President Donald Trump's new Environmental Protection Agency chief Scott Pruitt has said he is not convinced carbon dioxide emissions from human activity are the primary driver of global warming.

"I think that measuring with precision human activity on the climate is something very challenging to do and there is tremendous disagreement about the degree of impact," he told CNBC.

"So no, I would not agree that it is a primary contributor to the global warming that we see. But we don't know that yet, we need to continue to debate, continue the review and analysis."

His comments contradicted the Environmental Protection Agency of which he is Administrator.

On its website the agency says: "Carbon dioxide is the primary greenhouse gas that is contributing to recent climate change."