>>Tulliu+32
I was thinking of countries more like India and Nigeria, both of which, despite becoming richer and having lower fertility themselves, have populations projected to exceed China's, and both projected to become too hot to live in without big problems. Its not literally an "endless" supply, but its easily enough to cover gaps in the west. If fertility fell 75% in the west, could probably fill it with people from those countries. And that might be a win-win in certain ways. The west then doesn't have an aging population. People in too hot countries get to move. The suffering happens to old people left in poor hot countries, which is a sad thing. In the end yes you are correct its not endless, but this must be a very long way off.