Thunberg, who made a name for herself by turning a one-person school-absenteeism-as-protest stunt into a global movement, joined in the chants at the rally. She spoke, calling for ready action, not waiting to see what happens.

Thunberg, who is now 16, soared to international recognition in 2018 by going not to school but to Parliament in Stockholm to protest. She had a wooden sign and some flyers, containing facts about carbon footprint and climate change. She spent what would have been her schoolday hours in front of Parliament, holding up the sign and handing out flyers. She went back the next day and found other people ready to stand with her. Every school from then until Sept. 9–the day of her country's general elections–Thunberg spent outside Parliament, holding her own vigil; the crowds with her grew and grew. She wanted to call attention to the fact that her country's environmental policies were not necessarily in line with the 2015 Paris Agreement on actions needed to combat climate change.

She is not attending school this year in order to focus fully on her campaign to raise awareness about climate change. She has led the charge for events around the world, including a series of Climatestrike days, in which students and adults in cities on most continents followed Thunberg's example and spent school hours protesting against the pace of climate change.

Thunberg plans to testify before Congress and to join a protest outside the U.S. Supreme Court building. (The Court might eventually consider a case in which a group of students are suing the federal government over its climate change inaction.) She will also attend the United Nations Climate Action Summit, which is September 23 in New York. That summit will take place inside a global weeklong Climate Strike, which begins Sept. 20.

Her travel plans after the summit include visits to Canada and to Mexico and then in December to Chile, for the annual U.N. Framework Convention on Climate Change. She has yet to decide how she will travel to those countries or how she will get home. One thing she does know is that she won't be getting on a plane.