An Exxon Mobil station in Cincinnati Luke Sharrett | Bloomberg | Getty Images

Exxon Mobil will donate $1 million to a campaign promoting a tax to curb emissions of planet-warming carbon dioxide to U.S. lawmakers and the American public. With the commitment, the world's largest publicly traded oil company is throwing its financial support behind Americans for Carbon Dividends, an organization tasked with lobbying for a carbon tax plan developed by Republican statesmen James Baker III and George Shultz. Exxon's support comes at a time when U.S. lawmakers remain at an impasse over putting a price on greenhouse gas emissions, with many Republicans opposed to a carbon tax or cap-and-trade system. The policy vacuum at the national level threatens to leave energy companies grappling with a patchwork of state and regional policies. A single, national tax policy would provide regulatory certainty to the energy industry, and the Baker-Shultz plan in particular seeks to limit the Environmental Protection Agency's rule-making authority. The contribution also marks Exxon's latest measure to tackle the challenge of global warming, following a period of intense scrutiny of the company's public record of downplaying the risks posed by climate change.

Exxon is the first oil company to fund Americans for Carbon Dividends and joins the group's three initial contributors: Chicago-based utility Exelon, solar power company FirstSolar and the American Wind Energy Association. Exxon's $1 million commitment brings the group's total funding to more than $3 million. "Exxon's contribution today is a very significant step in the promotion of the Baker-Shultz carbon dividend plan," said Greg Bertelson, senior vice president at the Climate Leadership Council. Exxon did not respond to a request for comment. Exxon — along with fellow oil majors BP, Royal Dutch Shell and Total — is a founding member of the Climate Leadership Council, a group of corporations, conservation groups and prominent individuals tasked with hammering out a more detailed version of the four-point Baker-Schultz policy. Americans for Carbon Dividends was formed in June to promote that plan, which is billed as a conservative, free-market approach to combating the human-caused carbon dioxide emissions fueling climate change. The burning of fossil fuels is a major contributor to those emissions. The plan advocates for placing a fee on carbon emitted by companies, which would start at $40 per ton and rise gradually. Revenues from the tax would be returned to Americans in the form of regular, automatic dividend payments. The policy would also seek to level the international playing field with countries that do not tax carbon emissions by offering a rebate on American imports going into those nations and placing a fee on their imports into the United States.