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Paleocene/Eocene Thermal Maximum (PETM)

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Paleocene/Eocene Thermal Maximum (PETM) numerical modelling Warm and sensitive Paleocene-Eocene climate 1) 1),2) 1) , Jochem Marotzke Malte Heinemann Johann H. Jungclaus 1) Max Planck Institute for Meteorology, Hamburg, Germany 2) IMPRS - Earth System Modelling http://en.wikipedia.org/wiki/Pangea bigbang Introduction (15billion years) (180 million years) (180 million breaks up Pangaea Eocene (55 million years) million (55 Eocene early to Paleocene late (4.6 billion years) (4.6 billion earth forms (photosynthesis) (3 billion years) (3 billion cyanobacteria cyanobacteria (60 million years) (60 million extinct dinosaurs (160 thousand years) (160 thousand homo sapiens homo today p i k i w . e d / / : p t t h g r o . a i d e Introduction Titanoboa cerrejonensis precloacal vertebrae compared to vertebrae of 3.4m Boa constrictor artist's reconstruction / Jason Bourque (2008) late Paleocene to early Eocene was the warmest period during the Cenozoic (last 65 million years) (Zachos et al 2001) crocodiles & turtles near Arctic (Estes and Hutchinson 1980) giant snake in Columbia (Head et al. 2009, snake paleo-thermometry) Introduction Paleocene/Eocene Thermal Maximum (PETM) Maximum Thermal Paleocene/Eocene the as known event warming global short-lived greenhouse gas concentrations concentrations gas greenhouse atmospheric of increase an with associated PETM temperature proxy δ18O (benthic forams) modified from Zachos et al. (2001) al. modifiedZachoset from(2001) Paleocene 60 time[million years ago] PETM 50 Eocene (e.g.,Dickens 1995)etal. 40 glaciation Antarctic Research question (1) (1) Can we reproduce the warm and equable Paleocene-Eocene climate using a state of the art climate model? the reconstructed warm high latitudes imply a low equator- to-pole temperature gradient — “equable” climate climate models could not reproduce the small equator-to-pole temperature gradient — suggesting that models lacked high- latitude warming (or tropical cooling) mechanism (Barron 1987, Huber and Sloan 2001) Research question (2) (2) What caused the Paleocene-Eocene Thermal Maximum? How sensitive was the PE climate to pCO2? magnitude of pCO2 increase not well constrained one suggested CO2 source: methane hydrates from marine sediments (Dickens et al. 1995) IFM-GEOMAR 2002 methane hydrate hypothesis requires a large climate sensitivity not previously simulated (Pagani et al. 2008) also: requires a trigger! Constraining pCO2 increase during PETM carbon isotope excursion major carbon reservoirs (after Nunes & Norris 2006) (after Ridgwell & Edwards 2007) ] 54.8 s r a e y n 55.0 o i l l i m [ e 55.2 g a 55.4 -2 -1 0 1 13 o δ C [ /oo] amount of carbon release necessary to explain carbon isotope excursion depends on carbon source Research question (3) (3) Can we confirm the hypothesis that an ocean circulation switch caused the methane hydrate melting — using a coupled model? present-day conveyor belt (W. Broecker, modified by E. Maier-Reimer) Research question (3) (3) Can we confirm the hypothesis that an ocean circulation switch caused the methane hydrate melting — using a coupled model? the dissociation of methane hydrate requires a trigger based on ocean modelling, Bice and Marotzke (2001) suggested that a large-scale ocean circulation change may have caused bottom water warming and methane hydrate melting paleo-reconstructions support the notion of an ocean circulation switch at the onset of the PETM (Nunes and Norris 2006) Outline (1) Can we reproduce the warm and equable Paleocene-Eocene climate using a state of the art climate model? (2) What caused the Paleocene-Eocene Thermal Maximum? How sensitive was the PE climate to pCO2? (3) Can we confirm the hypothesis that an ocean circulation switch caused the methane hydrate melting — using a coupled model? Summary Outline (1) Can we reproduce the warm and equable Paleocene-Eocene climate using a state of the art climate model? (2) What caused the Paleocene-Eocene Thermal Maximum? How sensitive was the PE climate to pCO2? (3) Can we confirm the hypothesis that an ocean circulation switch caused the methane hydrate melting — using a coupled model? Summary (1) climate Numerical climate model coupled atmosphere – ocean – sea ice general circulation model COSMOS-AO consists of: atmosphere: ECHAM 5.3 (T31 L19) developed from ECMWF operational forecast model; spectral dynamical core; parameterisation package developed in Hamburg (Roeckner et al. 2003) ocean and sea-ice: MPI-OM 1.2 (144x87 L40) ocean model based on primitive equations for hydrostatic Boussinesq fluid; simple sea-ice dynamics and thermodynamics (Marsland et al. 2003, Jungclaus et al. 2006) Paleocene-Eocene boundary conditions depth [m] height [m] 5000 2500 0 0 1500 3000 topographic reconstruction from Bice