One problem I see in such massive geoengineering proposals as this is that you are still measuring the cost in dollars. But money is just arithmetic; an abstract transform of information about the marginal value of commodities. And commodities require energy input for manufacturing. So available net energy, not money, is the foundation of any economy, whether subsistence or high tech. So where will you get the net energy to manufacture and deploy these interventions at scale, and whose money will fund the R and D to develop, research, design, and deploy this supposedly Earth-saving technology? Any such technological fix will need to be backed by a huge infusion of concentrated net energy—that is, fossil fuels. See the problem?