“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.”

Over an hour and a half, he delivers an endless stream of facts and trends from around the globe. Every minute in Bangladesh, two more homes get new rooftop solar panels. Dubai’s state utility accepted a bid for a solar power plant with a cost per kilowatt-hour of less than six cents. “Wow,” he says, his eyes wide. “That just set everybody on their ear.”

Such changes, he says, represent a sharp break with the past, not a slow evolution. That is the point of those slides on his laptop. In 1980, one shows, consultants for AT&T projected that 900,000 cellphones might be sold by 2000. In fact, there were 109 million by then. Today there are some seven billion. “So the question is: Why were they not only wrong, but way wrong?” he says. He presses a button, and up pops an old photo of a young Al Gore with a helmet of hair and an early mobile phone roughly the size of one of Michael Jordan’s sneakers.

The same kind of transformation that turned those expensive, clunkers into powerful computers in every pocket is happening now in energy, he says, with new technology leapfrogging old infrastructure. “It’s coming so fast,” he says. “It’s very, very exciting.”