Jacobs Journal of Environmental Sciences

Climatic Effects of Atmospheric Sulfur Dioxide Aerosol Emissions

Burl Henry
Department Of Environment Science, Freelance Writer , USA , United States

Published on: 2019-02-13


The injection of SO2 aerosols into the stratosphere to provide cooling to counteract global warming is shown not to be a viable option. However, their introduction into the troposphere can easily be done and will provide the same cooling effect.Further, it is shown that the actual cause of global warming is due to the reduction in anthropogenic SO2 aerosol emissionsdue to global Clean Air efforts. The warming due to their reduction is so large that it accounts for all of the anomalouswarming that has occurred since 1979, leaving no room for any additional warming due to” greenhouse” gasses.



It is well known that the SO2 injected into the stratosphere by a large volcanic eruption can cause a temporary reduction in average global temperatures. As a result, it has been suggested that SO2 (or some other material) could intentionally be introduced into the stratosphere in order to counteract the effects of global warming.Since the advent of satellite measurements in late 1978, it has become possible to quantify the amount of SO2 injected into the stratosphere for each eruption, and, together with temperature measurements of average anomalous global temperatures, an estimate can be made of the amount of SO2 that would need to be injected into the stratosphere to achieve a reasonable amount of cooling. The following WoodforTrees.org plot of the British Meteorological Office’s Hadcrut4.6.0.0 data set shows the Jan-Dec landocean average anomalous global temperatures for the period 1970-2018 On the plot, all of the VEI4 and higher eruptions have been located, and its accompanying Table includes the amount of SO2 injected for most eruptions, and their plume altitudes [1]. It can be observed that basically all of the downward temperature excursions are associated with volcanic eruptions, although the amount of decrease varies considerably because of a number of factors, such as ENSO temperatures at the time of eruption, plume altitude, the amount of SO2 in the plume, and coincident warming due to decreases in the amount of SO2 emissions in the troposphere due to global Clean Air efforts (black line at top of graph). (According to the NASA fact sheet on SO2 aerosols, both stratospheric and tropospheric aerosols have the same climatic effect) [2]. Also, since most tropospheric SO2 aerosol emissions come from continuous sources such as power plants, factories, smelters, home heating units, etc. they are constantly being replaced as they settle out, thus giving them essentially infinite lifetimes).Within the constraints of the above considerations, the VEI4 eruption of Kelut (#16), for example, generated ~0.2 deg. C. 

of cooling from an injection of 1.5 Megatons of SO2 aerosols into the stratosphere. And the nearly simultaneous eruptions of Pinatubo (VEI6) and Hudson (VEI5), (#’s 17 and 18) caused ~0.45 deg. C. of temporary cooling from the injection of ~22 Megatons of SO2 into the stratosphere. Even the Kelut SO2 injection is far beyond our capabilities, and its effects lasted for only about 2 years. Thus, the injection of dimming SO2 aerosols into the atmosphere for significant cooling purposes is simply not a viable option. With respect to the warming spikes on the graph, they all coincide with decreases in atmospheric SO2 aerosol levels, primarily due to volcanic-induced El Ninos [where the rain of stratospheric SO2 aerosols (fine droplets of Sulfuric Acid) descending to the Earth’s surface after an eruption] coalesce with those in the Troposphere and flush quantities of them out. This cleansing of the Troposphere allows sunshine to strike the Earth’s surface with greater intensity, causing increased warming, usually enough to form an El Nino, if not quenched by another closely following eruption. Additional warming spikes can also occur during business recessions (where there are fewer SO2 aerosol emissions into the atmosphere due to reduced industrial activity), as a result of global Clean Air efforts to reduce levels of anthropogenic SO2 aerosol emissions, and extended intervals (>3-4 years, where all volcanic aerosols have settled out) and there have been no new VEI4 or larger volcanic eruptions to add more SO2 aerosols to the atmosphere, thus causing temperatures to rise because of the cleaner air (as between #’s 21 and 22 on this graph). The following graph of ENSO temperatures (which have major impacts upon Earth’s climate) for the years 1990-2019 shows the correlations of its temperatures with changes in SO2 aerosol emissions due to VEI4 and larger volcanic eruptions [of the 29 VEI3 eruptions in the interval, only 7 showed a climatic response (red dots)]. Global efforts to reduce SO2 aerosol emissions were also clearly evident, with all of the higher peaks coinciding with El Ninos caused by reductions in SO2 aerosol levels. The major 2015-2016 El Nino was primarily caused by a massive 29 Megaton reduction in Chinese SO2 aerosol emissions [4]

