Oklahoma Attorney General Scott Pruitt is President-elect Donald Trump’s leading candidate to head the EPA. | Getty Trump picks oil ally Pruitt to head EPA

President-elect Donald Trump picked Oklahoma Attorney General Scott Pruitt to run the EPA, putting one of the agency's most hostile critics and a skeptic of climate change science at its helm, sources close to the transition said Wednesday.

As attorney general for a state that is one of the nation's biggest oil, natural gas and grain producers, Pruitt has been at the forefront of lawsuits challenging EPA regulations on carbon emissions and water pollution, and he is expected to lead the effort to erase much of President Barack Obama's environmental agenda. Pruitt has also faced accusations that he's unusually close to energy producers, including a 2014 New York Times story reporting that he and other Republican attorneys general had formed an “unprecedented, secretive alliance” with the industry.

But his agenda would mesh well with Trump, who unloaded on Obama's EPA during the campaign, calling it a "disgrace" that was strangling the economy. Trump promised to reduce the agency to "tidbits."

"We'll be fine with the environment," Trump told Fox News last year. "We can leave a little bit, but you can't destroy businesses."

The news of the expected nomination drew sharp criticism from green groups and environmental advocates in Congress, including former presidential candidate Bernie Sanders, who said he would oppose the "sad and dangerous" move.

"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 Vermont senator said in a statement. "The American people must demand leaders who are willing to transform our energy system away from fossil fuels."

Hawaii Sen. Brian Schatz also said he would fight Pruitt's nomination. “The health of our planet and our people is too important to leave in the hands of someone who does not believe in scientific facts or the basic mission of the EPA,” he said in a statement.

Dan Pfeiffer, a former top Obama adviser put it more succinctly, tweeting, "At the risk of being dramatic. Scott Pruitt at EPA is an existential threat to the planet."

Earlier this week, Trump raised eyebrows by meeting at Trump Tower with climate advocate and former Vice President Al Gore, who told reporters the two had a conversation that was a "sincere search for areas of common ground." Gore had been expected to only meet with Ivanka Trump.

But that meeting apparently had little effect on the president-elect, whose choice of Pruitt was welcomed by conservatives from his home state, including leading Senate climate change critic Jim Inhofe, as well as the coal industry advocates at the American Coalition for Clean Coal Electricity, which said Pruitt would be an advocate for good environmental polices "as well as mindful of the need for affordable and reliable electricity."

Pruitt has professed skepticism about climate change science, and his selection marks a major turning point for EPA, which even under Republican administrations stretching back to the 1980s has been led by administrators who accepted the scientific evidence that human activity was warming the planet. Pruitt has questioned just how much temperatures have risen, and has been skeptical that man-made greenhouse gas pollution has had an impact.

“Scientists continue to disagree about the degree and extent of global warming and its connection to the actions of mankind,” Pruitt wrote in an op-ed in May with Alabama Attorney General Luther Strange.

The vast majority of mainstream scientists agree that human activity is boosting global temperatures and lifting sea levels, and they have called for a rapid cut in carbon emissions from burning fossil fuels to avoid the most catastrophic impacts.

Pruitt joined a coalition of states and other challengers in a failed attempt to kill EPA’s 2009 scientific declaration that climate change poses a threat to public health and welfare. That EPA "endangerment finding" is the basis for many of the agency's subsequent greenhouse gas rules and is likely to come under new attack under Trump. Those include a suite of EPA regulations on power plants, known as the Clean Power Plan, which are expected to receive a judgment from the D.C. Circuit Court of Appeals in the coming weeks.

Pruitt has been supported by Trump's energy adviser Harold Hamm, the head of Continental Resources, one of the nation's biggest oil producers.

But his support for the oil and gas industry has also drawn scrutiny from sources like the Times. In 2014, for example, the newspaper reported that a letter Pruitt had sent to EPA three years earlier was actually written "almost entirely" by Oklahoma-based oil and gas producer Devon Energy.

