KEY POINTS
  • Negative-yielding sovereign debt shot up to $9.5 trillion in May, a 10.5 percent increase from April.
  • Investors have warned of the consequences, with Bill Gross calling negative yields a "supernova" doomed to "explode" some day.

The staggering level of government debt carrying negative yields, after falling from its peak a year ago, is back on the rise.

A slew of factors converged in May to send the global total to $9.5 trillion of sovereign debt — a situation where governments effectively are getting paid to borrow money, according to Fitch Ratings. The total represented a 10.5 percent increase from April.