US President Donald Trump (L) listens while Supreme Court Justice Anthony Kennedy speaks during a ceremony in the Rose Garden of the White House April 10, 2017 in Washington, DC.

WASHINGTON — The retirement of Justice Anthony M. Kennedy from the Supreme Court could significantly reshape environmental law in the decades ahead and potentially make it easier for the Trump administration to roll back Obama-era climate change policies in the coming years, legal experts said.

In his 30 years on the court, Justice Kennedy was frequently a crucial swing vote on major environmental questions. While he tended to be skeptical of expansive federal regulations that intruded on private property rights, he was also willing to break with the court’s conservative wing in favor of more aggressive government action to limit air and water pollution.

Perhaps most notably, in 2007, he sided with the court’s four liberal justices in Massachusetts v. Environmental Protection Agency to rule that the E.P.A. had the authority to regulate greenhouse gases under the Clean Air Act. That case laid the groundwork for many of the Obama administration’s major climate policies, including the Clean Power Plan to cut emissions from coal-fired power plants.

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“One can comfortably say that he was the single most influential justice for environmental law over the past 30 years,” said Richard J. Lazarus, a law professor at Harvard. “Many of those cases were sharply divided, but the one constant was that Kennedy was in the majority in every single case but one. He was the justice that advocates always tried to persuade, because he was persuadable.”

President Trump is widely expected to nominate a more conservative justice to fill the vacancy. If that nominee is confirmed by the Senate, he or she would give the court a five-seat conservative majority that is likely to take a dimmer view of federal environmental regulation.

It is far from certain that a new court would quickly overturn Massachusetts v. E.P.A. and take away the government’s authority to regulate greenhouse gases altogether, legal experts said. The court has already upheld that ruling twice in subsequent cases, and, during oral arguments in 2014, Chief Justice John G. Roberts Jr. indicated that he considered the case an established precedent.

“What’s more likely is that we could see a new court take a more narrow reading of how the Clean Air Act can be used to regulate greenhouse gas emissions,” said Ann E. Carlson, a professor of environmental law at the University of California, Los Angeles.

For example, Scott Pruitt, the E.P.A. administrator, announced in October that he would repeal the Clean Power Plan and replace it with less extensive carbon regulations on power plants. Environmental groups and states like New York planned to challenge Mr. Pruitt’s actions in federal court, arguing that the Obama-era rules were more appropriate. That argument may now find a less receptive audience if the case reaches the Supreme Court.

By the same token, a future president who wanted to direct the E.P.A. to cut emissions more aggressively in order to tackle climate change could face tougher scrutiny from the court.

The Trump administration is also crafting a proposal to weaken Obama-era emissions standards for cars and light trucks that, in one draft version, would rescind California’s authority to set its own stricter vehicle standards. California has threatened to challenge this move in court, but the state’s chances of prevailing now look somewhat murkier.

The shift at the court could also have broad implications for federal efforts to regulate water pollution. In a sprawling 2006 case, Rapanos v. United States, the court split over how the Clean Water Act, which imposes pollution limits in large bodies of water like the Chesapeake Bay, should extend to smaller rivers, streams and wetlands.

The court’s four conservative justices at the time — led by Antonin Scalia, who died in 2016 — argued for a narrow interpretation of the law that limited its reach. The court’s four liberals argued for much broader wetlands protections. Justice Kennedy wrote a separate opinion that ended up in the middle, establishing an elaborate test to determine which bodies of water could be regulated.

In 2015, the Obama administration published a new rule on water pollution, known as the Waters of the United States, that attempted to follow Justice Kennedy’s guidance. But after farmers and private landowners complained that the rule was overly invasive, Mr. Trump asked Mr. Pruitt last year to replace this rule with a much narrower regulation that followed Justice Scalia’s opinion. Mr. Pruitt’s rollback effort could now have a better chance of success if it goes before the Supreme Court.

Justice Kennedy’s retirement could also affect what types of environmental cases and questions get argued before the court.

“You can imagine the Scott Pruitts of the world feeling emboldened and saying, ‘Let’s adopt a more aggressive stance on deregulation and take our chances before the Supreme Court,’” said Jody Freeman, a law professor at Harvard who was the counselor for energy and climate change in the Obama White House. “By the same token, you also might see environmental advocates try to keep cases away from the court if they think they’ll get a worse decision there.”

Still, even a more conservative Supreme Court could prove unpredictable on certain environmental questions, said Jonathan H. Adler, a law professor at Case Western Reserve University. “The further you push into any doctrinal area, the more likely we’ll see differences emerge among the conservative justices,” he said.

For instance, he said, conservative justices in the past have often differed on whether to defer to the expertise of the E.P.A. and other federal regulators in areas where laws passed by Congress are ambiguous — a principle known as the Chevron deference doctrine — and on when the federal government can pre-empt state actions. The latter question could prove important if California’s vehicle case makes it to the Supreme Court.

It is still unclear whom Mr. Trump might pick as a replacement justice. One of the candidates on his short list, Brett M. Kavanaugh of the United States Court of Appeals for the District of Columbia Circuit, has written opinions that are deeply skeptical of expansive E.P.A. authority. But many other potential candidates have a less extensive track record in this area.

An early test of the new court could come in October, when the justices will hear arguments in Weyerhaeuser Co. v. United States Fish and Wildlife Service. That case revolves around the extent to which the Interior Department can impose restrictions on private land in order to protect endangered species — in this case, the dusky gopher frog in Louisiana.

Justice Kennedy often played a central role in these types of cases, concerned about government intrusions on private property but reluctant to sharply curtail the federal government’s authority under laws like the Endangered Species Act.

“With Kennedy gone, that larger issue is undoubtedly going to receive renewed attention,” said Mr. Lazarus. “It’s a very big deal.”