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| Titel |
The role of the North Atlantic overturning and deep ocean for multi-decadal global-mean-temperature variability |
| VerfasserIn |
C. F. Schleussner, J. Runge, Jascha Lehmann, A. Levermann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
2190-4979
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| Digitales Dokument |
URL |
| Erschienen |
In: Earth System Dynamics ; 5, no. 1 ; Nr. 5, no. 1 (2014-02-20), S.103-115 |
| Datensatznummer |
250115297
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| Publikation (Nr.) |
 copernicus.org/esd-5-103-2014.pdf |
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| Zusammenfassung |
| Earth's climate exhibits internal modes of variability on various
timescales. Here we investigate multi-decadal variability of the
Atlantic meridional overturning circulation (AMOC), Northern Hemisphere sea-ice extent
and global mean temperature (GMT) in an ensemble of CMIP5 models under control conditions.
We report an inter-annual GMT variability of about ±0.1° C
originating solely from natural variability in the model ensemble.
By decomposing the GMT variance into contributions of the
AMOC and Northern Hemisphere sea-ice extent using
a graph-theoretical statistical approach, we find the AMOC to
contribute 8% to GMT variability in the ensemble mean. Our
results highlight the importance of AMOC sea-ice feedbacks that
explain 5% of the GMT variance, while the contribution solely
related to the AMOC is found to be about 3%. As a consequence
of multi-decadal AMOC variability, we report substantial variations
in North Atlantic deep-ocean heat content with trends of up to
0.7 × 1022 J decade−1 that are of the order of
observed changes over the last decade and consistent with the
reduced GMT warming trend over this period. Although these
temperature anomalies are largely density-compensated by salinity
changes, we find a robust negative correlation between the AMOC and
North Atlantic deep-ocean density with density lagging the AMOC by 5
to 11 yr in most models. While this would in principle allow
for a self-sustained oscillatory behavior of the coupled AMOC–deep-ocean
system, our results are inconclusive about the role of
this feedback in the model ensemble. |
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