WASHINGTON - The new chief of the Environmental Protection Agency says he does not believe that carbon dioxide is a primary contributor to global warming.

EPA Administrator Scott Pruitt says measuring the effect of human activity on the climate is "very challenging" and says "there's tremendous disagreement about the degree of impact" of carbon dioxide and other greenhouse gases.

Pruitt told CNBC's "Squawk Box" Thursday that, "No, I would not agree that (carbon dioxide) is a primary contributor to the global warming that we see."

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, "a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere."