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Titel |
Non-equilibrium metrics for palaeo climate sensitivity in the presence of rapid transitions |
VerfasserIn |
Anna von der Heydt, Peter Ashwin |
Konferenz |
EGU General Assembly 2015
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 17 (2015) |
Datensatznummer |
250105035
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Publikation (Nr.) |
EGU/EGU2015-4479.pdf |
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Zusammenfassung |
Equilibrium climate sensitivity is one measure that is frequently used to predict long-term
climate change in GCMs. Despite much research over the last decades, little progress has
been made in constraining the uncertainty on climate sensitivity. One reason for this is the
fact that the climate has a strong internal variability on many time scales, is subject to a
non-stationary forcing and mostly out of equilibrium with the changes in the radiative
forcing.
Palaeo records of past climate variations can give insight into how the the climate system
responds to various forcings although care must be taken of the slow feedback processes at
comparing palaeo climate sensitivity estimates with estimates from (short time scale) model
simulations. In addition, for the late Pleistocene ice age cycles it has been shown from both
proxy data and a conceptual climate model that climate sensitivity varies considerably
between the cold and warm phases because the fast feedback processes change their relative
strength over one cycle.
Here we use a conceptual model with known dynamics modelling the late Pleistocene ice
ages to explore how climate sensitivity can be estimated from the model time series.
Extracting the climate sensitivity from the relation between radiative forcing and global mean
temperature leads to strongly state dependent behaviour and even negative values for climate
sensitivity at rapid transitions into the deep glacial states. The degree to which the system is
out of equilibrium and its relation to the equilibrium assumption of climate sensitivity needs
therefore to be taken into account. Furthermore, Milankovitch forcing is generally not
considered in palaeo climate sensitivity estimates. In the model time series we show how the
sensitivity to Milankovitch forcing can be accounted for in an estimate of the climate
sensitivity. We also investigate how the climate sensitivity in this non-equilibrium system
varies with the averaging time, dependent on the phase of the forcing and the phase of the ice
age cycle. |
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