Why do you believe inverted pyramids don't last? They last for a long time after you get the birth rate back up. And Japan's not gotten the birth rate back up.
Indeed, it seems like the drag from having an older population does a lot to keep the birth rate down.
Our best forecasts show Japan's population pyramid as still markedly inverted and still shrinking in 2100.
(I don't agree with your other point either, necessarily, but I chose to ask about this one).
> Why do you believe inverted pyramids don't last?
Death. And there are trivial ways to keep fertility at replacement level and not negative, on par with most other 1st-world countries.
A perpetually inverted pyramid would require that fertility rate shrink even further, until it approaches 0 - do we have a reason to believe this will happen?
Notwithstanding, in 100 years the entire global population growth is projected to stagnate, which will make this a moot point. No one will be able to rely on immigration to grow perpetually.
> A perpetually inverted pyramid would require that fertility rate shrink even further, until it approaches 0 - do we have a reason to believe this will happen?
Any fertility rate that's below replacement maintains an inverted pyramid, if you don't have a lot of death before old age. (Until the very last person dies, in a long long long time).
Each person in the current breeding population produces fewer people in the next breeding population; this produces an inverted pyramid.
> And there are trivial ways to keep fertility at replacement level and not negative, on par with most other 1st-world countries.
No country that has fallen into population decline has found these "trivial ways" in modern times. (Not sure what you mean here by "negative")
Indeed, it seems like the drag from having an older population does a lot to keep the birth rate down.
Our best forecasts show Japan's population pyramid as still markedly inverted and still shrinking in 2100.
(I don't agree with your other point either, necessarily, but I chose to ask about this one).