The U.S. president appeared to mock the environmental activist after her speech at the U.N. President Donald Trump, via Twitter The president is well-known for going after critics on Twitter. Trump also shared a video of Thunberg's address in which she bashed world leaders for inaction on climate change. Greta Thunberg, via U.N. Trump's name was not specifically dropped in the 16-year-old Swedish native's speech. She has appeared to respond with a new Twitter bio referencing his tweet. Greta Thunberg, via Twitter.