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| Titel |
The challenge of simulating the warmth of the mid-Miocene climatic optimum in CESM1 |
| VerfasserIn |
A. Goldner, N. Herold, M. Huber |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 10, no. 2 ; Nr. 10, no. 2 (2014-03-13), S.523-536 |
| Datensatznummer |
250116936
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| Publikation (Nr.) |
 copernicus.org/cp-10-523-2014.pdf |
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| Zusammenfassung |
| The mid-Miocene climatic optimum (MMCO) is an intriguing climatic period due
to its above-modern temperatures in mid-to-high latitudes in the presence of
close-to-modern CO2 concentrations. We use the recently released Community
Earth System Model (CESM1.0) with a slab ocean to simulate this warm period,
incorporating recent Miocene CO2 reconstructions of 400 ppm (parts per million). We simulate a
global mean annual temperature (MAT) of 18 °C, ~4 °C
above the preindustrial value, but 4 °C colder than the global
Miocene MAT we calculate from climate proxies. Sensitivity tests reveal that
the inclusion of a reduced Antarctic ice sheet, an equatorial Pacific temperature gradient
characteristic of a permanent El Niño, increased CO2 to 560 ppm, and variations in
obliquity only marginally improve model–data agreement. All MMCO simulations
have an Equator to pole temperature gradient that is at least
~10 °C larger than that reconstructed from proxies. The MMCO
simulation most comparable to the proxy records requires a CO2
concentration of 800 ppm. Our results illustrate that MMCO warmth is not
reproducible using the CESM1.0 forced with CO2 concentrations
reconstructed for the Miocene or including various proposed Earth system
feedbacks; the remaining discrepancy in the MAT is comparable to that
introduced by a CO2 doubling. The model's tendency to underestimate proxy
derived global MAT and overestimate the Equator to pole temperature gradient
suggests a major climate problem in the MMCO akin to those in the Eocene. Our
results imply that this latest model, as with previous generations of climate
models, is either not sensitive enough or additional forcings remain missing
that explain half of the anomalous warmth and pronounced polar amplification
of the MMCO. |
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