The first thing that occurred to me when I heard about the Sarychev eruption was whether it was going to be large enough to inject significant quantities of sulphate aerosol into the stratosphere. Apparently, it is.
When sulfur dioxide reacts with water vapor, it creates sulfate ions (the precursors to sulfuric acid), which are very reflective. Powerful volcanic eruptions can inject sulfate aerosols into the stratosphere, beyond the reach of cleansing rainfall. At these altitudes, the sulfates can linger for months or years, cooling the climate by reflecting incoming sunlight. (The effect is stronger when the eruptions occur at tropical latitudes.) Carn says the persistence of such high concentrations of sulfur dioxide in the OMI data throughout the week indicates that the plume from Sarychev Peak reached high altitudes. Data from other satellites (such as CALIPSO) suggest that the volcanic plume reached altitudes of 10–15 kilometers, and perhaps as high as 21 kilometers.
In 1991, the eruption of Mount Pinatubo in the Philippines injected enough sulphate into the atmosphere to cause a 0.5° C drop in global temperature. This was caused by about 20 million tonnes of SO2. We are nowhere close to these kind of emission levels. After all, Pinatubo was one of the two biggest volcanic events of the century.
Injecting sulphate particles into the stratosphere has been proposed for a while now, I first wrote about it in 2006 when a prominent atmospheric chemist, Paul Crutzen wrote an article proposing this. The science behind this proposal is basic, sulphate aerosols of the size that would be formed from the oxidation of SO2 are the right size to scatter and reflect solar radiation back into space (my Masters thesis did a first order estimate of this effect from Indian emissions!). If injected directly into the stratosphere, they can stay there for a long time and will not deposit to the the Earth’s surface as acid rain. The issue is managing all the crazy regional variations in climate that would result, and the attendant complications in assigning blame, etc. It would also not help the oceans, which would acidify to hell with all the CO2.
Anyway, so much for that, the volcano is causing all kinds of havoc with Pacific travel and making for all kinds of cool pictures, which are about the most interesting thing happening at this point in time. We shall see how the sulphate situation plays out in the days to come when the dust settles.