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          Institute: MPI für Meteorologie     Collection: Ocean in the Earth System     Display Documents

ID: 442251.0, MPI für Meteorologie / Ocean in the Earth System
Warm Paleocene/Eocene climate as simulated in ECHAM5/MPI-OM
Authors:Heinemann, M.; Jungclaus, J. H.; Marotzke, J.
Date of Publication (YYYY-MM-DD):2009
Title of Journal:Climate of the Past
Start Page:785
End Page:802
Review Status:Peer-review
Audience:Not Specified
Abstract / 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 CO2 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.

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 CO2 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 CO2 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.
External Publication Status:published
Document Type:Article
Communicated by:Carola Kauhs
Affiliations:MPI für Meteorologie/Ocean in the Earth System
MPI für Meteorologie/IMPRS Earth System Modelling
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