A lot of the press discussion, IPCC information and scientific inquiry about climate change refers to changes in the temperature of the atmosphere. I have not seen debates about changes in the composition of the atmosphere. In particular, could human activity make air unbreathable? This would be of course disastrous for human life (and for other species). Or perhaps this process would be so slow that our respiratory system would adapt to it?

There are some isolated scientists suggesting we could make air unbreathable (like here), but the lack of wider treatment of this issue suggests to me this is not really a problem. What is the scientific standing about this possibility?

Update: the suggested duplicate focuses solely on CO2. My question is broader. Air composition could change because of different factors, like the Oxigen-plankton relationship highlighted in the referred link. The other post is too narrow. This is broader.

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    $\begingroup$ Given that the atmosphere consists of 20.95% oxygen & the mass of the atmosphere is 5.1 x 10^18 kg I find it difficult to accept that if all Earth's plankton died the planet would have only 84 years of oxygen left, as stated in the article you refer to. Note 20.95% of 5.1 x 10^18 kg is 1.0685 x 10^18 kg or 1.0685 x 10^15 tonnes depleted in 84 years. On average, that's 1.272 x 10^13 tonnes per year. $\endgroup$
    – Fred
    Nov 18, 2021 at 12:22
  • $\begingroup$ @LShaver No. See update $\endgroup$
    – luchonacho
    Nov 19, 2021 at 8:49