For decades, population growth has been portrayed as one of humanity’s greatest environmental challenges. Policymakers, scientists, and environmentalists have often argued that a larger population places greater pressure on natural resources, increases energy demand, and accelerates carbon emissions. A United Nations survey of 50 Nobel laureates found that more than a third considered population growth and environmental degradation to be among the world’s biggest challenges. The world’s population has more than tripled since the 1950s, reaching nearly 7.8 billion in 2020, and is projected to exceed 8.5 billion by 2030.

At first glance, the conclusion seems obvious: slower population growth should reduce pressure on the environment. However, the relationship between population and environmental impact is more complex than it appears. While the global population continues to grow, many countries are now entering an era of demographic decline. According to United Nations projections, dozens of countries will experience shrinking populations in the coming decades. Europe is already witnessing this trend, while Latin America and Asia are expected to experience this in the 2050s. Japan offers one of the clearest examples. The country recorded its first population decline in the 2015 census and has continued to shrink since then. Has Japan’s population decline significantly reduced its energy consumption? To some extent, yes. According to data from the International Energy Agency (IEA), Japan’s electricity generation in 2024 was about 8 per cent lower than in 2000, while per capita electricity consumption declined by about 6 per cent. Yet these changes do not tell the full story. According to the scholars, the contribution of population decline to a decrease in energy consumption in Japan is limited; in the future, population decline may induce an increase in energy consumption due to the lack of productive labour, and the country may substitute capital........

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