President Barack Obama's former environment chief bemoaned Tuesday the Trump administration's efforts to roll back environmental oversight, but said moves to undo his climate legacy would not withstand legal challenges.

"We need to make sure people understand that pronouncements don't equal the law," Gina McCarthy, the Environmental Protection Agency's administrator during Obama's second term, said in an interview at the University of Pennsylvania, where she was accepting the Carnot Prize from the Kleinman Center for Energy Policy.

"You really have to work hard to show the prior administration made a mistake when it made the rules," she said. "Did we get the science wrong? The law wrong? The facts different? I think you're going to see we did a good job, so it's going to be a long time in discussions in the courts, and I think in the end things will continue to move forward."

McCarthy, a fellow at Harvard's Kennedy School of Government and the T.H. Chan School of Public Health, said the current administration's efforts to promote fossil-fuel development, especially coal, will not endure.

"What we see now is that the clean-energy train in the United States has left the station, so if you want to know who won, it's the United States," she said. "It's our economy, it's the safety of our communities, its the future of our kids. Because we are moving toward a low-carbon energy future."

McCarthy led the EPA when the Obama administration used executive powers to circumvent legislative obstacles to its climate-change agenda, which her opponents called government overreach.

It finalized the Clean Power Plan to reduce carbon emissions from electricity generation, tightened ozone-pollution standards, improved coal-ash disposal, issued rules to protect U.S. waters from pollution, and developed limits on methane emissions in the oil and gas sector.

Many of those initiatives are in retreat under the Trump administration, which proposed a $5.65 billion budget for the EPA for next year, a cut of about 30 percent. McCarthy said such a severe cut in EPA's oversight functions would "pose a significant burden and slowdown" on regulated businesses.

"Her career exemplifies the courage, creativity, and commitment required to make great changes in energy policy," Kleinman Center faculty director Mark Alan Hughes said in announcing the $25,000 Carnot Prize. "She is an inspiration to the rising generation of leaders at Penn and around the world."

McCarthy said the EPA under her successor, Scott Pruitt, was ignoring its public-health mission. A report in Tuesday's New York Times that examined Pruitt's daily schedule showed almost daily briefing sessions and speaking engagements with executives and lobbyists from industries that the EPA regulates, and almost no meetings with environmental groups or consumer or public-health advocates.

"I'm still waiting to understand how he's going to improve public health, because so far I've really not heard much of anything from the entire administration other than what is the cost to industry," she said.

The Carnot Prize memorializes the French scientist Sadi Carnot. Previous winners were Daniel Yergin, the energy historian, and Fatih Birol, executive director of the International Energy Agency.