PROVIDENCE — The U.S. Senate's most persistent voice for addressing climate change introduced a bill Thursday aimed at unlimited political spending, with fossil fuel companies in his crosshairs.

Sen. Sheldon Whitehouse, a Rhode Island Democrat, is targeting so-called "dark money" because he thinks opposition to addressing climate change in Congress is propped up by the fossil fuel industry.

"If you kicked out that support, the opposition would fall," said Whitehouse, who was sworn in for a third term in January.

His bill introduced Thursday would require organizations spending money in federal elections, including super PACs and certain nonprofit groups, to promptly disclose donors who gave $10,000 or more during an election cycle. Whitehouse has introduced similar legislation each Congress since 2012, but he said he's more hopeful now because Democrats control the House and there's mounting public pressure to address climate change.

A growing number of Republicans, including Senate Majority Leader Mitch McConnell, now say they believe climate change is real and humans play a role in it, though they don't agree with Democrats on possible solutions. Climate change was also catapulted onto the political agenda after the Senate blocked consideration last month of the Green New Deal, a nonbinding resolution that calls for the U.S. to shift away from fossil fuels, such as oil and coal, and replace them with renewable sources, such as wind and solar power.

The American Petroleum Institute said it strictly complies with all filing and reporting requirements, and the natural gas and oil industry is taking steps to address climate change.

"The risks of climate change are real and our industry is tackling the challenge head on, driving emissions to their lowest levels in a generation while at the same time meeting record consumer energy demand," the industry trade association said in a statement Thursday.

Whitehouse gives weekly speeches in the Senate, telling his colleagues to wake up to the threats of climate change. He'll give his 240th speech after Congress takes a two-week recess this month. He also reintroduced legislation Wednesday to institute a carbon fee.

Before the Supreme Court's landmark 2010 Citizens United ruling, Whitehouse said there were bipartisan climate hearings, discussions and negotiations. But those ceased after the Supreme Court ruling helped open the door to allowing businesses, unions and nonprofits to spend unlimited amounts to influence elections.

Groups that track political spending say it's difficult to verify Whitehouse's assertion about the fossil fuel industry propping up opposition to addressing climate change in Congress because dark money is secretive by nature. The ultimate source of funding behind most dark money groups remains hidden, said Anna Massoglia, a researcher at the nonprofit research group Center for Responsive Politics.

Climate opposition in Congress can potentially encompass a wide range of activities and groups, according to the Campaign Legal Center, though there's good reason to suspect that fossil fuel interests are responsible for a sizable portion of dark money.

A similar proposal to reduce the role of big money in politics passed the House in March as part of a sweeping elections and ethics overhaul. U.S. Rep. David Cicilline, also a Rhode Island Democrat, helped craft it.

Cicilline said he's targeting a range of special interests that spend money secretly on elections and adversely impact public policy, but like Whitehouse he said dark money spending by fossil fuel companies is impeding Congress' ability to respond to climate change. That spending needs to be exposed to make progress on the issue, he added.

McConnell, of Kentucky, said the elections and ethics overhaul proposal was dead on arrival in that chamber.

Cicilline plans to introduce a stand-alone bill to require the disclosure of political spending soon.