Two Democratic senators questioned President Trump's nominee for Department of Homeland Security secretary about the cause of climate change during a Wednesday hearing that otherwise focused on her credentials and views on national security.

Sen. Tom Carper of Delaware, asked Kirstjen Nielsen, the current White House principal deputy chief of staff, if human activity was to blame for global warming — despite other senators' focusing on cybersecurity and defense-related issues.

"I do absolutely believe that the climate is changing. I can't unequivocally state it's only caused by humans," Nielsen said.

"That's not my question," Carper interjected.

"There are many — there many contributions," Nielsen replied before Carper interrupted again.

"My question was do you believe that it's primarily caused by human beings?" he asked.

"I believe that climate change exists, I'm not prepared to determine causation," she responded.

"Really? Why not?" Carper asked. "Ninety-eight percent of our scientists say this is a problem. For you to sit there and say 'well, it's not really clear' -- something's happening here and I think it is clear."

Later in the confirmation hearing, Sen. Maggie Hassan of New Hampshire, criticized Nielsen's response to Carper's question and the DHS nominee explained her hesitance to answer Carper, in addition to his having run out of time to ask her questions.

"I just wanted to start by expressing my concern to one of Senator Carper's questions about climate change," Hassan said. "When you are in charge of our country's security - when you are in charge of our response to natural disasters - you need to be able to rely on science and technology, and consider and assess the science and technology that you are being advised with objectively and put it well before politics. And what I heard in your answer was politics before science."

"If you are willing to dodge a question when 99 percent of the world's scientists agree that the primary cause of climate change is human activity, that concerns me about your qualifications to take on this role," Hassan added.

Nielsen asked to speak and then said she did not fully answer Carper's initial question because she was cut off due to time constraints.

"What I would have said is that not only do I think that the climate is changing, but I think that it is vital that we in our response, change our modeling, our preparedness, and responses," Nielsen said.

"But if you are unwilling to acknowledge that the primary cause of it is human behavior, then you are not going to be able to change the modeling appropriately," Hassan finished.

President Trump nominated Nielsen in mid-October to take over for former DHS Secretary John Kelly.