Before a rapt audience, Al Gore flashed slides on a giant screen bearing the logos of 11 clean energy companies he predicted could help slow climate change.

“We can’t wait. . . . We have a planetary emergency,” the former vice president told industry leaders and scientists at the 2008 conference. “Here are just a few of the investments that I personally think make sense.”

Today, several of those clean tech firms are thriving, including a solar energy start-up and a Spanish utility company that has dotted rural America with hundreds of wind turbines.

Al Gore is thriving, too.

The man who was within sight of the presidency 12 years ago has transformed himself, becoming perhaps the world’s most renowned crusader on climate change and a highly successful green-tech investor.

Just before leaving public office in 2001, Gore reported assets of less than $2 million; today, his wealth is estimated at $100 million.

Gore charted this path by returning to his longtime passion — clean energy. He benefited from a powerful resume and a constellation of friends in the investment world and in Washington. And four years ago, his portfolio aligned smoothly with the agenda of an incoming administration and its plan to spend billions in stimulus funds on alternative energy.

The recovering politician was pushing the right cause at the perfect time.

Fourteen green-tech firms in which Gore invested received or directly benefited from more than $2.5 billion in loans, grants and tax breaks, part of President Obama’s historic push to seed a U.S. renewable-energy industry with public money.

Over the course of his metamorphosis, Gore became an environmentalist hero with release of his award-winning film and book warning of carbon emissions dangerously overheating the planet. He founded an investment firm devoted in part to backing green-minded companies and later partnered with a leading venture capital firm to invest in clean energy start-ups.

“We have work to do!” Gore recently exhorted an audience while showing his trademark slide show about melting polar ice caps and the urgent need to stop burning so much oil and gas.

That declaration, his friends say, captures his obsession — he’s unable to rest in his self-appointed mission to save the planet.

“Maybe there’s someone as knowledgeable and passionate about climate change. I just haven’t met that person,” said Orin Kramer, a leading New York hedge fund manager, friend of Gore and top Democratic campaign bundler. “His schedule is intensely busy, and my sense is he lives a life that profoundly reflects his values and passions.”

In building his new career, Gore’s name has become ensnared in a broader criticism from Republicans, who put him among political allies they say the Obama administration has unjustly enriched with stimulus and clean-energy funding.

In last week’s presidential debate, Romney criticized the $90 billion that went to promote green technology, saying a number of businesses owned by Obama campaign contributors were winners.