According to environmental writer Bill McKibben, and leading climate scientist James Hansen, 350 parts per million is the upper bound of safe CO2 levels on Earth. For a reasonable dissent that suggests 450 ppm, click here. McKibben has created an awesome website, www.350.org, to focus on getting to his magic number. The video below is a powerful demonstration of why humanity should keep CO2 at 350 ppm, a wordless demonstration that doesn't depend on language, just numbers and images, to make its point.
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