Try calculating, on an order of magnitude basis, the mass of pure sulfuric acid that would be reqired to change the PH of the worlds oceans by even .001%.
I brought up ocean acidification because we've all heard of the problem of acid rain from coal plants altering the PH of lakes.
I've read that aerosols precipitate out of the atmosphere much faster than CO2 "sinks" (carbon sinks), so we would have to continuously pump sulfur...
The sulfur would increase the acidification of the oceans, which some say already suffer from CO2-caused acidification.
In fact the greater threat from CO2 might stem not from global warming, but from ocean acidification.