|Over time, the reporting of minor volcanic activity has become more broad due to global population increase and better reporting methods and capability. This results in a definite charting bias toward increased activity as reported by The Smithsonian Institute's Global Volcanism Program. This, however, does not necessarily mean that all of any increase is due to such bias. Especially over the time frame in question above and currently. In such a short period, a significant part of reported increase can simply be more attributable to an actual increase in volcanism. In the Smithsonian long term chart, the charted final push up in reported overall volcanic activity is significantly outstripped by population increase so that effect on the data is diminished while reporting methods and capabilities, arguably have not had time to advance very significantly enough to account for the increase. A view supported by the three (3) papers cited below the graph:|
1.) "Impact of Minor Volcanic Eruptions on the Aerosol Loading of the Tropical Stratosphere"
In this study, we use a set of global satellite observations including CALIPSO, SAGE II, GOMOS and OSIRIS to show that the contribution of medium VEI events to the increase in the stratospheric aerosol load over the last decade is significant.From 2002 onwards, a systematic increase has been reported by a number of investigators.Note that the focus here is on "medium VEI events" - "minor" eruptions. Not the large VEI events normally associated with climate forcing.
2.) "A New Sulfur and Carbon Degassing Inventory for the Southern Central American Volcanic Arc: The Importance of Accurate Time-Series Data Sets and Possible Tectonic Processes Responsible for Temporal Variations in Arc-Scale Volatile Emissions"
We show that volcanoes in Central America are more active now than any time in the scientific record...This is also quite inclusive of minor eruptions.
3.) "A decade of global volcanic SO2 emissions measured from space"
We report here the first volcanic SO2 emissions inventory derived from global, coincident satellite measurements, made by the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite in 2005–2015. The OMI measurements permit estimation of SO2 emissions from over 90 volcanoes, including new constraints on fluxes from Indonesia, Papua New Guinea, the Aleutian Islands, the Kuril Islands and Kamchatka. On average over the past decade, the volcanic SO2 sources consistently detected from space have discharged a total of ~63?kt/day SO2 during passive degassing, or ~23?±?2?Tg/yr. We find that ~30% of the sources show significant decadal trends in SO2 emissions, with positive trends observed at multiple volcanoes in some regions including Vanuatu, southern Japan, Peru and Chile.It is apparent that so-called "minor" volcanic activity is being overlooked by both sides of the climate debate and perhaps too much emphasis on the "cooling" side is being put on cloud nucleation via cosmic ray increase.
There are two segments of Earth's atmosphere involved with all of the above, the troposphere and the stratosphere. It's obvious that any heat energy from the Sun that does not make it through the stratosphere, or not absorbed within it, can't add warming to the troposphere. So if that influence is being blocked, there has to be something blocking it. And if it's not done by increased albedo due to cloud nucleation via cosmic ray effects, it's quite possible, or even probable that the contribution of light scattering/reflecting sulfur compound aerosols contributed to the stratosphere by minor/medium volcanic events plays a significant role.
As far as I know, this factor has yet to be satisfactorily explored in a rigorous way.
There are several papers that are related to the question however. Some show that carbonyl sulfide plays a stratospheric role. I have detailed this in previous posts. I have also posted an entry on it in other forums.
