Many geo engineering ideas are not at all out of the reach of a nation state. I would guess China will just enact one of the hypothetical interventions one day, maybe 20 years from now when changing climates start causing serious social and political upheaval. I think of it like fiat money or the boiling frog problem, not really a problem until suddenly it is. Also not really the type of problem humans are good at solving proactively. Insurance markets are the first canary in the coal mine IMO. First consequential negative externality.