Climate sensitivity and meridional overturning circulation in the late Eocene using GFDL CM2.1

Hutchinson, David K.; Boer, Agatha M. de; Coxall, Helen K.; Caballero, Rodrigo; Nilsson, Johan; Baatsen, Michiel

doi:10.5194/cp-2017-161

Cited by 26 publications

(59 citation statements)

References 55 publications

(70 reference statements)

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“…The circulation pattern and associated temperature/salinity fields found here generally correspond well with those shown by Hutchinson et al (2018), who use the GFDL model with the same geographic boundary conditions. The ocean heat transport patterns in our 38Ma Eocene simulations generally agree with those seen in previous model studies.…”

supporting

confidence: 70%

“…Aditionally, using the 340 finite volume instead of a spectral grid greatly influences cloud radiative forcing and causes a warming compared to GH14. Indeed, similar global temperatures are found under comparable radiative forcing by Hutchinson et al (2018), using a lower resolution but comparable finite difference dynamical core in the Atmospheric component. Finally, a warm initialisation of the deep ocean, general circulation changes and aerosol changes may add further to temperatures differences.…”

Section: ∼2mentioning

confidence: 55%

“…This reduced mixing in the 4xPIC case causes the global mean deep ocean temperature to still increase about 0.1 • C over the last 500 years. As expected, changes in the up- stratified North Atlantic Ocean (Thomas et al, 2014;Baatsen et al, 2018;Hutchinson et al, 2018) and also suggested by proxy data (Hague et al, 2012).…”

mentioning

confidence: 51%

“…Abbot et al 2009;Kiehl and Shields 2013) and using a higher 60 spatial resolution with better resolved palaeogeographies (Baatsen et al, 2016;Lunt et al, 2016;Hutchinson et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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Equilibrium state and sensitivity of the simulated middle-to-late Eocene climate

Baatsen

Heydt

Huber

et al. 2018

Preprint

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Abstract. While the early Eocene has been considered in many modelling studies, detailed simulations of the middle and late Eocene climate are currently scarce. To understand Antarctic glaciation at the Eocene-Oligocene Transition (∼34Ma) as well as middle Eocene warmth, it is vital to have an adequate reconstruction of the middle-to-late Eocene climate. Here, we present a set of high resolution coupled climate simulations using the Community Earth System Model (CESM) version 1. 5Two middle-to-late Eocene cases are considered with new detailed 38Ma geographical boundary conditions with a different radiative forcing. With 4x pre-industrial concentrations of CO 2 (i.e. 1120 ppm) and CH 4 (∼2700 ppb), the equilibrium sea surface temperatures correspond well to available late middle Eocene (42-38 Ma) proxies. Being generally cooler, the simulated climate with 2x pre-industrial values is a good analog for that of the late Eocene (38-34 Ma). Deep water forma-10 tion occurs in the South Pacific Ocean, while the North Atlantic is strongly stratified and virtually stagnant. A shallow and weak circumpolar current is present in the Southern Ocean with only minor effects on southward oceanic heat transport within wind-driven gyres. Terrestrial temperature proxies, although limited in coverage, also indicate that the results presented here are realistic. The reconstructed 38Ma climate has a reduced equator-to-pole temperature gradient and a more sym-15 metric meridional heat distribution compared to the pre-industrial reference. Climate sensitivity is similar (∼0.7• C/Wm 2 ) to that of the present-day climate (∼0. for a 6-7• C offset between pre-industrial and 38Ma Eocene boundary conditions. These 38Ma sim-1

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supporting

confidence: 70%

Section: ∼2mentioning

confidence: 55%

mentioning

confidence: 51%

“…Abbot et al 2009;Kiehl and Shields 2013) and using a higher 60 spatial resolution with better resolved palaeogeographies (Baatsen et al, 2016;Lunt et al, 2016;Hutchinson et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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Equilibrium state and sensitivity of the simulated middle-to-late Eocene climate

