We build our reference scenario (business as usual scenario) based on UN population medium fertility projections with GDP per capita rates converging to 1% over time (consistent with other IAMS), and GHG per capita projections for each gas. The emissions per GDP rates reflect trends over the last decade, converging to business as usual rates of decreasing improvements over time. The resulting projections are consistent with trajectories between RCP8.5 and 6.0. For  more information, please consult the C-ROADS Reference Guide.