As headlines warn of falling birth rates and a “world gone gray,” a more urgent and overlooked story is unfolding: in too many places, women and girls are still being failed – with profound consequences for human health, economic growth, and sustainable development.

This week will mark the 35^th World Population Day, a day established to focus attention on how population trends – growth, decline, migration, urbanization – shape our shared future. These dynamics influence everything from natural resource use and governance models to, over time, relationships among nations. Understanding where and how populations are changing allows us to plan more effectively and strategically for the future, and to steward our resources toward development success that can be truly sustained.

Yet the dominant narrative today – focused primarily on declining populations – paints an incomplete picture. Countries around the world today are at vastly different stages of the “demographic transition” – the shift from high mortality and fertility rates to low. While some countries face population decline, others continue to grow rapidly. As a result, we are living through a moment of extreme demographic diversity, with stark implications for the global economy, migration, and security.

An Era of Demographic Diversity

As of 2024, 63 countries had reached peak population; 48 more are expected to do so in the next 30 years. But the populations of the remaining 126 countries – including heavily populated countries like India, Indonesia, Nigeria, Pakistan, and the United States – are projected to grow well into the second half of the century. All told, these trends indicate that global population will likely continue its upward trajectory for decades to come – though the trends in each country will vary widely.

This era of demographic diversity demands a nuanced approach. Applying a population lens to social, economic, and environmental goals helps guide investments that can address the challenges of today while setting the stage for improved outcomes in the future.

Rapid Growth and Youthful Age Structure Persist

A deeper examination of population trends in countries that remain in early stages of the demographic transition provides a powerful example. According to the UN Population Division, nine countries are on track to at least double their populations by 2054. Three of these – Chad, Mail, and Niger – are in the Sahel, a region already grappling with political violence, climate impacts and environmental degradation, and food insecurity.

Youthful population structures – with a high share of children compared to working-age adults – can create enormous development challenges. In the Sahel, high fertility rates, often driven by gender-based discrimination and gender inequities, are a central factor. In Niger, 76% of girls are married before age 18, and nearly a third are married before age 15, putting both young mothers and their children at heightened risk and curbing opportunities for education and economic participation.

This pattern is echoed around the world: in Afghanistan, where sustained conflict and Taliban rule have disrupted access to reproductive health services; in rural Guatemala, where one in four adolescent girls are pregnant or already mothers; and in Uganda, where growing populations are straining the local natural resource base.

The Real Demographic Imperative

Calls to boost birth rates in response to population decline ignore the unfinished business of reproductive health and rights – especially in countries where high fertility reflects a lack of access and autonomy, not choice. Access to high-quality family planning and reproductive health programs underpins rights and opportunities for women and girls in many corners of the world. These rights and opportunities accrue to the individual, and in places experiencing rapid population growth, serve as a down payment on sustainable development through progress that accelerates the demographic transition.

Understanding of this demographic reality lends validity to multisectoral approaches that recognize the multiplicity of challenges and opportunities people navigate in their lives. For women and girls the world over, there are vast untapped opportunities to integrate women’s empowerment and access to reproductive health care in efforts to build climate resilience, advance peace and security, and alleviate poverty.

Yet global support for reproductive health is backsliding. Since 2019, funding for high-quality, voluntary family planning has been on steep decline, even as the number of people of reproductive age continues to rise. The United States, once a global leader in this arena, has sharply scaled back its commitment to this linchpin of human progress – despite overwhelming evidence of the benefits.

Alarmism over population decline oversimplifies today’s complex demographic landscape.

Population trends offer vital insight into how people live today and how we can invest in the shape of our world tomorrow – particularly in refocusing our attention on the unfinished agenda for women and girls.

Kathleen Mogelgaard is President and CEO of the Population Institute.