The median forecast shown on Figures 2.2–5 is optimistic in two respects: first, because it assumes that productivity growth in the wealthy countries will continue at a rate of more than 1 percent per year (which assumes significant technological progress, especially in the area of clean energy), and second, perhaps more important, because it assumes that emerging economies will continue to converge with the rich economies, without major political or military impediments, until the process is complete, around 2050, which is very rapid. It is easy to imagine less optimistic scenarios