This is so dumb. The reflection of sunlight to reduce TSI should happen at the L1 Lagrange point using moon dust, not by further polluting our own atmosphere.
The benefit of L1 is that it’s not perfectly stable. Anything you throw up into that orbit will only stay there without course correction for about a decade.
Sounds like a cool sci-fi idea, but you would probably need to put a significant amount of material 1,500,000km away to put a shade over the Sun. Probably comparable to the mass of our atmosphere. And then repeat every decade.
It would surely cost a few trillion to deploy the moon base and railguns capable of deploying that much material on target, but doesn’t require any physics-bending materials or processes.
It would be an ongoing process of refinement and launch, there are some papers that have done the napkin math on the launch rate and energy requirements and it’s all perfectly feasible in the context of preventing an earth-shattering calamity.
The only problem with having a human-controllable thermostat over the entire Earth is that no one will agree on how to set it.
The benefit of L1 is that it’s not perfectly stable. Anything you throw up into that orbit will only stay there without course correction for about a decade.