Donald Trump's pick to head the Environmental Protection Agency cast doubt on whether California should continue to have power to impose its own emission rules for cars and trucks, an authority the state has enjoyed for decades that is also the cornerstone of its efforts to fight global warming.
Oklahoma Atty. Gen. Scott Pruitt said at a contentious confirmation hearing Wednesday that he cannot commit to keeping in place the current version of a decades-old federal waiver that allows California to set emissions standards stricter than elsewhere in the United States.
In recent years, California regulators have used the waiver to force automakers to build more efficient vehicles, which has helped the state cut its greenhouse gas emissions from cars and trucks by nearly a third since 2009.
More than a dozen other states have adopted the California standard as part of their own efforts both to clean their air and fight global warming.
Pruitt held out the possibility that he might take that power away during a hearing in which he also battled Democrats over his skepticism about aspects of climate science, his financial relationship with oil and gas companies, and his plans to substantially curb the EPA's role in fighting pollution.
Although Pruitt said he accepts that human activity is affecting the climate, he expressed doubt over the mainstream scientific consensus that the warming is happening at a catastrophic pace that must be confronted with aggressive actions.
"The ability to measure with precision the extent of [human] impact and what to do about it are subject to continued debate and dialogue," Pruitt said.
Pressed by Sen. Kamala D. Harris (D-Calif.) about whether he intends to leave California's authority in place, Pruitt would only say, "I don't know without going through the process to determine that. One would not want to presume the outcome."
His comments were met with strong protests by Democratic lawmakers in Washington and Sacramento. They charged that Pruitt, a self-styled crusader for states' rights, is less committed to the principle when states pursue policies that reduce the profits of big corporations.
If the Trump administration did succeed in eliminating California's waiver authority, the loss would be a major setback for the state's environmental policies.
The waiver was initially granted decades ago as the state grappled with an air quality crisis triggered by the traffic-induced smog that settled over Los Angeles and other cities.
The state expanded its use of that power in 2009, when, after years of fighting with federal regulators and car manufacturers, California officials and the then-new Obama administration agreed to expand the waiver to incorporate California's landmark effort to fight climate change. Reduction of greenhouse gas emissions has been a key function of the waiver since that agreement was struck.
Pruitt's hedging on the issue comes as California regulators have expressed confidence that the new administration would not interfere with homegrown efforts to shift the state economy away from fossil fuels. But their confidence has been based on the assumption that certain federal environmental policies, like the waiver and tax credits for wind and solar energy, would endure.
"When you say 'review', I hear 'undo' the rights of the states," Sen. Ed Markey of Massachusetts, which has adopted many of California's standards, told Pruitt.
"It's troublesome because obviously what we've heard all day is how much you support states' rights when it comes to these issues. But, now when it comes to the right of California or Massachusetts or other states' right to be able to reduce carbon pollution, you say you are going to review that."
"We are fearful what review would actually result in," Markey said. "I think it is going to lead to you undoing that right of states to be able to provide that protection."
Pruitt would say only that he could make no promise that California and other states will keep their waiver.
As Pruitt sparred with committee Democrats, California's chief regulator of air quality and greenhouse gas emissions, Mary Nichols, was testifying in Sacramento about the importance of the waiver to her agency, the California Air Resources Board.
Any failure to renew the waiver, state Senate Leader Kevin de Leon said in an email, "will be met with full resistance up and down the state."
Pruitt is among the more controversial of Trump's Cabinet picks, a longtime ally of the oil and gas industry who has built his career around fighting the agency he now seeks to run. He has sued the EPA 14 times since becoming his state's attorney general — often alongside oil and gas companies. He argues the agency has acted inappropriately in its robust enforcement of clean air and clean water rules that he says should be left to state discretion.
As head of the EPA, he would be empowered to undermine the signature Obama administration effort to combat global warming — a policy he has crusaded against.
"Regulators are supposed to make things regular," Pruitt said at his hearing, "to fairly and equitably enforce the rules and not pick winners and losers."
He charged that the issue of climate change had been overtaken by emotion and incivility. "We should not succumb to personalizing matters," he said.
The hearing follows a weeks-long assault by environmental groups against Pruitt that began the day Trump named him to lead the agency. One of the groups, the Environmental Defense Fund, said it had never lobbied against an EPA selection until now.
Democrats on the Senate Environment and Public Works Committee took up the fight on Wednesday, accusing Pruitt of ignorance of climate science, a disregard for millions of Americans whose health is being harmed by air pollution and an inappropriately cozy relationship with big energy companies.
Pruitt's close ties with energy companies were repeatedly brought up by Democrats as the hearing got underway. Sen. Jeff Merkley of Oregon presented a letter Pruitt sent to the EPA protesting its enforcement of methane rules.
The letter was written almost entirely by Devon Energy. Pruitt had changed just a few words.
"A public office is about serving the public," Merkley said. "You used your office as a direct extension of an oil company rather than a direct extension of the public health of the people of Oklahoma."
Pruitt said sending the letter written almost entirely by an oil firm was appropriate.
"The letter sent to the EPA was not sent on behalf of any one company; it was particular to an industry," he said. "There was concern expressed by many in the industry about the overestimating that occurred in relation to that methane rule."
Times staff writer Chris Megerian in Sacramento contributed to this report.
3:45 p.m.: This article was updated with additional information throughout.
9:50 a.m.: This story was updated with the start of the hearing.