KEY POINTS
  • "As real long-term interest rates rise, stock prices fall," but that's probably not the cause of the wild market swings, Greenspan tells CNBC.
  • "The last few weeks are responding to the good part of the tax cut," he says.
  • Greenspan says he's optimistic about growth in the short term due to the new GOP tax reform law.

Former Federal Reserve Chariman Alan Greenspan told CNBC on Thursday the decadeslong bull market in bond prices is coming to an end.

"We are in a bond market bubble" that's beginning to unwind, he said on "Squawk on the Street," as new Fed Chairman Jerome Powell appeared on Capitol Hill for the second time this week. "Prices are too high" on bonds, Greenspan added. Bond prices move inversely to bond yields, which spiked higher in the new year, recently hitting four-year highs of just under 3 percent.