An index of global shares was lower on Wednesday, pressured by choppy trading on Wall Street and a dip in European stocks, as U.S. President Donald Trump's latest tariff threats on auto, semiconductor and pharmaceutical imports injected a sense of caution into the markets.

Among the now-regular Trump tariff announcements is his plan for eventual “reciprocal tariffs”—a concept championed by the president and his loyal trade adviser Peter Navarro that would, if enacted, set U.