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| Titel |
On the background state dependency of (palaeo) climate sensitivity |
| VerfasserIn |
Anna von der Heydt, Henk Dijkstra, Peter Köhler, Roderik van de Wal |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091563
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| Publikation (Nr.) |
 EGU/EGU2014-5865.pdf |
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| Zusammenfassung |
| The equilibrium (Charney) climate sensitivity, here indicated by Sa, is the equilibrium
change in Earth’s global mean surface temperature due to a radiative forcing associated with
a doubling of pCO2, the atmospheric CO2 concentration. Although known for decades, little
progress has been made in constraining upper and lower limits for climate sensitivity.
Originally, Sa was derived from climate models where the atmospheric CO2 concentration is
doubled in typically about 100 years. Also palaeo data have been frequently used to
determine Sa, and — if slow feedback processes are adequately taken into account
— indicate a similar range as those based on climate models used in the IPCC.
However, palaeo data usually span a much larger time than the 100 year model
experiments.
Here, we focus on the last 800 kyr, where climate variability has occurred on time scales
ranging from the 100.000-year ice-age cycles to millennial-scale climate variations. The
traditional linear and equilibrium concept of climate sensitivity as is applied in typical (short
time scale) climate model simulations might not apply to the climate system’s non-stationary
and non-linear response to changing forcing.
One example is the background state dependency of the fast feedback processes. In this
presentation, we assess the dependency of the fast feedback processes on the background
climate state using data of the last 800 kyr and a conceptual climate model. Though still
(locally) linear, we propose a different approach to estimate climate sensitivity
which better accounts for a possible state dependency of the fast feedbacks. This
approach uses local slopes of temperature versus radiative perturbation and is most
suitable for palaeo-data spanning a range of background climate states. We find the
specific climate sensitivities generally lower during cold (glacial) than during warm
periods.
Within the conceptual climate model we further estimate how the background
state-dependency of the fast feedback processes might affect the distributions of feedback
factors and projected temperature change when noise is included in the forcing of the model.
In particular, we investigate the appearance of small but finite probabilities of a very large
temperature response and how the shape of the response distribution might be related to state
dependency. |
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