Volcaniceruption has long been known to have an influencing factors 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 Etnain 44 B.C. dimmed the Sun and suggested that the coolingwhich resulted from the eruption affected crop production and led to famine inRome and Egypt. The materials emitted from volcanic eruptions are important source of atmospheric gases, aerosols, and ash (Sparks, Bursik, Gilbert, Glaze, Sigurdsson and Woods, 1997Schmincke, 2004 and Rose and Durant, 2009).
“Volcanicgas emissions from the magma consist primarily of H2O, followed by CO2, SO2, H2S, HCl, HF, and othercompounds” (Symonds, Rose, Bluth, and Gerlach, 1994). Volcanicash 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). According to Ayris, Lee, Wilson, Kueppers, Dingwell and Delmelle, 2013, Hoshyaripour, 2013 and Aiuppa,Franco, von Glasow et al.,2007, Secondaryproducts like volcanic sulphate aerosols result from high- and low-temperaturechemical transformation processes in the conduit, the volcanic plume, and cloud.
Globalcooling as a result of volcanic eruption is explained as follows by (Robock,2000). According to him, sulphate aerosol particles which are emitted fromvolcanoe scatter solar radiation as they have a radius of around 0.5?m which isapproximately the same size as the wavelength of visible light. Some of thelight is backscattered, reflecting sunlight back to space and increasing thenet planetary albedo. Much of the solar radiation is also forward scatteredincreasing downward diffuse radiation partly offsetting the large reduction inthe direct solar beam. The forward scattering effect can be seen by the nakedeye making the normally blue sky a milky white colour.
The reflection of thesetting sun from the bottom of the dust veil produces the typical volcanicsunset. “The variations in atmospheric warming and cooling results in changesin tropospheric and stratospheric circulation (Robock, 2000). At the top of the aerosol cloud theatmosphere is heated by absorption of near infra-red solar radiation.
In thelower stratosphere the atmosphere is heated by absorption of upward long waveradiation from the troposphere and the surface. There is also increased InfraRed (IR) cooling due to enhanced emissivity caused by the presence of theaerosols ( Robock 2000). Fig 1. An AerosolcloudSource:Google image Themagnitude of volcanic eruption determine its influence on the temperature in winter and in summer asseen in the following scenarios. Accordingto (Fischer, Luterbacher , Zorita , Tett, Casty, and Wanner, 2007),” there exist a study whichelucidated the climatic response in Europe following 15 major tropicaleruptions over the last half millennium from the eruptions and confirmed the clear pattern of summertemperature cooling during the first and second post-eruptionyears”. Of these, the strongest signal of cooling isfound during the year after the eruption (Bradley1988;Robock 2000). One country known to have experienced summer temperature coolingfollowing the eruptions is Finland. Furthermore, (Helama, Lindholm, Merila¨inen , Timonen and Eronen , 2005; Salzer and Hughes2007;Helama, La¨a¨nelaid, Ti eta¨va¨inen , Macias Fauria, Kukkonen , Holopainen, Nielsen and Valovirta I.
2010) opinedthat the distant effects of explosive erruptions hasbeen may have caused the tree rings and their summer temperature reconstructions to exhibitedvolcanic signature eruptions in the same area.Moreso, identical eveidences have been observed in regionsbeside Northern Europe (Gervaisand MacDonald 2001).Amid- and late-Holocene chronology of climatic downturns.
(a) Tree-ringsensitivity (i.e., sudden change in growth conditions). Please note that onlynegative departures are given, the values therefore indicating growthreductions.
(b) Reconstructed summer (July) temperature variability (blackline) with the green and blue areas indicating the 95% and 99% confidenceintervals of the reconstruction. The study period was 5500 B.C. through 2005A.D. The years discussed in the text are shown as tree-ring dated calendaryears B.C.