Multidecadal dynamics project slow 21st-century economic growth and income convergence

Future economic growth will affect societal well-being and the environment, but is uncertain. We describe a multidecadal pattern of gross domestic product (GDP) per capita growth rising, then declining, as regions become richer. An empirically fitted differential-equation model and an integrated assessment model—International Futures—accounting for this pattern both predict 21^st-century economic outlooks with slow growth and income convergence compared to the Shared Socioeconomic Pathways, similar to SSP4 (“Inequality”). For World Bank income groups, the differential-equation model could have produced, from 1980, consistent projections of 2100 GDP per capita, and more accurate predictions of 2010s growth rates than the International Monetary Fund’s short-term forecasts. Both forecasts were positively biased for the low-income group. SSP4 might therefore represent a best-case—not worst-case—scenario for 21st-century economic growth and income convergence. International Futures projects high poverty and population growth, and moderate energy demands and carbon dioxide emissions, within the Shared Socioeconomic Pathway range.