One world leader who opted not to attend the summit (before popping by unannounced) was Donald Trump, who despite the science, opts to pretend climate change is totally made up. The President of the United States responded to Greta's emotional plea in the mature way you'd expect: by making a joke out of the teenager on social media.
"She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see!" he wrote above the viral video of Greta's speech.
Not one to take prisoners, Greta trolled the president right back, swiftly adding his words to her Twitter bio.
The Twitter feud comes just one-day after Greta stared down Trump in a now-viral meme when he made a surprise appearance at the U.N. General Assembly.