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In recent years, the idea of having fewer children or not having children at all has been put forward by some climate activists as way to tackle climate change. A few scientific studies have demonstrated some evidence that younger generations view climate change as a reason for intending not to have children.^1,2?This phenomenon may point to the Malthusian theory of the negative relationship between population and environment, whereby population growth is seen to cause environmental deterioration due to higher demand for food, water, land and other materials. With respect to climate change, the expansion from a world of 2 billion people in 1927 to the present world of 8 billion naturally means increased demand for energy, which is still mainly based on fossil fuels. Consequentially, as the global population grows, carbon emissions also increase.??

The impact of population on the environment was first systematically expressed in the form of the ¡°IPAT¡± equation:??

Impact (I) = Population (P) ? Affluence (A) ? Technology (T)?

¡°I¡±, representing environmental impact, is typically measured as carbon emissions; ¡°A¡±, representing affluence, is typically measured as gross domestic product (GDP) per capita. Generally, data on I, P and A are employed to solve for T (T=I/PA).³?While the IPAT equation recognizes that population is not the sole driver of climate change, it assumes linear relationships between population, affluence and technology, and their equal influence as drivers of environmental impact.⁴?However,?if population growth coincides with growth in greenhouse gas (GHG) emissions, we should observe in Figure 1 (below) similar growth rates for both the population component and carbon dioxide (CO₂) emissions, but this is not the case. Countries in the low-income group, where the population grew by almost 40 per cent from 1990 to 2021, experienced growth in CO₂ emissions of less than 5 per cent over the same period. In fact, environment and development researcher David Satterthwaite points out that it is not people who induce GHG emissions; rather, such emissions are caused ¡°by specific human activities by specific people or groups of people¡±.⁵?

Figure 1:?Contribution to the growth in world population and CO₂ emissions by groups of nations classified according to their average per capita income levels, 1990¨C2021.?
Sources: Income Classification, World Bank Atlas method, from World Bank Open Data: World Bank Country?and Lending?Groups:?; total population data from World Bank Open Data: ; CO₂ emissions data from IEA-EDGAR CO₂ (data release: September 2022), .

Essentially, GHG emissions are a result of the consumption of goods and services, which are not distributed evenly¡ªneither across countries nor across population subgroups and locations within countries. Countries where population growth remains high, such as those in Africa, appear to have a much lower share of global GHG emissions (~4 per cent) compared to high-income countries where fertility is low. The fact that approximately 3.9 billion people in the bottom 50 per cent of income distribution contribute only 11.5 per cent of GHG emissions, while the top 10 per cent (771 million) account for nearly 50 per cent of GHG emissions, implies that reducing population growth may not significantly contribute to the transition towards a low-carbon society.⁶?Accordingly, it has been suggested that the IPAT equation be reconsidered by replacing the variable P (population) with C, representing the number of consumers.⁷?This proposed adjustment reflects a shift in focus towards considering the impact of consumption patterns rather than population size alone.

Nevertheless, income levels are expected to increase in low- and middle-income countries, coupled with continued population growth in many of them; thus, such countries will contribute notably to global GHG emissions as energy consumption rises. For instance, in Nigeria, with an annual population growth rate of 2.4 per cent and its current (2023) population of 227 million, it has been shown that population growth continues to exert an almost equally influential role as GDP per capita in driving carbon emissions.⁸?Likewise, projections indicate that energy-related emissions in Africa are expected to remain persistently high. This is due not only to an increased demand for and consumption of fossil-fuel energy, but also to the challenges arising from insufficient financial resources and a lack of regulatory frameworks facilitating the transition to greener energy sources.⁹

However, a rise in the demand for energy linked to increasing incomes should not be justification for keeping people in poverty solely to avoid an escalation in emissions and its effects on climate change. Likewise, a focus on limiting population growth in high-fertility countries to mitigate climate change would not result in a radical reduction in GHG emissions, as the large share of emissions originates from high-income, low-fertility countries. Indeed, there has been a call to explicitly consider justice in the transition to low-carbon and sustainable economies and societies.¹⁰?While there are various forms of justice that could be applied with respect to energy and consumption, one could think of distributional justice following egalitarian, sufficientarian or limitarian patterns. Egalitarian principles aim to reduce disparities among individuals by ensuring that everyone receives an equal quantity. However, to reduce human impact on the global climate system, it is questionable whether every person in the world should have similar access to goods and services, for instance, at the same level of someone living in highly industrialized countries. There is no doubt that this pathway is certainly not sustainable.?

