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| Titel |
Climate and carbon-cycle variability over the last millennium |
| VerfasserIn |
J. H. Jungclaus, S. J. Lorenz, C. Timmreck, C. H. Reick, V. Brovkin, K. Six, J. Segschneider, M. A. Giorgetta, T. J. Crowley, J. Pongratz, N. A. Krivova, L. E. Vieira, S. K. Solanki, D. Klocke, M. Botzet, M. Esch, V. Gayler, H. Haak, T. J. Raddatz, E. Roeckner, R. Schnur, H. Widmann, M. Claussen, B. Stevens, J. Marotzke |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 6, no. 5 ; Nr. 6, no. 5 (2010-10-26), S.723-737 |
| Datensatznummer |
250003765
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| Publikation (Nr.) |
 copernicus.org/cp-6-723-2010.pdf |
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| Zusammenfassung |
| A long-standing task in climate research has been to distinguish between
anthropogenic climate change and natural climate variability. A prerequisite
for fulfilling this task is the understanding of the relative roles of
external drivers and internal variability of climate and the carbon cycle.
Here, we present the first ensemble simulations over the last 1200 years
with a comprehensive Earth system model including a fully interactive carbon
cycle. Applying up-to-date reconstructions of external forcing including the
recent low-amplitude estimates of solar variations, the ensemble simulations
reproduce temperature evolutions consistent with the range of
reconstructions. The 20th-century warming trend stands out against all
pre-industrial trends within the ensemble. Volcanic eruptions are necessary
to explain variations in pre-industrial climate such as the Little Ice Age;
yet only the strongest, repeated eruptions lead to cooling trends that
differ significantly from the internal variability across all ensemble
members. The simulated atmospheric CO2 concentrations exhibit a stable
carbon cycle over the pre-industrial era with multi-centennial variations
somewhat smaller than in the observational records. Early land-cover changes
have modulated atmospheric CO2 concentrations only slightly. We provide
a model-based quantification of the sensitivity (termed γ) of the
global carbon cycle to temperature for a variety of climate and forcing
conditions. We diagnose a distinct dependence of γ on the forcing
strength and time-scales involved, thus providing a possible explanation for
the systematic difference in the observational estimates for different
segments of the last millennium. |
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