[philipkglass]

Assuming carbon capture can be 100% efficient (preposterous) meaning it takes an equal amount of energy to remove the carbon as we got when we burned it, then we would have to devote an equal amount of renewable energy watt hours to the project.

The rest of your analysis is quite correct but this is too pessimistic. You don't have to turn carbon dioxide back into fuel to get it out of the atmosphere. You only have to turn it into a stable non-gaseous compound, like magnesium carbonate. That can be done by crushing silicate rocks rich in alkaline earth metals, like olivine, and spreading them in coastal areas to get exposure to water and wave action. The magnesium silicate exchanges with carbonic acid to form magnesium carbonate and silica. The chemical reaction is thermodynamically spontaneous. The energy input to crush the rocks is just to accelerate the kinetics of weathering by exposing more surface area.

It's an accelerated version of the geological carbon cycle that naturally removes CO2 from the atmosphere:

http://butane.chem.uiuc.edu/pshapley/Environmental/L29/2.htm...

See section 7.2.2 of this IPCC report "Mineral carbonation and industrial uses of carbon dioxide" for the chemistry and thermodynamic considerations:

https://www.ipcc.ch/site/assets/uploads/2018/03/srccs_chapte...

[sfn42]

If it's that easy, why are we wasting billions researching carbon capture? Why aren't we just doing this?

[philipkglass]

Accelerated silicate weathering seems like the most affordable carbon capture solution that actually works, but it's still a more expensive way to decarbonize than shutting down coal fired plants or partially displacing gas-generated electricity with non-combustion electricity sources. The vast majority of countries that want to decarbonize still burn coal and gas for energy; incrementally reducing combustion of these fuels is the most cost effective incremental move for the next several years. That's why (IMO) no country is doing large scale carbon capture yet.

As for the research efforts, some privately funded work is trying to get a saleable product out of carbon capture, like turning CO2 into useful polymers or other chemicals. Accelerated silicate weathering is simpler but it also has no hope of producing any valuable outputs. It's purely a mitigation measure for CO2 that has already been emitted. I don't think that these efforts are likely to yield profitable processes, but it would be great if they did because then even countries without government decarbonization mandates could improve via private business efforts.

On the government-funded side, I think that some unproductive R&D work is being funded either due to funding bodies not being savvy enough or due to politics. Kind of like how NASA has to go forward with the Space Launch System even though it's ridiculously expensive for what it does.

[Dylan16807]

This is one of the things being researched.