Collection of damn near all possible scenarios for The End of the World: http://exitmundi.nl/exitmundi.htm
Your favorite is bound to be in there somewhere. If not, explain ( with a pic too if possible )
kind of like choak but its just oxygen levels dropping to lethally low levels. current oxygen levels in cities is 15% .15 years ago it was 20% in cities
humans would be expected to do things before this became the sole cause of their own demise like cause a new world war to decrease the population
but the atmosphere is not normalized . pockets of higher and lower concentrations of gases exist. people could suffocate in a town or city and people in another district could be fine when we get to about 5% - 10% in cities
a invisible cloud killing people and the fear from that would again likely cause panic and a world war to try to stop it but a sudden failure of plants to produce enough oxygen could be impressive. the loss of knowledge could kill civilization since you need people to tech others how to do things and some things need to always be done like man nuclear power plants but you only have so many people who know how to do it at any 1 time in any area and the government might not even get a serious problem just emerged.
think about it when people die how often does the federal government take a interest in it? they got better things to do but if a whole city died would they even know day 1 ? how about a week later? its like those real mass disappearances how much time had passed before any one knew.
its the end game that keeps on giving. a WW3 to save the planet lmao, random deaths and even chernobyl esk destruction which could cause a real panic with radiation sickness