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EPA chief Scott Pruitt denies CO2 is a 'primary contributor' to global warming

Scott Pruitt, head of the Environmental Protection Agency, said Thursday he "would not agree" that carbon dioxide has been proven a "primary contributor" to global warming. Despite a statement from NASA and the National Oceanic and Atmospheric Administration in January noting the planet's rising temperature has been "driven largely by increased carbon dioxide and other human-made emissions into the atmosphere," Pruitt insisted "we don't know that yet" and need "to continue the debate." The EPA's website also cites carbon dioxide as the "primary greenhouse gas that is contributing to recent climate change."

"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 told CNBC's Squawk Box.

Watch Pruitt's denial below. Becca Stanek