Actually, some of the geoengineering has been tried/studied, the acid in atmo, and the ocean dumped iron.
The iron addition worked quite well, quadrupling the sea catch of fish, and creating a bloom of aquatic algae and plankton. If we can dump in a priming of shell creating plankton, along with the iron, you can pull down quite a bit of ocean CO2, and send it to sea bottom. I think they have only published one sci paper on it, but a couple other papers on econ gains were put out before they raided and arrested the folks that carried it out. The Canandian natives were pretty pleased with the results, tho.
The other easily reversible technique would be solar reflectors in orbit. These could be dual tasked to be solar power satts, to offset some power production. If you sent that power to the most polluting countries grids, they could de-commission some of the worst power plants and cement factories. Studies in progress, models launched to test, lots of theoretical studies under solar sail tech. And the SLS needs something to launch.....
If it's worth saying, but not worth its own post, then it goes here.
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