It's been a long time since an Australian government has given any serious thought to a national population policy. Indeed as the population has grown, there has been a corresponding decline in official interest in the subject. The report of the National Population Inquiry, usually known as the Borrie Report, was published over 40 years ago. In 1991, the Hawke government commissioned Population Issues and Australia's Future, a wide-ranging report by independent advisory body the National Population Council, which recommended a much stronger role for a population strategy in national policymaking. In particular, the report pointed to the link between national ecological integrity and the need for reduced rates of population growth.

At about the same time, in 1992, the government's inquiry into ecologically sustainable development (ESD) released its final reports. The ESD inquiry, while wide-ranging, was focused on specific economic sectors. Despite the previous work of the National Population Council, population rated only a brief overview as one of a number of "inter-sectoral" issues.

In 1994, a parliamentary committee devoted to long term strategies and chaired by Barry Jones bravely navigated the population question, without coming to any definitive conclusions. Since then, no parliament or government has wanted to broach the complex issues involved. In his autobiography, John Howard, one of the architects of the high immigration policies that have contributed so much to population growth, maintained a careful silence on the issue of population and its impacts.

In more recent times, former New South Wales state premier Bob Carr and current Premier Gladys Berejiklian have both voiced their concern at the effects of unplanned population growth on the city of Sydney. At the federal level, though, where any policy would need to be formulated, there has been little serious interest. The Morrison government's Planning for Australia's future population, launched in March in the lead-up to the 2019 election, promised better management of population growth, but chose to present population growth itself as inevitable, rather than a consequence of current choices.

The government clearly realised, though, that it had to respond to voter frustration at the stress and inconvenience caused by growing urban congestion. It promised a cap on permanent migration, more state-federal-local negotiation on planning matters, and renewed efforts to encourage migrants to settle in regional Australia. These measures did little to inspire confidence. In particular, the undertaking to reduce the cap on the permanent migration intake to 160,000 per year, while doing nothing to limit the intake of temporary migrants, amounted to little more than political sophistry.

But at least there was some acknowledgment of the need for change. Labor's election policies ignored population completely. High-mindedness on the economic front was combined with a good deal of cynicism elsewhere, as the party sought to shore up its vote in certain electorates by promising a visa specifically for families wanting to sponsor settlement by grandparents in Australia.

The Greens, who we might expect to have something to say on population, preferred to focus on the Adani coal mine and on climate change. Overall, the Greens' view seems to be that because of the link between population and immigration, the issue is simply too divisive to be publicly canvassed. Only one party, Sustainable Australia, has put forward a coherent population policy.

Of course, if you have no policy on a particular matter, what you end up with is the resultant of the various related policy systems already in place. In the case of population, this means that immigration numbers determine population numbers, rather than population preferences determining immigration numbers. Immigration is driven largely by whether the economy is growing or not. Thus, the future number of Australians, with all that this means for the shape and operations of our cities, and for our increasingly fragile environment, is shaped by year-on-year labour demands.

Over the past 20 years, this linkage has produced a rapidly growing Australian population. Powerful interests wish to see this situation continue. They include the universities (whose budgets require a continuing supply of international students), developers, real estate agents, builders, many business interests, and some unions (such as those in the construction sector).

Each group has arguments to advance, and it is important to acknowledge that self-interest does not necessarily make these arguments false. But it is worth noting that the structure of interest-representation in this area is quite asymmetrical. For those who benefit from high population growth, there are substantial incentives to maintain the pressure on governments. The benefits to these groups are obvious, while the costs of population growth are dispersed across the electorate in the form of added infrastructure costs and increased congestion. When policy benefits the few, and the costs are distributed across the many, we know we have a sure-fire prescription for lop-sided policy development.

If Australia were to have a population policy, what would it look like? Different population levels bring different impacts and pressures. Making choices between them requires the ability to make intelligent projections regarding patterns of resource use and pollution, employment choices, social change and technological possibilities. It's little wonder that the inquiries of the last century were reluctant to announce a preferred position or 'target' population.

While there are clearly technical issues involved, how many people we want is fundamentally a political question or more particularly, a values-based question. My impression is that those who think about this issue fall into two groups. The first prefers slower or no growth and a prudential approach to population, while the second prefers a total population that emerges from the demands of the economy. So far, the second group, those wanting a "bigger" Australia, have succeeded, not only in policy terms, but in controlling the policy agenda, by ensuring that population issues are permanently confused with the immigration intake.

The thing about population, though, is that the longer we delay even thinking about it, the more constrained our options become. In 1995, demographer Ronnie Harding framed the debate in terms of a choice between 23 million Australians by 2030 or 40 million. But we have already passed 25 million, so obviously 23 million is no longer an option. According to the UN's median projections, if we keep going the way we are, we are heading for 40 million by 2030. Most of these additional people will be living in Sydney, Melbourne and Brisbane.

Unfortunately, it is impossible for Australia's major cities to have it all - to add dramatically to their populations while retaining their general amenity. Infrastructure investment is costly, and not without its own environmental costs. To give just one example: with more people wanting to live in the Sydney basin, the state government is keen to open up more of the Nepean River floodplain for development. According to the government, the resulting need for flood mitigation requires raising the wall of Warragamba Dam by 14 metres. Filling the higher dam will negatively affect the world heritage-listed Blue Mountains National Parks, by inundating many kilometres of wild rivers, environmentally-significant bushland and remaining Aboriginal sites.

Public transport is portrayed as "green", yet rail lines and light rail cover more and more of the city in concrete, adding to heat sink effects and requiring the sacrifice of more and more street trees. High density housing leaves little room for gardens. There is little recognition, either by governments or developers, that high rise requires more, not less, recreational space to be set aside.

People living in Sydney and Melbourne complain about the length of their "commute". More and bigger roads will be built, but inevitably they, too, will clog up with cars. With continually increasing population, there is no such thing as "congestion busting" infrastructure.

Australia's cities are among the most liveable in the world, because their populations are relatively low, and they retain substantial areas of urban and near-urban open space and bushland. Continued population growth will destroy that heritage. Is that really what we want?