In a recent Science perspective Niemeier (Max Planck Institute for Meteorology) and Tilmes ( National Center for Atmospheric Research) nicely sum up the present state of climate engineering with sulfur (DOI). In a nutshell: somehow inject a lot of sulfur into the atmosphere and make it counter global warming. The cooling effect of sulfur is well-known and can be observed with vulcanic eruptions. The planet has a definite surplus of sulfur, a long time ago the acid rain threat was removed when industries started to remove sulfur from their exhaust pipes.
The current Wikipedia page on stratospheric aerosol modification (SAM) is unusually optimistic about its prospects, the line "It presently appears that this proposed method could counter most climatic changes" has been around for a while and did not even spark an edit-war. But is this optimism justified?
Let the numbers do the talking: Niemeier and Tilmes present the following figures , yes climate engineering can solve global warming and extreme weather but it will require sulfur injections lasting over 160 year with one degree of cooling costing 20 billion dollar per year and 6700 jumbo jet flights per day, the equivalent of one Mount_Pinatubo per year. They also point out there are a lot of unknowns and not all the negative effects of climate change are mitigated. So it is not all good news and more needs to be done. A quick look then at the text of the Paris agreement: what, climate engineering not mentioned?