The red solid line in the plot represents the FeliX BAU prediction, which is calibrated to historical data from the Maddison Project, a database developed and maintained by the Groningen Growth and Development Centre at the University of Groningen in the Netherlands. SSP projections, shown in dotted lines, are used for validation of the model results.
The BAU scenario uses the central value for population growth (10.6 billion in 2100), while the red shaded region shows the sensitivity of GDP to the 80% confidence interval (CI) for fertility rates (discussed in a previous post). On an absolute basis, GDP is correlated with population (more precisely, the number of able-bodied adults comprising the global workforce), and the outer bounds of the population 80% CI translate to ±9% effect on GDP.
GDP is shown below on a per capita basis in order to isolate the predicted additional contribution of global development to economic growth:
Historical data again comes from the GGDC, and the SSP projections are again displayed in dotted lines. This plot shows a much smaller dependence on population estimates, indicating that global development on a per capita basis is largely independent of fertility rates in the FeliX model.