[Pilsner]

reverse the impacts of global warming by injecting reflective particles into the stratosphere

I know a quick, certain, method of injecting large amounts of fine particulate matter into the upper atmosphere. The hard part is deciding where to use the process, because it does cause a temporary spike in local temperatures.

[Noumenon]

Start with Mecca, Medina, Riyadh, Damascus and Tehran.

[Jewbacca]

I could think of about 57 locations for that.