CANTON — Bill McKibben has a number he wants you to remember: 350.
As in 350 parts per million, the number that scientists say is the safe upper limit for carbon dioxide in the Earth's atmosphere.
The environmentalist and author told an audience of 500 people Thursday at St. Lawrence University that we've surpassed that amount already and must return to it in order to stem the destructive cycle of climate change.
"Science tells us that there's a window open. It's closing and it's not very wide, but it's open," he said. "At this time in human history, this is what we're supposed to be doing."
The author told SLU students and community members that they must act now to get the world's leaders focused on reducing our CO2 output more than 100 percent to bring us down from our current level of 387 parts per million.
Mr. McKibben, who in 1989 wrote "The End of Nature," which many call the first definitive book on global warming, now says we only have five years to make the strategic decisions necessary to wean ourselves from oil and coal.
He said college students, along with young people across the globe, have a special responsibility to urge change now — because they're the generation that will have to live with environmental havoc if nothing is done.
"Don't spend all your energy making St. Lawrence University perfect on carbon, and fighting with the board of trustees. You have to realize that making the rest of the world and country pretty good is more important," Mr. McKibben advised SLU's student environmental groups.
He also said reducing carbon footprints and becoming more active locally is good both for the psyche and for breaking the consumer cycle that fuels the rise in greenhouse gases, but concentrating only on those aspects is simply too little, too late.
"Because of the time pressure, doing what seems like practical work is essentially symbolic at this point. There's no way to make the math of that," he said. "It's an enormous challenge, but this is the only target that really and honestly will leave us with a livable planet."
So while it's good to replace your light bulbs with compact fluorescents and shop for organic items at the farmers market, Mr. McKibben told the audience in Gulick Theater, it's more important to demand political action.
"It doesn't take 51 percent of people to get something done. Five percent is more than enough, if they're engaged," he told students, pointing to the scale of the civil rights movement. "You guys have been politically conscious only during the Bush administration, so you have the idea that it's hard to get things done. It hasn't always been like this."
The 350.org group that Mr. McKibben sponsors gets its name from a paper written by NASA scientist James Hansen, which found that the Earth must return to 350 parts per million of atmospheric carbon dioxide "if humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted."
If it does not, the study says, "there is a possibility of seeding irreversible catastrophic effects."
Mr. McKibben founded 350.org in March, along with the team of young organizers behind last year's successful Step It Up campaign, which spurred 1,400 environmental demonstrations across the country.
He is the author of a dozen books, including "Deep Economy: The Wealth of Economies and the Durable Future," and was awarded SLU's North Country Citation in 2002. Mr. McKibben is a scholar-in-residence at Middlebury College, Middlebury, Vt.