The irreversible global catastrophe is imperialist militaries massacring people with little risk to themselves. 
The irreversible global catastrophe is assembly line robots at the Toyota plant becoming sentient and going on a freaking epic terminator style mass shooting and enslave everyone except me 
If AI ends the world, it won't be because it's superintelligent and gains sentience. It'll be because it's dumb as a bag of rocks and humans decide to make important shit rely on it.
Pretty much this. The current implementation of machine learning is a bunch of smug redditors throwing it at every single problem and trusting the output to make decisions. Then going "the computer says x who am I to argue?"