DAVOS, Switzerland (AP) — Greta Thunberg isn’t easily intimidated.

The 17-year-old Swedish activist wasted little time on Tuesday to push back against U.S. President Donald Trump’s description of climate campaigners as “the perennial prophets of doom” who predict the “apocalypse.”

Though Trump didn’t mention her directly in his speech at the World Economic Forum in the Swiss Alpine resort of Davos, it was clear he had his sights on Thunberg, who shot to fame a year ago by staging a regular strike at her school and sparked a global environmental movement. She then beat Trump to receive Time Magazine’s award as the 2019 Person of the Year.

“The facts are clear, but they are still too uncomfortable for you to address,” she told business and political leaders in Davos just after Trump’s speech, also without directly mentioning the president. “You just leave it because you think it’s too depressing and people will give up, but people will not give up. You are the ones who are giving up.”

Thunberg brushed aside Trump’s announcement that the U.S. would join the economic forum’s initiative to plant 1 trillion trees across the globe to help capture carbon dioxide from the Earth’s atmosphere.