Environmental Engineering Reference
In-Depth Information
small negative radiative forcing by increasing stratospheric aerosol concentrations
estimated a global surface temperature response of at least
0.07
C.
The June 2011 eruption of Nabro (VEI 3
-
4) injected about 1.3 Tg of SO
2
into
the upper troposphere (9
-
14 km), where seemingly the climate impacts would have
been more muted than for an injection into the stratosphere. Bourassa
et al
.(
2012
),
however, suggested that deep convection and interaction with the Asian summer
monsoon lofted Nabro
-
'
sSO
2
into the stratosphere, hence prolonging the aerosol
radiative forcing.
These recent
findings highlight the necessity for detailed observations of
small-magnitude eruptions (VEI of 3 to 4) to allow for a better understanding
of present-day climate change. Such
findings might also change our view of what
eruption magnitude and mass of SO
2
released into the atmosphere we need
to consider relevant for climate change on decadal timescales, and also provide
information of relevance for stratospheric geoengineering proposals with sulfuric
acid aerosol.
13.6 Summary
Observations have con
rmed that volcanic eruptions can have numerous impacts
on our environment, mainly via the sulfuric acid aerosol direct effects, resulting
in a reduction of surface temperatures, and changes in water-vapour concen-
trations and stratospheric heating rates. The latter results in pole-to-equator
gradients that induce an indirect advective effect on surface temperatures referred
to as winter warming. Transient and asymmetric volcanic aerosol forcings
have been shown to weaken the Asian and African summer monsoons and to
cause precipitation de
cits in the Sahel. There is no observational evidence
that eruptions force certain circulation modes such as El Niño but the issue
remains a matter of debate. There is increasing evidence for an aerosol indirect
effect on liquid water clouds induced by volcanic sulfuric acid particles but
whether, and to what extent, explosive volcanic eruptions affect ice clouds
remains debated.
Future eruptions will present an opportunity to test our current understan-
ding and
fill gaps in our ability to monitor volcanic clouds and to obtain
detailed measurements. Climate models and observations have greatly
enhanced our understanding of the climatic impacts of eruptions. However,
we have not yet obtained suf
cient observations of, for example, the temporal
evolution of the aerosol size distribu ioninboththes ratosphereand
troposphere for different eruption sizes, which will be an acid test for climate
and aerosol models.
