Video of the 16-year-old’s glare at Trump went viral after her face changed emotion during the encounter in the United Nations lobby in New York.
Trump, who has faced fierce criticism for his scepticism over man-made climate change, dropped by to listen to German Chancellor Angela Merkel’s detailed pledges, including going coal-free.
He then left without saying anything.
Thunberg had told the UN climate action summit that the eyes of future generations are on world leaders to take urgent action on climate change.
In an impassioned speech, she told delegates they would never be forgiven if they failed to tackle rising temperatures.
The teenager, who travelled to the US by yacht to avoid flying, said she should not be up on stage, but should be in school on the other side of the ocean.
She said: “You come to us young people for hope – how dare you? You have stolen my dreams, my childhood with your empty words.
“People are suffering, people are dying, entire ecosystems are collapsing, we are in the beginning of a mass extinction and all you can talk about is money and the fairy tale of endless economic growth. How dare you?
“How dare you continue to look away, and come here saying that you are doing enough, when the politics and solutions needed are still nowhere in sight.”