WASHINGTON (AP) — The Supreme Court wrestled Monday with the Environmental Protection Agency's authority to curb greenhouse gas emissions from the nation's power plants, a case that could hamstring the Biden administration's plans to combat climate change.

The justices heard more than two hours of arguments over whether to limit the EPA's power to regulate carbon dioxide emissions from electric utilities on the same day a U.N. science report painted a dire picture of global climate change.

A major report from a U.N. panel of hundreds of scientists detailed how climate change — caused by the burning of coal, oil and natural gas — is already taking a deadly toll and will get worse.

Just how much worse depends on how quickly the world cuts is carbon emissions, with coal being the biggest polluter, the report said.

At the high court, the justices took up an appeal from 19 mostly Republican-led states and coal companies that contend the EPA has only narrow authority to regulate carbon output.

Some conservative justices appeared skeptical of broad EPA authority over carbon dioxide emissions, but there could be obstacles to issuing a major ruling. Among these are arguments from power plant operators serving 40 million people that call on the court to maintain the companies' flexibility to reduce emissions while maintaining reliable service.

President Joe Biden has pledged to cut greenhouse gas emissions in half by the end of the decade, but he has so far failed to win congressional approval of climate change proposals contained in his Build Back Better plan.

A new policy to regulate carbon productions from power plants is not expected before the end of the year, Elizabeth Prelogar, Biden's top Supreme Court lawyer, told the justices Monday.

But the court did not appear interested in Prelogar's argument that it should dismiss the case because there is no current EPA plan in place to deal with carbon output from power plants.

Environmental groups have worried that the court could preemptively undermine whatever plan Biden's team develops to address power plant emissions.

 A broad ruling by the court also could weaken regulatory efforts that extend well beyond the environment, including consumer protections, workplace safety and public health. Several conservative justices have criticized what they see as the unchecked power of federal agencies.

Those concerns were evident in the court's orders throwing out two Biden administration policies aimed at reducing the spread of COVID-19. Last summer, the court's 6-3 conservative majority ended a pause on evictions over unpaid rent. In January, the same six justices blocked a requirement that workers at large employers be vaccinated or test regularly and wear a mask on the job.

West Virginia Attorney General Patrick Morrisey, speaking at a recent event in Washington, cast the power plant case as about who should make the rules. "Should it be unelected bureaucrats, or should it be the people's representatives in Congress?" Morrisey said. West Virginia is leading the states opposed to broad EPA authority.

But David Doniger, a climate change expert with the Natural Resources Defense Council, said the Supreme Court's consideration of the issue is premature, a view shared by the administration.

He said the administration's opponents are advancing "horror stories about extreme regulations the EPA may issue in the future. The EPA is writing a new rule on a clean slate."

The power plant case has a long and complicated history that begins with the Obama administration's Clean Power Plan. That plan would have required states to reduce emissions from the generation of electricity, mainly by shifting away from coal-fired plants.

But that plan never took effect. Acting in a lawsuit filed by West Virginia and others, the Supreme Court blocked it in 2016 by a 5-4 vote, with conservatives in the majority.

With the plan on hold, the legal fight over it continued. But after President Donald Trump took office, the EPA repealed the Obama-era plan. The agency argued that its authority to reduce carbon emissions was limited and it devised a new plan that sharply reduced the federal government's role in the issue.

New York, 21 other mainly Democratic states, the District of Columbia and some of the nation's largest cities sued over the Trump plan. The federal appeals court in Washington ruled against both the repeal and the new plan, and its decision left nothing in effect while the new administration drafted a new policy.

Adding to the unusual nature of the high court's involvement, the reductions sought in the Obama plan by 2030 already have been achieved through the market-driven closure of hundreds of coal plants.

Prominent businesses that include Apple, Amazon, Google, Microsoft and Tesla are backing the administration.

A decision is expected by late June.

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This story has been corrected to fix the spelling of West Virginia Attorney General Patrick Morrisey.

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AP Science Writer Seth Borenstein contributed to this report.