Warm Paleocene/Eocene climate as simulated in ECHAM5/MPI-OM

We investigate the late Paleocene/early Eocene (PE) climate using the coupled atmosphere-ocean-sea ice model ECHAM5/MPI-OM. The surface in our PE control simulation is on average 297 K warm and ice-free, despite a moderate atmospheric CO<sub>2</sub> concentration of 560 p...

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Main Authors: M. Heinemann, J. H. Jungclaus, J. Marotzke
Format: Article
Language:English
Published: Copernicus Publications 2009-12-01
Series:Climate of the Past
Online Access:http://www.clim-past.net/5/785/2009/cp-5-785-2009.pdf
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spelling doaj-8fb9976659ca4c04924672782319aea52020-11-25T00:31:57ZengCopernicus PublicationsClimate of the Past1814-93241814-93322009-12-0154785802Warm Paleocene/Eocene climate as simulated in ECHAM5/MPI-OMM. HeinemannJ. H. JungclausJ. MarotzkeWe investigate the late Paleocene/early Eocene (PE) climate using the coupled atmosphere-ocean-sea ice model ECHAM5/MPI-OM. The surface in our PE control simulation is on average 297 K warm and ice-free, despite a moderate atmospheric CO<sub>2</sub> concentration of 560 ppm. Compared to a pre-industrial reference simulation (PR), low latitudes are 5 to 8 K warmer, while high latitudes are up to 40 K warmer. This high-latitude amplification is in line with proxy data, yet a comparison to sea surface temperature proxy data suggests that the Arctic surface temperatures are still too low in our PE simulation. <br><br> To identify the mechanisms that cause the PE-PR surface temperature differences, we fit two simple energy balance models to the ECHAM5/MPI-OM results. We find that about 2/3 of the PE-PR global mean surface temperature difference are caused by a smaller clear sky emissivity due to higher atmospheric CO<sub>2</sub> and water vapour concentrations in PE compared to PR; 1/3 is due to a smaller planetary albedo. The reduction of the pole-to-equator temperature gradient in PE compared to PR is due to (1) the large high-latitude effect of the higher CO<sub>2</sub> and water vapour concentrations in PE compared to PR, (2) the lower Antarctic orography, (3) the smaller surface albedo at high latitudes, and (4) longwave cloud radiative effects. Our results support the hypothesis that local radiative effects rather than increased meridional heat transports were responsible for the "equable" PE climate. http://www.clim-past.net/5/785/2009/cp-5-785-2009.pdf
collection DOAJ
language English
format Article
sources DOAJ
author M. Heinemann
J. H. Jungclaus
J. Marotzke
spellingShingle M. Heinemann
J. H. Jungclaus
J. Marotzke
Warm Paleocene/Eocene climate as simulated in ECHAM5/MPI-OM
Climate of the Past
author_facet M. Heinemann
J. H. Jungclaus
J. Marotzke
author_sort M. Heinemann
title Warm Paleocene/Eocene climate as simulated in ECHAM5/MPI-OM
title_short Warm Paleocene/Eocene climate as simulated in ECHAM5/MPI-OM
title_full Warm Paleocene/Eocene climate as simulated in ECHAM5/MPI-OM
title_fullStr Warm Paleocene/Eocene climate as simulated in ECHAM5/MPI-OM
title_full_unstemmed Warm Paleocene/Eocene climate as simulated in ECHAM5/MPI-OM
title_sort warm paleocene/eocene climate as simulated in echam5/mpi-om
publisher Copernicus Publications
series Climate of the Past
issn 1814-9324
1814-9332
publishDate 2009-12-01
description We investigate the late Paleocene/early Eocene (PE) climate using the coupled atmosphere-ocean-sea ice model ECHAM5/MPI-OM. The surface in our PE control simulation is on average 297 K warm and ice-free, despite a moderate atmospheric CO<sub>2</sub> concentration of 560 ppm. Compared to a pre-industrial reference simulation (PR), low latitudes are 5 to 8 K warmer, while high latitudes are up to 40 K warmer. This high-latitude amplification is in line with proxy data, yet a comparison to sea surface temperature proxy data suggests that the Arctic surface temperatures are still too low in our PE simulation. <br><br> To identify the mechanisms that cause the PE-PR surface temperature differences, we fit two simple energy balance models to the ECHAM5/MPI-OM results. We find that about 2/3 of the PE-PR global mean surface temperature difference are caused by a smaller clear sky emissivity due to higher atmospheric CO<sub>2</sub> and water vapour concentrations in PE compared to PR; 1/3 is due to a smaller planetary albedo. The reduction of the pole-to-equator temperature gradient in PE compared to PR is due to (1) the large high-latitude effect of the higher CO<sub>2</sub> and water vapour concentrations in PE compared to PR, (2) the lower Antarctic orography, (3) the smaller surface albedo at high latitudes, and (4) longwave cloud radiative effects. Our results support the hypothesis that local radiative effects rather than increased meridional heat transports were responsible for the "equable" PE climate.
url http://www.clim-past.net/5/785/2009/cp-5-785-2009.pdf
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