Fig. 1: Differential-equation model (DEM).
From: Multidecadal dynamics project slow 21st-century economic growth and income convergence
a shows gross domestic product (GDP) per capita (in inflation-adjusted purchasing-power-parity (PPP) units) compared to GDP per capita growth (purple lines show DEM fits)25,31,67. Country-level data come from the 95 large countries used by Tilman et al.35 (accounting for ~90% of the world’s population; see Methods and Supplementary Table 1), and country-level GDP per capita growth rates are 11-y moving averages, to reduce noise. b shows world GDP per capita projections that the fitted DEMs could have made starting in 1980, 1990, 2000, 2010, and 2020, compared to Shared Socioeconomic Pathway (SSP)15 projections to 2100 (calculated from regional projections, weighting by population; see Methods). Global DEM projections are aggregated from income-group-level projections assuming the United Nations Medium population scenario56. Bars at right show ranges of 2100 GDP per capita projections from the DEM (purple, solid) and asymptotic DEM (purple, dashed) projecting forward from different years (1980–2020). Distributions at right show the ranges of 2100 GDP per capita projections of 1000 bootstrap runs (see Methods) of the DEM (purple, solid) and asymptotic DEM (purple, dashed) fits, each starting in 2020. c shows projections (purple, dotted) that switch from DEM-projected GDP per capita growth rates to SSP5-projected growth rates in the years indicated.
