Official White House Photo by Andrea Hanks(DAVOS, Switzerland) -- U.S. Treasury Secretary Steve Mnuchin said teen climate activist Greta Thunberg can talk about divesting from fossil fuels "after she goes and studies economics."

Mnuchin made the comments to reporters Thursday in Davos, Switzerland, where world and business leaders are gathering for the annual World Economic Forum meeting.

Thunberg, 17, and Mnuchin, 57, were both headline speakers at this year's gathering.

When asked by a reporter if Thunberg's call for an end to fossil fuel investment would threaten U.S. economic growth, Mnuchin responded with: "Is she the chief economist or who is she? I'm confused."

He then followed up with, "that's a joke."

"After she goes and studies economics in college, she can come back and explain that to us," Mnuchin said.

The Swedish teen, who is currently taking a gap year from school for her activism work, said she intends to return to school and have a "normal life" in August.

She responded to Mnuchin's remarks on Twitter, saying "it doesn't take a college degree" to see the impact of fossil fuel subsidies and investments on carbon emission.

"My gap year ends in August, but it doesn’t take a college degree in economics to realise 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," she added in a follow-up tweet.

This isn't the first time world leaders have come after the teen.

President Donald Trump has famously feuded with Greta on Twitter, telling her to "chill."

President Jair Bolsonaro of Brazil called her a "brat."

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