Could earth run out of O2? [closed]

Question

Death in a closed environment due to lack of O2 is actually not that bad:

https://www.youtube.com/watch?v=kUfF2MTnqAw

And as far as I know as we are cutting down our life saving woods and jungles less $O_2$ is being produced and more $CO_2$ is not converted back to $O_2$. Greenpeace and others tell us how bad this fact is.

But: If it continues like this, is it possible for humanity to extinct itself because we run out of $O_2$ and breath in too much $CO_2$?

Wouldn't it be much nicer than like burning to death if the $O_2$ would disappear?

Answer 1

No, that will not happen. There is just too much oxygen in the atmosphere.

Over 20% of our atmosphere is oxygen. Only about 0.04 % of our atmosphere is CO₂, so too much CO₂ would kill us much sooner than the lack of oxygen.

If you reduced the oxygen concentration in the atmosphere from 20.8% to 19.8%, you wouldn't even feel the difference. If you reduced it to 15 %, you would still survive it. You could even survive 10 % for short time periods.

However, let's see what would happen if you added CO₂ as a replacement for the oxygen you removed: at 1%, you would feel extreme dizziness. At 5% you would lose consciousness and die.

But the real danger in CO₂ lies elsewhere. Even an increase from our current 0.040 % to 0.045 % could cause a lot of damage to the climate, and an increase above 0.055 % could be disastrous. Unless you are locked in a small room, the reason why the increase of CO₂ and decrease of oxygen will be dangerous won't be because you wouldn't be able to breathe. Changes significantly smaller than those required to make breathing difficult, would be enough to wreck the ecosystem, cause drought, desertification, starvation, and economic collapse.

Also note, that trees are very important for the water cycle, as a habitat for many species, and for preventing soil erosion, but they play an insignificant role in producing oxygen. Most of our oxygen is produced by algae.