Eocene Climate Modelling, and the causes of the Palaeocene-Eocene Thermal Maximum (PETM)

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)