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| Titel |
Boreal and temperate snow cover variations induced by black carbon emissions in the middle of the 21st century |
| VerfasserIn |
M. Ménégoz, G. Krinner, Y. Balkanski, A. Cozic, O. Boucher, P. Ciais |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1994-0416
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| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 7, no. 2 ; Nr. 7, no. 2 (2013-03-26), S.537-554 |
| Datensatznummer |
250017949
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| Publikation (Nr.) |
 copernicus.org/tc-7-537-2013.pdf |
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| Zusammenfassung |
| We used a coupled climate-chemistry model to quantify the impacts of aerosols
on snow cover north of 30° N both for the present-day and for the
middle of the 21st century. Black carbon (BC) deposition over continents
induces a reduction in the mean number of days with snow at the surface
(MNDWS) that ranges from 0 to 10 days over large areas of Eurasia and
Northern America for the present-day relative to the pre-industrial period.
This is mainly due to BC deposition during the spring, a period of the year
when the remaining of snow accumulated during the winter is exposed to both
strong solar radiation and a large amount of aerosol deposition induced
themselves by a high level of transport of particles from polluted areas.
North of 30° N, this deposition flux represents 222 Gg BC
month−1 on average from April to June in our simulation. A large
reduction in BC emissions is expected in the future in all of the
Representative Concentration Pathway (RCP) scenarios. In particular,
considering the RCP8.5 in our simulation leads to a decrease in the spring BC
deposition down to 110 Gg month−1 in the 2050s. However, despite the
reduction of the aerosol impact on snow, the MNDWS is strongly reduced by
2050, with a decrease ranging from 10 to 100 days from present-day values
over large parts of the Northern Hemisphere. This reduction is essentially
due to temperature increase, which is quite strong in the RCP8.5 scenario in
the absence of climate mitigation policies. Moreover, the projected sea-ice
retreat in the next decades will open new routes for shipping in the Arctic.
However, a large increase in shipping emissions in the Arctic by the mid-21st
century does not lead to significant changes of BC deposition over
snow-covered areas in our simulation. Therefore, the MNDWS is clearly not
affected through snow darkening effects associated with these Arctic ship
emissions. In an experiment without nudging toward atmospheric reanalyses, we
simulated however some changes of the MNDWS considering such aerosol ship
emissions. These changes are generally not statistically significant in
boreal continents, except in Quebec and in the West Siberian plains, where
they range between −5 and −10 days. They are induced both by radiative
forcings of the aerosols when they are in the snow and in the atmosphere, and
by all the atmospheric feedbacks. These experiments do not take into account
the feedbacks induced by the interactions between ocean and atmosphere as
they were conducted with prescribed sea surface temperatures. Climate change
by the mid-21st century could also cause biomass burning activity (forest
fires) to become more intense and occur earlier in the season. In an
idealised scenario in which forest fires are 50% stronger and occur 2
weeks earlier and later than at present, we simulated an increase in spring
BC deposition of 21 Gg BC month−1 over continents located north of
30° N. This BC deposition does not impact directly the snow cover
through snow darkening effects. However, in an experiment considering all the
aerosol forcings and atmospheric feedbacks, except those induced by the
ocean–atmosphere interactions, enhanced fire activity induces a significant
decrease of the MNDWS reaching a dozen of days in Quebec and in Eastern
Siberia. |
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