• Introduction, and history of Eocene modelling• Atmosphere-Ocean coupled models• ‘EoMIP’• Solutions? – sensitivities to uncertainties
Modelling Eocene Climates: Can any model get it ‘right’?!
Dan LuntM. Heinemann, M. Huber, A. Legrande, A. Ridgwell, P. Valdes, A. Winguth
Zachos et al, Nature, 2001
Orientation…
Bijl et al., Nature 2009
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?!
General Circulation Models (GCMs)
2001 2007
2007
2001
1995
1995
1990
1990
History of GCMs
Surface Temperature: observations
Surface Temperature: HadCM3
How good are GCMs?(1) temperature
Precipitation: observations
Precipitation: HadCM3
Seaice: observations vs models
How good are GCMs?(2) Precip and seaice
Topography
Veg
Eocene: boundary conditions
(1) Palaeogeography
Eocene: boundary conditions
(2) CO2
Zachos et al, Nature, 2008
Eocene Model Intercomparison Project (‘EoMIP’) results
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
New SST/terrestrial data compilation soon, led by Tom Dunkley Jones
280 560 1120 2240 4480 ppmv
What are the reasons for the differences…?
Boundary conditions: 2 x CO2
0.4% decrease in solar constant palaeogeography uniform vegetation/soil everything else modern
Sensitivity to uncertainties:(1) Internal model parameters and clouds
“Control” climate (after 1000 years):
• 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?
• 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
• 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
Sensitivity uncertainties:(2) Effects of Open Arctic:
Change in climate due to opening Arctic connections to rest of ocean
DJF
JJA ANN
See also Roberts et al, 2009, EPSL
Change in surface air temperature due to orbital parameter changes
Orbital parameters similar to 9kyr BP Obliquity = 25.5o (c.f. 23.5o)
Sensitivity to uncertainties:(3) Orbits:
• 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??!
Warm Climates of the Past – a lesson for the future?10 - 11 October 2011The Royal Society, London