You may have come across this idea. Societies like the Maya and Easter Island suffered massive population crash due to the exhaustion of natural resources. Others almost too many to mention were overthrown by rivals when their systems became unsustainable. Diamond argues that, as we aren't special, the same thing could happen to us. And, as our culture comes to cover the whole planet, there literally won't be anywhere to escape to. Of course everyone won't die, they never do, but a lot of people might. And our lifestyles might deteriorate a long, long way. It could easily happen in my lifetime.
As an SF reader I often think about the future, and I'm fairly optimistic about life in general. Some people think that technology will inevitably keep pace with the depletion of resources, for example providing new cheap power sources as fossil fuels run out, or letting us live on other planets. Are you convinced by this? Would you bet your life on it? Is it really 'inevitable'?
A Crooked Timber discussion here reviews technological optimism and pessimism.
"Jared Diamond is a pretty commonsensical guy who hedges his conclusions because dogmatism wouldn’t go very well with his empiricism. That he’s getting denounced as some sort of Postmodern treehugger shows how distorted debate about environmental issues has become."
Here's a good one
"I share the faith that we can solve problems with technology the question is whether we will. Because, as Diamond points out, civilizations can fall. Ours has the potential not to — but as long as we deny the danger, we increase it. My heart is with the people who say “we can make it to the stars” and firmly against the people who say “we must lower expectations and live smaller” — but I am terrified by the fantasy that reaching the stars is inevitable."