@elaterite
There's a theory that metal oxide particles (including aluminum oxide) in the upper atmosphere might reduce global warming. I believe that opinions are mixed about how safe or effective this would be (if at all). I think it's generally agreed that even if a cooling effect is achieved, it would be accompanied by global dimming.
I'm not a climate scientist, but "global dimming" seems like it might be harmful to the ecosystem. How much metal oxide would be required to cause such effects? I don't know! But as you said, it's a massive uncontrolled experiment.