Probabilistic population projections with migration uncertainty

TLDR

Projected populations to the end of this century are crucial for policy decisions, yet forecasts become less reliable over time and deterministic migration projections ignore a major source of uncertainty. The study aims to incorporate a probabilistic migration model alongside probabilistic fertility and mortality models to produce probabilistic population projections for all countries through 2100. The authors combine probabilistic models of migration, fertility, and mortality to generate country‑level projections through 2100. The projections reveal a substantial increase in uncertainty for Europe and Northern America, while uncertainty for Africa, Asia, and the global population remains largely unchanged.

Abstract

Significance Projected populations to the end of this century are an important factor in many policy decisions. Population forecasts become less reliable as we look farther into the future, suggesting a probabilistic approach to convey uncertainty. Migration projections have been largely deterministic until now, even in probabilistic population projections. Deterministic migration projections neglect a substantial source of population uncertainty. We incorporate a probabilistic migration model with probabilistic models of fertility and mortality to produce probabilistic population projections for all countries until 2100. The result is a substantial increase in uncertainty about the populations of Europe and Northern America, with very little change to uncertainty about the population of Africa, Asia, and the world as a whole.