some key points:
The Sun provides the energy that drives Earth’s climate, but not all of the energy that reaches the top of the atmosphere finds its way to the surface. That’s because aerosols—and clouds seeded by them—reflect about a quarter of the Sun’s energy back to space.Different aerosols scatter or absorb sunlight to varying degrees, depending on their physical properties. Climatologists describe these scattering and absorbing properties as the “direct effect” of aerosols on Earth’s radiation field. However, since aerosols comprise such a broad collection of particles with different properties, the overall effect is anything but simple.Although most aerosols reflect sunlight, some also absorb it. An aerosol’s effect on light depends primarily on the composition and color of the particles. Broadly speaking, bright-colored or translucent particles tend to reflect radiation in all directions and back towards space. Darker aerosols can absorb significant amounts of light.Pure sulfates and nitrates reflect nearly all radiation they encounter, cooling the atmosphere.And from:
"The natural atmospheric sulphur cycle and its response to anthropogenic perturbations"
Oxidation states of sulphur vary between -2 and +6. Sulphur compounds are generally emitted in reduced form. They are then oxidised in the Earth’s atmosphere, generally to SO2 , a +4 oxidation state. Around 65% (the remainder is removed by dry deposition) of this sulphur dioxide is eventually oxidised to the +6 state of H2SO4 , where SO2 – 4 is the sulphate ion. Sulphur is stable in the presence of oxygen in this state. The higher-state compounds also generally have a greater affinity to water, meaning they are more readily removed from the atmosphere by wet deposition. Sulphate aerosols are common cloud condensation nuclei, which means they have important interactions with clouds and the hydrological cycle.Sulphur usually cycles from low-oxidation gas to sulphate particles and back to the surface in rain in less than a week. COS (Carbonyl Sulfide) 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.In the stratosphere particles between 0.1 and 2 microns in diameter have a peak concentration of around 0.1 cm-3 between 17 and 20 km. According to Wallace and Hobbs (2006) these particles are 75% H2SO4 and 25% water, so this region is called the stratospheric sulphate layer. Aerosols in this layer reflect incoming solar radiation, increasing the planetary albedo and thus having a cooling effect. This can be seen on a global scale after major volcanic eruptions, where the effects last for several years before the excess aerosol is removed from the atmosphere.Because there has been a systematically observed increase in global volcanic activity in the last 30 yrs, the above COS information must be considered in relation to that. ie:
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, "In addition: atmos-chem-phys.net
"Direct oceanic emissions unlikely to account for the missing source of atmospheric carbonyl sulfide"
Abstract. The climate active trace-gas carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere. A missing source in its atmospheric budget is currently suggested, resulting from an upward revision of the vegetation sink. Tropical oceanic emissions have been proposed to close the resulting gap in the atmospheric budget. We present a bottom-up approach including (i) new observations of OCS in surface waters of the tropical Atlantic, Pacific and Indian oceans and (ii) a further improved global box model to show that direct OCS emissions are unlikely to account for the missing source. The box model suggests an undersaturation of the surface water with respect to OCS integrated over the entire tropical ocean area and, further, global annual direct emissions of OCS well below that suggested by top-down estimates. In addition, we discuss the potential of indirect emission from CS2 and dimethylsulfide (DMS) to account for the gap in the atmospheric budget. This bottom-up estimate of oceanic emissions has implications for using OCS as a proxy for global terrestrial CO2uptake, which is currently impeded by the inadequate quantification of atmospheric OCS sources and sinks.
Another paper, unrelated to COS but pertinent to global cooling, explores the influence in the troposphere of variations in ice crystal shape within cirrus clouds. This particular work is so far nowhere to be found in GSM community expoundings.
"Additional global climate cooling by clouds due to ice crystal complexity"
Abstract. Ice crystal submicron structures have a large impact on the optical properties of cirrus clouds and consequently on their radiative effect. Although there is growing evidence that atmospheric ice crystals are rarely pristine, direct in situ observations of the degree of ice crystal complexity are largely missing. Here we show a comprehensive in situ data set of ice crystal complexity coupled with measurements of the cloud angular scattering functions collected during a number of observational airborne campaigns at diverse geographical locations. Our results demonstrate that an overwhelming fraction (between 61% and 81%) of atmospheric ice crystals sampled in the different regions contain mesoscopic deformations and, as a consequence, a similar flat and featureless angular scattering function is observed. A comparison between the measurements and a database of optical particle properties showed that severely roughened hexagonal aggregates optimally represent the measurements in the observed angular range. Based on this optical model, a new parameterization of the cloud bulk asymmetry factor was introduced and its effects were tested in a global climate model. The modelling results suggest that, due to ice crystal complexity, ice-containing clouds can induce an additional short-wave cooling effect of -1.12Wm2on the top-of-the-atmosphere radiative budget that has not yet been considered.