In January 2009, Rex W. Tillerson, the chief executive of Exxon Mobil, gave a speech in Washington that might have seemed impossible even a few years before. He announced that his company supported a carbon tax to help fight climate change.

Carbon taxes are a fee on fuel use, based on how much carbon dioxide that fuel puts into the atmosphere. “As a businessman, it is hard to speak favorably about any new tax,” Mr. Tillerson told reporters in his speech at the Woodrow Wilson International Center for Scholars. But, he said, it was “a more direct, a more transparent and a more effective approach” than an alternative gaining support in Congress known as cap and trade, which would set an upper limit on carbon dioxide emissions and then rely on a permit-trading system to meet the target.

Mr. Tillerson’s speech was years in the making — part of a turnaround after decades of public denial that the planet was warming, even as Exxon’s own research suggested that it was. It had paid outside organizations to spread doubts about the science. But pressure on the company was building, and the newly elected President Obama had pledged to fight climate change and had singled out Exxon as an example of corporate greed.

Mr. Tillerson — President-elect Donald J. Trump’s nominee to be secretary of state — presided over the company’s shift, which appears to have begun with public statements delivered without fanfare by the company in 2006. In 2007, he personally acknowledged that climate change was happening and that human activity was a contributing factor. Now, at the Wilson Center, he was taking it further, saying that Exxon was willing to accept action from Congress on the problem.