Your question isn’t entirely a hypothetical - this happened at the dawn of time, when photosynthetic life forms first evolved. First, it won’t ever happen again, no matter how good we get at scooping CO2 from the atmosphere. Second, the result is theoretically catastrophic for aerobic life forms, but it’s also a negative feedback loop, meaning it self corrects.
Your question isn’t entirely a hypothetical - this happened at the dawn of time, when photosynthetic life forms first evolved. First, it won’t ever happen again, no matter how good we get at scooping CO2 from the atmosphere. Second, the result is theoretically catastrophic for aerobic life forms, but it’s also a negative feedback loop, meaning it self corrects.