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York University
GEOG 3700
Scott Menary

VOLCANIC AEROSOLS AND THE RESULTING CLIMATE CHANGE GEOG 3700 WINTER 2013 A natural hazard is a threat of a naturally occurring event that can have a negative impact on the environment or people. Many natural hazards are interrelated such as; earthquakes can cause tsunamis, or droughts that can lead to famine. One such phenomena of nature, Volcanoes, have existed since the beginning of times. They’ve created the earth we live in and the climate we’re exposed to. It has taken a extensive amounts of time and study to recognize the important role of volcanic eruptions in climate change (Peter L. Ward, 2009). Volcanoes erupt when there is a sudden or continuing release of energy caused by the magma near the earth’s surface. Their duration of eruptions can range from a few minutes to thousands of years (Grainger & Highwood, 2003). Volcanic eruptions inject several different types of particles and gases into the atmosphere (Alan Robock, 2000). In this paper I will be discussing the chemical properties of such gases and particles, and their disturbance in the atmosphere that can lead to a climate change. I will also go into details about how this disturbance can affect the surface of the earth and it’s environment. To prove my point further I will put forward examples of ancient and recent volcanoes that have influenced the climate of the world we live in now. Additionally, I will explore the idea of using volcanic climate changes to stop global warming. When the near surface gases rising in the magma become insoluble, they explode. The greater the gas content of magma, the more explosive the eruption will be. Volcanic eruptions that has a Volcanic Explosivity Index (VEI) greater than 4, are more likely to seep into the atmosphere. There are many gases that are erupted from a volcano such as water vapor (H O2, Nitrogen (N ), 2arbon dioxide (CO) (Grainger & Highwood, 2003), but the most chemically active gas that is erupted in significant amounts is Sulphur dioxide (SO )2(ALAN ROBOCK, 2000). Our atmosphere is a thin blanket of very delicately balanced gases, aerosols and small particles that maintains an average temperature around the globe. It prevents the earth from plummeting into an ice age. The atmosphere reflects, refracts, scatters or absorbs UV rays from the sun. Very small changes in the atmospheric chemistry can lead to drastic changes in the global climate (Peter L. Ward. 2009). The atmosphere goes through a constant chemical process called Oxidation. It is a way for the atmosphere to cleans itself of impurities by oxidizing them to form larger molecules that can fall down to the earth as rain. When volcanoes erupt large amounts of Sulphur in to the stratosphere, they can be oxidized into other Sulphuric compounds such as Sulphur dioxide that attach themselves to aerosol particles (Peter L. Ward, 2009). Depending on their size, these Sulphur dioxide aerosol particles can stay in the stratosphere from a few days up to several years before they can fall into the troposphere and are washed down to the surface of the earth in form of acid rain (Yang & Schlesinger, 2002). Volcanic aerosols can influence the climate a great deal. Since the sulfate aerosol particles are about the same size as visible light, with a radius of 0.5 μm, they act on the incoming sunlight by reflecting it back to space and reducing the amount of solar energy that reaches the Earth’s surface (Alan Robock, 2000). This effect is known as ‘radiative forcing’ (Eliseev & Mokhov, 2008) that results in a net cooling at the surface (Alan Robock, 2000) and can decrease direct solar beam by 20% to 30% for many months over a particular area following a great volcanic eruption (B. K. Mukherjee et al., 1987). The effect of aerosols on solar radiation is so strong that it can be easily seen by the naked eye, it can make a normally blue sky look milky white or produce spectacular red sunsets. One such famous example of a red sunset is in 1893 Edvard Munch’s painting, ‘The Scream’, it shows a red volcanic sunset over the Oslo harbor produced by the 1892 Awu eruption (Alan Robock, 2000). A vivid red sunset in Hong Kong, a year after Mount Pinatubo eruption in Philippines in 1991 The volcanic aerosol veil causes the global annual average surface temperature to drop (Shindell & Schmidt, 2003). This can lead to a decrease in evaporation and a decline in the precipitation (A. V. Eliseev, 2008), resulting in a disturbed hydrologic cycle (Joseph & Zeng, 2011) that may be followed by a drought and famine (Peter L. Ward, 2009). Volcanic aerosols not only cause radiation instability in the stratosphere but also damage the ozone layer (Alan Robock, 2000). The ozone layer is in the stratosphere, 15 to 50 kilometers above Earth, works as a shield against ultraviolet radiation. Sulphur rich aerosols from volcanic eruptions chemically react with other gases in the ozone layer, breaking it down to molecules of oxygen (Greg Peterson, 2003). This weakens the ozone layer, causing it to let more UV light through rather than absorbing it (Alan Robock, 2000). A damaged ozone layer can be incredibly harmful to humans causing diseases such as skin cancer, eye cataracts etc. (Greg Peterson, 2003), as well as potentially damaging to marine ecosystems, agricultural production, forest productivity, and biogeochemical cycles (William C.G. Burns, 2012) In addition to the release of gases, an explosive volcanic eruption also blasts molten and solid rock fragments into the air. Of these, the largest fragments fall back to ground but ash, fragments with diameter of less than 2 mm, continue to rise in the air forming an eruption column capable of growing as high as 20 km above the volcano. They are also capable of expanding in diameters from 20 km to 50 km within ten minutes. After this initial expansion the ash cloud follows the local wind patterns, thus separating itself from the volcanic source. At equatorial latitudes these ash and dust clouds can circle the globe in approximately 22 days, where as the travel time for them at higher latitudes is approximately 7 days (Grainger & Highwood, 2003). They form a veil of dust in the sky temporarily blocking out the sun and cause the temperatures to drop for a few hours or days (Gerald J. Dittberner, 1978). These ash and dust particles from volcanic eruptions fall to the surface of the earth in the form of