Why Did Trump Pick a Fight With This Teen Activist?

Greta Thunberg has been calling out world leaders for failing to act on climate change.

President Trump is taking on teenage climate fighter Greta Thunberg after their frosty encounter at the United Nations Monday.

The Swedish 16-year-old has criticized world leaders for their lack of action against climate change. Though she has not mentioned Trump by name, the president has suggested the climate change does not exist or is not an immediate threat. When the two crossed paths at the U.N., she gave the president an icy glare, a face that quickly went viral.

Greta has used strong words in addressing politicians. Her time at the U.N. was no different, saying, “You have stolen my dreams and my childhood with your empty words."

On Monday night, the president appeared to mock her outlook, tweeting, “She seems like a very happy young girl, looking forward to a bright and wonderful future, so nice to see.”

Greta has also been the target of attacks from others in the U.S. A conservative guest appearing on Fox News called the teenager, who has Asperger’s syndrome, "mentally ill."

A spokesman for Fox News called the remark "disgraceful" and said the pundit, Michael Knowles, will not be invited back.

But Greta seems to be taking the criticism in stride. She adopted Trump’s words as the new motto for her Twitter page, writing in her bio that she is “a very happy young girl, looking forward to a bright and wonderful future.”