New Orleans in the forefront of a green building revolution

When hurricane Katrina blew into New Orleans four years ago, Matt Petersen watched in shock as the floodwaters retreated, revealing one of the most devastating natural disasters in US history: billions of dollars in damages, 80 percent of the city flooded with filthy water, and a government response that provoked a firestorm of criticism.
“I watched everything play out in horror,” says Mr. Petersen. “And, like everyone else, I went through the process of thinking, ‘What can I do?’ ”

Petersen donated money and considered volunteering, but that wasn’t enough. “I kept feeling this well up inside me, I felt compelled to act,” he says.

As the city’s cleanup began, Petersen, the president and CEO of Global Green, an environmental nonprofit that promotes green building, saw a silver – or green – lining in Katrina’s catastrophic wake