Most CO2 Increase not Man Made, page-150

For humans and many animals to sustain normal functions, the percentage of oxygen required to sustain life falls within a small range. The Occupational Safety and Health Administration, OSHA, determined the optimal range of oxygen in the air for humans runs between 19.5 and 23.5 percent.


Notice, no matter how much we pollute the air, smoke cigars... etc, we somehow manage to get the correct o2 % from the air.

Mother earth can moderate the % composition for use to survive.

So i would not be too fixated on increased CO2 in atmosphere because its just a measurement of how many aircraft in flight.

mother earth will always keep things in proper balance.

or else we would all be dead eveytime a volcano erupts.