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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 
In the second book of the Rifters trilogy by Peter Watts, spineless corpo types leave the major strategic decision-making on how to handle the emergence of a primordial proto-organism dubbed "Behemoth" to a bunch of lab-grown neural network computers running AIs. The computers eventually skew things in the direction of allowing Behemoth to take over because it created more predictable outcomes than the chaos of human activity that kept forcing the AIs to reallocate resources to deal with new variables, leading to global mass death via the proliferation of a thing not complex enough to be called a virus stripping all the phosphorous out of people's cells to perpetuate itself.
Watts seems like an absolute maniac, but I do enjoy his books.
All of the best writers are absolute maniacs, but if your favorite authors aren't on the Do Not Fly list what are you even doing with your life