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-bend

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.