Forcing the World To Sit Up and Listen.(Jeffrey Sachs)

Jeffrey Sachs is a macroeconomist by training, an expert in the vagaries of business cycles and international finance. But give the man 10 minutes onstage, and a scholarly symposium starts to feel like a revival meeting. "Let me take you to Malawi," he urges a typical audience, leaning into the mike and lowering his voice. Like most countries in southern Africa, Malawi has been ravaged by AIDS for two decades. One adult in seven is HIV-positive, and some 2 million children have been orphaned. But instead of hurling numbers at his listeners, Sachs transports them to Queen Elizabeth Central Hospital in Blantyre, a site he visited this year while traveling with the rock star Bono.

At one end of the facility is a small out-patient clinic where people who can pay $1 a day receive life-sustaining AIDS drugs. "They take the medicine and they get better," Sachs declares. "They return to work. They go back to caring for their children." Unfortunately, $1 a day is nearly twice what a typical Malawian lives on. So most AIDS patients end up in wards like the one just down the hall from the outpatient clinic. There 450 emaciated souls lie crammed into 160 cots, moaning softly and waiting for death to end their misery. "Ladies and gentlemen," Sachs tells the now hushed hall, "this plague is exploding. Its consequences will make the world quake. Rich countries could stop the devastation. And most are still looking away."

Sachs is not the first to sound this alarm, but he speaks with special authority. As the newly appointed director of Columbia University's Earth Institute, he heads a huge, interdisciplinary effort to help poor countries build sustainable economies. Instead of treating soil depletion, climate change, epidemic disease and social upheaval as distinct phenomena, the institute's 800 scientists study the links among such ...