acid rain (Yang & Schlesinger, 2002), contaminating the water that can be absorbed and ingested by marine or land plants and animals (Gael Le Roux et al., 2013). Cronin, in his 1971 study, suggests that the high altitude eruptions may affect the atmosphere layer more than the low latitude eruptions, this is mainly due to the lower altitude of the stratosphere at high latitudes (Bruce M. Jakosky, 1986). Picture taken on March 27 1992, less than 1 year after the Pinatubo eruption, taken at Mauna Loa Observatory. The milky appearance of the sky due to volcanic ash and dust clouds is clearly visible. In 1970, a scientist named Lamb created a Dust Veil Index, DVI, specifically designed for analyzing the effects of volcanoes on surface weather and the atmosphere along with its global wind circulation. To create the DVI, Lamb used the data from historical reports of eruptions and their optical observations, temperature information, radiation measurements, which were available only after 1883, and their estimates of the volume of ejected particles (Alan Robock, 1981). So now when an intensity of a volcanic eruption is explained using a Volcanic Explosivity Index, VEI model, the DVI is used as well to further describe the dust and ash cover in the sky due to the eruption. Ash and dust ejecting from the eruption of Mount St.Helens, Washington on  May 18, 1980 Volcanic eruptions have been shaping the world since the beginning of times. Historical volcanic eruptions have contributed to climatic changes in various areas leading to distress and chaos amongst humans and animals. One such event was in 1450 BC in Thera, also known as Santorini. The consecutive eruptions of Thera beginning in 1628 and ending in a last major eruption in 1450 BC caused a catastrophic event unparalleled by any other eruption in history. It destroyed the entire Minoan Fleet at Crete. There was a massive loss of life from ejected gases, volcanic ash, volcanic bombs, and lava flows (P. E. LaMoreaux, 1995). The collapse of a large mountain into a caldera, about 15 km in diameter caused a tsunami and further wrecked havoc. The eruption easily affected world climate, spreading dust in the stratosphere over much of the world. The volcanic ash spread upward as a pillar of fire and clouds into the stratosphere, obstructing sunlight for many days and spreading darkness over the western Mediterranean and in certain areas of Asia and Africa. The blockage of sunlight, lead to a change in the composition of ice in the Polar Regions. It also reduced the growth of the bristlecone pine in California and bog oaks in England, Ireland and Germany. Deadly gases emitted by volcanoes probably caused boils on animals and humans, and even deaths in some cases (P. E. LaMoreaux, 1995). Another past event that clearly demonstrates the impact of an altered climate on people and the environment due to a volcanic eruption is the mysterious eruption of 1259. No one as yet can figure out where exactly that eruption might have occurred but the samples of debris retrieved in recent times from dated ice cores in Green Land, Canadian Arctic and Antarctica suggest that the event must have been a tropical eruption. The samples indicate that there was a total production 300 to 600 megatons of Sulphuric acid that fell out of stratosphere as rain onto the north and south polar ice caps. You can say that it was one of the greatest volcanic eruptions of the past two millenniums (Richard B. Stothers, 2000). Such a large eruption obviously had easy observable meteorological effects. Although there were no instrumental measurements made at that time, due to lack of technology, careful remarks made by observers reporting in different areas and time zones can serve as an alternative for such information (Richard B. Stothers, 2000). There were reports of constant dry fog present in the atmosphere across Europe. A convincing evidence of this large aerosol veil comes from the different accounts of two lunar eclipses during the year and a later year. When the earth’s stratosphere contains plenty of volcanic aerosols, the incident sunlight cannot be refracted and scattered, thus during an eclipse the moon can appear completely dark. This seemed to be the case on 18 May 1258 in northern and southern hemispheres, hence confirming that aerosols obscured both the hemispheres (Richard B. Stothers, 2000). Whereas, in the year later the moon seemed red, just the way it’s supposed to look. The obstruction of sunlight also changed the weather patterns for the following two years. France experienced severe cold and snow during April whereas western Germany and northern Italy experienced very rainy and chilly summers with a lot of hail. On the other hand England had a brief hot summer but was followed by a disastrous autumn of heavy rains beginning as early as August, destroying all the crops. Europe subsequently suffered a very harsh winter, the winter of 1260-1261 struck Iceland so severely that people were forced to slaughter their livestock. In Alsace, east of France, a river froze (Richard B. Stothers, 2000). The heavy summer and autumn rains ruined crops throughout England, western Germany, France and northern Italy that lead to a severe famine. England was especially disturbed. Thousands of villagers in the countryside flocked into London because of famine, where not many of them survived and mostly died of hunger. The famine raised the price of food throughout England, leading to social and political unrest (Richard B. Stothers, 2000). Epidemic diseases of various kinds often break out in times of prolonged wet weather and famine. Outbreaks of murrain in sheep and other diseases were reported within the human population, they especially spread quickly amongst people living in the cities. It was impossible to diagnose such diseases and so it resulted in high mortality rate (Richard B. Stothers, 2000) In recent times the volcanic eruption of Mount Pinatubo, in June 1991 on the Island of Luzon, Philippines, is considered to be the best-observed major volcanic eruption on record. It provided scientists and geologists all around the world with a rare opportunity to better understand it’s natural impacts on the climate and environment(Yang & Schlesinger, 2002). Mount Pinatubo had been inactive for 635 years but when it erupted, it injected about 10 million tons of Sulphur into the stratosphere (William C.G. Burns, 20
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