NEVER before had America’s Supreme Court acted in such a way. On February 9th, divided five to four along partisan lines, the justices placed a stay on a regulation before its review in a federal appeals court. The rule in question? The Clean Power Plan, Barack Obama’s flagship environmental policy. The plan gives orders to each state which, when totted up, should see the removal of 870m tonnes of carbon dioxide from power-station emissions by 2030 (as measured against 2005 levels). States maintain some flexibility over how and when to cut emissions. But the plan required each one to submit plans for doing so by 2018 and to show some progress on them by 2022. The deadline for submitting first plans for cutting back was supposed to be September; the court’s decision put paid to that schedule. Then Antonin Scalia, a conservative member of the bench, died just days after it was announced. His demise may mean the survival of the Clean Power Plan.

The United States Court of Appeals in Washington is considering a challenge brought by 27 mostly Republican states against the rule. Fossil fuel firms and others are also involved. The legal obstacles were expected; the fact that the regulation depends on the Clean Air Act of 1970, rather than on new legislation, shows Mr Obama’s administration thought the courts more likely to support the rule than Congress. And recent rulings suggest why. In 2007 the Supreme Court declared carbon dioxide a pollutant, placing it under the EPA’s remit. It then upheld most of an agency rule requiring new or rebuilt factories and power plants to use the “best available control technology” to limit their emissions of greenhouse gases in 2014. That year the justices also supported the EPA’s regulation of pollution that drifts over state lines. But the agency was rebuked for its overreach in 2015: the Supreme Court reprimanded it for regulating mercury, arsenic and other substances emitted by power plants without taking proper account of the costs. Scalia led the charge.

If the federal appeals court rules in favour of the Clean Power Plan, as it may well later this year after oral arguments on June 2nd, an appeal will almost certainly be brought to the chief justices. Just four votes are required to « grant a writ of certiorari »—the taking up of a case—so Scalia’s death will not prevent proceedings of the highest kind. What happens next may depend on whether or not Mr Obama manages to nominate his successor. If he does, it is likely the freeze on the rule will thaw. But probably not before June 2017. If he doesn’t, a 4-4 deadlock would result in the lower court’s decision holding sway instead. Alternatively, the rule’s fate may be determined by the next president and his or her inclinations. In three of these four scenarios, however, it looks likely that the Clean Power Plan will endure. Even so, the delay in the meantime will undermine its potency.

As the regulation forms the core of America’s climate pledges in Paris last December—to cut emissions 26-28% below 2005 levels by 2025—this is a serious problem. American and Chinese co-operation made the UN deal possible in the first place. And although weak in many ways, it is the most significant step ever taken to address climate change. An empty seat on the bench of the Supreme Court has improved its chances of success.