There was a book once called SuperFreakonomics sequel to Freakonomics that said that global warming could be combated by putting sulfur dioxide into the atmosphere, that would dim the effect of the sun and cool the planet, for relatively low cost.
I don't know how realistic it is.
Here's some links -
https://en.wikipedia.org/wiki/Strato...osol_injection
https://en.wikipedia.org/wiki/SuperF...arming_section
https://www.technologyreview.com/s/5...lobal-warming/
https://www.wired.com/2008/06/ff-geoengineering/