Lots of pretty words that translate to "reduce population and living standards or die." If true this is the hardest warning that people refuse to hear. If false it is a way to co-op guilt and fear to sell control. How I wish I knew which it was.
We all know endless growth with finite resources is impossible. We can innovate do things more efficiently or differently and find solutions to previous limits of course.
The hypothesis in the paper is simply that eventually a civilisation will encounter circumstances in which the timescale to solve it is longer than the time they have to do it. Then they must either achieve a form of homeostasis (and no growth) or die off (or retreat and start again).
The boundary for this doesn't have to be a planet. It could be a solar system, or maybe more than one.
It seems to be a sociology paper. I find the writings of sociologists impossibly dense and obscure.
It may not be 10 years, 20 years, or even 100 years away but at the moment we have limited quantities of many resources. At some point these lines are going to cross and it is going to lead to a reduction in quality of life.
Whether or not that will be blunted by trends in developed nations toward negative population growth remains to be seen. Novel technology that lets our resources go farther or allows us to gain new sources via space (asteroid capture or mining on other planets, etc.) could also change the tipping point.
The doom and gloom of Malthusian theory is so far unrealized but I think it is hard to argue that the theory is sound at its base. Whether or not we can keep the lines from crossing is the only thing that keeps it unrealized.
There is no reason at all to think that 1Bn humans can't live on earth at early 21st C standards more or less indefinitely.
11bn at twice that level.... that's harder to see.