There have been many approaches to CO2 removal proposed over the years, but very few attempt to estimate the dollar cost per ton of CO2 removed have been published. Here is a recent proposal that does estimate costs:
Beerling, D.J., Kantzas, E.P., Lomas, M.R. et al. Potential for large-scale CO2 removal via enhanced rock weathering with croplands. Nature 583, 242248 (2020).
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Extracted from the Abstract: "Enhanced silicate rock weathering (ERW), deployable with croplands, has potential use for atmospheric carbon dioxide (CO2) removal (CDR), which is now necessary to mitigate anthropogenic climate change. ... China, India, the USA and Brazil have great potential to help achieve average global CDR goals of 0.5 to 2 gigatonnes of carbon dioxide (CO2) per year with extraction costs of approximately US $80180 per tonne of CO2. These goals and costs are robust, regardless of future energy policies. Deployment within existing croplands offers opportunities to align agriculture and climate policy. ... "
That's a pretty wide cost range, so we will use the geometric mean, Sqrt[80*180]= 120 US dollars per metric ton of CO2 removed.
Also note that this is an academic analysis, and so is most likely quite optimistic compared to a contractually-binding full engineering cost estimate. However, here is another datapoint reinforcing that estimate:
"Carbon Capture Is Key to Companies Net Zero Pledges -- Some carbon-dioxide removal techniques that companies rely on to improve their environmental footprints are riskier than others", By Rochelle Toplensky, March 17, 2021 6:09 am ET, The Wall Street Journal.
Relevant quote: "Project economics depend on the volume and purity of CO2 and the distance to the carbon reservoir, but it is 'highly likely' a facility can be economic at carbon prices of around $100 a ton, says Syrie Crouch, vice president of CCS at Shell. "
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The CDIAC tells us that one ppmv of CO2 in the Atmosphere weighs 7.816 metric gigatons, of which 2.133 gigatons is the elemental carbon component, so 100ppmv of CO2 will weigh 781.6 gigatons. Using Beerling's estimate of US $120 per metric ton to remove CO2 from the atmosphere, we find that the cost to remove 100ppmv of CO2 to be US
93.8 Trillion US dollars. To return to pre-industrial CO2 levels would cost twice that, or 188 Trillion US dollars.
For comparison the 2020 GDP of the entire world is 88 Trillion US dollars. The GDP of the West is about 40 Trillion, or slightly less than half the world GDP.
Datapoint: Over the five years of WW2, the US spent on average 27% of their GDP, squeezing everything else out to the margins, and they are probably still paying for it.
Joe Gwinn