【文章內容簡介】 erosols fall out of the stratosphereNucleate clouds in troposphere increase albedoRecent major volcanic eruptions produced significant cooling anomalies () in the troposphere for periods of 1 to 3 yearsMagnitude of volcanic effects masked by natural variations (. El Nino)2. Stratospheric warmingAcid aerosols absorb ining solar radiation, heating the tropical stratosphere, . Mt. Agung (1963), El Chichon (1982), and Pinatubo (1991) all caused warming of the lower stratosphere of ~2oC3. Enhanced destruction of stratospheric ozoneEl Chichon PinatuboLower stratospheric temperature (global mean)Localised heating in the stratosphere can influence how far volcanic aerosol veils spread, by influencing stratospheric wind patterns+3oC3oC0oCStratospheric warmingVolcanoes do not inject chlorine into the stratosphere.Aerosols improve efficiency with which CFC`s destroy ozone,by activating anthropogenic bromine and chlorine, indirectly leading to enhanced destruction of stratospheric ozoneRelatively short lived aerosols last only 23 years in the stratosphereReduction in ozone following the June 1991 eruption of Pinatubo Enhanced destruction of stratospheric ozoneSeveral factors bine to determine whether a volcanic eruption has thepotential to influence the global atmosphere1. Eruption styleEnergetic enough to inject aerosols into the stratosphereLarger eruptions do not necessarily have greater effects Increased SO2 results in larger particles, not moreFall from the stratosphere faster, smaller optical depth per unit massvolcanic effects on the atmosphere may be selflimiting2. Magma chemistryImportance of acid aerosols means that large eruptions of sulphurpoormagma less significant than sulfurrich magmas. Mt St Helens sulfur poor negligible global effectsAtmospheric “effectiveness”3. LatitudeProximity to the stratosphere: smaller eruptions at high latitude can inject as much SO2 into the stratosphere as larger eruptions at lower latitudesStratospheric dispersal: Aerosols from tropical eruptions have the potential to spread around the globe ( Pinatubo). Atmospheric influence of eruption outside the tropics is contained within the middle and polar latitudes of the hemisphere of originAtmospheric“effectiveness”Atmospheric processes are plex !Understanding how an atmospheric perturbation influences climate and weather is still problematic, even for largest eruptionsHowever, understanding how volcanoes effect climate necessary to isolate other forcing processesComparison of chronology of known eruptions and climatic data shed light on the ways climate responds to large volcanic eruptions Volcanic eruptions and climate1.ThewrittenrecordCompareeruptionchronologieswithwrittenrecordsofunusualclimaticevents.BenjaminFranklin(1784)``During several months of the summer of the year 1783, when the effects of the Sun`s rays to heat the Earth should have been the greatest, there existed a constant fog over all of Europe, and great parts of North America.`` = 1783Lakifissureeruption,IcelandDisadvantages:recordonlyacoupleofthousandyears,humansunreliable,eruptionchronologiesinplete,geographicalbias(.nohumans=norecord)Makingtheconnection2. Ice coresAcid aerosols fall on ice fieldsAccumulation of ice preserves information acidity profileClimatically significant eruptions can be identified with great precisionAdvantages: objective, precise, records `climatically significant` eruptions onlyDisadvantages: Which eruptions and why? Only those with high sulfur contents. Geographical bias. HALF of known large eruptions not recorded in Greenland ice coresMaking the connection3. Tree ringsProxy witnesses to eruptionsTemperate trees r