>muh doomsday scenario
Capitalist elite will inherently have more survival chances in any scenario(search "neo-feudalism"), even if half the plankton goes extinct(plankton : the primary source of oxygen in the atmosphere).https://earthsky.org/earth/how-much-do-oceans-add-to-worlds-oxygen
As the pollution(microplastic) and CO2(ocean acidification) start killing off plankton in large amounts, the percentage of oxygen will begin dropping,
which will start killing animals, starting with less efficient lung-less supply system - sort of a "canary in the coalmine", such as insects( we live in a world with 'dwarf insects' because larger insects died off due inefficient oxygen supply system. https://www.sciencedaily.com/releases/2010/10/101029132924.htm
) (human might create a "bottled air" economy or domed cities to prolong civilization) and eventually life on the "unprotected" surface will either die or adapt to low oxygen levels(think spacesuits and oxygen balloons):
populations which can't afford to buy bottled oxygen will slowly choke to death and die from anoxia. The elite might survive with robotic industry and automation in some way, but there will be no "consumer economy" or grand-scale civilization with billions.
The future is not looking good, even if you stop most CO2 the pollution in the ocean will takes decades to clear off(microplastic is especially vile stuff that poisons the marine food chain https://www.dailymail.co.uk/sciencetech/article-4420992/Shocking-photos-reveal-plankton-consuming-microplastics.html
The scale of pollution, the plastic-filled oceans is not known, the microplastic is invisible, tiny specks.
Here is how the marine food chain collapses:
Plankton eat microplastic.
The fish bio-accumulate plastic by eating plankton.
Sea predators eat plastic-filled fish.
They all receive a hefty dose of endocrine disrupting chemicals and various plastic-bound toxins( https://www.mdpi.com/1660-4601/17/5/1509/htm
Now trees: you see articles everyday about forest fires, amazon burning, but it doesn't occur to you its oxygen-generating capacity burning off: the "oxygen capital" of entire planet is systematically wasted and destroyed. With no trees and no plankton, the planet dies.
Find a flaw:
1.plankton produces oxygen
2.plankton eats microplastic
3.plankton dies. Plankton breed less due acidic, warmer water and chemicals in plastic -filled water.
4.Trees produce oxygen.
5.Trees are burned off.
6.Remaining sources of oxygen are insufficient to sustain the current ecosystem.
7.Mass extinction of oxygen-dependent life begins.
8.No economic solutions will stop the process.
9.Oxygen becomes a commodity product.
10.Hyper-capitalism develops where oxygen is a currency.
11.Oxygen producing factories become critical industry.
12.People need to live in domed cities and use spacesuits to travel.
13.Eventually the elite class holds the entire(remaining) population on stranglehold by monopolizing oxygen supply and controlling society with Strong AI.