We're on the path for stratospheric sulfide injection to be the utilitarian choice, and I wouldn't be surprised to see Effective Altruism groups discussing it as a very cost effective way to save lives in 30 years. The primary effects are relatively short lived (a few decades) and fast-acting (months). It will reduce global temperatures. Sulfide is cheap, the cost is mostly in fighting gravity. It probably won't happen until there is a stronger narrative around human life lost due to climate change. A bad summer with lots of catastrophes hitting the front page. The global political environment is setup so a non-superpower might act alone or with few allies.

While it sounds great on paper, the secondary order effects will last longer than primary and are very hard to quantify. It's clearly 10x-1000x cheaper to cut CO2 emissions now than to try to block out the sun with geoclimate engineering in a few decades.