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| Titel |
Amplification of European Little Ice Age by sea ice-ocean-atmosphere feedbacks |
| VerfasserIn |
Flavio Lehner, Andreas Born, Christoph C. Raible, Thomas F. Stocker |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250079769
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| Zusammenfassung |
| The transition from the Medieval Climate Anomaly (~950-1250Â AD) to the Little Ice Age
(~1400-1700Â AD) is believed to have been driven by an interplay of external forcing and
climate system-internal variability. While the hemispheric signal seems to have been
dominated by solar irradiance and volcanic eruptions, the understanding of mechanisms
shaping the climate on continental scale is less robust. Examining an ensemble of transient
model simulations as well as a new type of sensitivity experiments with artificial sea ice
growth, we identify a sea ice-ocean-atmosphere feedback mechanism that amplifies the Little
Ice Age cooling in the North Atlantic-European region and produces the temperature pattern
expected from reconstructions. Initiated by increasing negative forcing, the Arctic sea ice
substantially expands at the beginning of the Little Ice Age. The excess of sea ice is exported
to the subpolar North Atlantic, where it melts, thereby weakening convection of the ocean. As
a consequence, northward ocean heat transport is reduced, reinforcing the expansion of
the sea ice and the cooling of the Northern Hemisphere. In the Nordic Seas, sea
surface height anomalies cause the oceanic recirculation to strengthen at the expense
of the warm Barents Sea inflow, thereby further reinforcing sea ice growth in the
Barents Sea. The absent ocean-atmosphere heat flux in the Barents Sea results in
an amplified cooling over Northern Europe. The positive nature of this feedback
mechanism enables sea ice to remain in an expanded state for decades to centuries and
explain sustained cold periods over Europe such as the Little Ice Age. Support for the
feedback mechanism comes from recent proxy reconstructions around the Nordic Seas. |
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