(Fortune Magazine) -- It's lunchtime on Sand Hill Road, and Al Gore wants answers. "How does the efficiency decline with latitude?" he asks. "What size community could be served by one plant? If a manufacturer like GE wanted to make smaller turbines, would the technology support a smaller scale?"

We're sitting in the giant conference room at Kleiner Perkins Caufield & Byers, where the partners hold their weekly meetings. After loading his plate with Chinese food from a buffet, Gore is firing detailed questions at the management team of Ausra, a Kleiner-backed company in Palo Alto whose technology uses mirrors the width of a flatbed truck that focus the sun's energy to generate electricity.

Once Gore is satisfied -- sunlight lags north of South Dakota, an Ausra plant can serve 120,000 homes, and yes, smaller turbines will work fine -- he shifts from inquisitor to fixer. He was chatting with California Senator Barbara Boxer "on the way over," he reports, and he isn't optimistic that Congress will extend the tax credits Ausra has been relying on. On the upside, he offers on the spot to organize a summit highlighting the company's solar thermal technology to educate lawmakers and other policymakers on its potential. He also thinks a powwow at General Electric (GE, Fortune 500) would be beneficial, even though Ausra is a tiny customer.

"I know Immelt well," he says, referring to GE's CEO. "We ought to set up a meeting."

Gore appears utterly comfortable with this drill, but in fact he's engaging in some on-the-job training. The recovering politician, environmental activist, and Nobel laureate is adding another title to his r�sum�: venture capitalist. After "a conversation that's gone on for a year and a half," according to Gore, he has decided to join his old pal John Doerr as an active, hands-on partner at Kleiner Perkins, Silicon Valley's preeminent venture firm.

The move is more than another Colin Powell moment (the former Secretary of State signed on as a Kleiner "strategic limited partner" two years ago and has hardly been heard from since). Gore is joining the firm as Kleiner makes a risky move beyond information technology and health-care investing into the fast-growing and increasingly competitive arena of "clean technology."

According to Doerr, by 2009 more than a third of Kleiner's latest fund, which was raised in 2006 and totals $600 million, will be invested in technologies that aim to reduce emissions of carbon dioxide. Already Kleiner has invested more than $270 million from various funds in 26 companies that make everything from microbes that scrub old oil wells to electric cars to noncorn ethanol. Twelve of Kleiner's 22 partners now spend some or all of their time on green investments.

In turn, Doerr, the master networker whose greatest hits include initial investments in Netscape, Amazon (AMZN, Fortune 500), and Google (GOOG, Fortune 500), will join the exclusive advisory board of Generation Investment Management. That's the $1 billion investment company Gore started three years ago in London with David Blood, the former head of Goldman Sachs Asset Management, to analyze and invest in publicly traded "sustainable" companies. Over the past five weeks Gore, Doerr, and Blood agreed to give Fortune an exclusive look at their new alliance.

Already they've begun to pool information. Generation came across a small company engaged in carbon trading that Kleiner is analyzing, and Kleiner has shared intelligence about which startups could threaten the established companies in Generation's portfolio. In the long term, though, they want to help drive something much larger, "bigger than the Industrial Revolution and significantly faster," as Gore puts it.

They argue that to halt global warming, nothing less will be required than a makeover of the $6 trillion global energy business. Coal plants, gas stations, the internal-combustion engine, petrochemicals, plastic bags, even bottled water will have to give way to clean, green, sustainable technologies. "What we are going to have to put in place is a combination of the Manhattan Project, the Apollo project, and the Marshall Plan, and scale it globally," Gore continues. "It'd be promising too much to say we can do it on our own, but we intend to do our part."

Does that sound grandiose? Sure. Will they be accused of being partisan? Probably. Is there something incongruous about globetrotting rich guys jetting between multiple homes and lecturing the rest of us about climate change? Of course.

But there are good reasons to take Gore and Doerr seriously. Gore, who never seemed fully at ease as a presidential candidate, has demonstrated a real knack for using mass communications to influence public opinion. (He estimates that he's shown his homespun slide show on global warming more than 1,000 times, while the documentary version, An Inconvenient Truth, won him an Oscar.) Doerr, meanwhile, has displayed a real talent for deploying venture capital to create or disrupt whole industries.

