As Barack Obama's political foes vow to shred his environmental reforms and foreign allies worry US commitments at Paris climate talks could unravel, EPA administrator Gina McCarthy told AFP the new rules are here to stay.

"Every decision that we have made has been bounded in climate science and bounded in the laws of the United States," said McCarthy, the Environmental Protection Agency boss tasked with implementing the president's climate agenda.

Republicans, from Donald Trump to Jeb Bush, have promised to tear up Obama's "job destroying" regulations after the 2016 elections.

"I think we need to repeal every rule that Barack Obama has," said Jeb Bush during a Republican debate Tuesday, specifically citing environmental regulations.

"We should repeal the rules because the economic costs of this far exceed the social benefit."

McCarthy gives that kind of rhetoric short shrift.

"We always anticipate that there are going to be challenges to our rules," said the native Bostonian. "We have protected against it, and we are going to win when push comes to shove."

McCarthy said that the EPA has endured "changes in administrations for 40 years, but they have not been undoing the necessary work that we have to do to protect public health and safety."

"Legally, it's very difficult to undo these," she said. "It's going to stand the test of time."

- Eying Paris --

McCarthy's combative tone is also a message to foreign governments, who nervously eye US politics as they consider red lines and compromises that may be made at a key UN climate summit in December.

Obama and others hope the meeting will result in a plan to help limit global warming to around 2.0 degrees Celsius (3.6 degrees Fahrenheit)above pre-industrial levels.

The United States has pledged to reduce its own emissions by 26-28 percent by 2025 compared to 2005, and has prodded others to take similar steps.

But many delegates still feel a sting of US betrayal from previous climate negotiations. Senior Obama administration officials report frequent queries about the longevity of US commitments.

Two decades ago foreign capitals watched in horror as president George W. Bush and his Republican allies refused to ratify the Kyoto Protocol that his predecessor, Democrat Bill Clinton, had signed up for.

Wary of that history, the White House has jumped through legal hoops to make sure the Paris accord is not a formal treaty, which would need congressional ratification.

Instead, US commitments rely on White House executive orders and rules based on the Clean Air Act that bypass lawmaker opposition.

McCarthy said public opinion, business sentiment and environmental facts on the ground may be the ultimate safeguards.

"The data and the facts show something very different" from Republican job-killing economic arguments, she said.

"Under the Clean Air Act, for 40 years we have found a way to reduce pollution by 70 percent while we have continued to grow the economy."

Popular attitude about the climate has changed, she said. "The people in this country know we have to take action now, they feel the effects of climate change now."

"This is not just one action and things could go back to the way they used to be, this is recognizing that things are changing."

A "handful of folks on the hill," she said, referring to opposition lawmakers, were not in the majority.

"The vast majority of people in Congress and the vast majority of the American people understand what the science is telling us. We are not projecting 20 years for now about what climate impacts might be, we are feeling them today.

"We are on very solid ground in the courts and in the court of public opinion," McCarthy said.