Extinction event level but not really, since some human groups didn't show a remarkable effect. A large percentage drop in total population doesn't mean much when it's concentrated in certain areas and the total number of humans is very low already because hunting/gathering isn't conducive to large species numbers. Did you note the one mention of the theory that adaptation of affected humans' behavior might have been the driver for aggressively taking over Neanderthals through killing and incorporating captives into the groups?
Circling back to the point at hand of the thread, climate change is far greater a threat on all species than past recent geologic events, even possibly surpassing ones such as the PETM which is the closest in comparison and definitely an extinction event. Humans haven't experienced that level, ever. They weren't around.