Mario Robles del Moral is an ambitious man: his goal is no less than to reforest the entire earth. Seven years ago, this 1996 Associate Laureate set up a foundation in his native Spain to encourage volunteers to plant and care for a single tree each. In its first few years 100,000 trees were planted in Spain alone.

Now Robles del Moral’s initiative has spread to dozens of countries around the world, and more than half a million people are planting trees in an effort to create a green belt stretching across the globe.