Ok, so worst case scenario all plankton die, what happens? How much O2 production is required for us to survive? ...Seems like we should be looking into solutions like genetic engineering for heat tolerance or whatever is killing the plankton.
I cross-posted this discussion in the Origins Group, and there is a useful discussion brewing about the mechanics of extinction events and the kind of percentage question you intimate with some links to the science behind it all. However the question is kind of broader it not merely the limit at which we will suffocate, it's the levels at which regulatory process fail and positive feedback drives them into a crisis
"Seems like we should be looking into solutions like genetic engineering for heat tolerance or whatever is killing the plankton."
This brings to mind Vonnegut's Cat's Cradle and Ice Nine. The cure may be worse than the disease if humans try to introduce a genetically engineered phytoplankton that would multiply quickly enough to replace all of the natural stuff in all bodies of water. Without the natural genetic growth and expiration limiting factors working or mutating we might just make all of the water on the planet unfit for human consumption.
plankton makes a significant amount of oxygen, and takes away a significant amount of CO2. IN addition, the oceans are greatly overfished, because the ocean fish provide a significant amount of foood to the world's population. FIsh are not needed to feed cattle or poultry, I don't know how much fish product goes into land-animal agriculture. Some fish are now farmed, with land-based foods being fed to fish.
The issue with plankton is that les plankton -> more CO2 -> worsening climate change in what appears to be a death spiral already.
Lets add some fun to that, with the large quantities of methane that are locked into frozen seabeds. Once it's warm enough for that to bubble out, that will have a greater effect on climate change than CO2.
I hope not too soon. Not so much because I want to survive until my time is up, but because I don't want to see the environmental descruction in my lifetime. It's too depressing. Even if I think it will happen, I would rather not see it.