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| Titel |
Dansgaard-Oeschger events: bifurcations in the climate system |
| VerfasserIn |
Andrea Cimatoribus, Sybren Drijfhout, Gerard van der Schrier |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050897
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| Zusammenfassung |
| The largest variability in temperature of the last sixty thousand years is connected with
Dansgaard–Oeschger events. These are fast warming episodes (in the North Atlantic region,
5 - 10°C in a few decades), followed by a cooling period that lasts from hundreds to
thousands of years, with a final small jump to initial conditions. They occur with a periodicity
of approximately 1500 years. The connection between Dansgaard–Oeschger events and large
changes in the Atlantic meridional overturning circulation is today generally accepted.
Various prototype models from different authors have been able to qualitatively reproduce the
climatic signal, but no observational constraint has been forwarded to choose between
different theories.
We use high–resolution ice core isotope data to investigate the multimodality of the
system and the statistical properties of fluctuations in the period before the onset of the
abrupt change. Through a phase space reconstruction based on Takens’ theorem, we
show that the time series has a robust bimodal behaviour. We show that techniques
previously suggested for detecting early warning signals of abrupt transitions can
provide important constraints to climate models. In particular, it is found that the
statistical properties of fluctuations are fully compatible with a model that connects
Dansgaard–Oeschger events with the crossing by the climate system of fold bifurcation
points, in response to an external forcing. This view implies hysteresis and switches
between two equilibria of a component of the climate, most likely the Atlantic
meridional overturning circulation. Other hypotheses, that explain Dansgaard–Oeschger
oscillations as noise–induced transitions or motion along an homoclinic orbit, can be
rejected.
These results demonstrate that abrupt transitions in the climate system can happen in
response to a forcing that crosses a critical threshold. Dansgaard–Oeschger events are an
example of this behaviour. |
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