Pruitt later told local media that his alliance with energy companies isn’t so secretive.

“It should come as no surprise that I am working diligently with Oklahoma energy companies, the people of Oklahoma and the majority of attorneys general to fight the unlawful overreach of the EPA and other federal agencies,” he said.

Pruitt has also been a leading critic and challenger of the Obama administration’s controversial Waters of the U.S. rule, also known the Clean Water Rule, which has drawn fierce attack from energy, agricultural and development interests. Trump has cited that regulation, which increases the number of streams and wetlands protected under the Clean Water Act, as one of his top targets when he takes office.

Pruitt will now be charged with deciding how to follow through on gutting the regulation. He could let ongoing court challenges play out and hope the rule dies there, or ask the court to let the agency take the rule back — a move that could then put the Oklahoman in the driver’s seat for a new rulemaking aimed at resolving the longstanding uncertainty about the reach of the Clean Water Act.

He has also been a foe of other Obama programs, including Obamacare implementation, the White House’s transgender bathroom guidance and Interior Department protections for the lesser prairie chicken.

His LinkedIn biography boasts that he is “a leading advocate against the EPA’s activist agenda,” and says that as chairman of the Republican Attorneys General Association he “led the charge with repeated notices and subsequent lawsuits against the U.S. Environmental Protection Agency for their leadership’s activist agenda and refusal to follow the law.”

Pruitt’s op-ed with Strange, which asserted that scientists disagree about climate science, was written to criticize Democratic attorneys general in New York and other states who were investigating whether Exxon Mobil had quashed its internal research on climate change.

That dispute — known as “#ExxonKnew” after the Twitter hashtag — quickly escalated into a battle between Democrats looking for evidence of fraud at the oil and gas giant and Republican attorneys general who argued the Democrats were stomping on Exxon’s free speech rights. Various court battles related to that dispute are ongoing.

Pruitt has also been a critic of the Renewable Fuel Standard, the law put in place by Congress a decade ago that requires oil refiners to blend corn ethanol and other biofuels into the nation’s fuel supply. EPA implements the rule.

He argued in a 2013 Supreme Court brief that EPA ignored the risks that gasoline with more than 10 percent ethanol pose to cars' fuel systems, as well as the mandate's effect on food prices. The high court declined to take up that case.

Fossil fuel interests have given significant sums to Pruitt’s political campaigns.

During his 2014 reelection, in which he ran unopposed, Pruitt raised $114,000 from energy company PACs and executives, about 14 percent of his total fundraising. That included $5,000 from Devon’s PAC and $100 from William Whitsitt, the Devon executive who commended Pruitt’s Devon-penned letter to EPA as “outstanding,” according to the New York Times report.

Pruitt also garnered donations from oil magnate Hamm; PACs connected to Exxon Mobil, Koch Industries, Alliance Coal, Alpha Natural Resources, Spectra Energy, ITC Holdings, Chesapeake, ONEOK, OGE Energy and Tulsa-based oil and gas producer Unit Corp.; and executives from Continental Resources, the Oklahoma Independent Petroleum Association, the American Coalition for Clean Coal Electricity, the American Gas Association, American Fuel & Petrochemical Manufacturers, Peabody Energy, AEP, Southern Co. and Oklahoma Gas & Electric.

Pruitt started off as a private lawyer before spending eight years in the Oklahoma Senate, where he served stints as GOP whip and assistant floor leader.

From 2003 until his election as attorney general in 2010, Pruitt was co-owner and the managing general partner of the Oklahoma City Redhawks, a minor league baseball team. Pruitt’s official biography says that during his tenure, the team “regularly rated among the league’s leaders in attendance and merchandise sales.”

He earned his bachelor degree at Georgetown College, a Christian school in Kentucky, and his law degree from the University of Tulsa.

Alex Isenstadt contributed to this report.