The incoming head of the US Environmental Protection Agency said Thursday that carbon dioxide is not the main driver of global warming, a position starkly at odds with the scientific consensus on climate change.
A known ally of the fossil fuel industry, Scott Pruitt's appointment to head the EPA - a department he repeatedly sued as a state attorney general - was deeply contentious.
"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," Pruitt told CNBC.
"We need to continue the debate and continue the review and the analysis," he added.
Pruitt's stance runs counter to the scientific consensus that underpins last year's landmark Paris Agreement, which saw more than 190 world leaders agree to lower emissions that lead to global warming.
It also clashes with the positions of agencies like NASA and the National Oceanographic and Atmospheric Administration, which have concluded that global warming is driven largely by increased carbon dioxide and other man-made emissions.
Some 97 percent of scientists worldwide agree that human activity - primarily the burning of fossils fuels like oil, gas and coal - has largely contributed to the sharp rise in the planet's temperature in recent decades.
The past three years in a row have broken modern records for global heat, a trend scientists say is due to global warming in combination with a strong El Nino weather pattern.
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Scientists quickly lashed out at Pruitt for his comments, describing his stance as dangerous and flat-out wrong, and calling on him to resign.
"Pruitt has demonstrated that he is unqualified to run the EPA or any agency," said Kevin Trenberth, a distinguished senior scientist at the National Center for Atmospheric Research.
"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."
The UN's Intergovernmental Panel on Climate Change has found that increased carbon dioxide has been the dominant source of global warming, said Kerry Emanuel, professor of atmospheric science at MIT.
This is followed by methane, halogenated gases, and nitrous oxide, "all of whose concentrations have increased primarily from human activity," Emanuel said.
John Abraham, a professor in the school of engineering at the University of St. Thomas, said "scientists have known since the mid-1800s that carbon dioxide was a major greenhouse gas.
"This means Mr. Pruitt's knowledge is close to 200 years out of date."