Some other form of atmospheric sulfur must be contemplated for achieving earth-cooling. It's just not on the tip of my tongue at these moments. Increasing reflectivity of the atmosphere using sulfur has been mentioned more than once, in different places.

(Friday add) I just googled this up. They are talking about using high atmospheric baloons. There/here again I want to ask what's wrong with gunpowder propelled rockets, since the gunpowder is sulfur, saltpeter, and charcoal. '0)

http://www.sciencedaily.com/releases/2006/07/060727180326.htm

"In Crutzen’s experiment, artificially enhancing earth’s reflective powers would be achieved by carrying sulfur into the stratosphere on balloons, using artillery guns to release it. In contrast to the slowly developing effects of global warming associated with man-made carbon dioxide emissions, the climatic response of the albedo enhancement method could theoretically start taking effect within six months. The reflective particles could remain in the stratosphere for up to two years.

'Given the grossly disappointing international political response to the required greenhouse gas emissions,…research on the feasibility and environmental consequences of climate engineering of the kind presented in this paper, which might need to be deployed in future, should not be tabooed,” says Crutzen. He adds that his experiment should only be used as an emergency measure: “the possibility of the albedo enhancement scheme should not be used to justify inadequate climate policies but merely to create a possibility to combat potentially drastic climate heating.'"

http://vulcan.wr.usgs.gov/Glossary/VolcWeather/description_volcanoes_and_weather.html

From: Self, et.al., 1996, The Atmospheric Impact of the 1991 Mount Pinatubo Eruption: IN: Newhall and Punongbayan, (eds.), 1996, Fire and Mud: Eruptions and Lahars of Mount Pinatubo, Philippines: University of Washington Press As observed after several eruptions, including Agung in 1963 (Indonesia) and El Chichon in 1982 (Mexico), stratospheric warming and lower tropospheric and surface cooling have been documented after the Pinatubo eruption. Labitzke and McCormick (1992) show that warming in the lower stratosphere (16 to 24 kilometers or 30 to 100 mbar) of up to 2 to 3 degrees C occurred within 4 to 5 months of the eruption between the equator and 20degreesNorth latitude, and it was also later noticed in middle northern latitudes (Angell, 1993).