Long volcanoes are important source of atmospheric gases, aerosols,

Long
before now, the influencing  factors  of volcanic eruption is known to be capable
of causing changes  in weather and
climate. For over  2000 years ago, Plutarch and others ( Forsyth 1988) pointed out
that the eruption of Mount Etna in 44 B.C. dimmed the Sun and suggested that
the cooling which resulted from the eruption affected
farm produce and led to hunger in Rome and Egypt. The
materials ejected  from eruptions of volcanoes are important source of atmospheric gases, aerosols, and ash (Sparks, Bursik, Gilbert, Glaze, Sigurdsson and Woods, 1997
Schmincke, 2004 and Rose and Durant, 2009). “Volcanic
gas emissions from the magma

 consist primarily of H2O, followed by CO2, SO2, H2S, HCl, HF, and other
compounds” (Symonds, Rose, 
Bluth, and  Gerlach, 1994).  Volcanic
ash is formed by fragmentation processes of the magma and the surrounding  rock material within volcanic vents (Sparks, Bursik, Gilbert, Glaze, Sigurdsson and
Woods, 1997 and Zimanowsk, Wohletz, Dellino and Buttner, 2003).

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According to Ayris, Lee, Wilson, Kueppers, Dingwell and Delmelle, 2013, Hoshyaripour, 2013 and Aiuppa,
Franco, von Glasow et al.,2007, Secondary
products like volcanic sulphate aerosols result from high- and low-temperature
chemical transformation processes in the conduit, the volcanic plume, and cloud.

 

 

Global
cooling as a result of volcanic eruption is explained as follows by (Robock,
2000). According to him, sulphate aerosol particles which are emitted from
volcanoe scatter solar radiation as they have a radius of around 0.5?m which is
approximately the same size as the wavelength of visible light. Some of the
light is backscattered, reflecting sunlight back to space and increasing the
net planetary albedo. Much of the solar radiation is also forward scattered
increasing downward diffuse radiation partly offsetting the large reduction in
the direct solar beam. The forward scattering effect can be seen by the naked
eye making the normally blue sky a milky white colour. The reflection of the
setting sun from the bottom of the dust veil produces the typical volcanic
sunset. “The variations in atmospheric warming and cooling results in changes
in tropospheric and stratospheric circulation (Robock, 2000).

At the top of the aerosol cloud the
atmosphere is heated by absorption of near infra-red solar radiation. In the
lower stratosphere the atmosphere is heated by absorption of upward long wave
radiation from the troposphere and the surface. There is also increased Infra
Red (IR) cooling due to enhanced emissivity caused by the presence of the
aerosols ( Robock 2000).

 

Fig 1. An Aerosol
cloud

Source:
Google images.

 

 

The
magnitude of volcanic eruption determine its influence on  the temperature in winter and in summer as
seen in the following  scenarios.  According
to (Fischer, Luterbacher , Zorita ,  Tett
, Casty,  and Wanner, 2007),” there exist a study which
elucidated the climatic response in Europe following
15 major tropical eruptions over the last half millennium  from the 
eruptions  and confirmed the clear
pattern of summer temperature cooling during the first and second post-eruption
years”.  Of these, the strongest
signal of cooling is found during the year after the eruption (Bradley 1988;Robock 2000).  One country known to have experienced summer
temperature cooling following the eruptions is Finland. Furthermore,
(Helama, Lindholm, Merila¨inen , Timonen 
and 
Eronen , 2005; Salzer and  Hughes
2007;Helama, La¨a¨nelaid, Ti eta¨va¨inen , Macias Fauria, Kukkonen , Holopainen
, Nielsen and  Valovirta I. 2010) opined
that the distant effects of explosive erruptions has
been may have caused the tree rings and their summer temperature reconstructions to exhibited volcanic
signature eruptions in the same area.

Moreso, identical eveidences have been observed in regions
beside Northern  Europe (Gervais
and  MacDonald 2001).

A
mid- and late-Holocene chronology of climatic downturns. (a) Tree-ring
sensitivity (i.e., sudden change in growth conditions). Please note that only
negative departures are given, the values therefore indicating growth
reductions. (b) Reconstructed summer (July) temperature variability (black
line) with the green and blue areas indicating the 95% and 99% confidence
intervals of the reconstruction. The study period was 5500 B.C. through 2005
A.D. The years discussed in the text are shown as tree-ring dated calendar
years B.C. and A.D.

 

 

 

 

 

Source:(Helama, Holopainen, 
Macias-Fauria,  Timonen and  Mielikäinen 2013).

 

“A look at the plot of the
tree-ring variability reveals a characteristic paucity of anomalously poor
growth in terms of dendrochronological sensitivity (Fig.
1a).
The most negative years of growth are not clustered within a limited period but
are spread over several millennia. Considering the late-Holocene (here, 1–2005
A.D.), the tree-ring record shows extreme drops in growth as having occurred in
1601 A.D. and 536 A.D. These years were reconstructed as having been exceptionally
cool (Fig.
1b).
For both of these years, the summer temperatures were reconstructed to have
been cooler than 10°C on average, which is more than three standard deviations
from the reconstructed mean of 13°C. The year 536 A.D. was followed by another
year of reduced growth, in 542 A.D., during which the temperatures are
reconstructed to have been nearly as cool as six years before” ( Helama,  Holopainen,
Macias-Fauria, Timonen and Mielikäinen 2013).

