https://www.technologyreview.com/s/603974/harvard-scientists-moving-ahead-on-plans-for-atmospheric-geoengineering-experiments/     2017

https://www.technologyreview.com/s/610007/were-about-to-kill-a-massive-accidental-experiment-in-halting-global-warming/    2018

https://www.aps.org/publications/apsnews/201710/hand-hubris.cfm     2017

https://www.technologyreview.com/video/609390/climate-disruption-technical-approaches-to-mitigation-and-adaptation/     2017

(Full disclosure:  I have a Bachelor's degree in Chemistry from MIT, Class of 1980).

While I am not sufficently convinced that, quantitatively, "global warming" ("climate change"), or more specifically AGW (Anthropogenic Global Warning) is a genuine problem,  I'd say it would be irresponsible to not prepare for the possibility that this sulfur-injection protocol will be necessary, or at least useful.  It should be quite cheap. Further, there are likely to be various (positive) feedback-loops associated with global warming, such as the thawing of permafrost, whose magnitude aren't well-understood.  

I suspect that the main opposition to this idea comes from people who see "climate change" as simply an opportunity to increase government control over the world.  They think that they've found themselves one hell of a problem, but a problem which would be threatened,  like garlic or a silver bullet, or a gold cross, to a vampire.  

                   Jim Bell