An extremely bad option that might beat the alternative
Aerosol shading will decrease global precip even more than it decreases temps, so it would cause drought.
It works evenly everywhere, while AGW overheats the Arctic. So you have to choose between undershading the Arctic or overshading everywhere else.
Aerosols will have to be maintained for hundreds of years, or else you get rebound warming that will be truly scary.
Won't do anything about ocean acidification.
I agree that this option is better than some plausible future scenarios under AGW, and should be studied in case we need to do it despite its drawbacks.