Rex Tillerson, President-elect Donald Trump’s pick for secretary of state, will likely face plenty of tough questions during his confirmation hearings on Wednesday: about his close ties to Russian President Vladimir Putin’s inner circle, deals his former company made with Iran, and the secretive oil venture he oversaw in the tax haven of the Bahamas.

But senators will also probably focus on the outgoing Exxon Mobil Corp. CEO’s climate change record. Tillerson, 64, is a Texas-born oil man who spent 41 years at the world’s largest publicly listed energy company and has a complicated history on the subject.

Under his decade-long tenure as chief executive, Exxon Mobil shifted its public messaging on climate change by ending years of funding a Big Tobacco-style disinformation campaign and finally acknowledging that human activity is causing the Earth to get warmer. The company announced in 2009 that it was in favor of taxing carbon and that it had begun investing in algae-based biofuels. It came out in support of the Paris climate accord in 2015, which more than 180 countries have signed.

Despite these attempts to burnish Exxon Mobil’s public image, Tillerson’s record at the helm remains less straightforward. The company has continued to lavish money on think tanks and advocacy groups that deny fossil fuels worsen climate change, even though it pledged in 2007 to stop doing so. Its political donations overwhelmingly have gone to Republicans who have battled environmental regulations, including the Obama administration’s rules curbing greenhouse gas emissions. And Tillerson has openly mocked the renewable energy industry, even as rival oil giants sunk money into wind, solar and battery storage projects.

“While we’ve seen some shifts in rhetoric, the company’s conduct does not back up its words,” Kathy Mulvey, climate accountability campaign manager at the nonprofit Union of Concerned Scientists, told The Huffington Post on Monday. “We’re still seeing Exxon Mobil, for example, playing a leadership role in funding groups that spread disinformation on climate science and policy.”

Despite the firm’s supposed evolution on global warming, neither Exxon Mobil nor Tillerson owned up to the years the company spent funding organizations whose chief purpose seemed to be seeding doubt over climate science. That funding has been under increased scrutiny since October 2015, when InsideClimate News and the Los Angeles Times published documents revealing that Exxon Mobil chose to continue funding disinformation campaigns even though its scientists understood global warming decades ago. The reports provoked a group of state attorneys general to begin investigating corporations, including Exxon Mobil, for allegedly misleading the public on climate change.

“I’m deeply interested in the record of Exxon Mobil when Mr. Tillerson was in leadership in funding organizations that tried to muddy up or deny the reality of climate science,” Sen. Tim Kaine (D-Va.), who sits on the Senate committee tasked with grilling Tillerson, said Tuesday on “CBS This Morning.”

“Exxon Mobil is an organization filled with scientists and engineers and from what I’ve read, they understood decades ago that humans were affecting climate in ways that could be dangerous, but the allegation is that they then made the decision to cover that evidence up as long as they could for their own financial benefit,” Kaine said. “And I want to explore what Mr. Tillerson knows about that.”

Five of the 10 Democratic senators on the committee scored 100 percent on the League of Conservation Voters’ 2015 ranking, meaning they voted in favor of environmentally friendly bills whenever presented with one. Kaine ranked the lowest, with 88 percent, despite a 91 percent lifetime score.

The environmental advocacy group NextGen Climate released an ad on Tuesday that shows Tillerson, while in his role leading Exxon Mobil, telling an audience at the University of Texas that he was “not here to represent the United States government’s interests.” Tom Steyer, the group’s billionaire founder, said the ad shows how Tillerson “puts corporate interests over American interests” ― and may continue to do so as secretary of state.

“The American people deserve more assurance than we’ve received so far that he will be able to represent their values when U.S. policy goals conflict with Exxon’s ongoing corporate interests,” Sen. Tom Udall (D-N.M.) said in a statement.

Tillerson’s meager record of public service could become another sticking point as senators probe his résumé. Sen. Jeff Merkley (D-Ore.) said Monday that he planned to pepper Tillerson with questions about how his career as an oil executive qualified him to lead the State Department.

“After talking with him, I still have significant questions about Mr. Tillerson’s foreign policy views and how his four-decade career at one of the largest oil companies in the world prepares him to be our nation’s top diplomat,” Merkley said in a statement. “I look forward to further exploring Mr. Tillerson’s views at his confirmation hearing.”