Jeffrey Sachs -- the renowned economist who devised a grand plan in 2005 to rid the world of poverty -- is now focused on an even broader ambition: saving the planet and all of us who call it home.
His new book, Common Wealth: Economics for a Crowded Planet, explores the crises of climate change and ecological degradation in a world squeezed by soaring population and industrial growth. But it's no doomsayer's lament. Sachs is a practical problem solver who's made his name advising big players in international politics and drawing up detailed plans for tackling the world's biggest challenges -- plus palling around with do-gooding celebs like Bono and Angelina Jolie. A professor of sustainable development and director of the Earth Institute at Columbia University, Sachs is also a bigwig at the United Nations, where he advises Secretary-General Ban Ki-moon. He previously served as special adviser to Secretary-General Kofi Annan from 2002 to 2006, during which time he oversaw the U.N.'s Millennium Project.