Things might get really really bad for a minute, but unless we turn Earth into Venus 2 there's probably going to still be people. Though they're gonna hate us for how badly we fucked everything up.
America's prison system is glaringly barbaric today.
But aside from the immense amount of greenhouse gases released by the farming of livestock, what's barbaric about our agriculture? Note that I'm not being an asshole, I'm genuinely curious and want to learn more.