This is "only" a crisis in the sense that our current economies break down if the influx of new consumers slows down. We'll adapt. Won't be painless, but it is not catastrophic, at least not in the same sense that climate change is catastrophic > “Do you know how hard you need to abuse a mammal to make them not have children?” If you asked Leahy what the explanation was, “my answer is technology,” he said. “My answer…
Also, the global fertility crisis isn't too few births, it's too many. Pretty much all of the world's problems boil down to too many people competing for too few resources. Less humans competing for and consuming everything imaginable, less problems.