Greek students take part in a school strike for climate change in Athens, Greece, on Sept. 20, 2019. The School Strike for Climate on Fridays for Future (FFF) is an international movement of students who take time off from class to participate in demonstrations, in order to prevent further global warming and climate change. In Greece, high school students in 14 cities all over the country decided to skip classes, joining the initiative. (Xinhua/Marios Lolos)