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| Titel |
Reducing uncertainty in Climate Response Time Scale by Bayesian Analysis of the 8.2 ka event |
| VerfasserIn |
A. Lorenz, H. Held, E. Bauer, T. Schneider von Deimling |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028135
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| Zusammenfassung |
| We analyze the possibility of uncertainty reduction in Climate Response Time Scale by
utilizing Greenland ice-core data that contain the 8.2 ka event within a Bayesian
model-data intercomparison with the Earth system model of intermediate complexity,
CLIMBER-2.3.
Within a stochastic version of the model it has been possible to mimic the 8.2 ka event
within a plausible experimental setting and with relatively good accuracy considering the
timing of the event in comparison to other modeling exercises [1]. The simulation of the
centennial cold event is effectively determined by the oceanic cooling rate which depends
largely on the ocean diffusivity described by diffusion coefficients of relatively wide
uncertainty ranges. The idea now is to discriminate between the different values of
diffusivities according to their likelihood to rightly represent the duration of the 8.2 ka event
and thus to exploit the paleo data to constrain uncertainty in model parameters in analogue to
[2]. Implementing this inverse Bayesian Analysis with this model the technical difficulty
arises to establish the related likelihood numerically in addition to the uncertain model
parameters: While mainstream uncertainty analyses can assume a quasi-Gaussian shape of
likelihood, with weather fluctuating around a long term mean, the 8.2 ka event as a highly
nonlinear effect precludes such an a priori assumption. As a result of this study [3] the
Bayesian Analysis showed a reduction of uncertainty in vertical ocean diffusivity
parameters of factor 2 compared to prior knowledge. This learning effect on the
model parameters is propagated to other model outputs of interest; e.g. the inverse
ocean heat capacity, which is important for the dominant time scale of climate
response to anthropogenic forcing which, in combination with climate sensitivity,
strongly influences the climate systems reaction for the near- and medium-term
future.
1 References
[1] E. Bauer, A. Ganopolski, M. Montoya: Simulation of the cold climate event 8200
years ago by meltwater outburst from lake Agassiz. Paleoceanography 19:PA3014,
(2004)
[2] T. Schneider von Deimling, H. Held, A. Ganopolski, S. Rahmstorf, Climate sensitivity
estimated from ensemble simulations of glacial climates, Climate Dynamics 27, 149-163,
DOI 10.1007/s00382-006-0126-8 (2006).
[3] A. Lorenz, Diploma Thesis, U Potsdam (2007). |
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