Some 600 people, many with gray ponytails, fill the auditorium at the Sonoma Country Day School. Their earnest metal water bottles clank as they settle into their seats. A short film plays, featuring ugly potato puppets portraying John and Yoko in bed. Instead of protesting the Vietnam War, the two are protesting climate change. Even as a tuber, Yoko remains a fresh object of derision to boomers. Her little potato mouth promises to "scream a song to Mother Nature." The audience howls delightedly. They remember John and Yoko. A short documentary screens, showing area high school students working for climate change. The audience claps heartily. They're proud of their grandchildren. An elderly musician in Birkenstocks is ushered on. Dreary songs about the earth's demise commence, the musician exhorting the dutiful audience to sing along.

Sitting in the front row, author and climate change activist Bill McKibben is game. "Save some trees for me," he mouths, his head bobbing. The musician thankfully finishes and, after a brief introduction, McKibben quickly mounts the stage steps.

The feeling in the room changes instantly. Having flown down from Alaska that morning, McKibben has been on five continents during the last nine days. "If the planet isn't warming up," he jokes, "it's not for lack of me trying."

But the planet is warming up. Unable to stop it personally, McKibben is instead the relentless messenger of its alteration.

Like food activist Michael Pollan, McKibben is tall, lean, ascetic, ridiculously well-educated and somewhat ill at ease in his role of scientific soothsayer. Like Pollan, he'd rather be in his home office writing than lecturing on our imminent demise. Unlike Pollan, he's still stuck—on this night at least—with the earnest, the gray ponytails, the activists who remember John and Yoko. He's preaching to the converted, as the Prius-packed parking lot connotes. He's telling educated, concerned citizens what they already know. Almost nothing, other than the plain dire facts of his humor-laced presentation, is new to them. His message couldn't be more important, yet he's not a household name. Not yet, at least.

While Pollan's meme can be memorized like a short poem—eat food, not much, mostly plants—McKibben's is even easier. It's simply a number: 350. Three hundred and fifty, the amount of carbon parts per million in the atmosphere that NASA's top climate scientist Jim Hansen has counseled will most closely support the earth upon which human civilization arose.

McKibben has organized an international day of action in countries as disparate as Yemen and Croatia slated for Oct. 24 and known as 350 Day to highlight the number because 350 parts per million (ppm) is 37 numbers lower than the 387 ppm level that the atmosphere is currently at now. In other words, we've already crossed what McKibben calls "the red line" for succoring the climate upon which human civilization arose. By lots.

The author of 12 books, including the seminal 1989 global-warming text The End of Nature, McKibben, 49, is the kind of easy intellectual who joined the staff at the New Yorker magazine just after graduating Harvard. He has written about subjects ranging from Hundred Dollar Holiday, in which he outlines spending just that amount on winter festivities, to Maybe One: A Case for Smaller Families, which advocates having just one child, as he and his wife, the novelist Sue Halpern, have done with their daughter, Sophie. But all is not simply an orange stuck in a stocking for the lonely Christmas of an only child with McKibben. His relentless sense of humor and his indefatigable energy make him a fascinating magnet.

A religious man who teaches Sunday school at the Methodist church near his Vermont home, McKibben needs that energy to survive the task he has set himself this year, one in which he will have spent 355 of the annum's 365 days on the road, away from his wife and daughter, spreading the word about climate change. For McKibben, it is a moral necessity. He knows the truth about global warming—he's seen it first-hand from Bangladesh to Pakistan to Phuket to Mongolia to China. Global warming and climate change are not coming, he counsels: they're here. The 10 feet—feet—of water that fell last month on Taiwan is just one of an alarming number of natural calamities that attest to that.

McKibben has had dengue fever in Bangladesh, seen a rock new to human eyes suddenly emerge from a Mongolian glacier and knows that rising sea levels are already salinating the fresh Ganges River. If he doesn't personally deliver this truth to every person he can possibly grab by the lapels, he will have failed himself. He will have, in fact, harmed his own soul.

