Some scientists, including the Harvard biologist Edward O. Wilson, have concluded that at least half the planet needs to be protected to save a large majority of plant and wildlife species from extinction. Indeed, the food, clean water and air we need to survive and prosper depends on our ability to protect the planet's biological diversity. In other words, we have to protect half to save the whole. Every one of us - citizens, philanthropists, business and government leaders - should be troubled by the enormous gap between how little of our natural world is currently protected and how much should be protected. For my part, I have decided to donate $1 billion over the next decade to help accelerate land and ocean conservation efforts around the world, with the goal of protecting 30 percent of the planet's surface by 2030. This money will support locally led conservation efforts around the world, push for increased global targets for land and ocean protection, seek to raise public awareness about the importance of this effort, and fund scientific studies to identify the best strategies to reach our target. I believe this ambitious goal is achievable because I've seen what can be accomplished. Indigenous peoples, local leaders and conservation groups around the world are already busy setting aside protected areas that reflect the conservation, economic and cultural values of nearby communities. Financial support from philanthropists and governments is critical to helping these leaders conserve places like the coral reefs of the Caribbean, the glaciers of Argentina and what is known as the "place of many elephants" in Zimbabwe.