So-called "geoengineering" is a popular thing to discuss, even in polite company. The idea is simple: inject sulfur dioxide gas into the lower stratosphere and add a little bit - a few percent - to the natural sulfuric acid cloud layer there. The man made sulfuric acid particles would reflect a little bit more sunlight back into space than normal, thus cooling the planet. Massive volcanoes do this every decade or so and we think we understand how gases turn into particles and reflect sunlight and so on......
This plot is from a paper by Keith, Parker, and Morgan (Nature, 436, 2010) called "Research On Global Sunblock Needed Now". This idea is seductive. Relatively cheap and quick. But there are problems. First in line: this "purposeful pollution" of the stratosphere would cause a lot of ozone depletion, maybe 20%. Maybe more.
Second: It is sort of like a drug; each sulfur dioxide injection is temporary so once you start you can't stop. Look at the plot.
So where is the trade a good one? How much global ozone loss can we accept for a given amount of global cooling? Who decides?