How did fish manage during the climatic optimum [1] some 8500 to 5500 years ago when it was between 1.5°C and 4°C warmer than it is now, let alone during the previous interglacial periods [2] which were markedly warmer than the Holocene (i.e. the current interglacial period)? If there was a marked reduction in ocean life due to reduced oxygen levels that should be visible in fossil records. If there was no such reduction then why would there be one now?
Increased CO₂ has led to a markedly "greener" planet [3] - the increase was enough to cover the US twice in vegetation by 2016. Those plants produce oxygen during photosynthesis (6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂) which is released to the environment (air or water) during daylight hours leading to a higher oxygen concentration. I suspect this balance between higher atmospheric CO₂ which leads to an increase in vegetation which then leads to an increase in oxygen production is what kept ocean life from succumbing due to oxygen deprivation during those periods when the average temperature was much higher than it is now. If this happened then, why would it not happen now?
Increased CO₂ has led to a markedly "greener" planet [3] - the increase was enough to cover the US twice in vegetation by 2016. Those plants produce oxygen during photosynthesis (6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂) which is released to the environment (air or water) during daylight hours leading to a higher oxygen concentration. I suspect this balance between higher atmospheric CO₂ which leads to an increase in vegetation which then leads to an increase in oxygen production is what kept ocean life from succumbing due to oxygen deprivation during those periods when the average temperature was much higher than it is now. If this happened then, why would it not happen now?
[1] https://en.wikipedia.org/wiki/Holocene_climatic_optimum
[2] https://en.wikipedia.org/wiki/Quaternary_glaciation#/media/F...
[3] https://www.nature.com/articles/nclimate3004