New Delhi, Oct. 12 -- FOREVER, IT TURNS out, was temporary. For much of the 2010s economists worried that interest rates would remain near zero indefinitely, held down by too much saving and too little investment. All of a sudden, the reverse is true. Borrowing costs are leaping across the rich world and governments are starting to sweat.

On October 5th the yield on America's ten-year bonds topped 5.3%, its highest in more than 20 years. Even in Japan, long a byword for near-zero rates, the ten-year yield has climbed above 3% for the first time since 1996. The median ten-year government bond in the rich world now yields 4%, the highest in more than 15 years and over 2.5 percentage points above the average in 2015-19 (see chart 1). A new ...