Treasury Secretary Steve Mnuchin becomes the latest member of the Trump admin to bash climate activist Greta Thunberg, condescendingly telling the 17-year-old to study economics in college before talking.

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UPDATE, 1/21/20, 5:15pm ET: Greta Thunberg responded to Steven Mnuchin on Twitter by posting a graph (see below) showing how continuing to use fossil fuels will destroy the environment. “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.”

ORIGINAL: Treasury Secretary Steven Mnuchin, 57, claimed to not know who Greta Thunberg is before insulting her at the World Economic Forum. The former film producer lashed out at the 17-year-old climate activist after she gave impassioned speech urging business leaders to stop investing in fossil fuels immediately. “Is she the chief economist? Who is she, I’m confused. After she goes and studies economics in college she can come back and explain that to us,” Mnuchin said at a press conference during the annual event in Davos, Switzerland. He added after a pause that he was only “joking.”

Thunberg, whose tireless activism got her named TIME’s Person of the Year 2019, told world leaders at the conference that their inaction on climate change would condemn their children to inescapable environmental catastrophe. “I wonder, what will you tell your children was the reason to fail and leave them facing the climate chaos you knowingly brought upon them?” Thunberg told a hushed room on January 22. “Our house is still on fire. Your inaction is fueling the flames by the hour. We are still telling you to panic, and to act as if you loved your children above all else” she added, echoing the powerful speech she gave at 2019 World Economic Forum. Thunberg’s Davos speech came shortly after US President Donald Trump‘s, in which he attacked climate activists as “heirs of yesterday’s foolish fortune tellers.”

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. 1/3

— Greta Thunberg (@GretaThunberg) January 23, 2020

Thunberg was in the sixth row as he spoke, calling activists such as herself “perennial prophets of doom” and mocked what he called “their predictions of the apocalypse.” Trump claimed that he was a “big believer” in the environment, and pledged for the United States to join the UN’s Trillion Tree Campaign. Thunberg did not mention Trump in her own speech, but said that planting trees was “good, but nowhere near enough.”

Mnuchin defended the United States’ environmental policies at Davos after his quip about Thunberg, saying that Trump “absolutely” believes in “clean air and water, and a clean environment.” The United States and China are the world’s largest emitters of greenhouse gases.