I’m not sure what you’re trying to convey here. Carbon sequestration is unarguably a way to mitigate climate change, and sequestration of CO2 is probably the most reasonable way to do so. It doesn’t need to be as a gas, as taking CO2 and exposing it to various oxides creates carbonates, which are generally very stable compounds like limestone.
The other commenter simply said carbon could be captured as CO2 and sequestered without being reduced, which is absolutely true and frankly makes much more sense from a physics/thermodynamics POV.
You guessed right - without reductions or conversion it simply becomes a ticking time bomb. Anything secure enough to capture and contain a gas reliably for millennia without maintenance will be too expensive to be practical.
Methane is a greenhouse gas more potent than CO2 that was stored underground for millennia. You would need actual data to conclude that storing CO2 is too expensive.
