Neil Stephenson's 'Termination Shock' is about an organizarion that decides to start lofting sulfur dioxide into the upper atmosphere (where it tends to stay, just like it did after Krakatoa when it resulted in 'the year without summer') on their own initiative. Like most other Stephenson novels, it gets into a number of other areas (notably the 'line of actual control' between India and China and how that's mostly determined by high altitude brawling w/o weapons).
The novel points out that even if this succeeds in cooling the planet, there will be regions that win - and others that lose.
It's my second or thist favorite novel of his.