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| Titel |
Sensitivity of radiative forcing and surface temperature to sulfate injection area in stratospheric geoengineering. |
| VerfasserIn |
Anton Laakso, Antti-Ilari Partanen, Harri Kokkola, Kari Lehtinen, Hannele Korhonen |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250098017
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| Publikation (Nr.) |
 EGU/EGU2014-13652.pdf |
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| Zusammenfassung |
| Geoengineering by injecting sulfur to the stratosphere has been shown to have a potential to
counteract global warming. In the future, such a method may be considered as an option in
slowing down global warming, if reducing of greenhouse gases has not been achieved fast
and effectively enough. In the stratosphere sulfate particles reflect solar radiation back to
space and thus cool the climate. Cooling effect would last 1-2 years because of the
stability of the stratosphere combined with lack of effective removal processes.
Usually sulfur is assumed to be injected as SO2 which oxidizes and forms sulfate
particles after injections. However, if the amount of injected sulfur is increased,
its effect can be saturated and the increase in the stratospheric sulfate burden and
global radiative forcing becomes smaller. When sulfur concentration increases,
stratospheric particles would grow to larger sizes, which have a shorter lifetime in the
atmosphere and do not reflect radiation as efficiently as smaller particles. In many
previous studies, sulfur has been assumed to be injected along the equator where
yearly mean solar intensity is the highest and where sulfur is spread more or less
equally to both hemispheres. Because of this, sulfate has been assumed to be injected
and spread to the hemisphere also during winter time, when solar intensity is low.
Thus sulfate injection would be more effective, if sulfur injection area is changed
seasonally.
In this study we use global aerosol-climate model ECHAM6.1-HAM2.2-SALSA to
investigate radiative forcing from the different injection areas and to study if a more effective
injection strategy would be varying the injection area seasonally. The model describes aerosol
size distribution by 10 size sections and calculates the microphysical processes of
nucleation, condensation, coagulation and hydration. Thus the formation from gaseous
SO2 to sulfate particles, particle growth and also how sulfate is distributed in the
atmosphere after different injection strategies are described in the model. We will
also use coupled climate-ocean model MPI-ESM to study climate effects from
these scenarios by using aerosol effective radius and aod fields from simulations by
ECHAM6.1-HAM2.2-SALSA.
We carried out simulations, where 5 Tg of sulfur is injected as SO2 to the stratosphere at
height of 20-22 km in an area ranging over a 20 degree wide latitude band. Preliminary
results show that global radiative forcing is slightly larger if the injection area is changed
depending on the season of the year compared to a case where sulfur is injected to the area
between 10 N and 10 S. Oxidation time from SO2 to sulfate particles and the time that new
particles needs to grow particles large enough has major role to how effective temporally
depended injection scenarios are. |
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