Swedish climate activist Greta Thunberg and President Donald Trump offered two opposing visions Tuesday at the World Economic Forum in Davos, Switzerland, with Trump lashing out at what he said were “perennial prophets of doom and their predictions of the apocalypse” as Thunberg inveighed against the sowers of “climate chaos.”

“We will never let radical socialists destroy our economy, wreck our country or eradicate our liberty,” Trump said at the conference.

Even though Trump said he was a “big believer in the environment” and did not explicitly name climate change as he lashed out at “alarmists,” his remarks stood in stark contrast to the 17-year old Thunberg’s renewed call to “start listening to the science” on climate change. The world, she said on Tuesday, needs to “treat this crisis with the importance it deserves.”

Thunberg’s remarks echoed her prior warning in Davos last year, when she told world leaders: “I don’t want your hope. I don’t want you to be hopeful. I want you to panic. I want you to feel the fear I feel every day. And then I want you to act.”

The Swedish teenager’s activism helped inspire a global climate action movement, which earned her Time Magazine’s Person of the Year title in December.

“Without treating it as a real crisis we cannot solve it,” Thunberg said at the annual conference, which brings together political and economic leaders from around the world.

Thunberg is also set to give a second speech Tuesday afternoon. “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,” Thunberg is set to say, according to a transcript of her planned remarks, shared with the New York Times.

While she and Trump did not mention each other directly in their speeches, their remarks represented a head-on collision of worldviews. In his remarks, according to reports, he referred to today’s activists as “the heirs of yesterday’s foolish fortune tellers.”

Robert Habeck, the leader of the German Greens, said he “hadn’t expected much, but [Trump’s] speech was a disaster for the conference, for the idea of the conference, for the idea of multilateralism.”

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