There is also the opposite crazy idea. Burning fossil fuels produce CO2 that enhances plant growth and photosynthesis then produces more oxygen. This increase in oxygen is claimed to be a benefit of burning fossil fuels. Proponents don’t accept that burning fossil fuels consumes more oxygen than the extra plants can produce.
We know that oxygen levels are dropping, although not enough to worry about.
https://gml.noaa.gov/obop/mlo/programs/coop/scripps/o2/o2.html
