The writer of the essay seems to contradict himself. First he says, "I’ve spent my whole life assuming we were getting smarter and we’d become a rational species before we made ourselves extinct. I now think I’m wrong."
Then a little further along, he says, "We won’t go extinct, but our global civilization will be stillborn, and collapse. The once mighty homo sapiens will end up being subsistence farmers and fishing folk, and the industrial civilization will fade into distant myths."
The most likely scenario, I think, is that there will be a drastic drop in human population, down to about one billion, which I have read is roughly what the Earth can sustain indefinitely at a present 1st world standard of living.