"The evidence is overwhelming, the science is clear," Energy Secretary Ernest Moniz told a hearing of the energy and commerce committee at the House of Representatives, where a slate of Republican legislators remain skeptical about climate change.
"The increase in the quantities of greenhouse gases in the atmosphere as a result of human activity, above all the combustion of fossil fuels, has reached the point that it is profoundly affecting the climate."
Questions from lawmakers to Moniz and his colleague, Gina McCarthy, head of the powerful Environmental Protection Agency, focused on upcoming greenhouse gas emissions standards for existing power plants — regulations that opponents say will have a devastating economic impact on coal-producing states.
"Man-made problems only represent four per cent of all the emissions of the globe; natural issues represent 96 per cent," an indignant David McKinley, a Republican from the coal state of West Virginia, told the hearing.
"The administration is putting our nation at risk .... This president must not prevent people from around the world from obtaining affordable energy and dependable jobs."
Henry Waxman, a climate hawk from California and a member of the House committee, interjected to call McKinley's remarks "incredibly inaccurate and contrary to everything else that people in the scientific community have to say."
At the U.S. Senate, meantime, Mitch McConnell, the Senate minority leader from coal-producing Kentucky, is pondering a bill that would block the EPA from issuing the new standards. The legislation would be entitled "Save Coal Jobs Act of 2013."
Keystone XL wasn't a subject of discussion at the House hearing on Wednesday, possibly because both McCarthy and Moniz have steered clear on weighing in on the merits of the pipeline in previous public appearances. The U.S. State Department is currently assessing the project.
But outside the hearing, Eric Cantor, the majority leader of the House of Representatives, told the media that Republican House leaders plan to advance Keystone XL by inserting a resolution into legislation to raise the U.S. debt ceiling — the latest attempt to force the White House into green-lighting the project by attaching pro-pipeline language to bigger bills.
"In the coming week, we will unveil a plan to extend our nation's ability to borrow, while delaying Obamacare and protecting working middle-class families from its horrific effects," Cantor said.
"Those discussions will also focus on a path forward on tax reform and the Keystone pipeline, and a variety of other measures designed to lower energy prices, simplify our tax system, and get our economy going for the middle class, working people of this country."
Kevin McCarthy, the House majority whip, defended the move.
"House Republicans are advocating for pro-growth measures to be included in any agreement to raise the government's borrowing authority, so adding swift approval of the Keystone XL pipeline is an easy fit," he said in a statement.
Pipeline approval has become a top priority for many congressional Republicans, as well as some Democrats.
The pipeline, meantime, is a flashpoint for the U.S. environmental movement, which has been urging the Obama administration for years to nix Keystone XL.
Dozens of rallies are planned across the country this weekend in what's billed a "Draw The Line" national day of action by U.S. environmentalists.
In the U.S. Senate this week, Democratic lawmakers Mary Landrieu and Heidi Heitkamp, along with Republican John Hoeven, have been urging Keystone XL approval. They've also added a non-binding, pro-Keystone resolution to an energy efficiency bill currently working its way through the upper chamber.
"This measure is structured as a joint resolution, putting both the House and the Senate on record that the Keystone XL pipeline project is in the national interest," Hoeven told a North Dakota newspaper. "Energy independence is tied to national security and being independent makes us safer."
Senate majority leader Harry Reid, meantime, has threatened to kill that bill outright because Republicans are demanding votes on amendments to the legislation that would stall the implementation of Obama's health-care overhaul upheld by the U.S. Supreme Court a year ago.