One of the most powerful climate pollutants on earth, hydrofluorocarbons or HFCs, account for a small portion of U.S. climate pollution, but scientists say it’s important for countries to urgently cut them just because they’re so potent—and growing.

Efforts to cut HFCs became more difficult both in the U.S. and globally on Tuesday, when a federal appeals court in Washington, D.C., ruled that the Environmental Protection Agency has overstepped its authority in regulating HFCs under the Clean Air Act.

…

“As we’ve moved away from ozone destroyers, we’ve moved toward climate destroyers,” said Michael Wara, a climate and energy law professor at Stanford University unaffiliated with the case.

…

The regulation was seen as a way to accomplish the goals of the Kigali agreement without requiring it to be ratified by the Senate, which is unlikely to do so under GOP control, Wara said.

…

The ruling calls into question the U.S. ability to control HFCs without congressional action — something unlikely to happen because Trump opposes new regulations and Republicans are not inclined to create new ones, Wara said.

Wara said the court’s decision could be appealed in two ways. The federal government or another intervener in the case, such as NRDC, could appeal the ruling to the Supreme Court. Or, they could ask the full panel of 11 D.C. Circuit Court judges to review the ruling, he said.