Did Scott Pruitt's recent climate denial cross a red line and violate the scientific integrity rules of the Environmental Protection Agency? That's a question now being reviewed by an agency watchdog with a long record of pushing for credibility and transparency in government science.

The agency turned that matter over to Francesca Grifo after the Sierra Club demanded an investigation of Pruitt for publicly questioning carbon dioxide's role in global warming last month. Grifo is a holdover from the Obama administration who in 2013 became the agency's first scientific integrity official.

Before that, she spent eight years with the Union of Concerned Scientists (UCS), an advocacy group that is now squarely at odds with the Trump administration on climate change and other issues.

At UCS, Grifo advocated for stronger scientific integrity policies, testifying before Congress and writing papers accusing the George W. Bush administration of interfering with science and peddling uncertainties over the causes of climate change.

Now Grifo, who is not a political appointee, is tasked with investigating her boss on the issue.

"She'll have to be very gutsy," said Rena Steinzor, a professor at the University of Maryland School of Law, who studies environmental regulation and science in regulatory policy. "She's shaking her fist at a hungry lion."

Pruitt sparked the inquiry when a CNBC interviewer asked him if carbon dioxide was the "primary control knob" for climate change. He replied: "So no, I would not agree that it's a primary contributor to the global warming that we see. But we don't know that yet...We need to continue the debate and continue the review and the analysis."

The comment, which goes against the overwhelming scientific consensus on climate change, prompted the Sierra Club to ask the agency's Office of Inspector General to conduct an inquiry into Pruitt's statements. The Sierra Club said the statements violated the agency's own scientific integrity policy. "We respectfully urge you to investigate and remedy this violation as soon as possible to prevent further erosion of scientific integrity at the agency," Sierra Club's attorneys wrote in the letter on March 14.

The agency's Office of Inspector General (OIG) responded by saying it would refer the Sierra Club's request to the Scientific Integrity Official (SIO), who would then report back to the OIG. "If after the SIO review, [Grifo] concludes there is some aspect of the letter itself, or her findings or conclusions that she believes are appropriate for further consideration by the OIG, she will so notify the OIG," the agency said on March 30.

EPA implemented its scientific integrity policy, along with other science-centric agencies, after the Obama administration called for agencies to strengthen internal reviews on science in 2009. The move was in response to the previous administration's rewriting of regulations based on questionable or politically motivated science.

"It just got so out of control during Bush-Cheney that people began recognized it as an issue, so much so that it was one of the first actions Obama took," said Jeff Ruch of Public Employees for Environmental Responsibility, a watchdog group of former government employees and scientists.

Grifo joined the EPA in 2013, charged with implementing its new scientific integrity policy and coordinating with a new scientific integrity committee. While the Office of Inspector General handles investigations into scientific misconduct, Grifo handles matters of scientific integrity.

"The losses of integrity, which is a much more nebulous category, are in Francesca's bailiwick," Ruch said. "To our knowledge she has never found a single case where there's been a loss of integrity."

Ruch also noted that much of the agency integrity policy has yet to be completed. For example, after the Trump transition team arrived at the agency earlier this year, it announced the work of the agency's scientists would be released only after a review by the administration and on a case-by-case basis. In fact, Ruch noted, that was also the case under the Obama administration.

In 2010, the Obama White House's Office of Science and Technology Policy issued guidelines for federal agencies to develop scientific integrity policies. The office was also in charge of keeping an eye on how those policies were working. Now that office has only one appointee—a deputy chief technology officer.

"There's no leadership," said Kei Koizumi, a former senior advisor at the office. "Although the agencies are independent, there's no White House watchdog on this policy issue right now."

Koizumi, now a visiting scholar at the American Association for the Advancement of Science (AAAS), said Grifo participated in a panel on scientific integrity organized by the association last week. "EPA is one of the agencies people are concerned about in terms of scientific integrity, and I wanted people to see she's still there, she's still on the case," Koizumi said. "As one of the people who set up the scientific integrity policy, it was important to appoint a career person, and they be empowered to take on cases that involved political officials, to last between administrations."

It's also unclear whether Grifo's office will survive the Trump administration's proposed cuts to the agency, although there is no specific recommendation so far for cutting the office.

"If they're serious about cutting 31 percent, they could abolish the office and reassign her," Steinzor said. "But anything they do like that would make them look pretty bad."

Ruch's organization filed a Freedom of Information request with the agency after Pruitt's comments. It asked for the agency to turn over any documents that provide the scientific basis for his statements.

"He was speaking as the EPA administrator and if he said that without a shred of evidence, we want that to be widely known," Ruch said.

His group plans to sue the agency for failing to respond to the request.

The EPA did not immediately respond to questions and a request for comment. The Office of Inspector General said there was no specified timeframe for Grifo's review.

"As far as EPA staff are concerned, these scientific integrity policies are still in place and as the administration continues to take shape, we'll see how the policies get tested, but it's a little early to determine their effectiveness," said Michael Halpern, a deputy director at UCS. "As we see Pruitt and his group roll back the science-based public protections that were put in place under Obama, that's where we'll more likely see the more egregious examples of interfering in science."