Australian fertility rates of around 1.88 babies per woman are quite high by developed country standards but still well below replacement fertility which many claim is around 2.1. Thus Australia could achieve ZPG simply by controlling the migration intake. The intake would still be non-negligible because Australia exports many residents each year who seek to return to their country of origin. The building industry claim that we need high rates of immigration to boost private investment in housing but this has always seemed to me to be a “tail wagging the dog” policy – housing investment should not be needed to keep the economy afloat. Housing should provide a place to live. The resources devoted to housing could instead be directed to education, leisure, improving the stock of existing housing and helping to deal with a population of existing people who will live longer.
There would be transitional costs in making this shift since so much private investment is housing investment. But the intent of macroeconomic policy should be high living standards not growth for its own sake. It would be better if we became unhooked from dependence on an ever-expanding population which drives housing which drives incomes.
This seems a better way of thinking about the future than planning to double our current population to 50 million by 2100 with planned populations in Sydney and Melbourne of over 8 million.
The argument that this fails to address humanitarian concerns of overpopulation elsewhere is not strong. Taking an extra 25 million will have no discernible impact on a world population of 8 billion but will leave Australia with a less attractive environment and resource (specifically water) shortages.