Correlations between eruption magnitude, SO2 yield, and surface cooling
Sulphurous gases from explosive eruptions have the potential to form stratospheric aerosols and so produce surface cooling on a hemispheric to global scale. However, testing for any correlation between SO2 yield and surface cooling is hampered by instrumental SO2 and temperature measurements being available for time periods that include only a few large eruptions. To overcome this, published dendroclimatological data, satellite (Total Ozone Mapping Spectrometer) data on SO2 emissions, stratospheric optical depth data, and volcanological observations are integrated, revealing several relevant new correlations. First, the efficient conversion of SO2 into stratospheric aerosols occurs when the ratio of plume height to tropopause height is greater than about 1.5. Second, the mass of emitted SO2 correlates well with the mass of erupted magma. The SO2 yield is 0.1 to 1% by mass of magma, irrespective of composition. The best-fit power law (r2=0.67) is mass of SO2 in Mt=1.77(mass of magma in Gt)0-64. Third, of the eruption clouds that are believed to have entered the stratosphere in the period 1400-1994, those with masses <5 Gt magma (DRE <2 km3) appear to have had insignificant effects on Northern Hemisphere summer temperature. The scattered data for eruptions of >10 Gt (>4 km3) magma suggest a mean cooling effect of about 0.35 °C.