Saturday is '350 Day,' focusing attention on what many think maximum level of CO2 in air should be

UPDATE 10/26: 350 day went off as planned Saturday, but some scientists and environmentalists are questioning the campaign's message. "Three-fifty is so impossible to achieve that to make it the goal risks the reaction that if we are already over the cliff, then let’s just enjoy the ride until it’s over," John M. Reilly, an economist at the Massachusetts Institute of Technology, tells Andrew C. Revkin of The New York Times. Despite questions about his group's validity, McKibben held steady to his its goal: "We need to be thinking about reducing, not going up more slowly. Tree-fifty is the number that says wartime footing, let’s see how fast we can possibly move, and let’s hope against hope that it’s fast enough." (Read more)

Bill McKibben, founder of the new environmental campaign 350.org, hoped his project would help raise awareness of the goal to lower atmospheric carbon-dioxide concentrations to 350 parts per million, the amount of CO2 scientists believe the atmosphere can safely hold before climate systems start to "go haywire," Douglas Fischer of The Daily Climate reports. But McKibben said he never imagined his "350 Day" event this Saturday would have the success it seems to be having.

"As of Thursday morning some 4,227 actions and rallies are planned in 170 countries, with 300 events in China, 1500 across the United States, 500-plus in Central and South America," Fischer reports. Organizers credit the interconnectedness of the Web, cellular telephones and social networks for the viral appeal of the single-day event that hopes to raise awareness for 350.org's cause. "We couldn't have done this two or three years ago," McKibben tells Fischer. "We needed not just the Web, but the Web built out over cell phones."

"For the millennia before the industrial revolution, when humans started pumping industrial emissions into the atmosphere, carbon dioxide levels had held fairly steady at about 280 parts per million," Fischer notes. "Carbon dioxide concentrations rose gradually but steadily to the mid-20th century, when they started to skyrocket. Today the level is 387 ppm, with many analysts expecting the globe to hit 450 ppm or even 550 ppm before world economies 'decarbonize' sufficiently to radically reduce emissions. The problem is that data from the past 100 million years suggests the planet was largely ice-free until carbon dioxide levels fell below 450 ppm, plus or minus 100 ppm. Somewhere between 350 ppm and 550 ppm, climatologists suspect, is a critical threshold that triggers irreversible climate change, loss of major ice sheets, abrupt sea-level rise and massive shifts in forests and agriculture.

"Until recently the notion of bringing atmospheric carbon dioxide levels back to 350 ppm – voiced most vocally by McKibben and NASA's Jim Hansen – was dismissed as wild-eyed optimism. The Earth last saw 350 ppm in 1987," and CO2 takes 200 years or more to break down in the atmosphere. "We know better than anybody exactly how difficult this is and how politically unrealistic it is at the moment," McKibben tells Fischer. "Our job is to change the political reality, because the physical and chemical reality is not going to change." (Read more)