Baatsen

Heydt

Huber

et al. 2018

Preprint

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“…CC BY 4.0 License. and thus influence the meridional mass transport (Bryan, 1987) affecting the large-scale ocean circulation and its sensitivity (Scott and Marotzke, 2002;Prange et al, 2003;Rahmstorf et al, 2006;Green and Huber, 2013;De Boer and Hogg, 2014;de Lavergne et al, 2016;Hutchinson et al, 2018). Lambeck (1977) calculated the total rate of energy dissipation based on the numerical tide model, indicating a dominant role of ocean continent geometry and sea floor topography.…”

Section: Meridional Temperature Gradient In a Complex Modelmentioning

confidence: 99%

Temperatures from Energy Balance Models: the effective heat capacity matters

Lohmann

2019

Preprint

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Abstract. Energy balance models (EBM) are highly simplified systems of the climate system. The global temperature is calculated by the radiation budget through the incoming energy from the Sun and the outgoing energy from the Earth. The argument that the temperature can be calculated by the simple radiation budget is revisited. The underlying assumption for a realistic temperature distribution is explored: One has to assume a moderate diurnal cycle due to the large heat capacity and the fast rotation of the Earth. Interestingly, the global mean in the revised EBM is very close to the originally proposed value. The time dependent-EBM predicts a flat meridional temperature gradient for large heat capacities which can be related to very effective vertical diffusion. Motivated by this finding, sensitivity experiments with a complex model are performed where the vertical diffusion in the ocean has been increased. The resulting climate shows a flat meridional temperature gradient and a deeper thermocline. The common pattern of surface temperature anomalies and climate reconstructions suggests a possible mechanism for past climate changes prior to 3 million years ago.

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Proxy-Model Comparison for the Eocene-Oligocene Transition in Southern High Latitudes

Tibbett

Burls

Hutchinson

et al. 2022

Preprint

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The Eocene-Oligocene Transition (EOT) marks the shift from greenhouse to icehouse conditions at 34 Ma, when a permanent ice sheet developed on Antarctica. Climate modeling studies have recently assessed the drivers of the transition globally. Here we revisit those experiments for a detailed study of the southern high latitudes in comparison to the growing number of mean annual sea surface temperature (SST) and mean air temperature (MAT) proxy reconstructions, allowing us to assess proxy-model temperature agreement and refine estimates for the magnitude of the pCO forcing of the EOT. We compile and update published proxy temperature records on and around Antarctica for the late Eocene (38-34 Ma) and early Oligocene (34-30 Ma). Compiled SST proxies cool by up to 3°C and MAT by up to 4°C between the timeslices. Proxy data were compared to previous climate model simulations representing pre- and post-EOT, typically forced with a halving of pCO. We scaled the model outputs to identify the magnitude of pCO change needed to drive a commensurate change in temperature to best fit the temperature proxies. The multi-model ensemble needs a 30 or 33% decrease in pCO, to best fit MAT or SST proxies respectively, a difference of just 3%. These proxy-model intercomparisons identify pCO as the primary forcing of EOT cooling, with a magnitude (-200 or -243 ppmv) approaching that of the pCO proxies (-150 ppmv). However individual model estimates span -66 to -375 ppmv, thus proxy-model uncertainties are dominated by model divergence.

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Climate sensitivity and meridional overturning circulation in the late Eocene using GFDL CM2.1

Abstract: 2 salinities approximately agree with Eocene proxy estimates. North Atlantic salinity increases by 1-2 psu when CO 2 is halved, and similarly freshens when CO 2 is doubled, due to changes in the hydrological cycle.

Cited by 26 publications

References 55 publications

Equilibrium state and sensitivity of the simulated middle-to-late Eocene climate

Equilibrium state and sensitivity of the simulated middle-to-late Eocene climate

Temperatures from Energy Balance Models: the effective heat capacity matters

Proxy-Model Comparison for the Eocene-Oligocene Transition in Southern High Latitudes

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