Listless US Stock Market Masks Record Volatility Beneath Surface

A trader works on the floor of the New York Stock Exchange.

Photographer: Michael Nagle/Bloomberg

The placid surface of an equity market that’s treaded water for months is masking dramatic swings underneath, as stock moves whipsaw traders and threaten more turbulence ahead.

Though the S&P 500 Index has notched its narrowest trading range to start a year since the 1960s, according to Barclays Plc, worries over disruptions from artificial intelligence have sparked dizzying swings in one sector to the next. Single-stock volatility stands at about seven times that of the broader market, the widest divergence in at least 30 years, according to the firm.