A sunshade doesn't involve chemical modification of our atmosphere, and its effects are reversible (it's a solar sail and can change its orbit when required).

A sunshade doesn't involve chemical modification of our atmosphere, and its effects are reversible (it's a solar sail and can change its orbit when required). As to expense, it's an opportunity for the space industry to contribute to solving the #1 problem on Earth. The Starship fleet is being built anyway. As a fringe benefit, if made of thin-film photovoltaics a sunshade could generate ~300TW of electricity. Compare that to current terrestrial consumption of 17TW. It creates enough energy and in-space manufacturing capacity to unlock the solar system.