Actually, you are wrong in several respects, George. Consider the Mauna Loa observations of atmospheric transmission caused by a 7 Mt injection vs a 20 Mt injection:
View attachment 4300
http://climate.envsci.rutgers.edu/pdf/EGECVolcanicEruptions.pdf
Encyclopedia of Global Environmental Change, Volcanic Eruptions by Alan Robock
Volume 1, The Earth system: physical and chemical dimensions of global environmental change,
pp 738–744 (ISBN 0-471-97796-9)
So, from the ground, the effect of even a 7 megaton eruption is quite clearly evident.
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Another way that injections of SO2 are continually monitored and would be observed is by satellite. The TOMS satellite continually scans the earth looking for SO2.
Here is what Pinatubo looked like:
View attachment 4301
Again, you can clearly see the result of a 20 Mt injection.
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Now, let's compare how El Chicon and Pinatubo showed up on TOMS:
View attachment 4302
View attachment 4303
Again, even a 7 Mt injection is clearly visible. Remember, this is using 30 year old technology.
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So, now you are going to say that under your covert geoengineering scenario, the releases would necessarily be much smaller and hence undetectable.
Let's look at how a much smaller release of SO2 looks, using modern technology.
Here is the ruption of Mt Merapi, which released 1% of Pinatubo, or 200,000 tons:
View attachment 4306
Here is the European MACC image for today, note that a release of SO2 from Mt. Etna in Italy is clearly visible in red:
View attachment 4304
Also, note the plume from Beijing!
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Again, confirmable by a completely different NASA satellite which focuses in on the area:
View attachment 4305
In the image above,
the mass being released by Etna is less than 0.1 kiloton!
George you r claim that geoengineering could be practiced covertly simply doesn't hold up under scrutiny. I am no aerosol scientist, but was able to find out that even moderate releases of SO2 are easily monitored by the common man in detail spatially, temporally and quantitatively. Your speculation that geoengineering could be done covertly is debunked.