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| Titel |
What caused Earth's temperature variations during the last 800,000 years? Data-based evidences on radiative forcing and constraints on climate sensitivity |
| VerfasserIn |
P. Köhler, R. Bintanja, H. Fischer, F. Joos, R. Knutti, G. Lohmann, V. Masson-Delmotte |
| 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 |
250030667
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| Zusammenfassung |
| The temperature on Earth varied largely in the Pleistocene from cold glacials to warmer than
present interglacials. To contribute to an understanding of the underlying causes of these
changes we compile various environmental records (and model-based interpretations of some
of them) in order to calculate the direct effect of various processes on Earth’s radiative budget
and, thus, on global annual mean surface temperature over the last 800,000 years. The
importance of orbital variations, of the greenhouse gases cO2, CH4 and N2O, of the albedo of
land ice sheets, sea ice area and vegetation, and of the radiative perturbation of mineral dust
in the atmosphere are investigated. Furthermore, changes in annual mean snow cover on
surface albedo and of ice sheet elevation and sea level change on orography are considered
as additional contributors to glacial cooling. Increased Antarctic temperatures in
Marine Isotope Stages 5.5, 7.5, 9.3 and 11.3 are difficult to explain. The unaccounted
feedbacks would, if taken at present day feedback strengths, ask for another cooling
at the LGM of 2 to 10Â K. If compared with other studies, such as PMIP2, this
gives supporting evidence that the feedback strength themselves are not constant,
but depend on the mean climate state. The best estimate and uncertainty for the
reconstructed radiative forcing and LGM cooling support a present day climate
sensitivity (excluding the ice sheet and vegetation components) between 1.3 and 5.2 K,
with a most likely value near 2.3Â K, somewhat smaller than other methods but
consistent with the consensus range of 2 - 4.5Â K derived from other lines of evidence.
Climate sensitivities above 6Â K are difficult to reconcile with LGM econstructions. |
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