This is an incredibly misleading use of graph axes.

The baseline should be 200000 ppm, but a change of 500 wouldn't be noticeable. So they just show the change from a recent year, which lets them baseline at zero.

https://www.co2levels.org/ (same source, apparently) shows the amount of CO2 from 1990 until now has gone from about 355 ppm to 420 ppm, so 65 ppm. Each CO2 binds an O2, so I guess that could account for 65 ppm of the "missing" oxygen.

But each CO₂ produced by burning a hydrocarbon also means 2 H₂O (or 4 H₂O for methane), so that accounts for another 65 ppm (or more).

Only ~40% of the CO₂ produced since 1850 has stayed in the atmosphere. 130 ppm / 0.4 = 325 ppm. That's half the missing oxygen right there.

I wonder if humanity's cognitive levels have been affected? [1]

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4107523/

No. This a tiny change in O2 concentration.

Tiny changes could be relevant, especially over time, no?

Over like 10,000 years this rate of change would matter, but since this seems to be related to binding O2 into CO2 and H2O due to burning fossil fuels, increased CO2 over 10,000 years would cause world shattering effects before we continue to cause it for 10,000 years. Also we would probably run out of fuels before the O2 concentration becomes an issue.

Interesting to think about... I wonder if there would be a snowball effect of O2 loss with losing vegetation on land and in sea, having an effect as temperatures rise.

Sorry :/