Twenty-seven-year-old Brent Schulkin has a theory: The best way to stop global warming isn’t with radical activism, but by politely asking businesses to make environmentally responsible changes, and then rewarding the most cooperative business by inviting friends and friends of friends to buy exclusively from it.

Schulkin, a former corporate team builder, tested his theory last March: He asked 23 minimart owners in San Francisco’s Mission District what percentage of their profits they’d be willing to put toward greening up their businesses. In exchange, he would invite the quickly multiplying network he calls the “Carrotmob” to shop at their store for two hours.

Song Lee, owner of K & D Market, made the top bid of 22 percent. And much to his delight, some 400 people—lured by mass e-mails, Facebook and MySpace alerts, and neighborhood flyers—bought $9,276.50 worth of products, everything from Lucky Charms to compact fluorescent lightbulbs to whiskey. The store would ordinarily have grossed about $3,000, the manager says.

Schulkin videotaped the event, even editing in a raunchy spoof of a Lil Wayne hip-hop video that he shot before the shopping began; he hoped mobbers would pass it along via e-mail or Facebook pages and attract more converts. The video’s best moment may be when a 20-something sporting a flame-orange mohawk earnestly tells his interviewer, “What really impressed me about this idea is how scalable it is.”

Lee held up his part of the bargain, too; and then some. Following the advice of experts from the San Francisco Energy Watch program, he put 22 percent of the entire day’s revenue toward a wholly green lighting system.

So what’s next for Carrotmob, now 2,000 strong? Since Schulkin has just acquired an anonymous partner to fund the nonprofit organization, it’s on to whatever the mobbers want, he says. And he’s sure they’ll make an even bigger impact. As he writes on Carrotmob’s Web site, “companies will do what we want, not because of negative pressure, or morality, or a boycott, or a petition … there are enough sticks out there. We need a big juicy carrot. They will do what we say because they won’t be able to resist the profits.”

Read more stories by Jennifer Roberts.