The Republican Scott Pruitt has spent much of his time as Oklahoma's top law enforcement official battling the very agency he is now being nominated to lead, with his official biography proudly highlighting his role as "a leading advocate against the EPA's activist agenda".
Republicans have long argued that President Barack Obama's administration, through the EPA, has imposed burdensome environmental regulations such as anti-pollution measures on US corporations, many in the name of fighting climate change.
Trump campaigned this year on vows to terminate or curtail such regulations.
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With the maverick businessman now set to assume the office in January, such Republicans, and notably the energy industry, can expect to have an ally running the EPA.
The EPA chief also has a strong impact on US actions to combat climate change: the agency both determines what international commitments the country is able to make, and implements the measures.
Trump's transition team has yet to officially announce the nomination.
Pruitt, 48, has sued the EPA on behalf of Oklahoma utilities, seeking to "roll back our landmark environmental laws" in the words of outgoing Senator Barbara Boxer, the top Democrat on the Senate Environment and Public Works Committee.
He has sought to limit federal regulations and restore more regulatory oversight to US states. In a pending lawsuit with several states Pruitt has attempted to halt Obama's Clean Power Plan to reduce carbon dioxide emissions from power plants.
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In an opinion piece in the National Journal, he described the debate over global warming as "far from settled".
Pruitt's "reluctance to accept the facts or science on climate change couldn't make him any more out of touch with the American people - and with reality," Chuck Schumer, who will lead US Senate Democrats beginning in January, said, adding Pruitt will face "many tough questions" in his Senate confirmation hearings.
In a more forceful statement, Senator Bernie Sanders called the nomination "sad and dangerous" and said he would oppose it.
"Mr. Pruitt's record is not only that of being a climate change denier, but also someone who has worked closely with the fossil fuel industry to make this country more dependent, not less, on fossil fuels."
The Sierra Club, a leading environmental organization, equated the nomination to "putting an arsonist in charge of fighting fires."
But Republican Senator James Lankford, a fellow Oklahoman, praised Trump's EPA pick and said he was looking forward to working with Pruitt "to restore a balanced approach to regulations".
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