In August 2018, a teenager named Greta Thunberg missed school to sit outside the Swedish parliament with a sign that read School Strike for Climate. She was demanding that government leaders take stronger action against climate change due to global warming. At first, Greta sat alone. But her message spread. Other students joined her in the movement that became known as Fridays for Future. By September 2019, millions of activists from around the world marched in protests to protect the future of the planet.