The last chart is a bit different. It concerns Piketty’s theory that capitalism has a “central contradiction”: when the rate of return on capital exceeds the rate of economic growth, inequality tends to rise. (That’s because profits and other types of income from capital tend to grow faster than wage income, which is what most people rely on.) The purple line shows Piketty’s estimate of the rate of return on capital at the world level going back to antiquity and forward to 2100. The yellow line shows his estimate of the global growth rate over the same period.
The important point to note is this: setting aside the period from the late nineteenth century to the early twenty-first century, which is roughly what we would call modernity, the growth rate has been below the rate of return, implying steadily rising inequality. The twentieth century, far from representing normality, was a historic exception that is unlikely to be repeated, Piketty argues. In the coming decades, he says, the growth rate will most likely fall back below the rate of return, and the “consequences for the long-term dynamics of the wealth distribution are potentially terrifying.”