|Act III, Scene i is all about Rising Action. Another parabolic step up. Let's take a big step:|
Volcanic eruptions contribute to global cooling across TWO mechanisms.
The first, and most obvious, is simply by blocking sunlight through large ash cloud production. This though, requires a very large eruption of "biblical' proportions that clouds the sky globally. The effect from this factor is immediate.
The other mechanism is more "stealthy".
"Pure sulfates and nitrates reflect nearly all radiation they encounter, cooling the atmosphere."
The term sulfate aerosols is used for a suspension of fine solid particles of a sulfate or tiny droplets of a solution of a sulfate or of sulfuric acid (hydrogen sulfate). They are produced by chemical reactions in the atmosphere from gaseous precursors (with the exception of sea salt sulfate and gypsum dust particles). The two main sulfuric acid precursors are sulfur dioxide (SO2) from anthropogenic sources and volcanoes, and dimethyl sulfide (DMS) from biogenic sources, especially marine plankton. These aerosols can cause a cooling effect on earth.
The SO2 spreading across the Pacific Ocean invariably will convert to sulfate aerosol rather quickly and/or settle out of the air. When it's injected higher up into the stratosphere this is a cooling agent among all the other cooling effects being induced by cosmic ray cloud nucleation and volcanic ash cloud blockage of sunlight and increased albedo on Earth's surface from increased range of snowfall, longer lasting snow cover and glacier/ice cap growth.
There's been a lot of "excitement" over the SO2 emitted by Kilauea. Some of it made reference to SO2 actually reaching Guam and setting off alarm about air quality becoming harmful to inhabitants there.
I have to say I'm dubious about that claim. For SO2 to get that far it would have to get up into the stratosphere. Whether it does or doesn't reach that altitude it would have to somehow avoid conversion into H2SO4. Then, it would have to descend...in concentration...on Guam. If there's SO2 in the air at concentrations enough to be a health concern...4000 miles away, it's not coming from Kilauea.
Of the SO2 that remains in the Troposphere...where people exist..."most sulphur compounds have a short residence time in the troposphere, of the order of a few days. Sulphur usually cycles from low-oxidation gas to sulphate particles and back to the surface in rain in less than a week."
Near the equator, the stratosphere starts at 18 km (59,000 ft; 11 mi).
But a quantity of SO2 from even minor eruptions can find its way that high:
"Overall, these minor eruptions are seen to have a clear impact on the tropical stratospheric aerosol load. As an example, the amount of SO2 injected in the stratosphere by the Soufriere Hills was estimated to be 0.1 TgS (109 g of sulfur) by the Ozone Monitoring Instrument (OMI) onboard AURA [Prata et al., 2007]. Assuming that SO2 is entirely transformed into gaseous H2SO4 and further condensed into a 75%-25% H2SO4-H2O solution, the total aerosol mass added by this single volcanic event would be 0.25 TgS. This is ten times more than the 0.01–0.02 Tg S/year required to explain the average aerosol increase of 4–7%/year after 2002 estimated by Hoffman et al. . Moreover, injections from the other smaller volcanic injections events in the last decade in the tropics are of a similar magnitude."
At higher latitudes though, the stratosphere begins at a lower height.
"at mid latitudes, it starts at 10–13 km (33,000–43,000 ft; 6.2–8.1 mi)
This is where Sakurajima resides which VERY regularly sends plumes over 30,000 feet as mentioned in other places on this thread.
Other volcanoes such as Dukono, Ambae, Agung, etc, etc, etc are contributing regularly as well so there is already volcanic cooling of the Earth underway.
WHAT'S REALLY INTERESTING ABOUT VOLCANIC EMISSION INTO THE ATMOSPHERE IS THIS TIDBIT:
(also from the Ferraro paper)
"COS is an exception. It is very stable in the troposphere, with a two-year residence time, and a large and relatively uniform distribution. Although it is the most abundant sulphur gas compound in the atmosphere, it is so unreactive that it is largely ignored in tropospheric chemistry. The long residence time means it can be mixed up into the stratosphere, where it is converted by UV radiation and is the dominant non-volcanic source of stratospheric sulphate aerosols."
And from en.wikipedia.org
"Carbonyl sulfide is the most abundant sulfur compound naturally present in the atmosphere, at 0.5±0.05 ppb, because it is emitted from oceans, volcanoes and deep sea vents. As such, it is a significant compound in the global sulfur cycle. Measurements on the Antarctica ice cores and from air trapped in snow above glaciers ( firn air) have provided a detailed picture of OCS concentrations from 1640 to the present day and allow an understanding of the relative importance of anthropogenic and non-anthropogenic sources of this gas to the atmosphere.  Some carbonyl sulfide that is transported into the stratospheric sulfate layer is oxidized to sulfuric acid.  Sulfuric acid forms particulate which affects energy balance due to light scattering.  The long atmospheric lifetime of COS makes it the major source of stratospheric sulfate, though sulfur dioxide from volcanic activity can be significant too.  Carbonyl sulfide is also removed from the atmosphere by terrestrial vegetation by enzymes associated with the uptake of carbon dioxide during photosynthesis, and by hydrolysis in ocean waters.   Loss processes, such as these, limit the persistence (or lifetime) of a molecule of COS in the atmosphere to a few years."
Along with the above, COS and cosmic rays together may be the dominant factor in "spontaneous" origin of new species on Earth after each great extinction.
"This compound is found to catalyze the formation of peptides from amino acids. This finding is an extension of the Miller–Urey experiment and it is suggested that carbonyl sulfide played a significant role in the origin of life. "
Carbonyl sulfide-mediated prebiotic formation of peptides.
"Almost all discussions of prebiotic chemistry assume that amino acids, nucleotides, and possibly other monomers were first formed on the Earth or brought to it in comets and meteorites, and then condensed nonenzymatically to form oligomeric products. However, attempts to demonstrate plausibly prebiotic polymerization reactions have met with limited success. We show that carbonyl sulfide (COS), a simple volcanic gas, brings about the formation of peptides from amino acids under mild conditions in aqueous solution. Depending on the reaction conditions and additives used, exposure of a-amino acids to COS generates peptides in yields of up to 80% in minutes to hours at room temperature."