I think what's coming is going to make 29 look like a picnic, so many bubbles in our economy ready to burst. What scares me more is climate change, just read some articles that say many of the predictions are way too conservative and if drastic action isn't taken soon it's game over for the human race.
The severity and duration of the crash and resultant Depression will depend on how tenaciously the current order clings to power in the face of the suffering of the many. We need another FDR, but he didn't rise until well after the Crash, when those who thought things were fine were totally discredited.
I believe I've been reading the same articles, that human habitation will become impossible in 100 years. I think that's polemic and extreme. If sea level rises 2m or 6', that will spell serious trouble for coastal cities and island nations worldwide but it won't flood the whole planet.
An increase of 5 degrees C won't make the planet uninhabitable, it will shift climate bands northward, as has already been happening.
The results will be mass disruption, billions of climate refugees and an increased likelihood of large scale conflict.
If that conflict spirals out of control into nuclear exchange, THAT will be the end of human civilisation.
The situation as I see it is that the few rich have opposing goals to the many, a situation known as 'tragedy of the commons' that if left unchecked will lead to the above Doomsday scenario. The rich are foolish to think they'd survive- or even if they did, that the world they'd have left would be worth surviving in.
Tragedy of the Commons is the reason for government, laws and regulations on the first place; to protect the many from the destructive desires of a few.
If we are to end the runaway destruction of our planet, we must end the stranglehold of the oligarchs on governments worldwide and restore an environment of laws that benefit the many, not the few.
The irony is that the richest would continue to prosper if this happens.