T ORONTO — Former central banker Mark Carney was sworn in as Canada’s new prime minister on Friday, and will now try to steer his country through a trade war brought by U.S. President Donald Trump, annexation threats and an expected federal election.

He was born near the Arctic, led the central banks of two major economies and has become Canada's prime minister despite never having served in parliament. Climate has been central to the latter part of Carney's career,