“In this presentation, I make certain observations grounded in global data. First, that the models to explain population change are Euro-centric and have limited application to non-Western societies. Second, unlike Western societies, non-Western societies have divergent demographic futures, characterised by continued rapid growth in some regions and consequential declines in others. Third, the drivers and experiences of population decline in non-Western societies differ from those of Western societies and there is, therefore, a need for new models to understand and explain them. These unique drivers of population decline in non-Western societies make population decline consequential to future improvement of their societies and call for clear policy responses grounded in science,” said Alex Ezeh in the fourth STIAS public lecture of 2025.
Ezeh pointed out that concern about rates of population growth has been a constant feature in global development discourses. “With climate change posing an existential threat today, this concern has not abated. Starting in the 1970s, population ageing began to gain momentum, especially in Western and high-income societies with concerns focusing on the effects of rapid ageing on pension systems and the care economy,” he explained. “The past two decades, however, has witnessed a new concern around population bust – a significant and sustained decline in a country’s population size. All these have created fuzziness on the role of population in the future improvement of society.”
“Are we growing too fast? Are we declining too fast? What role does or can migration play in addressing rapid growth or decline of populations?” he asked.
Dr Ezeh is Dornsife Professor of Global Health and Associate Dean for Human Rights and Global Health at the Dornsife School of Public Health, Drexel University. His work focuses on urban health, population change, and models to strengthen knowledge-based institutions. Previously, he served as the founding Executive Director of the African Population and Health Research Center (APHRC), guiding APHRC to become one of Africa’s foremost research institutions. He also initiated and directed the Consortium for Advanced Research Training in Africa. He serves on numerous international and nonprofit boards, including the UN High-Level Advisory Board for Economic and Social Affairs and the Guttmacher Institute. He recently co-chaired the Second Lancet Commission on Adolescent Health and Wellbeing which released its report in May 2025. He received the London School of Hygiene and Tropical Medicine and Royal Society for Tropical Medicine and Hygiene’s 2020 George MacDonald Medal; the World Academy of Sciences 2018 Prize for the Social Sciences; and, holds a PhD and two Honorary Doctor of Science degrees.
Ezeh explained that the global population is 8.2 billion currently, by 2050 it will be 9.7 billion and by 2100 10.2 billion.
“But population size is actually an irrelevant conversation,” he said. “What matters is the rate of change – both growth and decline – of a country’s population size.”
Ezeh is interested in understanding the rate of growth and decline of populations in non-Western societies, which he explained as countries that did not originate or are heavily influenced by European and Western-derived traditions. They are defined in the UN Sustainable Development Goal grouping of regions as Europe (excluding some parts of southern and eastern Europe), North America (USA and Canada), and Australia and New Zealand (ENANZ).
Ezeh explained that the Demographic Transition Theory, which traces changes from high to low birth and death rates as societies attain more technological, education (especially of women), and economic development, is built on the experiences of Western societies and fits their experiences of demographic change quite well. Although the expectation has been that non-Western societies will follow the same trajectory, current evidence suggests that the demographic transition model may not fit the experiences of non-Western societies. Ezeh explored why this may be the case. He identified three factors that could explain why non-Western societies are following a different path in their demographic transition compared to Western societies.
“These factors include the differential role of migration, the differential pace of fertility decline, and reverse momentum for growth (or momentum for decline) which is specific to non-Western societies. These factors, together, create a new pattern of demographic transition in non-Western societies that differ fundamentally from those of Western societies”, he noted.
With respect to migration, he pointed out that the ENANZ group is a net recipient of migration inflows with an average of 2.5 to 3.2 million net in-migrants per year between 2025 and 2100. Africa, Asia, Latin America and the Caribbean, lose people every year through out-migration. Africa will lose nearly 1 million each year and Asia between 1.4 to 2.4 million annually between 2025 and 2100 to migration. Who moves and who is allowed to enter another country is not a random event. Migration policies in Western societies often favour the in-migration of younger individuals who emigrate with their productive and reproductive potentials. The divergent migration flows in Western and non-Western societies is also rooted in Western societies’ colonial past and their long history of multicultural and pluralistic values that are more accommodative of immigrants.
“Negative net migration will increase the pace of population decline and create an existential threat for many non-Western societies.”
In addition, he noted that “it is the pace of fertility decline, rather than low fertility, that drives future changes in population size. In Western societies, it took centuries for fertility to drop from its peak level to below replacement (about two children per woman). In many non-Western societies that have achieved below replacement level fertility, this process took place within a couple of decades. In France, for example, it took 220 years to move from the peak fertility to below two children per woman, while in Ukraine it took 39 years and in Hong Kong only 18 years.”
“When fertility declines slowly over a century or longer, it does not affect the age structure of the population,” said Ezeh. “However, when fertility drops quickly to below replacement over two or three decades, there is a dip in the base of the population pyramid, which continues and over a relatively short period, creates a new and distinct shift in the age structure with an inherent momentum for decline.”
While Western societies will not experience momentum for decline, many non-Western societies would, even at the same levels of fertility. This third factor, momentum for decline, would create different patterns of demographic change between Western and non-Western societies with below replacement level fertility.
“The 2024 Revision of the UN World Population Prospects projects the same fertility rates for Canada and Jamaica for 2025-2100, for instance. However, while Canada’s population is projected to increase by 34% (from 40 million to 54 million) between 2025 and 2100, that of Jamaica is projected to decline by 62% (from 2.8 million to 1.1 million).”
