It's precisely the unknowns and unknowables that make unmitigated climate change so costly.

And yes, not acting on climate costs trillions. Please take a look at the "social cost of delay" calculations: https://www.pnas.org/content/116/42/20886#sec-3

$1/gallon is certainly more than the Exxon-supported $40/ton CO2 carbon price would suggest (~$0.35/gallon). That doesn't make it "radical" -- and it certainly doesn't imply going back to the stone age. Sweden has had a carbon tax since the early 1990s. By now it's >$120/ton CO2. Life goes on -- it's just much more carbon-efficient than without a carbon price.

Indeed, one important aspect of this kind of research is that it must be in the public domain; i.e. no private patents.

We need all-of-the-above. Yes, we need to cut CO2 -- to net zero. And that (likely) requires large-scale systemic change. The big step there is pricing carbon. Not the only step. http://www.nature.com/news/energy-policy-push-renewables-to-spur-carbon-pricing-1.18260

But it's also clear that solar geoengineering tackles aspects of the problem that cutting CO2 does not.

We need all-of-the-above. Yes, we need to cut CO2 -- to net zero. And that (likely) requires large-scale systemic change. The big step there is pricing carbon. Not the only step. http://www.nature.com/news/energy-policy-push-renewables-to-spur-carbon-pricing-1.18260

But it's also clear that solar geoengineering tackles aspects of the problem that cutting CO2 does not.