Australia's fertility rate is at a record low.

Last week, Bureau of Statistics data showed Australia's fertility rate was just 1.5 babies per woman in 2023.

Experts say we need a replacement rate of 2.1 babies per woman for our population to sustain itself (when assuming there will be no immigration).

What should we do about it? Falling fertility rates are a global phenomenon, so Australia's not alone.

But is there something deeper we need to discuss?

The global decline in fertility rates

Earlier this year, the medical journal The Lancet published a large study of global fertility trends covering 204 countries and territories.

The authors of the study had some things to say.

They said global fertility rates had declined dramatically since 1950 and would continue declining in almost all countries and territories this century.

They said human civilisation was "rapidly converging on a sustained low-fertility reality".

However, they said, there were going to be comparatively high fertility rates in some low-income regions of the world this century, particularly in some countries in western and eastern sub-Saharan Africa.

It was going to result in a "demographically divided world", they said.

"As much of the planet contends with challenges related to low fertility, many low-income countries will still be facing issues associated with high fertility during the 21st century," they warned.

The graph below shows the decline in total fertility rates (TFRs) in different regions of the world, with forecasts out to 2100.

The report's authors said for nearly all countries outside of sub-Saharan Africa, sustained low fertility would produce contracting populations with fewer young people relative to older people as the century rolled on.

The change in the age structure of high-income countries (such as Australia) would present considerable economic challenges.

But the problems facing higher-fertility, low-income countries would be intense.

"Broadly, over the coming decades, the majority of livebirths will become concentrated in the areas of the world that are most vulnerable to climate change, resource insecurity, political instability, poverty, and child mortality," they warned.

"Many higher-fertility, low-income countries will also face increasingly frequent droughts, flooding, and extreme heat as climate change worsens," they warned.

They said high-income, low-fertility countries would increasingly have to rely on immigration to sustain economic growth.

And, they said, the shifting global distribution of births, with a higher proportion of births occurring in lower-income countries, could make immigration a viable way to address many global issues.

"However, this approach will only work if there is a shift in current public and political attitudes towards immigration in many lower-fertility countries and if there are sufficient incentives in place for people to migrate from higher-fertility countries," they said.

"Continued skilled worker migration to high-income, low-fertility economies — a concept referred to as brain drain — can also have devastating effects on the economies these workers leave behind.

"This underscores the importance of developing ethical and effective immigration policies with global cooperation."

Is this a conversation Australia is ready to have?

One of the most difficult questions

However, the study's authors also broached a controversial topic:

"Although sustained below-replacement fertility will pose serious potential challenges for much of the world over the course of the century, it also presents opportunities for environmental progress," they wrote.

"Alongside strong pro-environmental regulations, a smaller global population in the future could alleviate some strain on global food systems, fragile environments, and other finite resources, and also reduce carbon emissions.

"A 2012 study suggests that if global population were to follow a low-growth rather than a medium-growth path, worldwide carbon emissions would be 15 per cent lower by 2050 and 40 per cent lower by 2100.

"The 2023 Intergovernmental Panel on Climate Change (IPCC) report likewise suggests that low population growth (a result of low fertility) is an important factor in limiting global warming.

"However, increasing consumption per capita due to economic development could offset the benefits of smaller populations."

That's obviously controversial.

Why? Because it's very difficult to publicly wonder what the environmentally sustainable human population might be for different countries (given our state of technology, our modern consumption preferences, and our rapid global burning of fossil fuels) without being accused of certain things.

It's why national debates about fertility rates and future population sizes often skirt the issue.

For example, the last time Australia panicked about our declining fertility rate and population decline was in the late 1990s and early 2000s.

At the time, we had a national debate that contributed to the decision by the Coalition government of John Howard (in office from March 1996 to November 2007) to lift Australia's overall immigration intake to record levels.

That debate occurred in the shadow of a 1994 parliamentary report on the "carrying capacity" of Australia's population. It was also accompanied by a 2002 CSIRO report titled Future Dilemmas: Options to 2050 for Australia's population, technology, resources and environment.

The Business Council of Australia also made a contribution to the debate.

In 2004, it released a 53-page paper titled Australia's Population Future and written by Glenn Withers of the ANU.

And one of the pages in that paper carried a quote from two different people, apparently set in opposition to each other:

Would you say that the conflict represented by those two opposing world views has been resolved since then?

Australia's national debate in the late 1990s and early 2000s didn't seem to resolve them.

Remembrance of things past

In fact, in May last year, we were reminded of the conflicting pressures in that very debate when Ken Henry, the former Treasury secretary, appeared as a guest on Joe Walker's podcast.

Henry told Mr Walker about a conversation he had with Kevin Rudd in 2007, after Mr Rudd had just won the 2007 federal election (which swept Labor back to power after 11 years in opposition).

Here's how Henry remembered his conversation (you can read the whole transcript here):

"I was Treasury secretary, certainly at the time, and I remember having a conversation with Kevin Rudd only a few days after the November 2007 election. In fact, it was the first conversation I had with him after he became prime minister.

"And we were just talking about a whole range of issues, and I think he said something like, 'Oh, and by the way, what do you think the maximum sustainable population for Australia is?'

"And I said, 'Probably 15 million thereabouts.' And he thought I said 50, and he leant forward and he said, '50 million? Ah right, good.'

"I said, 'No, no, I said 15.'

'How can you say that? The population is already much more than 15.'

"And I said, 'I don't think you can argue that human activity on this continent is sustainable, not in any way I think about it. And so I think we'd have to cut our population quite a bit if that's all we're going to do in order to achieve a sustainable population.'

"And he was obviously shocked and obviously disappointed. He may even have been appalled, I don't know.

"And then I said to him, 'But although that's my view, it's also my view that it would be possible to construct a set of policies that would sustain a population of 50 million. 5. 0. That's possible, but it would mean that we'd have to do a lot of things very differently.'

"And in that conversation, I said, for example, we might have to build a whole brand new city for 10 million people, one that doesn't presently exist.

"So then we subsequently in the [Treasury] department — and it wasn't just in the department, there were other people involved in this as well — started exploring where you might build, not a whole brand new city of 10 million, but, say, a number of cities of 1 million, where you'd put them throughout Australia.

Fascinating huh?

In 2009, two years after that conversation between Henry and the then-prime minister, Rudd announced plans for a "Big Australia" with a desire to increase Australia's population to 35 million by 2050 — a 60 per cent increase in the size of the population.

Interestingly, press reports from the time record that Henry publicly expressed concerns about Australia's ability to sustain a 60 per cent increase in the population over the next 40 years.

And it's also interesting to remember that, months later in early 2010, Rudd publicly dampened his enthusiasm for a "Big Australia" when his government ran into political trouble.

"The announcement came as another boatload of asylum seekers — the 102nd to be intercepted since Mr Rudd took office — was placed in detention at the Christmas Island facility, which has reportedly reached capacity," The Sydney Morning Herald reported at the time.

Big demographic changes will occur this century. Perhaps some questions will resolve themselves naturally.