Humanity After the Peak: Extending Shared Socioeconomic Pathway Population and Human-Capital Projections to 2300

The Wittgenstein Centre’s population projections for the Shared Socioeconomic Pathways (SSPs) resolve each country’s population by age, sex, and six levels of educational attainment, serving as the standard demographic input for global environmental change research. Like most projections, they end in 2100, at the world’s population peak—precisely when pivotal transitions begin. This paper extends these projections to 2300 for 200 countries, retaining the full age–sex–education structure and applying explicit long-run assumptions for fertility, mortality, migration, and educational transition. The global population peaks and then declines over centuries. Under the middle-of-the-road pathway, it falls to 4.2 billion by 2300, with 22.5% aged 80 or older and 16.8% below age 20; under the sustainability pathway, it approaches 1 billion, with the oldest-old share peaking above 30% before stabilising near 26%. In the reference pathway, 23 countries reach their peak population only after 2100, and Africa’s share of the world population rises from 17% in 2020 to 43% in 2300, while Asia’s falls from 60% to 39%. Divergence between pathways increases from a 1.6-fold difference in 2100 to a 16-fold difference in 2300; thus, truncating projections at 2100 understates the consequences of the underlying assumptions. Post-peak decline represents a prolonged demographic regime, not a brief episode, and robust analysis of ageing, labour, care, migration, and environmental change requires population pathways extending beyond 2100 that retain age, education, and geography.