Buy some weather balloons, hijack a truck load of helium, load the balloons with a few hundred pounds of sulfur dioxide plus enough helium to make them float away, and release the balloons to float away into the stratosphere where the balloons native helium pressure will cause them to burst releasing the SO2 into the atmosphere to block incoming solar radiation.

Crazy idea right? Lots of Loons in the word today. Proof linked below

Make Sunsets