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| Titel |
Emulating atmosphere-ocean and carbon cycle models with a simpler model, MAGICC6 – Part 2: Applications |
| VerfasserIn |
M. Meinshausen, T. M. L. Wigley, S. C. B. Raper |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 4 ; Nr. 11, no. 4 (2011-02-16), S.1457-1471 |
| Datensatznummer |
250009358
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| Publikation (Nr.) |
 copernicus.org/acp-11-1457-2011.pdf |
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| Zusammenfassung |
| Intercomparisons of coupled atmosphere-ocean general circulation
models (AOGCMs) and carbon cycle models are important for
galvanizing our current scientific knowledge to project future
climate. Interpreting such intercomparisons faces major challenges,
not least because different models have been forced with different
sets of forcing agents. Here, we show how an emulation approach with
MAGICC6 can address such problems. In a companion paper
(Meinshausen et al., 2011a), we show how the lower complexity carbon
cycle-climate model MAGICC6 can be calibrated to emulate, with
considerable accuracy, globally aggregated characteristics of these
more complex models. Building on that, we examine here the Coupled
Model Intercomparison Project's Phase 3 results (CMIP3). If forcing
agents missed by individual AOGCMs in CMIP3 are considered, this
reduces ensemble average temperature change from pre-industrial
times to 2100 under SRES A1B by 0.4 °C. Differences in the
results from the 1980 to 1999 base period (as reported in IPCC AR4)
to 2100 are negligible, however, although there are some differences
in the trajectories over the 21st century. In a second part of
this study, we consider the new RCP scenarios that are to be
investigated under the forthcoming CMIP5 intercomparison for the
IPCC Fifth Assessment Report. For the highest scenario, RCP8.5,
relative to pre-industrial levels, we project a median warming of
around 4.6 °C by 2100 and more than 7 °C by 2300.
For the lowest RCP scenario, RCP3-PD, the corresponding warming is
around 1.5 °C by 2100, decreasing to around 1.1 °C
by 2300 based on our AOGCM and carbon cycle model
emulations. Implied cumulative CO2 emissions over the 21st
century for RCP8.5 and RCP3-PD are 1881 GtC (1697 to 2034 GtC, 80%
uncertainty range) and 381 GtC (334 to 488 GtC), when prescribing
CO2 concentrations and accounting for uncertainty in the carbon
cycle. Lastly, we assess the reasons why a previous MAGICC version
(4.2) used in IPCC AR4 gave roughly 10% larger warmings over the
21st century compared to the CMIP3 average. We find that
forcing differences and the use of slightly too high climate
sensitivities inferred from idealized high-forcing runs were the
major reasons for this difference. |
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