Bending the curve by 2030: on the path to a population safe harbour

Updated: Aug 30

Commentary by Dr Christopher Tucker, Chairman, American Geographical Society

This article first appeared in The Journal of Population & Sustainability, August 2022, vol. 6.


Half the global population has birth rates below replacement and several advanced nations already have birth rates half that. There is no question that restoring a sustainable population via low birth rates is feasible. There is even a scientific consensus around the non-coercive, empowering strategies focused on women and girls that could expedite the inevitable process of bending the global population curve. The question is simply the level of investment required to make it happen. As such, this article explores the ‘art of the possible’, walking us through how we could approach a safe harbour population of three billion soon after 2100 – a new lower population plateau that would enable humanity to pay down the massive ecological debt it has accrued over recent centuries.

Keywords: population; population restoration; 1.5 TFR by 2030; empowering women and girls; climate restoration

We have been lulled into thinking that our ever-growing population has no role in driving the destruction of our planet. We have also been lulled into believing that the only way modern, prosperous societies can function is through perpetual economic growth that is fundamentally dependent on perpetual population growth. Of those who understand that neither of these propositions are true, still too many seem convinced that nothing can be done about it, short of unethical and coercive measures. This article rejects these notions.

Here we seek to draw attention to the art of the possible in bending the global population curve, in order to avert climate catastrophe, ecological annihilation and the untold human misery, instability, conflict and insecurity born of runaway population growth. This paper will strike many as strange and unrealistic, based on their reading of the many different efforts to ‘predict’ population growth, typically centred on validating or challenging the United Nations population projections. This paper is explicitly not an effort to predict, but rather an effort to determine what demographic dynamics might be desirable for the wellbeing of future generations and feasible with regard to achieving a long-term sustainable human population. In a world where half the global population has birth rates below replacement and several advanced nations already have birth rates half that, there is no question that restoring a sustainable population via low birth rates is feasible. The question becomes, what is a sustainable population for humanity, and how we might achieve this goal without coercion.

For those that say bending the population curve is unfeasible without coercion, we respectfully disagree, and undertake this analysis with a sober commitment to the well-being of our planet, our species and the families and children that will comprise the future of humanity. For those that say it is too late, and that even bending the population curve will not be enough to avert climate and ecological catastrophe, we again respectfully disagree that every action possible should not be taken to increase probability of our collective survival over the coming decades.

Demography runs ‘open loop’, meaning that the modeler sets parameters such as education levels, the average starting date of childbearing, access to family planning technologies, assumptions on longevity and the like, and sees what happens. In this exercise in ‘restoration modelling’ we ask, what Total Fertility Rate (TFR) would need to be encouraged and normalised in order to restore something akin to the historically sustainable population plateau that preceded the runaway population growth of the past two centuries, through ethical, non-coercive and empowering strategies. For those who believe that we have not yet overshot the carrying capacity of our planet, this will appear a silly exercise. And, for those who believe that there is no such thing as just, ethical and empowering strategies for nudging reproductive behaviours and norms toward a more sustainable future, and that any initiative is necessarily coercive in nature, this will seem to be a morally repugnant exercise. To be clear, we reject both of these notions. Humans long ago exceeded our planet’s carrying capacity. There are non-coercive, indeed empowering, strategies available for bending the curve. There is no reason to resort to coercive measures to achieve this goal, as has been attempted in the past. It is important to note that these coercive measures never actually worked at bending the population curve.We recommend conservative goals regarding the survival of humanity, as we may only have one chance to fail. The most conservative baseline is to return to the stable global population at the start of the industrial revolution (1740, roughly 800 million), which was a population our planet sustained for centuries. A less conservative, more aspirational baseline would be roughly three billion (Tucker, 2019a).

We consider this lower population plateau a ‘safe harbour’ which we should all strive for. Per person consumption is far higher now than in the distant past, but there are good reasons to believe that a newer, more sustainable technology mix is possible that would allow a more efficient use of many natural resources with a safe harbour that is, say double the sustainable population plateau that existed before the historic population ‘blip’ that we are currently experiencing. Of course, it would take decades to come close to any such safe harbour, leaving us plenty of time to calibrate our long-term target. In the case of restoration modelling, there is a recognised feedback loop. This feedback loop is based on our appreciation of the scientific consensus that shows that more resources applied to initiatives around girl’s education, integration into the workforce, access to family planning and the promotion of modern reproductive norms can indeed have a powerful impact on TFR (Ripple et al., 2019).

