I hope he's wrong, but I think he's likely to turn out right. I'm not saying every last human will die, and I'm not saying 50 years is the right timeframe. But the odds of modern society surviving long term in anything like its current form are low.
Climate change is the ticking time bomb. Again and again we've proven unable to address it, and we're still not addressing it today. I have to conclude we likely never will, or not until it's too late. And that will destabilize everything. What do you think will happen when rising sea level drives 100 million people from their homes? When killer heat waves make parts of the Middle East uninhabitable? When the AMOC collapses and makes much of northern Europe uninhabitable? People will be desperate, and desperate people do stupid things, often involving killing each other. Throw nuclear weapons into the ring and I'm not optimistic.
It doesn't have to be like that. We just need to stop burning fossil fuels. We already have the technology. We just need to choose to do it. And nothing is stopping us from eliminating nuclear weapons except us. We are the problem. We know what we need to do, but we seem incapable of doing it.