In The Past
Volcanic eruptions emit gases and microscopic particles which in the past have led to changes in global climate patterns. After any volcanic eruption, it is expected that a period of global cooling occurs, followed by global warming depending on the reactions that can occur in the atmosphere. An example of a Plinian eruption is that of Mount Pinatubo, on the Island of Luzon, which recently erupted on the 15th of June, 1991. The eruption measured 6 for the Volcanic Explosivity Index (VEI), whereby 1.1x1010 tonnes of magma was released and 2.2x107 tonnes of sulphur dioxide was emitted [1]. A large quantity of dust and aerosols was released into the stratosphere, from which a haze of sulphuric acid vapour was created as a result of the sulphur dioxide reacting with available oxygen. This haze layer decreased the transmission of solar radiation by 12 %, as shown in figure 6. The resulting effects included a decrease in the mean surface temperature of 0.5-0.6 degrees Celsius in the Northern Hemisphere, and a decrease in global temperatures of 0.4 degrees Celsius over a one year period after the eruption [2].The gas cloud however remained in the atmosphere for approximately 3 years, resulting in a decrease of global average temperatures of 0.35 degrees Celsius till 1993, as shown in figure 7 below.
Figure 6: Transmission of Solar Radiation observed at the Mauna Loa Observatory
1: http://en.wikipedia.org/wiki/Mount_Pinatubo
2: http://geography.about.com/od/globalproblemsandissues/a/pinatubo.htm
Figure 6: http://en.wikipedia.org/wiki/File:Mauna_Loa_atmospheric_transmission.png
2: http://geography.about.com/od/globalproblemsandissues/a/pinatubo.htm
Figure 6: http://en.wikipedia.org/wiki/File:Mauna_Loa_atmospheric_transmission.png