Environmental Protection Agency Administrator Scott Pruitt said Thursday he does not believe carbon dioxide is a primary contributor to global warming.
"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, so no, I would not agree that it's a primary contributor to the global warming that we see," he told CNBC's "Squawk Box."
"But we don't know that yet. ... We need to continue the debate and continue the review and the analysis."
The statement contradicts the public stance of the agency Pruitt leads. The EPA's webpage on the causes of climate change states, "Carbon dioxide is the primary greenhouse gas that is contributing to recent climate change."
Pruitt's view is also at odds with the conclusion of NASA and the National Oceanic and Atmospheric Administration.
"The planet's average surface temperature has risen about 2.0 degrees Fahrenheit (1.1 degrees Celsius) since the late 19th century, a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere," NASA and NOAA said in January.
Sen. Brian Schatz, D-Hawaii, co-chair of the Senate Climate Action Task Force, slammed Pruitt for his comments, calling his views "extreme" and "irresponsible."
"Anyone who denies over a century's worth of established science and basic facts is unqualified to be the administrator of the EPA. Now more than ever, the Senate needs to stand up to Scott Pruitt and his dangerous views," he said in a statement.
Schatz said lawmakers would hold Pruitt accountable through the appropriations process and oversight of the EPA, and by making sure he follows the Clean Air Act and Clean Water Act.
Pruitt previously served as Oklahoma attorney general, where he rose to prominence as a leader in coordinated efforts by Republican attorneys general to challenge President Barack Obama's regulatory agenda. He sued or took part in legal actions against the EPA 14 times.
Democrats and environmentalists opposed Pruitt's nomination to lead the EPA due to his close relationship with fossil fuel companies and his history of casting doubt on climate change. Conservatives and the energy industry have cheered his efforts to push back on what they view as over-regulation under Obama.
Pruitt maintained on Thursday it's possible to be pro-growth, pro-jobs and pro-environment all at once.
"This idea that if you're pro-environment you're anti-energy is just something we've got to change so that attitude is something we're working on very much," he said.
Asked whether he would seek to roll back the EPA's 2009 determination that carbon dioxide and five other greenhouse gases are a danger to public health, Pruitt suggested he would like to see Congress take up the issue.
"I think all those things need to be addressed as we go forward but not least of which is the response by the legislative branch with respect to the issue," he said.
The Supreme Court ruled in 2007 that the EPA has the authority to regulate heat-trapping gases from automobiles. In 2014, it determined the agency could also regulate some sources of greenhouse gases, such as power plants.
Pruitt also called the Paris Agreement, an international accord aimed at mitigating the impacts of climate change, "a bad deal." He said it puts the United States on a different playing field than developing countries like China and India.
The United States has vowed to reduce its greenhouse gas emissions to 26 to 28 percent below 2005 levels by 2025. In comparison, China has committed to reach peak carbon emissions levels by 2030, but will try to reach that point sooner.
"I happen to think the Paris accord, the Paris treaty, or the Paris Agreement, if you will, should have been treated as a treaty, should have gone through senate confirmation. That's a concern," he said.
The Paris Agreement was negotiated by the State Department, and future adherence to U.S. commitments made under Obama will be guided by Secretary of State Rex Tillerson.
Tillerson, the former chief of Exxon Mobil, said during his Senate confirmation hearing that he believes the United States should remain a party to the Paris Agreement.