What’s next for carbon emissions regulation in the US?

Between existing levers in the federal government to regulate coal waste or require efficiency measures, options at the state and regional levels, and the strength of private industry, the effort to save the planet from runaway global warming — while hobbled —will go on.

“There’s more than one way to skin a coal plant,” said Patrick Parenteau, an environmental law professor at Vermont Law School.

Todd Snitchler, president of the Electric Power Supply Association, said he expects to see additional regulations that will affect the coal industry, but also that regulators will “tread more carefully” in what they do.

“I would welcome legislative action if the members of Congress think there’s more to be done,” he said. “That seems to be the lesson the court wanted the members to take out of the decision.”

The 6-3 decision ruled that the EPA can’t force the national energy market to switch from one source to another — say, from coal to wind or solar — without express authorization from Congress. That ability was widely considered the EPA’s most effective tool for switching the nation’s remaining coal plants to cleaner power, enabling it to provoke an industrywide transition with one stroke.

Even without that broad tool, it can still force power plants to move away from dirty fuels one at a time, experts said.

“The agency is authorized to limit carbon emissions and impose technical controls at individual power plants,” said Mekela Panditharatne, counsel for the Brennan Center’s Democracy Program.

Doing so would be costly and take time, experts said, and isn’t likely to be the agency’s favored option.

The agency could also mandate that coal plants be more efficient, for example by requiring them to add natural gas as a fuel, or forcing them to add equipment that captures and isolates carbon emissions so they are not released into the atmosphere.

“These technologies can reduce emissions to near zero and would put the costs of pollution cleanup on industry,” said Jay Duffy, an attorney with the Clean Air Task Force.

That option has steep downsides, too, said Parenteau, because making a coal plant more efficient would likely extend its life; adding natural gas would introduce methane emissions, which are far more potent than carbon dioxide; and carbon capture is so prohibitively expensive, any requirement would likely run into legal problems.

“But, being clever, there may be some other approaches for power plants that EPA comes up with,” he said.

The agency is currently rewriting a rule that governs not what coal plants put into the air but what they leave behind — the highly toxic waste called coal ash. Currently the waste is largely kept in unlined pits around the United States. The rule would require coal plants to clean up existing pits and impose strict guidelines for storage going forward — changes that are likely to be so expensive that some plants may be forced to shut down.

When the Tennessee Valley Authority was ordered to upgrade an ash pit at one of its power plants in 2017, the company estimated the cleanup would cost nearly $2 billion.

The EPA is also updating a rule that governs the toxicity of the water runoff from coal plants — another change that, once implemented, would make the cost of doing business for coal plants more expensive.

Meanwhile, the court ruling puts a spotlight on the efforts of individual states and regional compacts, such as one that Massachusetts belongs to, called the Regional Greenhouse Gas Initiative.

That compact between 12 states is a so-called cap-and-trade effort that saw carbon emissions from the power sector drop 53 percent from 2009 to 2020, according to Cooper Tamayo, a spokesman for RGGI. In the same period, customers’ electricity rates declined faster than the national average, Tamayo said.

“Even more important than RGGI itself is the idea that regions have to pull together to form markets,” said Joseph Curtatone, president of the Northeast Clean Energy Council, a trade association for clean energy companies. “RGGI has and continues to be a powerful tool, grounded in the acts of legislatures.”

Recently, Virginia Governor Glenn Youngkin has said he wants to pull out of the initiative. But on the whole, legal experts and clean energy advocates said interest in such compacts appears to be growing, thanks to success in cutting emissions while also raising revenue that gets distributed back to states.

Michigan, Minnesota, and North Carolina are all considering joining RGGI. Another cap-and-trade compact, the Western Climate Initiative, between California and Quebec, has also been successful in lowering power plant emissions.

Another local regional effort — the Transportation Climate Initiative — had been set to help reduce emissions in the transportation sector before the agreement crumbled earlier this year as states backed out. “Even if we cannot resurrect TCI, we need to do something big in the transportation sector to cut emissions and fund public transit,” said Kyle Murray, senior policy advocate in Massachusetts for Acadia Center, a clean energy advocacy group.

At the state level, several experts pointed to the recent Rhode Island law that commits to 100 percent renewable electricity by 2033 as an example of how states can lead. On Thursday, the Baker administration unveiled a new blueprint for how it will rapidly cut emissions by 2025 and 2030, on the way to net-zero emissions by 2050.

“States can also adopt the strong California clean car standards, like Massachusetts has done, and can transition their transit and school buses to clean electric vehicles,” said Janet Domenitz, executive director of MassPIRG. “There are no shortage of opportunities to make progress on climate change, even with this new constraint via SCOTUS.”

Despite the Supreme Court’s ruling, the outlook for the coal industry is not good, with coal output nationally dropping 35 percent from 2015 to 2021, according to the Energy Information Administration.

Private industry is helping with the demise of coal by increasing investment into clean energy, said Mindy Lubber, president of CERES, a Boston-based environmental group that promotes climate action in the corporate world.

She said investors are gravitating away from coal and more often toward clean energy.

“They’ve already invested in this new system,” she said, “They’re not going to turn around.”

Sabrina Shankman can be reached at sabrina.shankman@globe.com. Follow her @shankman. David Abel can be reached at david.abel@globe.com. Follow him @davabel.