In short, the foremost eco-activist and the dean of Sand Hill Road could, together, draw a huge amount of attention and cash to companies that are aiming to reduce our reliance on fossil fuels.

There is, however, one thing standing in their way. Five years after Kleiner Perkins made its first green investment, the firm hasn't had one "exit" -- VC-speak for an IPO or a sale of a company that validates the investment thesis. Doerr equates this moment to Internet investing (which he famously called "the greatest legal creation of wealth in the history of the planet") before Kleiner took a certain web browser public in 1995. Now, he wonders, "what's the company that will lead the boom? What's the Netscape of green innovation?"

A bleary-eyed Al Gore needs another cup of coffee, and no wonder. It's a Tuesday morning, and four days earlier he and his wife, Tipper, were up into the wee hours in San Francisco waiting to learn if he'd won the Nobel. (He was cited "for informing the world of the dangers posed by climate change.") They then flew home to Nashville after a stopover in Phoenix, where Gore spoke to an advertising industry convention about Current TV, the youth-oriented cable television network he co-founded in 2002. Over the weekend, Tipper threw him a party with 150 or so of their closest friends. Country singers Kathy Mattea and Kim Richey preformed at the bash, at Nashville's Park Caf�.

"It was a good weekend," Gore says with a grin.

Now Gore, Doerr, and Blood are gathered on the back patio of Gore's $2.3 million, 10,000-square-foot home in the Belle Meade section of Nashville. That's the mansion -- to Gore's critics it's always a mansion -- that tagged the former Vice President as an energy hog. He's quick to point out that the house generates electricity from more than 30 solar photovoltaic panels on the roof as well as seven 300-foot geothermal wells in the ground, and that it has been certified as an energy-efficient home by the U.S. Green Building Council.

After offering everyone coffee or bottled water (hey, no one's perfect), Gore explains why he's combining his advocacy work with a profit motive. "We want to give a big shout-out, though that's not the corporate term, to every inventor and entrepreneur and idea generator at the micro, macro, systems-integration, and global-thinker level to create with this alliance a clearinghouse for the identification and selection of the most promising ideas on the planet for quickly solving this climate crisis," he says, without pausing to take a breath. Then, clearly catching himself in a moment of speechifying, Gore boils it down: "We all believe that markets must play a central role."

Professionally Gore, Doerr, and Blood have little in common. Once the boy wonder of American politics, Gore turns 60 in March. In addition to his roles at Kleiner, Generation, and Current, he's an advisor to Google and a director at Apple (AAPL, Fortune 500). He also founded an advocacy organization in Palo Alto called the Alliance for Climate Protection.

At times his schedule seems downright presidential: the week after our interview in Nashville, Gore visited the leaders of France, Germany, and Austria to talk about the environment. Says Gary Hirshberg, a climate-change activist and the CEO of Stonyfield Farm, who has known Gore for years: "I had an easier time seeing him when he was in the White House."

Technically, of course, Gore was never "in" the White House. But he's been dealing with continual speculation about whether he still has designs on the place. Is there a chance he'll jump into the race? "It's a luxury to be able to focus on what you are most passionate about all the time," he says. When asked to elaborate he adds, "Casting about for words to describe this with precision is less productive than just saying that what I'm doing feels like the right thing to do." So the answer is probably not, though like any good politician, he's left the door open.

For now Gore truly seems to enjoy kicking around Nashville, where he'll continue to be based. Since he won't be on Sand Hill Road daily, he explains, he's installed a high-definition videoconferencing system to dial into Kleiner's weekly partner meetings.

If Gore is the elder statesman of the group, Doerr is the salesman. Famous both for his boundless energy and his high-end hucksterism, at 56 he is wiry and birdlike in his tendency to flit from topic to topic. He specializes in making everyone around him believe as passionately about his current cause -- -first the PC, then the Internet, now the environment -- as he does.