and Marotzke (2001) rivers flow along height gradients, no lakes, no glaciers homogeneous soil and vegetation parameters some parameters Paleocene/Eocene pre-industrial reference Simulated annual mean surface temperature Paleocene-Eocene pre-industrial reference [K] 210 240 260 270 280 285 290 295 300 305 310 315 Paleocene-Eocene simulation is on average 9.4K warmer than the pre-industrial reference Paleocene-Eocene high latitudes are sea-ice-free Comparison to temperature reconstructions ] K 310 crosses indicate reconstructed [ e r 2) 3) 4) pre-PETM sea surface u t 300 a temperatures r n 5) e a p e m 6) m 290 e l t a 1) e n c o a z f 280 r u s a e 270 s -90 -45 -30 -15 0 15 30 45 90 latitude [oN] most sea surface temperature reconstructions within seasonal variability simulated Arctic surface 11 to 13K colder than reconstructed 1) Thomas et al. (2002) [δ18O]; 2)+3) Tripati and Elderfield (2004) [Mg/Ca]; 4) Zachos et al. (2003) [TEX86]; 5) Zachos et al. (2006) [TEX86]; 6) Sluijs et al. (2006) [TEX86] Warming relative to pre-industrialreference reference (PR) reference gradient temperature equator-to-pole a exhibits (PE) simulation Paleocene-Eocene zonal mean PE-PR surface temperature difference [K] 30 20 10 40 -90 0 -45 -30 -15 latitude[ 0 o N] 15 high latitudes high at largest is warming 30 45 than the pre-industrial pre-industrial the than 90 smaller smaller of 9.4 K 9.4 of warming average Analysis of the warming / radiative budget pre-industrial PE = ↑ ↓ planetary albedo α SWtop SWtop 0.318 0.292 = ↑ ↑ longwave emissivity ε LWtop LWs 0.585 0.541 reduced albedo and reduced emissivity in the Paleocene- Eocene run (PE) cause a warming 0-D energy balance model compute surface temperature from model balancing incoming shortwave and outgoing longwave radiation albedo emissivity surface temperature ↓ ∂ SW (y)[1− α(y)] + F(y) = ε(y)σ T4 (y) (y: latitude) top ∂y incoming Stefan-Boltzmann constant shortwave radiation 1-D energy balance model compute zonal mean surface temperature from simple model balancing incoming shortwave radiation, outgoing longwave radiation and horizontal energy transport albedo emissivity surface temperature ↓ ∂ 4 SW (y)[1− α(y)] + CvF(y) = ε(y)σ T (y) (y: latitude) top ∂y incoming Stefan-Boltzmann constant shortwave convergence of radiation meridional energy transport 1-D energy balance model energy balance model nicely fits ECHAM5/MPI-OM fits nicely model balance energy energy transport convergence to energy balance model balance energy to convergence transport energy and emissivity, albedo, ECHAM5/MPI-OM-diagnosed apply zonal mean PE-PR surface temperature difference [K] 30 20 10 40 -90 0 -45 -30 -15 latitude[ ECHAM5/MPI-OM energy balance model balance energy 0 o N] 15 30 45 — 90 results Energy balance model 2/3 of warming due to emissivity, 1/3 due to planetary albedo planetary to due 1/3 emissivity, to due warming of 2/3 zonal mean PE-PR surface temperature difference [K] 30 20 10 40 -90 0 -45 -30 -15 latitude[ black line: total warming total line: black blue line: effect of emissivity of effect line: blue 0 o N] 15 — 30 results 45 90 Energy balance model hardly influence the pole-to-equator temperature gradient temperature pole-to-equator the influence hardly but effects, regional have changes transport energy meridional albedo planetary to due 1/3 emissivity, to due warming of 2/3 zonal mean PE-PR surface temperature difference [K] 30 20 10 40 -90 0 + -45 -30 -15 latitude[ + black line: total warming total line: black blue line: effect of emissivity of effect line: blue black – red: meridional energy transport energy meridional red: – black emissivity of effect line: red - 0 + o N] 15 — 30 - results 45 - 90 and albedo Conclusions (1) (1) Can we reproduce the warm and equable Paleocene-Eocene climate using a state of the art climate model? we get close the simulated Arctic surface temperature is still too cold reduction of PE equator-to-pole temperature gradient due to radiative effects, rather than due to meridional energy transport changes Outline (1) Can we reproduce the warm and equable Paleocene-Eocene climate using a state of the art climate model? (2) What caused the Paleocene-Eocene Thermal Maximum? How sensitive was the PE climate to pCO2? (3) Can we confirm the hypothesis that an ocean circulation switch caused the methane hydrate melting — using a coupled model? Summary (2) climate sensitivity CO2 sensitivity experiments ] 1120 4 x pre-industrial m p p 840 [ 3 x pre-industrial 2 O 560 2 x pre-industrial C p 280 1 x pre-industrial 2000 2070 2500 3200 simulated time [years] pCO2 increase necessitates 2 modifications of ECHAM5: 1- ensure positive definite optical thicknesses in longwave radiation scheme; else: ECHAM5 crashes (not shown) 2- adapt ozone climatology to increased tropopause height in warming climate; else: artificial warming (not
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