“In Hong Kong, the number of women of reproductive age (15-49) is projected to decline from 1.8 million in 2025 to 186,000 by 2100 – an 89% drop. Even though fertility is projected to increase from 0.74 in 2025 to 1.2 children per woman by 2100 (a 62% increase), the total number of births is projected to drop from 39,000 in 2025 to less than 6,000 per year by 2100.”
“The pace of population decline in non-Western societies with rapid declines in fertility rates will be fast, consequential, and very different from the experiences of Western societies,” said Ezeh.
“While the population of many Western societies will continue to grow, some by as much as 60% (like Australia), those of many non-Western societies with similar levels of fertility currently, will decline by more than 50% by 2100.”
“More importantly, increasing numbers of non-Western societies will experience rapid declines in their population size by 2100. In the 1950s, about 279 countries and territories experienced high rates of population growth (above 0.69% per annum). By 2025 this number had dropped to 158 with 71 countries and territories experiencing negative growth. By 2100, 199 countries and territories will be experiencing negative growth while only 7 will have positive growth rates of 0.69% or higher.”
What we do know and what we need to know
Ezeh pointed out that we know a lot about how policies and programmes can induce lower fertility, but can they help to increase fertility in very low fertility settings? We simply don’t know what policies and what levels of change in fertility rates are needed to reverse the momentum for decline.
“As an example – South Korea spent more than $200 billion in a bid to increase their fertility levels – it did nothing; fertility rates continued to decline in the country. What may be needed is an evaluation of the various components of the policy and exploration of other approaches not currently included in the policy like facilitating more shared responsibility for childrearing between fathers and mothers; reducing taboos and stigma around non-marital childbearing, and addressing broader gender inequality in the country.”
“We also need to rethink migration policies from a non-Western perspective. This means understanding the right to leave versus the right to enter. As many non-Western societies come to appreciate the compounding impact of negative net migration flows, especially of their young and better-educated population, on the rapid decline of their populations, might the right to leave become more contentious than the right to enter? It is important to note that the right to leave is not universally shared and emigration remains highly contested, especially in many autocratic countries. More research is needed to fully understand the role of migration flows in population change in Western and non-Western societies.”
“Historically, responses to population concerns have often taken a coercive stance, impinging on the rights of individuals, especially women. We must avoid emotional and irrational responses,” he continued. “Coercive policies are neither effective nor sustainable and conscious efforts must be made to avoid mistakes of the past and to ensure respect of individual rights in any effort to address concerns around low fertility or rapid declines in population size.”
“We need new models of demographic transition that adequately captures the experiences of non-Western societies. And discussions about negative population growth must go beyond ageing, pension systems, and the care economy. It needs to address consequential declines in population sizes of non-Western societies with below replacement level fertility and its implications for various sectors of society, including education, housing, the environment, and health and wellbeing. Attention must also be paid to regions that continue to experience rapid population growth rates such as West and Middle Africa. We need honest, well-reasoned approaches to address both continued rapid growth in some regions and rapid decline in others. We need to invest in research to fully understand population change in global context.”
In the lively discussion that followed, Ezeh was challenged to explain more about population growth in Africa as well as the impact of climate change.
“Africa may be closer to the Western model of population decline than to the experiences of non-Western societies. In sub-Saharan Africa (SSA), fertility started to decline around 1980. Forty-five years later, it is still above 4 children per woman. Despite differences across countries and regions in SSA, fertility is projected to still be above 2 children per woman by 2100, meaning that it will take the region more than 120 years to achieve below replacement level fertility. Over this period, the age structure of the population will change only minimally, meaning that the impact of reverse momentum will be negligible in the region”.
“The relationship between climate change and population is not linear,” he said. “It’s about what we do as humans. If population grows at a reasonable rate, the change in size can be meaningfully accommodated with limited consequences for the environment.” However, as many regions achieve socio-economic growth, environmental pressures will increase, primarily due to changes in consumption patterns.
“Based on the evidence presented here, a more concerning fact is the growth in the populations of Western societies, which already have much higher carbon footprints. The non-Western societies with high carbon footprints currently, are likely to experience significant declines in their population sizes. Those with more rapidly growing populations have very low carbon footprints. With its abundant sunlight – Africa does not need to rely only on fossil fuel to power its growth. Expanding access to green energy in Africa is feasible; it is only constrained by political, rather than economic or technological, constraints”.
He noted that to some extent population growth in Africa will compensate for declines in other regions – it’s projected to increase from 1.5 to 2.5 billion by 2050 and 3.8 billion by 2100 – accounting for about 38% of the global population.
“But it’s about the rate at which the numbers change, not the absolute numbers, that matter. The fast rate of growth in some parts of Africa is too high to sustain investments to improve human capital. Investments in health, nutrition, education, and employment are critical to supporting the population to achieve its full potential. When the population doubles every 20 years so, no central government can sustain investments to maintain current levels of inadequate coverage of basic services. In such settings, unmet expectations may result in constant agitations for change of government. The recent declines in donor support for development programs, including family planning, could further worsen already dire situation in some African countries by increasing fertility and population growth rates.”
Asked about how to address the negative net migration rates in non-Western societies, Ezeh noted the “need to create an enabling environment for young people to want to stay in their countries of origin. Demography is not destiny. Political leadership, policy instruments, and programmatic action can radically shift the projected course and trajectory of population change.”
“These issues go beyond the nation state,” he concluded. “We need to bring regions together. There are positive and negative outliers in every region. They can learn from each other about approaches to achieving sustainable rates of population change. While conversations around population concerns can be emotive, having such conversations is key to developing a clear and pragmatic framework to move forward.”
Michelle Galloway: Part-time media officer at STIAS
Photograph: SCPS Photography