In the past decade, planting trees has come to represent many things: a virtuous act, a practical solution and a symbol of hope in the face of climate change. But can planting a trillion trees really save the world? Visiting the Eden Reforestation Projects in Goiás, Brazil, and interviewing numerous international scientists and activists, the journalist Zach St. George offers a vivid insight into the root of the tree-planting movement — from the Green Belt Movement of the 1970s to the Trillion Tree Campaign of the 2010s — and considers the concept’s environmental potential, as well as the movement’s shortcomings.