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| Titel |
The Norwegian Earth System Model, NorESM1-M – Part 2: Climate response and scenario projections |
| VerfasserIn |
T. Iversen, M. Bentsen, I. Bethke, J. B. Debernard, A. Kirkevåg, Ø. Seland, H. Drange, J. E. Kristjánsson, I. Medhaug, M. Sand, I. A. Seierstad |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 6, no. 2 ; Nr. 6, no. 2 (2013-03-22), S.389-415 |
| Datensatznummer |
250017798
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| Publikation (Nr.) |
 copernicus.org/gmd-6-389-2013.pdf |
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| Zusammenfassung |
| NorESM is a generic name of the Norwegian earth system model. The first
version is named NorESM1, and has been applied with medium spatial resolution
to provide results for CMIP5
(http://cmip-pcmdi.llnl.gov/cmip5/index.html) without (NorESM1-M) and
with (NorESM1-ME) interactive carbon-cycling. Together with the accompanying
paper by Bentsen et al. (2012), this paper documents that the core version
NorESM1-M is a valuable global climate model for research and for providing
complementary results to the evaluation of possible anthropogenic climate
change. NorESM1-M is based on the model CCSM4 operated at NCAR, but the ocean
model is replaced by a modified version of MICOM and the atmospheric model is
extended with online calculations of aerosols, their direct effect and their
indirect effect on warm clouds. Model validation is presented in the
companion paper (Bentsen et al., 2012). NorESM1-M is estimated to have
equilibrium climate sensitivity of ca. 2.9 K and a transient climate
response of ca. 1.4 K. This sensitivity is in the lower range amongst the
models contributing to CMIP5. Cloud feedbacks dampen the response, and a
strong AMOC reduces the heat fraction available for increasing near-surface
temperatures, for evaporation and for melting ice. The future projections
based on RCP scenarios yield a global surface air temperature increase of
almost one standard deviation lower than a 15-model average. Summer sea-ice
is projected to decrease considerably by 2100 and disappear completely for
RCP8.5. The AMOC is projected to decrease by 12%, 15–17%, and 32%
for the RCP2.6, 4.5, 6.0, and 8.5, respectively. Precipitation is projected
to increase in the tropics, decrease in the subtropics and in southern parts
of the northern extra-tropics during summer, and otherwise increase in most
of the extra-tropics. Changes in the atmospheric water cycle indicate that
precipitation events over continents will become more intense and dry spells
more frequent. Extra-tropical storminess in the Northern Hemisphere is
projected to shift northwards. There are indications of more frequent
occurrence of spring and summer blocking in the Euro-Atlantic sector, while
the amplitude of ENSO events weakens although they tend to appear more
frequently. These indications are uncertain because of biases in the model's
representation of present-day conditions. Positive phase PNA and negative
phase NAO both appear less frequently under the RCP8.5 scenario, but also
this result is considered uncertain. Single-forcing experiments indicate that
aerosols and greenhouse gases produce similar geographical patterns of
response for near-surface temperature and precipitation. These patterns tend
to have opposite signs, although with important exceptions for precipitation
at low latitudes. The asymmetric aerosol effects between the two hemispheres
lead to a southward displacement of ITCZ. Both forcing agents, thus, tend to
reduce Northern Hemispheric subtropical precipitation. |
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