 

 

 

 

 

Historically, there has
been  significant effects of volcanic
eruption in winter, although this modest on scale. Examples are as follows; The
1991 explosion of Mount Pinatubo, a stratovolcano in the Philippines, cooled
global temperatures for about 2–3 years” (Brohan ,  Kennedy, Haris, Tett, and  Jones, 2006). ” In 1883, the explosion of
Krakatoa (Krakatau) created volcanic winter-like conditions The four years
following the explosion were unusually cold, and the winter of 1887-1888
included powerful blizzards” (Hansen, 1997). “Record snowfalls were recorded
worldwide”.

 

 

Source:
(Google image)

 

 The 1815 eruption of Mount Tambora, a
stratovolcano in Indonesia, occasioned mid-summer frosts in New York State and
June snowfalls in New England and Newfoundland and Labrador in what came to be
known as the “Year Without a Summer” of 1816. A paper written by
Benjamin Franklin in 1783 ( Funkhouser, 2016), blamed the unusually cool summer
of 1783 on volcanic dust coming from Iceland, where the eruption of  Laki volcano had released enormous amounts of
sulfur dioxide, resulting in the death of much of the island’s livestock and a
catastrophic famine which killed a quarter of the Icelandic population.
Northern hemisphere temperatures dropped by about 1 °C in the year following
the Laki eruption. However Franklin’s proposal has been questioned” (Davis,
2008). In 1600, the Huaynaputina in Peru erupted. Tree ring studies show that
1601 was cold. The supervolcano Caldera Lake Toba famine in 1601-1603. From
1600 to 1602, Switzerland, Latvia and Estonia had exceptionally cold winters.
The wine harvest was late in 1601 in France, and in Peru and Germany, wine
production collapsed. Peach trees bloomed late in China, and Lake Suwa in Japan
froze early.  (Cantor and  Norman. L, 2001 ). In 1452 or 1453, a
cataclysmic eruption of the submarine volcano Kuwae caused worldwide
disruptions. The Great Famine of 1315–1317 in Europe may have been precipitated
by a volcanic event,( Nairn, Shane, Cole, Leonard, Self  and Pearson, 2004  ) perhaps that of Mount Tarawera, New
Zealand, lasting about five years(Hodgson and 
Nairn, 2005).

 

 

 

Question
2a.2

 

 answer

 

The
sustenance or diminishing effects of volcanic eruption on global cooling is
determined by the frequency and magnitude of eruptions.”Volcanic eruptions are a major driver of
climate variability on a variety of timescales. Large tropical eruptions are capable of injecting sulphur dioxide into the stratosphere
where it forms sulphate aerosol that may persist with an e-folding time of
around 1 year, spreading globally with a resultant negative radiative forcing
(Rampino and Self 1982; Robock 2000). After the eruption of Mount Pinatubo
in 1991, an estimated 20 Mt of SO2  was introduced into the stratosphere (Robock 2000) leading to a global cooling of around
0.3 °C (Lehner et al. 2016) and a reduction in global
precipitation (Trenberth and Dai 2007). Repeated eruptions have shaped
climate evolution, likely causing periods of cooling, such as during the
15–19th Centuries (Briffa et al. 1998; Schurer et al. 2014; Miller et al. 2012; Stoffel
et al. 2015). More recently, a series of smaller
eruptions may have offset a small portion of anthropogenic warming (Solomon
et al. 2011; Vernier et al. 2011; Santer et al. 2014). Understanding the influence of
volcanic eruptions therefore contributes to understanding climate variability
(Timmreck 2012; Zanchettin 2017).

The climatic response to volcanic
aerosols is complex. The negative radiative forcing
induces several responses in the Earth system (Timmreck 2012; Zanchettin 2017), including expansion of sea-ice
(Miller et al. 2012), changes in atmospheric (Robock and Mao, 1992) and ocean circulation (Ding
et al. 2014), and perturbations to modes of
variability (Lehner et al. 2016; Maher et al. 2015). These responses are partly dependent
on the climate state prior to an eruption, as well as the location of the
volcano and the season of eruption (Stevenson et al. 2017). While much attention has focused on
short-term variability, less is known about the influence of longer-term
changes in the background climate (Zanchettin et al. 2013). The future response to an eruption
may be different because of changes in the climate system caused by
anthropogenic warming. Aubry et al. (2016) have recently shown that
warming-induced changes in the vertical structure of atmosphere (particularly
changes in the tropopause height) would impact on the rise of volcanic plumes, but the impact of future changes on the
radiative forcing and response to a volcanic eruption has not been quantified.

Here we analyse an ensemble of
comprehensive Earth System model simulations of a large volcanic eruption to
evaluate the climate system response to a large
volcanic eruption in a future climate state. We performed an ensemble of
simulations with the HadGEM2-ES Earth System model (HadGEM2 Development Team 2011; Collins et al. 2011) of a Tambora 1815 -like eruption in
pre-industrial (Kandlbauer et al. 2013) and Representative Concentration
Pathway 6.0 (RCP 6.0) conditions for the years AD1860 and AD2045, respectively.
Tambora was chosen because it provides a very strong forcing
which can be more easily separated from simulated internal variability.ss