I don't know.. poisoning the very air we breathe sounds pretty scary to me, and we're doing it in an immense scale right now
Fossil-fuels powerplants produce surprisingly low air pollution due to all required by law filters, technologies etc.
(Source: it's discussed in the book The Uninhabitable Earth, although I don't have a copy to hand so can't find the exact citations.)
Very minor cognitive impairment levels can happen in worst-case scenario in 2100 and assuming current increase of CO2 concentration over time, it shouldn't happen before 2300.