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A big argument for carbon capture and storage is true reversal; while switching to renewable energy and eliminating CO2 emissions is a must, it will not reverse the massive movement of carbon from underground hydrocarbons to the atmosphere and biosphere.

However, prevailing strategies are not exact reversals of burning fuels, either. Rather than converting CO2 to hydrocarbons to be buried, CO2 may be directly injected deep into the ground or converted to carbonates first. Would there be consequences for the biosphere if we do manage to bury 2-3 oxygen atoms for every carbon atom that will also be buried, that so far would have been released into the atmosphere?

EDIT: For the sake of argument, let's assume a hypothetical method of capture and storage that uses only renewable energy and that the buried matter does not leak back out. This question should not be construed as an endorsement of current carbon capture and storage technology.

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  • $\begingroup$ CCS isn't a "true reversal". It's a way to use even more energy, usually generated by creating even more CO2, to store something underground which might or might not stay down there, which shouldn't be generated in the first place. Nobody can ensure that the captured CO2 stays underground for ever, or at least a reasonable long enough time, doesn't interact with ground water, etc. CCS is just an argument for "let's continue as before". $\endgroup$
    – Erik
    Commented Jan 25, 2019 at 12:31
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    $\begingroup$ Yes, there are many limitations of CCS's efficacy, and it has been used by the fossil fuel industry to justify continued reliance on fossil fuels for energy. But for the sake of the very hypothetical question, let's assume that the energy used to bury carbon is renewable and that the buried carbon stays buried. With this best-case scenario, would there still be a cost from the loss of oxygen? $\endgroup$
    – BatWannaBe
    Commented Jan 25, 2019 at 13:00

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No, I think there are not. At least not at the scale of the proposed projects. I say this just because $\text{CO}_2$ makes up only a 0.04% of the atmosphere, so even if you burn fossil fuels until you double the pre-industrial amount of CO$_2$ and then capture and bury it back (both the Carbon and Oxygen). You would only drop Oxygen levels from its current 20.95% to 20.91% or something like that, which is not very significant. In a closed space like your bedroom for instance, you would probably make a bigger change in the Oxygen level by just breathing inside for a few minutes.

Also, many chemical reactions that sequester Oxygen and are sensitive to its concentration (oxidation and combustion for example) would work towards keeping equilibrium: they will slow down if there is less Oxygen allowing the concentration to bounce back. Or they will accelerate if there is too much Oxygen, dropping the level back down.

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