The new chief of the US Environmental Protection Agency has said he does not believe that carbon dioxide is a primary contributor to global warming.
EPA administrator Scott Pruitt said measuring the effect of human activity on the climate is "very challenging" and that "there's tremendous disagreement about the degree of impact" of carbon dioxide and other greenhouse gases.
"So, no, I would not agree that (carbon dioxide) is a primary contributor to the global warming that we see," Mr Pruitt told CNBC's Squawk Box.
Mr Pruitt's view is at odds with mainstream climate science, including Nasa and the National Oceanic and Atmospheric Administration.
The two agencies reported in January that earth's 2016 temperatures were the warmest ever.
The planet's average surface temperature has risen by about 2F since the late 19th century, "a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere", the agencies said in a joint statement.
Environmental groups seized on Mr Pruitt's comments as evidence he is unfit for the office he holds.
"The arsonist is now in charge of the fire department, and he seems happy to let the climate crisis burn out of control," said Sierra Club executive director Michael Brune.
Mr Pruitt "is spewing corporate polluter talking points rather than fulfilling the EPA's mission of protecting our air, our water, and our communities," Mr Brune said, noting that the EPA has a legal responsibility to address carbon pollution.
Senator Brian Schatz said the comments underscore that Mr Pruitt is a "climate denier" and insisted politicians will stand up to him.
"Anyone who denies over a century's worth of established science and basic facts is unqualified to be the administrator of the EPA," Mr Schatz said in a statement.
Mr Pruitt previously served as Oklahoma attorney general, where he rose to prominence as a leader in co-ordinated efforts by Republican attorneys general to challenge former president Barack Obama's regulatory agenda.
He sued or took part in legal actions against the EPA 14 times.
Mr Pruitt said during his confirmation hearing in January that climate change is real - breaking with President Donald Trump and his own past statements.
Mr Pruitt told Democratic senators that he disagreed with Mr Trump's earlier claims that global warming is a hoax created by the Chinese to harm the economic competitiveness of the United States.
"I do not believe climate change is a hoax," Mr Pruitt said.
The Republican has previously cast doubt on the extensive body of scientific evidence showing that the planet is warming and man-made carbon emissions are to blame.
In a 2016 opinion article, Mr Pruitt suggested that the debate over global warming "is far from settled" and he said "scientists continue to disagree about the degree and extent of global warming and its connection to the actions of mankind".