"The thing I am doing today is the single most important thing I can be doing," McKibben says. "We're going to find out in the next few years whether this big brain [that humans have] was a good idea and if it's linked with a big enough heart."

And so, with red-rimmed eyes and a practiced presentation, McKibben finds himself on yet another stage in yet another town in yet another country trying to convince some 600 people at a time that this is something they should be concerned about.

As comfortable in front of the microphone as at the dinner table, McKibben has told his tale hundreds of times, changing it only to include the newest natural tragedy briefly grabbing international headlines, all of it, save Katrina, in far-off nations that, he passionately declares, "did nothing to deserve it!"

But even with an audience of the Prius-driving graybeards reasonably versed in the actual way of the world, McKibben must explain the petty basics of the earth's ecology. A plant that has for the millennia flowered at a certain week in April when the light and heat conspire perfectly and has been a fecund food source for an insect whose life cycle is keyed to the plant and is itself a delicious meal for an amphibian which awakens from the mud just as the insect is at its plumpest, which is itself a gorgeous lump of protein for a bird whose migration pattern is in part set by the availability of frogs in the area and whose eggs are a yummy treat for a mammal that has come to live year-round there due to the certainty of the eggs for its own breeding is in turn eaten by another mammal larger and more adept. Its remains are ravaged by scavengers, its gristle dissolved by bugs (which in turn are eaten by the migrating birds whose excrement nourishes the April-blooming plant).

All of this rapacious blooming and pollinating and eating and excreting and reproducing and dying has eventually led humans to the establishment of such unnatural wealth as is found within any provincial supermarket. It is a cycle so seemingly robust that we simply take it for granted. But this life chain can be—and already has been—enormously upset by something as seemingly simple as a Fahrenheit degree, by an extra centimeter's worth of water, by a wind that should never have been whipped.

A scholar-in-residence at Vermont's Middlebury College, McKibben has plenty of access to young people and their sturdy energy. In 2006, he led a group of students and colleagues on a five-day walk through the Vermont woods that began at the poet Robert Frost's cabin ("'The road not taken' seemed apropos," he says) to make a global-warming statement that would end in Burlington. There, his group was joined by others until its ranks swelled to a thousand people marching upon Burlington's city hall. It was, he realized sadly, the largest public protest for climate change ever yet staged.

Astonished that the plight of the globe was so little remarked by its inhabitants, McKibben formed Step It Up in late 2006. Using a student team from Middlebury and the endless swathe of the internet, Step It Up promoted some 1,400 climate-change actions worldwide in April of 2007. McKibben was feeling pretty good about his work. And then the summer came, and then the Arctic melted.

"The Arctic sea was slowly melting, and then it suddenly fell off a cliff," he says. "We were losing ice sheets the size of California every month, at a rate 200 percent above what was predicted. My scientist friends panicked. This was on, and not just Arctic ice; there is 25 percent less sea ice than ever before. Satellite photos revealed that there was a lot less ice up top. Glacial ice is the most unsettling loss of all."

McKibben estimates that 300,000 people will die annually from global warming with just a one-degree temperature rise. "But we expect the planet to warm by five to six degrees more in this century if we do nothing.

"We have the technology to imagine what the future will look like," he continues. "The scientific method has worked, but so far the political method has utterly failed. We've had a 20-year bipartisan effort to do nothing, and it's succeeded brilliantly."

Asher Miller, executive director of the Post-Carbon Institute, a global think tank that counts McKibben and peak oil theorist Richard Heinberg among its fellows, looks at fossil fuels almost fondly, as in thoughtful reminiscence. "The big human story is that we won the lottery," Miller says. "We found this amazing energy source that fueled our society and changed it completely, giving us luxuries and altering the course of human history entirely. Can you blame us for going nuts over it?

"But it's now a moot point. We're living in a difficult time. We're changing, and it's being dictated by climate. We have to be realistic, and we can't live the way we've been living."

