We are heading towards a CO2 level that has been shown to cause cognitive impairment...
https://eartharxiv.org/repository/view/527/
It wont be a sudden change from one day to the next... And don't worry- the rich can afford supplemental oxygen, so they will be just fine.
The bad news is as CO2 increases the more our effective IQs will drop, compromising our abilities to deal with the problem. Whats more, lower IQs will be great for the Republican party, so they can whip up larger crowds and get them to chant 'DRILL BABY DRILL' as we all slowly choke to death.