Republicans hit another roadblock on Monday in their quest to repeal or weaken recent environmental rules restricting methane emissions.

In a split ruling, the federal appeals court for Washington, D.C., told EPA Administrator Scott Pruitt that he cannot suspend enforcement of the agency’s “methane rule” while his staff considers whether to rewrite it.

The ruling is a rare victory for climate advocates during the Trump administration—and their first win in court this year. Methane, the key ingredient in natural gas, is also a super-efficient greenhouse gas. Each molecule of methane traps dozens of times more heat than each molecule of carbon dioxide, making methane a big short-term influence on the intensity of global warming.

The ruling suggests that some of the Obama administration’s environmental rules may prove more resilient than once seemed. In May, the Senate failed to repeal a slightly different “methane rule” from the Bureau of Land Management. That rule requires pre-existing oil and gas wells to limit their methane emissions—but it only applied to operations on federal or Native American land.

The EPA’s methane rule—which was upheld in court on Monday—takes a broader approach. It mandates that all new oil and gas operations everywhere in the United States reduce their methane emissions.

The Obama administration published the final version of the EPA rule under the authority of the Clean Air Act last year. It would have gone into effect on June 3, 2017, after which oil companies would have had to begin measuring waste methane emissions so they could repair leaks and faulty equipment.

Instead, there was a flurry of legal activity. In March, Donald Trump ordered a review of the rule’s legality in his omnibus executive order on climate change. A month later, the EPA began to undertake it.  

In late May, fossil-fuel companies begged the EPA to put the deadline for enforcement off. Pruitt granted their request twice over. First, he delayed the entire rule’s implementation by 90 days. Then, two weeks later, he announced that the rule would lose the force of law for two years. The EPA would fully reconsider the methane rule’s standing under the Clean Air Act, he said.

Thirteen states and six environmental groups immediately sued Pruitt, alleging that many of the fossil-fuel companies’ problems with the rule had already been addressed when the EPA was writing it. They alleged he had no right to put a 90-day stay on the rule’s implementation. It wasn’t that the rule had been illegally written, they alleged—it was just that Pruitt didn’t like it.

A panel of federal judges agreed with them on Monday. Pruitt’s decision was “arbitrary, capricious, [and] in excess of statutory . . . authority,” they said. They struck down the 90-day stay, allowing the EPA methane rule to gain the force of law.

The judges write that the “administrative record”—that is, the body of scientific and legal evidence that Obama’s EPA put together while writing the methane rule—already addressed all the oil and gas firms’ complaints. The rule was sometimes even changed at the urging of the firms themselves, they added.

But the news is not all good for climate advocates. The panel said that the EPA was free to begin the process of rewriting the methane rule. And Judge Janice Rogers Brown, the only member of the panel nominated by a Republican president, dissented from its ruling. Blocking the temporary 90-day stay simply wasn’t within the court’s powers, she said, because only final EPA decisions are reviewable by the courts.

Just because environmental groups “are anxious to see their victory implemented and impatient with [the] delay does not make EPA’s action final,” Brown writes. “It may be annoying, disappointing, ill-advised, even unlawful, but that does not transform a stay to facilitate reconsideration into ‘final agency action.’”

These arguments could carry more weight if the case rises to the more conservative Supreme Court.

Both the EPA and BLM methane rules were meant to help bring about President Barack Obama’s commitment for the United States under the Paris Agreement on climate change. Obama hoped to cut the greenhouse-gas emissions from fossil-fuel companies by 40 percent by 2025, as compared to 2012 levels.

Reducing methane emissions is key to those goals. The amount of methane in the atmosphere has surged since the mid-2000s, though scientists aren’t sure if that is due to the global fracking boom or some other combination of causes.

Methane leaves the atmosphere within a century of its release—much faster than carbon dioxide, which can linger for a millennium—but it captures heat much more powerfully. Its effects can also remain long after it is gone: A recent study found that methane released today could continue to raise sea levels for another 800 years.