# Sulfur dioxide may have warmed Mars, but is being considered for geoengineering on Earth. How is this possible?

So I was reading a title called Terraforming: The Creation of Habitable Worlds and came across mention of the idea that sulfur dioxide was a greenhouse gas on Mars. This can't be a mistake because I saw it elsewhere, like here. And yet at the beginning of that same book there is a scenario in which artillery is being used to launch sulfur dioxide into the Earth's upper stratosphere to serve as a cooling agent. How can these two things be the case?

• It can have both a warming and a cooling effect. The relevant difference between its role on Mars and on Earth is that our atmosphere has an oxygen composition of 21% compared to 0.13% on Mars, and so sulfur dioxide quickly oxidises in Earth's atmosphere to form sulfates that precipitate and fall back to the earth, whereas it persists in the Martian atmosphere. – lemon Feb 26 '15 at 13:01
• @lemon shouldn't that be an answer, not a comment? Also Sadiq if you don't get an answer here, you might try posting this on Earth Science Stack Exchange earthscience.stackexchange.com – pentane Feb 26 '15 at 13:15
• @pentane It's a good question and I feel it deserves a much more detailed answer than my comment. Specifically, I'd like to see an answer that describes the various mechanisms by which SO$_2$ can warm/cool a planet. Although I agree that it might be better suited in Earth Science. – lemon Feb 26 '15 at 13:17