16-year-old climate activist Greta Thunberg watched as Donald Trump walked past at the UN Climate Change Summit on Monday. She did not look pleased.

Trump was initially expected not to attend the summit and was meant to be at a session on religious persecution instead. But he showed up, making a brief appearance just before Indian prime minister Narendra Modi's remarks. According to a pool report, he was there for 14 minutes.

Now footage is circulating of Thunberg's reaction to Trump's entrance. It is truly a glare among glares, which makes sense: Trump has called climate change a "hoax," despite incontrovertible evidence to the contrary, and he has promoted a ruthlessly anti-environment agenda during his time as president.

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SEE ALSO:Greta Thunberg scolds apathetic grown-ups at U.N. Climate Summit

Before Thunberg set sail for the U.S. in mid-August, she made it clear that she had no plans to speak with Trump during her stay. "Why should I waste time talking to him when he, of course, is not going to listen to me?" she said in an interview with CBS. "I can't say anything that he hasn't already heard." (Extremely good call.)

She did deliver a summit address of her own on Monday, admonishing leaders for prioritizing money over the planet and patting themselves on the back for work that's not nearly sufficient.

"For more than 30 years the science has been crystal clear," she said. "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."

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