Naturally (without human influence) a combination of biosphere (decades) and geosphere (millenia) would keep CO₂ levels in check.

We (humans) have accelerated emissions (by burning, thus reversing, geosphere capture via oil) and destroyed the biosphere through deforestation. This has also been accelerated as raising temperatures thaw permafrost & destroy ocean life (among others).

Anything we can do to reverse this is beneficial.