"Stratospheric aerosol injection is a proposed method of solar geoengineering (or solar radiation modification) to reduce global warming. This would introduce aerosols into the stratosphere to create a cooling effect via global dimming and increased albedo, which occurs naturally from volcanic winter."

Will resolve yes so long as someone in the world does this on purpose for the purpose of mitigating climate change. Does not need to be a state actor - for instance, if a rogue organization did this on their own, it would still count.

EDIT: In order to resolve YES, there would need to be a large enough effort that it is generally projected to have a measurable impact on climate. Small-scale trial runs do not count.