Will charcoal (carbon) oxidize in the air?

[Wikipedia — Carbon sequestration](https://en.wikipedia.org/wiki/Carbon_sequestration) claims that burying charcoal into the soil offsets $\ce{CO2}$ and thus reduces the greenhouse effect:



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> In the soil, the biochar carbon is unavailable for oxidation to $\ce{CO2}$ and consequential atmospheric release.
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Is it a must to cover charcoal/biochar with the soil to prevent the air and rain water exposure to avoid oxidation, i.e. offset carbon dioxide? Would it otherwise oxidize to $\ce{CO2}$ under normal conditions (no fire) if left above the ground?


