim. Past, 2007: On the importance of initial conditions for simulations of the mid-Holocene climate

4. Transient Paleoclimate Simulations with EMICs • Last deglaciation • 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 • Lunt et al., Clim. Past, 2006: Comparing transient, accelerated and equilibrium simulations of the last 30000 years with the GENIE-1 model. • Timm and Timmermann, J. Clim., 2007: Simulation of the last 21000 years using accelerated transient boundary conditions. • Timm et al., Paleoceanography, 2008: On the definition on Paleo-seasons in transient climate simulations

5. 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. Accelerated orbital, GHG and ice-sheet forcing Study the ‘anatomy’ of the last glacial termination inclusive Heinrich 1, Antarctic Cold Reversal, Younger Dryas Additional freshwater forcing scenarios In the ocean

6. LOVECLIM Transient external forcing Ice-sheet forcing from ICIES (GLIMMER) In progress ECBilt – atmosphere T21, L3 VECODE – vegetation Albedo + orography aia aia Air-sea fluxes CO2 fluxes CLIO – ocean sea-ice 3x3, L20 LOCH – Marine carbon cycle

7. 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

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

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

10. Southern Hemisphere polar warming driven by austral spring insolation and sea-ice feedback Orbitally driven net shortwave irradiance changes at surface 80S-50S Combined effect on net downward SW flux Timmermann et al., 2009

11. Southern Hemisphere polar warming driven by austral spring insolation and sea-ice feedback Timmermann et al., 2009

12. Observational evidence for strong austral spring forcing of Southern Ocean climate change Timmermann et al., 2010, in preparation

13. Quantifying the role of external forcings in driving seasonal and annual mean deglacial climate change Antarctica Greenland Timmermann et al., 2009

14. 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.

15. Disentangling the effects of orbital forcing on climate and carbon cycle Orbital forcing F Complex spatio-temporal signature G(F) Climate Response R: Seasonal sensitivities (Sea ice, westerlies, MLD) Carbon cycle Response C Proxy Response D: Seasonal sensitivities (accum. etc) D(R)

16. Proposed mechanisms: Orbital forcing - Climate “North forces South” Boreal summer insolation at 65 N Kawamura et al. 2007 Denton et al., 2010 “South forces South” Austral spring insolation or summer duration 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?

17. 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

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

19. 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

20. 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 ?

21. LOVECLIM Transient external forcing Ice-sheet forcing from ICIES (GLIMMER) In progress ECBilt – atmosphere T21, L3 VECODE – vegetation Albedo + orography aia aia Air-sea fluxes CO2 fluxes CLIO – ocean sea-ice 3x3, L20 LOCH – Marine carbon cycle Freshwater Forcing

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

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

24. ODP 1002 MD03-2707 Menviel et al., 2010, in preparation

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

26. ODP1233 RC11-83 TN057-21 TN057-13PC H214 MD97-2120 EPICA C Vostok Menviel et al., 2010, in preparation

27. Alkenone content MD97-2120 opal flux TN057-13PC Menviel et al., 2010, in preparation

28. 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 CO2 should have increased 26ka BP, but the observed increase lacks the forcing.

29. online version online