WASHINGTON—U.S. unit labor costs surged in the third quarter, while productivity declined at its sharpest pace since 1981, adding to signs that high inflation could last for a while. The Labor Department said on Thursday that unit labor costs, the price of labor per single unit of output, increased at an 8.3 percent annualized rate last quarter after rising at a 1.1 percent pace in the April-June quarter. Outside the coronavirus distortions in 2020, the jump in labor costs last quarter was the largest since the first quarter of 2014. Labor costs advanced at a 4.8 percent rate compared to a year ago. Economists polled by Reuters had forecast unit labor costs accelerating at a 7.0 percent pace. The report followed on the heels of news last month that wage growth in the third quarter was the largest on record. The pandemic has upended labor market dynamics, leading to 10.4 …