DAVOS, Switzerland — U.S. Treasury Secretary Steven Mnuchin mocked the Swedish climate change activist Greta Thunberg on Thursday, urging her to go to college and study economics before she tells countries what to do.

Thunberg and Mnuchin are both attending the World Economic Forum this week. Thunberg called on world leaders, including President Trump, to “start listening to science” and end carbon emissions immediately. Thunberg is 17 years old and was named Time Magazine’s “Person of the Year" in 2019.

At a news conference on Thursday, Mnuchin was asked for his reaction to Thunberg’s insistence on fossil fuel divestment. “Who is she?” he tried to joke to reporters before taking a jab at Thunberg, suggesting she didn’t understand what she was talking about.

Here is the full exchange:

Reporter: “Greta Thunberg has called for public and private sector divestment from fossil fuel companies. Does that pose a threat to this U.S. economic growth that you guys are talking about?”

Mnuchin: “Is she the chief economist or who is she? I’m confused.”

Reporter: “Greta Thunberg.”

Mnuchin: “It’s a joke!” [some laughter follows.] “After she goes and studies economics in college she can go back and explain that to us.”

Mnuchin’s comments have gone viral, adding yet another blow between Trump and Thunberg, whose dueling views of the future have been the dominant discussion at Davos this year.

Thunberg responded later on Twitter.

"My gap year ends in August, but it doesn’t take a college degree in economics to realize that our remaining 1.5° carbon budget and ongoing fossil fuel subsidies and investments don’t add up,” she wrote. “So either you tell us how to achieve this mitigation or explain to future generations and those already affected by the climate emergency why we should abandon our climate commitments.”

Trump said Tuesday that climate activists are “prophets of doom” who just want to “control every aspect of our lives.”

Thunberg and numerous European leaders spent the week saying the world is in a state of emergency and urgent action is required. The European Union has pledged to be carbon neutral by 2050.

German Chancellor Angela Merkel talked about the divide between European leaders and Trump on climate change on Thursday.

“The lack of conversation between those who believe in climate change and those who don’t worries me. They speak rarely with one another,” Merkel said Thursday in a speech in Davos. “It’s almost worse than in the Cold War. We must overcome it.”

When asked about whether the United States is doing enough for a more sustainable future, Mnuchin talked about how he used to drive a Tesla. He added there’s a “misinterpretation” of Trump’s policy.

“President Trump absolutely believes in clean air, clean water and having a clean environment,” Mnuchin said. “The U.S. has been a leader in reducing carbon emissions.”