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Eocene Climate Modelling, and the causes of the Palaeocene-Eocene
Thermal Maximum (PETM)
1) Introduction to the PETM
2) Modelling the PETM
3) Modelling the Eocene – a model intercomparison and model-data comparison
4) Sensitivity studies
Zachos et al, Nature, 2001
Orientation…
Zachos et al, Science, 2005
Dunkley Jones et al, 2010
Nunes and Norris, 2006
Bice and Marotzke, 2004
Topography
Veg
Eocene: (1) boundary conditions
Palaeogeography + CO2
Zachos et al, Nature, 2008
Winguth et al, 2010
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
Eocene: (2) MIP results
280 560 1120 2240 4480 ppmv
What are the reasons for the differences…?
Heinemann et al, 2009
Eocene FAMOUS
Boundary conditions: 2 x CO2
0.4% decrease in solar constant palaeogeography uniform vegetation/soil everything else modern
Initialised from previous simulation and then ran for 1000 years
“Control” climate (after 1000 years)
18
• 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?– What parameters most influence the warm climates?– Do any of the “warm pole” models correspond to good
simulations of the modern too?
• First step towards including Eocene in probabilistic predictions of climate sensitivity?
Methodology• 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
Range of values from literature (Murphy et al. 2004)
Perturbed Physics Simulations
• 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
Range of Global Mean Temperatures
FAMOUS Control
“Good” present day models give:
3 models 24-26C2 models 26-28C2 models 31-34C
23
24
Sensitivity to boundary condition uncertainties:
Effects of Open Arctic:
Change in climate due to opening Arctic connections to rest of ocean
DJF
JJA ANN
Sensitivity to Orbital ParametersChange in surface air temperature due to orbital parameter changes
Orbital parameters similar to 9kyr BP Obliquity = 25.5o (c.f. 23.5o)