Prolific author and activist Bill McKibben is on a mission to make 350 the most important number in the world. It represents the uppermost safe parts per million limit of carbon dioxide in Earth's atmosphere—a number he hopes will take center stage at the upcoming climate negotiations in Copenhagen.
People from Africa to Washington, D.C to the Maldives are spreading the word on October 24, with demonstrations on lawns, beaches, snowfields, and even underwater.
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Interested? Citizens build a climate movement around a number.