Perhaps the most sobering part of the global warming message is that we can swap out all the light bulbs we like, grow every bit of lettuce that we'll ever eat ourselves, ride our bikes everywhere—and none of it will mean a thing unless our political leaders act. "How do we muster the will to get a global agreement that puts a price on carbon?" McKibben asks. "We can't solve it one bulb at a time, not one state at a time, not even one country at a time. We have to deal with it one planet at a time.

"We have to build a movement. I say that as if I know what I'm talking about. I don't. No one really knows how we're going to muster it." 350 Day is his latest idea, a creative, almost joyful attempt to unite people the world over in protest against the lethargy of large, First World governments to alter policies, agreements, coal and oil consumption.

Miller isn't pessimistic—exactly. "The environmental movement has failed," he says. "Guilting people, talking about abstractions like polar bears. Boiling down complex stuff into a simple number like 350 is a good way to use what otherwise has become a battle of data and talking points.

"It would be great if people take to the streets on Oct. 24," he says. "But that's just one day. This is going to be every day. And it's already started."

McKibben could be said to agree. "There are no guarantees that any of this will work," he tells the Sonoma Country Day School audience. "There are scientists who think that the machination we've put in process is unstoppable. But the best science says that we still have a window. Because we have that window, we have to fight. For 20 years, I wondered what this fight would look like—and it's very beautiful. We're an amateur movement. This is a homemade operation, and that's the best thing about it."

McKibben's next focus after 350 Day is the December climate-change conference planned in Copenhagen. The United States will attend, as will other powerful polluting countries. "Whatever we do at Copenhagen isn't enough," he admits. "We know what the bottom line is, and we have to keep at it. The negotiations are occurring between human beings and physics and chemistry. Physics and chemistry have stated their bottom line: 350 is our demand."

The most promising bit of national legislation, according to Ann Hancock, executive director of the Climate Protection Campaign, is something called "cap and dividend."

"It means putting a cap on carbon and every year reducing that cap so that every year, and rapidly, we meet the scientific imperative," she explains. So-called gross polluters—think Exxon and its ilk—will have the option to purchase rights to use fossil fuels. Cap and dividend will raise energy prices, it's true, but the current proposal, put forward by Democratic representative Christopher Van Hollen of Maryland, would also offer customer rebates on energy use. Those who use less fossil fuel would receive more money back; those who use more, less.

"I think that cap and dividend is the most powerful solution we need to have and that's worldwide," Hancock says. "[Sixties activist] Sal Alinsky said that most people will do the right thing for the wrong reasons, and I agree. We're more concerned with our comfort and mortgage than we are with the climate. Pricing is the way to do it. The option of the right to pollute will generate perhaps trillions of dollars. It will torque the whole economy in a green direction. If people have to pay more money for fossil fuel and they aren't made whole, they won't reelect those people."

Bill McKibben is exhausted. After rallying the audience for an hour of passionate speech, his voice drops. "We set out to organize the world, a ludicrous proposition. Only McDonald's and Coca-Cola have succeeded. The only part of the climate-change movement that's been left out is the movement part." But the key, he stresses, is the newest generation. "The real leaders of the moment are young people," he tells the sea of gray ponytails. A handful of students on the top tier applaud.

Asher Miller agrees. "There's this generational gap in the larger environmental movement," he says, "and Bill is helping to close that."

The next generation has every reason to be involved, as it's their adult lives, their children and probable grandchildren most affected. Climate change is here, and even if every coal facility in the world stopped production today, McKibben estimates that it will take two generations before we can return the earth's atmosphere to 350 ppm.

Miller, who has a toddler, chooses to be sanguine. "I fully expect that the next 10 years will be significantly different than the last 10 years," he says. "Things are different, and the sooner we can internalize that, the sooner we can make changes.

"The world is going to be different, but it may not be all bad."

For 350 Day events in the North Bay , go to www.350.org or look in our Events calendar.

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