President Trump has dismissed global warming as a hoax, snubbed the Paris emissions pact and scrapped U.S. EPA climate rules.

But executive actions can be fleeting—as the Trump administration has shown by moving swiftly to unravel many of President Obama's climate change policies.

Yet there's a major piece of Trump's climate legacy that could be more enduring: his court picks. The Trump administration has acted expeditiously to fill vacancies on top courts around the country, including the Supreme Court and powerful lower courts that could decide the fate of regulatory challenges and novel lawsuits, like localities suing oil companies for damages caused by sea-level rise. Those judges could be weighing in on climate change cases long after Trump leaves 1600 Pennsylvania Ave.

Trump's judicial appointments rank "pretty high" in terms of his climate change legacy, said Glenn Sugameli, who runs the Judging the Environment project, which tracks judicial nominees' environmental records.

"They're the ones that are going to determine whether the actions taken by the Obama administration, by states and local governments are justified, are legal, are sustainable," he said. And "they're the ones that are going to decide whether the actions taken by the Trump administration are legal."

Richard Lazarus, an environmental law expert and professor at Harvard Law School, said courts have played an "outsized role" in climate policy in recent years because regulators are working with an old law to deal with a problem its authors weren't specifically addressing.

"The reason why the courts play a big role right now is that, whether the executive branch is run by [President George W.] Bush or the executive branch is run by Obama, each time they're kind of stuck with old language," Lazarus said, noting that the 1970 Clean Air Act hasn't seen a major overhaul since 1990.

The Obama administration tried to use the existing language to support the administration's signature climate rule, the Clean Power Plan, and "you can expect that Trump judges would be more skeptical of those activities."

Trump has already picked one Supreme Court justice, Neil Gorsuch, a conservative whose appointment was viewed by some as a nail in the coffin for legal efforts to preserve the Clean Power Plan. Court watchers predict Trump may make one or more additional Supreme Court nominations before his term expires.

Legal experts note that judges' opinions in environmental cases won't necessarily fall strictly along ideological lines, but that conservative judges are often more likely to reject arguments calling for more regulation or trying to fit climate change rules within the existing Clean Air Act.

Lazarus pointed to Brett Kavanaugh, a conservative judge on the U.S. Court of Appeals for the District of Columbia Circuit, as an example of a jurist who "is not ready to give EPA a lot of deference if they're taking language which was crafted at one time and trying to push it at the edges to deal with a problem of another time, like climate change." Kavanaugh, a Bush appointee who sits on the court that hears challenges to Clean Air Act rules, became known as a vocal critic of Obama EPA rules.

Kavanaugh's name was tacked on earlier this month to a list of Trump's potential Supreme Court nominees. Trump has touted the fact that the names on his list—some of whom he has already appointed to lower court jobs—have been vetted by "respected conservative leaders."

The judiciary's role over climate policy could change, Lazarus said. "If Congress steps up to the plate, then the courts won't be so significant."

But recent efforts on Capitol Hill to tackle climate change have foundered, and the political polarization in Congress makes the prospects for such controversial legislation dim. So in the near term, executive actions are likely to continue, as are efforts to unravel them in court.

Beyond challenges to federal rulemaking, many of which are resolved in the D.C. Circuit court, there are other climate lawsuits underway across the country that could ultimately be heard by Trump appointees.

In California, for example, a city and two counties are suing oil companies, arguing that the companies' greenhouse gas emissions are pushing sea levels up. In another case at a federal district court in Oregon, a group of kids is suing the federal government over its contributions to climate change.

Michael Gerrard, director of the Sabin Center for Climate Change Law at Columbia Law School, said he's also expecting to see "a lot more litigation about fossil fuel extraction, especially on federal lands and waters," as the Trump administration seeks to expand domestic energy production.

Can Trump tip ideology?

With widespread vacancies in federal courts at the end of Obama's term and more openings since Trump took office, the administration has the potential to remake the federal judiciary and shape numerous legal decisions related to climate and environmental policy.

Trump has already appointed eight appellate court judges, a rapid pace that's been fueled by the GOP-controlled Senate and pressure from conservative advocacy groups. The administration has focused on longevity over experiences in some cases, ensuring that the judges would shape key legal decisions for years. Brett Talley, 36, was nominated for a federal district court in Alabama even though he has virtually no trial experience.

The swift pace of confirmations is in large part due to a rule change enacted by Democrats when they controlled the Senate and were flustered by efforts to stymie Obama's court picks. In 2013, the Democrats enacted the so-called nuclear option, requiring 51 votes instead of 60 to clear executive branch and some judicial nominees.

Another rule shift in the Senate could signal that Republicans are open to an even quicker approval process that also strips Democrats of what's been their primary leverage in blocking court appointees. The so-called blue slip process allows lawmakers to weigh in on judicial nominees in their states. It was kept in place during the Obama administration, by agreement of Republicans and Democrats. But earlier this month, Senate Judiciary Chairman Chuck Grassley (R-Iowa) threw out the process for some judicial nominees after Sen. Al Franken (D-Minn.) blocked a Trump nominee from his state.

While the pace of appointments is significant, it would likely take years for the Trump administration to equal the influence of the Obama administration, said Jonathan Adler, director of the Center for Business Law and Regulation at the Case Western Reserve University School of Law. He noted that the Obama administration appointed about 40 percent of the federal judiciary in active service. He said if Trump is president for eight years, he could have a similar influence. But it will take years for Trump to tip the ideological balance of the courts, he said.

"What's interesting here is that this administration is moving more aggressively and more quickly than administrations usually do at the beginning of their terms, and that may be a cause or a consequence of the fact that the administration has not been able to do much else, certainly not legislatively," he said. "There is every reason to think this will be a lasting legacy of the Trump administration, but it takes awhile for that effect to really manifest itself."

Still, when Trump was inaugurated, there were more than 110 vacancies on the federal courts, representing about 12 percent of the total judiciary, and the most for any incoming president since Bill Clinton took office, according to Adler.

For now, the effect of Trump's appointments on environmental policy is limited because his appointments have not tipped the balance of liberal and conservative judges in any of the key appeals courts, including the 9th Circuit in California that encompasses Nevada, Oregon, Washington, Idaho, Montana, Alaska, Arizona, Hawaii, Guam and the Northern Mariana Islands. Trump has also not tipped the balance in the 10th Circuit, where federal land cases might be heard, and which includes Utah, Wyoming, Colorado, New Mexico, Kansas and Oklahoma.

The administration has nominated a judge to the D.C. Circuit, which is tremendously influential in federal policy, but that move would replace a conservative with a conservative. The balance on that court still favors Democratic nominees, who make up seven active members of the court compared with four Republicans.

Any shift in the courts toward a more conservative bent on environmental policy would reset the balance of power away from the federal government and back toward the states where it belongs, said Hans von Spakovsky, senior legal fellow at the Heritage Foundation, which has been instrumental in helping the Trump administration shape the courts.

He said EPA and other federal agencies that set environmental policy have exceeded the bounds of their authority in recent years and that the federal role has overshadowed the state role in environmental policy, where the two should be equal. He said Trump's judicial appointments will bring the federal government back inside the bounds of legislation passed by Congress.

"Conservatives, just like liberals, want a clean environment," Spakovsky said. "But we expect federal agencies to act within the authority delegated to them by Congress and to do so in compliance with all applicable laws and regulations. Trump's judges will help make sure that happens."

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.