Although it is not practical to insert SO2 aerosols into the stratosphere for cooling purposes, the same effect can easily be obtained simply by increasing their emissions into the Troposphere. Rather than continuing to reduce SO2 aerosol emissions via Clean Air efforts (which will guarantee increasingly higher temperatures), they need to be judiciously re-introduced into the atmosphere until the desired amount of cooling is achieved. A corollary of the above, of course, is that the increased warming since 1979 is actually due to the reduction in anthropogenic SO2 aerosol emissions due to Clean Air efforts, rather than to the accumulation of CO2 in the atmosphere, which is a harmless gas with no adverse climatic effects.

This can be proven as follows

(1) The Pinatubo/Hudson eruptions injected ~22 Megatons of SO2 into the stratosphere, resulting in a temporary temperature decrease of ~0.45 deg. C, which equates to .02 deg. C. of temp. change for each Megaton of change in global SO2 aerosol emissions.

(2) Between 1979 and 2014 anthropogenic SO2 aerosol emissions fell by 25 Megatons, from 136 to 111 Megatons [4], [5], and Hadcrut4 temperatures rose by 0.5 deg. C, also equating to a temp. change of .02 deg. C. for each Megaton of change in global SO2 aerosol emissions.

(3) With changes in both stratospheric and anthropogenic SO2 aerosols having the same temperature response, the “Rule of Thumb” or Climate Sensitivity Factor for temperature changes due to changes in the level of SO2 aerosol emissions in Earth’s atmosphere is .02 deg. C. of temp change for each Megaton of change in SO2 aerosol emissions, for either increasing or decreasing emissions.

(4) Thus, the expected rise in Jan-Dec average land-ocean anomalous global temperatures, from 1979 to 2014 would be .02 x 25 = 0.5 deg. C. [+ 0.2 deg. C. of natural warming from Earth’s recovery from the Little Ice Age cooling (bottom dashed line on the first graph), which is a projection of the .05 deg. C. per decade of warming from 1900 to 1970], for a total of 0.7 deg. C.

(5) The Hadcrut4 anomalous J-D temperature for 2014 was reported as 0.58 deg. C. (NASA 0.73 deg. C). Either way, the temperature rise due to the reduction in anthropogenic SO2 aerosol emissions leaves essentially NO room for any additional warming due to “greenhouse” gasses.


Earth’s temperatures are extremely sensitive to the amounts of SO2 aerosols in the atmosphere, with average anomalous global temperatures responding in some degree to all VEI4 or higher stratovolcano eruptions. There is an initial cooling period, which can lead to a La Nina if its SO2 emissions are sufficiently large, and which can be followed by a volcanic-induced El Nino, as their SO2 emissions settle out, again if there are sufficient SO2 aerosols injected, as they drift down from the stratosphere. Global anthropogenic SO2 aerosols behave identically, with the exception that they have far longer effective lifetimes, and their quantities dwarf those emitted from volcanos. Consequently, when their quantities are reduced by Megatons, due to global Clean Air efforts, warming (at the rate ~.02 deg. C. of temp. rise for each Megaton of reduction in global SO2 aerosol emissions) ensues, and the amount of this warming closely matches all of the warming that has occurred since 1979, leaving no evidence of any additional warming due to the accumulation of CO2 in the atmosphere! 


1 http://volcano.si.edu/

2 Atmospheric Aerosols: What Are They, and Why Are They So Important ;1996.

3 A Community Emissions Data System (CEDS) for Historical Emissions.

4 Hoesly R, Smith J S, Feng L. Historical (1750–2014) anthropogenic emissions of reactive gases and aerosols from the Community Emissions Data System (CEDS). Geosci. Model Dev 2018 ;11: 369-408.