After viewing a semi-joking video about using nuclear winter to counteract climate change, I searched ways to inject gigatons of soot into the stratosphere without gigatons of burning cities and the associated megadeaths.
Then I remembered the patent for the atmospheric vortex engine, a thermodynamic engine using an artificial tornado to connect warm ground and cold high altitude air then extract energy from the temperature differential. In this case, the tornado carries soot into the troposphere-stratosphere boundary where it absorbs sunlight and keeps it from reaching the ground.