The Supreme Court just gutted a major policy tool the US might have used to tackle climate change. Its decision today on West Virginia v. Environmental Protection Agency essentially says that the EPA shouldn’t be allowed to determine whether the US gets its electricity from clean or dirty sources of energy.

That derails previous efforts by the agency to transition the US away from fossil fuels to clean energy sources like wind and solar by regulating the power sector. With the new decision, the agency might be able to push a power plant to install technology to reduce its emissions on-site, but it can’t influence states’ decisions on where they get their energy from in the first place. To make things worse, the premise of the court’s decision could erode any federal agency’s ability to regulate industry in order to tackle climate change and even other major issues.

Now, whether the US can follow through on the climate commitments it’s made on the global stage will depend heavily on individual states’ actions and the ability of a deeply divided Congress to come together to pass legislation. Biden has pledged to slash the country’s CO2 emissions in half from peak levels this decade and achieve a carbon pollution-free power grid by 2035.

Major questions and the EPA

The drama surrounding this case started back in 2015, when the Obama administration took arguably the biggest step the US had yet taken on climate change. At the time, the EPA tried to set new standards, called the Clean Power Plan, that would cut power plants’ greenhouse gas emissions. Before the plan ever went into effect, the Trump administration tried to replace it with its own weaker rule. A federal court blocked that, too, and that left it up to the Biden administration’s EPA to try to craft a new rule to deal with power plants’ climate pollution. The Supreme Court’s decision today affects how that new rule might take shape.

The Verge wrote a primer on the saga surrounding this case earlier this week. But it boils down to whether federal agencies have the authority to interpret more ambiguous language in statutes — in this case, invoking the Clean Air Act to push states to turn to clean sources of energy — or whether it should be left up to Congress to write those kinds of measures into legislation.

The Supreme Court ultimately decided to leave it up to Congress by strengthening something called the “major questions” doctrine. Essentially, it argues that if Congress hasn’t passed legislation that explicitly details how to address an issue of major national significance, then a federal agency doesn’t have the leeway to craft regulation based on its own interpretation.

“It does hamstring federal agencies in cases in which they’re trying to regulate in a way that’s going to have significant impact on the economy,” says Robert Glicksman, a professor of environmental law at the George Washington University Law School. “One of the things that case basically says is if it hasn’t been done before, it’s probably illegal, which is a devastating blow to the ability of agencies to act flexibly and proactively to address new and emerging problems.”

Justice Elena Kagan outlined the high stakes in her dissent. “Whatever else this Court may know about, it does not have a clue about how to address climate change,” Kagan wrote. “Yet the Court today prevents congressionally authorized agency action to curb power plants’ carbon dioxide emissions. The Court appoints itself—instead of Congress or the expert agency—the decisionmaker on climate policy. I cannot think of many things more frightening.”

Since the 1970 Clean Air Act wasn’t written to grapple with climate change, and since Congress hasn’t passed legislation to get the grid running on clean energy, the EPA isn’t left with a whole lot of options in the wake of this court decision.

What climate moves can the US make?

Even so, the agency can still take some actions to cut greenhouse gas pollution — even if those actions aren’t as ambitious as the Obama administration originally intended. The decision that came out today could have been far more restrictive, according to Ethan Shenkman, a partner in the Environmental Practice Group at the law firm Arnold & Porter who previously served as EPA deputy general counsel during the Obama administration. The Supreme Court didn’t question the EPA’s ability to regulate carbon dioxide as a pollutant under the Clean Air Act, which was something that some environmental advocates feared.

“EPA absolutely anticipated this decision,” Shenkman says, and is likely already thinking about what it can still do to limit power plants’ climate pollution in a way that can’t be construed as an attempt to overhaul the nation’s entire energy system. He points to a white paper the EPA put out in April that considers a range of tech fixes for power plant pollution. That includes the use of carbon capture technologies that draw the greenhouse gas directly out of smokestack emissions.

The agency could potentially require that those technologies be installed on power plants that burn coal or gas. That kind of technology, however, has drawn sharp criticisms from environmentalists worried that it further entrenches the nation’s reliance on fossil fuels — which release pollutants other than CO2 that clean energy advocates also want to see eliminated.

With today’s decision, any hopes of cleaning up the nation’s power grid are even more dependent on Congress passing legislation to promote clean energy. But there are roadblocks on that avenue, too.

Democrats have struggled to pass comprehensive climate legislation with a slim majority in Congress, which they could soon lose in midterm elections. West Virginia Senator Joe Manchin has repeatedly derailed Democrats’ attempts to pass a budget reconciliation bill that included $555 billion for climate action. The bill’s climate provisions largely centered on efforts to clean up the nation’s power grid — which were watered down over months of negotiations from a plan that would have penalized utilities for sticking with fossil fuels to a newer iteration that relies primarily on tax incentives for clean energy.

Even passing those watered-down provisions is proving to be a tall order, but advocates haven’t given up on the bill yet. Hundreds of billions of dollars in tax incentives could still go a long way toward slashing power plant pollution, especially with the Supreme Court decision today potentially imperiling any further moves federal agencies might take on climate.

Meanwhile, states are already taking more ambitious steps to phase out fossil fuels. “You’ve seen governors and states over the last several years rapidly pass binding 100 percent clean energy standards. And I think you will see more and more states doing that,” says Jared Leopold, a communications advisor for the nonprofit Evergreen Action.

After all, cleaning up the power sector is the linchpin of any strategy to take serious action on climate change. Electricity is responsible for a quarter of the US’s planet-heating carbon dioxide emissions. And plans to decarbonize other heavily polluting sectors, including transportation and buildings, also rely on a clean grid so that things like electric vehicles and stoves can run on renewable energy instead of fossil fuels.

So even if the Supreme Court just made that task harder, “It’s not a time for people who care about the planet to back away,” Leopold says. “It’s a time for climate advocates, including the Biden administration, to get more aggressive.”