A federal appeals court in San Francisco wants to hear as soon as possible the novel lawsuit brought by a group of mostly teenagers suing the federal government over climate change.

An expedited briefing schedule sought by the youth plaintiffs in the case, known as Juliana v. United States, was set Jan. 7 by the U.S. Court of Appeals for the Ninth Circuit.

In a 2-1 order Dec. 27, the court agreed to hear the Trump administration’s appeal of the case—an initial victory for the government, which has long been fighting to get the case dropped...