NEW YORK – President Donald Trump posted a mocking tweet of a 16-year-old climate activist who drew headlines this week for her speech at the United Nations.

Trump quoted a particularly emotional line from Greta Thunberg's address to the Climate Action Summit in a late night tweet on Monday. In it, the Swedish teen said that "people are dying" and "we are in the beginning of a mass extinction."

"She seems like a very happy young girl looking forward to a bright and wonderful future," Trump wrote over Thunberg's quote. "'So nice to see!"

Trump, who is also in New York for the U.N., posted the message in a series of late night tweets. Thunberg has Aspergers syndrome and has previously chided her critics on Twitter: "I'm sometimes a bit different from the norm," she posted on Twitter last year. "And – given the right circumstances – being different is a superpower."

Thunberg appeared to troll Trump back, changing her Twitter profile to embrace the president's words: "A very happy young girl looking forward to a bright and wonderful future."

Trump, who once called climate change a hoax perpetrated by the Chinese, was expected to skip the climate summit at the U.N. on Monday but instead make a surprise visit for about 15 minutes. Many world leaders gathered here are angry that the president is working to pull the U.S. out of the 2016 Paris climate agreement, but Trump has argued that it puts the country at a competitive disadvantage.

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