TOKYO -- U.S. President Donald Trump's high tariff policy means the global economy is facing "challenging times in uncharted waters," said General Manager Agustin Carstens of the Bank for International Settlements. In an exclusive interview with Nikkei, Carstens also said a 2% inflation target, which many central banks around the world have adopted, is "the right level." After serving as BIS general manager for seven and a half years, Carstens will step down from his post on Monday.