Over the last year, however, the prophet of doom has become much more a prophet of possibility — even, perhaps, an optimist. Still an object of derision for the political right, Mr. Gore has seen support for his views rising within the business community: Investment in renewable energy sources like wind and solar is skyrocketing as their costs plummet. He has slides for that, too. Experts predicted in 2000 that wind generated power worldwide would reach 30 gigawatts; by 2010, it was 200 gigawatts, and by last year it reached nearly 370, or more than 12 times higher. Installations of solar power would add one new gigawatt per year by 2010, predictions in 2002 stated. It turned out to be 17 times that by 2010 and 48 times that amount last year.

“I think most people have been surprised, even shocked, by how quickly the cost has come down,” Mr. Gore says in his office in an environmentally friendly building in the prosperous Green Hills neighborhood of Nashville. He sports a style that might be called Southern business casual: a blazer and dress shirt, bluejeans and cowboy boots. At age 66, he is also trimmer than he was during his bearish, bearded period after the 2000 election, thanks in part to a vegan diet he has maintained for two years. In this city? Home of heavenly meat-and-three platters?

He smiles and says proudly, “There are 10 vegan restaurants in Nashville now.”