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Is there, globally, a balance of the concentrations of oxygen and carbon dioxide in the atmosphere?

Plants convert CO₂ to O₂,
and with the concentration of O₂, the tendency of plants to oxidize to CO₂ increases. That is, plants burn better with more oxygen.

Based on this there may be a feedback of increasing CO₂ concentration to increasing O₂ concentration back to increasing CO₂.

This feedback requires that plant growth increases with increasing CO₂ concentration.

Otherwise there would be only a limit to the oxygen concentration as at some concentration of O₂, even a wet rainforest burns explosively.

Does a feedback loop like that exist?

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  • $\begingroup$ Actually no. Even if there were a feedback loop, CO2 concentrations are only a few hundred parts per million. Convert all the CO2 to O2, and you change the percentage of O2 in the atmospere by less than 1%. Also, ~78% of the atmosphere is nitrogen. $\endgroup$
    – jamesqf
    Commented Dec 23, 2019 at 18:28

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Yes, increase in CO₂ concentration increases the rate of photosynthesis in plants. The rate of photosynthesis is linealy proportinal to CO₂ concentration in range up to 225ppm and slowly increases range 225-650ppm.[Limiting Factors in Photosynthesis, Plant Physiol. (1984) 75, 82-86] (Now CO2 concentration is about 400ppm). You can read more in Educational article on Nature journal website or in More scientific review on the topic.

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  • $\begingroup$ Not generally true in nature. The rate of photosynthesis is almost always limited by factors such as the availablility of sunlight, water, and soil nutrients. It's only when all those other factors are in sufficient supply (which probably happens only in the lab) that CO2 concentration becomes a factor. And since atmospheric CO2 hasn't been below 280 ppm for at least 10,000 years, rates below that level are hardly relevant to modern conditions. $\endgroup$
    – jamesqf
    Commented Dec 23, 2019 at 18:24

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