WASHINGTON — Scott Pruitt, the head of the Environmental Protection Agency, said on Thursday that carbon dioxide was not a primary contributor to global warming, a statement at odds with the established scientific consensus on climate change.

Asked his views on the role of carbon dioxide, the heat-trapping gas produced by burning fossil fuels, in increasing global warming, Mr. Pruitt said on CNBC’s “Squawk Box” that “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.”

“But we don’t know that yet,” he added. “We need to continue the debate and continue the review and the analysis.”

Mr. Pruitt’s statement contradicts decades of research and analysis by international scientific institutions and federal agencies, including the E.P.A. His remarks on Thursday, which were more categorical than similar testimony before the Senate, may also put him in conflict with laws and regulations that the E.P.A. is charged with enforcing.