(This is the second of two parts. Click here for Part 1)

Fortunately for them, the young leaders committed to broadening the green base enjoy the privilege of having inherited a billion-dollar movement infrastructure: offices, websites, and, most important, membership lists. Everyone I spoke with was appreciative of this fact, and had nothing but kind things to say about the people who came before them.

“Our predecessors did an amazing job with what they had,” Jennifer Krill, the 38-year-old head of the mining and natural gas watchdog group Earthworks said. At the same time, there’s a feeling that the legal and regulatory tactics that have become the bread and butter for so many environmental groups may have reached the limits of their effectiveness.

“At some point in the late seventies, early eighties, we got really aggressive and successful at lobbying Capitol Hill and the White House, and that was a transition from being more of a grassroots environmental community,” Pica said. “And I think that the successes that we had … I think we took some of the wrong lessons away. That transformed the movement into this lawyerly, regulatory, DC Beltway-focused community. And we’ve kind of forgotten, neglected the power base that got us to that point.”

To be fair, lawsuits and lobbying have been useful for enforcing – and, when under threat, defending – the country’s landmark environmental laws. The attorney-centric NRDC, for example, has played an invaluable role in preventing rollbacks of earlier gains. But the insider strategy is unlikely to build the popular momentum needed to address the twenty-first-century threats to the environment. You’re not going to overhaul the foundation of industrial society with a relatively small group of lawyers and scientific experts.

“There’s a decreasing return on investment for this strategy of the dominant DC groups,” Radford said, “investing in smart policy people, but not investing in the grassroots.”

I heard some variation of “investing in the grassroots” from almost everyone I spoke with. To do that successfully, the new leaders must overcome challenges their predecessors didn’t face – most notably, a graying membership and the tricky terrain of the internet.

Over the last 40 years, the green groups have built large lists of members mostly through direct mail. Now that membership is aging, and the twenty- and thirty-somethings coming up behind are immune to the mail request. This poses a threat to green groups’ political strength and their financial health. Of course, many younger people do have a sense of civic engagement: The Obama campaign’s success with the Millennial Generation proved as much. But they engage in a different fashion – online.

And that represents the second major challenge for the new leaders’ aspirations: finding a way to ensure that internet activism is just as effective as the tried-and-true tactics of marching and petitioning and calling your legislator. This isn’t easy. In the last decade, figuring out how to convert online “awareness raising” to real world action has become the Philosopher’s Stone of political organizing. When it works, the Internet can be an awesome tool for social change, as proven by the continued strength of the 4 million-member Moveon.org. But sometimes it becomes simply “clicktivism” – mouse maneuvering as a substitute for real organizing.

Greenpeace’s Radford is one of the leaders who has had some success in growing membership. As Greenpeace’s organizing director, he increased membership from 100,000 people to 280,000 people, a success that propelled his precocious rise. He accomplished this mostly through old-school canvassing – college kids with clipboards going door-to-door and standing on street corners. The result, Radford said, is a membership more likely to take action when it comes time to press a campaign. “If you’re saying, ‘Hey, do you want a cloth tote?’ then you see your numbers jump dramatically,” he said. “But what you end up with is a donor pool that responds far less to your mission or things that are just about taking action or being part of something bigger. It’s just a really different dynamic.”

Of all the environmental organizations, 350.org has probably been the most successful at translating online connections into real-world actions. The group has built a global activist community knit together by, of all things, a number referring to parts per million of carbon dioxide in the atmosphere. “When we set out with 350, we really were trying to spread it as a meme, and the day of action was a tool to do that,” said May Boeve, another 350 organizer. Boeve (rhymes with movie) is a California blonde who, like most of the 350 staff, started working with McKibben while a student at Middlebury College. The 350 staff is organized as a consensus-based collective, but with her executive focus and force of personality, Boeve operates as the de facto chief of staff. “I don’t know if there’s any campaign comparable to ours where all of these people all around the world who aren’t on the payroll and who we don’t even know send us 350 photos and set up their own 350 chapters. I think we were effective at trying all kinds of things just to get the number out there, and brand it as a symbol of climate safety and the science, but as something you could belong to.”