Introduction, and history of Eocene modelling Atmosphere-Ocean coupled models ‘EoMIP’

1. Modelling Eocene Climates: Can any model get it ‘right’?!Dan LuntM. Heinemann, M. Huber, A. Legrande, A. Ridgwell, P. Valdes, A. Winguth • Introduction, and history of Eocene modelling • Atmosphere-Ocean coupled models • ‘EoMIP’ • Solutions? – sensitivities to uncertainties

2. Orientation… Zachos et al, Nature, 2001

3. Reduced latitudinal temperature gradients compared to modern… ‘Warm’ mid-high latitudes also supported by a wealth of terrestrial evidence, e.g. Croccodillians, pollen data, etc. BUT…. ‘early’ models, e.g. Huber and Sloan, Bice, etc etc. UNABLE to reproduce, given palaeogeography and CO2 changes. Is this still the case in 2010?! Bijl et al., Nature 2009

4. General Circulation Models (GCMs)

5. History of GCMs 1990 1990 1995 1995 2001 2001 2007 2007

6. Surface Temperature: observations Surface Temperature: HadCM3 How good are GCMs? (1) temperature

7. Seaice: observations vs models Precipitation: observations Precipitation: HadCM3 How good are GCMs? (2) Precip and seaice

8. Eocene: boundary conditions (1) Palaeogeography Topography Veg

9. Eocene: boundary conditions (2) CO2 Zachos et al, Nature, 2008

10. Eocene Model Intercomparison Project (‘EoMIP’) results

11. Lunt et al, Geology, 2010 Heinemann et al, Climate of the Past, 2009 Winguth et al, Journal of Climate, 2010 Huber et al, PPP, 2006 Roberts et al, EPSL, 2009 Panchuk et al, Geology, 2008

12. New SST/terrestrial data compilation soon, led by Tom Dunkley Jones

13. 280 560 1120 2240 4480 ppmv What are the reasons for the differences…?

14. Sensitivity to uncertainties:(1) Internal model parameters and clouds Boundary conditions: 2 x CO2 0.4% decrease in solar constant palaeogeography uniform vegetation/soil everything else modern

15. “Control” climate (after 1000 years):

16. Select 10 poorly defined parameters • Select reasonable possible ranges for each parameter • Vary them together (using a ‘latin-hypercube’ sampling method) • Clouds: • Threshold of relative humidity for cloud formation (RHcrit) • Precipitation ice fall out speed (VF1) • Conversion rate of cloud liquid water droplets to precipitation (CT) • Threshold value of cloud liquid water for formation of precip. (CW) • Convection : Convective roughness length over the sea (Z0FSEA) • Gravity wave parameters (WAVE) • Sea ice low albedo (ALPHAM) • Diffusion in ocean and atmosphere • Perform 100 simulations for the Eocene, varying some key model parameters. • Do any of these simulations result in a good (i.e. warm pole) simulation?

17. 100 simulations performed, each simulation set for 1000 years. • 59 simulations failed within 100 years! • 4 further simulations failed to complete 1000 years. • Hence only 37 simulations completed to 1000 years. • Of these, 19 failed to complete 4000 years • But 18 have completed 10,000 years

20. Sensitivity uncertainties:(2) Effects of Open Arctic: See also Roberts et al, 2009, EPSL DJF Change in climate due to opening Arctic connections to rest of ocean JJA ANN

21. Sensitivity to uncertainties:(3) Orbits: Change in surface air temperature due to orbital parameter changes Orbital parameters similar to 9kyr BP Obliquity = 25.5o (c.f. 23.5o)

22. EoMIP – comparison of ‘current’ Eocene model simulations • ‘State of the art’ models still unable to reproduce Eocene climates • Model uncertainty, Arctic gateways and orbital variations could combine to reconcile models and data • ……What about issues with the data??!

23. Warm Climates of the Past – a lesson for the future? 10 - 11 October 2011 The Royal Society, London