Exxon Mobil Corp’s latest shift on climate includes a $1 million donation to a political action committee’s lobbying campaign to promote a U.S. tax on carbon-gas emissions, a central factor in global warming.

The contribution, made to the Americans for Carbon Dividends political action committee of the Climate Leadership Council (CLC), was disclosed by the group on Tuesday, less than a month after Exxon agreed to contribute $100 million to oil companies’ efforts to develop technologies to reduce greenhouse gas emissions.

“Applying a uniform cost across the economy is consistent with our principles on how to manage the risk of climate change,” Exxon spokesman Scott Silvestri said in an email. “We’ve been supportive of a revenue-neutral price on carbon for a decade.”

The $1 million contribution will be spread over two years.

Exxon, the world’s largest publicly traded oil company, has supported a carbon tax in the past and has stepped up efforts to reduce greenhouse gas emissions in its operations. Those efforts came amid lawsuits brought by U.S. city and state officials seeking damages to pay for seawalls and other infrastructure to guard against rising sea levels that result from global warming.

The Climate Leadership Council’s PAC aims to spend $5 million on an initial lobbying campaign to win support for the tax, said Greg Bertelsen, senior vice president at the group.

“We’re in the very early days of this organization,” said Bertelsen, who said the PAC is looking to build legislative support for its carbon tax. It proposes an initial $40-a-ton tax on carbon dioxide that would increase over time, with the money raised to be returned to consumers.

The PAC, led by former U.S. Senators John Breaux and Trent Lott, also has raised $1 million each from Exelon Corp, First Solar Inc and the American Wind Energy Association, he said. It expects to reach its goal of a $5 million in coming months, he said.

The council’s proposal was developed by former Secretaries of State James Baker and George Schultz. The council’s members include BP Plc, Total SA and General Motors Co .