WASHINGTON — EPA Administrator Scott Pruitt’s phones have been ringing off the hook – literally – since he questioned the link between human activity and climate change.

The calls to Pruitt’s main line, (202) 546-4700, reached such a high volume by Friday that agency officials created an impromptu call center, according to three agency employees. The officials asked for anonymity out of fear of retaliation.

Interns were dispatched to answer some of the incoming calls, according to one employee. At times, calls to that number ended up going to voicemail. The EPA did not respond immediately to a request for comment.

While constituents sometimes call lawmakers in large numbers to express outrage over contentious policy issues, it is unusual for Americans to target a Cabinet official.

Pruitt’s comments on the CNBC program “Squawk Box – that “we need to continue the debate and continue the review and the analysis” over climate change – prompted an immediate outcry from many scientists and environmental groups.

“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 said.

The U.N. Intergovernmental Panel on Climate Change has concluded that it is “extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century” – a position reiterated on EPA’s own website.

On Friday, the National Oceanic and Atmospheric Administration announced that the level of carbon dioxide in the atmosphere rose at a record pace for the second straight year.