Climate change is a pressing concern for Bill Gates, who has just published a new book on the subject. He spoke with HBR's editor-in-chief about the need to reduce carbon emissions to zero by 2050--and the difficulty of that undertaking. It will require new government policies, changes in corporate and individual behavior, and, above all, more R&D funding and innovation to create cleaner technologies and green products. Gates is optimistic that we can succeed but clear-eyed about what lies ahead if we don't: rising temperatures, the disappearance of ecosystems, disastrous crop failures, economic pain, and massive loss of life.

Bill Gates and Warren Buffett are by far the two most successful and admired businessmen in the United States. They share a unique friendship, a love of business, and a passion for hamburgers and mathematical puzzles. In a review of Roger Lowenstein's Buffet: The Making of an American Capitalist, Gates reflects on his relationship with the man he affectionately calls Warren. In his first-person account of their time together, Gates talks about creating value and sharing values. Of Buffett, Gates says, "I had never met anyone who thought about business in such a clear way."