Story highlights Bernie Sanders was asked by a high school student about the science behind global warming

"It is already causing devastating problems in our country and the world," he responded. "That is what the scientists are saying"

Des Moines, Iowa (CNN) Bernie Sanders has made fighting climate change a central part of his message, and he's not about to hold back when challenged by someone who questions the scientific consensus that human-caused emissions are behind global warming -- even if it's a teenager.

The Vermont senator, old enough to be the grandfather to many of the attendees at a town hall at Roosevelt High School Thursday, was asked by a 17-year-old about his position on climate change. She said that she was not convinced it was caused by humans.

"I haven't seen any actual scientific evidence that global warming is actually happening," she said. "It's only very recent. So I'd like to know why you think it's happening."

Sanders respond with a polite but firm: "You're wrong."

"It is already causing devastating problems in our country and the world. That is what the scientists are saying," he told her.

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