While some may say that it is impossible to ethically achieve a global 1.5TFR over the next decade, from the 2.3TFR (2021) of today, we will assert that the current reproductive norms are much more malleable than most appreciate (PRB, 2020). We argue that ethical, just and empowering investments focused on women and girls – in their education, their integration into the workforce and their access to family planning technologies and programmes, as well as reproductive norms shifting media investments could rapidly change the fertility patterns in most, if not all, nations. This, plainly, includes investments in boys and men which would coax more just, equitable and empowering behaviours toward women and girls. There is a large community of thoughtful practitioners, who have spent decades building data-driven foundations for their programmes’ effectiveness, who would simply argue, ‘Give us the budget to do it, and we will achieve the goal – ethically’.

Modelling the Art of the Possible

This exercise is illustrated in the simple plot below. Total population change is births minus deaths. As in the recent past, mortality levels continue to improve gradually over the coming decades. The total fertility rate (TFR) is assumed to be 1.5 births per woman, i.e., approximately a half child less than the fertility replacement level of about 2.1. Even in this exercise’s assumed peak TFR of 1.5 by 2030, so-called ‘demographic momentum’ would delay any decrease in total population by two decades after the 1.5 TFR change is achieved.

It is important to note that this model assumes that the age of first birth will remain at today’s global average of 25. Measures to end child marriage and children having children would see this average age drift upward slightly. This is certainly a global cultural norm we should all strive to achieve through proactive investment. However, we do not need to rely on that change to occur for us to reach a total population of about three billion in about one hundred years, or around 2125.



The ‘World Scientists’ Warning of a Climate Emergency’ article of November 2019, which had 14,000+ cosignatories from the global scientific community, made it clear that:

"Still increasing by roughly 80 million people per year, or more than 200,000 per day, the world population must be stabilized – and, ideally, gradually reduced – within a framework that ensures social integrity. There are proven and effective policies that strengthen human rights while lowering fertility rates and lessening the impacts of population growth on GHG emissions and biodiversity loss. These policies make family-planning services available to all people, remove barriers to their access and achieve full gender equity, including primary and secondary education as a global norm for all, especially girls and young women. (Ripple et al., 2019, 11)"

It is critical that we begin investing in stabilisation and reduction of humanity’s numbers if we are to avert climate catastrophe. This includes the reduction of fertility in many wealthier nations that are already below replacement value fertility. After all, the carbon footprint of children in wealthier nations can be eight to thirty times the size of that of children in developing nations. A sustainable population that lives within the carrying capacity of our planet must be achieved if any of our other climate and ecological interventions are to have the desired effect. The only foreseeable way to achieve this goal is to empower women and girls in a way that encourages small, educated and prosperous families through the end of the century. This will require achieving a global birth rate in the 1.5 range, sooner than later – recognising that some countries will lag in this demographic transition. The suggestion that we must all passively await some immutable population peak of more than nine billion, ten billion or even eleven billion (as the UN projects) sometime after 2050 is insulting, disempowering and misguided.

In the end, women and girls should enjoy gender equity, everywhere on Earth – as a good in and of itself. In the end, small families – on average – live better. In the end, small families are better for the climate and for the natural world in general. It is entirely possible for humanity to step up to this challenge. But first, we must all collectively embrace the art of the possible. Acknowledgements

Thanks to Mr Peter Fiekowsky for his support in modelling the art of the possible.


Fiekowsky, Peter and Carole Douglis. 2022. Climate Restoration: The Only Future That Will Sustain the Human Race. Irvington, NY: Rivertowns Books.

HIP 2017. Mass Media: Reaching audiences far and wide with messages to support healthy reproductive behaviors. High Impact Practices in Family Planning (HIP). Washington, DC: USAID. (Accessed 1 February 2022).

Penna, Anthony. 2009. The Human Footprint: A Global Environmental History. New York, NY: Wiley-Blackwell.

PRB. 2020. ‘Population of Older Adults Increasing Globally Partly Because of Declining Fertility Rates’. Washington DC: Population Research Bureau. (Accessed 1 February 2022).

Ripple, W.J., et al. 2019. ‘World scientists’ warning of a climate emergency’. BioScience70 (1): 8–12.

Shao, Elana. 2021. ‘More young people don’t want children because of climate change. Has the UN failed to protect them?’ Inside Climate News, 16 November. (Accessed 1 February 2022)

The Track 20 Project, 2019. The S-Curve: Putting mCPR Growth into Context. (Accessed 1 February 2022)

Tucker, C.K., 2019a. A Planet of 3 Billion. Washington, DC: Atlas Observatory Press.

Tucker, C.K., 2019b. ‘A planet of 3 billion by Christopher Tucker – book extract’. World Economic Forum. (Accessed 1 February 2022).

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