Greta Thunberg delivered a fiery speech to the world’s elite at the World Economic Forum in Davos, Switzerland, escalating her message that world leaders needs to step up their efforts to fight climate change before it’s too late.

“Let’s be clear: We don’t need a ‘low-carbon economy,’ we don’t need to ‘lower emissions,’” Thunberg said Tuesday. “Our emissions have to stop.”

One person who wasn’t impressed with Thunberg’s words was Donald Trump’s pick for Secretary of the Treasury, Steven Mnuchin.

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Asked about her speech, reported the Associated Press, Mnuchin made a dismissive joke. “Is she the chief economist? Who is she? I’m confused,” Mnuchin said. After a brief pause, he clarified, “It was a joke.”

He added: “After she goes and studies economics in college, she can come back and explain that to us.”

The 17-year-old activist responded to Mnuchin’s mockery with a scathing tweet that came equipped with a visual aid representing some serious science.

RELATED: Prince Charles Meets Greta Thunberg At World Economic Forum In Davos

“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 tweeted.

“So either you tell us how to achieve this mitigation,” she continued, “or explain to future generations and those already affected by the climate emergency why we should abandon our climate commitments.”

Another member of the Trump administration, however, chose to avoid dissing Thunberg. Ivanka Trump, who serves as a White House aide in her father’s administration, was quoted by The New York Times as saying Thunberg has an “elevated awareness and that’s a positive thing.”

She added: “I’m not going to criticize anyone who’s bringing their energy and voice. That’s not my style. I think she’s elevated awareness, and that’s a positive thing.”

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