Long-standing historical dynamics suggest a slow-growth, high-inequality economic future

Long-run economic growth is deeply uncertain, but will profoundly affect societal scale, well-being, and challenges. Statistical forecasts, expert opinions, and socioeconomic scenarios from integrated assessment models (IAMs) project an order-of-magnitude range of 2100 global GDP per capita values, with an even wider range for today’s developing countries. Definitive multidecadal predictions are impossible, but here we show that a long-standing historical relationship between GDP per capita growth and GDP per capita is most consistent with 21st-century scenarios projecting relatively slow economic growth and high inequality, though still projecting rising affluence in all regions. We show that a simple differential equation-based model that empirically fits this relationship to a Kuznets curve would have, since 1980, consistently projected a 21st-century economic future similar to the Shared Socioeconomic Pathway (SSP) scenario SSP4. Moreover, we show that the Kuznets model’s projections from 1980 onwards would have consistently outperformed short-term IMF forecasts for the 2010s, except in low-income regions, where both tend to over-project growth. We show that a complex empirically grounded IAM (International Futures, IFs) produces nearly identical 21st-century GDP per capita projections as the Kuznets model. Compared to the SSP scenarios, the IFs model projects a 21st century with relatively high poverty and population growth, and moderate energy demands and GHG emissions.