A British scientist recently warned some American Congressmen: geoengineering schemes are not a magic bullet. Furthermore, there's no guarantee any human effort can reverse global warming.
The testimony also covered issues of how to calculate and then govern any major geoengineering experiments. Various schemes have been suggested for either CO2 removal from the lower atmosphere, or reducing the amount of solar radiation hitting the earth or its atmosphere.
The first semi-large geoengineering experiment did not go as hoped with nature reacting in an unforeseen way to seeding the South Atlantic with iron to increase plankton to increase CO2 capture. That Greman-Indian joint project was named Lohafex. Natural predators, shrimp, came in and devoured much of the extra plankton, their usual food source.