Recently, a new philosophical concept of the sufficientarian principle has been introduced, whereby emphasis is placed on ensuring a minimum threshold of goods or services to fulfil basic human needs, such as those defined by decent living standards (DLS).¹¹ The DLS framework is highly relevant for just transition. Defined as ¡°essential material conditions necessary for achieving basic human well-being¡±,^12??DLS focuses on minimum requirements enabling a decent living standard. This can be differentiated into physical well-being, which includes essential elements, such as having adequate housing, nutrition, sanitation, thermal comfort and health care; and the social dimension, which encompasses factors enabling physical and social connection via transportation and communication technologies as well as access to education.??

Providing DLS requires energy, both for operational services, and to build and maintain necessary infrastructures. If the entire world population was set to achieve DLS, would this compromise climate mitigation? To support a decent standard of living for the global population after 2040, the minimum annual energy requirements are estimated to be 156 EJ yr?1 (¡°EJ¡± is an abbreviation of exajoule, a unit used to measure energy) with population growth and without assuming strong technological efficiency improvements.¹³?Within the middle-of-the-road scenario of the framework for Shared Socioeconomic Pathways (SSP2), which represents the continuation of the current social, economic and technological trends, total global energy demand is projected to be much higher¡ªabout four times the level of minimum annual energy requirements to achieve DLS. The research of Jarmo Kikstra and his colleagues also demonstrates that achieving DLS for all is not incompatible with climate mitigation, since the annual energy requirements would be still much lower than the global total in a scenario in which the global temperature is kept under 1.5¡ãC, especially when taking into account that the energy efficiency improvements associated with climate mitigation policies are likely to reduce the minimum energy requirement.?

Tackling inequity in consumption is considered to be more relevant than population growth for achieving just transition towards net-zero emissions.?

Note that the much higher annual energy requirements under SSP2 are due to excess energy consumption beyond the hypothetical DLS energy needs in most countries. This scenario requires consumption reduction that is in line with the philosophical principle of limitarianism. This principle asserts the importance of establishing an upper threshold for valuable goods, and that policies should be designed to ensure no one surpasses the limitarian threshold.¹⁴?Therefore, tackling inequity in consumption is considered to be more relevant than population growth for achieving just transition towards net-zero emissions.?

Addressing population growth, however, remains crucial in the context of climate action. A larger population means that more people will be exposed to climatic hazards.¹⁵?Population growth is also associated with a reduction in per capita income growth, which, in turn, results in increased poverty.¹⁶?This subsequently increases vulnerability and reduces adaptive capacity. Population thus plays a fundamental role in climate change adaptation efforts, and this calls for a holistic view of the synergies between addressing population and climate change challenges. One example is the work of Camille Belmin and her colleagues,¹⁷?which empirically shows how access to modern energy contributes to fertility decline through female empowerment, health improvement and changes in time allocation. This presents a feedback loop from providing a decent living, i.e., access to modern energy compatible with climate mitigation, which, in turn, contributes to fertility decline and, as a result, a reduction in vulnerability due to a smaller population number. Given that ¡°people are part of the problem of climate change and part of the solution¡±,¹⁸?it is high time to explicitly incorporate population demographic perspectives into climate change action.?

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The author acknowledges support from the European Research Council (ERC) Consolidator Grant under grant agreement number 101002973 (POPCLIMA), and thanks Itza Akari Olgu¨ªn Z¨²?iga for producing Figure 1 in this article.?

