Wrapping himself unabashedly in the mantle of climate science denial, Environmental Protection Agency Administrator Scott Pruitt declared on Thursday that he does not believe carbon dioxide is a primary contributor to global warming.
The statement contradicts a firmly established tenet of climate change science. By questioning it, Pruitt appeared to signal a coming challenge by the Trump administration to the agency's key science finding that obligates it to regulate carbon dioxide pollution from the burning of fossil fuels.
It sparked a chorus of unambiguous contradiction from leading scientists, including those working at the foremost government institutions.
"Mr. Pruitt is wrong," said one of them, Ben Santer of the Lawrence Livermore National Laboratory. "Embracing ignorance is not an option."
In an interview on CNBC's Squawk Box program, Pruitt was asked by host Joe Kernen if he believes that carbon dioxide is the "primary control knob for climate."
"I think that measuring with precision human activity on the climate is something very challenging to do and there's tremendous disagreement about the degree of impact," Pruitt answered. "So no, I would not agree that it's a primary contributor to the global warming that we see." Pruitt added, "We need to continue the debate and continue the review and the analysis."
Kernen also denied that the science was "settled."
The most recent authoritative statement of the Intergovernmental Panel on Climate Change, which represents the global scientific consensus, declared that "it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century." That human influence comes mainly from increased atmospheric concentrations of greenhouse gases (primarily carbon dioxide) from burning fossil fuels, deforestation, agriculture and the like.
Former EPA Administrator Gina McCarthy denounced her successor's remarks. "The world of science is about empirical evidence, not beliefs," she wrote in a statement. "I cannot imagine what additional information the administrator might want from scientists for him to understand that."
McCarthy went on to condemn the Trump administration's larger campaign to remove government scientists who believe human activity contributes to global warming. "Giving pink slips to scientists across the federal government, including 43 percent of EPA scientists, and proposing to eliminate the U.S. Climate Global Research Program in its entirety, makes one question who this administration will rely on for scientific research and facts." She was referring to a plan that, if approved, would cut funding for the EPA's Office of Research and Development by 43 percent.
Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research in Boulder, Colo. said Pruitt is denying what has been indisputably verified.
"There is no doubt whatsoever that the planet is warming and it is primarily due to increased carbon dioxide in the atmosphere from burning of fossil fuels," he said. "Carbon dioxide is a greenhouse gas and we can demonstrate clearly that the observed warming of the planet would not have occurred without that change in atmospheric composition. These are scientific facts, not opinion, and it is incumbent on politicians to take account of the scientific evidence."
John Holdren, director of the White House Office of Science and Technology Policy under President Obama, called Pruitt's claim "the purest ignorance."
"There is simply no scientific question," Holdren said. "The evidence for climate change caused by humans and principally by CO2 comes from many different lines of observation, monitoring, research, analysis. It's all consistent."
Pruitt's statement on CNBC went beyond his more guarded words at his Senate confirmation hearings, when his record of climate denial was under intense scrutiny by Democrats.
"The climate is changing and human activity contributes to that in some manner," he said in response to a question from Sen. Bernie Sanders. "I believe the ability to measure with precision the degree of human activity's impact on the climate is subject to more debate."
This time, there was no way to construe his remarks as being consistent with mainstream science.
In a written response to questions from senators that he submitted during his confirmation process, Pruitt said he would fulfill the duties of the administrator in regulating greenhouse gases.
"As Pruitt testified before Congress, it is the legal duty of the EPA to tackle the carbon pollution that fuels the climate crisis," Sierra Club's executive director, Michael Brune, said in a statement. "Pruitt is endangering our families, and any sensible senator should demand he be removed from his position immediately for misleading Congress and being unfit and unwilling to do the job he has been entrusted to do."
David Doniger, director of the climate and clean air program at the Natural Resources Defense Council, said he considered the situation bizarre. "After obscuring his true views during his Senate confirmation hearings, Scott Pruitt has outed himself as a pure climate denier," Doniger said. "Having an EPA administrator who claims carbon pollution is not the primary cause of climate change is like having a U.S. surgeon general who says smoking is not the primary cause of lung cancer.''
Sabrina Shankman contributed reporting to this story.