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Notes

¹ Steven Arnocky, Daniel Dupuis and Mirella L. Stroink, ¡°Environmental concern and fertility intentions among Canadian university students¡±, in Population and Environment, vol. 34, No. 2 (December 2011), pp. 279¨C292. Available at

² Heather M. Rackin, Alison Gemmill and Caroline Stern Hartnett, ¡°Environmental attitudes and fertility desires among US adolescents from 2005¨C2019¡±, in Journal of Marriage and Family, vol. 85, No. 2 (October 2022), pp. 631¨C644. Available at

³ Thomas Dietz and Eugene A. Rosa, ¡°Effects of population and affluence on CO₂?emissions¡±, in Proceedings of the National Academy of Sciences of the United States of America, vol. 94, No. 1 (January 1997), pp. 175¨C179. Available at

⁴ Thomas Dietz, ¡°Drivers of Human Stress on the Environment in the Twenty-First Century¡±, in Annual Review of Environment and Resources, vol. 42, No. 1 (October 2017), pp. 189¨C213. Available at

⁵ David Satterthwaite, ¡°The implications of population growth and urbanization for climate change¡±, in Environment and Urbanization, vol. 21, No. 2, pp. 545¨C567. Available at

⁶ Lucas Chancel, ¡°Global carbon inequality over 1990¨C2019¡±, in Nature Sustainability, vol. 5, No. 11 (September 2022), pp. 931¨C938. Available at

⁷ David Satterthwaite, ¡°The implications of population growth and urbanization for climate change¡±, in Environment and Urbanization, vol. 21, No. 2 (September 2009), pp. 545¨C567. Available at

⁸ Laura Scherer, Arjan de Koning and Arnold Tukker, ¡°BRIC and MINT countries¡¯ environmental impacts rising despite alleviative consumption patterns¡±, in The Science of the Total Environment, vol. 665 (May 2019), pp. 52¨C60. Available at

⁹ Ibrahim A. Tajudeen, ¡°Examining the role of energy efficiency and non-economic factors in energy demand and CO₂ emissions in Nigeria: Policy implications¡±, in Energy Policy, vol. 86 (November 2015), pp. 338¨C350. Available at

¹⁰ Caroline Zimm and others, ¡°Justice considerations in climate research¡±, in Nature Climate Change, vol. 14, No. 1 (January 2024), pp. 22¨C30. Available at

¹¹ Narasimha D. Rao and Jihoon Min, ¡°Decent Living Standards: Material Prerequisites for Human Wellbeing¡±, in Social Indicators Research, vol. 138, No. 1 (May 2017), pp. 225¨C244. Available at

¹² Caroline Zimm and others, ¡°Justice considerations in climate research¡±, in Nature Climate Change, vol. 14, No. 1 (January 2024), pp. 22¨C30. Available at

¹³ Jarmo S. Kikstra and others, ¡°Decent living gaps and energy needs around the world¡±, in Environmental Research Letters, vol. 16, No. 9, 095006 (September 2021). Available at

¹⁴ Ingrid Robeyns, ¡°Why Limitarianism?¡±, in Journal of Political Philosophy, vol. 30, No. 2 (January 2022), pp. 249¨C270. Available at

¹⁵ Jenna C. Dodson and others, ¡°Population growth and climate change: Addressing the overlooked threat multiplier¡±, in Science of the Total Environment, vol. 748, 141346 (December 2020). Available at

¹⁶ Dennis A. Ahlburg, ¡°Population Growth and Poverty¡±, in The Impact of Population Growth on Well-being in Developing Countries, Dennis A. Ahlburg, Allen C. Kelley and Karen Oppenheim Mason (eds.) (Berlin, Heidelberg, Springer, 1996), pp. 219¨C258. Available at

¹⁷ Camille Belmin and others, ¡°Fertility transition powered by women¡¯s access to electricity and modern cooking fuels¡±, in Nature Sustainability, vol. 5 (December 2021), pp. 245¨C253. Available at

¹⁸ Joel E. Cohen, ¡°Population and climate change¡±, in Proceedings of the American Philosophical Society, vol. 154, No. 2 (June 2010), pp. 158¨C182. Available at

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